LIU Xing-ping1, ZHOU Lian-sheng1, YOU Jing1, LI Sui-yun1, LIU Rui2*
(1. Sixth Geological Team of Hubei Geological Bureau, Xiaogan 432000, China;
2. Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China)
Abstract: The Waliaoge Pb-Ag deposit is located in the northeastern part of Karuo District (about 150 km away from the downtown of Qamdo City), Qamdo City, Tibet, China. The stratum exposed in the deposit is the Upper Triassic Jiapila Formation in which orebodies are mainly hosted in its second sub-member limestone (T3j2-2). There is no magmatic rock outcropped in the deposit. There are main structures of dominant NW-trending faults. 7 industrial ore bodies were outlined in the deposit, with the Pb metal resource of 504 kt and associated Ag metal resource of 580 t, respectively. This means that the deposit is a large scale one in terms of both Pb and Ag resources. Based on the detailed study of the geological characteristics of the deposit, studies of fluid inclusions and multiple isotopes (C-O-S-Pb) geochemistry of the deposit have been carried out in this paper, in order to explore properties of ore-forming fluids and sources of ore-forming materials of the deposit and to provide more abundant geochemical information for understanding genesis of the deposit. The results show that: (1) orebodies of this deposit are obviously controlled by stratum and structures; (2) the measured homogenization temperatures (concentrated in 130－180 ℃) and salinities (concentrated in 6%－17% NaCl equiv.) of fluid inclusions indicate that the ore-forming fluid was characterized with low temperature and medium-low salinity. (3) the C and O isotopes of ore-bearing strata (δ13CPDB values varying from -2.7‰ to 4.3‰) and hydrothermal calcite (δ13CPDB values varying from 2.6‰ to 4.0‰) samples are similar to those of the normal marine sedimentary limestone, inferring that the carbon of hydrothermal fluid could mainly be sourced from wallrocks. The sulfur isotopic compositions (δ34S values), varying from -3.8‰ to 1.6‰, of galena samples are quite similar to mantle sourced sulfur (from -3‰ to 3‰). However, considering that there is no magmatic activity and the δ34S values of sedimentary rocks vary from 6.2‰ to 20.5‰ in the deposit area, it is speculated that the sulfur of ore-forming fluid could be mainly sourced from strata as the product of thermochemical reduction of sulfates. In addition, lead isotopes of sulfides, which have crustal sourced lead characteristics, and the similarity of Pb isotopes of most ore samples to those of host rocks indicate that the metallogenic metals could be mainly sourced from ore-hosted wallrocks. In summary, it is believed that the ore-forming materials of the Waliaoge Pb-Ag deposit were mainly sourced from the ore-hosted strata, . In terms of the genetic type, the Waliaoge deposit belongs to the low temperature hydrothermal Pb-Ag one.
Keywords: fluid inclusions; C-O-S-Pb isotopes; the source of ore-forming materials; the Waliaoge Pb-Ag deposit; Tibet
ACTA MINERALOGICA SINICA Vol. 40, No.2, 2020, page 223
