IN SITU RECOVERY SMI SEMINAR-final1

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IN-SITU RECOVERY OF METALS

Nenad DjordjevicUQ

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In many Cu mines only 1-2% of ore are minerals of value

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Gangue Minerals

Cu Concentrate Minerals

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~70% of known mineralised Cu is in the form of Chalcopyrite

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70%

30%

ChalcopyriteChalcocite, Bornite, Covellite, Malachite, Azurite, Cuprite, Chrysocolla, …

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In California, open pit mining becomes difficult & costly

“Performance Standards for Backfilling Excavations and Recontouring Lands Disturbed by Open Pit Surface Mining Operations for Metallic Minerals (a) An open pit excavation created by surface mining activities for the production of metallic minerals shall be backfilled to achieve not less than the original surface elevation, ….”

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Ref. State Mining and Geological Board Information Report 2007-02

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In-Situ Recovery?

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Main factors governing the choice of Cu processing technology (after du Plessis et al, 2007)

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In-Situ Recovery

• There are several modalities for in-situ recovery of metals:• Leaching of ore between boreholes• In-stope leaching• Post-caving leaching (ore losses during caving ~25-30%)• Open-pit leaching

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Post-Caving Leaching

• Aspects which is characterised with lowest risk, is the in-situ leaching of fragmented ore, post block caving.

• Due to nature of the fragmented ore, fully discounted value of the remaining ore, this application of in-situ leaching is likely to be financially attractive.

• Due to dilution, for advance caving operation about 25-30% of ore remain in-situ, mixed with waste rock.

• In the case of large caving mine, such as planed to be Chuquicamata, amount of additional Cu that can be recovered through in-situ leaching, could be in order of 50,000t/year

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In-Stope Leaching

• More complex will be underground In-Stope leaching. In this case, marginal grade ore will purposely blasted and dumped into prepared stopes; followed by in-situ leaching.

• During preparation of leaching stopes, blast damage to stope walls needs to be minimized, to minimize loss of leaching fluids.

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Borehole based In-Situ Leaching

• Potentially the most rewarding, would be in-situ leaching of ore, untouched by previous mining.

• In the case of deeper deposits dominant mineral will be primary sulphides.

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Previous copper focused ISR attempts failed due to:

• Dealing with oxide copper, which tends to be close to ground surface: environmental concerns

• Leaching based on naturally fractured rock: development of preferential flaw channels, resulting in poor recovery

• Leaching based on the use of diluted H2SO4 at low pressure/temperature: resulting in slow leaching of sulphides (deposition of jarosite, preventing acid access to the sulphide grains)

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• Fortunately, recent technological developments, creates opportunity for new methods for in-situ recovery of copper (gold).

• (At present In-Situ leaching is used commercially for extraction of uranium and potash)

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Cornerstones of New In-Situ Recovery Method

• Advanced geosteerable horizontal/directional drilling• Multi-Stage Hydraulic Fracturing• Measurement while drilling/Logging while drilling• New explosive formulations and initiation systems• Advanced modeling capabilities (coupled thermomechanical +

fluid flow + fracture mechanics)• Bio-technology and use of thermophilic bacteria• Experience gained through leaching of chalcopyrite concentrates

(high pressure/high temperature)

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Many horizontal/directional holes can branch-out from single deep vertical borehole

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Aim is to drill into the mineralised region at depth,precondition ore and leach-out metal from mineralized zone,(recovering ~1-2% of ore mass and leaving ~99% of gangue in place)

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Sulphide map at depth- Olympic Dam at depth ~500m(opportunity for extraction of metal with surgical precision)

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Project

• In-situ recovery of metals is multi-disciplinary project: geology, drilling, explosive engineering, geophysics, mining, petroleum engineering, hydrogeology, chemistry, micro-biology as well as social sciences.

• Proposed Project builds on technologies perfected in Oil/Gas Industry in the last 5 years, recent advances in hydro-(bio)-metallurgy, as well as modelling capabilities of rock fracturing and fluid flow.

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• Technology based on the oxidative dissolution of sulphide mineral by microorganisms that facilitate recovery of metals; in two modalities:

• Bioleaching: metals are transferred from the minerals into solution (e.g. Cu)

• Bio-oxidation: metals are made accessible to chemical extraction (e.g., refractory gold)

• In both cases insoluble metal sulphides are converted into water-soluble metal sulphate

Biomining

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• The bacteria oxidise ferrous iron (Fe2+) and sulphur, to produce ferric iron (Fe3+) and sulphate

• The Fe3+, reacts with sulphide minerals to produce Fe2+ and S• Fe2+ oxidising bacteria can accelerate conversion rate of Fe2+

into Fe3+ by up to 10^6

• Issue is how to create conditions suitable for growth of bacteria as well as regeneration of Fe3+

