【作者】 朱江；

【导师】 吕新彪；

【作者基本信息】 中国地质大学 ， 矿产普查与勘探， 2013， 博士

【摘要】 中亚造山成矿域是全球最显著的显生宙大陆增生区,该区域大陆增生改造过程中的壳幔相互作用和大规模成矿机理是国内外研究的重要课题。北山造山带地处中亚造山成矿域南缘,是我国西部重要的金、铜、镍、铅锌成矿带。论文以北山南带为研究区,以区域构造-岩浆活动-成矿作用为主线,在深刻认识造山演化过程和动力学背景基础上,对典型矿床展开进一步解剖研究,对区域金多金属成矿作用和成矿规律进行了探讨。取得主要成果如下：1、地质背景与动力学演化研究选取相关中酸性侵入岩体展开系统的锆石U-Pb年代学、岩石地球化学和Sr-Nd-Pb同位素分析,并探讨了其岩石成因及起源。研究对象分别为：小西弓钾长花岗岩(841.34±8.1Ma)、拾金坡岩体(405.5±1.8Ma)、辉铜山钾长花岗岩(424.4±2.5Ma)、白山堂流纹斑岩(374.9±2.3Ma)、石板泉花岗岩(280.5±5.5Ma)、小西弓石英正长斑岩体(246.4±2.5Ma)、花牛山钾长花岗岩(225.6±2.2Ma)、金场沟钾长花岗岩。研究区造山演化过程可大致划分为前造山期(前寒武纪-早寒武世)、洋陆演化期(奥陶纪-二叠纪)、造山后(三叠纪-)。综合本文研究及前人资料,划分出四次中酸性侵入岩活动峰期：新元古代(880Ma-840Ma)、晚奥陶世-泥盆纪(451-374Ma)、石炭纪-二叠纪(310Ma～270Ma)、三叠纪(240Ma～220Ma)。不同阶段岩浆活动反映了不同的动力学环境：i.新元代的s型花岗岩、榴辉岩共同反映了早期陆块(地块)的汇聚拼合事件,并暗示同碰撞岩浆活动的峰期可能在860～880Ma。小西弓钾长花岗岩(841Ma)是北山地区目前发现最古老的A型花岗岩,侵位于新元古代中期,暗示了后碰撞伸展背景。属首次在北山地区解离出的新元古代后碰撞环境。ii.早中古生代-晚古生代研究区处于俯冲背景下,发育大量的I-S-A型花岗岩、埃达克质花岗岩、岛弧火山岩,代表岩体有辉铜山钾长花岗岩(424.4±2.5Ma)、拾金坡岩体(405.5±1.8Ma)、白山堂流纹斑岩(374.9±2.3Ma)、石板泉花岗岩(280.5±5.5Ma)。岩浆活动时间从奥陶纪一直持续到早二叠世,记录了洋陆体制下陆壳侧向增生作用。iii.三叠纪区域进入造山后伸展环境,中酸性岩浆活动依然强烈,代表性岩体有花牛山钾长花岗岩(225Ma)、金场沟钾长花岗岩等,侵位时间集中在240Ma～220Ma,属中晚三叠世。岩石成因类型主要为高分异I型-A型,岩浆起源于伸展背景下幔源岩浆底侵(受到混染改造的富集地幔)导致的年轻地壳物质(可能为早期洋壳和岛弧建造)重熔。该期岩浆活动揭示了三叠纪造山后伸展环境和陆壳垂向增生作用。2、典型矿床解剖与矿床成因新认识在充分吸收消化前人成果基础上,对拾金坡金矿床、小西弓金矿床和花牛山金多金属矿田展开进一步解剖研究,并获得一些新的认识。特别是对花牛山金多金属矿田的成因综合研究,较大程度填补了前人研究空白。拾金坡金矿床产在花岗岩体边部,受断裂构造控制明显,属受构造控制石英脉型金矿。获得热液蚀变绢云母40Ar/39Ar坪年龄为364.6±3Ma,表明成矿作用发生在晚泥盆世。成矿时间与赋矿花岗岩成岩年龄(405.5±1.8Ma)相差近40Ma,二者不存在直接成因联系。结合氢氧同位素和野外地质特征认为,初始成矿流体来自深部(变质)热液。主成矿阶段石英中流体包裹体群具明显沸腾作用特征,不同气液比的水溶液包裹体和含CO2包裹体集群分布,均一温度范围集中于270～340℃,盐度为4.65%～9.21%NaCl。晚阶段石英中仅发育水溶液包裹体,均一温度集中在160～230℃,盐度为9.47%～11.1%NaCl。成矿流体属中温、低盐度、富CO2流体。流体从早阶段演化到晚阶段,温度降低100℃,压力由约113MPa骤减到约11Mpa。温度和压力降低是石英大脉中金沉淀、富集的最主要原因。石英脉型矿石硫主要来自地层,蚀变岩型矿石硫更多地继承了花岗岩围岩硫。该矿床形成于晚泥盆世俯冲作用的应力松弛阶段。小西弓金矿床受韧性剪切带控制明显,矿体赋存于中元古界西尖山群变质岩和新元古代钾长花岗岩中。主成矿阶段流体温度为281～325℃,盐度变化范围为3.2%-9.2%NaCl,富含CO2、CH4组份,属于中高温、低盐度、CO2-H2O-CH4-NaCl热液体系。矿石硫化物63nS值范围为1.2‰～12.79‰,具有混源特征,暗示成矿物质来自花岗岩类和中元古界片岩。成矿流体为变质热液与大气降水的混合流体。该矿床形成于中二叠世主碰撞晚期。花牛山金多金属矿田由花牛山金矿床、花西山金矿床、花黑滩钼矿床、花牛山铅锌矿床组成,矿床类型包括矽卡岩型、高温岩浆热液型、中低温岩浆热液型以及沉积-改造型,构成与岩浆热液有关的Au-Mo-Pb-Zn-(W)成矿系列。论文对花牛山金多金属矿田进行了详细了年代学、矿床地球化学、流体包裹体及矿床成因分析：1)花牛山金矿床具典型矽卡岩型矿床特征,矿体产在钾长花岗岩体与大理岩接触部位,受断裂构造控制,磁黄铁矿和黄铁矿是最重要的载金矿物。矿石中辉钼矿Re-Os模式年龄为221.0±3.4Ma,与花岗岩侵位年龄(225Ma)基本一致。金成矿作用发生在晚三叠世。主成矿阶段石英中捕获了不同气液比H20溶液包裹体和含CO2流体包裹体,均一温度为280～425℃,峰值为330～370℃,盐度介于6.59%～14.04%NaCl。成矿流体属中高温、中等盐度、富CO2流体。石英中流体包裹体的δ18O和δD值分别为-0.01‰～0.29‰和-109‰--116‰,投点在岩浆水与大气降水区范围之间。成矿流体是岩浆水与大气降水的混合热液,且大气降水所占比重较高。矿石金属硫化物δ34s值变化范围集中在4.21‰-6.53‰,硫源较为单一,成矿物质来自岩浆。2)花西山金矿床产在钾长花岗岩体边部,属中低温岩浆热液型金矿。矿体以石英脉和蚀变岩形式产出,赋存在EW、NE和NNE向次级断裂破碎带中。流体包裹体研究表明,矿化发生在154～408℃这一较宽的温度区间,早阶段流体为中高温246～334℃、中等盐度(16.24%～9.86%NaCl)、富CO2热液；晚阶段成矿流体具中低温(154-214℃)、低盐度(2.41%～6.88%NaCl)特征。矿石硫化物δ34S值范围为2.6%‰～4.25‰,表明硫源单一,且均一化程度较高,成矿物质主要来自岩浆。3)花黑滩钼矿床产于钾长花岗岩体边缘及其外接触带,赋矿围岩为震旦系洗肠井群第二岩组黑云长英角岩。