Ore mineralogy of tin-polymetallic (Sn-Sb-FePb-Zn-Cu-Ag) ores in the Dachang tin field, Guangxi, China and their implications for the ore genesis
Peng, Zhenan; Watanabe, Makoto; Hoshino, Kenichi; Shibata, Yasuhiro
published: Dec 1, 1999
ArtNo. ESP154017502002, Price: 29.00 €
The Dachang tin field includes a number of structurally-controlled tin-polymetallic deposits, represented by Longtaoshan, Changpo-Tongkeng, Lamo and Dafulao, which are hosted by the Devonian sedimentary sequence. Three types of orebodies are distinguished: veins including veinlets and networks (e. g., Longtaoshan, Dafulao and the upper part of Changpo-Tongkeng); stratiform orebodies (e. g., No. 91 and No. 92 orebodies of Changpo-Tongkeng and No. 20, No. 21 and No. 22 orebodies of Dafulao); and skarns (e. g. Lamo). Generalized paragenetic sequences observed in each deposit are divided mainly into three stages: early-, intermediate- and late-stages of mineralization. Mineralogy of the early-stage of mineralization is characterized by the close association of cassiterite with mainly pyrite, pyrrhotite, sphalerite (about 15 to 21 mole % FeS), arsenopyrite (about 27 to 32 atom % As) and quartz. On the other hand, the close association of jamesonite with mainly chalcopyrite, tetrahedrite-series ("freibergite" with Ag contents up to about 23 wt. %), galena and stannite with Zn contents up to about 6 wt. % is characteristic of the intermediate-stage of mineralization. Some of stannite disseminated in the host limestone of Changpo-Tongkeng is highest in Zn content up to 13.5 %. Hocartite and herzenbergite, closely associated with cassiterite, sphalerite and stannite, are present in traces in both the Longtaoshan and Changpo-Tongkeng deposits. Mineralogy of the late stage of mineralization is characterized by the close association of calcite with siderite and/or trace amounts of jamesonite, chalcopyrite, stannite and herzenbergite. The evidence presented in this study strongly supports an epigenetic origin for the tin-polymetallic mineralization throughout the Dachang tin field, which has occurred related in time and space to the Yanshanian granitic magmatism. Except for Lamo, they have formed by fracture-fillings by hydrothermal fluids mainly derived from the granite source. Homogenization temperatures of fluid inclusions trapped in the earlystage quartz, as well as compositions of sphalerite and arsenopyrite of the same stage, indicate that the mineralization of the early stage took place in the temperature and sulfur fugacity ranges of about 3000 to 450 °C and 10-10 to 10-5 atm, respectively.