Abstract

The Xiaoqinling vein-style gold district (reserves of >630 t Au) has a very pronounced tellurium signature. The Yangzhaiyu gold deposit is one of the largest gold deposits in this district. The ore-mineral assemblage consists of pyrite, chalcopyrite, galena, bornite, sphalerite, gold, and native tellurium together with a wide variety of telluride and Bi-sulfosalt minerals. The telluride mineral assemblage comprises Phase A, sylvanite [(Au,Ag)2Te4], hessite [Ag2Te], petzite [Ag3AuTe2], calaverite [AuTe2], stützite [Ag5−xTe3], rucklidgeite [PbBi2Te4], altaite [PbTe], volynskite [AgBiTe2], tellurobismuthite [Bi2Te3], tetradymite [Bi2Te2S], and buckhornite [AuPb2BiTe2S3]. The Bi-sulfosalt minerals observed are Phase B, aikinite [PbCuBiS3], felbertalite [Cu2Pb6Bi8S19], and wittichenite [Cu3BiS3]. We observed two unnamed phases: Phase A and Phase B. Phase A, with the empirical formula of AgTe3, occurs in small intergrowth aggregates with sylvanite and chalcopyrite, and locally with bornite, galena, and altaite. Phase A and its associated minerals occur along healed micro-fractures in pyrite. It has a distinctly golden reflection color, without discernable reflectance pleochroism or anisotropy. AgTe3 was synthesized in 1982, but its natural occurrence has not been reported to date. Phase B, with the empirical formula of Cu20FePb11Bi9S37, was observed in an intergrowth aggregate together with hessite, galena, chalcopyrite, bornite, and buckhornite. It has a pinkish grey reflection color, without discernable reflectance pleochroism or anisotropy. The telluride and gold mineralization took place at or below ca. 220 °C and evolved towards decreasing fTe2. The ore-forming fluids and components of the Yangzhaiyu gold deposit may ultimately stem from refertilized upper mantle, either directly from devolatilization or from a magmatic system resulting from partial melting.

You do not currently have access to this article.