东天山玉峰金矿热液蚀变作用与元素迁移规律

Hydrothermal alteration and element migration in the Yufeng gold deposit,Eastern Tianshan Orogen

玉峰金矿位于中亚造山带东天山东缘,是近年来新发现的含银高品位金矿床。该矿床目前已探明6个金矿体,均赋存在石英斑岩中。矿区热液蚀变作用发育,与成矿关系最密切的为黄铁绢英岩化和硅化,显示明显的蚀变分带:以石英硫化物脉为中心,黄铁绢英岩化带在其两侧大致对称分布。本文选取矿体上盘和下盘的石英斑岩、黄铁绢英岩进行了全岩的主、微量元素及成矿元素测试,并对其中的长石和绢云母进行电子探针成分分析。测试结果表明,黄铁绢英岩中的Au含量较蚀变前呈指数级增长,Ag、Cu、As等成矿元素大量增加,CaO、Na2O、P2O5、P2O5、Sr、Pb、Th、U、Sb等元素显著迁出,而SiO2、Al2O3、TiO2含量和稀土元素含量变化较小,表现稳定。热液蚀变过程中,石英斑岩中71%~76%的正长石发生绢云母化,导致K2O大量迁出;而钠长石几乎全部蚀变为绢云母,造成Na2O大量迁出。热液流体的贡献使得蚀变岩中MgO、Fe2O3T含量成倍增加,并主要富集在绢云母和/或黄铁矿晶格中。综合分析认为,绢英岩化蚀变带,Au、Cu、As和Bi等元素的综合化探异常,低电阻率、高激化率的地球物理特征可以作为玉峰矿区深部和外围找矿的标志。研究区内的石炭纪石英斑岩带,尤其是在构造叠加部位,热液活动使其更有利于矿化富集,是找矿勘探的有利部位。

The Yufeng gold deposit is located in the eastern margin of the Eastern Tianshan Orogen in the Central Asian Orogenic Belt.It is a newly discovered silver-bearing high-grade Au deposit.Six gold ore bodies have been discovered,and all of them are hosted in quartz porphyry.Different types of hydrothermal alterations are well developed in the mining area,among which the beresitization and silicification are closely related to mineralization.Obvious alteration zoning occurred in the ore bodies where the quartz sulfide veins are centered with a beresitization zone roughly symmetrically distributed on both sides.In this paper,we selected samples of the quartz porphyry and beresite from the hanging wall and footwall around the ore bodies,analyzed their major,trace,rare earth elements and ore-forming elements compositions of the whole rocks,feldspars and sericites.Compared to a fresh quartz porphyry,the Au content in the beresite is increasing exponentially,contents of Ag,Cu,As,and ore-forming elements increase significantly,while the CaO,Na2 O,P2 O5,Sr,Pb,Th,U and Sb contents decrease obviously.The contents of SiO2,Al2 O3,TiO2,and rare earth elements are slightly changed,indicating their stable characteristic.During hydrothermal alteration,71%~76% of the orthoclase in the quartz porphyry was replaced by sericite,which caused a large amount of K2 O to migrate out;while almost all albite was altered to sericite,causing a large amount of Na2 O to migrate out The contributions of MgO and Fe2 O3 from hydrothermal fluids increase several times,and are finally fixed in the sericite and/or pyrite lattice.Based on the comprehensive analysis,we think that the phyllic alteration zone,Au-Cu-As-Bi comprehensive geochemical anomalies,geophysical characteristics of low resistivity and high polarizability can be used as indicators of prospecting in the study area.The Carboniferous quartz porphyry zone,especially superimposed with a proper structure,is a favorable location for prospecting and exploration,where the hydrothermal activity makes it more conducive to mineralization.