Evaluation of a Diagnostic Leaching Technique for Gold In

Pergamon

0892-6875(00)00156-4

Minerals Engineering, Vol. 14, No. 1, pp. 1-12, 2001 2000 Published by Elsevier Science Ltd

All fights reserved 0892-6875/01/$ - see front matter

EVALUATION OF A DIAGNOSTIC LEACHING TECHNIQUE FOR GOLD IN NATIVE GOLD AND GOLD _+ SILVER TELLURIDES*

K. J. HENLEY ~, N.C. CLARKE I and P. SAUTER*

~mdel Limited, Osman Place, Thebarton, South Australia 5031, Australia E-mail: [email protected]

q[ Imtech Pty Ltd, 2 Lindeith Court, Sandy Bay, Hobart, Tasmania 7005, Australia -~ Homestake Gold of Australia Limited, 2 Mill Street, Perth, Western Australia 6000, Australia

(Received 16 May 2000; accepted 17 October 2000)

ABSTRACT

A detailed investigation of the stability in cyanide solutions of native gold and gold ~ silver teUurides in a flotation concentrate from the Golden Mile, Kalgoorlie, has been undertaken to assess whether leaching under different conditions can be used to quantify the distribution of Au between native gold and gold i- silver tellurides, as suggested by, for example, Chryssoulis and Cabri (1990).

The leaching was carried out on +20 Inn native gold and gold ~ silver tellurides separated from a high-grade flotation concentrate and then diluted with barren quartz. The material leached assayed 270 ppm Au and 118 ppm Te. About 77% of the Au was present as native gold (largely liberated) and about 23% was in gold i- silver tellurides (predominantly calaverite with trace petzite and Au- bearing hessite, also largely liberated). The grainsize of the gold-bearing minerals was mainly in the range 20/~n to lOOpm. The leach conditions used were:-

Stage 1:

Stage 2:

Leaching in dilute cyanide (0.1%) at pH 9.5for 24 hours to dissolve native gold but not gold :~ silver tellurides. Leaching the residue from Stage 1 in strong cyanide (2%) at pH 12.5for 96 hours to dissolve gold ~ silver tellurides.

Extractions of native gold and gold i-silver tellurides in the two stages of leaching were found to be as follows:

Mineral

Native gold Calaverite Au-bearing hessite (and petzite)

% Extracted in

Stage I

94 6

53

% Extracted in Stage 2

5 11 40

Total % extracted

in Stages 1 and 2 99 17 93

* Presented at Hydromet 2000, Adelaide, Australia, April 2000

2 K.J. Henley et al.

The results showed that the bulk of the native gold dissolved in the Stage 1 leach (weak cyanide, moderate pH), along with about half the hessite and petzite but hardly any of the calaverite. The estimate of Au in native gold from the Stage 1 leach corresponded fairly closely to the native gold content as the hessite/petzite concentrations were low. However, although the Stage 2 leach (strong cyanide, high pH) dissolved almost all the remaining hessite/petzite, only a small proportion o f the calaverite dissolved.

The main conclusions of the investigation are that calaverite is very refractory to cyanidation, much more so than hessite/petzite, and that the diagnostic leaching procedure studied did not provide a good estimate of Au in gold 4-silver tellurides. For the diagnostic leach procedure to be effective, a treatment, such as chlorination, which breaks down calaverite prior to the Stage 2 cyanidation is required. 2000 Published by Elsevier Science Ltd. All rights reserved.