辉钼矿Re-Os等时线年龄为225.2±2.4Ma,与花岗岩U-Pb年龄(225Ma)一致。主成矿阶段流体温度为342～583℃,盐度为15.67%～16.53%]NaCl,属高温、中等盐度热液；晚阶段流体具中低温(142-306℃)、中低盐度(12.62%～15.66%NaCl)特征。矿石硫化物δ34S值范围为3.3‰～3.9‰(除一个样品为负值外),暗示矿石硫主要来自岩浆,有少量地层组份的贡献。4)花牛山铅锌银矿床产在岩体与地层接触部位,矿体呈脉状、透镜状；矿体中心到边部,由块状矿石向浸染状矿石过渡。成矿流体属中高温(276-362-C)、中等盐度(10.23%～21.11%NaCl)热液。闪锌矿形成于高温条件。矿石S、Pb同位素组成较为复杂,一矿区(主矿区)矿石矿δ34S值均为负值,范围是-10.1‰～3.68‰;三矿区范围是δ34S值0.71‰-4.82‰。综合矿床地质特征及成因研究认为,花牛山铅锌银矿床属于岩浆中高温热液矿床,但成矿物质具有继承性。蓟县纪区域处于海底火山喷发和稳定沉积交替环境,大量成矿物质在地层中预富集,形成原始矿源层或矿胚。晚三叠世花岗质岩浆活动促使成矿元素不断活化、迁移、富集成矿。整体上,花牛山矿田金、钼、铅锌多金属成矿作用与花牛山钾长花岗岩存在密切的时间、空间及成因联系,岩浆侵位为成矿提供了丰富的热能、流体和成矿物质。不同矿床之成矿流体构成一个与岩浆热液有关的流体演化系统。成岩-成矿作用发生在三叠纪造山后伸展环境,幔源岩浆底侵诱发地壳物质部分熔融和花岗岩浆上侵,继而导致金多金属成矿作用发生。3、金多金属成矿系列与成矿规律研究以区域成矿学为理论指导,对北山南带金多金属矿床成矿系列进行了研究,将其划分为：①与志留纪-泥盆纪沟弧盆体系有关金铜成矿系列;②与石炭纪-早三叠世岩浆弧体系有关金铜(铁)成矿系列;③与二叠纪强应变构造带有关的金(铜)成矿系列;④与三叠纪造山后中酸性岩浆活动有关金钼铅锌(钨)成矿系列。分别对其成矿时间、地质特征和成矿地质条件进行了探讨,并建立了成矿模式。初步构建了区域金多金属矿床的时空分布格架,指出晚泥盆世、二叠纪和三叠纪是金成矿的主要峰期。不同地质体边缘、构造体制转换环境是金成矿有利条件。对地球动力学演化过程与金成矿作用之间关系进行了探讨。对北山南带金矿床的成矿远景进行了评价,指出二叠纪绿岩带型金矿床和三叠纪与岩浆热液有关金钼多金属矿床具有较好的找矿潜力,花牛山-金场沟找矿远景区和小西弓-乌龙泉找矿远景区具有明显的化探异常和较好成矿条件。更多还原

【Abstract】 The Central Asian Orogenic Belt (CAOB), situated between the Siberian, North China, Tarim and East European cratons, represents one of the most important sites of juvenile crustal growth in the Phanerozoic. The interaction between mantle and crust and multiple metallogeny in the processes of the continental growth have attracted many people’s attention.The South Beishan area is located at the south margin of CAOB. It has experienced complicated geological process with multiple accretion and collision events, and hosts a large number of porphyry copper, orogenic gold, magmatic copper-nickel, and epithermal gold deposits.In this paper, the Shijinpo gold deposit, Xiaoxigong gold deposit and Huaniushan gold-polymetallic ore district are detailed studied. On the basis of the accurately age dating, combined with the geology and geochemistry analysis, the genesis of these granitoids and gold deposits, and their temporal and spatial relationships have been evaluated. The main results and conclusions are summarized as following:1. Magmatic formation and geodynamic evolutionLA-ICP-MS U-Pb Zircon dating yields the age of Xiaoxigong K-feldspar granite(841Ma), Huitongshan granite (424.4±2.5Ma), Shijinpo granite (405.5±1.8Ma)、Baishantang rhyolite-porphyry (374.9±2.3Ma), Shibanquan granite (280.5±5.5Ma), Xiaoxigong quartz synenite (246.4±2.5Ma), and Huaniushan granite (225.6±2.2Ma), respectively. Though geochemistryand Sr-Nd-Pb isotope analysis, petrogenesis and tectonic implications of these granitoids have been discussed. Based on the geochronological and geochemical data concerning the other Paleozoic magmatic rocks from the South Beishan area, this paper outlines the evolved