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Direct oxidation of sulphide mineral with oxygen in presence of bacteria

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Indirect oxidation of metal sulphides

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• Mineral oxidation by ferric iron (abiotic) is separated from ferrous iron oxidation (biological) in a two stage process

• Each process can be operated at optimum conditions of temperature, pH and oxygen concentration

• Demonstrated at plot scale for processing of zinc sulphide concentrates

• Regeneration of Fe3+ from Fe2+ can be performed in bio-reactors, located on the ground surface

• Fe3+ rich solution can be than pumped underground to perform oxidation of sulphide minerals

Recent Developments in Biomining Technology

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• Thermophilic bacterial leaching is fast; copper can be leached from chalcopyrite before creation of by-products on the fragments surface (jarosite).

• Efficient leaching at elevated pressures and temperatures is also possible without microbes

• At depth, due to low thermal conductivity of rock, oxidation of common sulphides will elevate temperatures within ore, accelerating leaching of chalcopyrite

In-Situ High Pressure & Temperature Natural Autoclave

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Geothermal gradient- works in our favor• With depth, rock temperature increases (~25-35degC/km),

creating favorable conditions for leaching of copper sulfides/chalcopyrite.

• Particularly around Pacific Rim, average rock temperature at depth of 1.5-2km, will be about 60-70degC, which is optimal temperature for bio-assisted leaching of primary copper sulphides.

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Hot geothermal regions host most of the world’s copper deposits

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Major Cu deposits in Australia are within relatively hot rock

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Applications: How to extend life of open pit mine

• Many open pit mines are getting close to their productive life• Due to ever increasing stripping ratio and geotechnical

constraints, cost of recovery of ore at depth becomes too high.• Traditional solution is to continue with underground mining of

some kind, perhaps caving• This project will add one more option: In-Situ Recovery of Metals

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New way for extension of open pit to underground mine

Old way, huge cost of removal of overburden withunknown long term environmental liability; or traditional underground mining

New way, cheap and safealternative to traditional mining options

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Simplified layout for deep in-situ recovery method

Ground Surface

Depth ~500-3000m

Fragmented ore Temperature ~40-60degC

Single vertical and multiple lateral holes

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Stress redistribution around fractured ore, creates stress “cage” inhibiting leak-off of leaching fluids

Ground water

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Rock Preparation-Critical First Step

• In the case of in-situ mineral recovery, leaching fluids needs to come close to sulphide mineral grains

• Creation of high density fracture network can be achieved by: – 1. Blasting (Explosives & Propellants)– 2. Hydraulic Fracturing, and/or– 3. Chemical Dissolution of Gangue

• In the case of vein/channel or similar deposits, objective is to keep fluids within fractured vein zone

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Problem of Flow Channeling

• The key reason for poor performance of previous attempts for in-situ recovery (Cu oxides) from naturally fractured rock, is due to preferential flow of fluids.

• Due to uneven permeability of rock in-situ, flow of fluids will be biased towards the paths of least resistance. Small differences in fracture paths permeability are likely to grow over time.

• “Nature is Not Enough”: Ore needs to be prepared for In-Situ Recovery of Minerals

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Fracture initiation and propagation is rate sensitive

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Explosive Induced Fracturing

• In-situ recovery of minerals is likely to proceed in stages. The most critical part is leaching of the first ore block.

• Induced fractures are kept open by shear dislocations, and/or by placing proppants of sufficient strength

• Required extra void for the first block, will come from the volume of the blastholes used to fracture the rock

• Within ore, blasthole diameter can be enlarged by under-reaming; increasing mass of explosive ~10 times

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High Energy Efficiency of Explosives

• One significant aspect of rock fragmentation by confined explosions is its energy efficiency.

• About 75% of chemical energy of explosives will be consumed within the fragmented volume of rock (Hinzen, 1999)

• Initial modelling of rock fragmentation under conditions relevant for in-situ recovery, has been performed using HSBM code.

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Modelling with relief hole

• For heavy confined blasting, use of empty central relief hole is common; same approach can be applied for in-situ recovery (confined quartzite 20m cube)

34 Post peak blasthole pressure shows rock-damaging oscillatory pattern.

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ISR = f(Texture of Cu minerals, …)

• Traditional modelling of rock leaching is based on the assumption that copper minerals are uniformly distributed within ore fragments

• 3D X-ray tomography results clearly show that for many copper ores, there is preferential distribution pattern of chalcopyrite grains: to be located near surface of rock fragments

• Opportunity for very fast leaching of such ores, under favorable P/T and fluid flow conditions.

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Blast induced rock preconditioning and enhanced propensity for leaching

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Rock fragments, after high intensity blasting are with increased number of micro-cracks, stimulating penetration of leaching fluids into the rock. Micro-cracks will be associated with presence of relatively soft minerals, (chalcopyrite).

