Characteristics of Hydrothermal Superimposed Mineralization and Source of Ore-Forming Fluids in the Dahenglu Co-Cu Deposit

The Dahenglu Cu-Co deposit is a large Cu deposit with associated Co.The ore bodies mainly occur in the carbonaceous sericite phyllite from the Dalizi Formation.This deposit has experienced four stages of mineralization:submarine exhalative origin, metamorphic reformation, hydrothermal superimposition and supergenetic oxidation.The vein and disseminated ores were formed in the hydrothermal superimposition stage, which were subjected to the local transformation for the layered ore bodies.And this stage can be divided into 2 sub-stages:quartz-pyrite sub-stage (I) and quartz-galena sub-stage (Ⅱ).In this paper, the petrography, microthermometry of fluid inclusions, as well as C, H and O isotopes have been studied.The results show that, the quartz-pyrite sub-stage (I) mainly contains aqueous inclusions, their homogenization temperatures are 178~229℃, whereas their salinities range from 6.0% NaCleqv to 11.8% NaCleqv, suggesting the characteristics of the medium temperature and low salinity H₂O-NaCl system.The δ D_H2O, δ¹⁸O_H2O and δ¹³C_PDB of fluid inclusions from this sub-stage vary from -82.3‰ to -84.8‰, from 5.5‰ to 6.4‰ and from -9.7‰ to -5.1‰ respectively, showing that the ore-forming fluid mainly sourced from magmatic water.The quartz-galena sub-stage (Ⅱ) are also dominated by aqueous inclusions, with the homogenization temperatures are 113~169℃, whereas the salinities are 3.0%~8.5% NaCleqv, which belong to the low temperature and low salinity H₂O-NaCl system.For the fluid inclusions from this sub-stage, the δD_H2O, δ¹⁸O_H2O and δ¹³C_PDB range from -96.3‰ to -90.7‰, from 1.2‰ to 2.5‰ and from -20.7‰ to -16.7‰ respectively, showing the features of magmatic water mixed with atmospheric water.