Tetrahedrite group minerals of the Kekura reduced intrusion-related gold deposit, Western Chukotka, Russia

Abstract

The Kekura gold deposit in Western Chukotka, Russia is spatially related to the granitic rocks of the Early Cretaceous Gvardeisky Complex. The deposit was formed during five mineralization stages: (1) cassiterite-scheelite-chalcopyrite-bornite-arsenopyrite, (2) molybdenite, (3) chalcopyrite-gold-bismuth tellurides, (4) arsenopyrite-gold-scheelite, and (5) stibnite-gold-silver. The tetrahedrite group minerals (Ttgs) were identified in stages 2, 4, and 5. In the molybdenite stage Ttgs are associated with digenite, bornite, chalcopyrite, molybdenite, and arsenopyrite. Ttgs from the arsenopyrite-gold-scheelite stage are associated with scheelite, chalcopyrite, sphalerite, galena, and native gold with fineness of 800–850. Along with tetrahedrite, stibnite-gold-silver mineralization includes Ag-Au and Au-Ag-Hg alloys, native silver, sphalerite, stibnite, boulangerite. The molybdenite stage Ttgs display a wide range of the Sb/(Sb + As + Bi) ratio (sb) 0.06–0.85 and a narrow range of the Fe/(Fe + Zn) ratio (fe) 0.78–1.00, and are enriched in Cu (up to 5.767 apfu Cu at the M(1) site); the Ag content does not exceed 0.080 apfu. Ttgs of the arsenopyrite-gold-scheelite stage have the Cu-free at M(1) site, but are highly variable in the sb and fe values, ranging from 0.24 to 1.00, and from 0.14 to 1.00, respectively; the Ag concentration is higher than that in the molybdenite stage Ttgs, reaching 0.365 apfu. The stibnite-gold-silver tetrahedrite has high Ag (up to 3.442 apfu) and sb and fe ranging from 0.68 to 1.00 and from 0.10 to 0.84, respectively. Some Ttgs compositions of the molybdenite and stibnite-gold-silver stages are Bi-bearing that is caused by the replacement of previous Bi-minerals.