甘肃阿尔金东段余石山西金矿赋矿火山岩岩石学特征及构造环境

Effects of Additive Content Petrological Characteristics and Tectonic Environment of Yushishanxi Gold Deposit Ore-bearing Volcanic Rocks in the Eastern Aljin Section of Gansu Province

余石山西金矿是近年来阿尔金构造带东段新发现具有较大找矿前景的金矿床,矿体赋存于寒武—奥陶系拉配泉岩群变火山岩系中,目前对该矿床成矿时代和构造环境鲜有研究。为认识阿尔金东段拉配泉岩群金矿成矿地质条件和开展区域金矿找矿工作,首次通过金矿赋矿变火山岩岩石学、地球化学、锆石U-Pb年代学等方法研究了余石山西赋矿变火山岩岩石地球化学特征、形成时代和构造环境,结果表明,余石山西赋矿变火山岩形成时代为(471.3±2.1) Ma,轻重稀土分异明显,稀土配分曲线呈轻稀土富集、重稀土亏损的右倾模式,具有弱负Eu异常。变火山岩微量元素特征表现为大离子亲石元素富集的隆起形曲线,显示Th、U、Nd、Zr、Hf等大离子亲石元素富集,Ti、Sr、P等高场强元素明显亏损。结合区域构造背景和岩石地球化学特征,判断火山岩构造背景可能为岛弧环境。区域上,在寒武-奥陶系拉配泉岩群变火山岩中可能会有该类型金矿找矿的更大突破。

The Yushishanxi gold deposit is a newly discovered gold deposit with great prospecting prospect in the eastern part of Altun tectonic belt in recent years.The ore body occurs in the metamorphic volcanic series of the Cambian-Ordovician Lapeiquan Group.In order to understand the metallogenic geological conditions of the gold deposits in the Lapeiquan Group in the eastern Altun section and carry out the gold prospecting work,the petrochemical,formation age and tectonic environment of the ore-bearing volcanic rocks in Yushishanxi were studied for the first time by means of the petrology,geochemical characteristics and zircon U-Pb chronology of the ore-bearing volcanic rocks.The results show that the formation age of the mineralized volcanic rocks in Yushishanxi is(471.3±2.1) Ma,and the differentiation of heavy and heavy rare earths is obvious.The distribution curve of rare earths shows a right-leaning pattern of light rare earth enrichment and heavy rare earth deficit,with a weak negative Eu anomaly.The characteristics of trace elements in metamorphic volcanic rocks show the uplift curve of large ion lithophile elements enrichment,which shows that large ion lithophile elements such as Th,U,Nd,Zr,Hf are enriched,and high field strength elements such as Ti,Sr,P are obviously depleted.Combined with the regional tectonic setting and geochemical characteristics of rocks,it is concluded that the volcanic rock tectonic setting may be an island arc environment.In the region,there may be a greater breakthrough in this type of gold prospecting in the metamorphic volcanic rocks of the Cambrian-Ordovician Lapaiquan Group.