黔西南架底金矿床载金黄铁矿成矿物质来源和成矿机制探讨:来自原位硫同位素的证据  

Source of Ore-forming Materials and Mineralization Mechanism of Gold-bearing Pyrite in the Jiadi Gold Deposit,Southwestern Guizhou:Evidence from in situ Sulfur Isotope

作　　者：何虎军[1,2] 田冲 张文高 杨兴科[1,2] HE Hujun;TIAN Chong;ZHANG Wengao;YANG Xingke(School of Earth Science and Resources,Chang’an University,Xi’an 710054,Shaanxi,China;MOE Key Laboratory of Western Mineral Resources and Geological Engineering,Xi’an 710054,Shaanxi,China;Shaanxi Branch of China National Geological Exploration Center of Building Materials Industry,Geological Survey Institute,Xi’an 710003,Shaanxi,China;Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China)

机构地区：[1]长安大学地球科学与资源学院,陕西西安710054 [2]西部矿产资源与地质工程教育部重点实验室,陕西西安710054 [3]中国建筑材料工业地质勘查中心陕西总队地质调查院,陕西西安710003 [4]中国地质科学院地质力学研究所,北京100081

出　　处：《大地构造与成矿学》2023年第4期791-800,共10页Geotectonica et Metallogenia

基　　金：中国地质调查局地质调查项目(DD20190161);中国地质科学院基本科研业务费项目(DZLXJK201904);陕西省自然科学基金项目(2023-JC-YB-261);贵州省科技计划项目(黔科合支撑[2021]一般408);贵州地矿局重大项目(黔地矿科合[2021]1号)联合资助。

摘　　要：架底金矿床是黔西南玄武岩分布地区较为典型的金矿床之一,该矿床载金黄铁矿普遍具有环带结构,显示出多期次、多来源的特征,对成矿物质来源和矿床成因研究提出挑战。本文基于野外认识和室内显微镜下的观察,将不同形态的黄铁矿划分为三个期次:①成矿前的黄铁矿为草莓状黄铁矿,是沉积期黄铁矿的典型代表;②成矿期的黄铁矿有两种:一种呈自形‒半自形,粒径较大,几十微米到100μm不等,核部有较多的裂隙发育,背散射图像显示核部周围发育有环带,通常呈脉状产出;另一种为均质结构的细粒五角十二面体的黄铁矿,粒径大约都在50μm左右,无环带结构;③成矿期后的黄铁矿颗粒较大,多为立方体和不规则状产出,同样也发育有环带结构。在此基础上,利用LA-MC-ICP-MS分析方法对不同期次的黄铁矿进行原位S同位素测试,结果显示:成矿前无环带黄铁矿δ34S的值为-23.47‰~-19.76‰,表现为较大的负值,显示沉积硫的特征;成矿期的环带黄铁矿以及同期均质五角十二面体黄铁矿的δ34S值为-1.39‰~4.45‰;成矿期后的环带黄铁矿δ34S的值为-1.57‰~-0.91‰,两者整体均显示岩浆硫的特征,但属于不同阶段的产物。综合前人研究成果,推测成矿物质主要来源于地幔,有部分地壳物质的混入,可能经历了两个过程,首先是铁白云石与富集CO_(2)的流体反应,释放出Fe^(2+)、Mg^(2+)、Ca^(2+)离子,形成白云石,为之后的硫化、黄铁矿化提供必需的Fe质,随后含H3AsO_(3)^(0)、[Au(HS)2]–、富H_(2)S的还原性流体与Fe^(2+)反应形成含砷黄铁矿、黄铁矿,金以Au+的形式进入含砷黄铁矿,完成富集。The Jiadi gold deposit is one of the typical gold deposits in the basalt distribution area of southwestern Guizhou.The Au-bearing pyrite in this area is generally zoned and has the characteristics of multi-period and multi-source,therefore,it is very challenging to delineate the source of ore-forming materials and the genesis of the deposit.Based on the field observation and laboratory microscope study,three stages of pyrite were recognized.The pre-ore pyrite is strawberry-shaped pyrite,which is typically formed in sedimentary period.The ore stage pyrite can further be subdivided into zoned and non-zoned types.The zoned pyrite usually occurs as veins,euhedral-subhedral,10 to 100μm in size,the zonation around the pyrite cores is obvious in back-scattered electron images,and the cores are highly fissured.The non-zoned pyrite is commonly pentagonal-dodecahedral pyrite of about 50μm in size.The post-ore pyrite is large,cubic or irregular in shape,and zonation is common.LA-MC-ICP-MS in situ sulfur isotope analysis of pyrite of different stages showed that theδ34S values of the pre-ore pyrite vary from-23.47‰to-19.76‰,indicative of sedimentary S.δ34S values of the ore-stage pyrite are-1.39‰to 4.45‰,andδ34S values of the post-ore pyrite are-1.57‰to-0.91‰,suggestive of magmatic S.On the basis of previous studies,it is inferred that the ore-forming materials were mainly derived from the mantle,along with some crustal materials.The ore mineralization may involve two processes:firstly,the reaction between ankerite and a CO_(2)-rich fluid releases Fe^(2+),Mg^(2+),Ca^(2+)ions,forms dolomite and necessary Fe for the subsequent sulfidation or pyritization.The H3AsO_(3)^(0),[Au(HS)2]-and H_(2)S-rich reductive fluid reacts with Fe^(2+)to form arsenian pyrite and pyrite,during which gold enters into the lattice of arsenian pyrite in the form of Au+and consequently,the gold enrichment.

关 键 词：架底金矿床 成矿期次 原位S同位素 成矿物质来源 成矿机制 

分 类 号：P611[天文地球—矿床学] P597[天文地球—地质学]