Keywords Gold ores; cyanidation; hydrometallurgy; leaching; ore mineralogy

INTRODUCTION

The solubility of gold + silver tellurides in cyanide solution has been debated for many years but there is relatively little definitive experimental work in the technical literature on the subject. It is generally agreed that gold + silver tellurides dissolve at a slower rate than native gold and electrum (Marsden and House, 1992; Cornwall and Hisshion, 1976; Cathro and Walkley, 1961) and leaching tests on synthetic sylvanite (AuAgTe4) and calaverite (AuTe2) have shown low gold extractions (Lu and Lawson, 1994; Padmanaban and Lawson, 1991). However, leaching rates can be increased by ultrafine grinding (Liddell and Dunne, 1988,1989), increasing the pH to 12.0 to 12.5 (Jayasekera et al., 1988, 1991) and use of oxygen rather than air as oxidant (Jackman and Sarbutt, 1990). Chryssoulis and Cabri (1990) use the difference in Au extraction at pH 10.5-11.0 and 12.0-12.5 as a measure of the Au attributable to gold + silver tellurides and this method can be considered to be an example of diagnostic leaching.

Diagnostic leaching involves a series of leaches, each designed to destroy specific minerals (preferably only one), followed by cyanidation of the residue from each stage to measure the amount of gold released from the mineral,s) at each stage (Bruce, 1976; Tumilty et al., 1987; Lorentzen and Van Deventer, 1992; Lorentzen, 1995). Table 1 from Lorentzen (1995) summarises various pre-treatment leach stages and the minerals destroyed. The sequence of leaches used is designed on the basis of knowledge of the mineralogy of the sample.

TABLE 1 Selective pre-treatment leach stages and the minerals destroyed (from Lorentzen, 1995)

Pre-treatment stage 1 NaCN washes 2 NaCN 3 Na2CO3 4 HC1 5 HC1/SnCI2 6 H2SO4

7 FeC13

8 HNO3 9 Oxalic acid washes 10 HF 11 Acetonitrile elution

Minerals likely to be destroyed Precipitated gold Gold Gypsum and arsenates Pyrrhotite, calcite, dolomite, 8alena, goethite, calcium carbonate Calcine, hematite, ferrites Uraninite, sphalerite, labile copper sulphides, labile base metal sulphides, labile pyrite Sphalerite, galena, labile sulphides, tetrahedrite, sulphide concentrates Pyrite, arsenopyrite, marcasite Oxide coatings Silicates Gold adsorbed on carbon, kerogen, coal

Evaluation of diagnostic leaching technique for gold 3

A disadvantage of diagnostic leaching is that the pre-treatment leach stages are generally not specific to a single mineral and may dissolve several minerals, or partially dissolve several minerals to different extents. This complicates the interpretation of the leaching/cyanidation data but can be overcome to a certain extent by analysing the leach liquors for elements characteristic of the minerals being leached (e.g., Pb for galena, Zn for sphalerite) and using simultaneous equations and a knowledge of the mineralogy to calculate the gold distribution ;among the minerals (Tumilty and Schmidt, 1986). However, although the leach sequence selected is based on the mineralogy of the sample, there is little in the published literature on diagnostic leaching to indicate that the mineralogy of the residue from each leaching stage has been studied to confirm the assumptions as to which minerals have been leached. In our investigation of diagnostic leaching to quantify the Au distribution among native gold and gold + silver tellurides, we have addressed this problem by quantifying gold mineral proportions before and after each stage of leaching, so that we have a direct measure of the extent of dissolution of individual gold minerals.

Our investigation, which was carried out for Kalgoorlie Consolidated Gold Mines Pty Ltd (KCGM), was to test the validity of a diagnostic leach procedure for quantifying the Au attributable to native gold and gold + silver tellurides in ores and mill products from the Golden Mile, Kalgoorlie. The basis of this procedure, which is similar to that used by Chryssoulis and Cabri (1990), is to leach in dilute cyanide (0.1%) at pH 9.5 for 24 hoursto dissolve native gold but not gold + silver tellurides (Stage 1), followed by a strong cyanide (2%) leach at pH 12.5 for 96 hours to dissolve gold + silver teUurides (Stage 2). A summary of the results of this investigati,an was given in Henley et al. (1995) and this paper gives the detailed results.

