Report on beneficiation studies on a complex low grade Copper-Lead-Zinc ore from Bhotang Mine, Rangpo, Sikkim

Abstract

A Sample of Copper-Lead- Zinc ore assaying % Cu 0.67; % Pb, 1.48; % Zn, 4.50; % Fe, 15.22;% S, 8.68 % SiO2, 58.20; % Al2O3, 6.70 and Ag, 2.1 bz/ton with traces of Co, Cd, Ni and Au was received from the Indian Bureau of Mines at the instance of the Department of Mines and Fuel, of the Ministry of Steel, Mines and Fuel, for beneficiation tests at the National Metallurgical Laboratory. Chalcopyrite, galena, sphalerite and pyrrhotite were the chief sulphide minerals, whereas quartz and chlorite constituted the bulk of the gangue. Though the copper, lead and zinc minerals were fairly free from the siliceous gangue at about 48 mesh size, these were in intimate association with each other as well as with pyrrhotite, thereby necessitating very fine grinding to about 400 mesh for their liberation. Bulk flotation of the copper-lead minerals followed by repeated cleanings of the rougher copper-lead floats after grinding to -325 mesh yielded good copper and lead refloat concentrates assaying 27.55% Cu and 53.58% Pb with estimated recoveries of 75% copper and 60% lead respectively Activation of sphalerite from the copper-lead rougher tailing, followed by grinding to -325 mesh size refloat concentrate assaying 51.2% Zn with an estimated recovery of 76.0% zinc. Heavy media separation of the original -1”+6 mesh ore at a separating density of 2.8 rejected 43.7% by weight of the barren rock with a loss of only 5.9% copper, 2.8% lead and 3.1% zinc in it. Flotation performed with the mixed sink product and the -6 mesh untreated fraction is expected to yield results similar to those obtained by straight flotation. A definite advantage in adopting the Heavy Media Separation/Flotation process is that crushing and grinding costs would thereby be considerably lower, as more than 43% by weight of barren rock could be eliminated at a relatively coarse size.