东昆仑五龙沟金矿田地质特征与成矿地质体厘定

Geological characteristics of the Wulonggou gold ore field and determination of metallogenic geological bodies in East Kunlun Mountains

五龙沟金矿田位于东昆仑造山带中段,矿田内金矿床主要沿岩金沟、萤石沟-红旗沟、三道梁-苦水泉三条NWW向构造破碎带发育。本文通过金矿床地质特征的综合分析,认为金矿床类型属于中—低温热液型,矿化类型为构造破碎带蚀变岩型,金成矿作用的温度为195~319℃,成矿物质具有壳源为主,部分幔源混合特征,成矿流体为岩浆水和大气降水的混合,矿物组合以微细黄铁矿、微细针状毒砂和不可见金为特征。同时通过地质体与矿床的空间关系、地质体与矿床物质成分的相关性、地质体形成时代与矿床形成时代及其时间差的对比研究,确认红旗沟脑片麻状花岗闪长岩体是五龙沟金矿田成矿地质体,也是金元素重要提供者。岩体含有大量被拉长的闪长岩包体,矿物发生明显的韧性变形,具有壳源为主的壳幔同熔作用形成、在定向应力作用下同构造侵位的特点,成岩年龄239~244Ma。壳幔同熔作用过程中幔源物质的加入带来了更多的金元素,定向应力作用下同构造侵位使金元素更容易活化迁移,进入成矿作用过程。金矿床主成矿期为印支早期,成矿年龄237Ma左右;后期被210Ma含浸染状黄铁矿的中酸性杂岩体侵位吞噬破坏。金矿床受成矿地质体和NWW向构造破碎带联合控制,矿化主要发育于距成矿地质体1.0~3.0km范围内的NWW向构造破碎带中;如果在成矿地质体影响范围内,没有NWW向构造破碎带,金矿体就没有赋存空间;而虽有NWW向构造破碎带,但离开成矿地质体的影响范围,金矿化则迅速减弱。进一步找矿方向是红旗沟脑片麻状花岗闪长岩成矿地质体影响范围之内有NWW向偏脆性构造破碎带发育的部位,或者是有隐伏成矿地质体的附近。

The Wulonggou gold ore field is located in the middle part of East Kunlun orogenic belt,which hosts several gold deposits occurring mainly along three NWW-trending fault fracture zones,i.e.Yanjingou,Yinshigou-Hongqigou and Sandaoliang-Kushuiquan zones.Comprehensive analysis of the geological characteristics indicates that gold deposits are low-middle temperature hydrothermal in genesis and mineralization type is altered rocks in structural fracture zones.Gold mineralization occurred at about 195~319℃ of temperature,mineralization material derived mainly from the crust with part from the mantle,and ore-forming fluid was mixing of magmatic water and meteoric water.The mineral assemblage is characterized by fine-grained pyrite,fine needle arsenopyrite and invisible grains of gold.Comparison study was conducted in aspects such as spatial distribution of geological bodies and deposits,correlation of geological bodies and ore-forming materials,as well as the diagenetic epoch and metallogenetic epoch between geological bodies and deposits.The results show that the Hongqigounao gneissic granodiorite belongs to metallogenic geological bodies of the Wulonggou gold deposits and provides most of ore-forming elements.A large amount of elongated diorite are entrapped within the geological bodies and minerals underwent distinct ductile deformation,suggesting characteristics of syntexis with dominant crust material and minor mantle material,and emplacement of syn-tectonic intrusive rock under the condition of NEtrending stress in Early Indo-Chinese epoch about 239~244 Ma.During the process of syntexis,the addition of mantle material brought more metallic elements,and syn-tectonic emplacement facilitated gold element easily to activate and migrate into mineralization process under the influence of directional stress.Based on Rb-Sr isochron age of quartz fluid inclusion,the gold deposits formed at about 237 Ma,indicating that mineralization occurs in Early Indo-Chinese epoch,followed the replacement of the disseminated pyrite-rich granitic complex at 210 Ma.The gold deposits are controlled by ore-bearing geological bodies(Hongqigounao granodiorite)and NWW-trending structural belts,with gold mineralization occurring in the NWW-trending structural belts about 1~3.0 km far away from ore-bearing geological bodies.If no NWW-trending structural zone with effect range of the metallogenic geological bodies,there are no space for Au-bearing bodies.Even the places in which there are NWW-trending structural zones far from effect range of ore-forming geological bodies,gold mineralization weakens quickly.The direction of further prospecting for gold deposits should concentrate on the places with well-developed NWW-trending structural belts,on which the Hongqigounao gneiss granodiorite still impose its influence,or the places close to hidden geological bodies.