EXPERIMENTAL PROCEDURE

The starting material for the investigation was a re-cleaner concentrate obtained by laboratory flotation of over 60 kg of KCGM plant flotation concentrate with a head grade of approximately 37 ppm Au and 47 ppm Te. The re-cleaner concentrate assayed 1466 ppm Au and 677 ppm Te and contained 53% of the Au and 19% of the T,~ in the plant flotation concentrate.

The re-cleaner concentrate was screened at 20 Ixm and from the +20 ~tm fraction a small amount of very high grade telluride/gold concentrate containing predominantly liberated native gold and gold + silver tellurides was prepared using a combination of heavy liquid, magnetic and magnetohydrostatic separation methods. This telluride/gold concentrate represented the non-magnetic fraction with a specific gravity greater than 6.5 and assayed 43.5% Au and 19.03% Te.

The subsequent investigation carried out on the telluride/gold concentrate is summarised in Figure 1.

A polished section was prepared of the telluride/gold concentrate and selected mineral grains were circled and analysed quantitatively by electron microprobe. Some of these analysed grains were then used by CSIRO to calibrate QEM*SEM (now known as QEMSCAN) to identify and quantify the proportions of the various gold + silver tellurides present. A full QEM*SEM analysis was then carried out on the telluride/gold concentrate to quantify the proportions of all minerals present.

Because of the very small weight (

4 K.J. Henley et al.

I Chemical

Mmeragt~hy

QEM*SF.IVl

~ysis

Dilulioa with quartz

analysis

Stage 1 lcJtch Stage 2 laeh

__ Che~cal analym

>2.96 spA~

P

Fig. 1 Flowsheet for processing the teUuride/gold concentrate.

On completion of the Stage 1 leach, the liquor was analysed for Au and a range of other elements and the residue was filtered, washed, dried and rotary subsampled to give portions which were analysed for mercury-soluble Au, mercury-insoluble Au, total Au and a wide range of elements. A portion was separated centrifugally in a heavy liquid of specific gravity 2.96 to concentrate residual heavy minerals (from the quartz diluent) for microscopic study.

The major portion of the residue from the Stage 1 leach was subjected to 96 hours strong cyanide bottle-roll leaching nominally to extract gold + silver tellurides (termed the Stage 2 leach). Leaching was carried out as specified by KCGM at 40% solids in distilled water, pH 12.5, 2.0% NaCN initial concentration and 1 kg/t PbO. The NaCN concentration decreased to 1.74% NaCN after 96 hours, at which point the recorded pH was 12.54.

On completion of the Stage 2 leach, the liquor was analysed for Au and a range of other elements and the residue was filtered, washed, dried and rotary subsampled to give portions which were analysed for mercury-soluble Au, mercury-insoluble Au, total Au and a wide range of elements. A portion was separated centrifugally in a heavy liquid of specific gravity 2.96 to concentrate residual heavy minerals (from the quartz diluent) for microscopic study.

The >2.96 sp. gr. products from the residues from Stages 1 and 2 were examined mineragraphically and the mineral proportions were quantified by QEM*SEM analysis.

MINERALOGY

The gold + silver telluride minerals identified in the telluride/gold concentrate were calaverite (AuTe2), petzite (AgaAuTe2) and Au-bearing hessite ((Ag,Au)2Te), with calaverite predominating. Quantitative electron-probe microanalyses of typical grains of native gold and the gold + silver tellurides are given in Table 2, from which it can be seen that there is some variability in the Ag content of native gold, from 4.24% to 15.54% with an average of 7.45%. There is also some variation in the compositions of Au-bearing hessite and calaverite. The native gold and gold + silver tellurides were predominantly liberated and between 100 ~tm and 20 ktm size. Other minerals present in significant proportions in the telluride/gold concentrate included coloradoite (HgTe), altaite (PbTe), pyrite, sphalerite, galena, tetrahedrite, pyrrhotite, chalcopyrite and arsenopyrite. A photomicrograph of a typical field is given in Figure 2.

