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    吉林白山五道羊岔新太古代大型钒钛磁铁矿床地质特征及锆石U-Pb年龄

    Geological characteristics and zircon U-Pb age of the Wudaoyangcha Neoarchaean vanadic titanomagnetite deposit in Baishan, Jilin Province

    • 摘要: 吉林白山五道羊岔新太古代大型钒钛磁铁矿是国内外首次发现的产于斜长角闪岩层状侵入体内的岩浆型铁矿,对于相似成矿地质条件区矿产资源勘查具有重要意义。该矿床位于吉林省南部龙岗古陆核南部边缘,板石沟绿岩带北侧。Ⅰ、Ⅱ、Ⅵ号矿体位于斑杂状斜长角闪岩层状侵入体内,并具有成因联系。该岩体原岩为正角闪岩,构造环境为汇聚边缘岛弧环境。矿体形态为层状,矿石结构主要为自形-半自形-他形晶粒状结构、固熔体分离结构、海绵陨铁结构,矿石构造有致密块状构造、条带状构造、浸染状构造等。矿石金属矿物主要为磁铁矿、钛铁矿。对磁铁矿、钛铁矿进行了电子探针微区成分分析,磁铁矿成因类型为岩浆熔离钛磁铁矿型。钛铁矿与理论化学成分基本一致。对斑杂状斜长角闪岩层状侵入体中锆石进行了地球化学分析,其稀土元素及微量元素特征显示锆石为岩浆锆石,采用LA-ICP-MS 法进行了U-Pb 定年,获得一条较好的不一致线,上交点年龄为(2526±35)Ma。

       

      Abstract: Located in Baishan City of southern Jilin Province, the Wudaoyangcha vanadic titanomagnetite deposit is a large- size magma type iron deposit lying in amphibolite layered intrusions in Archaean strata, founded for the first time in the world. The discovery of the deposit has important implications for mineral resource exploration in areas with similar geological conditions. The deposit is located in northern Banshigou greenstone belt on the southern margin of Longgang paleo-continental nucleus of the Liao- Ji paleocontinent. No. Ⅰ, Ⅱ and Ⅵ orebodies lie in Wudaoyangcha amphibolite layered intrusions, and vanadic titanomagnetite mineralization is closely related to the layered intrusions. The protolith of the layered intrusions belongs to orthometamorphite, and its tectonic environment belongs to the island arc basalts in the convergent margin of the plate. Orebodies are mainly in layered form. Ore textures include mainly crystallization texture, solid solution separation texture and sideronitic texture. Ore structures are dominated by massive structure, disseminated structure, spongy- meteoritic structure and layered structure. Magnetite- ilmenitepyrite makes up most metallic mineral association of the ore. The magnetite and ilmenite of the vanadic titanomagnetite ore was investigated by means of EPMA. The magnetite is genetically magmatic liquation titanomagnetite. The chemical composition of the ilmenite is generally consistent with the theoretical constituents of ilmenite. The authors carried out U-Pb dating and micro-scale in situ trace elements and REE research on zircons separated from the Wudaoyangcha amphibolite layered intrusions. The characteristics of trace elements and REE show that these zircons are magmatic zircons. Zircon LA-ICP-MS U-Pb dating yielded a discordant age, with the discordant upper intercept age for 28 spots of sample WCD1 being (2 526±35) Ma. This age represents the crystallization age of layered intrusions.

       

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