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首页> 外文期刊>Journal of Asian earth sciences >Petrogenesis and oxidation state of granodiorite porphyry in the Jurassic Chuankeng skarn Cu deposit, South China: Implications for the Cu fertility and mineralization potential
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Petrogenesis and oxidation state of granodiorite porphyry in the Jurassic Chuankeng skarn Cu deposit, South China: Implications for the Cu fertility and mineralization potential

机译：华南侏罗系川坑矽卡岩型铜矿床中花岗闪长斑岩的成因和氧化态：对铜的肥力和矿化潜力的启示

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摘要

Large-scale Jurassic porphyry-skarn Cu mineralization in the Qin-Hang metallogenic belt of South China has attracted much attention, but comparative studies of porphyries in large- and small-scale deposits are lacking. In this paper, we present new zircon U-Pb ages, trace element composition and Hf isotopic composition as well as whole-rock geochemical and Sr-Nd isotopic compositions for the porphyries associated with mineralization in the small-scale Chuankeng Cu deposit. Drawing on our data for the Chuankeng deposit and existing data for the nearby giant Dexing Cu deposit, we aim to identify factors controlling the mineralization potential of both deposits. Granodiorite porphyries of Chuankeng deposit were emplaced at ca. 161-158 Ma. They have moderate SiO2 contents of 61.9-66.1 wt% and high Sr/Y (59-135) and (La/Yb)(N) (4-14) ratios. Their high MgO contents (0.2-29 wt%), lack of negative Eu anomaly, depletion in Y and Yb, relatively high initial Sr-86/Sr-87 ratios (0.7076-0.7078), and low epsilon(Nd)(t) values (- 4.5 to - 4.9), indicating that the Chuankeng porphyries were derived from partial melting of delaminated lower crust. The Middle-Late Jurassic Chuankeng porphyries are considered to have been formed in a localized infra-continental extension environment along the Jiangshao Fault in response to far-field stress from Paleo-Pacific Plate subduction. Although no Middle-Late Jurassic magmatic arc rocks have been found in the study area, the Chuankeng porphyries display similar characteristics to arc rocks. On the basis of their zircon epsilon(Hf)(t) values (- 2.6 to +0.9), two-stage Hf model ages (1.4-1.1 Ga), and regional geological history, we infer that magma source of Chuankeng porphyries were mainly Neoproterozoic juvenile crust with the involvement of Paleoproterozoic ancient crust. Thus their arc-like features were inherited from the Neoproterozoic juvenile crust that formed by subduction of oceanic crust during the Jiangnan orogeny. Chuankeng porphyries have lower zircon Ce4+/Ce3+ and higher Ti-in-zircon temperatures and lower whole rock epsilon(Nd) and zircon epsilon(Hf) values than the Dexing porphyries, indicating they are less oxidized and less hydrous and with more involvement of the ancient crustal material in the magma source, which could explain the relatively small-scale Cu mineralization in Chuankeng. This study highlights the values of integrated studies of whole rock Nd and zircon trace element and Hf isotopic compositions in assessing the potential for Cu mineralization.
机译：华南秦杭成矿带侏罗系斑岩-矽卡岩型铜的大型成矿作用引起了人们的广泛关注，但目前尚缺乏大型，小规模矿床斑岩的对比研究。在本文中，我们介绍了与小型川坑铜矿床成矿有关的斑岩的新锆石U-Pb年龄，痕量元素组成和Hf同位素组成以及全岩地球化学和Sr-Nd同位素组成。根据我们的川坑矿床数据和附近巨型德兴铜矿床的现有数据，我们旨在确定控制这两个矿床成矿潜力的因素。川坑矿床的花岗闪闪岩斑岩约埋于左右。 161-158马。它们具有适中的SiO2含量为61.9-66.1 wt％，并且具有较高的Sr / Y（59-135）和（La / Yb）（N）（4-14）比。它们的高MgO含量（0.2-29 wt％），没有负Eu异常，Y和Yb耗尽，相对较高的初始Sr-86 / Sr-87比（0.7076-0.7078）和低epsilon（Nd）（t）值（-4.5至-4.9），表明川坑斑岩是由层状下地壳的部分融化产生的。响应中古太平洋板块俯冲的远场应力，认为中侏罗世川坑斑岩是在江绍断裂带沿局部局部陆下伸展环境中形成的。尽管在研究区未发现中晚侏罗世岩浆弧岩，但川坑斑岩具有与弧岩相似的特征。根据其锆石ε（hf）（t）值（-2.6至+0.9），两阶段Hf模型年龄（1.4-1.1 Ga）以及区域地质历史，我们推断川坑斑岩的岩浆来源主要是新元古代的地壳与古元古代的地壳有关。因此，它们的弧状特征是从江南造山运动中俯冲大洋地壳形成的新元古代少年地壳继承而来的。与德兴斑岩相比，川坑斑岩的锆石Ce4 + / Ce3 +较低，锆石中的Ti-in锆石温度较高，全岩epsilon（Nd）和锆石epsilon（Hf）值较低，表明它们的氧化程度和含水量较小。岩浆源中的古代地壳物质，可以解释川坑的铜矿化程度相对较小。这项研究突出了对Nd和锆石全微量元素以及Hf同位素组成进行综合研究在评估Cu矿化潜力方面的价值。

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