Gold and silver in Cu-Zn massive sulphide deposits of the Urals

The increasing production of processed ores of VMS deposits of the Urals (15 million ton per year) has aggravated a problem of gold recovery: 50-80% of gold and 33-50% of silver are lost in the pyritic concentrates and tailings. Gold and silver are relatively uniformly distributed in massive sulphide ores (Au: 0.5-1.5 ppm, Ag: 10-50 ppm), but local enrichments occur (up to 90 ppm Au and 600 ppm Ag). Au contents in Cu and Zn concentrates are commonly 20-50% more than those in ores and vary from 1.5 to 5 ppm. Most (50-90%) of the gold in common VMS ores containing 0.5-2 ppm Au are incorporated in the sulphides, mainly in pyrite and chalcopyrite, which have an Au range of 0.7-20 ppm. Au enrichment in reniform pyrite (5.5-20 ppm) and sphalerite with emulsion-like chalcopyrite (1.8-10.6 ppm) has been recognized. Tennantite-tetrahedrite is the main host of Ag, low-iron tennantite (0.05-0.6 wt% Ag, 1.2-2200 ppm Au) being the dominant variety. While Au contents in the ores are greater than 3-5 ppm, Au generally occurs as electrum and native gold (fineness 520-974), which form individual minute grains and/or aggregates with size of about 2-50 mu m (up to 150 mu m). These mineral parageneses were usually formed in the latest stage of mineralisation.