金矿床中金与黄铁矿和毒砂的关系  

Hydrothermal evolution of gold-bearing pyrite and arsenopyrite from different types of gold deposits

作　　者：卢焕章[1,2] 朱笑青[2] 单强[3] 王中刚[2] 

机构地区：[1]University of Quebecat Chicoutimi,Quebec G7H2B1,Canada [2]中国科学院地球化学研究所,贵州贵阳550002 [3]中国科学院广州地球化学研究所,广东广州510640

出　　处：《矿床地质》2013年第4期823-842,共20页Mineral Deposits

基　　金：国土资源部公益性行业科研专项经费项目(编号:201011046)资助

摘　　要：卡林型金矿中的金,以肉眼,甚至在显微镜下都看不到,因而称之为"不可见金"。经过金的物相分析,发现Au与毒砂、黄铁矿有关。进一步的问题是:Au在毒砂、黄铁矿中呈何状态分布,是呈微细的独立矿物?还是类质同象?是以化学键进入毒砂、黄铁矿的晶格?还是吸附在其表面?进一步的研究表明,世界上其他类型金矿,如浊积岩型金矿、造山带内太古代绿岩带金矿、变质金矿、与火成岩有关的金矿,甚至含金的块状硫化物矿床,其中的金除了以自然金(可见金)产出外,在黄铁矿、毒砂、辉锑矿、雄黄等硫化物中还含有不可见金。从不可见金到可见金,需经过热液蚀变作用,在高As条件下,温度和硫逸度的升高,可溶出不可见金,在温度下降和还原条件下,Au以可见金形式存在于蚀变环带中。这种从不可见金到可见金的转换过程,反映了Au、As、S以及Fe等元素的地球化学特征。金矿中的黄铁矿和毒砂具有相似的结构,包括在其原始生长的晶体中含有不可见金,并且在稍后的成矿阶段内形成赋存有可见金的蚀变环带。蚀变环带以As含量高为特征,并且,后期的可见金是沿裂隙或毒砂与黄铁矿的粒间分布。可见金是热液活化了矿物内的不可见金而形成的。This study investigates the microstructures, geochemistry, and hydrothermal evolution of gold-bearing pyrite and arsenopyrite from Carlin type （ both in the USA and China）, turbidite hosted gold deposits of China, intrusion related gold deposits, epithermal gold deposits and six orogenic gold deposits in the Archean Eastern Goldfields Province, Western Australia. Scanning electron microscope （SEM）, EPMA, and LA-ICP-MS analy- ses show that the gold-bearing pyrite and arsenopyrite possess a number of similar textural features, including the occurrence of invisible gold within initial phases of growth, and later-stage visible gold associated with alte- ration rims. The alteration rims are characterized by a higher-than-average atomic mass （mainly owing to arsenic enrichment） and are preferentially located along fractures and grain boundaries in the pyrite and arsenopyrite. These observations suggest that visible gold formation is associated with hydrothermal alteration of preexistingpyrite and arsenopyrite. Textural observations and LA-ICP-MS data suggest that some invisible gold was remo- bilized from early-formed pyrite and arsenopyrite to form visible gold during the development of these alteration rims and fractures. Based on sulfide stability relations, the authors hold that the development of arsenopyrite al- teration rims associated with late-stage visible gold formation was related to an increase in temperature （maxi- mum increase from 310℃ to 415℃ ） and up to six orders of magnitude increase in sulfur [ugacity. It is suggested that the transform from invisible to visible gold depends on the fluid conditions and chemistry.

关 键 词：地球化学 不可见金 可见金 黄铁矿 毒砂 热液 蚀变环带 

分 类 号：P618.51[天文地球—矿床学]