geodynamic scenarios inherent in these magmatic sequences. The generation of syn-and post-orogenic granitoids represents horizontal (lateral) and vertical crustal growth. And four magmatic activities stages have been yielded, such as:(1) Neoproterozoic (ca.880Ma to840Ma),(2) Ordovician to Devonian (ca.451Ma to374Ma),(3) Carboniferous to Permian (ca.310Ma to270Ma),(4) Triassic (ca.240Ma to220Ma). The detailed research can be described as follows: ⅰ. Petrology, major and trace elements data all indicate that the Xiaoxigong K-feldspar granite (841Ma) is typical A-type granite which intruded in a post-collisional extensional tectonic setting. It is the oldest A-type granitic pluton in the Beishan area. Combined with the Gubaoquan elogite which has an eclogite-facies metamorphic age of857±71Ma, it indicates an important subduetion-collision and post-collision extension event in the Neoproterozoic.ⅱ. The Paleozoic granitoid intrusions in the Beishan area are mainly I-type granite, with some adakites, Nb-enriched basalts and A-type granite,suggesting subducted oceanic slab-melting was frequent during451Ma to270Ma.iii. Triassic granitic plutons have also been identified, such as the Huaniushan granite(225.6±2.2Ma), Xiaoxigong quartz synenite(246.4±2.5Ma),and Jingchanggou granite. They belong to the high-K calc-alkaline and shoshonitic series and have alkalic and alkali-calcic characteristics, and are weakly peraluminous-metaluminous. These granitoids are mainly highly fractionated I-type granite and A-type granite, suggesting a post-orogenic extensional setting during the Triassic.2. Ore genesis studies of gold-polymetallic depositsThe Shijinpo gold deposit is hosted in the early Devonian granite, and consists primarily of auriferous quartz veins that confined to the EW-trending faults.Laser incremental heating40Ar/39Ar analysis of hydrothermal sericite yields a plateau age of364.6±3Ma (2σ), which suggests that the gold mineralization took place in the late Devonian. A comprehensive fluid inclusion study shows that in the early stage there are three major types of fluid inclusions: liquid-rich, gas-rich aqueous fluid inclusions and CO2-bearing fluid inclusions, with intermediate homogenization temperature (270℃to340℃), and low salinity (4.65%to9.21%NaCl). Fluid boiling are evidenced by the co-existence of three types of fluid inclusions with similar homogenization temperatures. Fluid pressures declined from ca.113MPa to ca.11MPa through the early stage to the late stage, and the ore-forming fluids are assumed to undergo boiling in a transitional setting (from compression to extension). Oxygen and hydrogen isotopes for ore fluids range from1.39‰to3.39‰and-71‰to-99‰, respectively, suggesting that the ore fluids are mainly sourced from