Metasomatic alteration of volcanic-sedimentary terrane in the Early Devonian: implication for the formation of the Mengxi porphyry copper deposit, eastern Junggar, Central Asian Orogenic Belt
Metasomatic alteration of volcanic-sedimentary terrane in the Early Devonian: implication for the formation of the Mengxi porphyry copper deposit, eastern Junggar, Central Asian Orogenic Belt
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早泥盆世火山沉积地体交代蚀变：对中亚造山带东准噶尔蒙西斑岩铜矿床形成的启示
DOI：
10.1002/gj.3055
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发表时间：
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影响因子：
1.8
通讯作者：
Li Rongxi
中科院分区：
文献类型：
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作者：
Zhang Haidong;Wang Dequan;Wang Ruimei;Liu Jianchao;Li Rongxi
蒙西斑岩铜矿床位于中亚造山带准噶尔东部，并非典型的斑岩型铜矿床，其成因一直是人们争论的焦点。蒙西斑岩铜矿矿体主要发育于花岗岩斑岩附近的火山-沉积地体（黄朝坡组）中，围岩蚀变强烈，具有垂直分带和裂隙相关的脉体充填作用。锆石U-Pb定年结果表明，该花岗斑岩的侵位时间为432.6±6.7 Ma。花岗岩斑岩初始87Sr/86Sr比值较低（0.70465 ~ 0.70537），全岩ƐNd(t)值较高（-2.2 ~ 6.6），且与安第斯岛弧火山岩具有相似的地球化学亲缘性，表明蒙西花岗岩斑岩形成于板块流体改造的上地幔部分熔融作用，地壳同化作用可忽略。斑岩和火山-沉积地体黄铁矿的δ34S和Pb同位素组成相似，表明不同黄铁矿可能来源相似。通过详细的野外调查、矿物组合及横切关系观察，确认黄朝坡群中块状细粒黄铜矿和斑铜矿浸染，黄铜矿包裹体在接触带黄铁矿脉中，含铜矿物由地体向脉体增加。这些结果表明，蒙西铜矿床的成矿物质主要来源于广泛的早泥盆世构造-岩浆事件引发的黄朝坡组交代蚀变。
The Mengxi porphyry copper deposit, situated in the eastern Junggar, Central Asian Orogenic Belt, is not a typical porphyry copper deposit, and the origin of the deposit has been a topical debate for a decade. The ore bodies of the Mengxi porphyry copper deposit mainly developed in the volcanic-sedimentary terrane (Huangchaopo Formation) near a granite porphyry, with strong wall-rock alteration as well as vertical zonation and fracture-related vein fillings. The result of zircon U-Pb dating indicates that the granite porphyry was emplaced at 432.6±6.7 Ma. The granite porphyry has relatively low initial 87Sr/86Sr ratios (0.70465-0.70537), high whole-rock ƐNd(t) values (-2.2-6.6), and similar geochemical affinities of adakites and Andean island arc volcanic rocks, indicating the Mengxi granite porphyry was derived from the partial melting of the upper mantle modified by slab-derived fluids, with negligible assimilation of crust. Pyrites from the porphyry and volcanic-sedimentary terrane have similar δ34S and Pb isotopic compositions, indicating that different pyrites may have a similar source. Based on the detailed field investigation, observed mineral assemblages and crosscutting relationships, massive fine anhedral chalcopyrite and bornite disseminated in the Huangchaopo Group, chalcopyrite as inclusion in pyrite veins in the contact zone and the amount of Cu-bearing minerals increased from terrane to veins have been recognized. All these observations reveal that the ore-forming materials of the Mengxi copper deposit were mainly derived from the metasomatic alteration of the Huangchaopo Formation triggered by the extensively Early Devonian tectonic-magmatic events.