【作者】 康鸿杰；

【导师】 孙柏年；

【作者基本信息】 兰州大学 ， 古生物学与地层学， 2010， 博士

【摘要】 金佛寺花岗岩体位于北祁连西段,目前在岩体接触带发现有大道口、青大坂、西柳沟、干巴河脑钨钼矿和索铜沟铅锌矿、松木沟铜矿等多处矿点,构成了一个以钨钼为主的多金属成矿带,显示出该区域具有良好的钨钼等多金属成矿地质背景条件,系统分析该成矿带的成矿地质条件和成矿机制,对进一步在区域内寻找与金佛寺花岗岩有关的钨钼多金属矿产具有重要的理论和实践意义。本文在系统分析研究区地质资料的基础上,综合采用岩石学、矿物学、矿床学、元素地球化学、成矿流体地球化学、同位素地质学等理论和方法,通过对干巴河脑和青大坂钨钼矿两个典型矿床的深入研究,探讨了多金属成矿带的成矿地质条件和成矿机制,建立了成矿模式,并对区内的资源潜力做了初步预测,同时提出了区内的找矿前景和方向。金佛寺岩体外围的多金属成矿带主要赋存在花岗岩体的接触带内,受区域内深大断裂的控制,单个矿床主要产于岩体接触带内NW向与NE向或近EW向次一级断裂内。通过野外观察和矿物组合特征研究表明,研究区内钨钼成矿过程可划分为热液期和表生期两期,热液期又可细分为硅酸盐、多金属硫化物和碳酸盐三个成矿阶段。包裹体研究表明：成矿期包裹体均为原生包裹体,未见次生和假次生包裹体,形态多样,有长条形、椭圆形、菱形、矩形、梯形、三角形和各种不规则形状,大小变化不大,多在2-20μm之间；从相态看,有富液、富气的气液两相包裹体和单一液相以及含子矿物包裹体四类。流体包裹体热力学研究表明,主成矿阶段成矿流体温度集中在200-300℃之间,成矿流体盐度为5.7-8.7wt%,密度为0.998-1.018g/cm3,对应成矿压力和成矿深度分别为17.28-27.56MPa和0.64-1.02km,表明研究区成矿流体具有中低温、低盐度、低密度特征,矿床类型为浅成中低温热液型矿床。成矿流体碳-氢-氧同位素分析和包裹体成分研究显示：成矿流体δDv-SMOW值在-67--91‰之间,对应热液水的δ18OH20在-1.21-4.04‰之间,δ13CV-PDB值介于-6‰--4.2‰之间,成矿流体属于K+-Na+-SO4+-Cl-型流体,流体中气相组分以H20为主,其次为少量的CO2和N2。以上研究表明,成矿流体起源于岩浆热液,随着成矿作用的进行,成矿期有大量大气降水的混入,显示出氧同位素“漂移”的特点,因而主成矿阶段成矿流体是以岩浆热液水和大气降水为主的混合热液,流体曾发生的不混溶作用是矿质沉淀富集的主要原因。研究区内矿石δ34S平均值约为4.7‰,与花岗质岩浆δ34S值(5‰-15‰)最为相近,显示金佛寺花岗岩与成矿的密切关系,同时区内岩矿石微量元素地球化学特征分析显示,围岩花岗岩和矿石微量元素和稀土元素配分曲线具有近似一致的特点,说明侵入的花岗质岩浆和重熔的结晶基底(北大河岩群)为多金属矿床的形成提供了重要的成矿物质来源。综合以上研究认为,在北祁连西段金佛寺岩体外围形成的多金属成矿带内的多金属矿床为浅成的中低温岩浆期后热液型矿床,成矿与金佛寺花岗岩体的侵入关系密切,成矿热液为岩浆期后热液和大气降水的混合热液。更多还原

