粤西古水剖面震旦系顶部层状硅岩的热水成因属性:岩石学和地球化学证据

古水剖面震旦系顶部硅岩主要发育层状构造、纹理状构造、块状构造和假角砾状构造,化学成份以ＴｉＯ_２、Ａｌ_２Ｏ_３和大部分微量元素亏损（相对地壳克拉克值）为特征。但Ｂａ、Ａｓ和Ｓｂ等少数已知的热水沉积特征元素显示富集。在Ａｌ－Ｆｅ－Ｍｎ三元图上,古水硅岩投映在“热水沉积”域内。因子分析和对应分析显示了大部分金属元素在代表热水淋滤作用的因子上均有反映。稀土元素以低含量为特征,在对北美页岩组合样（ＮＡＳＣ）正规化后的稀土配分模式落在典型热水沉积的上、下限之间,而在正常沉积的之外。各种岩性和地球化学证据表明,古水硅岩具有热水成因。

Hydrothermal Origin of Top Sinian Chert Formation at Gusui, Western Guangdong,China:Petrologic and Geochemical Evidence

The Sinian(Precambrian) chert formation amours at Gusui, western Guangdong Province,southern China, and is an integral part of the source strata of the Hetai gold field. The presence of the chert formation offers an excellent opportunity to evaluate the possible hydrothermal system and its role in the formation of the source strata.The Precambrian chert from Gusui is characterized by bedded, laminated, massive and pseudobrecciated structures, and the depletion of TiO2,Al2O3 and most trace elements. However,it is enriched in Ba, As, Sb, Hg and Se, which are considered as diagnostic elements of hydrothermal sediments. In the Al-Fe-Mn ternary diagram, it falls into the "hydrothermal field ".Correspondence analysis the factor analysis reveal that many elements show up in the factot that represents the leaching of country rocks by hydrothermal solution, and is the very characteristic element association of the geochemically anomalous South China basement. REE are characterized by a low total content and a gradually increasing NASC-normalized value with increasing atomic number of REE, ranging between the upper and the lower limits of typical hydrothermal deposits.The petrologic and geochemical evidences suggest a hydtothermal origin for the chert. It may have formod in a Precambrian rift or extension zone develope within the Yunkai marginal geosyncline,with a fault system linkihg to an unknown heat source at depth.