Geochemical characteristics of the Shujiadian Cu deposit related intrusion in Tongling: Petrogenesis and implications for the formation of porphyry Cu systems in the Middle–Lower Yangtze River Valley metallogenic belt, eastern China
Geochemical characteristics of the Shujiadian Cu deposit related intrusion in Tongling: Petrogenesis and implications for the formation of porphyry Cu systems in the Middle–Lower Yangtze River Valley metallogenic belt, eastern China
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DOI：
10.1016/j.lithos.2016.02.013
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发表时间：
2016-05
期刊：
影响因子：
3.5
通讯作者：
Shiwei Wang;Taofa Zhou;F. Yuan;Yu Fan;D. Cooke;Lejun Zhang;B. Fu;N. White
中科院分区：
文献类型：
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作者：
Shiwei Wang;Taofa Zhou;F. Yuan;Yu Fan;D. Cooke;Lejun Zhang;B. Fu;N. White
斑岩型铜矿床可形成于陆内或碰撞后环境，但对富饶岩浆的成因和金属的富集性机制仍存在争议。舒家店斑岩铜矿床位于长江中下游铜陵地区。其赋存于舒家店杂岩中，主要由石英闪长斑岩(143.7 Ma±21.7 Ma)和辉石闪长岩(139.8 Ma±21.6 Ma)组成。它们都属于钙碱性系列，富含大离子亲石元素(LILE)和轻稀土元素(LREE)，亏损高场强元素(HFSE)和重稀土元素(HREE)，略有负Eu异常。石英闪长斑岩和辉石闪长岩均与埃达克岩具有地球化学亲缘关系，其低的氧化镁(1.5~3.7wt%)、低的镍(3.7~6.9ppm)、铬(2.0~44ppm)和Th/Ce(0.06~0.11)表明侵入岩具有埃达克岩的特征，起源于增厚的下地壳，熔体来自变质玄武岩和榴辉岩。石英闪长斑岩中的斜长石为安山石(An值=31.8-40.5)，辉石闪长岩中的斜长石为长钠长石和单斜长石，且An值变化较大(An值为88.9-18.3)，铁、锶含量变化较大，表明浅层岩浆房中可能发生了镁铁质和长英质岩浆的混合。与贫瘠的石英闪长斑岩相比，相对较低的SiO_2含量(49.5wt.%)、较高的εND(T)值(−_(7.4)~−_(6.9))、ε_Hf(T)值(−_(11.0)~−_(9.1))、锆石中钛的温度(714~785℃)以及与成矿有关的辉石闪长岩的HREE含量的变化表明与高温镁铁质岩浆混合。计算了辉石闪长岩在Ni-NiO缓冲层(NNO)和磁铁矿-赤铁矿缓冲层(MH)之间的Ce4+/Ce3+比值，以及在Ni-NiO缓冲层(NNO)下的贫石英闪长斑岩样品。相对富集的LILES、亏损的HFSEs和显著的负Nb-Ta异常的地球化学特征表明，镁铁质岩浆是由富集型岩石圈地幔部分熔融形成的，这些地幔被新元古代俯冲大洋岩石圈的板片流体交代，导致母岩浆富含H2O、S和高fO2的金属(如铜)。
Porphyry Cu deposits can form in intracontinental or post-collision settings; however, both the genesis of fertile magmas and the mechanism of metal enrichment remain controversial. The Shujiadian porphyry Cu deposit is located in the Tongling area of the Middle–Lower Yangtze River Valley metallogenic belt. It is hosted by the Shujiadian complex, which mainly consists of quartz diorite porphyry (143.7 ± 1.7 Ma) and pyroxene diorite (139.8 ± 1.6 Ma). They both belong to the calc-alkaline series, with enrichment in large-ion lithophile elements (LILE) and light rare earth elements (LREE), depletion in high field-strength elements (HFSE) and heavy rare earth elements (HREE), and slightly negative Eu anomalies. Both quartz diorite porphyry and pyroxene diorite have geochemical affinities with adakite, and their low MgO (1.5–3.7 wt%), and Ni (3.7–6.9 ppm), Cr (2.0–44 ppm), and Th/Ce contents (0.06–0.11) indicate that the intrusive rocks have some characteristics of adakite-like rocks derived from thickened lower crust and melts from metabasaltic rocks and eclogites. Plagioclases from the quartz diorite porphyry are andesine (An value = 31.8–40.5) and from the pyroxene diorite are felsic albite and oligoclase with large-scale zones and variable An value (An value = 8.9–18.3), Fe and Sr contents, which indicate that mixing of mafic and felsic magma may have occurred in the shallow magma chamber. Compared to the barren quartz diorite porphyry, relatively lower SiO2contents (49.5–55.2 wt.%), higher εNd(t) values (− 7.4 to − 6.9), εHf(t) values (− 11.0 to − 9.1) compositions, Ti-in-zircon temperatures (714–785 °C), and variations of HREE contents of the mineralization-related pyroxene diorite suggest mixing with high-temperature mafic magma. Calculated Ce4 +/Ce3 +values of pyroxene diorite plot between the Ni–NiO buffer (NNO) and magnetite–hematite buffer (MH), and barren quartz diorite porphyry samples plot below the Ni–NiO buffer (NNO). Geochemical features of relatively enriched LILEs, depleted HFSEs, and markedly negative Nb–Ta anomalies, imply that the mafic magma was generated by partial melting of enriched lithospheric mantle, which had been metasomatized by slab-derived fluids from Neoproterozoic-subducted oceanic lithosphere; as a result, the parental magma was rich in H2O, S, and metals (e.g. Cu), with highfO2.