山东桃科太古代岩浆铜镍硫化物矿床成矿作用研究

The formation age of the Ni-Cu sulfide deposits in China is from Neoproterozoic to Mesozoic, with two peaks in Neoproterozoic and late Paleozoic. There have no reported with the Archean magmatic Ni-Cu sulfide deposit in China. The Shandong Taoke magmatic Ni-Cu sulfide deposit is located in the 17 km southeast of Jinan city, eastern part of the North China Craton and distributed in the area of Trondhjemite – Tonalite – Granodiorite (TTG) granite and the amphibolite facies metamorphic rock of the Taishan group. The Taoke deposit formed in Neoarchean (2.7Ga), it may be the oldest magmatic Ni-Cu sulfide deposit in China. However, it almost has no research about this deposit. This study plan to use the single-grain zircon dating and Hf, O isotope, major and trace elements in situ of olivine, pyroxene and magnetite, whole rock trace element and Sr–Nd–Pb isotopes, sulfide platinum group elements (PGE) and Re-Os, S isotopes to assess mantle source characteristics, magma evolution and crustal contamination of the parental magma for sulfide saturation, and the hydrothermal superimposed transformation for the contribution of mineralization, discuss the Archean mantle magmatism in North China Block. We also discuss the metallogenic mechanism of Ni-Cu sulfide deposits which within the craton stable conditions in China, with Taoke deposit as an example. This project study on the Archean magmatic Ni-Cu sulfide deposit in China. Our results will provide new data for the metallogenic theory and mineralization, as well as theoretical basis for the prospecting exploration in this type of ore deposit.

我国铜镍矿床形成时代较广，主要集中在新元古代与晚古生代时期，太古代未见有报道。山东桃科矿床位于华北板块东部陆块，形成于新太古代时期（2.7Ga），可能是我国形成时代最老的铜镍矿床；然而，该矿床的成矿作用尚未有研究。本项目拟在野外地质调查和矿物岩石学、矿床学研究基础上，对岩体开展锆石U-Pb定年和Hf、O同位素、矿物原位微量元素、全岩Nd-Sr-Pb以及硫化物Re-Os、S同位素与铂族元素研究，示踪岩体的岩浆源区和母岩浆性质；从大地构造背景、岩浆源区性质、岩浆演化和地壳混染与硫化物熔离等方面综合研究，探讨华北板块太古代时期地幔岩浆作用；以桃科矿床为例，探讨我国在克拉通内部稳定环境下的铜镍硫化物矿床成矿作用。该项目对我国太古代时期岩浆铜镍硫化物矿床开展深入、全面的研究工作，成果将为丰富和完善我国岩浆铜镍硫化物矿床成矿理论和成矿作用提供新资料，也可为我国该类型矿床的找矿勘查提供理论依据。

山东桃科镁铁-超镁铁质杂岩体位于华北克拉通东部陆块，由边部为一个大的辉长苏长岩体、中心为一个小的硫化物矿化的橄榄二辉岩体以及一些辉绿岩脉组成。硫化物矿体镍平均品位0.66%、铜0.62%和~1g/t PGE，硫化物矿物主要有黄铜矿、镍黄铁矿、磁黄铁矿和针镍矿。镁铁质岩石和超镁铁质岩石的锆石U-Pb年龄分别为2520.3 ± 6.5 Ma、2537 ± 12 Ma，地球化学表现为与现代弧玄武岩类似的轻稀土富集Nb-Ta负异常特征，εNd(t)=1.0~3.3，锆石εHf(t)=0.2~2.3。通过模拟计算认为，桃科岩体是新太古代镁铁-超镁铁质弧岩浆作用的产物，其岩浆源区为含石榴子石的二辉橄榄岩地幔源区，部分熔融深度>85 km。Pd与IPGE和Ir与PPGE均具有较好的相关性表明PGE主要受母岩浆中初始PGE浓度和R因子的影响。Os、S同位素特征表明分离结晶和地壳硫的加入是发生硫饱和的主要原因。从桃科的弧岩浆作用成矿特征来看，可以在鲁西地区以及世界上其他具有类似弧岩浆作用的地区寻找桃科这种类型的矿床。