Multi-stage growth and invisible gold distribution in pyrite from the Kundarkocha sediment-hosted gold deposit, eastern India
Multi-stage growth and invisible gold distribution in pyrite from the Kundarkocha sediment-hosted gold deposit, eastern India
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DOI：
10.1016/j.oregeorev.2013.05.006
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发表时间：
2013-11
影响因子：
3.3
通讯作者：
Pranjit Hazarika;B. Mishra;S. S. Chinnasamy-S.;H. Bernhardt
中科院分区：
文献类型：
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作者：
Pranjit Hazarika;B. Mishra;S. S. Chinnasamy-S.;H. Bernhardt
印度 Kundarkocha 的金矿化位于碳质黄铁矿千枚岩中的剪切灰色石英脉中。金以硫化物中的封闭颗粒和石英中的游离颗粒形式存在。根据 X 射线元素成像、电子探针微量分析和激光烧蚀电感耦合等离子体质谱分析记录的特征结构和化学特征，在碳质千枚岩和金脉中鉴定出了四种黄铁矿类型。岩石中的细粒同沉积到早成岩黄铁矿片 (PyI) 的 Co 和 As 含量较低，但金价始终较高。下一代黄铁矿（PyII）含有大量硅酸盐和稀有的硫化物包裹体； Co、Ni含量较低，As值适中；看不见的金的最高平均值和Li、Ti、Zn、Rb、Sr、Y、Zr、Nb、La、Ce、Ta、Th、U和Cr等微量元素的最高浓度。第三代黄铁矿（PyIII）显示出比PyII过度生长的证据，同时含有硅酸盐和硫化物包裹体，其特点是Co含量适中，Ni含量高，Au含量低，大离子亲石元素浓度较高，但高场强元素含量较少。最新类型的黄铁矿 (PyIV) 以多晶聚集体的形式出现，其中含有金、硫化物和稀有硅酸盐的内含物，显示出 Co 和 As 的振荡分带以及所有其他微量元素的最低浓度。从 PyII 到 PyIV 的大多数微量元素含量的连续下降归因于成岩作用期间的流体辅助重结晶和低级变质作用。后来的黄铁矿（PyII 到 PyIV）无论其 As 值如何，都表现出较高的 Au 含量，表明不可见的金主要以纳米颗粒的形式存在，有时高达 500 ppm。与大多数经历大规模再利用的微量元素不同，黄金以某种方式被锁在黄铁矿中，导致昆达科查的矿床相当贫乏。
Gold mineralization at Kundarkocha, India, is hosted in sheared gray quartz veins that were emplaced in carbonaceous pyritic phyllite. Gold occurs as enclosed grains within sulfides and free grains in quartz. Based on characteristic textural and chemical features, documented by X-ray element imaging, electron probe microanalysis and laser-ablation inductively-coupled plasma mass spectrometry analyses, four pyrite types were identified in carbonaceous phyllites and auriferous veins. Rock-hosted fine-grained syn-sedimentary to early diagenetic pyrite framboids (PyI) have lower contents of Co and As but consistently high gold values. Pyrite of the next generation (PyII) has numerous silicate and rare sulfide inclusions; lower contents of Co and Ni, moderate As values; the highest mean value of invisible gold and maximum concentrations of trace elements such as Li, Ti, Zn, Rb, Sr, Y, Zr, Nb, La, Ce, Ta, Th, U and Cr. Pyrite of the third generation (PyIII) shows evidence of overgrowth over PyII, contains both silicate and sulfide inclusions, and are characterized by moderate contents of Co, high Ni and low Au values and higher concentrations of large ion lithophile elements, but lesser amount of high field strength elements. Pyrites of the latest type (PyIV) occur as polycrystalline aggregates that contain inclusions of gold, sulfides and rare silicates, show oscillatory zoning of Co and As and the lowest concentrations of all other trace elements. Successive decrease in contents of majority of trace elements from PyII to PyIV is attributed to fluid-assisted recrystallization during diagenesis and low grade metamorphism.Later generation pyrites (PyII through PyIV) exhibit higher Au contents regardless of their As values, indicating occurrence of invisible gold mostly as nanoparticles, at times reaching up to 500 ppm. Unlike the majority of trace elements that underwent large-scale remobilizations, gold was somehow locked up in pyrite resulting in a rather lean deposit at Kundarkocha.