【作者】 闫升好；

【导师】 陈毓川； 王安建； 殷先明；

【作者基本信息】 中国地质科学院 ， 矿床学， 1998， 博士

【摘要】 甘肃大水金矿是近年来在西秦岭地区新发现的一个特大型金矿床，也是一个国内外十分罕见的新类型金矿。本文首次对该类金矿开展了较为全面系统的成矿学研究工作。金矿化主要赋存于三叠纪灰岩、白云质灰岩地层中，其次产于二叠系灰岩、侏罗系砾岩和燕山陆内造山阶段的中酸性脉岩杂岩墙与灰岩的接触带内。矿体形态复杂，呈不规则的脉状、囊状和漏斗状等，其产出严格受NWW-EW向、近SN向和NEE-NE向断裂或断裂交叉复合部位、接触带构造等控制。矿石矿物组合为金+赤铁矿+隐晶-微晶石英。金矿化与硅化、赤铁矿化密切有关。矿石结构构造主要有交代残余结构、隐晶-微晶结构、胶状结构、鲕（豆）状结构；纹层状-条带状构造、角砾状构造、细脉-网脉状构造、多孔状构造和块状构造等。矿石类型主要有赤铁矿化硅化花岗闪长岩型、赤铁矿化硅化碳酸盐岩型、似碧玉岩型、赤铁矿化硅化砂砾岩型、纹层状-条带状硅质岩型、水热角砾岩型、块状硅质岩型和水成沉积砾岩型。矿石的矿物组成和结构构造明显反映出成矿作用是在浅成—超浅成的开放空间氧化环境下进行的，矿化方式有热液交代、热液充填和热液沉积等，矿化产物有热液硅质岩、热液隐爆角砾岩、热液沉积砾岩、热液碳酸盐岩等，构成一个完整的具内在时空分布规律的热液交代—充填—沉积成岩成矿体系。空间上，以热液活动中心的热液隐爆角砾岩墙（筒）向外依次为热液充填硅质岩和热液方解石脉体—热液交代似碧玉岩和蚀变花岗闪长岩—热液交代灰岩或白云质灰岩等；自下而上由热液交代充填细脉-网脉状硅质岩、脉状碳酸盐过渡到热液沉积纹层状-条带状硅质岩、热液沉积鲕（豆）状砾岩和近水平覆盖于矿体之上的厚大方解石壳体。时间上，热液交代蚀变矿化略早于热液充填和热液沉积矿化，热液体系的物质组成由早期富铁硅质成分向晚期富碳酸盐质成分演化。作为热液活动主要产物之一的富赤铁矿硅质岩矿石普遍呈红色、紫褐色等氧化色，系本身即富含铁质、硅质的矿液于开放氧化环境下交代或直接充填沉积而成的，并非次生氧化成因的。矿床的地质地球化学特征、成矿环境地质体的含金性、稳定同位素（Si、C、O、H）和稀土元素示踪等综合研究表明，大水式金矿成矿作用与燕山期构造岩浆活动密切有关，成矿物质主要来源于深部，成矿期浅层构造活动、中酸性岩浆侵入或喷发、含矿热液喷流及其后来的地表热泉活动是统一的受深部地质构造制约的构造—岩浆—热液活动体系的系列演化产物。它们不仅表现出空间上伴生、时间上紧随、活动范围逐渐缩小、活动强度逐渐减弱的特点，而且在成岩成矿物质成分上具相同渊源和继承演化的特点。金在热水溶液中主要呈金-硅络合物形式输运的。当富铁硅质的含矿热液由深处相对封闭体系快速上升到达地表完全开放环境时，由于温度、压力等的急剧降低使热液SiO₂的浓度处于过饱和状态。于是，热液中呈AuH₃SiO₄⁰络合物形式迁移的金等成矿物质便伴随着大量隐晶-微晶玉髓质石英的快速沉淀而卸载成矿。成矿温度变化区间较大，在105—386℃之间，说明成矿作用经历了一个从高温到低温急剧变化的过程。由流体包裹体获得的成矿压力在5—70bar之间，也说明成矿深度非常之浅，几近地表环境。流体包裹体成分表明，成矿热液富含碱质、且K⁺＞Na⁺，反映成矿流体与深部偏碱性岩浆活动有关；气体还原参数（R）远小于1，也说明成矿体系处于较强的氧化环境，与矿石富含赤铁矿而极贫硫化物的宏观地质特征相吻合。成矿时代为燕山早期。矿床成因类型为岩浆热液浅成—超浅成交代—充填—沉积矿床。更多还原

