MINING OPERATION and Metallurgy of POLYMETALLIC DEPOSIT WITH PRECIOUS METALS

MINING OPERATION
The Carhuanco was mined in past in small scale employing the cut-and-fill technique trying to get an optimum grade ore for the processing plant. Thus, were obtained lead concentrates with appreciable contents of precious metals. Few people employed the amalgamation process in order to the recover the free gold present in the ore body. The zones treated by amalgamation were Fragua and Cedruyoc.

During the underground labors were used few amounts of wood due to the structural strength offered by the host rock and the carefully control of the width in each labor.

METALLURGY
The metallurgical behaviour of the ore was done using 13 samples which were sent to two research laboratories. The samples were taken in several zones considering width 0.80 m which is the parameter to be used in scale industrial.

The conclusions and results obtained were the following:

• The composite assayed 0.19% Cu, 2.2% Pb, 0.48% Zn, 6.0 oz/t Ag, 0.10 oz/t Au, 12.7 %Fe, and 3.4% As.
• The oxidized material reported 0.5% Cu, 10.2% Pb, 0.4% Zn, 10.8 oz/t Ag, 0.34 oz/t Au, 6.9% As. The cyanidation test indicated that silver can be leached until 63% and the remanent silver is present in galena and refractory material. The gold can be recovered until 87%. This value indicated the existence of free gold in the deposit.

• Flotation tests indicated that the mixed ore is not appropriate to be treated by this concentration method. The lead concentrate contents precious metals but the lead content is not enough for trading. The main reason of this behaviour is the high content of oxides, arsenic, sulphur, and the natural acidity of the ore.

• Direct cyanidation of mixed ore let recoveries of 40% and 70% in silver and gold, respectively. Gold extractions can be considered good but no silver, because more than 50% is into refractory species.

• When the mixed ore was treated by a combined method of flotation and cyanidation, recoveries were 77% and 91% in silver and gold, respectively. The sample was treated by flotation trying to get a lead concentrate and pyrite concentrate with precious metals. And the tails were treated by cyanidation. Without any doubt, the investigation of the ore behaviour by combined processes is the best way. An aspect to be considered is the recovery of free gold by gravimetric equipments such as jig, table, or centrifugal concentrator.

• Also, was investigated the possibility of getting a sulphides bulk concentrate by flotation in order to recover galena and the precious metals present in pyrite and arsenopyrite. The best results indicated that recoveries could be 50% lead, 60% silver and 70% gold. The concentrate bulk assayed 18% lead, 73 oz/t silver and 1.0 oz/t gold.

• As the mineral has an oxidized part is natural a low recovery only by flotation. Old labors present sulphides which are been weathered and it is possible to expect a similar behaviour than mixed ore. Although, deeper zones could give a good performance by flotation.

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