The sulfur isotope composition of tin-silver-polymetallic deposits of Verkhoyansk folded belt (Sakha-Yakutia, Russia)

Category Environmetal Geology
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Anikina, Elena; Bortnikov, Nikolay S.; Gamyanin, Gennady N.
Holding Date 28 September 2008

Sn-Ag-polymetallic deposits of Verkhoyansk fold belt are considered to have been originated during collision of the Kolyma-Omolon superterrane with the Siberian continent. The later results in the formation of steeply dipping faults that controlled a distribution of transverse granite belts. Sn-Ag-polymetallic deposits are spatially related to these granite massifs. Three stages of formation of these deposits were recognized: cassiterite-silicate, cassiterite-sulphidic and silver-polymetallic. Earliest assemblages include quartz, arsenopyrite, pyrite, cassiterite, bismuthinite. Cassiterite-sulphide aggregates, consisting of siderite, pyrrotite, arsenopyrite, cassiterite, pyrite, sphalerite, galena are next in a depositional sequence. The late aggregates are composed of quartz, galena, sphalerite, and salphosalts. A sulfur isotope composition in arsenopyrite, pyrite, pyrrotite, galena and sphalerite of various associations from tin-silver-polymetallic deposits has been studied. The δ34S values of sulfides from cassiterite-silicate deposits range from -4.8 to +3,5‰ in general. These figures obtained for arsenopyrite, pyrite, pyrrotite, sphalerite, and galena are +2,4 to +3,5‰, +1,5 to +3,5‰, +2,7‰, -2,1 to 2,5‰, and -4,8 to-2,5‰, respectively. Sulfides from the cassiterite-sulphie association exhibit wider range of δ34S values of -6,9 to +6,3‰. The data measured for arsenopyrite, pyrite, pyrrotite, sphalerite, and galena are -6 to +4,7‰, -1,8 to +6,3‰, -1,9 to +2,8‰, -3,1 to +4,6‰, -6,9 to +1,8‰. The δ34S values of sulfides from silver-polymetallic deposits vary from -7,4 to +6,8‰. These figures obtained for arsenopyrite, pyrite, pyrrotite, sphalerite, and galena are -1,8 to +3,8‰, -2,6 to +4,7‰, +0,4 to +1,9‰, -3 to +5,2‰, -7,4 to +6,8‰. The change of values δ34SH2S in oreforming fluid can be responsible for these variations. Calculated values δ34SH2S in oreforming fluid, supposing that δ34S∑S of fluid equal to δ34SH2S, suggest that cassiterite-silicate association deposited from fluid with δ34SH2S from -2,8 to +2,3‰, cassiterite -sulphide association - from -4,5 to +5‰, silver-polymetallic association from -5,1 to +9,1‰. These infer some increase in a heavy sulfur isotope content in the fluid through cassiterite-silicate to silver-polymetallic association. The majority of points are clustered near to zero value. This indicates that sulfur in mineralforming systems was derived from a same most likely magmatic source. Relatively high δ34SH2S values typical for fluid of last mineralisation stages can indicate the involvement of oxidized forms of sulfur in ore deposition site in a subsurface environment. The negative δ34S values are interpreted to have resulted from a fractionation of sulfur isotopes between coexisting minerals during the mineral crystallization. Results obtained indicate that the granitoid related sulfur was a principal component of oreforming fluid deposited tin-silver-polymetallic ores of the Verkhoyansk fold belt.