摘要:
20世纪90年代,在新疆西天山北段晚古生代火山岩区内相继发现了阿希大型金矿床及其外围的伊尔曼得、恰布坎卓它等金矿床(点),并进一步确定了其系产于晚古生代火山岩内的浅成低温矿床.矿床赋存于伊犁晚古生代火山岩区的吐拉苏-也里莫墩火山岩带中.矿床围岩为下石炭统大哈拉军山组中基性-中酸性陆相火山岩系,以钙碱性为主,少量碱性系列岩石,具有富硅、钠、贫钾、铝、镁、钙成分和里特曼指数偏高的特点;岩石稀土元素含量中等(ΣREE=41.59×10-6~135.83×10-6),属于轻稀土富集型(含量29.05×10-6~95.37×10-6),分镏程度较高;容矿火山岩以K、Rb、Ba、Th等大离子元素富集和Ti、Y、Yb、Sc等亏损为特征,接近于板内过渡型玄武岩系列岩石;火山岩和矿石206Pb/204Pb值为17.5269~18.6644,207Pb/204Pb值为15.1073~16.0108,208Pb/204Pb值为37.3670~38.1958,具壳幔混合源特征;含金石英脉锶同位素初始值与区内容矿火山岩、矿化有关蚀变矿物十分接近,介于0.705~0.709之间,显示成矿作用与火山岩系的密切成因联系;文中结合容矿火山岩时空分布和成矿地球化学特征的讨论分析,揭示了金矿成矿与容矿火山岩的内在联系,确立了金矿化的陆内裂谷环境特点,建立了浅成低温热液型金矿的第三种成矿背景,拓宽了找矿区域.
Abstract:
Axi gold deposit and its peripheral deposits Yiermande,Jingxi,Qiabukanzhuota,etc.,which were found in succession in the Yili Late Paleozoic volcanic rock province in the north section of West Tianshan Mountains,are considered as epithermal mineralizing type,and furtherly divided into adular-sericite sub-type and silicated rock sub-type.The gold deposits are formed in Tulasu-Yelimodun volcanic belt of Yili Late Paleozoic rift, hosted by the acid-intermediate to intermediate-basic volcanic rocks of Lower Carboniferous Dahalajunshan Formation,which belongs to calc-alkalic/alkalic series,characterized by rich silicon and sodium and poor potassium,aluminum,magnesium and calcium.The host rocks with medium contents of rare earth elements (ΣREE=41.59×10-6-135.83×10-6) belong to LREE riched type (LREE=29.05×10-6-95.37×10-6) with fairly high REE fractionation.And the host rocks enriched with macro ion elements of K,Rb,Ba and Th while lacking of Ti,Y,Yb,Sc etc.are similar to the intraplate transitional basaltic rocks.With 206Pb/204Pb 17.5269-18.6644,207Pb/204Pb 15.1073-16.0108 and 208Pb/204Pb 37.3670-38.1958,the lead isotope contents of host volcanic rocks and ores show their crust mantle mixed origin.The strontium isotope initial ratios of Au-bearing quartz vein,host volcanic rocks and mineralization-related altered minerals are very closed from 0.705 to 0.709,showing the close genetic relation between metallogenism and volcanism.By analyzing the characteristics of metallogeno-geochemistry and the distribution of host volcanic rocks,this paper reveals the internal relations between the metalloginism and the host volcanic rocks,confirms the Au-forming environment of intracontinental rift,sets up the third metallogenitic setting and develops the ore-exploration regions of the epithermal gold deposits.
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