After Lin et al, 2005

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Propellants as fracturing agent

• Propellants are similar to explosives, in terms of specific volume of gas and energy released; apart that they burn at slower rate.

• Pressure created by propellants can be used to fracture rock in tension, along the paths of least resistance (contrary to gas rich shale, for hard ore, paths of least resistance are mineralised fractures).

• Induced pressure is lower than yield strength of steel casing, allowing for multiple firing along same section of the hole, using perforated casing.

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Hydraulic Fracturing (HF) as Primary Rock Fracturing Method • Modeling of HF shows (Damjanac et al, 2013), that pressured

fluid prefer to open closed fractures (in-situ stress only); rather than break cohesive bond between “glued”, naturally mineralized fractures (in-situ stress plus cohesive bond strength).

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Efficiency of HF as function of In-situ stress and nature of ore

• In order to evaluate efficiency of hydraulic fracturing, it is necessary to consider in-situ stress field.

• Orientation of the mineralised structures relative to the present day in-situ stresses will be of critical significance for hydraulic fracturing

• Geomechanical contrast between “hard” host rock and relatively “softer” veins will be beneficial for HF

• Under favourable conditions, hydraulic fracturing could be highly effective tool for in-situ recovery.

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Fracture Connectivity/Aperture

• Blasted rock, will be characterized with most connected fracture network, allowing for superior penetration of pressurized leaching fluids.

• Cost of blasting is likely to be lower than of hydraulic fracturing• Research challenge is to have connected fractures,

sufficiently open, to allow percolation of leaching fluids.• Stiff nature of hard ore at depth, will make proppants an efficient

tool for keeping fractures open.

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Cost of In-Situ Recovery

• Cost of main vertical well, is small fraction of cost for constructing shafts and declines to reach same depth.

• Additional cost of lateral/directional holes is fraction of cost for excavation of galleries/tunnels (drilling cost will be much lower in US vs. Australia)

• Cost of underground blasting is known to be fraction of crushing/grinding cost

• Operational cost of ISR will be also relatively small, with much reduced workforce required

• Opportunity to recover metal from deposits, now considered untouchable (onshore/offshore)

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Copper production costs for selected current operations

ISR(mainly oxides)

For in-situ recovery to be a viable mass-mining method, production costs need to be comparable to

current conventional mining methods

Indicative OPEX is attractive relative to industry peers(based on Gunnison ISR Prefeasibility Study 2014)

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Environmental/Social Aspect

• Environmental impact will be minimal (no open pits & waste dumps, no acid mine drainage, no smelting)

• Due to depth, impact on groundwater likely to non-existent (although monitoring will be required)

• Safety for workforce, will be superior to the one in conventional mining

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Transforming Mineral Resources into Reserves

• Available numerical tools can model rock preparation for in-situ recovery

• Geosteerable directional drilling is technology ready to be used for ISR of minerals

• HF will be effective where mineralization is associated with fracture planes/veins

• Combination of blasting with hydraulic fracturing, appears to be more versatile approach.

• Use of thermophilic bacteria, or use of O2 under high P/T conditions, results in relatively fast leaching of primary sulphides

• Method can be also used for underground off-shore extraction of minerals!

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Accessing the ore deposit

Rock mass conditioning

Mineral recovery methods

Surface operations

(bi-products and residues)

License to operate

Prepared by:D. Weatherley, N. Djordjevic and G.P. Chitombo, 23 January 2014.

Ore deposit characterisation

Sustainable recovery of

valuable minerals from depth via

innovative in-situ extraction

technologies.

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In-Situ Recovery of MineralsTransforming Mineral Resources into Reserves

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Copper/Gold Deposits (Boreholes)

In-Place Leaching: Caving Mines; In-Stope; Open Pit

Mines

Narrow Vein/Reef/

Palaeochannels(Boreholes)

Based on Creative Synergy of Enabling Technologies: Steerable Directional Drilling; Hydraulic Fracturing; High Intensity

Blasting; Hydro (Bio) Metallurgy; Genetics; MWD/LWD

Structurally Complicated

Deposits (Boreholes)

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(Incomplete) List of Collaborators

• Dr Nenad Djordjevic• Prof Gideon Chitombo/BRC-SMI• Prof Doug Rawlings/University of Stellenbosch• Prof Gordon Southam/Earth Sciences/UQ• Prof Stephen Tyson/Earth Sciences/UQ• Prof Lars Nielsen/Inst. of Bioengineering/UQ• Prof Kirill Alexandrov/Inst. of Bioengineering/UQ• Dr Dion Weatherley/JKMRC-SMI • Dr Mansour Edraki/CMLR-SMI• Prof Christopher Leonardi/Mining Engineering/UQ• Potential participants from Chile• Potential participants from US

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