Fülöppite Pb3Sb8S15 from the Darasun Volcanogenic–Plutonogenic Gold Deposit (Eastern Transbaikalia)

The Late Jurassic orogenic volcanogenic–plutonogenic Darasun gold deposit (the Eastern Transbaikalian segment of the Mongolia-Okhotsk Foldbelt) includes post-gold antimony mineralization. Aggregates of rice-like quartz, minerals of the jordanite–geocronite–schulzite series, sphalerite, galena, arsenopyrite, tennantite–tetrahedrite, calcite, and Mn–Mg siderite are its earlier formations; the later ones include rice-like quartz, low-iron sphalerite, Pb–Sb sulphosalts, antimonite, and berthierite. The Darasun trend of the sequence of Pb–Sb sulphosalts from bulangerite to fülöppite is typical of post-magmatic hydrothermal gold deposits and differs from that of telethermal ones. There are two fülöppite types in Darasun ores: fülöppite enriched in arsenic (up to 7.5 wt %), which is probably the product of replacement of geocronite and fahlerz mineral series, and arsenic-free fülöppite associated with antimonite and calcite. The composition of arsenic-bearing fülöppite is Pb 2.90 Ag 0.06 Cu 0.05 ) 3.01 (Sb 7.05 As 0.91 Bi 0.04 ) 8.00 S 14.99 and the composition of arsenic-free fülöppite is (Pb 2.83 Cu 0.18 ) 3.01 Sb 7.98 S 15.01 , which are close to stoichiometric. The Darasun fülöppite is characterized by a positive correlation between As, Bi, and Ag; arsenic-free fuloppite is enriched in copper.