| Most well-known graphite deposits belong to regional-metamorphic and contact-metamorphic types.The magmatic and hydrothermal types(fluid-deposited type)of graphite deposits related to magmatism are rare both in China and abroad.The recently discovered Huangyangshan graphite deposit,located in East Junggar area in Xinjiang,is the first super-large graphite deposit hosted in alkaline granite,implying metallogenic and prospecting potential for super-large deposits.This deposit has closely temporal,spatial and genetic relationships with the Huangyangshan alkaline granite complex and is characterized by unique spherical ore structure and coexisting of the graphite with metallic sulfides,which lead to its important research significance.In this paper,based on the detailed geological investigation and petrographic and mineralogical studies,element-isotope geochemical analyses of granites and ores,in-situ microanalysis of single mineral,carbon isotope analyses of graphite,S-Pb isotope compositions of symbiotic sulfides,and zircon U-Pb and graphite Re-Os isotopic dating have been carried out,and the ore-forming geological conditions,geological and geochemical characteristics,and material sources of ore-bearing(metallogenic)rocks have been studied and discussed.The genetic type,graphite metallogenic mechanism,diagenetic and ore-forming ages,and tectonic setting of the Huangyangshan alkaline granite complex and associated graphite deposit have been systematically studied.The diagenetic and graphite metallogenic model of the Huangyangshan pluton have been established,and the metallogenic regularities and prospecting criteria have been summarized.Based on metallogenic and prospecting information of geological,geophysical,remote sensing and deposit,a prospecting model has been established,and the further prospecting direction has been proposed.According to the previous data and the research results of this paper,the Huangyangshan pluton is mainly composed of medium-grained arfvedsonite granite,medium–fine-grained arfvedsonite granite,medium–fine-grained amphibole granite,medium-grained biotite granite and fine-grained biotite granite.Among them,the medium–fine-grained amphibole granite(the third phase)in the central part,the medium-grained biotite granite(the fourth phase)in the southern part,and the small-scale fine-grained biotite granite(the fifth phase)are closely related to graphite mineralization.LA–ICP–MS zircon U–Pb dating results of typical rock samples show that the crystallization ages of the five lithofacies overly range from 330 to 300Ma,indicating they all emplaced at the late Carboniferous,and the pluton gradually crystallized from north to south.Moreover,there are two groups of hydrothermal zircons of different ages in the graphite orebodies,indicating that they have experienced two phases of superimposed hydrothermal transformation after crystallization,and the first hydrothermal event was closely related to graphite mineralization.Both the corrected graphite Re-Os isochron age(308±18 Ma),and the hydrothermal zircon age,limit the graphite mineralization age to no later than300Ma,indicating the graphite mineralization approximately occurred at the late Carboniferous.Data on regional tectonic evolution indicate that the Kalamaili area had entered into the continent-continent collision stage during the early Carboniferous.The Kalamaili alkaline granite belt formed in the post-collisional extension stage during the middle to late Carboniferous.The five lithofacies of the Huangyangshan pluton have similar geochemical characteristics,and all belong to typical post-collisional A-type granite.The original magma experienced marked fractional crystallization during its evolution and the initial magma was mainly derived from the partial melting of oceanic crustal materials in the juvenile lower crust.Fine-grained biotite granite shows slight tetrad REE patterns,implying the formation of the granite was related to fluid-melt interaction.The pluton experienced intensive magmatic mixing during its formation,and the addition of mantle derived basic magma had important impact on the evolution and differentiation of magma.The ore-bearing medium–fine-grained amphibole granite and medium-grained biotite granite experienced intensive magmatic assimilation and contamination,which provided a material source basis for carbon enrichment and graphite precipitation.The Huangyangshan graphite orebodies mainly occurs at the contact boundaries of different lithofacies in the Huangyangshan alkaline pluton.The graphite ores mainly develop spherical structure,secondary disseminated and stockwork structures.Associated silicate minerals mainly include feldspar,quartz,amphibole,and biotite,etc.,and symbiotic metallic sulfides are mainly pyrrhotite,chalcopyrite,and pentlandite,etc.Graphite grew along the edges of the orbicules to form graphite shells.The lithologies of the orbicules cores are neutral and enriched in dark-colored minerals such as amphibole and biotite.The mineralization process can be divided into three stages:the early magmatic stage,the formation stage of graphite orbicules and the formation stage of graphite veins.The laser Raman spectrum analysis of graphite shows that the graphite crystallization degree is extremely high,close to the characteristics of ideal graphite single crystal.The crystallization temperature was about 650–700?,similar to typical magmatic hydrothermal graphite.The results of C–S–Pb isotope analyses show that the carbon of graphite deposits in this area was mainly derived from organic carbon,with a small amount of magmatic carbon carried by magma mixed during magmatic evolution process.The metallic sulfides coexisting with graphite are of magmatic origin,and their?34S values are close to the original mantle value,suggesting that the sulfur was mainly derived from mantle.Their Pb isotopic results show that the ore-forming metals mainly come from mantle and have been affected by later hydrothermal metasomatism.According to the comprehensive studies,the Huangyangshan graphite deposit can be determined as high-temperature magmatic hydrothermal deposit.The immiscibility of magma took place in the late stage,resulting in differentiation of hydrothermal fluid rich in volatile and carbonaceous and residual melt,which is the main cause for the formation of spherical structure of ores.The graphite crystallized in high-temperature hydrothermal stage,and the main factors causing graphite precipitation were cooling and the catalysis of sulfides.Based on the research results of this paper,a metallogenic model of the Huangyangshan graphite deposit was established.The metallogenic regularity and geological,geophysical and remote sensing prospecting signs were also preliminarily summarized,and a comprehensive prospecting model of the Huangyangshan deposit was established.Three ore-prospective areas for graphite mineral resources in the Huangyangshan pluton are delineated,which provides a basis for the further ore-exploration deployment and geological prospecting. |
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