Multistage pyrites in the Nibao disseminated gold deposit, southwestern Guizhou Province, China: Insights into the origin of Au from textures, in situ trace elements, and sulfur isotope analyses
Multistage pyrites in the Nibao disseminated gold deposit, southwestern Guizhou Province, China: Insights into the origin of Au from textures, in situ trace elements, and sulfur isotope analyses
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中国贵州省西南部泥堡浸染状金矿床多期黄铁矿：从结构、原位微量元素和硫同位素分析洞察金的成因
DOI：
10.1016/j.oregeorev.2020.103446
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发表时间：
2020-03
影响因子：
3.3
通讯作者：
Liu Xi-Jun
中科院分区：
文献类型：
--
作者：
Wei Dong-Tian;Xia Yong;Gregory Daniel D.;Steadman Jeffrey A.;Tan Qin-Ping;Xie Zhuo-Jun;Liu Xi-Jun
泥堡金矿床是贵州省西南部独特的逆冲断裂控制层控浸染型金矿床。泥宝矿中，黄铁矿是主要的硫化物矿物，金在黄铁矿晶格中以结构结合(Au+)的形式存在。本研究利用激光烧蚀电感耦合等离子体质谱(LA-ICPMS)和激光烧蚀多集电极电感耦合等离子体质谱(LA-MC-ICPMS)分别对泥堡黄铁矿化学组成和S同位素组成进行了详细的分析。通过岩相学和黄铁矿化学研究，划分出四个黄铁矿世代(PY1-PY4)：框架状黄铁矿(PY1，矿前沉积阶段)、洁净黄铁矿杂生框架状黄铁矿(PY2，矿前成岩阶段)、“海绵状”黄铁矿(PY3，矿石早期)，以及围绕PY2/PY3的狭窄黄铁矿边缘和与毒砂共生的浸染型黄铁矿(PY4，主矿期)。其中PY2和PY4含量最高，As、Cu、Sb和Pb值范围较大(分别为2480~58100、55.4~1610ppm、29.1~232ppm和24.1~376ppm)，而PY4的Au、As、Cu和Se含量最高(分别为~70ppm、4200、1630ppm和38.3ppm)。用LA-MC-ICPMS测定的矿石前黄铁矿的δ34S值与文献中已有的数据基本一致，范围在−53.3~114.8‰之间，表明它们很可能是在沉积/成岩过程中由海相硫酸盐的细菌还原所产生的。同时，矿石黄铁矿的δ34S值具有相对较窄的δ34S值，大多变化在−5~5‰之间，表明S来自沉积岩的平均值或岩浆来源。由于该区火成岩稀少，出露的岩浆(~77~99 Ma)明显晚于泥堡金矿床的成矿年龄(~141Ma)，因此泥堡金矿不太可能有岩浆来源。所有黄铁矿中的Co与Ni呈正相关(R2=0.71)，且PY4主期的Co/Ni和Zn/Ni比值接近或处于沉积-成岩成因范围内，表明泥堡更有可能存在沉积物源。
Nibao is a unique thrust fault-controlled and strata-bound disseminated gold deposit in southwestern Guizhou Province, China. In Nibao, pyrite is the major sulfide mineral and Au is structurally bound (Au+) within the pyrite lattice. In this study, we conducted detailed analyses of the pyrite chemistry and S isotope composition in Nibao using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS), respectively. Through petrographic and pyrite chemical studies, four pyrite generations (Py1–Py4) were distinguished: framboidal pyrite (Py1, pre-ore sedimentary stage), clean pyrite overgrowing framboidal pyrite (Py2, pre-ore diagenetic stage), “spongy” pyrite (Py3, early ore stage), and overgrowth of narrow pyrite rims surrounding Py2/Py3 and disseminated pyrite associated with arsenopyrite (Py4, main ore stage). Among these, Py2 and Py4 are the most abundant.The trace element content in Py2 is characterized by a wide range of As, Cu, Sb, and Pb concentrations (~2480–58100 ppm, ~55.4–1610 ppm, ~29.1–232 ppm, and ~24.1–376 ppm, respectively), while Py4 has the highest Au, As, Cu, and Se contents (~70 ppm, ~4200, ~1630 ppm, and ~38.3 ppm, respectively). The δ34S values of pre-ore pyrites measured by LA-MC-ICP-MS in this study and the available data in the literature range broadly from −53.3 to 114.8‰, indicating that they were most likely generated by bacterial reduction from marine sulfate during sedimentation/diagenesis. Meanwhile, the δ34S values of ore pyrites have relative narrow δ34S values, mostly varying from −5 to 5‰, and indicating that the S was derived either from the average of sedimentary rocks or from a magmatic source.Since igneous rocks are scarce in the region and the exposed (~77–99 Ma) are clearly younger than the mineralization age of the Nibao gold deposit (~141 Ma), a magmatic source is unlikely in Nibao. All pyrites in this study show a positive correlation (R2= 0.71) between Co and Ni, and the Co/Ni and Zn/Ni ratios of main stage Py4 are close to or within the range defined for a sedimentary–diagenetic origin, suggesting a sedimentary source is more likely in Nibao.
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