Merlin Resource Estimate for The Merlin Project NT, Australia Author: Tom Reddicliffe Date: 18 th October 2011 Report No: 11-067 Copies To: NADL The contents of this Report remain the property of North Australian Diamonds Limited and may not be published in whole or in part, nor used in a company report without the written consent of the company.
295
Embed
Merlin Resource Estimate for The Merlin Project NT, Australia...Merlin Resource Estimate for The Merlin Project NT, Australia Author: Tom Reddicliffe Date: 18th October 2011 Report
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Merlin Resource Estimate for The Merlin Project
NT, Australia
Author: Tom Reddicliffe
Date: 18th October 2011 Report No: 11-067 Copies To: NADL
The contents of this Report remain the property of North Australian Diamonds Limited and may not be published in whole or in part, nor used in a company report without the written consent of the company.
1.4.1 Previous Production .............................................................................................................13 1.4.2 Resource on Closure ...........................................................................................................14
1.5 History of Evaluation ................................................................................................................14
9 GRADE MODEL.................................................................................................................................63 9.1 Introduction .....................................................................................................................................63 9.2 Merlin Grade Models.......................................................................................................................63 9.3 Merlin Size-Frequency Distribution .................................................................................................64 9.4 Gawain Grade Model ......................................................................................................................64
9.4.1 RIO Records ........................................................................................................................64 9.4.2 Bulk Sample 2006 ................................................................................................................65 9.4.3 NADL 2006/2009/2010 ROM ...............................................................................................65 9.4.4 Grade Control Samples........................................................................................................65 9.4.5 Grade Model ........................................................................................................................65
9.5 Ywain Grade Model.........................................................................................................................65 9.5.1 RIO Records ........................................................................................................................65 9.5.2 Bulk Sample 2006 ................................................................................................................65 9.5.3 NADL 2006 ROM .................................................................................................................65 9.5.4 Grade Model ........................................................................................................................65
9.6 Excalibur Grade Model....................................................................................................................66 9.6.1 RIO Records ........................................................................................................................66 9.6.2 Grade Model ........................................................................................................................66
9.7 PalSac Grade Model .......................................................................................................................66 9.7.1 RIO Records Palomides.......................................................................................................66 9.7.2 RIO Records Sacramore......................................................................................................66 9.7.3 RIO LDC Drilling PalSac ......................................................................................................66 9.7.4 RIO Bulk Sample PalSac .....................................................................................................67 9.7.5 2009 Palomides Pit Cleanup................................................................................................67 9.7.6 Grade Model ........................................................................................................................67
9.8 Launfal Grade Model.......................................................................................................................67 9.8.1 RIO Records ........................................................................................................................67 9.8.2 Grade Model ........................................................................................................................67
9.9 Kaye Grade Model ..........................................................................................................................67 9.8.1 RIO Records ........................................................................................................................68 9.8.2 Bulk Sample 2006 ................................................................................................................68 9.8.3 NADL 2009/2010 ROM ........................................................................................................68 9.8.4 Grade Control Samples........................................................................................................68 9.8.5 Grade Model ........................................................................................................................68
9.10 Ector Grade Model ........................................................................................................................68 9.10.1 RIO Records ......................................................................................................................68
9.10.2 Grade Model ......................................................................................................................68 9.11 Gareth Grade Model .....................................................................................................................69
9.11.1 RIO Records ......................................................................................................................69 9.11.2 Grade Model ......................................................................................................................69
9.12 Bedevere Grade Model .................................................................................................................69 9.12.1 Grade Model ......................................................................................................................69
9.13 Tristram Grade Model ...................................................................................................................69 9.13.1 Grade Model ......................................................................................................................70
9.14 Summary of Grade Models ...........................................................................................................70 10 DIAMOND VALUATIONS ................................................................................................................71
LIST OF TABLES Table 1.1 Project Tenement Table 1.2 Summary of Total Production 1998-2003 Table 1.3 Reconstructed Summary of Past Mining Operations 1998-2003 Table 1.4 Inferred Resource Summary 2003 Table 1.5 Merlin Total Resource Table 2.1 Age of Merlin Fossils Table 2.2 Dimensions of Merlin Kimberlite Pipes Table 2.3 Thickness of Infill Sediments within the Merlin Kimberlite Pipes Table 2.4 Geochronology Table 4.1 Summary of Grades from Merlin Bulk Sampling Programme 1994 Table 4.2 Summary of Grades from Merlin Phase II Sampling Table 4.3 1996 Bulk Sample Results Table 5.1 Summary of Total Production 1998-2003 Table 5.2 Pre-constructed Summary of Past Mining Operations 1998-2003 Table 5.3 Inferred Resource Summary 2003 Table 5.4 Summary of Merlin Production Table 5.5 Carats Recovered per Pipe Table 5.6 Summary Site record of Production By Flitches 1999-2003 Table 5.7 Excalibur Sorthouse Sizing Record Table 5.8 Palomides Sorthouse Sizing Record Table 5.9 Sacramore Sorthouse Sizing Record Table 5.10 Launfal Sorthouse Sizing Record Table 5.11 Launfal North Sorthouse Sizing Record Table 5.12 Gawain Sorthouse Sizing Record Table 5.13 Ywain Sorthouse Sizing Record Table 5.14 Kaye Sorthouse Sizing Record Table 5.15 Ector Sorthouse Sizing Record Table 5.16 Gareth Sorthouse Sizing Record Table 5.17 Merlin Rejects Sorthouse Sizing Record Table 5.18 Size Distribution Comparison Table 5.19 Stones per Carat - Full Profile Table 5.20 Stones per Carat - Truncated Table 5.21 All Pipe Carats Table 5.22 All Pipe % Carat Contribution Per Size Table 5.23 All Pipe Values Table 5.24 All Pipes Price per Carat Table 5.25 All Pipes per Carat Contribution per Size Table 5.26 Production September 1999 Table 5.27 Production October 1999 Table 5.28 Production November 1999 Table 5.29 Production February 2000 Table 5.30 Production March 2000 Table 5.31 Production June 2000 Table 5.32 Production August 2000 Table 5.33 Production September 2000 Table 5.34 Production November 2000 Table 5.35 Production February 2001 Table 5.36 Production May 2001 Table 5.37 Production October 2001
Table 5.38 Production December 2001 Table 5.39 January 2001 Table 5.40 Excalibur Production and Valuation Table 5.41 Palomides Production and Valuation Table 5.42 Sacramore Production and Valuation Table 5.43 Launfal Production and Valuation Table 5.44 Launfal North Production and Valuation Table 5.45 Gawain/Ywain Special Parcel Table 5.46 Kaye Production and Valuation Table 5.47 Ector Production and Valuation Table 5.48 Gareth Production and Valuation Table 5.49 Pipe Summary Production and Valuation Table 5.50 Price per Carat per Pipe Table 5.51 All Pipes by Quality Table 5.52 All Pipes by Colour Table 5.53 Pipes by Sale Table 5.54 Merlin Summary Table 5.55 Diamond Exports 1999-2003 Table 5.56 PalSac LDC Drilling Programme 2001 Table 5.57 PalSal Bulk Sample RIO 2002 Table 6.1 Merlin Primary Resource 2005 Table 6.2 Reject Ore and Tailings Resource Table 6.3 Merlin Primary Resource 2008 Table 6.4 Sorthouse Rejects Samples Table 6.5 Merlin Sorthouse Rejects Diamond Fortnightly Recovery Table 6.6 Tails Size Distribution Table 6.7 Samples from ROM Pad Stockpiles 2005/2006 Table 6.8 Samples from Pits Table 6.9 Processing Schedule 2006 - Tonnes Processed Table 6.10 Processing Schedule 2006 - Carats Recovered Table 6.11 Processing by Quarter 2006 Table 6.12 Processing Summary 2006 Table 6.13 Production Trials by Pipe 2009/2010 Table 6.14 Production Trials Summary 2009/2010 Table 6.15 Merlin 2009-2010 Carat Recoveries Table 6.16 Merlin 2009-2010 Stone Recoveries Table 6.17 Grade Control Sample Results Table 7.1 Depth of Infill Sediments Table 7.2 Kimberlite Facies Table 8.1 Gawain Table 8.2 Ywain Table 8.3 Palsac Table 8.4 Launfal Table 8.5 Kaye Table 8.6 Ector Table 8.7 Gareth Table 8.8 Excalibur Table 8.9 Bedevere Table 8.10 Tristram Table 9.1 Merlin Production DTC Size Profile Table 9.2 Grade Model Average Size Frequency Distribution Tables Table 9.3 Gawain RIO ROM 1999-2003 Table 9.4 Gawain Comparison of Mined Flitches
Table 9.5 RIO Special Valuation Parcel Table 9.6 Gawain/NADL Bulk Sample 2006 Table 9.7 Gawain/NADL ROM 2006, 2009 and 2010 Table 9.8 Gawain Grade Control Samples 2010 Table 9.9 Summary of Gawain Processing Table 9.10 Gawain Model Grade Table 9.11 Ywain Sorthouse Sizing Record Table 9.12 Ywain Comparison of Mined Flitches Table 9.13. Ywain Special Parcel Table 9.14 Ywain Bulk Sample 2006 Table 9.15 Ywain/NADL 2006 ROM Table 9.16 Ywain Grade Model Table 9.17 Excalibur Sorthouse Sizing Record Table 9.18 Excalibur Comparison of Mined Flitches Table 9.19 Excalibur Production 1999/2003 Table 9.20 Excalibur Grade Model Table 9.21 Palomides Sorthouse Sizing Record Table 9.22 Palomides Comparison of Mined Flitches Table 9.23 Palomides Production 1999-2002 Table 9.24 Sacramore Sorthouse Sizing Record Table 9.25 Sacramore Comparison of Flitches Table 9.26 Sacramore Production 1999-2002 Table 9.27 LDC Drilling Recoveries Table 9.28 LDC Sizing Table 9.29 Palsac Bulk Sample RIO 2002 Table 9.30 2009 Palomides Pit Cleanup Table 9.31 Palsac Grade Model Table 9.32 Launfal Sorthouse Sizing Record Table 9.33 Launfal Comparison of Mined Flitches Table 9.34 Launfal Production 1999-20002 Table 9.35 Launfal Grade Model Table 9.36 Kaye Sorthouse Sizing Record Table 9.37 Kaye Comparison of Mined Flitches Table 9.38 RIO Production 1999-2001 Table 9.39 Kaye Bulk Sample 2005 Table 9.40 NADL/Kaye ROM 2009-2010 Table 9.41 Kaye Grade Control Samples Table 9.42 Kaye Grade Model Table 9.43 Ector Sorthouse Sizing Record Table 9.44 Ector Comparison of Mined Flitches Table 9.45 Ector Production 2000-2001 Table 9.46 Ector Grade Model Table 9.47 Gareth Sorthouse Sizing Record Table 9.48 Gareth Comparison of Mined Flitches Table 9.49 Gareth Production 2000-2002 Table 9.50 Gareth Grade Model Table 9.51 Bedevere Grade Table 9.52 Tristram Grade Table 9.53 NADL Grade Resource Model Table 9.54 Production Grade Models Table 9.55 Historic Mining Grades Table 10.1 Rio Production 1999-2003
Table 10.2 Rio 1999-2003 All Pipes by Quality Table 10.3 Rio 1999-2003 All Pipes by Colour Table 10.4 Pipes by Sale Table 10.5 Merlin Summary Table 10.6 Diamond Exports 1999-2003 Table 10.7 Sorthouse Tails Daimond Valuation Details Table 10.8 Valuation of Sorthouse Tails Diamonds Table 10.9 NADL Valuation 2006 Table 10.10 Summary of NADL Sales 2006/2007 Table 10.11 2008 NADL Valuation Table 10.12 NADL 2010 Valuation Table 10.13 Summary of Valuations Table 11.1 Mineral Resource Table 11.2 Production Resources
LIST OF FIGURES Figure 1.1 Location of Merlin Mining Lease Figure 1.2 Kimberlite Pipes on the Merlin Mining Lease Figure 2.1 Satellite Image of the Merlin Plateau Figure 2.2 Tuffisitic Kimberlite Figure 2.3 Pelletal Tuffisitic Kimberlite Figure 2.4 Micaceous Tuffisitic Kimberlite Figure 2.5 Tuffisitic Kimberlite Figure 2.6 Tuffisitic Kimberlite Breccia Figure 3.1 1m3 sample taken from Gawain Figure 3.2 100m3 sample taken from Gawain Figure 6.1 Reprocessing of Sorthouse Tailings Figure 6.2 HPGR Crushing Unit 50tph Figure 6.3 Location of Reject Samples on ROM pad
LIST OF PLANS Plan 1 Gawain/Ywain Plan 2 Palsac Plan 3 Launfal Plan 4 Kaye/Ector Plan 5 Gareth Plan 6 Excalibur Plan 7 Bedevere Plan 8 Tristram
11
1 EXECUTIVE SUMMARY
1.1 Introduction The Merlin diamond field was discovered in 1993 by Ashton Mining Limited and after limited evaluation trial mining commenced in late 1998 as a means of evaluating the diamond field as it was deemed too expensive to continue with testing due to the number of pipes involved and their small size. The trial mining operations continued for 5 years and ceased in 2003 with a total of 507,000 carats of diamonds being produced and sold during this period. In late 2000 Rio Tinto acquired the project following the takeover of Ashton Mining Limited and continued the trial mining until 2003 when operations ceased. NADL acquired the project from Rio Tinto in 2004 after they were unable to sell the project as a going concern. Since that time NADL has been evaluating the project with a view to recommencing commercial mining operations.
1.2 General Location and Geology The Merlin kimberlite field is located in the Batten region of the Northern Territory, Australia, 100km south of the township of Borroloola (Figure 1.1). The field comprises fourteen kimberlite intrusions distributed in four discrete clusters (Figure 1.2). The two largest kimberlite pipes within the field, E.Mu1 and E.Mu2, were discovered in 1985 by CRA Exploration. The remaining kimberlite pipes were discovered by Ashton Mining seven years later. The pipes are dated at 360 Ma, and represent the preserved upper diatreme facies of the kimberlite system. Structurally the pipes are located on interpreted tension fractures spatially associated with the regional northwest trending Calvert Fault.
Figure 1.1 Location of Merlin Project
MERLIN
12
Figure 1.2 Merlin Project Area
1.3 Status of Mining Tenure The Merlin diamond deposit is secured under a Mining Lease which was granted in 1998 for a period of 20 years. The detail of this tenure is shown in Table 1. Table 1.1 Project Tenement
Lease Project Lease Status
Grant Date Expiry Date
Area (Ha) NADL Interest
MLN1154 Merlin Granted 15/6/98 31/12/22 2350 100% The project is subject to two gross revenue royalties totalling 1.75%, details are as follows;
R.M. Biddlecombe Royalty – This royalty of 0.75% is payable to prospector R. M. Biddlecombe who was the original holder of EL6424 which preceded the application for MLN1154. Ashton Mining (Rio Tinto) – This royalty of 1% is payable to Ashton Mining Limited now owned by Rio Tinto and was acquired by them as part of the conditions of sale when NADL Acquired the project.
The project also operates under a Native Title agreement with relevant Traditional Owners who have traditional links to the area. This agreement allows for a Nett Profit Interest to be paid annually at the rate of 2% and scaling up to 4% for a more profitable operation and with a minimum annual payment of $10,000 if operations are scaled back. Renegotiation of this agreement has been proposed by the Northern Land Council who administers the agreement.
MMiinniinngg LLeeaassee
BBeeddeevveerree Northern Cluster
KKaayyee GGaarreetthh EEccttoorr
Southern Cluster
TTrriissttrraamm
EExxccaalliibbuurr PPeerrcceevvaall
LLaauunnffaall PPaallSSaacc
Central Cluster
YYwwaaiinn GGaawwaaiinn
13
1.4 Historic Resources 1.4.1 Previous Production The Merlin mining operation commenced in 1998 and ceased mid 2003. In total 2,237,447 tonnes of kimberlite were processed, with 507,000 carats of diamonds recovered. The operations are summarised in Table 1.1. Table 1.2: Summary of Total Production 1998 - 2003
Ref: Mine management Plan 2002-2003 The numbers in Table 1.1 were reported in mine records and are at odds with other reports of carats sold and recorded process tonnes. These are provided in the following Table 1.2, and provide a more accurate assessment of the mining activities. Table 1.3: Reconstructed Summary of past mining operations 1998 - 2003
*Excludes Tailings Ref: Summary of Mining and Evaluation 1999-2007.
1.4.2 Resource on Closure On closure of the project in 2003 the remaining insitu resources were reported as follows; Table 1.4: Inferred Resource Summary 2003
1.5 History of Evaluation The following is a short summary of the history of the project. 1986 E.Mu pipes discovered by CRAE. 1989 Ashton Exploration commences. 1991-1993 Merlin pipes discovered. 1994-1996 Evaluation testing. 1996-1997 Feasibility Studies. 1998 Mine development and commencement of mining operations. 2000 Rio Tinto acquires project following takeover of Ashton Mining. 2001 PalSac development options evaluated. LDC drilling program. 2002 Merlin project offered for sale as a going concern, but no offer accepted. 2003 Mine closed having produced 507,000cts from 2.24Mt ore. 2004 NADL acquires Merlin project from Rio Tinto. 2005 Reprocessing of sorthouse tails produces 13,550cts. HPGR testwork highlights liberation issues. 2006 Pilot plant established. Trial production produces 11,812cts from 24,958 tonnes. Scoping study completed. 2007-2008 Resource definition drilling increases resources. 2009-2010 Pilot plant upgraded to incorporate HPGR and Optical Sorter. Trial production produces 10,600cts diamonds. Pre-feasibility study completed. Additional resource definition drilling increases resources. 2011 Commencement of Detailed Feasibility Study.
1.6 Modelling Approach Modelling of the resource comprises three components namely, resource volume, diamond grade and diamond value. The basis of these models is as follows;
1.6.1 Resource Volume The volume of the resource is based on lithological boundaries which have been identified by drilling and reasonable assumptions as to the formation and nature of the kimberlite bodies. These assumptions are that kimberlite bodies are volcanic intrusives and hence have depth continuity and that the wall rock contacts are invariably sharp as opposed to diffuse and gradational.
15
1.6.2 Diamond Grade The diamond grade models are based on plant recovered grades and hence are sensitive to liberation issues, lower screen sizes, plant recovery efficiency, final recovery techniques utilised, and security. Hence the measured grades are not a measure of total diamond content but rather a reflection of what may reasonably be recovered from a processing operation using similar processing and recovery methodology. The commercial diamond grade is that which would be recovered from a commercial mining operation and hence is subject to commercial operating considerations. Consequently the commercial diamond grade can be somewhat lower than the recoverable diamond grade determined by sampling testwork. Detailed diamond grade models are established based on the contribution to grade of various diamond size fractions. Inherent in grade assessment is the assumption that diamonds are homogenously distributed throughout any particular kimberlite facies and that this distribution does not vary with increasing depth within the pipe. While these assumptions can be tested at surface interpolation at depth is solely reliant on the interpretation of microdiamonds recovered from small drill core samples, since with the exception of PalSac no pipes have been tested for their commercial diamond content below their currently mined depth.
