【作者】 张彩华；

【导师】 刘继顺；

【作者基本信息】 中南大学 ， 矿产普查与勘探， 2007， 博士

【摘要】 南澜沧江弧火山岩带属全球特提斯构造成矿域的一部分，是中国极具潜力的铜多金属找矿远景区之一。本文在详细研究区域成矿地质背景及其演化和全面收集研究区内矿床（点）的地质、遥感、物探、化探、勘探、开采资料的基础上，以区域成矿学和弧火山岩成矿理论为指导，以构造—岩浆—成矿作用为主线，首次对区内的典型矿床——官房铜矿、有代表性的花岗质小岩体及中晚三叠世富钾火山岩进行深入剖析和系统研究。取得的主要成果与认识如下：（1）研究区内晚三叠世小定西组基性火山岩为高钾钙碱性—钾玄岩系列，富集轻稀土元素，无Eu或弱的负Eu异常。火山岩的微量元素配分分布模式显示大离子亲石元素（LILE）K、Rb、Ba、Th强烈富集而高场强元素（HFSE）Nb、Ti、Ta等则明显亏损。大量的常量和微量元素构造环境判别图解及岩石组合等地质特征表明小定西组基性火山岩具活动大陆边缘的弧火山岩的特征。同位素研究显示小定西组火山岩具高⁸⁷Sr／⁸⁶Sr值，其平均值为0.708，高于均一储集库(⁸⁷Sr／⁸⁶Sr)_UR的现代值0.7045；ε（Nd）值均为负值，介于-2.48～-1.21之间；¹⁴³Nd／¹⁴⁴Nd值低，小于未分异的球粒陨石地幔值。微量元素和Sr、Nd同位素特征表明小定西组富钾基性火山岩既显示出一些壳源岩石的特点，但同时具有幔源岩石的特征。这种具有双重特征的岩石与来源于EMⅡ富集地幔的岩石一致，显示其源区具有壳幔混源性质，即存在部分大洋沉积物、陆壳物质和地幔岩的深部混合作用，这种源区的形成与特提斯澜沧江洋板块向东的俯冲消减作用有必然的因果关系。（2）研究区内中三叠世忙怀组流纹质火山岩的化学成分具有高硅、高钾、低钛、中等Al₂O₃、CaO＜1％、ALK＜8％、铝饱和指数A／CNK＞1.1、里特曼指数σ小于3.3，但K₂O＞Na₂O的特征，属于弱碱质流纹岩中的钾质流纹岩，为钙碱性系列，与晚三叠世小定西组玄武质火山岩共同构成两个大的喷发旋回。忙怀组酸性火山岩也富集轻稀土元素和大离子亲石元素，具强的Eu负异常，但贫高场强元素Ta、Nb、Ti和亲铁元素。火山岩的⁸⁷Sr／⁸⁶Sr平均值为0.755，高于下地壳的上限值0.710；ε（Nd）均为负值，介于-3.63～-1.66之间，远大于大陆地壳的平均值-15。岩石的地质地球化学特征表明忙怀组酸性火山岩的岩浆来源以壳源为主，主要为陆壳物质的重熔产物，同时有消减带物质的参与，从而表现出“碰撞型”弧火山岩的特点。（3）小定西组基性火山岩中所夹硅质岩化学成分以SiO₂为主，含量为96.28％～97.92％，其次为FeO和Al₂O₃，其它成分含量都很低。硅质岩主要属于生物成因，其常量和稀土元素判别图解表明，硅质岩形成于大陆边缘区，这与中晚三叠世火山岩形成于大陆边缘弧构造环境的结论一致。（4）老毛村岩体的岩石类型主要为二长花岗岩，具有高硅、富钾、过铝、钙碱性“S”型花岗岩特征。岩体的常量元素、稀土元素和微量元素特征与其围岩之一的中三叠世忙怀组“碰撞型”高钾流纹质弧火山岩有很大的相似性，体现了它们之间的演化关系。成岩物质主要为壳源，多种氧化物与微量元素构造环境判别图解结果表明，老毛村岩体兼具有火山弧花岗岩和后造山花岗岩的特征，为特提斯澜沧江洋板块向东与思茅地块碰撞之后转入伸展引张体制下地幔底辟上隆发生地壳深融作用的产物。老毛村岩体形成的构造环境为“后造山”，岩体的Rb-Sr同位素年龄为169Ma±5Ma，形成时代为晚侏罗世。（5）官房铜矿的矿体严格受断裂构造和火山岩岩性双重控制，脉状矿体切割地层，穿切小定西组不同亚段的地层，矿石中脉状、角砾状构造发育等特征充分表明矿床的形成时代晚于小定西组基性火山岩的形成年代。小定西组各分段在区域地层剖面中均无铜的初始富集，矿石与围岩的稀土元素地球化学特征有着显著的差别，这表明官房铜矿在形成过程中小定西组富钾基性火山岩不能作为初始矿源层，虽然地层中的铜对成矿可能有一定的贡献，但主要成矿物质应该来源于深部，不过需要指出的是小定西组火山岩每一次喷发旋回顶部由气孔杏仁熔岩和角砾岩组成的高渗透区域是矿床尤其是似层状矿体形成的良好容矿空间，对似层状矿体的形态具有控制作用。（6）官房铜矿与典型的“火山红层铜矿”相比，有一些共同点，但官房铜矿玄武质火山岩的铜背景值低，基本上没有发生绿片岩相的变质作用，黄铁矿化和硅化等围岩蚀变十分发育且与成矿关系密切等特征又清楚地显示官房铜矿有自己鲜明的特点。矿区H、O、S、Pb同位素、稀土元素、微量元素和包裹体等地球化学特征表明矿床成矿物质主要来源于深部下地壳或上地幔；成矿流体为低—中盐度的H₂O-NaCl-CO₂体系；成矿流体主要为岩浆水和大气降水的混合流体；矿床形成于一种相对开放的体系。结合矿床产出构造环境、围岩蚀变类型、控矿要素、流体包裹体和同位素特征等分析，笔者认为官房铜矿属浅成中—低温火山次火山热液矿床，成矿与同火山机构有关的次火山岩体或中酸性隐伏岩体的岩浆作用有密切的成因联系。（7）南澜沧江带火山岩的演化历史表明，晚三叠世是区域应力场转折时期。晚三叠世时大规模的伸展作用、高钾钙碱性—钾玄岩系列岩石的大量发育以及后来的成矿作用事件不是偶然孤立的，而是受某种统一的深部作用机制的制约，而岩石圈拆沉作用可能是一种合理的深部作用机制。晚三叠世之后，由于印度板块向北冲挤，引发弧后陆内产生大规模下切地幔的逆冲推覆—走滑—伸展构造（澜沧江超壳断裂）的重新活动，可能导致滞留于构造带内地幔中的大洋板块残片（可能具有Cu、Ag等矿化元素的高背景值）部分熔融，沿构造薄弱部位（如古火山机构、大断裂交汇部位等）上侵。熔融形成的初始富Cu等矿化元素的富挥发份和钾质的中酸性岩浆，经多次上侵、不断分异演化，到晚期阶段演变成富含Cl^-和HS^-等挥发份和Cu²⁺、Pb²⁺、Ag⁺等矿化元素的中酸性熔融体。在构造动力和本身挥发份的作用下成矿流体不断沿断裂运移，上侵至小定西组基性火山岩或忙怀组酸性火山岩中的有利部位淀积成矿。因此，南澜沧江带的构造背景演化与岩浆作用，岩浆演化与成矿作用是一个统一作用的整体，成矿作用只是其中最后的一个环节。（8）通过研究和总结官房铜矿的地质特征和成矿规律，阐述了铜矿体与火山岩的时空关系和成因联系，突破了“顺层鸡窝矿”的观点，提出了“矿带陡倾斜矿体成层”的“层楼结构”成矿规律，并首次建立了官房铜矿的成矿模式和南澜沧江弧火山岩带云县段铜矿床的综合找矿模型，明确了地质找矿标志，肯定了研究区的找矿前景，优选了找矿靶区和找矿远景区。与此同时，官房铜矿的地质找矿也实现了历史性的突破现，已初步控制121+333+334级铜金属资源量近50万吨，银资源量1500吨，产生了巨大的经济和社会效益。更多还原

