湘西大溶溪钨矿床矽卡岩矿物的矿物学、地球化学特征及其形成机制  

Mineralogical, geochemical characteristics and formation mechanism of skarn minerals in the Darongxi tungsten deposit, western Hunan

作　　者：张龙升 彭建堂[2,3] 林芳梅[1,2,4] ZHANG Longsheng;PENG Jiantang;LIN Fangmei(Exploration Unit of North China Geological Exploration Bureau,Langfang,Hebei,065201;School of Geosciences and Info-physics&Key Laboratory of Non-ferrous Metals Metallogenic Prediction of Ministry of Education,Central South University,Changsha,410083;State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang,550002;Hebei Huakan Geological Exploration Co.,Ltd.Langfang,Hebei,065201)

机构地区：[1]华北地质勘查局综合普查大队,河北廊坊065201 [2]中南大学地球科学与信息物理学院,教育部有色金属成矿预测重点实验室,长沙410083 [3]中国科学院地球化学研究所,矿床地球化学国家重点实验室,贵阳550002 [4]河北华勘地质勘查有限公司,河北廊坊065201

出　　处：《地质论评》2020年第1期113-139,共27页Geological Review

基　　金：国家自然科学基金资助项目(编号:41972090、41473043);国家重点研发计划项目(编号:2016YFC0600207,2018YFC0603500)的成果~~

摘　　要：大溶溪钨矿床为湘西地区一层控型白钨矿矿床,白钨矿主要分布于矽卡岩和石英网脉中。在详细野外地质调查和室内镜下观察的基础上,利用EPMA和高精度LA-ICP-MS测试技术,对该矿主要矽卡岩矿物的矿物学和地球化学特征进行了研究,并初步揭示了其形成机制。研究表明,大溶溪矿区含钨矽卡岩为还原型类矽卡岩,矽卡岩矿物主要为辉石和石榴子石;辉石为透辉石-钙铁辉石-锰钙辉石系列;石榴子石以钙铝榴石为主,但锰铝榴石+铁铝榴石含量也较高。该区辉石REE具有总量较低、轻重稀土元素分馏不明显、正Ce和正Eu异常的特征;而石榴子石REE具有较高的稀土总量,呈现明显的重稀土元素富集、轻稀土元素亏损、负Ce异常、强烈正Eu异常的特点。辉石Ce和Eu异常可能与其形成时的水/岩反应及氧化还原条件有关。REE进入石榴子石的方式以REE3+等价置换Al3+的形式为主,正Eu异常主要为Eu2+等价置换钙铝榴石Ca2+所致,而负Ce异常则反映出热液沉淀正Ce异常辉石之后热液体系中贫Ce元素。该区含钨矽卡岩主要为热液与含锰灰岩在平衡机制下发生扩散交代作用所形成;而含钨石英网脉内发育的辉石、石榴子石等钙硅酸盐矿物,则是热液沿裂隙、孔隙对富钙变质砂岩进行交代的产物。矽卡岩形成过程中,相对贫Mn的辉石和石榴子石主要受交代流体作用控制,形成于一种相对高温、中等水/岩比的条件下;而相对富Mn的辉石和石榴子石,则可能是形成于靠近围岩一侧的相对低温、低水/岩比的环境中,部分锰质来自被交代的围岩。Objectives: The Darongxi tungsten deposit,situated in Xuefeng mountain of the Ghiangnania terrain between the Yangtze and Cathaysian blocks,western Hunan,is a typical strata-bound scheelite deposit where the W mineralization is hosted by skarn and quartz stockworks along the contacts among metasandstone,marble and slate in the Lower Member of Nantuo Formation belonging to Nanhuan System. The strata-bound scheelite skarns and stockworks in this deposit contain amounts of garnets and pyroxenes which are generated by the diffusion metasomatism between host rocks and the fluid deriving from the intrusion of the Dashenshan granitic stock. This work tries to provide some advices and evidences for how to reveal the formation mechanism of stratiform and stratabound tungsten skarn in the future.Methods: As the major skarn minerals,garnet and clinopyroxene from the scheelite skarns and stockworks were studied. Based on the field investigation and the microscopic observation,the major elements and trace elments compositons of garnet and clinopyroxene were analysed by EPMA and LA-ICP-MS at the State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences( Guiyang).Determination of the major element compositions of garnet and clinopyroxene was performed by wavelength-dispersive spectrometry using an EPMA-1600 electron probe microanalyser,at an accelerating voltage of 25 kV,a beam current of 10 n A,a beam diameter of 10 μm,and using artificial synthesized silicate and oxide minerals as standards. The calculations are based on the Geokit( 2010) excel program.Twenty eight trace elements of garnet and clinopyroxene were analysed by laser ablation inductively coupled plasma mass spectrometry( LA-ICP-MS) using Perkin-Elmer Sciex ELAN DRC-e ICP-MS. The laser was operated with a 40μm diameter beam and ablating number frequency 120. Calibration was performed using NIST SRM610 glass as external standard,and BIG-1 G,BHVO-2 G,BCR-2 G,GSE-1 G,QC KL2 and QC ML3 B standards,with29Si and44Ca,previou

关 键 词：矿物学特征 地球化学特征 形成机制 矽卡岩矿物 大溶溪钨矿床 湘西 

分 类 号：P618.67[天文地球—矿床学]