吉林官马金矿床成矿物质来源与形成时代

SOURCES OF ORE-FORMING MATERIALS AND MINERALIZATION AGE OF GUANMA GOLD DEPOSIT IN JILIN PROVINCE

官马金矿床位于华北地台北缘与兴蒙造山带东南端交汇部位,是吉林省中部地区的一个小型金矿床。矿床产于安山玢岩和中二叠统寿山沟组大理岩的接触带及其附近,矿体受NNW向构造破碎蚀变带控制明显。矿石中金属矿物主要有黄铁矿、毒砂、磁黄铁矿、闪锌矿和自然金等,非金属矿物有石榴子石、方解石、绿帘石等,围岩发育矽卡岩化、硅化、绿帘石化、绢云母化和碳酸盐化等蚀变现象。为确定该矿床的成矿物质来源和形成时代,本次研究主要开展了黄铁矿的S-Pb同位素分析以及黄铁绢英岩中绢云母40Ar-39Ar测年研究。结果表明,金矿石中3件黄铁矿的δ34S值分别为0.4‰,0.6‰,1.3‰,平均值为0.77‰,表现为深源硫的组成特征;黄铁矿中的206Pb/204Pb值为18.477,18.509和18.579,207Pb/204Pb值为15.599,15.603和15.611,208Pb/204Pb值为38.333,38.393和38.408,μ值为9.45,9.46和9.48,具有壳幔混源的特征;绢云母40Ar-39Ar坪年龄为190.88±4.09 Ma,限定其成矿时代为早侏罗世。根据官马金矿床的成矿地质条件、蚀变矿化特征以及与国内典型矽卡岩型金矿床的对比研究,综合确定官马金矿床成因类型为矽卡岩型;根据本次测年结果,并结合区内其它金矿床的成矿时代,认为官马金矿床与吉林中部的兰家、夹皮沟、海沟等金矿床同属于燕山早期古太平洋板块俯冲的构造背景之下大规模构造岩浆成矿作用的结果。

The small-scale Guanma gold deposit in central Jilin Province is tectonically located in the intersection of the southeastern segment of the Xing′an-Mongolian Orogenic Belt and the northern margin of the North China Platform.The deposit occurs in the contact zone between the andesitic porphyrite and the middle Periman Shoushangou Formation marbleand the gold ore body is controlled by the NNW-trending structural alteration zone,with pyrite,arsenopyrite,pyrrhotite,sphalerite and natural gold as metal minerals and with garnet,calcite,epidote,etc as nonmetallic minerals in the ores.Alterations of skarn,silicification,sericitization,etc.occur in the country rocks.Study of S-Pb isotope of the pyrite and sericite 40Ar-39Ar dating of the beresite is carried out in order to determine the source of ore-forming materials and mineralization age of the deposit.The results show that theδ34 S in three pyrite samples are 0.4‰,0.6‰,1.3‰,with an average of 0.77‰,characteristic of deep magma source.206Pb/204Pb values in pyrite samples are 18.477,18.509 and 18.579,207Pb/204Pb values are 15.599,15.603 and 15.611,and 208Pb/204Pb values are 38.333,38.393 and 38.408,respectively,with a calculatedμvalue of 9.45,9.46 and 9.48,indicating a crust-mantle mixed source origin.The sericite from the beresite yields a 40Ar-39Ar plateau age of 190.88±4.09 Ma(early Jurassic).According to the ore-forming geological conditions,alteration mineralization characteristics of the Guanma gold deposit,compared with the typical skarn type gold deposits in China,the Guanma gold deposit is assigned to skarn type.Based on the dating results,combined with the metallogenic ages of other gold deposits in the region,it is considered that the Guanma gold deposit and Lanjia deposit,Jiapigou deposit and Haigou gold deposits in central Jilin Province were resulted from large scale tectonic magmatic mineralization during the subduction of Pacific Ocean in the early Yanshan period.