1.6.3 Diamond Value Any recovered diamond parcel represents only a snapshot of the diamond population particularly with respect to less frequent large diamonds hence since the value of Merlin diamonds is skewed with 75% of the value attributed to only 11% of the weight of the recovered diamonds, the average diamond value cannot only be based on the grade model and a diamond parcel valuation. A diamond value model is not only based on the valuation of a representative ROM diamond parcel but must also factor in quality expectations of the recovered diamonds particularly for the larger less frequently recovered diamonds. Based on the 507,000 carats of diamonds recovered from Merlin during the previous mining operations it was concluded by RIO that there is no discernable difference in terms of size-frequency distribution or range of qualities for the diamonds recovered from any of the pipes mined to date hence there is a reasonable assumption that there is a single diamond population representative of the entire Merlin diamond field. More recent analysis undertaken by NADL and reported in this document indicates that there may be subtle differences in the size-frequency distributions between the micaceous pipes and the non-micaceous pipes.
1.7 Resource The Merlin project total resources are 30MT @ 23cpht for 7.2 million carats. Table 1.5: Merlin Total Resource
TOTAL 30,064,000 23 7,191,000 1Resource grade based on previous mining operation recovery using a +0.95 mm slotted bottom screen and a +0.95mm cut-off. 2Resource grade based on bulk sample test work using a +0.8 mm slotted bottom screen and a +0.95mm cut-off.
The Merlin Mineral Resources have been and classified and reported in accordance with The 2004 Australasian Code for Reporting of Mineral Resources and Ore Reserves (JORC Code). The Merlin Mineral Resources estimates have been prepared by T.H. Reddicliffe. T. H. Reddicliffe is a Fellow of the Australasian Institute of Mining and Metallurgy. T.H. Reddicliffe is a consultant to North Australian Diamonds Limited. T.H. Reddicliffe has sufficient experience, which is relevant to the style of mineralisation and type of deposit under consideration, and to the activity which they are undertaking. This qualifies T.H. Reddicliffe as a “Competent Person” as defined in the 2004 edition of the ‘Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves’
1.8 Risks The risks associated with assessing the Merlin Resources fall into 4 categories, these being;
1.8.1 Tonnage
Due to their volcanic intrusive nature the geometry of kimberlite pipes can be determined to a high degree of confidence with relatively limited drilling. While volumes are easily determined, equivalent tonnages can be more speculative. The issue is the susceptibility of the kimberlite to intense weathering, often to the point of volume reduction. At Merlin the upper portion of the pipes are invariably deeply weathered including the destruction of primary textures and the formation of clays with individual measured bulk densities as low as 1.3. Beneath the clay zone but within the upper 80m of the pipes, where mineral textures are preserved the bulk densities range up to 2.2. In the deeper portions of the pipe where the kimberlite is fresh and largely unaltered the bulk densities are normally around 2.6. The issue with bulk density is the varying moisture contents, which can be as high as 28% in the clay rich zones and reducing to 3% for the deeper fresh kimberlite. A further complication is that the weathering front is not planar but more a radial effect. The centres of the pipes can be relatively unweathered compared to the margins with an annulus of clay often developed around the periphery of the pipes. Hence at any specific flitch level there is a radial variation of bulk densities from low on the margins to high in the centres. The consequence of these issues is that during the mining operations undertaken by Ashton/RIO the measured volumes mined from the pits could not be reconciled with the processed tonnes despite the taking of large numbers of bulk density and moisture readings. Because of these issues, it is deemed to be more reliable to base all resource estimates on volume measurements. 1.8.2 Grade Determination Because of the issues outlined in a) above with respect to bulk density and moisture content grades are also best quantified in terms of a volume ie, carats per bank cubic meter (cpbcm). In determining grade it must be ensured that the material sampled has not been subject to volume change due to weathering and that the sample is a single representative block and of a singular geological rock type. Depending on the size of the sample the contained diamonds can be recovered by large processing plant for large samples or by laboratory processes for small samples. Because different processes can result in different grades for similar material it is important that lower and upper screen sizes are recorded along with processing procedures. Because diamond occurs as a particulate mineral, knowledge of the diamond size-frequency distribution and the stone frequency per unit of sample is required to establish grade. Grades determined solely from the carat weight recovered from a sample
17
can give a reasonable approximation of grade but is never definitive and can be erroneous for small sample sizes. The factors that determine primary diamond grade are as follows;
Diamond Source – According to generally accepted theory, diamonds form and reside in the lower portions of the lithosphere at depths exceeding 150km. These diamonds become entrained in kimberlite magmas which originate in the convecting mantle and are transported to the earth’s surface. This is a poorly understood process with the ultimate surface grades depending on the diamond richness of the lower lithosphere, the amount of diamond bearing material that becomes entrained in the magma, and the rate at which the diamond bearing material becomes entrained in the magma. The degree to which the diamond bearing material becomes disaggregated and dispersed throughout the kimberlite magma and the degree of preservation of the diamonds during the period of transport to the earth’s surface is also important. Country Rock Dilution – Near surface occurrences of kimberlite are usually dominated by ‘diatreme facies’ or kimberlite breccias (VKB). These breccias comprise kimberlite with >15% country rock xenoliths. These country rock xenoliths have been captured by the intruding kimberlite and have a diluting effect on grade as they are barren of diamond. Clearly the greater the dilution by the country rock the lower will be the grade. At Merlin VKB is the dominate kimberlite facies and is seen in all pipes with the exception of Ywain. For any pipe the amount of country rock dilution will be variable throughout the pipe, and while assumptions are made based on the interpretation of drill core the random nature of the dilution makes any definitive assessment speculative.
Ultimately the measured grades are based on plant recovered grades and hence are sensitive to liberation issues, lower screen sizes, plant recovery efficiency, final recovery techniques utilised, and security. The continuity of commercial grade at depth is difficult and costly to demonstrate due to the large sizes of the samples required. The careful use of microdiamond analyses can be useful in ascertaining whether surface grades are expected to persist at depth but it is not definitive. While there is risk in determining an average grade for a particular kimberlite pipe from limited surface sampling due to the number of factors that have to be considered the greater risk lies in assessing whether this grade is representative of the grade of the pipe at depth. 1.8.3 Geological Complexity It is generally the nature of individual kimberlite pipes to be host to different phases of kimberlite which more often than not will have different diamond grades and potentially but less likely different diamond populations. These variations are more likely seen in the larger kimberlite pipes and are less prevalent in smaller pipes or deeply eroded pipes. At Merlin all of the pipes are small by world standards and because there is only a single diamond population identified from all three mined pipe clusters suggests that the pipe clusters are related and are sourced from the same magma stream. At Merlin the following dominant kimberlite types have been recognised;
VKB – This is a kimberlite breccia and is by far the most common kimberlite facies represented at Merlin. It is defined as having >15% country rock xenoliths. PVKB(PLVKB) - This is similar to above but is dominated by pelletal autoliths. VK - This is similar to VKB but with <15% country rock xenoliths. VK1 – This is a very distinctive sandy kimberlite and although seen as rafts within Kaye and Gawain it is best represented within the upper portion of PalSac.
18
Micaceous VK – This is hypabyssal material with little or no country rock contamination. It is best seen in Ywain where it comprises the entire pipe. Bedded Tuffs – These have only been encountered in Gawain where a floating raft was encountered and also encountered preserved against wallrock at a depth of 250m. These represent remnants of initial kimberlite phases. They are volumetrically insignificant and specific grades have not been determined.
1.8.4 Diamond Value Unlike other commodities there is no singular value for diamonds, with the value of any particular diamond being subject to its size, shape, clarity and colour and the prevailing market conditions. While reasonable assessments can be made of the value of the smaller diamonds the difficulty arises in being able to attribute average expected value to the larger diamonds where fewer diamonds have been recovered and which may not be representative of the average diamond population. Because of the skewed contribution to value of the large diamonds at Merlin there is a significant risk that the determined value of any ROM diamond parcel will be overstated or understated.
1.9 Recommendations The following recommendations are aimed at increasing confidence in the resource.
1.9.1 Pipe Geology There is geological complexity in some of the pipes that needs to be quantified. In particular Kaye, PalSac and Launfal are known to contain potentially significant secondary subsidiary kimberlite facies. These secondary facies have not been individually quantified in terms of volume or grade. Further investigation of these possibly significant subsidiary facies is required to ensure global grades are not adversely affected.
1.9.2 Diamond Grades The continuity of grade at depth within the pipes has only been investigated through microdiamond analysis for Gawain and PalSac due to the availability of core. Additional core drilling will be required for those pipes for which core is currently unavailable. Grade control samples have only been taken from Gawain, Kaye and Sacramore. The Sacramore samples have not been processed and there has been insufficient samples taken from Kaye. Without these control samples the historic mining data may not accurately reflect grade. Further pit samples are required particularly for the pipes Palomides, Launfal and Ector which have not been tested.
1.9.3 Diamond Values Because of the skewed diamond value distribution and the relatively few data points within the high value diamond population, a thorough analysis of quality distribution within the entire diamond population and its relevance to the larger stone population is necessary. Diamond valuations heavily influenced by the large diamond population and few data points can result in misleading conclusions with respect to average diamond parcel value.
19
1.10 Qualifications and Technical Experience of Author Author: Thomas Reddicliffe, Mr T.H. Reddicliffe, BSc(Geol), BSc.(Hon), MSc, FAusIMM, has more than 30 years almost exclusive experience in diamond exploration, evaluation and mining in Australia and a 20 year association with the Merlin Project. T.H. Reddicliffe is a consultant to North Australian Diamonds Limited. T.H. Reddicliffe has sufficient experience, which is relevant to the style of mineralisation and type of deposit under consideration, and to the activity which they are undertaking.
This qualifies T.H. Reddicliffe as a “Competent Person” as defined in the 2004 edition of the ‘Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves’
20
2 GEOLOGY
2.1 Introduction The Merlin field comprises fourteen kimberlite intrusions distributed in four discrete clusters, which are mostly preserved on a sand drifted, poorly drained plateau. The Merlin diamond field has a surface footprint of some 10km by 5km.
2.2 Regional Geology The Batten region is situated on the eastern side of the North Australian Craton. The area south of the western edge of the Gulf of Carpentaria is dominated by the relatively undeformed Middle Proterozoic McArthur Basin which extends over an area of 180,000 km2 (Pietsch et al, 1991). The basin forms part of the North Australian Platform overlying the Early Proterozoic Pine Creek Inlier, Arnhem Block and Murphy Inlier (Plumb et al, 1990). Early Proterozoic basement rocks in the McArthur Basin include the Scrutton Volcanics which have been dated by U - Pb in zircon at 1857± 30 Myr (Pietsch et al, 1991). A major structural feature of the southern McArthur Basin is the Batten Trough, also known as the Batten Fault Zone, a 70km wide zone of extensive faulting, trending north northwest. The Batten Trough bounded on the east by the Emu Fault and obscured to the west by the Roper Group of sedimentary rocks is one of several asymmetric synsedimentary grabens which developed in the McArthur Basin after deposition of the Tawallah Group, possibly as a failed intra-continental rift similar and parallel to the Mt Isa orogen (Plumb and Wellman, 1987). Up to twelve kilometres of sediments was deposited within the Batten Trough in a westwards thinning wedge, compared to four kilometres of sediments on the adjacent Bauhinia and Wearyan shelves. Cambrian aged Bukalara sandstone, 30m to 100m thick, overlies the McArthur Basin sedimentary rocks in much of the Batten region and frequently forms topographic plateaux. Flood basalts of Cambrian age become prevalent in the southern portion of the region, although they are generally obscured by younger sediments. The Merlin kimberlite field represents the youngest known volcanic event in the region. Cretaceous aged sedimentation has been widespread in the area but the rocks have now been largely removed by erosion for a distance extending some 200km south from the Gulf of Carpentaria coastline. This stripped area is characterised by well-dissected drainage interspersed with isolated, remnant, poorly drained, pisolite covered planation surfaces. One such remnant surface is host to the Merlin kimberlite field. The southern limit of the stripped Cretaceous is marked by a well-defined escarpment, which also represents a major drainage divide. Streams to the south flow southwards to the Georgina Basin, while those on the north side of the escarpment flow north to the Gulf of Carpentaria.
2.3 Local Geology Merlin Plateau Geology The Merlin plateau is a preserved, Tertiary aged (Pietsch et al, 1991) planation surface, with a slight declination to the north of less than 1 degree. The plateau surface is a scrubby sand-drifted plain underlain by iron pisolites and, in some instances, ferricrete, which in turn is underlain by a flat-lying section of lower Cambrian Bukalara sandstone. A characteristically intensive jointing pattern dissects the sandstone sheet surface and controls a dendritic to trellis pattern of tributary drainage. The eastern margin of the plateau sharply abuts an uplifted block of Proterozoic aged sediments of the McArthur Group, while more regionally, the plateau lies between NNW trending faults which parallel the Emu fault to the west.
21
Two differing aged Cretaceous sedimentary rock units have been identified on the plateau. These are: 1. White Silicified Quartzite: This rock unit is easily recognisable by both its white silicified nature and the abundance of preserved plant fossil casts it contains. The quartzite is mostly massive, with a maximum preserved thickness of <3m but is usually <1m, and conformably overlies the Bukalara sandstone in all cases. This sandstone unit is reported by Pietsch et al (1991) as being common in the Bauhinia Downs 1:250,000 sheet area, and based on the recognised Neocomian plant fossils (Archbold, 1998), the sediments are believed to be deposited in non-marine, shallow water environments. Several plant fossil species have been identified in the rock unit (Archbold, 1998), namely:- Ptilophylum sp., Hausmannia sp., Cladophlebis sp. and Araucaria, sp. These plants date the rocks as belonging to the Neocomian – Early Barremian period of the Early Cretaceous. 2. Mottled, Bioturbated Sandstone: These sediments form a thin veneer of <1m in most instances and conformably overlie both Bukalara sandstone and, in rare instances, the white silicified Cretaceous aged quartzite. These sediments have not been dated directly, but are believed to equate to sediments in the kimberlite pipes, which have been age dated from marine ammonite fossils, namely Australiceras sp., (Archbold, 1998), which has a Late Aptian – Late Albian time range. Table 2.1: Age of Merlin Fossils
Albian Marine Aptian Fauna
Infill Sediments
Barremian Early
Cretaceous Neocomian
Flora On Plateau
Ref: Reddicliffe, T. H. (1999) Merlin Kimberlite Field The flora and fauna on the Merlin plateau is consistent with regional observations (Skwarko, 1966) and support the conclusion that widespread Early Cretaceous terrestrial sedimentation was followed by a marine transgression. Evidence of the latter is preserved within the kimberlite pipe structures at Merlin. The Cambrian aged sediments are represented by the Bukalara sandstone, which comprises a flat lying to gently warped, slightly feldspathic quartz sandstone. Thin interbeds (<2m) of micaceous siltstones are common throughout the formation. It is the dominant sedimentary rock in the area and is intruded by all of the Merlin kimberlite pipes. The thickness of the formation was determined by drilling to be 120m to 150m thick in the vicinity of the Merlin field, and appears to shelve to the south. The sandstone unconformably overlies McArthur River Group sediments in the area. Structural Setting The Batten region is conducive to structural analysis because of the relatively good exposure of structures, particularly in areas of flat lying, exposed Bukalara sandstone. While the structural setting of the Merlin field and local structural controls are generally apparent, the structural mechanism which controls the focus of the Merlin intrusives is speculative. Regional Setting Regional structural trends deduced from various interpreted data-sets have been summarised by Leaman (1998). A regional northwest southeast grain is present but is generally not dominant in terms of the rift and basin evolution. In the Batten area only portions of the rift system have been influenced by this orientation and hence Leaman (1998) concludes that the mapped Calvert Fault system is a much younger stress release even though there are local anomalous features along its general trend. The location of the Merlin kimberlite field on the interpreted trace of the Calvert Fault would support Leaman’s conclusions, given the Devonian age of the kimberlites. Leaman (1998) also revealed that although early basin patterns involved true rifts and half graben structures, there is no coherent, large, single structure evident within the broader McArthur Basin. Each rift element or region appears as a sub-basin or cell with its own rift and transform pattern within
22
a gross framework defined by the northwest crustal grain. Each cell revealed a varied stress field both between cells and at different times in the cycle. These patterns were developed early in the basin history and were sites for accumulation of thick continental lava piles. Although elements of the rift system trend roughly northwest or northeast, the most important regional trends are west northwest and east northeast. Each of the trends is associated with continental uplift or horst formation. A north northeast trending transfer style shear or wrench structure was recognised near the HYC lead-zinc deposit by Leaman (1998). He concludes that this structure remained very active until the end of the second sedimentary cover fill and rift stage mafics and continued to move until deposition of the McArthur Group. Some 40km south of the HYC Pb-Zn deposit and on this same north northeast structure is located the Abner sandstone breccia pipe and associated indicator mineral bearing north northeast trending fractures. Assuming that this pipe is of a similar age to the Merlin kimberlites then it would indicate that these structures have been active over an even greater time span than suggested by Leaman. This structure is readily recognisable on satellite imagery. Much smaller structures with the same trend are associated with the E.Mu pipes, some 40km due east of the Abner Range structure, suggesting that the Merlin field probably lies on a similar, regional structure. However, a north northeast trending regional structure is not evident on the satellite image (Figure 5.10). A northwest trending fault which parallels the Emu Fault is evident, which would intersect both the southern cluster of the Merlin pips and the Kay/Ector group.
Figure 2.1 Satellite Image of the Merlin Plateau showing location of Emu pipes
E.Mu Pipes
Fault parallel to Emu Fault
Emu Fault
23
Structure The local structural control for the Merlin kimberlites is best illustrated by Excalibur and its nearby breccia pipes where the pipes can be seen to be associated with indicator mineral bearing fractures trending 015o magnetic. Other structural features associated with the intrusives are concentric fracturing and marginal sandstone breccias. Concentric fracturing has been observed at E.Mu 2, Excalibur, Gawain, and Perceval, with the best developed examples being at E.Mu 2 and breccia pipe 1. The fractures are usually up to 1m apart and are constrained to within 10m of the edge of the pipe.
