Magmatic Sulfide Mineralization of the Cluster of Ni–Cu Deposits in the Eastern Tianshan and the Application of Cu Isotopes for Tracing Concealed Orebodies

Author:Zhao Yun

Supervisor:Xue spring discipline

Database:Doctor

Degree Year:2016

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Pages:139

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Magmatic Ni-Cu sulfide deposits along the Central Asian Orogenic Belt(CAOB)show many different characteristics with those formed within cratons or on their margins.The Huangshannan,Hulu and Tulaergen deposits in the Eeastern Tianshan were selected to investigate mantle source,sulfur saturation and mineralization mechanism.The behavior of Cu isotopes during high temperature sulfide-silicate differentiation is firstly presented.Besides,whether Cu isotopes can be used as an indicator for Ni-Cu(-PGE)sulfide deposits is discussed.The following achievements have been withdrawn in this study.1.The Huangshannan mineralized intrusion was formed in a post-collisional setting at 282.5 ± 1.4 Ma.The metasomatized mantle was modified by previous subduction and not related to the Tarim mantle plume activity.The parental magma is high-Mg basaltic in composition.The Ni content of this parental magma is much higher than those of many high Mg basaltic parental magmas that crystallized olivine with similar Fo contents compared to the Huangshannan intrusion.The anomalously Ni-rich composition of the parental magmas of the Huangshannan intrusion is created from moderately Ni-rich primary magmas by a process of upgrading and scavenging of metals from previously formed sulfide melts.The different compositions of the parental magmas indicate that they were generated from different magma pulses.The formation of the massive sulfides can be explained by MSS-sulfide liquid fractionation from the same magma pulse that formed the websterite.The sulfur saturation of the parental magma resulted from the contamination of crustal sulfur.2.The primary magmas of the Hulu intrusion experienced sulfide segregation and removal in the deep staging magma chamber,resulting in the PGE depletion in the evolved magma.After earlier sulfide removal from the primary magma at depth,the PGE-depleted parental magmas ascended up to shallow conduit system.The segregated sulfides experienced minor crystallization of monosulfide solid solution(MSS).When new magma pulses with unfractionated sulfide droplets entered the layered sequence,the sulfide slurry containing early crystallized MSS may be disrupted and mixed with the unfractionated sulfide droplets.The dike-like unit was expected to locate in the feeder dike of the magma plumbing system.The sulfide ore formed in the different magma pulses,resulting in a large variation of metal contents.3.The Cu isotopic composition of the Tulaergen deposit shows that Cu isotopes could be significantly fractionated(up to 2‰)during high temperature(from ~1000 oC to ~600 oC)sulfide-silicate differentiation.The fractionation of Cu isotopes might be significantly influenced by the redox equilibrium Cu+ + Fe3+ = Fe2+ + Cu2+ in the parental magma during high temperature sulfide-silicate differentiation.Copper isotopes may be a powerful exploration tool for tracking the Ni-Cu(-PGE)sulfide deposits.The direction of progressively decreasing δ65Cu values may point to potential orebodies with higher sulfide contents