The genesis of metal zonation in the Weilasituo and Bairendaba Ag-Zn-Pb-Cu-(Sn-W) deposits in the shallow part of a porphyry Sn-W-Rb system, Inner Mongolia, China

摘要

The Weilasituo and Bairendaba Zn-Pb-Ag-Cu-(Sn-W) sulphide deposits are located in the southern part of Great Xing'an Range of Inner Mongolia in China. The deposits are located at shallow depths in the newly discovered Weilasituo porphyry hosting Sn-W-Rb mineralization. The mineralization at Weilasituo and Bairendaba consist of zoned massive sulphide veins within fractures cutting the Xilinhot Metamorphic Complex and quartz diorite. The Weilasituo deposit gradually zones from the Cu-rich Zn-Cu sulphide mineralization in the west to Zn-rich Zn-Cu sulphide mineralization in the east. The Bairendaba deposit has a Cu-bearing and Zn-rich core through a transitional zone devoid of copper to an outer zone of Zn-Pb-Ag mineralization. Three main veins contain more than 50 wt.% of the contained metal in the two deposits with their metal ratios displaying a systematic and gradual increase in Zn/Cu, Pb/Zn and Ag/Zn ratios from the western part of Weilasituo to the eastern part of Bairendaba. Three stages of vein-type mineralization are recognized. Early, sub-economic mineralization consists of a variable proportion of euhedral arsenopyrite, pyrite, quartz, and rare wolframite, scheelite, cassiterite, magnetite and cobaltite. This was succeeded by main stage mineralization with economic concentration of zoned Cu, Zn, Pb and Ag sulphide minerals along strike within the veins. The zones consist of the assemblages: (1) pyrrhotite-Fe-rich sphalerite-chalcopyrite(-quartz-fluorite) at west Weilasituo; (2) pyrrhotite-Fe-rich sphalerite-chalcopyrite(galena-tetrahedrite-quartz-fluorite) at east Weilasituo; (3) pyrrhotite-Fe-rich sphalerite-chalcopyrite(-galenatetrahedrite-quartz-fluorite) in the centre of Bairendaba; (4) pyrrhotite-Fe-rich sphalerite-galena(-chalcopyrite-tetrahedrite-quartz-fluorite) in the transition zone of Bairendaba; and (5) pyrrhotite-Fe-rich sphalerite-galenatetrahedrite(-chalcopyrite-falkmanite-argentite-pyrargyrite-quartz-fluorite) in the outer zone at Bairendaba. Post-main ore stage is devoid of sulphides and characterized overprinting of fluorite, sericite, chlorite, illite, kaolinite and calcite.