【Abstract】 South Lancangjiang arc volcanic rock belt belongs to part of SanjingTethyan tectonic metallogenic domain, which is one of the most potentialcopper polymetal exploration prospective areas. Based on the study ofregional metallogery, geological setting and its evolution in detail and thegeneral gathering of geology, remote sensing, geophysical prospecting,geochemical exploration, prospecting and production data of the oredeposits（spot） in the study area, and guided by regional metallogeny andarc volcanic rock mineralization theory, this paper has studied the typicalore deposit——Guanfang copper deposit and representative granitoidsmall rock body and middle-late Triassic potassium-high volcanic rocksin the study area intensively and systematically for the fisrt time. Themain results and some new viewpoints can be summarized as following:（1） Late Triassic Xiaodingxi Formation basic volcanic rocks belongto potassium-high cacl-alkali basalt series-shoshonite series with theirRittmann index varying in the range of 2.23～9.24 （σ=6.27 on average）in the study area, which are enriched in LREE and potassium（K₂O=2.68% on average）. The REE distribution pattern is slightly rightoblique with an average∑REE of 171.83×10^-6, and they exist no orvery weak negative Eu anormalies. The rocks show evident LILE like K,Rb, Ba, Th positive anomalies and HFSE such as Nb, Ti, Ta negativeanormalies in the trace element distribution pattern. According to a lot oftectonic setting discrimination diagrams of the rocks as well as geologicalcharacteristics of the rock assemblage, it is suggested that the late TriassicXiaodingxi Formation basic volcanic rocks along South Lancangjiangbelt should be composed of active epicontinental arc-volcanic rocks. The characteristics of radiogenic Sr, Nd isotope show that XiaodingxiFormation basic volcanic rocks have a relatively high value of ⁸⁷Sr/⁸⁶Srwith an average of 0.708, which is higher than the (⁸⁷Sr/⁸⁶Sr)_UR presentvalue 0.7045 of chondrite uniform reservoir. The values ofε（Nd） arenegative, which vary from -2.48 to -1.21, and the values of¹⁴³Nd/¹⁴⁴Nd are obviously lower than the present value of chondriteuniformless reservoir. The characteristics of geochemistry and isotopicgeochemistry infer that the source of late Triassic Xiaodingxi Formationbasic volcanic rocks has the feature of crust-mantle mixed material,which is consistent with EMⅡ. So the potassium-high basic volcanicrocks in the study area were not directly from the remelting of normalmantle or crust material, but it’s from the partial melting of mantle source,enriched in large-ion lithophile elements and LREE, in which continentalcrust material and oceanic sediments are largely involved and inevitablyrelated to the subduction eastward of Tethyan Lancangjiang oceanic plate.（2） Middle Triassic acid volcanic rocks of Manghuai Formationbelong to potassium-rich calc-alkali rhyolitic volcanic rock series, whichis characteristic of high silica（SiO₂=75.49% on average）, medium Al₂O₃,CaO＜1%, ALK＜8%, rich potassium（K₂O=3.38% on average）, lowtitanium（TiO₂=0.136% on average）, Rittmann index （σ）＜3.3, K₂O＞Na₂O and A/CNK higher than 1.1（1.53 on average）. The rocks also havehigh LILE like K, Rb, Ba, Th and LREE concentrations with obvious Euanomalies but poor in HFSE such as Nb,Ti, Ta and siderophile element.The ⁸⁷Sr/⁸⁶Sr values of these acid potash-rich volcanic rocks are higherthan 0.710 （0.755 on average） andε（Nd） values of them are all less thanzero but far and away greater than the average of the crust（-15）, whichvary from -3.63 to -1.66. Based on a comprehensive analysis of thetectonic setting and geochemical characteristics, it is concluded that thesepotash-rich volcanic rocks of Manghuai Formation are mainly originatedfrom the remelting of continental crust materials, accompanied with theparticipation of subduction zone materials, which made them have thecharacteristic of collision type arc volcanic rocks.