华南热水沉积硅质岩建造及其成矿效应

HYDROTHERMALLY SEDIMENTARY FORMATIONS AND RELATED MINERALIZATION IN SOUTH CHINA

华南地区热水沉积建造发育。文中介绍该地区热水沉积建造 ,特别是震旦系顶部、泥盆系榴江组和二叠系当冲组 3个重要层位的硅质岩建造 ,分析它们的地质地球化学特征。研究表明 ,华南三层位沉积硅质岩的共同特征是TiO2 、Al2 O3 和K2 O含量一致偏低 ,大部分微量元素含量偏低 (与地壳克拉克值相比 ) ,但Ba、As、Sb富集 ,具有较为典型的热水沉积成因特点。多元统计分析显示 ,大部分微量元素在第一个主因子上均有显著因子载荷 ,与它们在基底的富集或亏损无关 ,代表了古地热系热水循环中的淋滤因子。华南三层位热水成因硅质岩具有相似的REE地球化学特征。REE总量低 ,稀土配分模式落在典型热水沉积物的上、下限之间 ,多数样品呈现δCe和δEu负异常。正常沉积的混入使部分硅质岩的REE配分模式复杂化。最后 ,讨论了与热水沉积建造相关的成矿效应 。

There exist several hydrothermally sedimentary formation in South China. This paper introduces hydrothermally sedimentary formation, especially the chert formations from the Top Precambrian, the Upper Devonian and the Permian strata in the area, and discusses their geological and geochemical characteristics. It is shown that the cherts are characterized by low content of TiO_2, Al_2O_3 and K_2O, and depletion of most trace elements relative to their crust abundance, but rich in Ba, As and Sb, indicating they are quite typical of hydrothermal origin. The presence of many trace elements in the first important factor with a high variance proportion represents the leaching factor of an evolving geothermal system. During circulation, the hydrothermal solution constantly leached and extracted all metal elements possible from the various country rocks that it passed through. The cherts from the studied three stratigraphic units are similar in geochemical characteristics of REE. They are generally characterized by low total REE, negative δCe and δEu, and the average REE abundance distribution pattern ranges between the upper and the lower limits of typical hydrothermal deposits. The ambiguous Ce anomaly, the complexity in REE patterns and higher REE abundance of some samples are due to an admixture of normal sediments to the hydrothermal chert. Finally, mineralization related to hydrothermally sedimentary formation is introduced, which provides constraints to the origin and the evaluation of metallic deposits.