【Abstract】 Dashui gold ore deposit, being of a superlarge deposit newly discovered in western Qinling orogenicbelt, has very unique ore-forming characteristics. A systematic studies including ore-generatinggeologic settings, ore-controlling geological factors, metallogenic mechanism and metallogenicregularities have been done in this paper for the first time.The gold mineralization in Dashui deposit mainly occurred in the Triassic limestones and dolomites.Other gold-hosted rocks include Permian limestones, Jurassic conglomerates and intermediate-basicvein-like magmatic rocks formed during Yanshannian intracontinental orogenic period. The orebodies were produced in major forms of vein-like, sack-like and funnels. The ore-controllingstructures are NWW-EW strike, nearly SN strike and NEE-NE strike faults. The convergent partsof different strike faults and the contact zones between vein-like magmatic rocks and sedimentaryroeks are the best ore-hosted structures. The ore mineral assemblages are golds+hematites+chalc-edonieso The gold mineralization was strongly related to silifications and hematitizations. Thefabrics of gold ores mainly consist of metasomatic relict texture, crypto-micro crystal texture,colloform texture and oolitic-pisolitic texture; laminated-banded structure, brecciated structure,veinlet-stockwork structure, porous or vuggy structure and massive structure etc. The ores can beclassified into three genetic types: hydrothermal metasomatic, hydrothermal infilling andhydrothermal sedimentary mmeralizationo They are the serial products of the one hydrothermal systemat different geological environments. The hydrothermal sediments or ores include hvdrothermalsiliceous rocks, hydrothermal explosive breccias, hydrothermal sedimentary, oolitic-pisoliticconglomerates and hydrothermal carbonate rocks. There is a very good regularity for the time-spatialdistribution of all the hydrothermal products: In space, from the center toward peripheral parts of thehydrothermal active systems, the hydrothermal sediments are produced in the order of hydrothermalexplosive breceias+hydrothermal siliceous rocks+hydrothermai carbonate veins, hydrothermalmetasomatic jasperoids+hydrothermal metasomatic granodiorites, hydrothermal metasomaticlimestones. From the lower to upper parts, the hydrothermal products are respectively hydrothermalfilling veinlet-stockwork siliceous rocks+carbonate veins, hydrothermal sedimentary laminated-banded siliceous rocks+oolitic-pisolitic conglomerates+horizontally occurred carbonate crusts. Intime, hydrothermal metasomatic mineralizations are a bit earlier than hydrothermal infilling andsedimentary mineralizations, and the compositions of the hydrothermal systems evolved from ferro-silico rich in the earlier stages towards carbonate rich in the late periods. The red or brown silicalitetype ores were formed due to the directly infilling or sedimentation of the ferri-rich siliceoushydrothermals.Evidences from the geological and geochemical characteristics of the deposit, the Au abundances ofgold-hosted geological bodies, the stable isotope elements （C, Si, O, H） and rare elements etc.indicate that the ore-forming materials mainly came from the deep sources which are closely related toYanshannian tectono-magmatism. The shallow tectonic activities, the magmatic intrusion orvolcanism, the hydrothermal eruptions and the late active hot-springs are all the serial evolutionaryproducts of the regional crust due to the deep upwelling and mantle-crust interactions. Thus, they accompanied and associated each other in time and space, and the active intensity and extensivenessof these serial products became much weaker and narrower with the time going on.Au was transported probably in the complex form of AuH₃SiO₄⁰. When the ore-containinghydrothermal solutions rapidly got to the surface being of full-open and oxidative environment from thedeep sources, the concentration of silica would be changed into supersaturated relative to quartzbecause of the abruptly descendment of the temperature and pressure of the hydrothermal systems.Therefore, the gold transporting in the complex of AuH₃SiO₄⁰ would be wholly depositedaccompanied with the depositing of quantities of chalcedonies. The ore-forming temperature andpressure obtained from the fluid inclusions show that the whole mineralization suffered a quite shortprocess with a wide range of temperature variation, and the metallogenic depth might be very shallowor almost near the surface of the crust. The compositions of the fluid inclusions demonstrate thehydrothermals might be rich in alkaline components and the concentration of K⁺ far more than that ofNa⁺. This implies the sources of the ore-forming fluid be closely related to the Yanshannian alkalinemagmatic rocks. The gas reduction parameters （R=（CO+H₂+CH₄）/CO₂） of fluid inclusions arevery low, showing a high oxidation metallogenic environment. The metallogenic epoch belongs tothe earlier stage of Yanshannian according to the geologic evidences.In a word, Dashui-type gold ore deposits should be classified into the magmatic hydrothermalshallow-near surface metasomatism-infilling-sedimentation ore deposits from whatever viewpoints ofthe mineralization.更多还原