陕西略阳煎茶岭镍矿床酸性侵入岩形成时代及成矿意义

Geochronology of Acid Intrusive Rocks of the Jianchaling Nickel Deposit in Lueyang,Shaanxi and Its Metallogenic Implications

煎茶岭镍矿是一个与镁质超基性岩和酸性侵入岩有关的镍矿床。矿床地质研究发现,矿体主要赋存于花岗斑岩北侧超基性岩体内,矿石中交代状、浸染状、网脉状结构发育,显示热液改造成因矿床的典型结构、构造特征。岩、矿石地球化学及同位素分析表明,煎茶岭镍矿床与典型的镁铁质岩浆硫化物矿床不同,镍矿床在成矿过程中虽继承了超基性岩中的成矿物质,但受到花岗斑岩强烈改造有关,矿床成因类型为岩浆热液改造型。花岗斑岩和钠长斑岩中锆石U-Pb测年表明,花岗斑岩U-Pb年龄为859±26 Ma,钠长斑岩U-Pb年龄为844±26 Ma,认为煎茶岭镍矿成岩成矿时代为新元古代晋宁期,非前人所认为的海西期或印支期,是全球Rodinia超大陆裂解事件在扬子板块西北缘的重要响应。

Jianchaling nickel deposit is related to a magnesium ultramafic rocks and acidic intrusive rocks.Geological studies have found that ore bodies mainly occur in ultramafic rocks which are north to granite porphyry.The ores is metasomatic,disseminated and network structure,which is the typical structure of hydrothermal alteration.Rock geochemistry,ore geochemistry and isotopic analysis showed that there are many differences between Jianchaling nickel deposit and typical magmatic sulphide deposits.Jianchaling nickel deposit,although inherited ultrabasic rocks into minerals,has been transformed by granite porphyry in the mineralization process and is a magmatic hydrothermal transformation type.Zircon U-Pb dating results show that the granite porphyry U-Pb age is 859±26Ma and albite U-Pb age is 844±26Ma.Thus,the formation of the rocks and ores of Jianchaling Nickel deposite is Neoproterozoic Jinningian rather than Hercynian or Indosinian as the predecessors perceived.It responds to the early bearkup of the Rodinia supercontinent in the northwestern margin of the Yangtze plate.