【作者】 刘晓煌；

【导师】 孙柏年；

【作者基本信息】 兰州大学 ， 古生物与地层学， 2008， 博士

【摘要】 前人对祁连山西段的花岗岩有一定的研究,但北祁连造山带西段最大的金佛寺岩体其研究程度明显低于较其它区域。由于其交通条件和自然条件十分恶劣,有关金佛寺岩体含矿性的研究更是不多见。本文在前人区域研究成果的基础上,运用岩石学、构造地质学、矿床学、遥感学、放射性Re—Os、Rb—Sr、Sm—Nd、Pb同位素测年和示踪,主量、微量、稀土元素,稳定同位素C、H、O、S,流体包裹体的研究,论证了金佛寺岩体的成岩时代、构造环境及与之有关的金属矿床成矿时代和成因机制问题。通过野外地质工作查明了区内岩体、地层的分布,断裂构造活动及控矿规律,研究了成矿地质条件,初步掌握了矿体分布范围、产状、规模、形态变化、矿石物质成份,为下步研究奠定了坚实的基础。(1)金佛寺岩体地质特征研究地质学、岩相学研究表明:金佛寺岩体分为两期,第一期副矿物以磁铁矿、磷灰石、锆石为主。次生矿物以绢云母、碳酸盐、绿泥石为主。且富含不含角闪石的绿泥石化黑云斜长花岗岩及黑云石英闪长岩包裹体。第二期副矿物以磁铁矿为主。次生矿物以绿泥石、绢云母、绿帘石为主;Rb—Sr和Nd—Sm全岩等时线年龄第一期为421.9—426.1Ma,属于中—晚志留世(温洛克世—罗德洛世)。第二期时间为389.6—391.3Ma。属于早—中泥盆世;流体包裹研究表明:第一期岩体包裹体温度均一为116—250℃,形成深度在0—0.9Km,压力为0—25 MPa。第二期岩体中包裹体均一温度为175—275℃,形成深度在0.28—1.5Km,压力为7.5—39 MPa。金佛寺岩体的主量、微量、稀土元素和Rb—Sr、Sm—Nd、Pb同位素特征暗示,其原始岩浆来源于地壳,岩体具有“S”型花岗岩的特征。(2)金佛寺岩体的成矿作用研究金属矿物生成顺序及划分成矿期次:1赤铁矿—2黄铁矿—3黄铜矿—4斑铜矿—5方铅矿1—6黑钨矿—7辉钼矿—8闪锌矿—9方铅矿2—10白钨矿—11(铅矾—白铅矿、褐铁矿、针铁矿、辉铜矿)。该区大体划分为2个矿化期5个矿化阶段,分别为:热液矿化期:Ⅰ磁铁矿—赤铁矿中高温阶段、Ⅱ石英—黄铁矿中低温热液阶段、Ⅲ黄铜矿—辉钼矿中、高温热液阶段、Ⅳ方铅矿—闪锌矿中低温热液阶段、Ⅴ方解石—方铅矿低温热液阶段。表生氧化期:部分金属化合物氧化为褐铁矿、针铁矿、铅矾—白铅矿、辉铜矿等。地球化学特征显示它们的成矿来源是地壳,成矿流体以岩浆为主并受大气水的影响;流体包裹体研究表明成矿温度差异不大,而成矿流体的成份也很相似,具有相似的成矿环境。西柳沟钨钼矿的辉钼矿Re—Os等时线成矿年龄为422.2Ma,属于中晚志留世。主量、微量、稀土元素和Rb—Sr、Sm—Nd、Pb同位素研究表明西柳沟钨钼矿形成于中晚志留世北祁连造山作用初期环境;索同沟的铅来源单一,可能与造山作用及其围岩—奥陶纪的火山有关。(3)成矿模式的研究西柳沟钨钼矿、索同沟Ⅲ号脉铅锌矿与金佛寺第一期岩体地球化学特征和包裹体特征相接近,索同沟Ⅲ号脉铅锌矿同时也具有Ⅰ号铅锌矿脉的部分地球化学的特征,而Ⅰ号脉与奥陶系的阴沟群(OY~a)地球化学特征相似。Pb同位素、包裹体和微量元素地球化学研究表明:岩体及与金佛寺岩体有关矿的源区主要是大陆壳,而不是地幔,它们都与造山作用有关。Ⅰ号铅锌矿脉形成于金佛寺第一期岩体就位前,与第一期岩体就位前的流体和奥陶系阴沟群a岩组(OY~a)有关;西柳沟钨钼矿形成于金佛寺第一期岩体就位后,与岩体及基底北大河岩群有关;Ⅲ号脉形成于第一期岩体形成后的金佛寺岩体的成矿作用晚期,是这一次成矿作用的结束。更多还原