Evaluation of diagnostic leaching technique for gold

TABLE 2 Electron-probe microanalyses of gold minerals

Grain

No.

1 83.49 15.54 NA* 99.03 2 84.09 13.94 NA 98.03 3 91.59 "7.06 NA 98.65 4 92.64 6.82 NA 99.46 5 91.49 6.70 NA 98.19 6 93.14 45.29 NA 99.43 7 92.83 6.16 NA 98.99 8 91.75 6.13 NA 97.88 9 93.76 ,1.67 NA 98.43 10 94.83 ,1.38 NA 99.21 11 93.78 ,1.24 NA 98.02

Avge

Weight, % Atomic proportions, %

Au Ag Te Total Au Ag ] Te Au

I Native gold

25.4 NA 74.6 76.8 23.2 NA 87.7 12.3 NA 88.1 11.9 NA 88.2 11.8 NA 89.0 11.0 NA 89.2 10.8 NA 89.1 10.9 NA 91.7 8.3 NA 92.2 7.8 NA 92.4 7.6 NA

Suggested formula

Ag (Au Te Total +Ag)

0.75 0.25 1.00 NA 1.00 0.77 0.23 1.00 NA 1.00 0.88 0.12 1.00 NA 1.00 0.88 0.12 1.00 NA 1.00 0.88 0.12 1.00 NA 1.00 0.89 0.11 1.00 NA 1.00 0.89 0.11 1.00 NA 1.00 0.89 0.11 1.00 NA 1.00 0.92 0.08 1.00 NA 1.00 0.92 0.08 1.00 NA 1.00 0.92 0.08 1.00 NA 1.00

91.22 '7.45 NA 98.67 87.2 12.8 NA 0.87 0.13 1.00 NA 1.00

Au-bearing hessite

8.97 53.93 37.02 99.92 5.4 59.9 34.7 0.31 3.45 3.76 2.00 5.76 9.41 53.30 36.90 99.61 5.7 59.5 34.8 0.33 3.42 3.75 2.00 5.75 9.90 53.88 37.10 100.88 6.0 59.4 34.6 0.35 3.43 3.78 2.00 5.78

11.06 54.77 35.85 101.68 6.6 60.1 33.3 0.40 3.61 4.01 2.00 6.01 11.29 53.19 36.19 100.67 6.9 59.1 34.0 0.41 3.48 3.88 2.00 5.88 10.13 53 .81 36 .61 100.55 6.1 59.6 34.3 0.36 3.48 3.84 2.00 5.84

Petzite

12 13 14 15 16

Av~e

17 24.35 4.4.16 28.20 96.71 16.4 54.3 29.3 1.12 3.71 4.83 2.00 6.83

Calaverite

18 37.13 13.83 58.80 99.76 19 41.42 0.63 57.63 99.68 20 41.53 0.58 57.58 99.69 21 41.57 0.63 56.92 99.12 22 41.75 0.56 57.88 100.19 23 41.82 0.32 56.98 99.12

Avge

27.5 5.2 67.3 31.5 0.9 67.6 3 i.6 0.8 67.6 3 ! .8 0.9 67.3 3 !.6 0.8 67.6 32.1 0.4 67.5

0.82 0.15 0.97 2.00 2.97 0.93 0.03 0.96 2.00 2.96

0.93 0.02 0.96 2.00 2.96 0.95 0.03 0.97 2.00 2.97 0.93 0.02 0.96 2.00 2.96 0.95 0.01 0.96 2.00 2.96

40.87 1.09 57.63 99.59 31.0 1.5 67.5 0.92 0.04 0.96 2.00 2.96 *NA = not analysed.

In both the Stage 1 and Stage 2 residues, calaverite was the main gold-bearing mineral present, with virtually all of the native gold having dissolved during eyanidation. The calaverite was present in both residues as angular and, in the case of the Stage 2 residue, slightly rounded particles showing little, if any, marginal corrosion by cyanide (Figures 3-7).