metamorphic water, and mixed with meteoric water later. Measured δ34S values for sulfide minerals range from4.44%o to11.33‰. Both Precambrian basement and granite might be the sulfur sources with respect to the sulfur isotopic composition of the ores, Precambrian metamorphic basement and Paleozoic granites. On the basis of our researches and the regional geology, we propose that the Shijinpo gold deposit is an orogenic gold deposit.The Xiaoxigong gold deposit is hosted in Mesoproterozoic metamorphic rock and Neoproterozoic granite, related to shear zone. Fluid inclusions in quartz of the major metallogenic stage are mainly two-phase vapor-liquid inclusions with small amount of CO2phase. The ore-forming fluids are CO2-H2O-CH4-NaCl system with intermediate homogenization temperature (281℃to325℃), and low salinity (3.2%to9.2%NaCl). Oxygen and hydrogen isotopes for ore fluids range from-2.95%o to13.79%o and-72.5%o to-107‰, respectively, suggesting that the ore fluids are mainly sourced from metamorphic water, and mixed with meteoric water later. Measured δ34S values for sulfide minerals range from1.2%o to12.7‰, suggesting that both Precambrian basement and granite might be the sulfur sources. We further propose that the Xiaoxigong gold deposit was formed in the late-collisional setting during the middle Permian.The Huaniushan gold-polymetallic ore district consists mainly of magmatic-hydrothemal and skarn Au, Mo, Pb-Zn ores, occur in the contact zone of the Huaniushan granite, respectively. LA-ICP-MS zircon U-Pb dating constrains the crystallization of the granite at225.6±2.2Ma (1δ). Five molybdenite samples from the magmatic-hydrothemal molybdenum ores yield Re-Os isochron age of225.2±2.4Ma (2δ), while a molybdenite sample from the skarn gold ores yields a Re-Os model age of143.0±0.3Ma and an isochron age of221.0±3.4Ma, indicating the gold-polymetallic mineralization occuring in a post-orogenic setting during the late Triassic.1)The Huaniushan skarn gold deposit controlled by EW trending faults. The auriferous quartz veins were deposited at intermediate-high temperature conditions (280℃to425℃) from aqueous or aqueous-carbonic fluids with moderate salinity (6.59%to14.04%NaCl equiv). Oxygen and hydrogen isotopes for ore fluids range from-0.01‰to+0.29‰and-109‰to-116‰, respectively, compatible with mixing of magmatic and meteoric components. Measured δ34S values for sulfide minerals are predominantly+4.2l‰to+6.53%o, indicating a deep-seated sulfur source of magmatic origin2) The Huaxishan magmatic-hydrothemal gold deposit was occurring in the Huaniushan granite and along the contact with the Mesoproterozoic clastic rock. The homogenization temperatures and salinities of inclusions in major stage vary from246℃to334℃,16.24%to9.86%NaCl