【Abstract】 The Jinfosi pluton,the biggest granite in the western part of the North Qilian Mountains,lies in about 40km southeast of Jiuquan city.Because of execrable transportation and natural conditions, the research level is still very low,and just a few works have been done there on the ore potentiality of the Jinfosi pluton.In order to research the age of the Jinfosi pluton and its tectonic settings as well as the age of corresponding ore deposit and metallogeny,we applied multidisciplinary methods of petrology, tectonics,ore deposit,remote sensing,radio geochemistry in this paper.Furthermore,the author discussed and studied the sources of ore-forming material and age of the deposits and the age of the Jinfosi pluton by isotopes of Re-Os、Rb-Sr、Sm-Nd、Pb,and the major elements,trace earth elements,and stable isotopes of sulfur,carbon,hydrogen and oxygen.We did some elaborate regional geological survey in this area,made sure that the distributions of granite and strata,structure and ore-controlling regularity and metallogenic geology condition. Additionally,we approximately ascertained the distribution range,occurrence,size,shape and component of the orebody.The above results will establish a reliable groundwork for the future researches.(1)The characteristics of the Jinfosi plutonTwo intrusive stages have been recognized.The earlier-staged granite is mainly composed of magnetite,apatite and zircon,and other secondary minerals such as sericite,carbonate and chlorite. The rocks contain abundant biotite plagiogranites and the inclusion of biotite quartz diorite without hornblende.The whole-rock isochron age of Rb-Sr and Sm-Nd are 421.9-426.1Ma,which indicates the intrusive age is the Wenlock to the Ludlow,with an inclusion temperature of 116-250℃,the corresponding depth of 0-0.9Km and pressure of 0-25 MPa.The later-staged granite is mainly composed of magnetite,and secondarily chlorite,sericite.The isochron age of Rb-Sr and Sm-Nd for the whole-rocks are 389.6-391.3Ma,which indicates that the intrusive age is the early-middle Devonian,with a inclusion temperature of 175-275℃,the corresponding depth of 0.28-1.5Km and pressure of 7.5-39 MPa. The original magma of the Jinfosi pluton which shows characteristics of S-type granite is derived from the crust.(2)Metallogeny of the Jinfosi plutonThe minerals sequences:1hematite-2pyrite-3chalcopyrite-4bornite-5galenitel-6wolframite-7molybdenite -8sphalerite-9galenite2-10scheelite-11anglesite-cerussite-limonite-goethite -chalcocite.The mineralization stages and mineral paragenesis orders:Hot liquid mineralization epoch:Ⅰmagnetite-hematite middle-high temperature phase;Ⅱquartz-pyrite low-middle temperature hydrothermal fluids phase;Ⅲchalcopyrite-molybdenite middle-high temperature hydrothermal fluids phase;Ⅳgalenite-sphalerite low-middle temperature hydrothermal fluids phase;Ⅴcalcite-galenite low temperature hydrothermal fluids phase.Surface oxidation epoch:parts of metallic compounds oxidizing(has been oxidized)into limonite,goethite,anglesite-cerussite and chalcocite.The ore-forming materials originate from the magma of crust and the ore-forming fluids are influenced by the atmospheric water,and their mineralization fluids have similar compositions and without visible differences in mineralization temperature.Based on Re-Os isotope dating,the age of Xiliugou W-Mo deposit is 422.2Ma,which indicates that the intrusive age is the Middle-Late Silurian,formed in the early period of the North Qilian mountains and the late period of the closure of the North Qilian residual ocean basin.The single source of the Suotonggou Pb deposit may be correlated with the Jinfosi pluton uplift and its wall rocks of the Ordovician volcano.(3)Ore-forming model;W-Mo deposit and the No.3 Pb-Zn deposit of SuoTonggou are similar to the early stage granite of Jinfosi in the rock geochemistry and inclusion characteristics.Moreover,the No.1 vein deposit is similar to the Ordovician Yingou Group(OY~a),and the No.3 Pb-Zn one possesses partial features of the former in geochemical studies and ore-forming fluids.The sources of the Jinfosi pluton and the correlative deposits are originated from the crust,and correlated with the mountain uplift.The No.1 Pb-Zn vein deposit was formed before the early stage granite of Jinfosi forming,and associated with the fluids of with the early stage of Jinfosi granite and a rocky team(OY~a),Yingou Group,Ordovician.Xiliugou W-Mo deposit was formed after the early stage granite of Jinfosi,and associated with the early stage granite and the base of Beidahe group.The No.1 Pb-Zn vein deposit was formed in the late Ore-forming of the Jinfosi pluton,which indicates that Ore-forming of the Jinfosi pluton ended.更多还原