Studies on the Nundydroog Gold ore with a view to improving gold recovery

Abstract

Extensive laboratory studies were undertaken in National metallurgical Laboratory on the three samples of gold viz., (i) Crushed run-of-mine ore,(ii) feed to the cyanidation plant and (iii) final cyanidation tailing, received from Nundydroog Mines, Kolar, with a view to minimizing loss of gold in the final cyanidation residue. Petrological studies on the run-of –mine ore (Sample No.1) indicated that gold was present in the native form associated with arsenopyrite and quartz. The run-of –mine ore assayed 5.6 dwt Au/ton. Cyanidation studies undertaken on the feed to cyanidation plant sample (Sample No.2) assaying 2.3 dwt Au per ton, indicated that it should be subjected to 27 hours agitation with sodium cyanide and lime to obtain a recovery of 87 % gold with respect to feed, equivalent to 94.6% gold recovery with respect to run-of-mine ore. Removal of graphite carbon, by floatation, prior to cyanidation did not improve the gold recovery. Wet magnetic separation followed by floatation of the cyanide residue yield an additional gold recovery of 3.3% with respect to run-of-mine sample. If wet magnetic separations followed by tabling, a product assaying 5.2 dwt Au per ton could be recovered with a distribution of 3.3% gold in it. The final rejects after tabling of floatation would assay 0.1 to 0.14 dwt gold per ton only, which would represent a loss of 1.6 to2.2 % of the total gold or an overall gold recovery of nearly 98%.Cyanidation studies under on the cyanide tabling (Sample No.3) assaying 0.54 dwt Au per ton indicated that an agitation time of 15 hours with NaCN and lime would recover 50% gold in the feed equivalent to a recovery of 95.2 % Au with tabling yielded a heavy mineral concentrate assaying 3.6 dwt per ton and recovering 47.4 % gold in it and representing an additional gold recovery of 3.8 % with respect to run-of-mine ore. This product will have to be roasted before cyanidation for recovery of gold from it.