【Abstract】 Jinfosi pluton is located in western part of the North Qilian Mountains, and a tungsten and molybdenum polymetallic metallogenic belt has been found, which is situated in the contact zone of Jinfosi pluton, and which is composed of some mineralization points, such as Dadaokou, Qingdaban, Ganbahenao wolfram-molybdenum deposits, Suotonggou lead-zinc deposit and Songmugou copper deposit and so on, all of those demonstrated that the region has a good geological conditions to form tungsten and molybdenum deposits. So there are important theoretical and practical significance to study the metallogenic geological conditions and mechanism of the metallogenic belt systematicly, and which can be helpful to find the W-Mo polymetallic deposits relate to the Jinfosi pluton.In this paper, based on systematic analysis to geological data of the study area, and synthetic studies on two typical deposits (Ganbahenao and the Qingdaban W-Mo deposits) by applying multiple disciplines and methods such as petrography, mineralogy, deposit theory, geochemistry, fluid inclusion, and isotope geology, the metallogenic geological conditions and mechanism of the polymetallic metallogenic belt have been discussed in the paper, and the metallogenic model has been established too. Through the above studies, the preliminary forecasting to the field resource potential has been done, and meanwhile, the prospects and direction of the prospecting area has been put forward, too.Polymetallic metallogenic belt on the periphery of the Jinfosi pluton mainly exists in the contract zone of Jinfosi granite. Because of the affect of regional deep and major fault zone, the individual ore body mainly occurs in the subsidiary faults, for instance the north-west, north-east and near east-west subsidiary faults in the pluton contact zone. Through the observation of the ore body and the research of the mineral assemblage characteristic, the mineralizing function can be divided into 2 mineralizing periods:hydrothermal and supergene stage, and the hydrothermal stage included silicates, polymetallic sulphides and carbonates three mineralization stages.Fluid inclusion in mineralization phase are primary inclusions, no secondary and pseudosecondar inclusions. They have variety shapes, including long strip, elliptic, rhombic, rectangular, trapezoidal, triangular, and various irregular shapes; their sizes change little, most sizes range from 2 to 20μm; The type of inclusions are simple, including liquid-rich phase, vapor-rich phase, single liquid phase, as well as inclusions containing daughter minerals. Thermodynamic parameters of fluid inclusions indicate that:the temperature of the main stage of mineralization is 200-300℃, the salinity is 5.7-8.7wt%, the density is 0.998-1.018g/cm3, and the corresponding depth and pressure of ore-forming are 17.28-27.56MPa and 0.64-1.02Km, which indicate that ore-forming fluid of the study area has a low-medium temperature, low salinity, low density characteristics, so the genetic type of the deposit is a epithermal deposits with low-moderate temperature.The studies of the composition and C-H-O isotopes of Ore-forming fluid shows that:δDv-SMOW values of ore-forming fluids are between-67--91‰, the relevant hydrothermal water’sδ18OH2O values are-1.21-4.04%o, and theδ13CV-PDB‰values range from-6%o to-4.2%o. The ore-forming fluids belonged to K+-Na+-SO4+-Cl-system, the gas phase constituent in fluid is mainly based on H2O, and a small amount of CO2 and N2 is in the next place. The above studies indicate that although ore-forming fluids come of magmatic, but with the process of mineralization, a large number of precipitation interlarded the fluid in the ore-forming period, led the oxygen isotopes shows the homothetic "drift" feature, so in the main mineralization stage, the ore-forming fluid was a mixed hydrotherm, which were magmatic hydrothermal fluids and meteoric water, and the fluid immiscibility action was the main reason of mineral precipitation and enrichment.The averageδ34S value is about 4.7‰, the value is most similar to the granitic magma’s values (5%o-15%o), which suggests that the close relationship between Jinfosi granite and mineralization. At the same time, the geochemical characteristics of minerals and rocks show that they have a similar characteristic that the trace elements character of granite and mineral, as well as the mineral’s REE distribution curves also consistent with Jinfosi granite’s, all of the evidence illuminates that the intrusive granitic magma and remelting of the crystalline basement (Beidahe Group complex) provided an important source of ore forming materials for the formation of polymetallic deposits.Based on the above studies, which suggest that polymetallic deposits in the polymetallic metallogenic belt, formed in the periphery of Jinfosi pluton, western part of North Qilian, belong to mesothermal-epithermal post-magmatic hydrothermal type deposit, between mineralization and the intrusion of Jinfosi pluton, the relationship is so close, ore-forming hydrothermal solution is mixed hydrothermal of post-magmatic hydrothermal and atmospheric precipitation.更多还原