2.4 Deposit Type The Merlin field is fortuitously preserved within a sand and iron pisolitic covered, poorly drained Tertiary aged land surface which equates to the basal Cretaceous unconformity. Preserved on the land surface are remnant, Barremian aged, silicious quartzites of terrestrial/lacustrine origin and Albian aged bioturbated sandstones of marine origin. These latter sediments are also preserved within the pipe structures. A possible explanation for this is that the pipes were intruded during the time hiatus between the two sedimentary sequences. However this explanation is not supported by the geochronological age of the pipes, which is Devonian based on both K-Ar and Rb-Sr dating of phlogopite. With the exception of the two E.Mu pipes which have no infill sediments associated with them, the Merlin pipes are variously ‘corked’ by infill sediments. The identical nature of the sediments and similarities with the regional Cretaceous stratigraphy indicates the infill sediments represent preserved basal Cretaceous sediments. The sagged nature of the infill sediments, the upturned edges with associated slickensides, the presence of a basal non-kimberlitic conglomerate and the thickened iron pisolite profiles, all suggest that the Cretaceous aged sediments have subsided into the pipe structures. This subsidence appears associated with the retreat of the kimberlite, which is likely due to solution weathering of the kimberlite. A greater retreat in some of the pipes allows a greater section of the overlying Cretaceous sediment to be captured and subsequently preserved within the pipes structures, and accounts for the presence or absence of the mudstone in the infill sediments. Five broad categories of kimberlite facies have been recognised; these being epiclastic kimberlite, tuffisitic kimberlite, tuffisitic kimberlite breccia, pelletal tuffisitic kimberlite and micaceous tuffisitic kimberlite. Collectively, particularly the presence of epiclastic kimberlite in the E.Mu 1 pipe and in Gawain, indicate the pipes are preserved at the upper diatreme level. 2.4.1 Pipe Geology and Mineralogy The fifteen kimberlite pipes comprising the Merlin field are regionally located on the eastern shoulder of the Batten trough, some 6km east of the Emu Fault and on the projected trace of the northwest trending Calvert Fault. Four discrete clusters of pipes are present in the elongate field, which extends over an area of 10km by 5km. Within each cluster the distances between the pipes varies from 100 to 400m, but in one instance, is 1500m. The distance between the clusters is usually 3km. The thirteen kimberlite vents representing eleven discrete pipes are situated within the mining lease and named Excalibur, Palomides, Sacramore, Launfal, Launfal North, Kaye, Ywain, Gawain, Tristram, Gareth, Ector , Bedevere and Perceval. All of the pipes in the field, including the two E.Mu pipes which are outside the bounds of the mining lease, have intruded the Cambrian aged Bukalara sandstone, which is flat lying and unconformably overlies Proterozoic sediments in this area. Pipe Sizes The pipes vary in diameters from 20m to 250m, and from limited drilling data appear to maintain their gauge at depth. The various dimensions are shown in Table 2.2.
24
Table 2.2: Dimensions of Merlin Kimberlite Pipes
Cluster Pipe Diameter Area Cluster Area
1 E.Mu 1 E.Mu 2
250m 100m
4.5 ha 1.8 ha 6.3 ha
2
Bedevere Ector Kay Gareth
40m 125m 125m 60m
0.13 ha 1.2 ha 1.2 ha 0.28 ha
2.81 ha
3 Ywain Gawain
25m 50m
0.05 ha 0.2 ha 0.25 ha
4
Excalibur Launfal Launfal North Palomides Sacramore Tristram Perceval
60m 50m 30m 60m 60m 50m 20m
0.28 ha 0.2 ha 0.07 ha 0.28 ha 0.28 ha 0.2 ha 0.03 ha
1.34 ha
Ref: Reddicliffe, T.H. (1995) Supplementary Report to the Australian Diamond Exploration Summary of Exploration Activity Report.
2.4.2 Pipe Infill Sedimentary Rocks A characteristic feature of the Merlin kimberlites, with the exception of the two E.Mu pipes is that the pipe structures are ‘corked’ by non-kimberlitic sedimentary rocks of Cretaceous age. Due to the planar nature of the Merlin plateau and the widespread distribution of iron pisolites and sand, the sedimentary rocks infilling the pipes are not distinguishable at the surface. Where they have been exposed in sample pits, in many instances, they are not easily distinguished from the surrounding sandstone country rocks. The pipes can be placed into three categories with respect to the infill sediment characteristics, the various thicknesses of which are shown in Table 2.3. These categories do not in general equate to the various clusters, and Ector is unusual in having both styles preserved in the one pipe structure.
(i) Sandstone Infill A bedded bioturbated sandstone infill sedimentary sequence is present at Launfal, Palomides, Sacramore, Gareth, Kay and the western portion of Ector. This infill is up to 15m thick with individual beds up to 1.5m thick and is not contiguous with the surrounding Cambrian aged sandstones. The sandstone has a sag appearance with the margins typically upturned. A thin basal conglomerate bed is present in all cases, and is particularly obvious at Palomides. This conglomerate is devoid of obvious coarse kimberlite material, as is the overlying sandstone. The conglomerate is matrix supported and consists of sub-rounded, sandstone cobbles (<10cm in diameter) in a fine grained, sandy matrix. Black chert cobbles are common in parts of the Palomides conglomerate. The bed is usually 30cm thick, but commonly thickens at the margins of the pipe to up to 1-2 metres. Overlying the sandstone is a 4m thick section of iron pisolites, which at the pipe margins, sharply abuts the <0.5m pisolite layer overlying the Bukalara sandstone. These pisolites represent a transported lag deposit and is very characteristic of all the pipes, suggesting that there has been subsidence of the kimberlite and overlying sediments at a late stage, ie, in the Late Tertiary or post Tertiary. The margins of the pipes are marked by a thin selvage of kimberlite, thinning upwards, which is wedged between the sandstone infill sediments and the Bukalara sandstone wall rocks. Slickensides are also occasionally observed in this zone.
25
(ii) Mudstone/Sandstone Infill The remainder of the pipes, Excalibur, Launfal North, Tristram, Gawain, Ywain, Bedevere and the eastern portion of Ector, have a combination infill of mudstone overlying sandstone. The sandstone unit appears similar to that present in the sandstone only infilled pipes, and evidence from drilling indicates the presence of a thin basal conglomerate bed. The thickness of this infill mudstone/sandstone sedimentary sequence varies between the pipes from 26m to 42m. The sandstone laps on to the margins of the pipes, with the mudstones filling the core. The mudstone is a massive unit varying in colour from white to grey. A selvage of kimberlite is usually present around the periphery of the pipes, similar to that seen in the sandstone infilled pipes. (iii) No Infill Sediments E.Mu 1 is expressed by a well developed amphitheatre, 250m wide and 30m deep. Within the amphitheatre, the kimberlite is covered by a thin veneer of soils and sand. The pipe is partially cut by Matheson Creek, which aided the development of the amphitheatre. E.Mu 2 lies within Matheson Creek and is partially covered by superficial stream deposits. Apart from well developed concentric fracturing, there is no amphitheatre development. It is possible that these two pipes had infill material, which is no longer preserved due to the incised erosion of the pipes, which are both traversed by Matheson Creek.
Table 2.3: Thickness of Infill Sediments within the Merlin Kimberlite Pipes
Cluster Pipe Sandstone Mudstone/ Sandstone None
1 E.Mu 1 E.Mu 2
30m scarp outcrop in river
2 Bedevere Ector Kay Gareth
15m 15m 15m
42m
3 Ywain Gawain
30m 26m
4 Excalibur Launfal Launfal North Palomides Sacramore Tristram
8m 8m 8m
26m 20m 32m
2.4.3 Age of Infill Sedimentary Rocks The stratigraphy of the sediments is equivalent to the Cretaceous aged sediments present elsewhere in the region. Fossil evidence dates these sediments as Cretaceous (Archbold, 1998) based on the presence of the marine deep-water ammonite Australiceras, which range up to 1m in diameter. There is no firm evidence of the older, silicified, plant bearing rocks within the pipe sediments. However, soft white sandstone has been intersected in drill holes in both Gareth and Gawain, generally beneath the harder sandstone beds. It is possible this soft sandstone is the equivalent of the silicified, white, fossiliferous sandstone seen at surface in the area. The sandstone unit is devoid of indicator minerals and diamond suggesting a time hiatus to allow erosion and removal of kimberlite ejecta prior to the deposition of the sediments. The deep nature of the infill, up to 42m at both Bedevere and Tristram, is enigmatic and difficult to explain by infilling of the pipe after erosion but rather is more suggestive of pipe retreat due to post emplacement settling
26
or, alternatively, solution weathering. The time hiatus between the geochronology age of the pipe and the overlying marine Cretaceous aged sediments is more supportive of the latter conclusion. The fact that the mudstone unit is only preserved in those pipes with a thick infill sequence, and always overlies the sandstone, is a reflection of the deeper pipe’s ability to preserve a thicker Cretaceous sedimentary sequence. The smaller discrete pipes have the thickest preserved infill sediments suggesting they are more susceptible to solution weathering, and hence allow deeper subsidence. Collectively, these factors support the premise that the Cretaceous aged sedimentary rocks have subsided into the kimberlite after cessation of intrusive activity.
2.4.4 Kimberlite Facies The Merlin kimberlites have been sufficiently core drilled to allow a definitive description of the various kimberlite lithologies which comprise the two kimberlite facies present within the kimberlite pipes. From available material from some of the pipes five broad kimberlite lithologies have been recognised, and are described below, using the classification of Mitchell (1985). (i) Crater Facies (a) Epiclastic Kimberlite
The most significance occurrence of bedded tuffs is within the E.Mu 2 pipe, which has been described in detail by Collier, 1987. No tuffs are present in E.Mu 1, or any of the other kimberlite pipes. Collier’s description is as follows:
‘A characteristic feature of the E.Mu 2 is the abundance of spherical lithic lapilli, indicating aerial ejection of consolidated fragments of adhering kimberlite, olivine megacryst or crustal xenoliths, each with molten magma. Bedding varies from 20o at 12.6m to 45o at 63.4m and is indicated by marked variations in the grain size, degree of sorting and by imbrication of clasts. There is also evidence of upward grading of the beds, with coarse bands containing clasts to 4mm. The rock is dominantly composed of rounded to sub-hedral olivine crystals and sub-rounded kimberlite clasts. Minute equant chrome spinels are common within the olivines. There is rare relict phlogopite and occasional pale ragged crystals of aegirine. There is a minor content of angular crustal xenoliths, chiefly white, fine grained dolomite.’ Epiclastic kimberlite in the form of bedded tuffs has also been observed as a raft within Gawain at a depth of some 200m below current surface. (ii) Diatreme Facies (a) Tuffisitic Kimberlite Breccia
This is the most common component of all of the pipes, with the exception of E.Mu 2 and Ywain, and represents the diatreme facies of kimberlite (Figure 2.6). The rock is characterised by two generations of mostly pseudomorphed olivine (25-30%), a rounded macrocrystal population <15mm diameter, and an anhedral to subhedral population <1mm. Phlogopite is present as <1mm laths (2-10%), which is typically altered to green chlorite. The fine grained groundmass is mostly altered to serpentine with primary minerals of mica, spinel, apatite and calcite. Two phases of mica were recognised by Lee et al (1995) who reported clear cores overgrown by later stage mica. Crustal xenolith content varies (15% to 40%) but is dominated by dolomite and sandstone fragments. Mantle xenoliths, are not common, appear to be of lherzolitic composition, are totally altered and <4cm in diameter.
(b) Tuffisitic Kimberlite
This is similar to the tuffisitic kimberlite breccia, but with a low (<15%) xenolith content (Figure 2.2). The olivine macrocrysts and microcrysts can represent up to 40% of the rock.
27
Figure 2.2 Tuffisitic Kimberlite (thin section mag x 40)
Figure 2.4 Micaceous Tuffisitic Kimberlite (thin section mag x 40)
Phlogopite
Olivine
Phlogopite
Olivine
Fine grained glassy rim with olivine
Dolomite
28
Figure 2.5 Tuffisitic Kimberlite (polished sections mag x 2)
Figure 2.6 Tuffisitic Kimberlite Breccia (polished section mag x 2)
(c) Pelletal Tuffisite Kimberlite Breccia The Palomides pipe is characterised by pelletal tuffisitic kimberlite breccia (Figure 2.3). The tuffisite consists of common rounded autoliths mostly nucleated on dolomitic fragments <2cm in diameter with lesser nucleated on olivine megacrysts. The kimberlite selvage is up to 5mm thick, and comprised of olivine phenocrysts, mica, carbonate and serpentine. Country rock xenoliths can represent up to 30% of the rock.
These large spherical structures are typical of globular segregationary hypabyssal kimberlites (Lee et al, 1998) and are believed to have formed either during diatreme formation or earlier during ascent in a more hypabyssal-like environment and then were carried though into the final fluidisation process during diatreme formation. This latter possibility would seem the most likely as the crater facies present in E.Mu 2 would indicate the pipes are currently exposed at the upper diatreme level.
(d) Micaceous Tuffisite Kimberlite
Micaceous tuffisite is present in many of the pipes, generally as a minority component, and is best developed in Ywain where it appears to be the only
Kimberlite fragments with olivine phenocrysts
Lithic Fragments
Olivine Macrocrysts
Olivine Microcrysts
Olivine Macrocrysts
Olivine Microcrysts
29
component (Figure 2.4). The kimberlite is extremely weathered and altered making petrographic study difficult. Two generations of olivine is present (10-20%) with phlogopite being up to 60% of the rock. The ground mass is completely altered to serpentine and no xenolith material has been recognised.
2.4.5 Geochronology of Pipes Two of the Merlin pipes have been dated giving consistent ages of approximately 360ma.
E.Mu 1: The E.Mu 1 pipe was dated using K-Ar (Atkinson et al) giving an age of 360 ma±4 ma.
Excalibur: The Excalibur pipe was dated using Rb-Sr techniques (Webb, 1994)
on phlogopite giving an age of 367±4 ma/352 ±3 ma. (Table 2.4) Table 2.4: Geochronology
Model Age (Ma) Sample Rb (ppm)
Sr (ppm)
87Rb/86Sr #87Sr/86Sr 0.705 0.710
BH113 Phlogopite
691.0 90.1 22.395 0.82179 367±4 352±3
30
3 EVALUATION TECHNIQUES AND METHODOLOGY
3.1 Introduction
The evaluation of a kimberlite body with a view to determining the potential commercial significance of the deposit requires the estimation of 5 main factors, these being deposit style, tonnage/volume, diamond grade, diamond value and diamond security. The techniques utilised and methodologies adopted to measure and quantify these factors for the Merlin kimberlites are outlined below.
3.2 Deposit Style Diamond deposits typically fall into 4 categories, these being;
Marine Deposit –onshore or offshore. Continental Alluvial Deposit –current or paleochannel. Primary Hardrock Deposit –diatreme, hypabyssal plug/blow or dyke. Sedimentary Hardrock Secondary Deposit
The identification of the style of the diamond deposit is determined through a geological assessment. Once the style is confidently determined it allows for a further assessment of additional factors pertinent to the deposit style that will be critical to determining techniques and methodologies to evaluate the commercial potential of the diamond deposit. In the case of Merlin, a hardrock deposit comprising 4 discrete clusters of pipes all of which have the upper levels of diatreme facies kimberlite preserved. The amount of kimberlite removed by post intrusive erosion processes is not known quantitively. Having been identified as typical diatremes, the following factors have to be assessed for each of the pipes under evaluation;
Kimberlite Facies – Being volcanic intrusives kimberlites are normally host to different kimberlite phases or facies which in turn can result in different diamond grades and/or less commonly diamond types. Hence these different facies have to be identified and quantified in terms of their volumetric significance relative to the entire pipe. Depth and intensity of Weathering – Kimberlites due to their mineralogy are extremely susceptible to weathering. The importance of weathering is that intense weathering can result in solution weathering which in turn can lead to volume reductions in the deeply weathered but mostly upper part of the pipes. The effect of volume reduction is to enhance grade since the diamonds are not dissolved. The second effect of weathering is to reduce rock density which in turn increases any grade measured in terms of tonnes. At Merlin the near surface upper portions of the kimberlite have SG’s as low as 1.3 while for the fresher deeper portions of the pipes it increases to 2.6, which represents a density change of 100%. This can result in erroneous conclusions if near surface weight based grades are extrapolated to depth.
Understanding and quantifying the above two factors is critical before any further assessment can be made of the pipes. This is primarily achieved through the undertaking of sufficient core drilling and to a lesser extent pit mapping where practical considerations such as depth of overburden allow.
3.2.1 Drilling Because the core may be utilised for additional analytical analysis such as determining microdiamond frequencies, either PQ or HQ is the preferred gauge of core but smaller diameter core such as NQ can be used if other practical considerations prevail. In addition it is important to used drill bits which use only synthetic diamonds if analysis of the core is likely, as synthetic diamonds are easily differentiated from natural diamonds. No unusual drilling techniques are required, although triple tube can be used in the weathered zones as a means of reducing core loss.
31
RC drilling methods have limited applicability in the investigation of kimberlites where visual information s required in identifying and classifying the rock. In logging the core the following information is collected as a means of classifying the kimberlite in terms of a facies type;
Groundmass mineralogy Type and abundance of macrocrysts Type and abundance of country rock inclusions Abundance of Pelletal kimberlite Presence of bedding or layering Degree of Weathering Specific Gravity
In addition representative samples may be taken for petrology and geochemical analysis.
Petrology – This is normally used in the early assessment and gross classification of the kimberlite so that the fine mineralogy can be correctly identified and the rock type confirmed. This is not normally a rigorous process unless the identity of the rock type is in doubt or the diamond bearing nature of the rock is not confirmed. There is normally no advantage in differentiating various kimberlite facies based on petrological inspection as opposed to visual inspection. . Geochemistry – This is used in the early assessment and classification of the rock as a kimberlite. The technique has little or no bearing with respect to the ongoing evaluation of the commercial potential of a particular kimberlite. There is normally no advantage in differentiating various kimberlite facies based on gross geochemistry rather than by visual inspection. Heavy Mineral Assemblage – This is used in the early assessment and classification of the rock as a kimberlite, as well as giving an indication of potential diamond content. The chemistry of the indicator minerals, chromite, pyrope garnet and picroilmenite can be used to determine the depth of origin of the kimberlite magma and hence determine whether the magma has originated from within the diamond stability field. The mineral chemistry information becomes irrelevant once direct testing for diamonds has been completed and hence has no bearing on the evaluation of the commercial potential of the kimberlite pipe.
3.2.2 Pitting This is usually the first technique to be used to establish the style of the deposit. However it is very dependent on the thickness of the overburden, the presence or absence of infill sediments and the degree of weathering. Notwithstanding the geometry of the body at surface can usually be established by pitting or costeaning if surficial overburden is not too thick. The nature of the kimberlite facies cannot always be clearly identified if weathering is intense and clays are well developed. Samples taken for petrology, geochemistry and identification of indicator mineral assemblages are usually severely compromised. When dealing with kimberlite pipes like those at Merlin it is generally universally accepted that;
-The pipes are intrusive volcanic magmas that have originated at depths >150km. -The pipe body will persist to a significant depth but may taper or change shape with depth. -Epiclastic facies represent the initial surface airfall ejecta from the volcanic event. -Diatreme facies represents the upper portion of the volcanic event and is heavily contaminated with country rock. The formation of this facies is in direct response to the volcanic event breaching the surface and degassing.
32
-Hypabyssal facies is regarded as late stage and may intrude the diatreme faces in places, but more often than not is representative of kimberlite events that have not breached the surface.
