贵州遵义锰矿区“白泥塘层”硅质岩地球化学特征及其地质意义

Geochemical Characteristics and Geological Significance of“Bainitangceng” Siliceous Rocks in Zunyi Manganese Ore Fields,Guizhou Province,China

遵义锰矿区锰矿体底部发育一套碳泥质硅质岩建造，称为“白泥塘层”，主要由微晶石英和隐晶质玉髓组成，常含少量的碳泥质、黄铁矿和碳酸盐矿物等。“白泥塘层”硅质岩与含锰建造呈连生关系，环绕含锰建造分布。本文通过对代表性的硅质岩样品主量和微量-稀土元素及氧同位素地球化学分析，发现其Si02含量范围为95．00％～98．80％，均值为96．86％，表明其属于化学成分比较纯净的硅质岩；TFeO、MnO含量相对富集，A1203、Ti02含量相对亏损，Fe／Ti、（Fe＋Mn）／Ti和A1／（AI＋Fe＋Mn）的均值分别为83．80、93．90和O.21，与热水沉积物相似，表明其具有热水沉积特征；微量以富集As、Sb、Cd、U，而亏损Co、Ni、Ga为特征，其中U／Th平均比值为2．66，Ni／Co平均比值为1．58，表现出热水沉积岩的微量元素地球化学特征；稀土总量较低，均值为56．91×10-6，6（Eu）=0．91～1．42，Eu异常不显著，5（Ce）=0．47～1．03，大部分样品具有负Ce异常特征，稀土元素北美页岩标准化配分模式图略呈重稀土富集特征，与典型热水沉积硅质岩稀土元素配分模式相似；硅质岩δ180sMow值，与热泉硅华及生物成因硅质岩比较接近。综上，“白泥塘层”硅质岩可能属于热水沉积成因，在沉积的过程中混有非化学沉积物。

There are carbon argillaceous siliceous rocks produced at the bottom of the manganese ore bodies in Zunyi Mn ore fields, known as the ＂Bainitangceng＂, which is mainly composed of microcrystaUine quartz and implicit crystal chalcedony, and often contains small amounts of carbon argillaceous, carbonate minerals and pyrite. Mn ore bodies were surrounded by ＂Bainitangceng＂ siliceous rocks in space. Based on field survey, trace and rare earth elements and oxygen isotopes the typical siliceous rock samples were analyzed. Results show that SiO2 ranges from 95.00% to 98.80%, with a mean value of 96.86%, indicating that they belong to the pure chemical siliceous rocks; contents of TFeO and MnO are relatively high, and contents of A1203 and TiO/are relatively low. The mean values of Fe/Ti, （Fe＋Mn）/Ti and A1/（AI＋Fe＋Mn） ratios are 83.80, 93.90 and 0.21, respectively, similar to that of the hydrothermal sediment. As, Sb, Cd and U are enriched, and Co, Ni and Ga are depleted. The mean values of U/Th and Ni/Co ratios are 2.66 and 1.58, respectively, suggesting the geochemical characteristics of hydrothermal sedimentary rocks. The mean ZREE value is 56.91×10-6, with 6（Eu）=0.91-1.42, 8（Ce）=0.47-1.03, indicating a weak negative Ce anomaly. In the North American shale standardized REE distribution pattern, the heavy rare earth elements were enriched, similar to hydrothermal sedimentary siliceous rock;δ18OsMowvalues of siliceous rocks are like hot springs and biogenic siliceous. The ＂Bainitangceng＂ siliceous rocks may belong to hydrothermal sedimentary genesis, and be mixed with non-chemical sediment.