（3） The chemical composition of siliceous rocks among late TriassicXiaodingxi Formation basic volcanic rocks is mainly SiO₂ in the range of 96.28%～97.92, secondly is FeO and Al₂O₃, other ingredient is very low.The siliceous rocks mostly belong to organic origin and formed in thecontinental margin according to some discrimination diagrams, which isin accord with the conclusion that the tectonic setting of middle-lateTriassic volcanic rocks in the study area is epicontinental arc.（4） The Laomaocun rock body in South Lancangjiang belt is mainlymonzonite granite-porphyry. Chemical composition of the rock body isSiO₂=77% on average, Al₂O₃=12.08%～14.33%, A/CNK （molecule ratio）＞1.1（1.68 on average）, K₂O/Na₂O=4.54 on average, Rittmann index（σ）=0.75～1.34 （1.14 on average）, DI=84.0～87.7,∑REE=204.27×10^-6～274.17×10^-6,∑LREE/∑HREE=3.43～5.44 andδEu=0.47～0.60.The rock body shows obvious negative Sr, P, Ti and Eu anomalies as wellas positive K, Rb, Ba, Th, U anomalies in the primitivemantle-normalized trace element spider diagrams, suggesting evidentfractional crystallization. According to its lithofacies and petrological andgeochemical characteristics, the Laomaocun rock body is silica-high,potassium-rich and belongs to peraluminous calc-alkaline S type granite,which is similar to collision type acid volcanics of Manghuai Formationin the middle Triassic period. Rb-Sr age of the rock body is 169Ma±5Ma.Various oxide and trace element diagrams for discrimination of tectonicsetting reveal that the Laomaocun rock body is post-orogenic granite（POG） formed in a post-orogenic extensional structural environment.（5） The ore bodies of Guanfang copper deposit are strictly controlledby the faults that radiate toward the outside and lithologic characters ofpotassium-high volcanic rocks, the vein orebodies cut off the strata ofdifferent sub-section of Xiaodingxi Formation basic volcanic rocks,brecciated structure and vein structure are widespread in the ore. Thementioned features of Guanfang copper deposit show that the forming eraof the ore deposit is posterior to that of Xiaodingxi Formation basicvolcanic rocks. Each subsection of Xiaodingxi Formation has no initialcopper enrichment in the regional section and the REE characteristic ofthe ore is quite different from that of the host rocks. Therefore theore-forming materials of Guanfang copper deposit should have comefrom the lower crust and upper mantle instead of Xiaodingxi Formation basic volcanic rocks in the process of mineralization. The zone of highpermeability is the best position for mineralization composed ofvolcanicclastics, breccias, amygdules and fractures on the top of eacheruption gyration of subaerial flood basalt, which is one of the major orecontrols of orebodies, especially quasi-strata-bound ore bodies.