3.3 Tonnage/Volume Once the style of the diamond deposit has been identified the volume/tonnage can be assessed by undertaking an appropriate amount of drilling. Initially this requires the surface expression of the pipe to be defined by shallow RAB drilling or pitting if the depth of overburden allows. The geometry of the pipe is then required to be defined at depth by either RC or core drilling. The drilling aims to define kimberlite/country rock boundaries and also to define the volumetric significance of different kimberlite facies if they are present. For small pipes such as those at Merlin it is difficult and costly to accurately define volumetrically less significant kimberlite facies. Hence calculated pipe volumes are usually attributed to the majority kimberlite facies.
1) Drilling – As drilling aims to collect information in addition to overall geometry, there is a preference for core drilling to be used, or a combination of RC pre-collars with core tails.
2) Surface Surveying – It is important that drill hole collars are located by surface survey
undertaken by a competent person and that the survey is tied into a national or local datum.
3) Downhole Surveys – It is critical that drill holes are surveyed at appropriate intervals which would normally not exceed 25m downhole.
3.4 Diamond Grade The determination of grade for a kimberlite relies heavily on two assumptions, namely; -The diamonds are distributed reasonably homogenously throughout any particular kimberlite facies.
-The size/frequency distribution of the diamonds remains constant for any particular kimberlite facies.
In addition diamond grade based on total diamond content as opposed to process plant recovered diamonds will be significantly different. The particulate nature of diamond and the variability of stone size is also a complicating factor, to the extent that any sample result is a snapshot of grade rather than an absolute grade. To address this latter issue, grades are in the first instance based on the average number of stones recovered per unit of sample which is then multiplied by the mean stone weight in carats. The plant recovered grades are however very sensitive to the size and shape of the lower screen aperture, so that this needs to be stated when grades are determined. Grades based on total diamond content need to be stated as such to avoid misinterpretation of the information. However, it is not normal procedure to quote grade inclusive of the non-commercially sized diamonds.
3.5 Diamond Value The valuation of diamonds is a specialised business undertaken by trained diamond valuers who may also be in the market buying or selling diamonds. It is commonly found that different valuers can attribute significantly different values to the same diamond or parcel of diamonds. Of the four factors that valuers use to determine specific value, namely, weight, shape, colour and clarity, it is the perception of the colour that is the common cause of disagreement. Like any commodity market conditions is also a significant factor which can see the demand for specific categories of diamonds fluctuate considerably relative to other categories.
33
The value of the diamonds from a particular project is, for simplicity, often quoted as a singular price and always in $US. Without any qualifications this can be misleading. Like grade the average value of a diamond parcel is significantly influenced by the contribution from the smaller diamond sizes. Hence if grades are quoted in this manner it is important that the diamond parcel represents ROM recovery, if it doesn’t then the average diamond value has no meaning. When using diamond value to determine revenues, a simplistic approach is to multiply the average diamond value by the grade provided the average grade and average diamond value are determined using the same diamond distribution. This approach is not adequate for detailed economic analysis but rather grade and value models have to be established. One of the weaknesses of this approach is that if the distribution of value is significantly skewed towards the large diamonds, as is the case for Merlin, then values based on small numbers of diamonds can give misleading results, in that they could be too high or too low. Although deposit dependant, generally a minimum 50 diamonds per diamond size category is required to establish confidence in the average carat value per size category. This is so the full variety of colour, size and shape and their relative abundance can be observed for each size category. At the sampling stage recovering 50 individual diamonds in size categories of 5cts and above can be problematical and hence the average carat value for these size categories need to be carefully assessed. A grade model is established by determining the contribution to grade for each diamond size category. In the first instance the number of stones per size category is established from sampling data. Then using the mean stone weight for each size category the grade in carats can be calculated. Using the average diamond value for each size category the contribution to value for each size category can be calculated in conjunction with the contribution to grade established in the grade model. The benefit of this approach is that the effect on revenue of varying the lower screen cut-off can be easily modelled.
3.6 Security and Integrity At all stages in the evaluation of a diamond deposit security is important to ensure integrity of the results that are obtained. The most effective approach to security is;
- Limit the opportunity of physical contact with the diamonds during processing. - Restrict access to final recovery areas of the process plant. - Record all diamonds that are recovered. - Chain of custody for diamonds once they are registered.
The danger with diamond loss is not that it will effect grades but more that a true reflection of the diamond size distribution and the diamond value could be compromised.
3.7 Sampling Techniques The purpose of sampling with respect to kimberlites is aimed exclusively at identifying kimberlite facies and determining diamond grade and diamond value. The specific sampling techniques and their purpose are discussed below; 3.7.1 Core Samples The collection and processing of core samples can serve three purposes; it allows for logging and visual identification of kimberlite facies types, italso provides material for microdiamond analysis and if the core is sufficiently large and there is sufficient volume then processing for commercial diamonds can be undertaken.
1) Logging – The visual logging of core to identify and differentiate different kimberlite facies is done using the following parameters;
- Groundmass mineralogy
- Type and abundance of macrocrysts
34
- Type and abundance of country rock inclusions - Type and abundance of mantle xenoliths - Abundance of Pelletal kimberlite - Presence of bedding or layering
2) Microdiamond Analysis – The core from different kimberlite lithologies can also be used
to establish their microdiamond content and hence compare the commercially sized diamond bearing potential of these different lithologies, both inter-pipe and intra-pipe. The interpretation relies on there being an established relationship between the microdiamonds and the commercially sized diamonds. Individual samples of core are usually in the range 50kg to 100kg. Only inferred diamond grades can be deducted from microdiamond analyses. No
information pertaining to diamond value can be established from microdiamond analyses. 3) Bulk Core Sampling – If grades are not too low than Large Diameter Core (LDC) drilling
can be undertaken to provide material from depth within the pipe. This material would be crushed and processed through a DMS plant in a similar manner as to the processing of larger surface bulk samples. This approach can provide reliable data if the samples are sufficiently large to provide a statistically significant number of diamonds.
3.7.2 Rock Samples
The collection and processing of rock samples of a specific kimberlite facies provides material for microdiamond analysis.
1) Logging – The visual identification of the kimberlite facies is done using the same parameters as for logging core.
2) Microdiamond Analysis – Rock/boulder samples from different kimberlite lithologies has
also be used to establish their microdiamond content and hence compare the commercially sized diamond bearing potential of these different lithologies, both inter-pipe and intra-pipe. The interpretation relies on there being an established relationship between the microdiamonds and the commercially sized diamonds. Individual rock samples are usually in the range 50kg to 100kg. The integrity of the sample result is dependant on the sample being a contiguous insitu block of kimberlite that has not suffered any volume reduction due to weathering processes and whose volume has been carefully measured or surveyed. If the boulder is sufficiently large then both microdiamonds and macrodiamonds may be recovered.
Only inferred diamond grades can be deducted from microdiamond analyses. No information pertaining to diamond value can be established from microdiamond analyses.
3.7.3 Pit Samples 1m3
The collection and processing of pit samples from different kimberlite facies types provides material for microdiamond and macrodiamond analysis.
1) Logging – The visual identification of the kimberlite facies is done using the same parameters as for logging core.
2) Microdiamond Analysis – Pit samples from different kimberlite lithologies can also be
used to establish their microdiamond content and hence compare the commercially sized diamond bearing potential of these different lithologies, both inter-pipe and intra-pipe. The interpretation relies on there being an established relationship between the microdiamonds and the commercially sized diamonds. Individual samples of core are usually in the range 50kg to 100kg. The integrity of the sample result id dependant on the sample being a contiguous insitu block of kimberlite that has not suffered any volume reduction due to weathering processes and whose volume has been carefully measured or surveyed.
35
Only inferred diamond grades can be deducted from microdiamond analyses. No information pertaining to diamond value can be established from microdiamond analyses.
3.7.4 Pit Samples 100m3
The collection and processing of large pit samples from different kimberlite facies types provides material for commercially sized diamond grade analysis.
1) Logging – The visual identification of the kimberlite facies is done using the same parameters as for logging core.
2) Commercial Diamond Analysis – Pit samples from different kimberlite lithologies is used
to establish their process plant recovered diamond grade and hence compare the commercially sized diamond bearing grade of these different lithologies, both inter-pipe and intra-pipe. Individual large pit samples are in the order of 100m3 or approximately 200t.
These samples are sufficiently large to establish a reliable plant recovered commercial diamond grade No reliable information pertaining to diamond value can be established from individual samples since insufficient numbers of diamonds are recovered.
3.7.5 ROM Samples The processing of larger volumes/tonnages of kimberlite serves a single purpose that being to recover sufficient diamonds to enable a reliable estimation of diamond value to be established. While a measurement of the volume/tonnage processed is useful it is not necessary for the purposes of recovering the diamond parcel. The size of the sample to be processed is dependent on the diamond grade, the lower the grade the greater the amount of material required to be processed to recover a representative parcel of diamonds. The size of the diamond parcel required to be recovered is dependent on the size-frequency distribution of the diamond population. The better the size-frequency distribution the larger the diamond parcel will need to be, as the larger diamonds will have a greater influence on average parcel value than for parcels that have fewer large diamonds. Depending on the range of colour, shape and clarity of the diamond parcel, approximately 50 diamonds are needed for each diamond size category to establish an average value for any size category. This is normally not a problem for the smaller diamond size categories, but for the larger size categories where diamond recoveries are less frequent recovering sufficient numbers of diamonds to get a reliable estimate of average value can be difficult.
3.8 Sample Collection The protocols adopted for the collection of samples is outlined below. 3.8.1 Core Samples Core samples are only selected from intervals of drill core that represent a single kimberlite facies and have suffered no core losses as a consequence of the drilling process. The core is selected either as a single run or as each alternate metre length. Sufficient core is selected so as the sample is approximately 100kg in weight. A number of selected pieces of core are used to determine the SG of the core. In addition the volume of the core is calculated using length and diameter measurements. The core is cleaned with a wet cloth to remove any adhering material and then bagged initially in standard calico sample bags which are then placed in plastic bags. The samples are tagged with an appropriate discriminating sample number for ongoing tracking and reference. The data is recorded on a sample card, which is dispatched to Perth for entry in the sample database.
36
3.8.2 Rock Samples Large singular boulders of a specific kimberlite facies occasionally provide an opportunity for testing provided the origin of these boulders is known with certainty. In the case of Merlin the boulders will have been discarded at one of the open pits or at the ROM pad. In the latter case the origin of the boulder is less likely to be known. The boulder is moved to a cement pad, washed and weighed and placed on a tarpaulin. The boulder is then broken into smaller pieces using a hammer. The rock pieces are placed into a large bulka bag along with the fines which are swept up with a brush and pan. Using selected representative fragments the SG of the boulder is determined by the weighing in air and water technique. The sample is tagged with an appropriate discriminating sample number for ongoing tracking and reference. The data is recorded on a sample card, which is dispatched to Perth for entry in the sample database. 3.8.3 Pit Samples 1m3 The taking of 1m3 pit samples at Merlin is possible due to the previous mining operations, an example taken from Gawain is shown in Figure 3.1. Pit sample sites are selected so as they represent a single kimberlite facies. The surface is cleaned, levelled and the proposed pit is marked out. The sample is dug by hand using a pick and shovel and depending on the hardness of the material the pit dimensions may be 1m by 1m and 1m deep, 1m by 2m and 0.5m deep or some other variation. The sample is required to be contiguous and be approximately 1m3 in volume. The sample is placed directly into a bulka bag, tied closed and tagged with an appropriate discriminating sample number for ongoing tracking and reference. The pit is measured and the volume calculated. Using a metal barrel of known volume a small sample is collected and weighed and the SG of the material is calculated. The data is recorded on a sample card, which is dispatched to Perth for entry in the sample database.
Figure 3.1 1m3 sample taken from Gawain
3.8.4 Pit Samples 100m3 The taking of 100m3 pit samples at Merlin is possible due to the previous mining operations, an example taken from Gawain is show in Figure 3.2. Pit sample sites are selected so as they represent a single kimberlite facies, the surface is cleaned, levelled and the proposed pit is marked out. The sample is dug using an excavator and the sample placed directly into a truck, so as to avoid rehandling and minimise spillage. The pit is ‘squared’ and the base scraped clean using the excavator bucket, and is then measured using a tape. The dimensions of the surface and base are made along with the depths for each side. From these calculations the volume of the excavated pit is calculated. Using a metal barrel of known volume a small sample is collected and weighed and the SG of the material is calculated. The weight of the sample is also recorded by the truck. The sample is transported to the ROM pad and placed on a prepared pad which has been sheeted with previously processed float material which has high country rock content. The data is recorded on a sample card, which is dispatched to Perth for entry in the sample database.
37
Figure 3.2 100m3 sample taken from Gawain
3.8.5 ROM Samples The taking and processing of ROM samples at Merlin is possible due to the previous mining operations. The ROM samples are differentiated by pipe and when appropriate by kimberlite facies. The sample material is excavated in the pits using an excavator, sometimes loaded directly into a truck but more often stockpiled either within the pit or at a staging point away from the pit. No volume measurement of the material excavated was done, but truck weights were measured when possible. Ultimately the material was transported to the ROM pad and stockpiled for future processing. The material was not placed on a contamination free surface. Prior to processing and due to the high moisture contents the material was spread out to encourage drying.
3.9 Sample Processing and Laboratory Procedures The standard procedures used both in the field and the laboratory for processing samples is outlined below. 3.9.1 Core Samples Core samples are weighed, crushed and digested in acid and fused in caustic to release the diamonds. The diamonds are then recovered by microscopic observation. 3.9.2 Rock Samples Rock samples are weighed, crushed and digested in acid and fused in caustic to release the diamonds. The diamonds are then recovered by microscopic observation. 3.9.3 Pit Samples 1m3
Pit samples of 1m3 are measured volumetrically and weighed, washed to remove dissolvable clays, crushed and then digested in acid and fused in caustic to release the diamonds. The diamonds are then recovered by microscopic observation. 3.9.4 Pit Samples 100m3
Pit samples of 100m3 are measured volumetrically and weighed, but due to their size require processing by DMS plant, with the diamonds recovered by hand sorting.
38
3.9.5 ROM Samples ROM samples are usually difficult to measure volumetrically but weights are recorded prior to processing by DMS plant with the diamonds recovered by hand sorting.
3.10 Surveying The surveying of pits and drill hole collars are all tied into the national grid. All drill hole collars have been located by ground survey and the majority of drill holes have downhole surveys.
3.11 Data Spacing and distribution Because of the nature of kimberlite pipes their geometry can be defined with relatively few drill holes sufficient for the establishment of Indicated and Inferred Resource categories. However, there has been insufficient drilling to identify different kimberlite facies spatially within the pipes when present and hence the pipes are treated as single lithologies. This has a significant bearing on why there are no resources in the Measured JORC category.
39
4 EVALUATION 1993-1998
4.1 Introduction Following discovery of the Merlin diamond field three significant phases of evaluation work were undertaken. These being two phases of RC Drill bulk testing which was followed by excavation of pit samples and a winze sample. The difficulties encountered in undertaking this work and the associated costs saw the project move to trial mining as a means of effectively evaluating the deposit. 4.2 Surface Delineation Following discovery the pipes were initially defined at surface by shallow RAB drilling. Costeaning was mostly ineffective due to the pipes being infilled with Cretaceous sandstones which were indistinguishable from the surrounding Bukulara Sandstone. 4.3 Phase 1 - 1994 RC Bulk Sampling A program of RC Drill bulk sampling was undertaken in 1994. The drill utilised a 215mm diameter roller bit and samples were collected in bulka bags. The moisture content of the samples was exceptionally high which created uncertainty in estimating dry weights for the samples. Eleven of the pipes were drill tested and a total 119.98 tonnes of material was collected and processed. All the holes were drilled from surface and apart from two holes all were vertical. The samples were processed through a MK3 DMS sampling plant located at Cape Crawford. Concentrates were hand sorted in the Ashton Laboratory in Perth. A total 607 diamonds were recovered weighing collectively 35.8 carats. Details of this sampling are shown in Table 4. 1. Although the diamond numbers recovered were recorded only total carat weights for the samples is available, rendering the data unsuitable for detailed grade model analysis. 4.4 Phase 2 - 1995 RC Bulk Sampling A second program of RC Drill bulk sampling was undertaken in 1995. The program was similar to that undertaken in 1994 with the exception that the drill utilised both 215mm diameter and 315mm diameter roller bits. Ten of the pipes including the E.Mu pipes were drilled during the program and a total 262.3 tonnes of material was collected and processed. The samples were processed through a MK3 DMS sampling plant located at Merlin and the concentrates were hand sorted in the Ashton Laboratory in Perth. A total 1,875 diamonds were recovered weighing collectively 57.74 carats. Details of this sampling are shown in Table 4.2. Although the diamond numbers recovered were recorded only total carat weights for the samples is available, rendering the data unsuitable for detailed grade model analysis. 4.5 Phase 3 - 1996 Bulk Sampling The phase 3 bulk sampling was limited to the pipes Palomides, Sacramore, Launfal and Excalibur. The sampling was done by way of open pitting and in the case of Palomides a winze was also sunk. A total 5,260 tonnes was excavated and processed resulting in the recovery of 29,222 diamonds for a total weight of 2,361.5 carats. Details of this sampling are summarised in Table 4.3. It was found that the grades varied radially across the pipes, increasing from the centre to the country rock contact. In Palomides the grades ranged from 17 to 34cpht, in Launfal the range was 28 to 133cpht and in Excalibur the range 35 to 124cpht. At the time there was no geological explanation for this variation. However it is now believed to be due to the uneven development of surface enrichment
40
which is a consequence of solution weathering. With hindsight this has rendered the sample results unsuitable for grade estimation and is an explanation for the large variations of -43% to +322% between the RC drill bulk sample results and the subsequent open pit bulk sample results. Only total carat weights and total diamond numbers for the samples is available, rendering the data unsuitable for detailed grade model analysis.
41
5 MINING AND TESTING OPERATIONS 1998-2003
5.1 Introduction The Merlin mining operation commenced in 1998 and ceased mid 2003. In total 2,237,447 tonnes of kimberlite were processed, with 507,000 carats of diamonds recovered. 5.2 Summary of Past Operations The operations are summarised in Table 5.1. Table 5.1: Summary of total production 1998 - 2003
Tailings/other 15,779 TOTAL 2,010,521 0.21 424,261
Ref: Mine management Plan 2002-2003 The numbers in this table were mine site generated and are at odds with other reports of carats sold and recorded process tonnes. The reconstructed summary is provided in the following Table 5.1, which provides a more accurate assessment of the mining activities. Table 5.2 : Reconstructed summary of past mining operations 1998 - 2003
*Excludes Tailings Ref: Reddicliffe, T.H. (1995) Supplementary Report to the Australian Diamond Exploration Summary of Exploration Activity Report.
