黑龙江金厂铜金矿床闪长玢岩地球化学及锆石U-Pb年代学

黑龙江省东宁金厂铜金矿床为最新勘查突破的特大型矿床,矿床矿体类型以角砾岩型为主,且角砾岩型矿体与闪长玢岩岩体空间关系密切。岩相特征显示闪长玢岩为多斑-基质隐晶结构,斑晶以斜长石、角闪石为主,并见少量辉石。闪长玢岩SiO2含量为54.62%～67.82%,平均60.33%;Al2O3含量为14.52%～18.25%,平均16.62%,且K2O/Na2O为0.06～0.31,均小于0.5,属于亚碱性岩系并具钙碱性演化趋势,但钾含量较低。稀土元素的LREE/HREE值较高,介于5.06～14.24之间,平均9.16;δEu为0.85～1.46,平均1.21,表现为正Eu异常。微量元素以低Y和Yb,高Sr为特征,其Sr/Y值为35.87～111.4,平均57.57(>40);此外,微量元素富集大离子亲石元素(LILE),亏损高场强元素(HSFE),尤以Nb、Ta和Ti亏损最为显著,且见Pb富集明显。地球化学特征显示闪长玢岩具有埃达克质岩的特征,表明闪长玢岩不仅为重要的含矿母岩,而且指示金厂金矿具备进一步找矿的潜力。同时,闪长玢岩的地球化学特征还显示其岩浆演化以结晶分异为主,而岩浆则可能起源于俯冲流体交代的地幔楔部分熔融,岩浆上涌时受地壳混染。闪长玢岩的锆石U-Pb年龄介于118.1±1.6Ma～115.7±2.0Ma之间,结果表明118.1±1.6Ma可以代表金厂斑岩型铜金矿床尤其是角砾岩型矿体的成矿时代,与区域120～110Ma的大规模岩浆活动时间一致,说明金厂斑岩型铜金矿床的成矿可能与早白垩纪太平洋板块的俯冲作用有关。区域上寻找同时期的斑岩型-浅成低温热液型铜金矿床潜力巨大。

Geochemisry and zircon U-Pb geochronology of the diorite porphyry associated with the Jinchang Cu-Au deposit, Heilongjiang Province

The Jinchang Cu-Au deposit,a super-large ore deposit explored in the latest,is mainly of breccia-type ore body and is spatially closely associated with diorite porphyry which is apophysis like and porphyry structure with mainly plagioclase,hornblende and little pyroxene as phenocryst.Major element data show that the SiO2 content of diorite porphyry is 54.62%～67.82%,average as 60.33%;Al2O3 content is 14.52%～18.25%,an average of 16.62%,and ratio of K2O/Na2O is 0.06～0.31,less than 0.5.All these indicate that diorite porphyry belongs to sub-alkaline series and have a calc-alkaline evolutionary trend with a lower potassium content.While the LREE/HREE ratio of the porphyry diorite is relatively higher,between 5.06 and 14.24 with an average of 9.16 and the δEu of 0.85 to 1.46 shows a positive anomaly.Then,trace elements of porphyry diorite shows low Y and Yb,but high Sr.The ratio of Sr/Y is between 35.87 and 111.4,average as 57.57(>40) .Moreover,the primitive mantle-normalized trace element spider diagram shows that the diorite porphyry enriched in large ion lithophile elements(LILE) while depleted in high field strength elements(HSFE) ,especially Nb,Ta and Ti depletion,besides some enrichment of Pb.The geochemical data suggests that the diorite porphyry is probably adakitic rock and were produced by crustal contamination and fractionation of mafic magmas generated from partial melting of mantle source which had been metasomatismed by the subduction fluid.In addition,an 118.1±1.6Ma to 115.7±2.0Ma diagenetic age and an 118.1±1.6Ma mineralization age of diorite porphyry in Jinchang deposit,consistence with the 120～110Ma magmatic activities epoch in the eastern part of Jilin and Heilongjiang provinces,revealed that the Jinchang porphyry Cu-Au metallogenesis possiblely related to the Early Cretaceous subduction of the Pacific plate.It is potential to exploration the porphyry-epithemal system copper-gold deposit of the same period in the eastern part of Jilin and Heilongjiang provinces.