The Chemical Compositions of Volatiles in Huangshan Cu-Ni Sulfide Deposit, Xinjiang, West China and Its Implications of Mineralization

Abstract: Cu-Ni sulphide deposit related to mafic-ultramafic rocks is the main type of copper, nickel,platinum group elements(PGE) deposits.Huangshan Cu-Ni sulphide deposit, Xinjiang,west China is located in the southern part of Central Asian Orogenic Belt.The lithologies of the ore-bearing intrusion are well developed,and mainly include peridotite,, pyroxenite,gabbro and diorite.The fluid composition of fresh olivine and clinopyroxene separates from the two dvilling cores have been measured by the improved vacuum stepwise heating mass spectrometers on the basis of their petrological and seochemcal research.The results are as follows:(1) The volatiles of different minerals from the mafic-ultramafic intrusion from the Huangshan Cu-Ni sulphide deposit have been released by stages during stepwise heating, The volatiles in olivine separates are released at the temperature intervals of 200-500℃, 500-1000℃and 1000-1200℃,whereas volatiles in clinopyroxene separates are released at 200-400℃,400-1000℃and 1000-1200℃(2) The volatiles of the minerals are composed mainly of H_2 and N_2+CO,secondary by SO_2,CO_2 and H_2S,with the minor O_2,CH_4 and Ar etc.(3) Volatiles released at different temperature interval have different contents of volatiles in minerals Huangshan Cu-Ni sulphide deposit.Volatiles released at mid-temperature interval has the highest contents(av.2474.57mm~3.STP/g),and those at low and high temperature intervals are relatively lower(av.133.04mm~3.STP/g and 433.05mm~3.STP/g,respectively).The contents of major volatiles such as H_2,N_2+CO,SO_2, CO_2 and H_2S are vary with temperature intervals.(4) Based on crystallization characteristics of magmatic minerals and chemical compositions of the volatiles at different temperature intervals,the volatiles of the minerals in Huangshan Cu-Ni sulphide deposit can be divided into three parts: ore-forming magmatic volatiles,post-magmatic hydrothermal volatiles and secondary processes volatiles.Ore-forming magmatic volatiles represented by the volatiles released at high temperatures are composed mainly of SO_2 and N_2+CO,with minor H_2,CO_2 and H_2S.Post-magmatic hydrothermal volatiles represented by the volatiles released at middle temperatures consisted of N_2+CO,H_2S and CO_2,secondary processes volatiles represented by the volatiles released at low temperatures and are mainly composed N_2+CO.(5) Metallogenic volatiles are characterized by primitive mantle in an early stage of magmatism,and then mixed with external oxidized fluids during crystallization in Huangshan Cu-Ni sulphide deposit.The post-magmatic hydrothermal volatiles have highest content of volatile and are dominated by reduced volatiles,which play an important role in transporting and precipitating the major metallogenic elements,increase evidently,and show the opposite characteristics to volatiles at the early stage.The volatiles in the secondary alteration are dominated by N_2 ect.air-devived components which deformed and alfer existed deposit in some extent…
Key words: volatile chemical composition; mafic-ultramafic rocks; Huangshan Cu-Ni sulfide deposit

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