5.4 Results of Past Mining Operations The data from the mining operations conducted during the period 1998 to 2003 was collated in 4 separate data sets. Although related the data sets are not easily integrated. A detailed summary of the trial mining results is shown in Tables 5.4 to 5.55 5.4.1 Mine Site Records The mine site records provided the surveyed mined volumes, calculated mined tonnes, processed tonnes and the recovered diamonds for each mined flitch. The flitch volumes and associated diamond recoveries are shown in Tables 5.4 to 5.20. Mined Volumes/Tonnes - The mined volumes were recorded up until late 2002, after which there are no survey records. This affects the lower portion of Gawain pit for which there is no survey data. Generally the surveyed volumes are considered to be very reliable. The mined tonnes on the other hand were calculated using numerous bulk density determinations with no adjustment for moisture content. Processed Tonnes – The processed tonnes are those recorded by the plant weightometer. Not all of the material mined was processed as large boulders and material that was too clayey was rejected and is now part of the ROM pad. The measured tonnes are all wet tonnes as no adjustment was made for moisture content. In some instances water was added to the feed material to assist the sizer in dealing with binding clays. The recorded processed tonnes cannot be reconciled with the calculated mined tonnes with 1,785,487 tonnes recorded as being mined and 2,376,314 tonnes reported as being processed. Diamond Recoveries – The diamond recoveries are reported in 3 size categories, -25ct to +6ct,-6ct to +3ct, -3ct to +1.2ct. These diamond size categories are of little use in determining size-frequency distribution and there is no explanation as to the purpose of this sizing. Total diamond recoveries of 484,298.77cts were reported in site records compared to the 507,000cts reported as being sold. 5.4.2 Perth Sorthouse Records The Perth Sorthouse received the diamonds from site and cleaned them in acid prior to sizing the diamonds using DTC sieves. This dataset is shown in tables 5.7 to 5.20 which reports both carats and stone numbers per DTC size category. It will be seen that in the early days of the operation the +12 DTC to +23 DTC diamonds were reported as a single size fraction. This did not change until the year 2000 for most of the production, and renders much of the early data unsuitable for detailed analysis.
43
In numerous instances the reported diamonds do not match those reported as being recovered at site. Gawain and Ywain are a good example in that very little of the production has been recorded. Records show that 389,962.69cts were sized compared to the 507,000cts reported as being sold, and the 484,298.77cts reported in the mine site records. 5.4.3 Pre-sale Valuation Records Prior to sale the diamonds were resized according to weight, with the results shown in Tables 5.21 to 5.50. Unfortunately stone numbers per weight category are not reported perhaps because they were never recorded. This data accounts for only 299,981.99 carats of the total 507,000 carats of diamonds that were reported sold. The diamonds are recorded by both month and pipe and cannot be related back to any specific mined flitch. In only a few instances can this data be reconciled with the Sorthouse DTC sizing records. It is not known whether the valuation prices were achieved when the diamonds were sold. 5.4.4 Sales Total sales of 507,000cts were reported with the gross carats assigned to their flitch of origin. Because selling can be an intricate process, there are no records as to how the diamonds were presented for sale or what sale prices were achieved. Details of the diamond qualities, and gross sale parcels are shown in Tables 5.51 to 5.55. 5.5 Testing of PalSac In 2001 RIO undertook a substantial evaluation program comprising Large Diameter Core (LDC) drilling and bulk sampling within PalSac to a depth of 100m beneath the current pits. The program was aimed at providing information on grade and lithology for the pipe sufficient to allow economic modelling of a potential large open pit mining operation. 5.5.1 RIO LDC Drilling PalSac The LDC drilling program provided 74.482 tonnes of core in the interval from the base of the Palomides and Sacramore pits at approximately 100mRL to a depth of 100m, approximately 0mRL, beneath these pits. The cored material, representing 53 discrete samples, was crushed and processed producing 18.22 carats of diamonds. The recovery of fine diamonds was generally poor and one sample accounted for 24 of the 83 diamonds recovered suggesting a possible spurious result. Although three different phases of kimberlite are identified, these were not tested separately. The samples were processed through a Mk3 DMS plant located at the Argyle mine site. A summary of results is shown in Table 5.56. Individual bulk density measurements taken using core samples varied from 2.1 to 2.6 with an overall weighted average of 2.35. For comparison bulk densities were also calculated using the measured volumes and overall weight of the core, but these proved to be 1 to 5% greater than the bulk densites calculated using individual core pieces. Moisture contents varied from 1% to 11% with averages of 6.39% for the PLVKB lithology and 4.26% for the VK1 lithology. 5.5.2 RIO Bulk Sample PalSac As part of the PalSac evaluation a bulk sample was excavated and processed so as to provide a means to calibrate the LDC sample results. The first sample of 1000 tonnes was excavated from Palomides PLO137.5 flitchand transported to Argyle mine site for processing through the MK3 DMS plant that was used to process the LDC samples. This first sample was contaminated with Argyle diamonds and had to be abandoned. A second sample was excavated from flitch PLO130.0 in Palomides pit and processed in the same manner as the LDC samples. Although the excavated sample was measured at 750 BCM or approximately 1,500 tonnes, the processed sample is reported as 845.85 dry tonnes. No explanation for this variance is recorded. The sample was processed in two parts using different grade ferrosilicon namely 270D and 150D to compare their efficiency. For the purposes of establishing a grade the sample results are combined and treated as one. The 150D
44
sample has reported 4030 diamonds in the -3DTC size category, which is considered erroneous. A summary of results are shown in Table 5.57.
Site RecordMine Mill Tonnes (t)
Mining BD Mill BD Mining Process Diff Carats/Size Range (cts) GradePIPE BCM (t/m³) BCM (t/m³) Insitu Wet % -25+6 -6+3 -3+1.2 Total (ct/t)
TABLE 5.17: MERLIN REJECTS Sorthouse Sizing Record
FLITCH
STONES FLITCH
CaratsCarats
Date received Sorthouse
STONES MERLIN MERLINDTC Sieve Size Excalibur Palomides Sacramore Launfal Gawain Ywain Kaye Ector Gareth TOTAL AVERAGE Total Average Total Average Total Average
LOG STONES MERLIN MERLINDTC Sieve Size Excalibur Palomides Sacramore Launfal Gawain Ywain Kaye Ector Gareth TOTAL AVERAGE Total Average Total Average Total Average
TABLE 5.25: ALL PIPES PRICE PER CARAT CONTRIBUTION PER SIZE
Contribution by Weight % Weight Contribution by Size Price per CaratSize Sacramore Launfal Kaye Tailings Total Size Sacramore Launfal Kaye Tailings Total Size Sacramore Launfal Kaye Tailings Total
Contribution by Weight % Weight Contribution by Size Price per CaratSize Sacramore Palomides Gareth Total Size Sacramore Palomides Gareth Size Sacramore Palomides Gareth Total
Contribution by Weight % Weight Contribution by Size Price per CaratSize Sacramore Launfal Palomides Total Size Sacramore Launfal Palomides Total Size Sacramore Launfal Palomides Total
Contribution by Weight % Weight Contribution by Size Price per CaratSize Sacramore Palomides Excalibur Total Size Sacramore Palomides Excalibur Total Size Sacramore Palomides Excalibur Total
Contribution by Weight % Weight Contribution by Size Price per CaratSize Palomides Launfal Launfal North Excalibur Total Size Palomides Launfal Launfal North Excalibur Total Size Palomides Launfal Launfal North Excalibur Total
Contribution by Weight % Weight Contribution by Size Price per CaratSize Sacramore Launfal Launfal North Excalibur MR Total Size Sacramore Launfal Launfal North Excalibur MR Total Size Sacramore Launfal Launfal North Excalibur MR Total
Contribution by Weight % Weight Contribution by Size Price per CaratSize Sacramore Launfal Launfal North Excalibur Gareth Ywain MR Total Size Sacramore Launfal Launfal North Excalibur Gareth Ywain MR Total Size Sacramore Launfal Launfal North Excalibur Gareth Ywain MR Total
Contribution by Value % ValueSize Sacramore Launfal Launfal North Excalibur Gareth Ywain MR Total Size Sacramore Launfal Launfal North Excalibur Gareth Ywain MR Total
Contribution by Weight % Weight Contribution by Size Price per CaratSize Sacramore Launfal Launfal North Excalibur MR Total Size Sacramore Launfal Launfal North Excalibur MR Total Size Sacramore Launfal Launfal North Excalibur MR Total
Contribution by Weight % Weight Contribution by Size Price per CaratSize Palomides Excalibur Kay Sacramore MR Total Size Palomides Excalibur Kay Sacramore MR Total Size Palomides Excalibur Kay Sacramore MR Total
Contribution by Weight % Weight Contribution by Size Price per CaratSize Palomides Excalibur Kaye Sacramore Total Size Palomides Excalibur Kaye Sacramore Total Size Palomides Excalibur Kaye Sacramore Total
Contribution by Weight % Weight Contribution by Size Price per CaratSize Sacramore Palomides Launfal North Launfal Kaye MR Total Size Sacramore Palomidies Launfal North Launfal Kaye MR Total Size Sacramore Palomides Launfal North Launfal Kaye MR Total
Special 35.81 0 0 49.57 19.5 0 104.88 Special 34.1% 0.0% 0.0% 47.3% 18.6% 0.0% 100% Special 1,116.28 1,908.98 1,487.91
Contribution by Value % ValueSize Sacramore Palomidies Launfal North Launfal Kaye MR Total Size Sacramore Palomidies Launfal North Launfal Kaye MR Total
Contribution by Weight % Weight Contribution by Size Price per CaratSize Sacramore Palomides Launfal North Launfal Gareth MR Total Size Sacramore Palomides Launfal North Launfal Gareth MR Total Size Sacramore Palomides Launfal North Launfal Gareth MR Total
Special 19.00 0 0 12.93 0 0 31.93 Special 59.5% 0.0% 0.0% 40.5% 0.0% 0.0% 100% Special 400.00 75.00 268.39
Contribution by Value % ValueSize Sacramore Palomides Launfal North Launfal Gareth MR Total Size Sacramore Palomides Launfal North Launfal Gareth MR Total
6.1 Introduction After acquiring the Merlin project in late 2004, NADL commenced a systematic re-evaluation of the diamond field, initially investigating liberation and recovery issues both known to be concerns during the previous RIO/Ashton mining operations. 6.2 Resource Upgrade 6.2.1 Resource Upgrade 2005 The resources at Merlin are divided into two categories, primary ore beneath the open pits and tailings and reject resources remaining from the initial mining operations. Following a drilling program in 2005 the Merlin resources were upgraded as follows; Table 6.1 Merlin Primary Resource 2005
*Reassessed mining grades reported at mine closure The reject ore resources comprise the sorthouse tailings, sizer rejects and trommel oversize material variously stockpiled at surface. Volumes have been calculated from survey data while the grades are based on limited bulk sample test results. Details are as follows; Table 6.2 Reject Ore and Tailings Resources
6.2.2 Resource Upgrade 2008 The 2007/2008 resource drilling allowed a significant upgrade to the PalSac and Gawain resource. This is summarised in Table 6.3; Table 6.3 Merlin Primary Resource 2008
Pipe Indicated Inferred Total Grade* Carats Southern Cluster
*Reassessed mining grades reported at mine closure 6.3 Sorthouse Tailings Diamonds 6.3.1 Non-Fluorescing Diamonds On the closure of the mining operations the sorthouse tailings which were known to contain diamonds were deposited within Ywain openpit, to subsequently become submerged when the pit became filled with water. The knowledge that the x-ray sorting machine was not recovering all of the diamonds prompted the testing of Merlin diamonds for their fluorescing characteristics. FTIRS (Fourier Transform Infra-red Spectrometry) and X-Ray fluorescence studies on an assortment of previously hand recovered ROM Merlin diamonds resulted in the identification of a population of good shaped non-fluorescing diamonds. This population is calculated to represent 8% of the Merlin diamond population. These diamonds would not be recoverable using x-ray fluorescent sorting techniques. A further 6.5% of the diamonds were found to have very low fluorescence characteristics and as such would also not necessarily be recovered by x-ray fluorescent sorting techniques. (Glass and Taylor, 2005).
The sorthouse diamond losses cannot be easily quantified, apart from the testing of the tailings and it is likely some of the quantified diamond losses attributed to poor liberation are also contained in the sorthouse tailings. The non fluorescing diamonds cannot be quantified in terms of quantity or value from the available data sets as they are never recovered and are hence not a part of the known diamond population. Results from the testing of the diamonds recovered from the tailings revealed 102 of the 255 diamonds were unrecoverable by x-ray fluorescent techniques. This represents 40% of the diamonds tested, or a tailings grade of 360cpht. This would represent about 5% of the total diamond population, and is consistent with previous tests which revealed 8% of the diamond population was non-fluorescent. The diamonds that are recoverable would form part of the non liberated population. The results of the test samples are as follows;
Reprocessing of the sorthouse tailings commenced in mid 2005 and continued through to early 2006. Recovery of the diamonds was achieved by size classification followed by magnetic separation for the fine size fractions and optical sorting for the large size fraction.
Fig. 6.1 Reprocessing of Sorthouse Tailings
From the 8th August to 30th November some 2,600 tonne of material was processed and in excess of 12,000 carats were recovered from the sorthouse tailings. Processing continued intermittently in 2006 resulting in a further 1,442 carats being recovered from 761 tonnes. A summary of diamond recoveries is shown in the Table 6.5 below. The largest diamonds recovered were 17.19cts, 14.21cts, 10.97cts and 10.27cts. The -4mm +1mm size fraction produced 167,008 diamonds. The overall grade was in the order of 450cpht. Table 6.5 Merlin Sorthouse Rejects Diamond Fortnightly Recovery
The size distribution of the tails diamonds is shown below and compared to the PalSac ‘run of mine’ size distribution. The tails population is clearly dominated by the finer diamond sizes with 93.4% less than +3gr, as compared to the ‘run of mine’ which has 67.6% in this size fraction. The x-ray sorter appears to have had a winnowing effect on the diamonds with the lower quality smaller diamonds being preferentially rejected. High quality large white fluorescing diamonds were not missed by the x-ray sorter and have not been recovered from the tailings. Table 6.6 Tails Size Distribution
*Average for PalSac ‘run of mine’ 6.4 Diamond Liberation Testwork During the previous mining operations with no primary crushing and limited secondary crushing, diamond liberation became a serious issue as the pits were deepened and the kimberlite became harder. As a consequence the ROM pad contains some 20,000m3 of ‘sizer reject’ material which was mined but not processed. The ‘trommel reject’ also contains varying amounts of washed kimberlite cobbles. An inspection of the ‘cyclone floats’ revealed size ranges up to 25mm, indicating that the recrush circuit which aimed at reducing the floats to 8mm, was not in operation during all operations.
49
6.4.1 HPGR Testwork To test this reject material as well as primary kimberlite, a HPGR crushing unit was hired from Koppern Engineering and established at site. The material tested was processed through an onsite MK3 DMS plant.
Figure 6.2 HPGR crushing unit 50tph
1) Testing of Rejects A summary of the samples excavated and crushed from the at surface sizer rejects, trommel oversize and cyclone float stockpiles is shown in table 6.7 below. A small sample of cyclone float material was processed between each sample as a means of flushing the processing plant. The source location of the samples is shown in Fig 6.3. Table 6.7 Samples from ROM pad stockpiles – 2005/2006
Total trommel oversize (tailings dam) 1844.5 262.7 158.1 8.6
*Contaminated sample excluded 2)Testing of Kimberlite Kimberlite samples were taken from three of the kimberlite pipes aimed at establishing the recoverable grades for the pipes. The work also provided information on crushing and scrubbing/milling requirements to allow the future design of a front-end for the Bateman DMS plant. Kimberlite samples from pits Kaye, Gawain and Ywain were excavated and HPGR crushed, with the exception of the Ywain sample which was deeply weathered. The samples were then processed through a MK3 DMS plant located at Merlin. Details are as follows; Table 6.8 Samples from pits
*not crushed due to material being deeply weathered 6.5 Trial Production 2006 NADL’s trial mining and processing operations commenced in early June, 2006 and continued until November and focused on excavating weathered kimberlite from Ywain and Gawain pipes. Details of mining, processing and recovery are shown in Table 6.9 below. Table 6.9 Processing Schedule 2006 – Tonnes Processed
ROM TR Oversize TAILS DAM TR Oversize 5.2 234.83 96.91 SORTHOUSE TAILS/MIX 128.83 1357.3 266.28 355.6
FLOATS 1.45 1.89 TOTAL CARATS 181.94 2039.7 4175.2 5414.73
Cumulative Carats 182 2222 6397 11812
A total of 24,958 tonnes was processed to cessation of operations in late November, resulting in the recovery of 11,812 carats. Details are as follows;
TOTAL 24,958.32 11,811.6 47.33 Although close to self sustainable levels of diamond production were achieved in the final two months of processing, throughput was severely hampered by insufficient and inefficient scrubbing and feeding capacity and water supply issues. These issues could not be addressed in the required timeframe due to capital expenditure constraints. Operations ceased in November 2006. 6.6 Trial Production 2009/2010 6.6.1 Production Trials
The summary in Table 6.14 below illustrates the high clay/slime content of the primary feed and the efficiency of the HPGR in generating additional slimes after the primary slimes are removed by washing. For the range of material being feed generally less than 15% of the primary feed was presenting to the DMS plant.
Table 6.14 Production Trials Summary 2009/2010
Month Feed ton
HPGR ton HPGR/Feed
DMS ton DMS/Feed
Carats
Sept, 2010 3980 1337 33.5% 622 15.6% 493.56* August 4203 954 26.70% 484 13.54% 484.54 July 4047 1386 32.64% 501 11.80% 413.23 June 8977 2479 27.64% 440 4.91% 785.92 May 10614 2709 22.41% 677 5.60% 1,401.35 April 5959 540.99 March 3879 500.26 February 2659 406.85 January 1492 307.25 December 1269 203 15.99% 1,657.05 November 4670 684 14.6% 1,704.41 October 4229 600.5 14.2% 541.00 September 5068 698 13.77% 583.05 August 3456 543.53 July, 2009 1500 235.03 Total 66,002 7528 26.07% 2101.8 7.28% 10,598.02
*Includes 189.7cts from Kaye that were not sized.
