新疆西天山备战铁矿床含矿地层岩石化学特征及形成时代探讨

Discussion on Petrochemical Characteristics and Formation Age of Ore Bearing Strata of Beizhan Iron Deposit in Western Tianshan,Xinjiang

以新疆西天山备战铁矿含矿地层为研究对象,通过开展系统的地质学、岩相学、主微量元素地球化学、锆石U-Pb同位素年代学等方面的研究,进一步分析铁矿岩浆源性质及成岩、成矿时代。研究结果表明,含矿地层下石炭统大哈拉军山组第三段火山岩富集轻稀土元素及Rb,Th,K等大离子亲石元素,亏损Nb,Ta,P,Ti等高场强元素。火山岩形成于岛弧环境,构成一次完整的火山喷发旋回,最早喷发的为一套爆发相的凝灰岩韵律,其次为溢流相的玄武岩韵律,再次为一套溢流相的英安岩韵律,最终为一套沉积砾岩、砂岩韵律组合。该组合中的每一组岩层在化学成分上具较好的相关性,反映其属于同源岩浆演化的结果,且此类成岩先后顺序与该区测定的U-Pb同位素测年结果相符合。

In this paper,it takes the Ore-bearing strata of Beizhan Iron deposit as the study objects.The paper further an-alyzes the Characteristics of magma source and diagenetic and metallogenic age of the iron ore through carrying out sys-tematic research on field geology,petrography,major and trace element geochemistry and zircon U-Pb isotopic chronolo-gy,etc.The findings show that the ore-bearing strata,namely the third volcanic rock of Dahalajunshan Formation of Lower Carboniferous,are enriched in LREE(Light Rare Earth Elements)and large ion lithophile elements(Rb,Th,K)and depleted in high field strength elements(Nb,Ta,P,Ti).Volcanic rocks are formed in the island arc environment,con-stituting a complete volcanic eruption cycle.The first eruption is a set of tuff rhythm of the eruptive phase,followed by basalt rhythm of the overflow phase,then a set of dacite rhythm of the overflow phase,and finally a set of sedimentary conglomerate and sandstone rhythm combination.Each group of stratas in the assemblage has a good correlation in chemical composition,which can reflect the result of homologous magmatic evolution.At the same time,the sequence of diagenesis is consistent with the U-Pb isotopic dating in study area.