黑龙江小多宝山矽卡岩型Fe-Cu矿床成矿时代及构造背景——来自岩石地球化学、锆石年代学及Hf同位素证据

Metallogenic epoch and tectonic setting of the Xiaoduobaoshan Fe-Cu deposit in Heilongjiang Province, China: Evidence from petrogeochemistry, zircon U-Pb geochronology and Hf isotopic compositions

黑龙江小多宝山Fe-Cu矿床是多宝山-三矿沟多金属成矿带内一典型的矽卡岩型矿床。根据矿物共生组合及矿脉穿切关系,将其成矿作用划分为两期:矽卡岩期和石英-硫化物期;进一步划分为五个阶段:石榴子石-辉石干矽卡岩阶段;绿帘石-阳起石等含水硅酸盐湿矽卡岩阶段;磁铁矿-镜铁矿-石英氧化物阶段;黄铁矿-黄铜矿-石英早期硫化物阶段以及方铅矿-闪锌矿-方解石晚期硫化物阶段。本文报道了该矿床成矿岩体花岗闪长岩的锆石U-Pb年龄、全岩地球化学及锆石Hf同位素数据。花岗闪长岩锆石加权年龄为176±1Ma(MSWD=0.10,n=23),反映小多宝山矿床成矿时代为早侏罗世。其岩石地球化学特征表现为:富钠(Na2O/K2O=1.45%~1.63%),准铝质(A/CNK=0.92~0.97),富集轻稀土元素(LREE)、大离子亲石元素(如Rb、Ba、Sr、K等),相对亏损高场强元素(如Ta、Nb、Ti等),(La/Yb)N=11.16~12.87,表现出弱的负Eu异常(δEu=0.85~0.92),显示出岛弧岩浆岩的地球化学亲缘性。综合岩石地球化学及同位素测试结果,小多宝山花岗闪长岩为准铝质高钾-钙碱性I型花岗岩,起源于幔源岩浆结晶分异作用。锆石Hf同位素εHf(t)为+7.6^+11.4,二阶段模式年龄(tDM2)为492~732Ma,指示其岩浆源区为古生代新生地壳的熔融。结合区域构造演化,推断小多宝山花岗闪长岩形成于古太平洋板块俯冲的构造环境。

The Xiaoduobaoshan Fe-Cu deposit is a typical skarn deposit which is located in the Duobaoshan-Sankuanggou metallogenic belt in Heilongjiang,China.Based on the mineral symbiotic assemblage and cutting relationships of ore veins,the mineralization process can be divided into two phases:skarn phase and quartz-sulfide phase.The two phases can be further divided into five stages:garnet-diopside(dry skarn stage);epidote-actinolite(wet skarn stage);magnetite-specularite-quartz(oxide stage);pyrite-chalcopyrite-quartz(early sulfide stage)and galena-sphalerite-calcite(late sulfide stage).The geochemistry,U-Pb chronology and Hf isotopic data of granodiorite in the Xiaoduobaoshan area were studied.The results of zircon U-Pb geochronology for the granodiorite show that the weighted mean age of the rock is 176±1Ma(MSWD=0.10,n=23),suggesting that the Xiaoduobaoshan deposit was formed in the Early Jurassic.Petrogeochemically,the granodiorite are characterized by high content of Na2O/K2O(1.45%~1.63%),the aluminum saturation index(A/CNK)is 0.92~0.97,belonging to metaluminous calc-alkaline rock series.The samples are enriched in LREE and large ion elements(e.g.,Rb,Ba,Sr and K),depleted in high field strength elements(e.g.,Ta,Nb and Ti).The index of(La/Yb)N is 11.16~12.87,with unobvious negative Eu anomalies(δEu=0.85~0.92),suggesting the island arc magmatic rocks geochemical relatedness.Integrating the study of geochemistry and isotopes,the granodiorite of Xiaoduobaoshan area belong to metaluminous high potassium calc-alkaline I-type granite,which originated from the crystallization differentiation of mantle magma.TheεHf(t)values of the granodiorite range from+7.6 to+11.4,and two-stage Hf model ages(tDM2)range from 492~732Ma,indicating that the magma source region is a partial melting of the new curst.Combined with regional tectonic environment,we concluded that the granodiorite of Xiaoduobaoshan area was formed in the tectonic environment of subduction of paleo-Pacific Plate.