胶东焦家金成矿带2420~3206 m垂深金矿物和黄铁矿微量元素特征

Characteristics of trace elements of gold minerals and pyrite in 2420~3206 m vertical depth in Jiaojia gold metallogenic belt,Jiaodong

在胶东莱州吴一村地区完成的3266.06 m深钻,是目前焦家金成矿带最深见矿钻孔,研究钻孔揭露的深部矿石中金矿物及黄铁矿微量元素特征,对探讨深部成矿作用演化具有重要意义。笔者采取深钻中2420~3206 m垂深的岩(矿)芯样品进行了详细的岩相学和矿相学研究,结合扫描电镜和电子探针微区分析,研究了矿石中金矿物的赋存状态和成分。对不同成矿阶段形成的黄铁矿进行了LA-ICPMS微量元素分析。研究结果表明,深部矿石中载金矿物主要为黄铁矿,其次为石英、黄铜矿、方铅矿,可见金主要以自然金和银金矿的形式存在,以晶隙金和裂隙金为主,其次为包体金。与浅部金矿床比较,深部金的成色较高。黄铁矿分为6种类型,第Ⅰ成矿阶段形成富Co型黄铁矿Py1,第Ⅱ成矿阶段形成富Ni型黄铁矿Py2a和Py2b,第Ⅲ成矿阶段形成富Au、As型黄铁矿Py3a和富Au、Ag、Pb、Bi型黄铁矿Py3b,第Ⅳ成矿阶段形成贫微量元素黄铁矿Py4。其中,Py1和Py2a发生强烈破碎,裂隙表面对热液中的Au络合物产生吸附作用,对金沉淀富集起重要作用。黄铁矿中Co、Ni、As等微量元素主要以类质同象形式赋存,而Au、Ag、Cu、Pb、Zn、Bi等主要以纳米级、微米级矿物包体形式赋存。Pb+Bi、Cu+Pb+Zn、Te+Bi与Au+Ag呈明显正相关,而Au与As相关性较差。黄铁矿中Co、Ni含量较低,而Au+Ag+As或Au+Ag+Pb+Bi+Cu含量较高指示成矿有利。另外,黄铁矿中Co、Ni含量较高,并且破碎强烈,成矿相关元素含量较高也指示成矿有利。

The 3266.06 m deep drilling completed in Wuyi Village,Laizhou,Jiaodong is the deepest ore-finding bore-hole in Jiaojia metallogenic belt at present.It holds great significance in studing the occurrence of gold and the composition of trace elements of pyrite in the deep ore revealed by the borehole,revealing insights into deep min-eralization evolution.Detailed petrographic and mineralogical studies were carried out on rock core samples ob-tained from 2420 to 3206 m vertical depth in deep drilling.The occurrence and composition of gold minerals in ores were examined using scanning electron microscope(SEM)and electron probe micro analysis(EPMA).LA�ICPMS analysis was performed on trace elements in pyrite from different ore-forming stages.The results indicate that the main gold-bearing minerals are pyrite,followed by quartz,chalcopyrite,galena.The visible gold mainly exists in the form of natural gold and electrum,mainly in the form of crystal interface gold and fissure gold,sec-ondly inclusion gold in the deep Jiaojia metallogenic belt.Compared with the shallow areas of the metallogenic belt,the deep gold exhibits higher fineness.Pyrite can be classified into six types:Co-rich Py1 formed in the first ore-forming stage,Ni-rich Py2a and Py2b formed in the second ore-forming stage,and Au,As-rich Py3a and Au,Ag,Pb,Bi-rich Py3b formed in the third ore-forming stage,Py4 with poor trace elements was formed in the fourth ore-forming stage.Py1 and Py2a are strongly crushed and the fracture surfaces adsorb Au complexes in the hydrothermal solution,which plays a crucial role in gold precipitation and enrichment.Trace elements such as Co,Ni and As in pyrite are primarily in the form of isomorphism,while Au,Ag,Cu,Pb,Zn and Bi mainly exist as nano-scale and micron scale mineral inclusions.Pb+Bi,Cu+Pb+Zn,Te+Bi are positively correlated with Au+Ag,while Au shows a weak correlation with As.The trace element characteristics of pyrite indicate the multi-ori-gin of ore-forming hydrothermal fluid and ore-forming materials which are mixed sources of Precambrian meta-morphic basement rocks,Mesozoic magmatites and a small amount of mantle materials.The content of Co and Ni in pyrite is low,while the content of Au+Ag+As or Au+Ag+Pb+Bi+Cu is high,indicating favorable mineraliza-tion.In addition,the content of Co and Ni in pyrite is high,and the crushing is strong,and the content of ore�forming related elements is high,indicating that the mineralization is favorable.