The Niujiaotang Cd-rich zinc deposit, Duyun, Guizhou province, southwest China: ore genesis and mechanisms of cadmium concentration
The Niujiaotang Cd-rich zinc deposit, Duyun, Guizhou province, southwest China: ore genesis and mechanisms of cadmium concentration
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DOI：
10.1007/s00126-011-0386-z
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发表时间：
2012-08
影响因子：
4.8
通讯作者：
L. Ye;N. Cook;Tiegeng Liu;C. Ciobanu;Wei Gao;Yulong Yang
中科院分区：
文献类型：
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作者：
L. Ye;N. Cook;Tiegeng Liu;C. Ciobanu;Wei Gao;Yulong Yang
贵州牛角塘锌存款矿床是产于早寒武世碳酸盐岩中的密西西比河谷型锌存款矿床。闪锌矿富含镉（平均1.4重量% Cd），其主要作为类质同晶杂质出现在闪锌矿晶格中。离散的镉矿物（绿钾镁矾和钙钛矿）是罕见的，几乎只发现在氧化带的存款，可能形成的风化淋滤过程中的次生矿物。地球化学数据表明，硫化物富集重硫，δ 34 S值为+10.0‰ ~+32.8‰，平均为+22.5‰。不同硫化物矿物中Pb同位素组成的一致性与寒武系地层中的Pb同位素组成相似。矿石铅可能来源于富铀、钍的上地壳岩石，如下寒武统乌浔组。成矿流体为低温（101°C ~ 142°C）型，成分以Na-Ca-Mg-Cl为主，属油田卤水。结果表明，金属元素主要来源于早寒武世地层（清虚洞组和五汛组），硫主要来源于寒武系地层中的硫酸盐或马江油气古油藏的油田卤水。该存款的成因模式援引了扬子地台早寒武世浅海环境。海水中的锌和镉通过未知的生物机制富集在丰富的藻类中，导致大量富锌和富镉的藻卵石。奥陶纪时期，在马江油气古储层遭到破坏的同时，油田卤水从盆地中心向盆地边缘迁移，浸出寒武系地层中的金属。在牛角塘地区，沿枣楼断裂沿着上升的热卤水进一步活化了原有的Zn、Cd，特别是清虚洞组和五汛组中的Zn、Cd，形成了产于活性碳酸盐岩中的层状、整合型锌镉矿体。
The Niujiaotang zinc deposit in southeastern Guizhou, China, is a Mississippi Valley-type Zn deposit within Early Cambrian carbonate rocks. Sphalerite is enriched in cadmium (average 1.4 wt.% Cd), which occurs mostly as isomorphous impurities in the sphalerite lattice. Discrete cadmium minerals (greenockite and otavite) are rare and are found almost exclusively in the oxidation zone of the deposit, probably formed as secondary minerals during weathering–leaching processes. Geochemical data show that the sulfides are enriched in heavy sulfur, with δ34S ranging from +10.0‰ to +32.8‰ (mean +22.5‰). The consistent Pb isotopic compositions in different sulfide minerals are similar to that of Cambrian strata. The ore lead probably came from U- and Th-rich upper crustal rocks, such as the Lower Cambrian Wuxun Formation. The ore fluid is of low-temperature (101°C to 142°C) type, with a Na–Ca–Mg–Cl-dominant composition, and is interpreted as oil-field brine. The data indicate that the metals were mainly derived from the Early Cambrian strata (Qingxudong and Wuxun Formations), whereas sulfur is sourced from sulfate in Cambrian strata or oil-field brines of the Majiang petroleum paleoreservoir. The genetic model for the deposit invokes an Early Cambrian shallow-sea environment on the Yangtze Platform. Zinc and Cd in seawater were concentrated in abundant algae via unknown biological mechanisms, resulting in large amounts of Zn- and Cd-rich algal ooliths. During the Ordovician, concurrent with destruction of the Majiang petroleum paleoreservoir, oil-field brines migrated from the center of the basin to the margin leaching metals from the Cambrian strata. In the Niujiaotang area, preexisting Zn and Cd, particularly in the Qingxudong and Wuxun Formation, were further mobilized by hot brines rising along the Zaolou fault system, forming stratiform and generally conformable Zn–Cd orebodies in reactive carbonate lithologies.