The Volatile Compositions And Its Geological Implications Of Baimazhai Ni-Cu Sulfide Deposit In Emeishan LIP, Western China

The Fe-Ti-V oxide deposits and Ni-Cu-PGE sulfide deposits two types of magmatic deposits were formed in Emeishan large igneous province (LIP). The Baimazhai sulfide deposit is a rich Ni-Cu poor PGE type. Rock with massive sulfide as the center, in order to orthopyroxenite, websterite and gabbro tubular distribution. The deposits is the best area to understand the world’s super large copper and nickel sulfide deposits main mineralization metallogenic type. Fluid composed research of ore forming from the Baimazhai magmatic deposit can can improve the process of the deposit and the ore-forming elements S saturation enriched acknowledgement. Based on the three major rock types such as orthopyroxenite, websterite and gabbro of Baimazhai Ni-Cu sulfide deposit(No.3), we separate pyroxene minerals, apply step-wise heating mass spectrometry to the analyses for volatile chemistry and carbon isotopical components and come to conclusions as follows:1. The volatiles of pyroxene from orthopyroxenite, websterite and gabbro in Baimazhai deposit is released in three temperature intervals,200-400 癈,400-900 and 900-1100℃, and the total amount is 136.64 mm3/g,19870.50 mm3/g and 996.54 mm3/g, respectively. The volatiles are dominanted by H2O(89%), with small amount of CO2, H2, O2, and C2H6.2. The amount of volatiles released in 400-900℃ decreases from orthopyroxenite (23243.3mm3/g) and websterite(19585.7mm3/g) to gabbro (16782.43 mm3/g) which major composition is H2O, CO2, H2 and O2. The trend of change is same as H2O and O2, but contrary to CO2 and H2.3. Baimazhai Deposit rock volatiles carbon isotope composition shows, CO2 and CH4 carbon isotope composition range in 200-400℃ release are 813Cco2-21.2‰～--9.6%o,δ13CCH4-54.5- -34.0‰, and 400-900℃ release are 813Cco2-21.2～-9.5‰, δ13CCH4-49.73～-23.30%o.900-1100℃ release are 813CCO2-22.9～-0.7%o δ13CCH4-53.3～-20.6‰. carbon isotopic composition of CH4 homologue has positive sequence distribution mode with carbon number.4. The chemical composition of volatiles from magma in Baimazhai deposit originated in H2O, CO2 and H2. The release of H2 improve indicate that the magama originated in H2O in the volitels, and is mainly H2 reducing environment. The composition of H2O, CO2 and H2 in volatiles have a positive correlation with Cu and Ni. It indicate a large amount of H2O let source area on a large scale high degree partial melting, makes it easier Cu, Ni enter the metallogenic magma. The CO2 may gatherd Cu and Ni ore-forming metals.5. The content of H2S is reduced in the ore body and the content of H2 is relatively large, It shows S saturation prompt sulfid melt crystal and due to the content of S2- decreased. The content of CO2 in the ore-forming stage has increased, resulting in Fe and Ti oxide crystallization, thereby reducing the solubility S, making it easier sulfide crystals.