53
The diamond recoveries from the different pipes are shown below. Table 6.15 Merlin 2009-2010 Carat Recoveries per Pipe
size Gawain Kaye Sacramore Palomides OS Rejects Total Special 37.43 74.26 - - - 111.69
Total 5,113.95 3,584.63 762.94 218.27 728.63 10,408.42
Table 6.16: Merlin 2009-2010 Stone Recoveries per Pipe
size Gawain Kaye Sacramore Palomides OS Rejects Total Special 3 4 - - - 7
+10cts 1 - - - - 1
+9cts - 2 2 - - 4
+8cts - 1 - - 1 2
+7cts 3 4 1 1 1 10
+6cts 6 4 - - - 10
+5cts 8 10 - - - 18
+4cts 20 7 1 1 3 32
+3cts 42 38 4 1 1 86
+2cts 120 103 16 5 15 259
+1cts 472 306 67 21 76 942
-10+4mm 1,941 975 331 85 267 3,599
-4+2mm 9,745 6,707 1,264 438 1,538 19,692
-2+1mm 40,937 26,646 7,001 1,340 4,834 80,758
-1+0.75mm 5,600 5,978 2,469 112 729 14,888
Total 58,898 40,785 11,156 2,004 7,465 120,308
54
6.6.2 Grade Control Samples
Grade control samples each of approximately 100m3 were taken from Gawain and Kaye pipes. The purpose of these samples was to obtain accurate volume based grades which could be used to assist in the calibration of the previous production data. Weight based grades generated from past production are unreliable due to fluctuating bulk densities and moisture contents. There have been no grade control samples taken from any of the other pipes apart from Sacramore which awaits processing. . Results are as follows;
Total 435.3 207.79 2.09 305.7 120.2 2.85 275.29 0.90 Kaye
10-330-100 231.3 109 2.12 117 38.2 22.41 0.21
10-330-102 210 94.08 2.23 87.38 55.5 5.93 0.06
10-330-104 196 87.66 2.24 8.05 0.15
Total 637.3 290.74 2.19 36.39 0.125 6.7 Microdiamond Analyses Microdiamond analyses of both core samples and 1m3 pit samples was instigated as a means of establishing a technique to investigate the commercial diamond grade of the pipes at depth and hence avoid the costly need of obtaining bulk samples from depth. This work, while showing promise is incomplete and is severely hampered by the unavailability of core and access to the mostly water filled pits. 6.7.1 Core Analyses The only core available for analysis is that obtained from drilling programs undertaken by NADL in the period since 2004, this being from the pipes Gawain, Ywain and PalSac. There was insufficient robust core available from the drilling of Bedevere to be able to undertake any comparative studies. The entire historic core was destroyed by RIO on cessation of the mining operations in 2003. Although some microdiamond analyses are completed there has been insufficient work done to confidently determine the commercial grade at depth for any of the pipes or to ascertain any trends in the diamond grade. A total of 11 core samples each of approximately 50kg have been analysed along with 5 boulder samples. 6.7.2 1m3 Pit Samples A total of 5 pit samples each of approximately im3 have been excavated from Gawain and Kaye pits and with one of the samples taken from Sacramore pit. These samples were totally digested to release all diamonds. There have been insufficient samples taken to allow confident grade determination analysis.
05-052-001 FLOATS05-052-002 TROMMEL O/S TAILINGSDAM05-052-003 FLOATS05-052-004 SIZER REJECT ROMPAD #4 TRENCH 1505-052-005 FLOATS05-052-007 FLOATS05-052-008 Sizer Reject ROM PAD #5 TRENCH 1405-052-009 FLOATS05-052-010 KIMBERLITE YWAIN06-006-001 FLOATS06-006-003 FLOATS06-006-004 TROMMEL O/S ROM PAD #3 TRENCH 1106-006-005 FLOATS06-006-008 FLOATS06-006-009 TROMMEL O/S ROM PAD #5 TRENCH 1406-006-010 FLOATS06-006-012 FLOATS06-006-013 TROMMEL O/S TAILINGSDAM06-006-014 FLOATS06-006-018 TROMMEL O/S TAILINGSDAM06-006-019 TROMMEL O/S TAILINGSDAM06-006-020 TROMMEL O/S TAILINGSDAM06-006-023 SIZE REJECTS ROM PAD #2 TRENCH 6/706-006-024 SIZE REJECTS ROM PAD #2 TRENCH 6/706-006-033 SIZE REJECTS ROM PAD #2 TRENCH 6/7
ROM PAD # 3
ROM PAD # 4
ROM PAD # 5
ROM PAD # 1
ROM PAD # 2
55
7 RESOURCE ESTIMATION AND REPORTING
7.1 Introduction
The modelling of the resource for the purpose of determining insitu value and undertaking mining studies requires an understanding of the geology and geometry of the pipes and the grade and value of the diamond population. Determining these parameters not only requires an assessment of available data but also the appropriateness of extrapolating the data both between and outside the data points. These parameters are discussed below. 7.2 Geological Interpretation In interpreting the geology of the pipes, they are looked at both individually and collectively as evidence suggests the pipes represent the near surface expression of a single intrusive magmatic episode. 7.2.1 Spatial and Genetic Relationship of Pipes The Merlin kimberlite field comprises 4 discrete clusters of pipes located within a NS trending zone 10km long and 5km wide. In total there are 15 identified pipe vents which drilling to date indicates represents 12 discrete pipes, due to the coalescing of some of the vents to form a single pipe at depth. Future drilling will likely demonstrate that other vents will also coalesce at depth. The main pipe clusters are 2km apart. Within each cluster individual pipes/vents are usually less than 300m apart. While not all the individual pipes have been age dated, a common emplacement date of 360ma has been determined for three of the pipes which suggest the field is the result of a single intrusive episode with the different clusters being a consequence of structural emplacement controls. This conclusion is supported by the singular geochemical signature of the kimberlite magma and the single diamond population. 7.2.2 Pipe Geometry and Emplacement Controls The surface expression of the vents/pipes is ovoid to circular with varying surface areas. Where surface observation permits the pipes can be seen to be associated with narrow fractures bearing 0150 mag. Previous exploration has demonstrated these fractures to be very narrow and to be kimberlite bearing. These fractures represent near surface emplacement controls for the pipes. By far the most dominant influence over pipe emplacement is the Cambrian aged Bukulara Sandstone unit. This unit which is a flat lying interbedded sequence of siltstones and sandstones sits unconformably over the Proterozoic aged McArthur River Group sediments. The intruding kimberlites have clearly had difficulty penetrating this unit which is currently 120m thick. Vents like Palomides and Sacramore coalesce at the base of this sandstone formation to form a single pipe. Gawain and Bedevere increase in diameter immediately beneath the sandstone while Launfal has a significant dogleg. 7.2.3 Effects of Weathering The Merlin kimberlites have been severely affected by an intense weathering event. Without exception all of the pipes on the Merlin plateau are ‘infilled’ with cretaceous aged sediments comprising fossil bearing sandstones and mudstones. Evidence including the presence of slickensides at the margins of the pipes supports the premise that the sediments have subsided into the pipes at a date much later than their deposition. The thickness of these sediments varies between the pipes and can be up to 42m thick. The various infill thicknesses are shown in Table 7.1.
For the southern and central cluster pipes there is no cretaceous aged sediments remaining in the vicinity of the pipes. For the Kaye and Ector pipes which belong to the northern cluster both pipes and surrounds are covered by cretaceous aged sediments. However excavation of Kaye and Ector revealed that the cretaceous aged sediments had subsided into the pipes. The cause of this subsidence is attributed to solution weathering of the kimberlite and subsequent volume reduction resulting in overlying sediments settling into the pipe. Differential weathering of the pipes has also played a part, with smaller pipes having deeper infill than the larger pipes. The differential weathering within individual pipes has also resulted in differential subsidence, with the periphery of the pipes weathering more than the centre resulting in greater thicknesses of infill sediments around the periphery of the pipes. This is best illustrated in Kaye pipe where the infill sediments are domed in the centre. Another effect of the solution weathering is that the material that does not solution weather, this being the diamonds and most country rock fragments concentrate at the base of the infill sediments. This phenomenon resulted in unrepresentative elevated diamond grades being reported in many of the early bulk samples that were excavated from the top of the kimberlites, after removing the infill sediments. A typical kimberlite profile beneath the infill sediments is for there to be 3m – 5m of clays, underlain by 10m – 15m of deeply weathered textureless kimberlite which has suffered volume reduction to the extent that pseudo bedding features are often present. Below this kimberlite textures are recognisable despite the weathering. The effects of weathering diminish with depth with fresh material generally being observed at depths of 120m to 140m. Laterally across a pipe the effects of weathering can be quite varied, with clay margins often being observed at considerable depths. This lateral variation of the intensity of weathering results in significant variations in the bulk density of the kimberlite at any vertical depth within the weathered zone. Deeply weathered kimberlite can have bulk densities as low as 1.3 while the less weathered kimberlite is usually in the order of 2.3. At depth the very fresh kimberlite has a bulk density of 2.6. 7.2.4 Kimberlite Phases It is accepted geological theory that volcanic magmas originate at depth and travel to or towards the surface. Kimberlite magmas are no exception and based on diamond crystallisation theory are postulated to originate from within the diamond stability field at depths exceeding some 150km. The kimberlite phases comprising the Merlin kimberlites have been classified using the nomenclature and genetic classification of Mitchell (1986). The pipes represent the preserved upper diatreme portion of the kimberlite intrusive. The top portion of the pipes was removed by erosion during the period post emplacement to the deposition of the marine cretaceous aged sediments, a time period of
57
some 250Ma. The depth of erosion during this period is not known. Although the cretaceous cover has been largely eroded no further erosion of the pipes has occurred due to them being preserved beneath infill sediments as was described in the previous section 2.4.1. The kimberlite phases identified at Merlin are described as follows;
A. Tuffisitic Kimberlite B. Micaceous Tuffisitic Kimberlite C. Pelletal Tuffisitic Kimberlite D. Tuffisitic Kimberlite Breccia E. Pelletal Tuffisitic Kimberlite Breccia F Epiclastic Kimberlite
The distribution of the different kimberlite facies within the various pipes is shown in Table 7.2. Table 7.2 Kimberlite Facies
Pipe A B C D E F Excalibur Y Y Y Y Launfal Y Y Y Y Launfal North
Y Y Y
Palomides Y Y Y Y Sacramore Y Y Y Y Tristram Y Gawain Y Y Y Y Ywain Y Gareth Y Y Kaye Y Y Y Ector Y Y Bedevere Y Perceval Y
Although most of the pipes contain more than one kimberlite facies, the subsidiary facies appear to represent less than 10% by volume within any pipe. Because of the difficulty of accurately defining these subsidiary facies and determining their diamond grade the pipes are considered as being entirely the dominant facies. The previous mining operations treated the pipes as comprising a single facies and hence all of the grade data pertains to the pipe as a whole. The size of the pipes is such that selective mining would be difficult to achieve. To test the reasonableness of this approach subsidiary facies will need to be tested for their diamond content to ensure that diamond grades are not lower than the dominant facies type for the pipe. Limited microdiamond testing completed to date indicates that this is the case, however there is only limited core available for the pipes PalSac, Launfal, Gawain, Ywain and Bedevere and no core available for the remaining pipes. The paucity of information on these subsidiary facies with respect to their relative diamond content creates potential uncertainty in the diamond resource should the abundancies of these facies change significantly. This remains one of the significant factors in the resources not being able to be upgraded to a Measured JORC category.
7.3 Moisture and Bulk Density Due to the variably weathered nature of the kimberlite both laterally and vertically both the moisture content and bulk density of the kimberlite varies considerably. The moisture content of freshly excavated material normally varies from 13% to 28% and if left on the ROM pad for any period will decrease over time. However during the wet season this same material can have high moisture contents due to rain. At significant depths below the depth of weathering the moisture content is usually 3%. The bulk density of the kimberlite varies with the degree of weathering of the kimberlite
58
and is as low as 1.3 for deeply weathered material and as high as 2.6 for very fresh unweathered material. Processed tonnes are always measured as wet tonnes and are difficult to reconcile with the excavated BCM which are converted to tonnes by the use of moisture and bulk density factors. While moisture and bulk density are important factor from a mining and processing perspective the resource estimates are best done based on BCM’s.
7.4 Estimation of Pipe Resources 7.4.1 Pipe Geometry The kimberlite pipes at Merlin have been defined by their surface expression, openpit excavation and drilling. The geometry of each pipe at depth has been established at 20m depth intervals based on drill intercepts. Boundary contacts are inferred between upper and lower established contacts and it is assumed that the overall boundary footprints maintain an ovoid/circular shape subject to evidence to the contrary. In general the pipes are vertically plunging and diminish in gauge with depth. With depth there are fewer drill contacts and confidence in the footprint shape decreases. To establish footprints with lower confidence limits, a known footprint is projected downwards along the projected plunge of the pipe, if the next actual contact fits the projected footprint then the shape of the footprint is maintained, but if it doesn’t then the shape of the footprint is amended within the constraints of the projection to accommodate the actual drill contact. The footprints are not projected further than 20m below the deepest drill contact. The establishment of the pipe boundaries by geological interpretation has a high degree of precision because of the vastly different nature of the volcanic pipe rock and the intruded country rock sediments. The contacts are usually very sharp despite the frequent increase in the abundance of country rock xenoliths close to the contacts. Once the pipe footprints are established the volume in BCM of the pipe resource is calculated for each 20m depth interval. Because of the inherent difficulties in determining robust moisture contents and bulk densities the volumes are not converted to tonnages for the purposes of reporting the resource statement. While there is a high degree of confidence in predicting the geometry of the pipes there is generally insufficient drilling to determine them to the accuracy required for a Measured JORC compliant Resource. 7.4.2 Pipe Volumes/Tonnes With the pipe footprints established at 20m depth intervals the volume of the resource for each pipe can be calculated. Resource estimates based on tonnes are somewhat more difficult to establish with certainty due to fluctuating bulk densities and moisture contents. In using the estimated volumes or tonnes for additional analyses aimed at establishing grade an understanding of the different kimberlite phases within each pipe is also required. Volume - The insitu volume estimate in m3 is based on the simple calculation;
V = (area of upper footprint + area of lower footprint)/2 * vertical distance between footprints. Tonnage - The insitu tonnage estimate requires the volume calculation to be converted to tonnes by using bulk density and moisture factors. While the general trends of increasing bulk density with depth and decreasing moisture content with depth hold true, specific measurements at any locality can be quite variable. In particular the lateral variability of both moisture content and bulk density in the weathered portions of a pipe can be up to 30%. This is the main reason that excavated tonnes estimated from surveyed volumes could never be reconciled with the processed plant tonnes during the historic mining operations. Hence in converting volumes to tonnages global bulk density and moisture estimates can only be applied.
59
For the purposes of estimating resource grades and resource values all calculations are based on volumes with results stated in BCM’s. While the BCM’s can be converted to tonnes by the application of the appropriate bulk density measurement this introduces another degree of uncertainty, due to the infrequency of bulk density measurements taken from the pipes at depth. Because all historic core was destroyed there is only limited core available from 4 of the pipes. 7.4.3 Pipe Grade Models In establishing a grade model for a pipe the following factors are considered; 1) Size-Frequency Distribution – Because of the past mining operations the size-frequency
distribution of the Merlin diamond population is well established and is identical for each of the pipes. This diamond distribution not only provides a template against which sample results can be validated and quantified but also identifies invalid data. Invalid data is rare and is identified when the size distribution of the diamond sample does not reflect the Merlin distribution in terms of the relative abundance of the different diamond sizes. This can occur when the sample is contaminated with a different diamond population or a large diamond is crushed resulting in too many smaller diamonds. In determining a grade it is the number of diamonds that are recovered in each size fraction that is most important rather than the collective weight.
2) Sample Size/Volume – While relatively small samples of 50t to 100t are sufficient to establish a
grade, large samples are required to establish the full size-frequency distribution and to establish statistically robust numbers of diamonds for each size category. Samples can be measured in either tonnes or BCM but the latter is the most effective as it does not require moisture and rock density to be factored into the grade calculations.
3) Sample Processing and Diamond Recovery – The diamond grades are plant recovered grades
and hence are influenced by the processing methodology. Of critical importance is the bottom screen size on the plant which arguably has the greatest impact on the recovered grade. The impact on grade of different mesh sizes can be easily seen in the recovered size-frequency distribution. Diamond liberation from the host rock is also a significant factor which is influenced by the degree of weathering of the rock and the use of crushers or HPGR technology in the circuit. The effectiveness of liberation techniques can only be measured against the results from material not processed in the same manner, or by the retreatment of rejected material. The effectiveness of final recovery can also influence grade and requires the regular auditing of the sorthouse tails material.
4) Continuity of Grade with Depth – The continuity of grade at depth is one of the more difficult
factors to determine in the absence of large bulk samples taken at depth. The determination of grade for a kimberlite relies heavily on two assumptions, namely;
- The diamonds are distributed reasonably homogenously throughout any particular kimberlite
facies.
- The size/frequency distribution of the diamonds will be constant for any particular kimberlite facies. Of equal importance is the defining of a particular kimberlite facies. While the definition of a Tuffisitic kimberlite breccia is based on the lithic fragments comprising >15% of the kimberlite, the abundance of the lithic fragments is usually not homogenous and may in fact blend into zones with <15% lithic fragments which would be a Tuffisitic kimberlite. As lithic fragments are barren of diamonds their specific abundance can impact significantly on local grade. While these factors affect grades locally, provided the containing kimberlite magma is the same intrusive phase it can be reasonably expected that similar diamond grades will occur both laterally and at depth throughout the specific intrusive phase.
The comparative microdiamond approach to this issue is underpinned by an understanding of the intrusive nature of the kimberlite facies being sampled. Hence depending on the kimberlite
60
facies the approach may not be universally applicable. The approach requires the micro-macrodiamond relationship to be established from samples taken at surface or within the open pits. By the digestion of core samples obtained at depth from the same kimberlite facies the microdiamond distribution can be determined and compared with that established for the larger samples taken at surface. Since microdiamonds represent the fine tail of a much broader size-frequency distribution they will be a reflection of the macro and commercial diamond grade. Unfortunately this work is incomplete and with the exception of PalSac no samples from below the base of the current pits have been taken, hence the continuity of grade at depth relies entirely on the assumption that this is the expected norm.
5) Data Quality – Of paramount importance is data quality both in the acquisition of the data and the recording of the data.
Three data sets have been examined, these being;
1993-1998 evaluation data 1998-2003 Ashton/RIO mining data 2004-2011 NADL trial mining and evaluation data
A. 1993-1998 Evaluation Data During this period two phases of large diameter RC sampling, a winze sample and bulk sampling was undertaken.
The results demonstrated lateral grade trends from lower grades in the centre of the pipes to higher grades towards the pipe margins. This is a consequence of the differential subsidence of the kimberlite due to the solution weathering. As the samples were taken from the top of the pipe which has suffered volume reduction, the bulk samples are unrepresentative of the deeper kimberlite thus rendering the results unsuitable for estimation of grades. B. 1998 – 2003 Ashton/RIO Mining Data During the period 1998 to 2003 trial mining operations were undertaken by Ashton/Rio Tinto resulting in the recovery of 507,000cts of diamonds from the processing of approximately 2.237 million tonnes of kimberlite. During these activities a total of 9 pipes were subject to open pit mining. These operations highlighted the difficulty of reconciling mined volumes with processed wet tonnes despite taking into account moisture and bulk density. Difficulties in reconciling the reported recovered diamonds with the diamonds that were valued and sold were also highlighted. In the first instance the recovered diamonds were sized according to size using standard DTC sieve plates and the number of diamonds recovered in each sieve size was recorded except for the -3DTC sieve plate. For valuation purposes the diamonds were then reclassified according to weight but in this instance the number of diamonds in each weight class was not recorded.
