西秦岭格娄昂金矿床赋矿斑岩岩石成因及其地质意义  

Petrogenesis of ore-hosting porphyry in the Gelouang gold deposit,West Qinling and its geological implications

作　　者：黄雅琪 邱昆峰[1] 于皓丞 金鼎国[2] 何登洋 肖昌浩 王玉玺 HUANG YaQi;QIU KunFeng;YU HaoCheng;JIN DingGuo;HE DengYang;XIAO ChangHao;WANG YuXi(School of Earh Science and Resources,China Unitersity of Geosciences,Bejing 100083,China;No.3 Inustiaule of Geology and Mineral Exploration,Gunsu Baureau of Gelogy and Mineral Resources,lanchou 730050,China;laborulory of Dyramic Digenesis and Metalloganeais,Institute of Geumehanics,Chinese Academy of Gealogical Seiences,Beyjing 100081,China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]甘肃省地矿局第三地质矿产勘查院,兰州730050 [3]中国地质科学院地质力学研究所动力成岩成矿实验室,北京100081

出　　处：《岩石学报》2020年第5期1567-1585,共19页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41702069);国家重点研发计划(2019YFA0708603);中央高校基本科研业务费(2652018125);高等学校学科创新引智计划(BP0719021);陇原青年创新创业人才项目(20200901);矿床地球化学国家重点实验室开放基金(201704)联合资助.

摘　　要：西秦岭造山带广泛发育印支期花岗质岩石,已探明超过1200吨金资源量与这些花岗质岩石具有密切空间关系;揭示赋矿花岗质岩石成因对于进一步约束金成矿与岩浆作用是否具有成因关系具有重要意义。格娄昂矿床(金资源量27.7t,平均品位2.18g/t)是西秦岭造山带西段甘南地区的大型金矿床,花岗质岩石和变沉积岩是其主要赋矿围岩。格娄昂金矿床赋矿英安斑岩与黑云英安斑岩属于过铝质高钾钙碱性系列,轻重稀土分异较大,(La/Yb)N比值为31.07~40.59,富集大离子亲石元素,亏损高场强元素Nb、Ta等,具有弱铕负异常(δEu=0.76~0.78)。英安斑岩和黑云英安斑岩被金矿脉切割,LA-ICP-MS锆石U-Pb年龄分别为250.8±2.5Ma和252.9±3.4Ma,磷灰石U-Pb年龄分别为248.9±7.3Ma和249.7±7.9Ma,为成矿前早三叠世岩浆作用的产物。锆石εHf(t)=-13.88^-7.84,对应的二阶段Hf模式年龄(tDM2)为2.15~1.78Ga。因此,格娄昂金矿床早三叠世赋矿英安斑岩和黑云英安斑岩为成矿前岩浆活动的产物,源于古元古代下地壳的部分熔融。可能与洋壳板片北向俯冲有关,形成于活动大陆边缘碰撞前构造环境,进一步支持阿尼玛卿-勉略洋在早三叠世尚未闭合。Understanding temporal and spatial relationship between 1200 t gold and the Indosinian granitoids in the Triassic West Qinling orogenic belt is of great significance to reveal the genesis of ore-hosting granitoids and further to constrain the genetic relationship between gold mineralization and magmatism. The Gelouang gold deposit with gold resource of 27. 7 t Au at an average grade of 2. 18 g/t,a large gold deposit in the Xiahe-Hezuo polymetallic district in southern Gansu Province,is hosted in the metasedimentary rocks and granitoids. Gold orebodies commonly crosscut dacite porphyry and biotite dacite porphyry,the dominant ore-hosting granitoids at Gelouang. Dacite porphyry and biotite dacite porphyry belong to the peraluminous high-K calc-alkaline rock series. They are enriched in light rare earth elements( LREE) and depleted in heavy rare earth elements( HREE) with( La/Yb)Nratio = 31. 07 ~40. 59 and minor Eu negative anomaly( δEu = 0. 76 ~ 0. 78). They are characterized by enrichment of Ba,Th,U,LILEs,and depletion of Nb,Ta,HSFEs. Dacite porphyry and biotite dacite porphyry yield LA-ICP-MS zircon U-Pb age at 250. 8 ± 2. 5 Ma and252. 9 ± 3. 4 Ma,respectively. These ages are consistent with 248. 9 ± 7. 3 Ma and 249. 7 ± 7. 9 Ma collected by LA-ICP-MS apatite UPb of the same samples. They have zircons yielding εHf( t) =-13. 88 ^-7. 84 and corresponding two-stage Hf ages( tDM2) of 2. 15 ~1. 78 Ga. We therefore proposed that the Early Triassic ore-hosting dacite porphyry and biotite dacite porphyry at in the Gelouang gold deposit emplaced earlier than gold mineralization,and were originated from partial melting of the Paleo-Proterozoic lower crust. Such rocks may form in an active continental margins in a pre-collisional regime attributed to the northward subduction of the oceanic slab,which therefore supports that the closure of the Animaqing-Mianlue ocean was not earlier than Early Triassic.

关 键 词：U-PB年代学 LU-HF同位素 岩石地球化学 赋矿斑岩 格娄昂金矿床 西秦岭 

分 类 号：P588.13[天文地球—岩石学] P597.3[天文地球—地质学]