6 K.J. Henley et al.

Fig. 2 General field of view in reflected light of the telluride/go!d concentrate. The field contains native gold (N), calaverite (C), coloradoite (O), Au-bearing hessite (H), petzite (P) and pyrite (Y). The native gold commonly shows flattened and irregular shapes.

Fig. 3 Residue from Stage 1 (24 hours leach). The field contains three particles of calaverite (C).

Mineralogical analyses of the telluride/gold concentrate and the >2.96 sp. gr. products of the Stage 1 and Stage 2 residues are given in Tables 3, and Table 4 gives the calculated chemical compositions Of the materials based on the QEM*SEM analyses.

Fig. 4

Evaluation of diagnostic le~clain$ technique for gold

Fig. 5

Enlargenaent of the calaverite particle shown in upper right of Figure 3. The calaverite shows minimal evidence of marginal dissolution by cyanide.

Residue from Stage 2 (96 hours leach). A particle of calaverite shows rounded margins possibly indicating some marginal dissolution by cyanide.

Using the data in Table 3 and the mercury-soluble Au values for the Stage 1 and Stage 2 residues (12.2ppm and 1.53ppm Au respectively), it is possible to calculate the Au distributions among the various gold- bearing minerals (Table 5). This shows that native gold accounted for ~77% of the total Au in the telluride/gold concentrate with calaverite accounting for the bulk of the remainder. In the Stage 1 and Stage 2 residues, calaverite accounted for most of the Au.

8 K.J. Henley et al.

Fig. 6 Residue from Stage 2 (96 hours leach). An angular particle of calaverite shows no obvious evidence of marginal dissolution by cyanide.

Fig. 7 Residue from Stage 2 (96 hours leach). A calaverite particle (C) shows possible slight evidence of marginal dissolution by cyanide (rounding, presence of marginal serrations). The altaite (A) particle shows more evidence of such dissolution (well developed marginal serrations).

Evaluation of diagnostic le~hing technique for gold 9

TABLE 3 Mineralogical compositions determined by QEM*SEM

Mineral

Native gold, % Calaverite, % Au-bearing hessite and petzite, % Hessite, % Coloradoite, % Altaite, % Pyrite, % Pyrrhotite, % Chalcopyrite, % Sphalerite, % Galena, % Arsenopy~dte, % Tetrahedrite, % Other minerals, %

Gold/telluride Concentrate

36.96 23.92 2.13 1.01

10.21 1.32

15.87 0.13 0.64 2.24 1.20 0.18 2.22 1.97

Stage 1 residue*

29.98 1.32 1.23 9.53 1.29

22.73 0.36 0.71 2.67 1.33 0.13 3.70

25.01

Stage 2 residue*

22.28 0.16 0.03

10.24 3.27

24.70 3.30 0.78 3.43 2.19 0.11 3.26

26.26 Total, % 100.00 100.00 100.00

*QEM*SEM data on the >2.96 sp. gr. products after recalculation free of -25% c uartz in these products.

TABLE 4 Chemical compositions calculated from QEM*SEM data

Element Gold/telluride Stage 1 Stage 2 concentrate Residue * residue *

Au, % Te, % Ag, % Hg, % Cu, % Pb, % Zn, % As, % Sb, % S,%

43.93 19.26 5.65 6.25 0.63 1.85 1.53 0.21 1.05

10.33

12.88 22.11 2.34 5.82 0.92 1.97 1.83 0.22 1.74

14.69

9.34 18.00 0.88 6.26 0.86 3.90 2.34 0.20 1.57

16.98 *QEM*SEM data on the >2.96 sp. gr. products after recalculation free of -25%

