镇旬盆地南缘淋湘金矿床地质特征及矿床成因探讨  

Geological characteristics and genesis of the Linxiang gold deposit in southern margin of the Zhenxun Basin

作　　者：薛仲凯 范堡程 李航 王长明[1] 高永宝 魏立勇 马承 孟五一 XUE ZhongKai;FAN BaoCheng;LI Hang;WANG ChangMing;GAO YongBao;WEI LiYong;MA Cheng;MENG WuYi(College of Geosciences and Resources,China University of Geosciences(Beijing),Beijing 100083,China;Xi’an Center of Mineral Resources Survey,China Geological Survey,Xi’an 710100,China;Technology Innovation Center for Gold Mine Exploration,China Geological Survey,Xi’an 710100,China;Department of Geology,Northwest University,Xi’an 710069,China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]中国地质调查局西安矿产资源调查中心,西安710100 [3]中国地质调查局金矿勘查技术创新中心,西安710100 [4]西北大学地质学系,西安710069

出　　处：《岩石学报》2024年第6期1748-1766,共19页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41872080);中国地质调查项目(DD20220975)联合资助.

摘　　要：淋湘金矿床是南秦岭镇安-旬阳盆地南缘一处典型的微细浸染型金矿床,矿体受近EW向断裂控制,赋矿围岩为下泥盆统西岔河组斑点状千枚岩和中泥盆统杨岭沟组灰岩夹千枚岩。由于对该矿床成矿物质来源的认识存在不同观点,致使对该矿床的成因存在热水沉积成因、喷流沉积-后期热液叠加改造等多种观点,难以建立统一的成矿模式。本文以淋湘金矿床的黄铁矿和自然金为研究对象,对其开展电子探针、LA-ICP-MS原位微区硫同位素和微量元素分析,探讨金的赋存状态,限定成矿物质来源与矿床成因。研究结果表明,淋湘金矿床的金以裂隙金和包体金为主,少数以显微纳米金(Au 0)形式赋存于黄铁矿晶格中。Ⅱ成矿阶段硫同位素在16.28‰~17.84‰之间,平均值为16.91‰;Ⅲ成矿阶段硫同位素在15.19‰~15.68‰之间,平均值为15.51‰。这一特征与金龙山卡林型金矿床相似,成矿阶段具有地层硫特征,后期有岩浆硫的混入。从PyⅡ-Ⅲ阶段,Au、Ag、Cu、Pb、Zn、Pb、Bi等成矿元素均呈增加趋势,As元素含量呈下降趋势,Co、Ni元素含量略有上升。PyII的Co/Ni比值差异较大,可能与黄铁矿后期变质重结晶有关;PyIII大部分Co/Ni比值大于1.00,表明其为热液成因黄铁矿。不同元素之间相关性具有较大差异,成矿流体为混合源,推测在主成矿阶段晚期可能遭受岩浆热液事件扰动。主成矿阶段流体包裹体气相成分中CO_(2)等挥发分的逸失及CH_(4)的加入,表明流体发生了不混溶作用。综上所述,淋湘金矿床成因过程可总结为:随着大气降水和变质流体沿构造裂隙向上运移,该混合流体萃取地层中成矿物质,并在成矿有利部位因为流体不混溶作用导致成矿物质沉淀析出,而后期岩浆热液的加入使成矿物质进一步富集。The Linxiang gold deposit is a typical fine disseminated gold deposit in the southern margin of Zhenan-Xunyang Basin,South Qinling.The distribution of its orebody is controlled by the EW trending fault,which occurred in the spotted phyllite of the Lower Devonian Xichahe Formation and the limestone interlayered with phyllite of the Middle Devonian Yanglinggou Formation.The ore genesis of Linxiang deposit remains controversial due to the inconsistency of ore-forming materials,and related viewpoints about its mineralization include hydrothermal sedimentation and later hydrothermal superimposition on an exhalative sedimentation.In this paper,pyrite and native gold in the Linxiang gold deposit were studied by in situ EPMA and LA-ICP-MS analysis of sulfur isotopes and trace elements,aiming to discuss the occurrence of gold,define the source of ore-forming materials and the genesis of the deposit.The results show that the gold in the Linxiang gold deposit is mainly composed of fissure gold and inclusion gold,with a little of micro-nano gold(Au 0).The sulfur isotope in theⅡmineralization stage ranges from 16.28‰to 17.84‰with an average value of 16.91‰;the sulfur isotope in theⅢmineralization stage ranges from 15.19‰to 15.68‰with an average value of 15.51‰,which is similar to those in the Jinlongshan Carlin-type gold deposit.The metallogenic stage has the characteristics of stratigraphic sulfur,while the later stage has the mixture of magmatic sulfur.From the PyⅡ-Ⅲstage,the Au,Ag,Cu,Pb,Zn,Pb,Bi and other ore-forming elements all showed increasing trends,while the content of As showed a decreasing trend,and the content of Co and Ni increased slightly.PyII Co/Ni ratios varied greatly,which may be related to the recrystallization of pyrite;and this value of most of PyIII was above 1.00,demonstrating that it is hydrothermal pyrite.The correlation between different elements is quite different,the ore-forming fluid is a mixed source,and it is speculated that it may be disturbed by magmatic hydrothermal event

关 键 词：LA-ICP-MS EPMA 微量元素 矿床成因 淋湘金矿 

分 类 号：P575.1[天文地球—矿物学] P618.51[天文地球—地质学]