新疆东准噶尔绿源金矿床地质特征与金成矿物质来源分析

摘要

绿源浅成低温热液型金矿床位于野马泉-琼河坝古生代岛弧带东段的琼河坝矿集区.赋矿地层为一套中酸性火山熔岩夹火山碎屑岩建造.矿体呈似层状、条带状、透镜状,多受断裂构造控制.其热液成矿作用可分为4个阶段:石英-黄铁矿阶段(S1)、石英(玉髓)-金-黄铁矿阶段(S2)、石英-金-多金属硫化物阶段(S3)、石英-碳酸盐阶段(S4).金主要赋存于S2和S3阶段.本文对该矿床开展S、Pb同位素及硫化物稀土元素研究,拟揭示其成矿物质来源.结果表明,绿源金矿床金属硫化物的硫同位素组成比较稳定,δ34S集中于+0.2‰～+2.8‰,均值为+1.35‰,显示出岩浆硫的组成特征.矿石与围岩中硫化物的硫同位素δ34S值一致,表明硫可能来源于矿区巴塔玛依内山组火山岩地层.S2和S3阶段硫化物的铅同位素206 Pb/204 Pb=16.457～18.084、207 Pb/204 Pb=15.267～15.635、208Pb/204 Pb=36.472～38.379,另一件长石的Pb铅同位素206 Pb/204 Pb=18.546、207 Pb/204 Pb=15.509、208 Pb/204 Pb=38.183,μ值介于9.11～9.58之间,ω值介于33.97～38.61之间.上述各铅同位素比值变化范围较大,远远大于正常铅同位素组成的变化范围.结合同位素组成特征及特征参数法认为绿源金矿床矿石Pb为异常Pb,铅源为混合来源,一部分来源于上地壳物质,一部分来源于地幔物质.硫化物稀土元素特征与火山岩类似,暗示成矿物质可能来源于火山岩地层.H、O同位素特征显示,绿源金矿成矿流体以大气降水为主,有少量岩浆水的加入.综合S、Pb同位素、稀土元素等分析,本文认为绿源矿区岩浆活动和成矿作用具有壳幔混合源特征,成矿物质具深源特征,主要直接来自赋矿火山岩.%The Luyuan epithermal gold deposit is located at the Qiongheba ore cluster area in the eastern segment of Yemaquan-Qiongheba Paleozoic arc belt,eastern Junggar.Ore-hosting strata contain one suite of intermediate-felsic volcanic lava intercalated with volcaniclastic rocks,with orebodies occuring as veins,banding,lentoid and controlled by faults.Four stages of hydrothermal mineralization were identified,which are quartz-pyrite stage (S1),quartz-Au-pyrite stage (S2),quartz-Au-polymetallic sulfide stage (S3) and quartz-carbonate stage (S4),with S2 and S3 as the main Au mineralization stages.In this paper,the authors carried out detailed study of sulfur and lead isotopic compositions and rare earth elements of the sulfide from the deposit so as to reveal the ore-forming material source.The results demonstrate that the sulfides have a narrow δ34S range of +0.2‰ to +2.8‰,with an average of + 1.35‰,suggesting that the sulfur is characteristic of magmatic sulfur.The δ34S values of sulfides in ores and country rocks are in agreement,indicating that sulfur mainly derived from the Batamayineishan Formation of Upper Carboniferous.The 206Pb/204Pb,207Pb/204Pb and 208Pb/204Pb ratios of sulfide from S2 and S3 are 16.457～18.084,15.267～15.635 and 36.472～38.379,respectively.The 206Pb/204Pb,207Pb/204Pb and 208Pb/204Pb values of one feldspar sample are 18.546,15.509 and 38.183,respectively.The μ values vary from 9.11 to 9.58,while the ω values vary from 33.97 to 38.61.The Pb isotopic ratios vary greatly,far larger the changing range of normal Pb isotopic compositions.Isotopic compositions and feature parameters suggest that the anomalous lead of the Luyuan deposit should have a mixing origin,with part from the upper crustal material and the other from the mantle material.REE geochemical characteristics of sulfides are similar to those of the ore-bearing volcanic rocks,implying that the ore-forming materials likely came from ore-bearing volcanic rocks.The hydrogen and oxygen isotopic compositions indicate that the ore-forming fluid of the Luyuan gold deposit mainly sourced from meteoric water with minor magmatic water.Finally,combined with S and Pb isotopic and REE analysis,the study suggest that the magmatic activities and mineralization of the Luyuan mining area are characterized by crust-mantle mixing and ore-forming materials by deep source,more directly from ore-hosting volcanic rocks.