TABLE 5 Gold distributions among various gold-bearing minerals

Telluride/gold concentrate Stage 1 residue Stage 2 residue

Au distribution (%) among mineralogical sites Native Calaverite Au-bearing hessite & gold petzite 76.7 22.8 0.5 15.8 83.2 0.9 3.1 96.7 0.2

Total

100.0 100.0 100.0

CYANIDATION RESULTS

Table 6 summarases the cyanide extraction data for Stage 1, Stage 2 and Stages 1+2 relating to mercury- soluble Au (i.e., liberated or exposed native gold), mercury-insoluble Au (i.e., Au in gold + silver tellurides and in occluded native gold), total Au (mercury-soluble Au plus mercury-insoluble Au) and Te in the diluted telluride/gold concentrate, which assayed 270 ppm Au and 118 ppm Te.

10 K.J. Henley et al.

TABLE 6 Stage cyanidation extractions of various types of gold and tellurium

Mercury-soluble Au Mercury-insoluble Au Total Au Te

Stage 1 93.6 27.9 73.9 0.2

Stage extraction, %* Stage 2

87.4 12.5 25.5 8.9

Stage 1 + Stage 2 99.2 36.9 80.5 9.1

*Percentage in the feed to a stage extracted by the stage.

Using the data in Tables 3 and 6 it is possible to calculate the amounts of Au in native gold, calaverite and Au-bearing hessite (and petzite) in the head, the residue after Stage 1 and the residue after Stage 2, and hence the proportion of each mineral leached after 24 hours and 96 hours. These are given in Table 7 and illustrated in Figure 8 and show that most (94%) of the native gold (with very little of the gold + silver tellurides) was extracted in Stage 1 but that only 11% of the calaverite and 40% of the Au-bearing hessite (and petzite) were extracted in Stage 2.

The evidence clearly indicates that the Stage 2 leach was relatively ineffective in dissolving calaverite and the photomicrographs of calaverite particles in the Stage 2 residue (Figures 5 - 7) show little, if any, evidence of marginal dissolution, as do those in the Stage 1 residue (Figures 3 and 4).

TABLE 7 Cyanide extractions of gold minerals from the telluride/gold concentrate (diluted)

In head Extracted in Stage 1 In Stage 1 residue Extracted in Stage 2 Extracted in Stages 1 + 2

Native gold Calaverite

207.09 194.89 12.20 10.67

205.56

Au, p 61.56 3.90

57.66 6.76

10.66

Au-bearing hessite and petzite

~m in mineral 1.35 0.71 0.64 0.54 1.25

Total

270.0 199.50 70.50 17.97

217.47 In Stage 2 residue 1.53 50.90 0.10 52.53

Au distribution, % in mineral In head Extracted in Stage 1 In Stage 1 residue Extracted in Stage 2 Extracted in Stages 1 + 2 In Stage 2 residue

100 94 6 5

99 1

100 6

94 11 17 83

100 53 47 40 93 7

100 74 26 7

81 20

CONCLUSIONS

Our investigation has tested a diagnostic leach procedure to quantify Au in native gold and in gold + silver tellurides in a telluride/gold concentrate in which the Au is present in native gold (~77%), calaverite (-23%) and Au-bearing hessite and petzite (

Evaluation of diagnostic leaching technique for gold 11

100 u)

i '

I . 20

0 0 20 40 60 80

GOLD [XSTRIBUTION (*/*) ~IONG ~ C N . SITES

Au-beaflng hesslte and petzlte

; Native gold Calaverite

~/ / / / / / / / / / / / / / / / / / / /~

100

In to,:l

sample Gold ex~action

Exlrscted In Stage 2

Exlmolecl in Stage 1

Fig. 8 Mineralogical distribution of gold in the telluride/gold concentrate.

The Stage 2 leach (12% NaCN, pH 12.5, 96 hours) dissolved most of the remaining native gold, Au-bearing hessite and petzite but only very little of the calaverite. The Stage 2 extraction of Au did not therefore provide a good estimate of the amount of Au in gold + silver tellurides.