C. 2004-2011 NADL trial mining and evaluation data Two phases of trial production were completed during this period, the first in 2006 which resulted in the recovery of 25,318 carats and the second in 2009/2010 which resulted in 10,598 carats being recovered. These trials provided sufficient diamonds mainly from Gawain, Ywain and Kaye to establish size-frequency distribution relationships. There was also sufficient diamonds to undertake valuations. In addition grade control each of approximately 100m3 were excavated from Gawain and Kaye pipes and processed. These samples were treated differently than the normal ROM samples in that all rejects were crushed and repassed and DMS floats were also reprocessed. This ‘overprocessing’ of the test samples results in higher grades being achieved largely due to the better recovery of the finer diamonds. It should be noted that lower grades are normally achieved during commercial operations due to a number of factors including, but not limited to, the lower screen size that is chosen and the recovery technique being utilised. The 2009/2010 trials also involved the testing an evaluation of new processing components namely an Optical sorter and an HPGR crushing unit.
61
7.4.4 Diamond Value To determine the value of the resource a representative parcel of diamonds is required to be recovered, cleaned and valued. It is not a specific requirement that the diamonds are recovered from a single sample or that they represent a known volume of resource. It is important that as many size, colour, shape and quality categories are represented as possible. In practise all categories can be found in the smaller sizes due to the greater abundance of the smaller diamonds. In the larger sizes however not all colour, shapes and qualities may be represented, hence the average values for the larger sizes may be significantly influenced either positively or negatively by the quality of one or two stones. Because of this it is important to compare the range of qualities for each size category to see if they are similar. If so then average values for the size categories with few stones can be better modelled. Because of the quantity of diamonds recovered during the previous mining operations the Merlin diamond population is well understood. The valuations completed on the 2006 diamond parcel provided a good snapshot of the diamond value at that time but unfortunately this parcel was sold and cannot be retested in current markets. The 2009/2010 diamond parcel remains in hand and has provided a snapshot of current market values. This value must be treated with caution because of the skewed distribution of value within the Merlin diamond population. A rigorous analysis of quality distribution as it pertains to value is required for all size categories so as assumptions can be made on the average values likely to be achieved for the less frequent larger sized diamonds. Currently there are insufficient numbers of diamonds recovered in the larger size categories to confidently determine average values for these categories.
62
8 VOLUME MODEL
8.1 Introduction
The kimberlite pipes at Merlin have been defined by their surface expression, openpit excavation and drilling. Because of the nature of kimberlite pipes, being vertically emplaced volcanic intrusive, there is a high degree of predictability to the geometry of the pipes. Drilling to date has demonstrated that some of the pipes comprise multiple lithologies but usually with a dominant lithology. Hence, in defining the geometry the pipes are considered to be homogenous and single lithology intrusions. 8.2 Methodology The geometry of each pipe at depth has been established at 20m depth intervals based on drill intercepts. Boundary contacts are inferred between upper and lower established contacts and it is assumed that the overall boundary footprints maintain an ovoid/circular shape subject to evidence to the contrary. The establishment of the pipe boundaries by geological interpretation has a high degree of precision because of the vastly different nature of the volcanic pipe rock and the intruded country rock sediments. The contacts are usually very sharp despite the frequent increase in the abundance of country rock xenoliths close to the contacts. The drill holes are located by surface surveying which is tied to the national grid. The majority of the drill holes and all of the deeper holes have been surveyed downhole during the drilling process. Downhole survey intervals are normally at 25m intervals or less. All of the drilling data is maintained in a database.
8.3 Pipe Volumes/Tonnes
With the pipe footprints established at 20m depth intervals the volume of the resource for each pipe can be calculated. Resource estimates based on tonnes are somewhat more difficult to establish with certainty due to fluctuating bulk densities and moisture contents. In using the estimated volumes or tonnes for additional analyses aimed at establishing grade an understanding of the different kimberlite phases within each pipe is also required.
Volume - The insitu volume estimate in m3 is based on the simple calculation;
V = (area of upper footprint + area of lower footprint)/2 * vertical distance between footprints.
Tonnage - The insitu tonnage estimate requires the volume calculation to be converted to tonnes by using bulk density and moisture factors. While the general trends of increasing bulk density with depth and decreasing moisture content with depth hold true, specific measurements at any locality can be quite variable. In particular the lateral variability of both moisture content and bulk density in the weathered portions of a pipe can be up to 30%. This is the main reason that excavated tonnes estimated from surveyed volumes could never be reconciled with the processed plant tonnes during the historic mining operations. Hence in converting volumes to tonnages global bulk density and moisture estimates can only be applied. For the purposes of estimating resource grades and resource values all calculations are based on volumes with results stated in BCM’s. The pipe footprints for each of the pipes are shown in Plans 1-6 along with the calculated volumes.
9 GRADE MODEL 9.1 Introduction Because any sample result only provides a snapshoot of grade due to the particulate nature of diamonds within the resource it is desirable to have a grade model that will better represent the global grade of the particular pipe. The estimation of grade models has been achieved through the merging of data sets built up over time and include trial mining results as well as small bulk samples. Fundamental to estimating the grade model is the size-frequency distribution for the diamonds. Past diamond recoveries are sufficient to provide robust size-frequency distributions for most of the pipes. Scrutiny of these distributions reveals two slightly different distributions, with the predominantly non-micaceous pipes (PalSac, Kaye, Ector, Gareth) having a greater frequency of larger stones than the predominantly micaceous pipes (Excalibur, Gawain, Ywain). The data for Launfal is ambiguous in that it has characteristics of both types of pipes. The average diamond size-frequency distribution is used as the template for each of the pipes irrespective of their grade. Specific grades are determined from a combination of production history where accurate volumes are known and the results of special grade control samples. Another important element in determining a grade model is the use of diamond numbers as opposed to carats recovered. Again this is because of the particulate nature of the diamond and their size variability. Hence a grade can be determined in terms of the number of stones per Bank Cubic Meter (BCM). The grades are estimated in BCM’s due to the difficulty of ascertaining tonnes for small samples due to the variability of moisture content and rock bulk density. 9.2 Merlin Grade Models Using historic sampling and mining data as well as more recent evaluation data both Resource and Production grade models have been established and these can be compared to historic mining grades in the same format. The grades are established by determining the contribution to grade for each diamond size category. The models rely heavily on past production records of volumes mined and diamonds recovered. Although multiple lithologies have been identified in some of the pipes there has been insufficient drilling for these to be accurately defined and there has been no individual testing of the minority lithologies to ascertain their diamond grades. During the past mining operations the pipes were mined as single entities with no discrimination of the different kimberlite lithologies if they were present. If the different lithologies have differing diamond grades and if their relative abundance changes significantly then this would affect the average diamond grade of the pipe. 9.2.1 Resource Grade Model The Resource Grade Model is not representative of the total diamond content of the rock but reflects the recovered grade established from carefully treated samples. In most instances a lower screen with a slotted aperture of 10mm x 0.8mm is used. As a consequence recoveries of fine diamonds are higher than would be expected from a production process plant which would likely use coarser bottom screens. It is important to note that the grades are based on what was previously mined from the pipes as no sample material deeper than the base of the current open pits has been tested with the exception of PalSac which has had a program of Large Diameter Core Drilling. While this provides an indication of the expected recoverable resource grade no account has been made for any geological complexity known to occur within some of the pipes. 9.2.2 Production Grade Model The Production Resource Grade is representative of the recovered grade using a processing plant similar to the Ashton/RIO production plant used for the 1999 – 2003 operations. This plant had a lower screen with a slotted aperture of 10mm x 0.95mm. Any changes to the aperture of this lower screen will have a significant impact on the recovered grade.
64
9.2.3 Historic Production Grade The Historic Production Grade is representative of the 1999 – 2003 mined grades. However it should be noted that not all production was reported, some records are corrupt and grades based on the DTC size distribution can be slightly different than grades based on the valuation diamond parcels. 9.3 Merlin Size‐Frequency Distribution 9.3.1 DTC Size-Frequency Distribution The production record for the period November 1999 to December 2002 and including the valuation parcels for Gawain and Ywain is used to provide a DTC size-frequency distribution profile representative of the Merlin diamond population (Table 9.1). The diamonds recovered from Merlin during the 1998-2003 mining operations were sized using DTC sieve plates, and in doing so both carat weights and stone numbers were recorded (Table 9.1). Hence the MSS for each DTC size can be calculated. In most instances these recoveries can be allocated to a specific mined flitch with a measured BCM. Prior to RIO assuming responsibility for the mine Ashton Mining had grouped the +12 DTC to +23 DTC size categories thus rendering the data useless for detailed analysis. Analysis of the usable data reveals two slightly different size-frequency distributions which reflect the micaceous higher grade pipes and the non-micaceous lower grade pipes. The DTC size data for Launfal appears to be corrupt or a mix of the two distributions. The data from each recorded mined flitch for each pipe have been assessed and non corrupted flitch data has been selected to establish the Mean Stone Size for each DTC size category. 9.3.2 Weight Size-Frequency Distribution In addition to the DTC sizing of the diamonds, the diamond recoveries were also sized according to their carat weight but with the -0.66ct diamonds still being classified according to DTC sizes (Table 9.2). While carat weights were recorded, no corresponding stone numbers are reported and the recoveries are recorded as production per month from each pipe. The recoveries have not been matched to a flitch and except in rare instances the weight sized recoveries cannot be matched to the DTC sized data. To assimilate the two data sets the Mean Stone Size is used to estimate the number of stones in each weight category. 9.4 Gawain Grade Model For Gawain two main data sets are used to establish grade, these being a valuation parcel which has an accurate mined volume and 3 measured grade control samples. In addition there are NADL ROM recoveries for which mined volumes are only estimates but which provides an expanded diamond distribution against which the grade control samples can be matched. 9.4.1 RIO Records Despite 35,000cts being produced from Gawain there is only sized data available for 4 flitches representing 4,236.48cts (Tables 9.3 & 9.4). Of these two flitches representing 3,634.87cts is the special valuation parcel reported separately by RIO as 3,623.5cts (Table 9.5). The cause of this slight discrepancy is not known. Flitch GWO1680 has sized data for only 290.41cts but 5,222.5cts was reported for this flitch hence there is no measured volume for the 290.41cts. Flitch GWO1690 which is the uppermost flitch in the pipe, reported 311.44cts but has a grade inconsistent with the pipe and hence must also be discarded.
65
9.4.2 Bulk Sample 2006 In 2006 an 86.67 wet tonne sample was processed producing 42.759cts of diamonds (Table 9.6). The sample was HPGR crushed and processed through a MK3 sampling plant using a 0.7mm square lower screen. The volume of the sample was calculated and appears slightly understated. 9.4.3 NADL 2006/2009/2010 ROM Trial mining in 2006, 2009 and 2010 resulted in the recovery of 10,182.5 carats of diamonds (Table 9.7). The recoveries have been weight sized and demonstrate the expected size-frequency distribution. The volume of material processed to produce these diamonds could not be accurately recorded. 9.4.4 Grade Control Samples In 2010 3 grade control samples each of approximately 100 BCM and totalling 306.6 BCM were excavated and processed through the Merlin pilot processing plant (Table 9.8). The 3 samples have been combined and treated as one sample. 9.4.5 Grade Model All of the data sets are matched against the combined grade control samples (Tables 9.9 & 9.10) by adjusting the BCM value until the contribution per size category matches. Due to the small size of the grade control samples the correlation is limited to the -11 DTC size categories. The +0.66ct size categories are taken from the Merlin average production for the micaceous pipes. 9.5 Ywain Grade Model For Ywain grade is based on the 2006 bulk sample and the RIO special valuation sample. In addition there are the 2006 NADL ROM recoveries for which mined volumes are only estimates but which provides an expanded diamond distribution against which the measured samples can be matched. 9.5.1 RIO Records Only 6,558.9cts was produced from Ywain with sized data available for 5 flitches representing 5,664.36cts (Tables 9.11 & 9.12). These five flitches represent the special valuation parcel reported separately by RIO as 5,680.72cts (Table 9.13). 9.5.2 Bulk Sample 2006 In 2006 a 14.1 wet tonne sample was processed producing 14.66cts of diamonds (Table 9.14). The sample was not HPGR crushed due to its extremely weathered nature and processed through a MK3 sampling plant using a 0.7mm square lower screen. The volume of the sample was calculated. 9.5.3 NADL 2006 ROM Trial mining in 2006 resulted in the recovery of 1,817.16 carats of diamonds. The recoveries have been weight sized and demonstrate the expected size-frequency distribution. The volume of material processed to produce these diamonds could not be accurately recorded (Table 9.15). 9.5.4 Grade Model All of the data sets are matched against the 2006 bulk sample (Tables 9.16) by adjusting the BCM value until the contribution per size category matches. Due to the small size of the control sample the correlation is limited to the -11 DTC size categories. The +0.66ct size categories are taken from the Merlin average production for the micaceous pipes.
66
9.6 Excalibur Grade Model The only data pertaining to Excalibur is the RIO Mining data (Table 9.17). No evaluation sampling has been undertaken by NADL. 9.6.1 RIO Records Of the 24 flitches mined only 4 have been fully DTC sized with the majority having all of the +12 DTC size categories combined into one (Table 9.6.1). In comparing the recoveries from the 4 available flitches it can be seen that only two are suitable for grade estimation (Table 9.18). Weight sized recoveries for 116,194.52 carats recovered during the period 2000 to 2001 have been reported (Table 9.19). However there are no accompanying mined volumes to allow direct grade estimations for the weighted size categories. 9.6.2 Grade Model With no grade control samples the resource models are based solely on the historic recovery and the average Merlin production for the micaceous pipes (Table 9.20). The fine diamond recoveries are estimated. 9.7 PalSac Grade Model The grade model for PalSac is based on the assimilation of the RIO mining data and the Large Diameter Core (LDC) and bulk sampling testwork undertaken by Rio. PalSac is unusual in that the pipe expresses itself as two discrete vents at surface, namely Palomides and Sacramore, which coalesce at a depth of approximately 120m to form a single pipe. 9.7.1 RIO Records Palomides Of the 24 flitches mined there are records for only 22 and of these 16 have been fully DTC sized with the remainder having all of the +12 DTC size categories combined into one (Table 9.21). In comparing the recoveries from the 16 available flitches it can be seen that 14 are suitable for grade estimation (Table 9.22). Weight sized recoveries for 49,882.55 carats recovered during the period 1999 to 2002 have been reported (Table 9.23). However there are no accompanying mined flitch volumes to allow direct grade estimations for the weighted size categories. 9.7.2 RIO Records Sacramore Of the 24 flitches mined there are records for only 22 and of these 14 have been fully DTC sized with the remainder having all of the +12 DTC size categories combined into one (Table 9.24). In comparing the recoveries from the 14 available flitches it can be seen that 12 are suitable for grade estimation (Table 9.25). Weight sized recoveries for 48,547.59 carats recovered during the period 1999 to 2002 have been reported (Table 9.26). However there are no accompanying mined flitch volumes to allow direct grade estimations for the weighted size categories. 9.7.3 RIO LDC Drilling PalSac In 2001 a LDC drilling program provided 74.482 tonnes of core in the interval from the base of the Palomides and Sacramore pits to a depth of 100m beneath these pits. This material, representing 53 discrete samples, was crushed and processed producing 18.22 carats of diamonds. The recovery of fine diamonds was poor and one sample accounts for 24 of the 83 diamonds recovered. Although three different phases of kimberlite are identified, these were not tested separately, hence the individual samples are treated as one (Table 9.27& 9.28).
67
9.7.4 RIO Bulk Sample PalSac As part of the LDC drill testing a bulk sample was excavated from flitch PLO1300 in Palomides pit and processed in the same manner as the LDC samples. Although the excavated sample was measured at 750 BCM or approximately 1,500 tonnes, the processes sample is reported as 845.85 dry tonnes. No explanation for this variance is recorded. The sample was processed in two parts using different grade ferrosilicon namely 270D and 150D to compare their efficiency. For the purposes of establishing a grade the samples are combined and treated as one (Table 9.29). The 150D sample has reported 4030 diamonds in the -3DTC size category, which is considered erroneous. This data point has been adjusted as the result does not affect the integrity of the overall sample. 9.7.5 2009 Palomides Pit Cleanup In 2009 the Palomides pit was dewatered and material was scavenged from the base of the pit in preparation for the taking of a measured grade control sample. This processing of this scavenged material resulted in the recovery of 218.27 carats of diamonds (Table 9.30). The volume of the processed material was not accurately recorded. The grade control samples were not excavated. 9.7.6 Grade Model With no specific grade control samples the resource model is based on the historic recovery, the average Merlin production for the non-micaceous pipes, the LDC samples and the bulk sample taken by RIO (Table 9.31). The fine diamond recoveries are estimated using the Palomides cleanup sample data done by NADL in 2009. 9.8 Launfal Grade Model The grade model for Launfal is based on the RIO mining data as no additional evaluation sampling has been undertaken since cessation of the mining operations in 2003. There is geological complexity within this pipe which may explain why the size –frequency distribution fits neither the micaceous pipe distribution nor the non-micaceous pipe distribution. 9.8.1 RIO Records Of the 28 flitches mined there are records for only 21 and of these 8 have been fully DTC sized with the remainder having all of the +12 DTC size categories combined into one (Table 9.32). In comparing the recoveries from the 8 available flitches it can be seen that only 5 are suitable for grade estimation (Table 9.33). Weight sized recoveries for 30,969.08 carats recovered during the period 1999 to 2002 have been reported (Table 9.34). However there are no accompanying mined flitch volumes to allow direct grade estimations for the weighted size categories. 9.8.2 Grade Model With no grade control samples the resource models are based solely on the historic recovery. The fine diamond recoveries are estimated from the recoveries observed in Palomides (Table 9.35). 9.9 Kaye Grade Model The grade model for Kaye is based on the assimilation of the RIO mining data, the trial production undertaken by NADL and 3 grade control samples.
