Geological features and origin of the Huize carbonate-hosted Zn-Pb-(Ag) District, Yunnan, South China

摘要

The Huize Zn-Pb-(Ag) district, in the Sichuan-Yunnan-Guizhou Zn-Pb-(Ag) metallogenic region, contains significant high-grade, Zn-Pb-(Ag) deposits. The total metal reserve of Zn and Pb exceeds 5 Mt. The district has the following geological characteristics: (1) high ore grade (Zn+Pb>=25 wt. percent); (2) enrichment in Ag and a range of other trace elements (Ge, In, Ga, Cd, and Tl), with galena, sphalerite, and pyrite being the major carriers of Ag, Ge, Cd and Tl; (3) ore distribution controlled by both structural and lithological features; (4) simple and limited wall-rock alteration; (5) mineral zonation within the orebodies; and (6) the presence of evaporite layers in the ore-hosting wall rocks of the Early Carboniferous Baizuo Formation and the underlying basement. Fluid-inclusion and isotope geochemical data indicate that the ore fluid has homogenisation temperatures of 165-220 deg C, and salinities of 6.6-12 wt. percent NaCl equiv., and that the ore-forming fluids and metals were predominantly derived from the Kunyang Group basement rocks and the evaporite-bearing rocks of the cover strata. Ores were deposited along favourable, specific ore-controlling structures. The new laboratory and field studies indicate that the Huize Zn-Pb-(Ag) district is not a carbonate-replacement deposit containing massive sulphides, but rather the deposits can be designated as deformed, carbonate-hosted, MVT-type deposits. Detailed study of the deposits has provided new clues to the localisation of concealed orebodies in the Huize Zn-Pb-(Ag) district and of the potential for similar carbonate-hosted sulphide deposits elsewhere in NE Yunnan Province, as well as the Sichuan-Yunnan-Guizhou Zn-Pb-(Ag) metallogenic region.