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Ore Genesis of the Kalatongke Cu–Ni Sulfide Deposits, Western China: Constraints from Volatile Chemical and Carbon Isotopic Compositions
Author(s) -
Piaoer FU,
Qingyan TANG,
Mingjie ZHANG,
Zhaowei ZHANG,
Liwu LI,
Wenyuan LI
Publication year - 2012
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.2012.00686.x
Subject(s) - pyroxene , geochemistry , geology , mineral redox buffer , olivine , sulfide , partial melting , sulfur , melt inclusions , mantle (geology) , mineralogy , chemistry , organic chemistry
The Kalatongke Cu–Ni sulfide deposits located in the East Junggar terrane, northern Xinjiang, western China are the largest magmatic sulfide deposits in the Central Asian Orogenic Belt (CAOB). The chemical and carbon isotopic compositions of the volatiles trapped in olivine, pyroxene and sulfide mineral separates were analyzed by vacuum stepwise‐heating mass spectrometry. The results show that the released volatiles are concentrated at three temperature intervals of 200–400°C, 400–900°C and 900–1200°C. The released volatiles from silicate mineral separates at 400–900°C and 900–1200°C have similar chemical and carbon isotopic compositions, which are mainly composed of H 2 O (av. ∼92 mol%) with minor H 2 , CO 2 , H 2 S and SO 2 , and they are likely associated with the ore‐forming magmatic volatiles. Light δ 13 C CO2 values (from –20.86‰ to –12.85‰) of pyroxene indicate crustal contamination occurred prior to or synchronous with pyroxene crystallization of mantle‐derived ore‐forming magma. The elevated contents of H 2 and H 2 O in the olivine and pyroxene suggest a deep mantle‐originated ore‐forming volatile mixed with aqueous volatiles from recycled subducted slab. High contents of CO 2 in the ore‐forming magma volatiles led to an increase in oxygen fugacity, and thereby reduced the solubility of sulfur in the magma, then triggered sulfur saturation followed by sulfide melt segregation; CO 2 contents correlated with Cu contents in the whole rocks suggest that a supercritical state of CO 2 in the ore‐forming magma system under high temperature and pressure conditions might play a key role in the assemblage of huge Cu and Ni elements. The volatiles released from constituent minerals of intrusion 1* have more CO 2 and SO 2 oxidized gases, higher CO 2 /CH 4 and SO 2 /H 2 S ratios and lighter δ 13 C CO2 than those of intrusions 2 # and 3 # . This combination suggests that the higher oxidation state of the volatiles in intrusion 1 # than intrusions 2 # and 3 # , which could be one of key ore‐forming factors for large amounts of ores and high contents of Cu and Ni in intrusion 1 # . The volatiles released at 200–400°C are dominated by H 2 O with minor CO 2 , N 2 +CO and SO 2 , with δ 13 C CO2 , values (–25.66‰ to –22.98‰) within the crustal ranges, and are considered to be related to secondary tectonic– hydrothermal activities.