68
9.8.1 RIO Records Of the 8 flitches mined there are records for 7 and of these 5 have been fully DTC sized with the remainder having all of the +12 DTC size categories combined into one (Table 9.36). In comparing the recoveries from the 5 available flitches it can be seen that only 2 are suitable for grade estimation (Table 9.37). Weight sized recoveries for 10,471.97 carats recovered during the period 1999 to 2001 have been reported (Table 9.38). However there are no accompanying mined flitch volumes to allow direct grade estimations for the weighted size categories. 9.8.2 Bulk Sample 2006 In 2006 a 76.6 wet tonne sample was processed producing 10.24cts of diamonds (Table 9.39). The sample was HPGR crushed and processed through a MK3 sampling plant using a 0.7mm square lower screen. The volume of the sample was calculated and appears slightly understated. 9.8.3 NADL 2009/2010 ROM Trial mining in 2009 and 2010 resulted in the recovery of 3,516.47 carats of diamonds (Table 9.40). The recoveries have been weight sized and demonstrate the expected size-frequency distribution. The volume of material processed to produce these diamonds could not be accurately recorded. 9.8.4 Grade Control Samples In 2010 3 grade control samples each of approximately 100 BCM and totalling 293.95 BCM were excavated and processed through the Merlin pilot processing plant (Table 9.41). Sample 10-330-102/103 appears corrupt and has not been used in the grade estimations. The remaining two samples have been combined and are treated as one sample. 9.8.5 Grade Model All of the data sets are matched against the combined grade control samples (Tables 9.42) by adjusting the BCM value until the contribution per size category matches. Due to the small size of the grade control samples the correlation is limited to the -11 DTC size categories. The +0.66ct size categories are taken from the Merlin average production for the non-micaceous pipes. 9.10 Ector Grade Model The grade model for Ector is based on the RIO mining data as no additional evaluation sampling has been undertaken since cessation of the mining operations in 2003. Although Ector is expected to coalesce with Kaye at depth to form a single pipe, this is yet to be demonstrated. 9.10.1 RIO Records Of the 10 flitches mined there are records for 9 and of these 7 have been fully DTC sized and have A recorded BCM with the remainder having all of the +12 DTC size categories combined into one (Table 9.43). In comparing the recoveries from the 7 available flitches it can be seen that only 5 are suitable for grade estimation (Table 9.44). Weight sized recoveries for 2,545.55 carats recovered during the period 2000 to 2001 have been reported (Table 9.45). However there are no accompanying mined flitch volumes to allow direct grade estimations for the weighted size categories. 9.10.2 Grade Model With no grade control samples the resource models are based solely on the historic recovery and the average Merlin production for the non-micaceous pipes (Table 9.46). The fine diamond recoveries have not been estimated.
69
9.11 Gareth Grade Model The grade model for Gareth is based on the RIO mining data as no additional evaluation sampling has been undertaken since cessation of the mining operations in 2003. 9.11.1 RIO Records Of the 24 flitches mined there are records for 19 and of these only 10 flitches have been fully DTC sized and have a recorded BCM with the remainder having all of the +12 DTC size categories combined into one (Table 9.47). In comparing the recoveries from the 10 available flitches it can be seen that only 6 are suitable for grade estimation (Table 9.48). Weight sized recoveries for 6,469.38 carats recovered during the period 2000 to 2002 have been reported (Table 9.49). However there are no accompanying mined flitch volumes to allow direct grade estimations for the weighted size categories. 9.11.2 Grade Model With no grade control samples the resource models are based solely on the historic recovery and the average Merlin production for the non-micaceous pipes (Table 9.50). The fine diamond recoveries have not been estimated. 9.12 Bedevere Grade Model The grade for Bedevere is based on the Ashton bulk sampling program which was undertaken in 1996 (Table 9.51). No additional evaluation sampling has been undertaken since cessation of the mining operations in 2003. Table 9.51: Bedevere RC Drill Sample Results
Drill Hole Interval (m) Sample
Wt (tonnes) Diamonds Carats
Grade (ctpt)
BH408 3 to 33 OB 946 0 0 0 33 to 96 Kimb 3.857 10 0.38 0.098
BH409 7 to 49 OB 1.909 0 0 0 49 to 96 Kimb 3.689 12 1.2315 0.333
Combined Kimb 7.546 22 1.6115 0.21 9.12.1 Grade Model With no detailed diamond recoveries the grade is stated as a global number. While these diamond recoveries provide an indicative grade they are not suitable for a detailed grade model. 9.13 Tristram Grade Model The grade for Tristram is based on the initial Ashton RC bulk sampling program which was undertaken in 1996 (Table 9.52), and a second bucket drill sampling program completed in 2006.
70
Table 9.52: Tristram Bucket drill Sample Results
Merlin Sample HMS Mark III O/S Floats Slimes Dia +4 Dia -4 Total Grade Freq
Sample No Pipe t t t t st ct st ct st ct ct/t st/t
9.13.1 Grade Model With no detailed diamond recoveries the grade is stated as a global number. While these diamond recoveries provide an indicative grade they are not suitable for a detailed grade model. 9.14 Summary of Grade Models The Resource Grade Models and Production Grade Models are detailed in Tables 9.53 and 9.54 respectively. The Historic Mining Grades are shown in Table 9.55.
10 DIAMOND VALUATIONS 10.1 Introduction Based on the 507,000 carats of diamonds recovered from Merlin during the previous mining operations RIO established that there was no discernable difference in terms of size-frequency distribution or range of qualities for the diamonds recovered from any of the pipes that were mined hence there was a reasonable assumption that there is a single diamond population representative of the entire Merlin diamond field. A reassessment of the available data indicates that there may be a slight difference in the size-frequency distribution between the micaceous pipes Excalibur, Gawain and Ywain and the non-micaceous pipes PalSac, Kaye, Ector and Gareth. The data for Launfal is ambiguous in that it has characteristics of both types of pipes. The slight difference in the size-frequency distributions affects the large stones portion of the profile and hence has considerable influence on the contained value per BCM for the pipes. 10.2 RIO 1999‐2003 Valuations 10.2.1 Valuations The Merlin Diamond production was sized and valued by Argyle diamond sales in Perth prior to dispatch to Antwerp for sale. In Antwerp the parcel was broken up into variety categories for sales purposes Details of the valuation for each pipe, undertaken in Perth for production from September 1999 to January 2002 are shown in Table 10.1. The average value for each size category reflects not only variation in quality but also estimated changing market condition. There is no record of valuation from diamond parcels produced after January 2002 through to closure in mid 2003. However there is a valuation of two relatively small parcels produced from Ywain and Gawain. 10.2.2 Diamond Quality The 1999-2003 production undertaken by Ashton/RIO has provided detail on value distribution as a consequence of colour, quality and size. This is shown in detail in Tables 10.2, 10.3, 10.4, and 10.5. 10.2.3 Sales A summary of the diamond sales completed in the period 1999 to 2003 is shown in Table 10.6.
10.3 NADL 2005/2006 Valuation 10.3.1 Sorthouse Tails Valuation In late 2005, Nick Yiannopoulos valued an 8338.38ct parcel of diamonds recovered from the reprocessing of the sorthouse tailings. Despite the presence of high value yellow diamonds the entire parcel achieved an average value of US$27/ct. This low value is a reflection of the high proportion of smaller diamonds. Details are shown in Table 10.7.
Ind Brown2 $0.79 3,332.12 $2,646 40.0 1.2 TOTAL $27.01 8,338.98 $225,198 100 100
In 2006, the entire parcel of tailings diamonds compising 11,517 carats was valued by both Nick Yiannopolus and Peter Talbot-Ponsonbury. Details are shown in Table 10.8. 10.3.2 Gawain/Ywain ROM Valuation The trial operations undertaken by NADL in 2006 provided 8,225.2 carats of diamonds exclusively from Gawain and Ywain pipes for valuation. They were valued by Peter Talbot-Ponsonbury and Nick Yiannopolous. Details are shown in Table 10.9. 10.3.3 Sales A summary of the diamond sales completed by NADL in the period 2006 to 2007 is shown in Table 10.10. 10.5 NADL 2008 Revaluation Although the diamonds produced in 2006 were sold, the described parcel was able to be revalued by Nick Yiannopolous based on market conditions at the time. Details are shown in Table 10.11. 10.6 NADL 2010 Valuation The trial operations undertaken by NADL in 2009/2010 provided 9,254.23 carats of diamonds from Gawain and Kaye pipes for valuation. The mixed parcel was valued by both Peter Talbot- Ponsonbury and Nick Yiannopolous. Details are shown in Table 10.12. 10.7 Valuation Summary The valuations are compared in Table 10.13. All valuations illustrate the important contribution from the high value large diamonds. However it is important to note that some of the large stone size categories have only one or two data points on which to base the valuation, and hence can have large differences in value between adjacent diamond size categories. 10.7 Value Model A diamond parcel represents a snapshot of the diamond population particularly with respect to the large diamonds. A value model cannot only be based on a grade model and a diamond parcel valuation but it must also factor in quality expectations of the recovered diamonds particularly for the larger less frequently recovered diamonds. This is particularly true of Merlin diamonds with 75% of the value attributed to only 11% of the weight of the recovered diamonds. With few data points in the large diamond population there is risk that any attributed value may not be representative of ROM
73
value. To overcome this issue a detailed analysis of quality and colour distribution amongst the various size categories is necessary.
There has been sufficient evaluation work done and including the results of previous mining operations to classify much of the Merlin resource as Indicated and Inferred Resources according to the JORC guidelines for the classification of mineral resources. However, it should be noted that there three limiting factors which prevent the resources being upgraded to Measured category. There has been insufficient drilling to adequately define the resources, grade continuity has not been demonstrated but rather is assumed to continue at depth and the effect of geological complexity within some of the pipes remains unresolved. 11.2 Mining Factors and assumptions The kimberlite pipes are well defined and identifiable bodies which will not require any unusual mining technique to exploit. The near surface resources will be exploited by conventional open pit methods which previous mining activities have demonstrated to be suitable. The underground resources will most likely be exploited by a conventional sub-level caving approach. Dilution is anticipated to be with acceptable limits and will be largely limited to the periphery of the pipes. 11.3 Metallurgical Test Work Diamond liberation is critical not only to ensure that modelled grades are achieved but more importantly to ensure the recovery of large high value diamonds. The use of HPGR technology to enhance diamond liberation and reduce diamond breakage has been proven in test work and is an essential component in any envisaged processing plant. The modelled Resource and Production grades are based on this assumption. A second benefit of HPGR technology is its superior ability to generate slime material over that of conventional crushing technology. A second assumption is that appropriate Optical Sorting technology will also be part of the process circuit to ensure ultra large diamonds are recovered and not crushed. The top size for Merlin diamonds is currently not known but previous mining operations recovered a 104.73ct diamond which was at the limit of the top screen size. Final recovery is also a critical area where diamonds can be lost as was demonstrated by the previous mining operations which were reliant on x-ray fluorescent technology. Approximately 8% of Merlin diamonds do not fluoresce and hence cannot b recovered with conventional x-ray technology. The use of dual energy and optical sorters will overcome this recovery problem. 11.4 Mineral Resource Statement The Mineral Resource is outlined below and is classified in accordance with JORC guidelines. These grades are unlikely to be achieved from a commercial mining and processing operation due to a number of factors such as lower screen size, cyclone efficiency and final recovery techniques. Hence prudence is required in the application of these grades to economic mining models.
TOTAL 30,064,000 24 7,191,000 1Resource grade based on previous mining operation recovery using a +0.95 mm slotted bottom screen and a +0.95mm cut-off. 2Resource grade based on bulk sample test work using a +0.8 mm slotted bottom screen and a +0.95mm cut-off. The Merlin Mineral Resources have been and classified and reported in accordance with The 2004 Australasian Code for Reporting of Mineral Resources and Ore Reserves (JORC Code). The Merlin Mineral Resources estimates have been prepared by T.H. Reddicliffe. T. H. Reddicliffe is a Fellow of the Australasian Institute of Mining and Metallurgy. T.H. Reddicliffe is a consultant to North Australian Diamonds Limited. T.H. Reddicliffe has sufficient experience, which is relevant to the style of mineralisation and type of deposit under consideration, and to the activity which they are undertaking. This qualifies T.H. Reddicliffe as a “Competent Person” as defined in the 2004 edition of the ‘Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves’
76
The Production Resources are those which a production plant is likely to achieve and are shown in Table 11.2. Table 11.2 Production Resource Indicated Res.
Sub-Total 8.74 0.93 0.82 TOTAL 14.12 15.95 30.07 0.16 4.89 1Resource grade based on previous mining operation recovery using a +0.95 mm slotted bottom screen and a +0.95mm cut-off
11.5 Mineral Resource Potential There remains significant potential for additional resources at Merlin since without exception all of the pipes remain open at depth. However it would not be expected that the pipes would maintain their gauge indefinitely but will taper and likely evolve into dike like bodies. Gawain has already demonstrated evidence of this with the pipe appearing to morph into a dyke below 0mRL. Similarly Excalibur has become significantly smaller at depth. The most attractive pipes in terms of significant additional tonnages are the PalSac and Kaye/Ector pipes. Although it has yet to be demonstrated that Kaye and Ector coalesce at depth the drilling to date indicates that this is highly probable and arguably should result in a reasonably sized pipe. PalSac which at surface is the two pipes Palomides and Sacramore appears to maintain a reasonable size at depth. 11.6 Discussion of relative accuracy/confidence The mineral resources are classified as Indicated and Inferred. There are no Measured Resources and no Proven Ore Reserves. With the completion of a Feasibility Study some of the Indicated Resources may be upgraded to Probable Ore Reserve status as per the JORC guidelines. There is a high level of confidence in the volume of the resource due to the fact that the mineral resource is physically contained within the intrusive kimberlite pipe. The pipes themselves are easily defined by drilling and generally have a predicable geometry. However there are insufficient pipe boundary contacts to upgrade the geometry sufficient for a Measured Resource.
77
Diamond grades are plant recovered grades, and are significantly affected by liberation, and recovery parameters such as the lower screen size. The Resource grades are often significantly higher than the Production grades due to the extra crushing and reprocessing undertaken and the smaller lower screen sizes used during evaluation test work. The Production grades reflect the likely recoverable grade for a large scale production processing plant. The reported grades are based on what has been previously mined from the pipes and in some instances additional samples have been obtained from the base of the open pits. It is important to note that no resources beneath the base of the pits have been tested for commercial diamond content. However provided there are no changes in the kimberlite lithology it is reasonable to assume that there would be no significant variations to grade, but it remains a risk factor particularly with increasing depth or distance from the pit sampling. Another risk factor is the geological complexity which is known to exist in some of the pipes. The previous mining operations did not distinguish between different lithologies when they were observed with the pipe being treated as a single geological unit. None of these subsidiary lithological units have been accurately defined spatially by drilling and based on limited microdiamond sampling are assumed to have a similar or better grade than the dominant kimberlite breccia phases. However, should the grades be significantly different and the phase more dominant then the grade of a pipe could change significantly.
78
12 BIBLEOGRAPHY Andrew, M.C & Noppe, M. (2004) Merlin Project Resource Estimate and Exploration Potential (2nd July 2004) Project Number 4805, Striker Resources. Archbold, N.W. (1997) Report on the Palaeontology and Sedimentological Materials from the Merlin Exploration Area, Northern Territory. Earth Sciences, School of Aquatic Science and Natural Resources Management, Rusden Campus, Deakin University, Clayton, Victoria 3168. Atkinson, W.J., Smith, C.B., Danchin, R.V., Janse, A.J.A. (1990) Diamond Deposits of Australia. In: F.E. Hughes (ed). Geology of the Minerla Deposits of Australia and Papua New Guinea. Australasian Insitute of Minig and Metallurgy, Melbourne, Mongraph 14, pp 69-76. Glass, L. & Taylor, W (2005) Technical Report: X-ray Flourescence - Merlin Diamonds, ‘X-Ray Flourescence Response of Merlin Diamonds’. Houwen, W.M (1995) Treatment of Merlin Bulk Samples Phase II, AML Report No. 51895. Hutton, W.A. (2002) The Crushing and Heavy Media Separation of a Second Bulk Sample of Merlin Ore. Leaman, D.E. (1998) Structure, Contents and Setting of Pb-Zn Mineralisation in the McArthur Basin, Northern Australia, Australian Journal of Earth Sciences, 45, pp 3-20. Marissen, C. (1996) Report on Trial Mining at Merlin Prospect on Excalibur, Launfal and Palomides Pipes, April to September 1996, Ashton Mining Ltd. Marissen, C. (2000) Notes to Accompany Resource Update Southern Pipe Cluster, Merlin Diamonds Pty Ltd. Merlin Diamonds Pty Ltd, Mining Management Plan 2002-2003 Appendix 5 Mineral Resources Development Inc, (1995) A Short Study of Sampling and Drilling at the Merlin Kimberlite Project, Snowden Associates Pty Ltd. Mitchell, R.H. (1995) Kimberlites, Orangeites and Related Rocks, Plenum Press, New York. Michelly, B.F Merlin Project Bulk Sampling Project Phase 3, Report No. 52049 Michelly, B.F. Merlin Project Bulk Sampling Report Phase III Report, Report No. 52049, Ashton Mining Ltd. Michelly, B.F. & Pooley, S.J. (1995) Merlin Project Preliminary Resource Report, December 1995, Report No. 51236. Michelly, B.F. & Pooley, S.J. (1995) Merlin Project Phase II Report, Volume 1, Part 1 of 2. Michelly, B.F. & Pooley, S.J. (1995) Merlin Project Phase II Report, Volume 1, Part 2 of 2. Pietsch, B.A., Rawlings, D.J., Creaser, P.M, Kruse, P.D., Ahmad, M., Ferenczi, P.A., Findhammer, T.L.R. (1991) Bauhinia Downs 1:250,000 Geological Series Explanatory Notes. Northern Territory Geological Survey. Plumb, K.A., Ahmad, M., Wygralak, A.S. (1990) Mid-Proterozoic Basins of the North Australian Craton - Regional Geology and Mineralisation. In: FE Hughes (ed). Geology of the Mineral Deposits of Australia and Papua New Guinea. Volume 1. Australasian Institute of Mining and Metallurgy, Melbourne, Monograph 14, pp 881-902.
79
Plumb, K.A. & Wellman, P. (1997) McArthur Basin, Northern Territory: Mapping of Deep Troughs Using Gravity and Magnetic Anomalies. BMR Journal of Australian Geology and Geophysics, 10(3), pp 243-252. Pooley, S. (1995) Merlin Project, Palomides Winze Geology Report on Winze Sink, October - November 1995, Ashton Mining Ltd. Pooley, S. (1996) Merlin Project Geological Report on Bulk Sampling Activities, Palomides, Sacramore, Excalibur and Launfal, October 1995 - October 1996. Pooley, S. (2001) Palsac LDC Drill Program, Merlin Project, December 2001, Merlin Diamonds Pty Ltd. Reddicliffe, T.H. (1993) Australian Diamond Exploration, Summary of Exploration Activity 6th April 1993 to 15th June 1993, Report No. 50101, Ashton Mining Limited. Reddicliffe, T.H. (1995) Merlin Project, Supplementary Report to the Australian Diamond Exploration Summary of Exploration Activity Report 7th December 1994 to 28th February 1995. Reddicliffe, T.H. (1999) Msc Coursework, Merlin Kimberlite Field, Batten Province, Northern Territory. Reddicliffe, T.H. (2005) Summary of Merlin Mine, Report No. 05-004. Striker Resources. Reddicliffe, T.H (2007) Technical Board Papers, 3rd April 2007, North Australian Diamonds Ltd. Reddicliffe, T.H. (2010) Summary of Merlin Resource, Report No. 10-002, North Australian Diamonds Ltd. Rio Tinto Exploration Pty Ltd on behalf of Ashton Mining Ltd, (2002) Confidential Information Memorandum, Sale of the Merlin Diamond Mine and Adjacent Tenements. Swarko, S.K. (1966) Cretaceous Stratigraphy and Palaeontology of the Northern Territory. Bureau of Mineral Resources, Geology and Geophysics, 73, pp 1-135. Webb, A.W. (1994). Rb-Sr Dating of One Phlogopite Sample, Amdel Limited.