Geology And Ore-forming Fluid Geochemistry Of The Guihuachong Copper Deposit, Anhui Province

Guihuachong copper deposit is a skarn-porphyry composite deposit newly discovered in the Shatanjiao ore field of the Tongling ore concentration area. This deposit is dominated by porphyry orebodies, different from other deposits of the area dominated by skarn orebodies. Field investigation and laboratory analysis have been carried out on the deposit so as to ascertain its geological characteristics and ore-forming fluid geochemical features. Derivation and evolution of ore-forming fluid and mineralization process of the deposit have been discussed based on the obtained geological and geochemical data.The alteration and mineralization zoning of the Guihuachong copper deposit is significant, from the granodiorite porphyry to stratum, occurring granodiorite porphyry, potassicalteration zone, pyritized-phyllite zone, kaolinization zone, propylitization zone, skarnization zone and marble. Orebodies mainly existed in the granodiorite porphyry and the contact zone between granodiorite porphyry and marble. Considering the skarn type mineralization are not developed, this paper focuses on a study of porphyry mineralization process, according to the crosscutting relationships of the veinlets and the mineral assemblages, the alteration and mineralization process can be divided into five stages as follows: potassic alteration, phyllic alteration, quartz-pyrite, quartz-polymetallic sulfides, and carbonation stages.The microscopic observation shows that fluid inclusions are mainly pure gaseous, daughter mineral-bearing, and gas-rich inclusions in the phyllic alteration stage, pure gaseous, daughter mineral-bearing, gas-rich, and liquid-rich inclusions in the quartz-pyrite stage, and liquid-rich inclusions in the quartz-polymetallic sulfides and carbonate stages. From the early phyllic alteration stage to the late carbonate stage, ore-forming fluids experienced a continuous evolution from high temperature(>472.9℃), high salinity(47.7~67.9%Na Cleqv.) conditions to medium-low temperature(140.2℃~280.3℃), low salinity(1.6~7.7%Na Cleqv.) conditions. The metallogenic pressure is mainly in the range of 1.1~49.0 MPa and the corresponding metallogenic depth is mainly in the range of 0.6~2.0 km.The hydrogen and oxygen isotopic analyses indicate that the early ore-forming fluid is predominated by magmatic water, whereas the late ore-forming fluid is a mixing fluid of magmatic water with meteoric water. The ore-forming fluids experienced boiling and mixing in the ore-forming process, and the mixing of magmatic water with meteoric water resulted in the precipitation of ore-forming materials.