2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 277-8
Presentation Time: 10:15 AM


MAO, Wei1, LI, Xiaofeng1 and RUSK, Brian2, (1)State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, 46 Guanshui Road, Nanming District, Guiyang, 550002, China, (2)Geology Department, Western Washington University, 516 High St. MS 9080, Bellingham, WA 98225

The Dabaoshan polymetallic deposits consist of porphyry and skarn-type Mo-W deposits in the north and strata-bound Cu-Pb-Zn deposit in the southeast of the mining area. Porphyry-related veins show a typical progression from early barren quartz and quartz-molybdenite veins to later quartz-pyrite veins followed by latest polymetallic veins including chalcopyrite, sphalerite and galena. Widespread quartz-pyrite veins extend from the porphyries into the mid-Devonian limestone and record the lateral transport of hydrothermal fluids from magmatic host rocks into adjacent sedimentary rocks.

We identified 6 types of fluid inclusions including B15, B35, B60, B85, B20H, and DB20, where B, H, DB, and the number denote bubble, halite daughter mineral, double bubble (CO2-bearing inclusions), and the average volume percent of the bubble, respectively. B35 and DB20 are most common in early barren quartz and quartz molybdenite veins. Their proportions decrease in later veins, while the proportions of B15 and B60 inclusions increase. Fluid inclusion populations in all vein types are unusual relative to typical porphyry deposits in that halite-saturated and vapor-rich inclusions are rare in any vein generation from the Dabaoshan deposits. We suggest that this may result from a lack of fluid unmixing which allowed Cu, Pb, and Zn to be transported outward into the surrounding limestone.

Quartz CL textures reveal a complex fluid evolution, with some veins characterized by up to 4 distinct generations of quartz growth. CL intensity decreases from bright blue in early barren quartz and quartz-molybdenite veins to dark green in late quartz-sulfide veins. This decrease in CL intensity is accompanied by a decrease in Ti concentration of quartz. Quartz-pyrite veins and later polymetallic veins are characterized by euhedral growth zones, whereas earlier barren quartz and quartz molybdenite veins are characterized by granular mosaics of quartz that largely lack internal growth zonation. With the important exception of molybdenite, ore minerals are typically surrounded by a dark brown quartz rim of 10-100um. These textural and trace element variations likely result from progressive temperature decrease of hydrothermal fluids as the hydrothermal system evolved.

  • Wei Mao-Dabaoshan.pptx (35.6 MB)