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56 Mineral Processing Technology (MPT 2007)Effect of Size Reduction in Complex Gold Ore

Cyanidation Recovery

Aghil Ojaghi, Ahmad Amini and M. Fattahi

M.Sc. in Mineral Processing, M.Sc. in Mineral Processing,managing director of Zarkavan Alborz Co. Geological Survey of Iran

B.Sc in geology, managing director ofZamin Rod Sepahan Co.

ABSTRACT: Generally gold recovery increases from size reduction although for polymetalic and complex ore,it seems not. Therefore polymetalic ore that contained 5.5% Pb, 0.3% Cu, 9% Fe, 1.4% Zn and 22 ppm Au were

investigated. Tests with several size fractions have done. Results showed that recovery increase up to a point after

that recovery goes down. It seems that in complex and polymetalic ores size reduction causes useless elementswill be free therefore, cyanide consumption increase and gold recovery decrease.

1. INTRODUCTION

Cyanidation is one of the popular and common

methods for gold processing. Several parameters

are effective in cyanidation although size reduction

and cyanide consumption importance of them.

Regards to ore dressing experts the more size

reduction the more increase recovery. But for

pollymetalic ores it seems different. Therefore inthis paper we concerned about this and effects of

size reduction in gold recovery were investigated.

Sample were taken from the Gandi gold deposit

is located 125 km SW of the Damghan city, NE

of Iran.

2. MICROSCOPIC MINERALOGY

Mineralization occurs as hydrothermal veinlets

containing gold, copper, lead and zinc minerals.

The upper ca. 25-35 m of the deposit has been

oxidized. The ore contained Au (22 ppm), Ag

(16.6 ppm), As (72 ppm), Pb (5.5%), Zn (1.4% )and Cu (0.3%). Ore samples were studied by

XRD, XRF and wet chemical analysis. Micro-

scopic studies showed that the ore is composed

of mineral assemblages goethite, galena, anglesite,

pyrite, chalcopyrite, cerussite, tetraedrite, covellite

and native gold (Up to 100 125 micron). The

image analyzer was investigated and processing

with QemScan software revealed that the goldwas associated with anglesite (PbSO4). Results of

microscopic study was shown in Figure 2-6.

Fig. 2

Fig. 3

Fig. 4

Galena

Pyrite

Au

Galena

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57 Mineral Processing Technology (MPT 2007)

Fig. 5

Fig. 6: Gold-bearing particles (red pixels)

3. MATERIAL AND METHODS

For investigation 500 Kg of the ore was taken

and crushed with jaw, cone crusher and roller

crusher less than 2 mm. The sample after homo-genate was separated to 1 kg head samples fortests. 3 kg of the sample was sieved by A.S.T.M.

screens (size details were shown in table 1 and

Figure 7) that determined gold distribution in

size fractions of main sample.

Table 1: Gold distribution in size fraction

Size

(micron)

Weight

(gr)

Gold

grade

(ppm)

Gold

distribution

(%)

+1000 654.9 15.53 17.29

+500 742.9 16.26 20.23

+250 436 17.36 12.87

+150 427.9 16.67 12.13

+75 383 18.5 12.04

+45 33.7 60 3.44

+20 96 96.94 15.82

-20 176 19.65 5.88

Total 2950.4 19.94 100

5.88

15.82

3.44

12.04 12.1312.87

20.5317.29

0

10

20

30

40

50

60

70

80

90

100

golddistribution(%)

20 20 45 75 150 250 500 1000

size fraction (micron)

Figure 7: Gold distribution in head sample

For cyanidation tests, head sample was

ground by ball mill (Denver 30 mm) indifferent times. In each case 1 kg with 1 liter

water was ground. Curves of grain size-grinding

time were draw and showed in each time how

much is less than 200 and 325 meshes (Table 2

and Figure 8).

Table 2: grinding time and grain size

Grain size less

than 325 mesh

(%)

Grain size

less than

200 mesh

(%)

Grinding

time

(minute)

-----6610

63.5------147180.8420

8090.630

-----94.2540

919750

90.6

94.2597

63.5

71

80

91

66

80.84

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60

Grinding Time (min)

Grainsize(%)

-200 mesh

-325 mesh

Fig. 8: curves of grain size and grinding time ratio

Au

1 pixel = 2m

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59 Mineral Processing Technology (MPT 2007)oxygen isotope constraints, MineraliumDeposita, 2004, No. 39, pp. 265-281.

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Effect of lead nitrate on cyanidation of goldores: progress on the study of the mechanisms,

Mineral engineering, 2000, Vol. 13, No. 14-15,pp. 1641-1646.

[7] Curreli, L., Loi, J., Peretti, I., Rossi, G., Trois, P.,Zucca, A.,Gold recovery enhancement fromcomplex sulphide ores through combined

bioleaching and cyanidation, MineralEngineering, 1997, Vol. 10, No. 6, pp. 567-576.

[8] Perry, R., Browner, R.E., Dunne, R., Stoitis, N.,Low pH cyanidation of gold, 1999, Mineral

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