青海锡铁山矿床硅质岩的地球化学特征及形成环境

Geochemical Characteristics and Formation Setting of Silicolites in the Xitieshan Deposit,Qinghai Province

锡铁山滩间山群中广泛发育与铅锌成矿作用关系密切的硅质岩.地质、地球化学特征研究表明,区内硅质岩具条带状和纹层状构造,与含矿层产状一致.岩石总体以贫Si,富A l、Fe、Mn、Na等为特征,属不纯硅质岩,主成分与火山—沉积盆地热水沉积硅质岩特征相似.硅质岩的Fe/Ti、(Fe+Mn)/Ti、N i/Co、Ti/V等比值与热水沉积物类似,As、Sb、Ba、Ag、Hg等指示微量元素显著富集,REE总量低、Ce亏损较明显.表明本区硅质岩为热水沉积成因,形成于陆缘裂谷环境.

A suite of silicolites closely relacted to Pb - Zn mineralization are widespreaded in the Tanjianshan Group of the Xitieshan deposit. This paper has studied the petrological and geochemical characterristics of the silicolites ,through microsection and chemical analysis. The silicolites distributed in the region are characterized by bedded,striped and laminar structures, and show consistent occurrence with ore -bearing strata. All samples of the silicolites have low silica content, and relatively enriched in A1, Fe, Mn and Na. The major elements composition of the silicolites are similar to those of the typical hydrothermal sedimentary cherts in the volcano - sed- imemtary basins. The ratios of Fe/Ti, （ Fe ＋ Mn）/Ti, Ni/Co and Ti/V of rocks are also similar to those of hydro- thermal sediments, the indicator trace elements like As, Sb, Ba, Ag and Hg are enriched obviously,the total REE is low and Ce is obviously depleted. These indicated that the silicolites are of hydrothermal origin and formed in the setting of continental margin rift.