（6） Compared to the typical ’Volcanic redbed copper deposit’ （VRC）,Guanfang copper deposit is characterized by its low Cu background valueand its absence of low greenschist facies metamorphism of the hostvolcanic rocks although they have some common points. Coppermineralization is close related to silicification and pyritization, which iswidespread in the ore deposit. It is suggested that the ore-formingmaterials mostly derived from the lower crust and uppermantle, themetal-bearing fluid is H₂O-NaCl-CO₂ system with low-middle salinity,the ore-forming fluid is of hybrid type that is composed of magma waterand meteoric water according to the study of trace elements, fluidinclusions and isotopes of the copper ores and ore-beating rocks. Thesulfur isotope composition of the main sulfides is within the range of-11.88‰～-5.67‰δ³⁴S_V-CDT. In combination with tectonic setting,wallrock alteration type and ore control element, it is concluded thatGuanfang copper deposit is hydrothermal Cu ore deposit that is ofgenetically low to medium temperatures and formed in a relatively opensystem and closely related to the evolution of the magmatic activity ofthe concealed intermediate-acidic rock or Indosinian sub-volcanic rock inthe volcanic apparatus.（7） The evolution history of volcanic rocks in South Lancangjiangbelt indicates that late Triassic epoch is a turn time of regional stress field,and the massive extensional activity and the eruption of potassium-highcacl-alkali basalt series-shoshonite series volcanic rocks and thesubsequent mineralization event are not insular and occasional, which isconstrained by some mechanism, and lithosphere delamination maybe is arational deep mechanism. The remobilization of the thrust-nappe andstrike-slip and extensional structure such as Lancangjiang major faultwithin the continental on a large scale that incise down to mantle owingto Indian plate’s northward impact and extrasion after late Triassic epoch perhaps result in the partial melting of the oceanic plate relic （maybe havehigh background value of the mineralization elements of Cu, Ag and soon） leaving in the mantle in the tectonic zone and intrude upwardsfollowing the dotty structure position such as volcanic mechanism and theconvergence of two major faults. Thus the formative magma withabundant initial Cu element and volatile flux and potassium became theintermediate-acidic fusant that is rich in fugitive constituent such as Cl^-and HS^-- and metallogenic elements such Cu²⁺, Pb²⁺, Ag⁺ and so on in thelate stage after ceaselessly differential evolution, the ore-forming fluidbeing drived by the power of structure and volatile flux through thefracture zone deposited in favorable place of Xiaodingxi Formation basicvolcanic rocks. So the evolution of tectonic setting of South Lancangjiangbelt and magma activity, the magmatic evolution and the mineralizationactivity is the all and the one, and the mineralization activity is the onlylast link among them.（8） Based on the study and summary of the geological features andmineralization law of Guanfang copper deposit, the relation of spacetimeand genesis between the copper orebodies and potassium-rich volcanicrocks is expounded, the metallogenic model of Guanfang copper depositand the comprehensive prospecting model of copper deposits in YunXiansection of Lancangjiang volcanic arc are set up, the prospecting signs aredesignated, the prospecting perspective is confirmed and the prospectingtargets are optimized in the study area. In the meantime the prospectingwork of Guanfang copper deposit obtained a great success and createdhuge economic and social benefit.更多还原