黑龙江三矿沟铁铜矿床花岗闪长岩锆石U-Pb定年、岩石成因及构造意义

Zircon U-Pb dating,petrogenesis and tectonic significance of the granodiorite in the Sankuanggou skarn Fe-Cu deposit,Heilongjiang Province

黑龙江三矿沟Fe-Cu矿床是中亚造山带东段大兴安岭北部裸河-多宝山-三矿沟NW向成矿带中矽卡岩型矿床的典型代表。LA-ICP-MS锆石U-Pb年代学表明,与成矿密切相关的黑云母花岗闪长岩的锆石谐和年龄和238U/206Pb加权平均年岭分别为175.9±1.6Ma和175.9±1.1Ma,二者在误差范围内具有良好的一致性,表明多宝山成矿区在早侏罗世晚期存在一期重要的岩浆-热液成矿事件。三矿沟花岗闪长岩的元素地球化学特征具有岛弧岩浆岩的地球化学亲缘性:岩石富钠(Na2O/K2O=1.39～1.59),准铝质(A/CNK=0.87～0.91),富集轻稀土元素(LREE),(La/Yb)N=8.02～10.45,Eu显示弱负异常(δEu=0.82～0.98),富集大离子亲石元素(LILE,如Rb、Ba、K)和元素地球化学性质活泼的不相容元素(U、Th、Pb),相对亏损高场强元素(HFSE,如Nb、Ta、Zr、Hf、Ti)。Sr-Nd-Pb同位素分析结果表明:三矿沟花岗闪长岩具有低的Sr同位素初始比值((87Sr/86Sr)i=0.7041～0.7045)、高的Nd同位素初始比值((143Nd/144Nd)i=0.512556～0.512576)、正的εNd(t)值(2.8～3.9)、年轻的二阶段亏损地幔模式年龄(tDM2=647～733Ma)和幔源铅同位素组成特征((206Pb/204Pb)t=18.121～18.418;(207Pb/204Pb)t=15.480～15.511;(208Pb/204Pb)t=37.628～37.713),上述同位素地球化学特征均显示花岗闪长质岩浆主要源于亏损地幔源区。结合东北地区区域构造演化和岩体微量元素及同位素组成特征反映该矿床形成于岛弧的构造背景,其形成可能与侏罗纪古太平洋板块的俯冲作用密切相关。

The Sankuanggou Fe-Cu deposit,located in northern Heilongjiang Province,is a typical skarn deposit which occurs in the NW trending Luohe-Duobaoshan-Sankuanggou metallogenic belt of northern part of the Da Hinggan Range.The ore-related Sankuanggou granodiorite yields a concordia LA-ICP-MS zircon U-Pb age of 175.9±1.6Ma in good consistently with 238U/206Pb weighted average age within error.This age indicates that there was an important Jurassic magmatic-hydrothermal Fe-Cu mineralization event in the Duobaoshan metallogenic district.The Sankuanggou granodiorite has a geochemical affinity of arc magmas：Na-rich（Na2O/K2O=1.39～1.59） ,metaluminous（ACNK=0.87～0.91） ,enrichment in LREE（（La/Yb） N=8.02～10.45） and LILEs（U,Th and Pb） with minor negative Eu anomalies（δEu=0.82～0.98） ,depletion in HFSE（Nb,Ta,Zr,Hf and Ti） .Sr-Nd-Pb isotope systematics display that the Sankuanggou granodiorite also has a low initial Isr（（87Sr/86Sr） i=0.7041～0.7045） ,high initial 143Nd/144Nd value（（143Nd/144Nd） i=0.512556～0.512576） ,positive εNd（t） （2.8～3.9） ,young depleted-mantle model ages（tDM2=647～733Ma） and mantle-derived Pb isotopic characteristics.These geochemical characteristics indicate that the magma source of the Sankuanggou granodiorite may be mainly derived from deleted mantle source.The geochronology,geochemistry and isotope characteristics of the Sankuanggou granodiorite,combined with tectonic evolution of northeastern China,suggest that this deposit was formed in the magmatic arc setting,implying that its formation is probably related to the subduction of the paleo-Pacific Ocean during the Jurassic Period.