Mineralogical and geochemical study of hydrothermal dolomite from the Daliang zinc deposit in Guizhou, Southwest China: new evidence for the genesis

摘要

The Daliang zinc deposit occurs in the southwestern Xiangxi-Qiandong Zn-Pb metallogenic belt and is located on the southeastern margin of the upper Yangtze block. In this study, we present results from petrographic observations, rare earth elements, C-H-O isotopes, and fluid inclusions. The zinc deposit is hosted by middle Cambrian dolomite. The ore-forming process is divided into three stages from early to late: pyrite-galena, sphalerite-pyrite-dolomite, and dolomite. The characteristics of the REEs suggest that multiple fluids were involved in hydrothermal dolomite precipitation under low-temperature conditions. Two types of hydrothermal dolomite fluid inclusions were identified: pure liquid phase inclusions and liquid-rich phase inclusions. The fluid inclusions of hydrothermal dolomite yield homogenization temperatures of 108-192 degrees C (average 153 degrees C), with salinities of 12.3-26.4 wt% (average 23.0 wt%) NaCl equiv. The delta C-13(fluid), delta D-fluid and delta O-18(fluid) values for ore-forming fluids range from -4.2 to -3.5 parts per thousand (mean -3.8 parts per thousand), -38.8 to -34.3 parts per thousand (mean -36.0 parts per thousand), and 6.2-6.4 parts per thousand (mean 6.3 parts per thousand), respectively. This study demonstrates that ore-forming fluid was sourced from a moderate- to high-salinity basinal brine and leached metals from metasedimentary rocks of the basement in the Yangtze block. The main transportation of ore-forming fluid occurred in the form of chlorine complexes along well-developed faults, and sulfides precipitated with decreases in pressure and temperature, as well as pH changes. Studies of the Daliang zinc deposit suggest that it is a medium- to low-temperature MVT-like deposit.