equivalent, and in late auriferous mineralization vary from154℃to214℃,2.41%-6.88%NaCl equivalent. Measuredδ34S values for sulfide minerals are predominantly+2.6%o to+4.25%o, indicating a deep-seated sulfur source of magmatic origin.3) The Huaheitan magmatic-hydrothemal molybdenum deposit was hosted in the granite and along the contact with the Mesoproterozoic hornfels. Fluid inclusion studies suggest that the molybdenum-quartz veins were deposited at high temperature conditions (342℃to583℃) from aqueous or aqueous-carbonic fluids with moderate salinity (15.67%to16.53%NaCl equiv). Measured δ34S values for sulfide minerals are predominantly+3.3‰to+3.9‰, also indicating a deep-seated sulfur source of magmatic origin.4) The Huaniushan Pb-Zn ore bodies occur in the contact zone between the granite and the marine carbonates. The ore bodies occurred mainly in terms of massive ores in big veins and lenticular ore bodies. Fluid inclusion studies suggest that the veins were deposited at intermediate-high temperature conditions (276℃to362℃) from aqueous or aqueous-carbonic fluids with moderate salinity (10.23%to21.11%NaCl equiv). Measuredδ34S values for sulfide minerals from NO.2mining area are predominantly-10.1%o to-3.68%o, which is quite different from the other Au, Mo deposits related to the granite. And δ34S values for sulfide minerals from NO.3mining area vary from0.71‰to4.82‰. According to the deposit geology characteristics, we propose that the Huaniushan Pb-Zn deposit was formed by multiple stage:a) the "ore source-bed" was formed by submarine exhalation-sedimentation in Late Mesoproterozoic, b) the magmatic-hydrothemal processes determine the Pb-Zn enrichment and mineralization in Late Triassic.3. Metallogenic series and metallogenic regularityIn South Beishan area, there are mainly four gold-polymetallic metallogenic series. They are the Cu-Au series formed in the island arc setting during the Silurian to Devonian, the volcano-subvolcano Cu-Au-Fe series formed in continental marginal volcanic arc setting during the Carboniferous to early Permian, the shear zone related Au(Cu) series formed in late-collisional setting during the middle-late Permian, and the potassium granite related Au-Mo-Pb-Zn-(W) series occured in the post-orogenic extensional setting during the late Triassic.By summarizing the regional metallogenic conditions and the temporal and spatial distribution regularities, the regional gold-polymetallic metallogenic model have been proposed. The geochronology study indicates that the Devonian, Permian and Triassic are the main gold mineralization epochs in this area. Five gold-polymetallic ore prospecting areas have been divided, and recommendations on the deployment of prospective areas have been put forward.更多还原