It is concluded that, overall, the diagnostic leach procedure tested was not effective in quantifying the amount of Au gold + silver tellurides in the KCGM material because of the refractoriness of calaverite. The refractoriness of calaverite found in the present investigation confirms previous works on synthetic calaverite by Padmanaban and Lawson (1991). For the diagnostic leach procedure to be effective, a treatment, such as chlorination (Cornwall and Hisshion, 1976), which breaks down calaverite prior to the Stage 2 cyanidation is required.

ACKNOWLEDGEMENTS

We wish to thank the management of Kalgoorlie Consolidated Gold Mines Pty Ltd and Amdel Limited for permission to publish this paper and G Wilkie and the QEM*SEM group at the CSIRO Division of Exploration and Mining for provision of the QEM*SEM analyses.

REFERENCES

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Cathro, K.J. and Walkley, A., The Cyanidation of Gold. CSIRO Division of Mineral Chemistry Publication, 54 pp, 1961, CSIRO, Melbourne.

Chryssoulis, S.L. and Cabri, L.J., Significance of gold mineralogical balances in mineral processing. Transactions of the Institution of Mining and Metallurgy, 1990, 99, C1-C10.

Cornwall, W.G. and Hisshion, R.J., Leaching of telluride concentrates for gold, silver and tellurium - Emperor process. Transactions of the Society of Mining Engineering of AIME, 1976, 260, 108-112.

Henley, K.J., Clarke, N.C. and Sauter, P., Evidence for the refractoriness of gold + silver tellurides. In Proceedings of the Randol Gold Forum, Perth '95, Randol International Ltd, Golden, Colorado, 1995, pp. 141-143.

12 K.J. Henley etaL

Jackman, I. And Sarbutt, K., The recovery of gold from a telluride concentrate. In Proceeding of the Randol Gold Forum, Squaw Valley, Randol International Ltd, Golden, Colorado, 1990, pp. 55-58.

Jayasekera, S., Ritchie, I.M. and Avraamides, J., Electrochemical aspects of leaching gold telluride. In Proceedings of the Randol International Gold Conference, Perth, Western Australia, Randol International Inc., Golden, Colorado, 1988, pp. 187-189.

Jayasekera, S., Ritchie, I.M. and Avraamides, J., Prospects for the direct leaching of gold tellurides - - recent developments. In World Gold '91, The Australasian Institute of Mining and Metallurgy, Melbourne, 1991, pp. 181-183.

Liddell, K.S. and Dunne, R.C., Ultra-fine grinding effect on leach recovery from refractory gold ores. In Proceedings of the Randol International Gold Conference, Perth, Western Australia, Randol International Inc., Golden, Colorado, 1988, pp. 120-122.

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Lu, Z. and Lawson, F., Metallurgical properties of synthetic sylvanite. The AuslMM Proceedings, 1994, 299(2), 89-93.

Marsden, J. and House, I., The Chemistry of Gold Extraction. 1992, Ellis Horwood, London, 597 pp. Padmanaban, V. and Lawson, F., Metallurgical properties of synthetic calaverite. The AuslMM

Proceedings, 1991,296(1), 31-37. Tumilty, J.A. and Schmidt, C.G., Deportment of gold in the Witwatersrand system. In Gold 100,

Proceeding of the International Conference on Gold, vol 2: Extractive Metallurgy of Gold, The South African Institute of Mining and Metallurgy, Johannesburg, 1986, pp. 541-553.

Tumilty, J.A., Sweeney, A.G. and Lorentzen, L., Diagnostic leaching in the development of flowsheets for new deposits. In Proceeding of the_International Symposium on Gold Metallurgy, ed. R.S. Salter, D.M. Wyslouzil and G.W. McDonald. Proceedings of the Metallurgical Society of the Canadian Institute of Mining and Metallurgy, Pergamon Press, Toronto, vol. I, pp. 157-167.

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