Study On The Characteristics Of Alteration-fluid Of Shaxi Porphyry Cu-au Deposit In Lujiang

Shaxi porphyry Cu-Au deposit is located at the north margin of the Luzong volcanicbasin in the Middle and lower Yangtze River metallogenic belt. Itcontains>1Mt Cu and40t Au. On the basis of previous work and our detailed field observations andpetrographic and mineralogical studies, we have characterised the mineralogy ofalteration type as potassic alteration, propylitization, feldspar-destructive alteration andkaolinization, the zoning of alterations from deep to shallow are potassic alteration,feldspar-destructive alteration and kaolinization, The characteristics of mineralization,the sequence of mineral deposition and the ore-forming stages were also discribed. Themineralization is divided into potassium silicate stage, quartz-sulfide stage andquartz-carbonate-sulfate stage.Chemical analysis of different alterated rocks show that the fluid of potassicalteration need a lot of Si, Al, Fe, Ca, K and release some Mg, Na, the porpyliticalteration need the addition of Fe, Ca, Mg, P and loss of Si, Na, K, Mn, Ba, whilefeldspar-destructive alteration was caused by addition of Si, Fe, K, P and loss of Na, Ca,Mg, Sr.Microscopic observation shows that chalcopyrite began to precipitate at the latestage of the potassium silicate alteration, reaching a peak during the quartzsulfide stage, and the quartz carbonate stage also contributed some copper.Detailed study of fluid inclusions suggested that the homogenization temperatureof the fluid inclusion in potassium silicate stage range from350to>600°C, with meanvalue of500°C, corresponding with calculated salinities of5.1%to77.6wt%NaCl eq..The homogenization temperature of quartz-sulfide stage is between250to550°C, withmean value of400°C, corresponding to calculated salinities of5.1%to77.6wt%NaCleq.. The quartz-carbonate-sulfate stage is between200to350°C, with an average of231.36°C and the calculated salinities of0.4%to21.5%NaCl eq., which maybe causedby the addition of meteoric water. Raman study indicates that the ore-forming fluid ofShaxi deposit is rich in H2O and with minor CO2.Based on ore geological, alterated chemistry and fluid inclusions study, a model isbuilt to describe the evolution of ore-forming fluid of the Shaxi deposit.