Study Of The Fluid Metallogenesis In Tongshan Cu Skarn Deposit, Anhui Province

The Tongshan copper deposit in Anqing-Guichi Cu-Fe-Au-Mo district is a typical skarn deposit in The Lower Yangtze River metallogentic belt, which is located at the northern margin of the Yangze craton and bordered by the Dabieshan orogenic belt to the north.The ore bodies are related to Tongshan granodiorite and quartz monzonite porphyry, which intruded mainly into Middle Carboniferous Huanglong-Chuanshan Formation, Lower Permian Qixia Formation carbonates and is characterized by porphyritic textures and carbonatization. The location of ore-forming intrusions were controlled by the intersecting places between the NE and EW trending fault structures. The ore-controlling and ore-bearing structures mainly include contact zone, interlayer fractures zone and unconformity structure, etc. The metalogenic processs can be devided into the skarn stage, the quartz-sulfide stage and the carbonate stage. In recent years, new ore layers have been discovered, but the study on fluid inclusions is urgently needed which restricts the ore genesis and metallogenic laws.This paper made further discussion on the source of ore-forming materials and the ore genesis in terms of fluid inclusions. Petrographic observations and temperature results indicate that the main types of fluid inclusions are aqueous inclusions, daughter-mineral-bearing multiphase inclusions, occasionally crystalline melt inclusions(recognized in garnet, quartz) which are the evidence of magmatic skarn. In the skarn stage, the ore-forming fluid is characterized by high temperature and high salinity, Th (homogenization temperature) is 478⁷69℃with salinity of 55.47 wt%. In the quartz-sulfide stage, the ore-forming fluid is characterized by middle-low temperature and middle-low salinity, Th is 86.2³99.5℃with salinity 0.18²2.91wt%; In the carbonate stage, the ore-forming fluid is characterized by middle-low temperature and low salinity, Th ranges from 154.6 to 368.5℃with salinity from 0.53 to 22.91wt%. The Metallogenic pressure is approximately 21Mpa, Metallogenic depth is 2.3km.The results of Raman analysis indicate that major components of gaseous or supercritical species are H₂O, CO₂, CH₄; the major ions in solution are Ca²⁺, K⁺, SO4^2-, Cl^-. From early to late stage, the contents of CO₂, CH₄, Ca²⁺, SO4^2-, Cl^- decreased, K⁺ increased, H₂O decreased firstly and then increased. The D-O isotopic analysis indicates that the ore-forming fluids were mainly magmatic hydrothermal fluids and mixed with meteoric water during the later mineralization stage; The S and Pb isotopic analysis indicate that metallogenic material derived from magma; the Re-Os dating indicates Metallogenic age is 150.98±0.78 Ma, Early Yanshanian.According to the assemblage and evolution characteristics of different fluid inclusions, the immiscibility of melt-fluids and the mixing of fluids are the main causes for mineralization.