The Central Asian Orogenic Belt(CAOB)in China can be divided into the eastern,central,and western segments based on convergent margin type:the eastern and western segments represent intra-oceanic convergent margins,while the central segment represents an Andean-style continental convergent margin.There are large numbers of mafic-ultramafic intrusions in the belt with ages spanning from the Silurian to the Triassic,however,economically important intrusions are from the Early Permian to the Late Triassic.In this study,we carried out a systematic study on the nature of the mantle source,the role of pyroxenite components in the partial melting of the mantle,the oxygen fugacity of the mantle and mantle-derived mafic-ultramafic magmas,the triggers of sulfide saturation of magmas,and the controls on metallogenic differences of the mafic-ultramafic intrusions in the CAOB to understand the origin of Ni-Cu sulfide deposits in the convergent margin settings.We summarized a few major features of Ni-Cu sulfide mineralization in convergent margin settings.We compared the formation ages of sulfide-bearing and barren intrusions in the Kalatongke area in the western segment of the CAOB along a major suture zone of the Irtysh shear zone,and found all sulfide-bearing intrusions were emplaced in a short-lived metallogenic epoch,which is consistent with the syn-collisional extension stage on a regional scale.This may lead to the rapid ascent and emplacement of mantle-derived mafic magmas at a shallower crustal level,preventing significant Ni loss from the magmas due to olivine crystallization at depths.Note that the stage of syn-collisional extension here cannot simply be considered as a post-collisional setting,which cannot explain the limited age range of Ni-Cu sulfide-bearing mafic-ultramafic intrusions.We examined the trace-element compositions of olivine from representative sulfide-bearing and barren intrusions in the CAOB and found that the involvement of pyroxenite during partial melting of the mantle sources is important for producing Ni-rich mafic magmas.However,the degree of involvement of pyroxenite components may be related to the pressure of partial melting of the mantle:in the intra-oceanic convergent margin,the addition of 10%pyroxenite during partial melting of the mantle would dramatically increase the Ni content of mantle-derived mafic magmas,whereas magmas produced by low degrees of partial melting of the mantle at depths in the Andeans-style continental convergent margins still have less potential to Ni-Cu sulfide mineralization even with greater pyroxenite involvement during partial melting of the mantle.We calculated the magma oxygen fugacity of representative sulfide-bearing mafic-ultramafic intrusions in the CAOB,the integrated S isotopic compositions of sulfides in the ores,and the C isotopic compositions of the ores.We found that their parental magmas are highly oxidized and can contain sufficient S to form medium-to small-scale Ni-Cu sulfide deposits.Sulfide saturation of such oxidized magmas was likely triggered by crustal organic carbon materials derived from external sources.The oxidized magmas were likely derived from a metasomatized mantle source and were therefore highly hydrated,such hydrated ore-forming magmas can lead to special ore textures such as globular,net-work,and breccia ores.We conclude that the Ni-Cu sulfide deposits in the convergent margin settings were likely formed from the metasomatized mantle-derived oxidized mafic magmas and were emplaced into the lower crust in a very short period against a long history of collision,and they have different formation mechanism from those in within-plate,mantle plume-related mafic magmatism.The exploration of Ni-Cu sulfide deposits in convergent margin settings needs new thoughts and methods.
MVT铅锌矿床和会泽型(HZT)铅锌矿床是全球最重要的铅锌矿床类型之一,其中大型矿床数量和铅锌金属储量均居于重要地位.基于勘查区找矿预测理论与方法,从"时间、空间、物质及其演化"四要素出发,厘定MVT铅锌矿床的成矿地质作用和成矿地质体,总结成矿结构面类型和矿化样式,概括成矿流体作用特征标志,并进一步揭示经典的MVT铅锌矿床"三位一体"的成矿规律:矿床产于前陆盆地地堑式构造带、不整合面上发育的溶塌角砾岩岩相组合、成矿正断层破碎带、区域性热卤水活动的"硅-钙面"成矿结构面中.在此基础上,综合构建经典的MVT铅锌矿床找矿预测地质模型:通过前陆盆地地堑式构造带研究确定勘查区找矿方向,通过成矿结构面研究判断矿体空间位置及其产状,硅-钙面等特征是判断矿床(体)存在的成矿流体作用标志.其勘查应用流程进一步概括为:看、查、识、厘、析、填、测、比、探、勘.该研究对同类矿床成矿规律研究和找矿预测评价具有启示意义.
黔西北矿集区作为川滇黔富锗铅锌多金属成矿区的重要组成部分,成矿条件优越,找矿潜力巨大.已有研究表明,该区铅锌矿床成矿时代为印支晚期,但对成矿流体运移方向的研究相对薄弱,这也直接影响到区内资源勘查部署.在综合剖析该矿集区典型矿床的矿体特征、成矿温度、同位素组成和成矿年龄等资料的基础上,本文划分成矿流体类型,系统总结铅锌成矿作用过程中与成矿流体运移相关的"行迹"标志,研判成矿流体在区域尺度的运移方向,进一步讨论流体运移的制约因素.研究表明,在黔西北富锗银铅锌矿集区,构造为成矿流体运移提供了主要的驱动力和通道,成矿构造的优势方位决定成矿流体的主体运移方向.成矿温度、同位素组成和成矿构造等方面的区域性变化特征均指示成矿流体在平面上主体从南东至北西方向运移;除印支期陆块碰撞作用导致古特提斯洋闭合的因素外,雪峰山陆内变形构造作用也可能为成矿流体运移提供了动力,进而控制了流体的运移方向.该研究不仅对黔西北矿集区的"战略性"铅锌找矿部署具有现实意义,而且为热液矿床成矿流体运移方向研究提供了路径.
近年来,随着普朗和红山-红牛等大型-超大型铜矿的投产,滇西北格咱地区已成为我国重要的铜资源勘查开发基地,在该区寻找类似"普朗-红山式"斑岩-矽卡岩型大型-超大型铜多金属矿床是本区找矿勘查的热点.本次在开展松诺地区铜资源远景调查的基础上,对松诺含矿石英闪长玢岩开展了锆石U-Pb年代学研究,结果显示石英闪长玢岩体锆石U-Pb年龄分别为229.7±1.1 Ma和222.3±0.7 Ma,早于矿区石英二长斑岩体,为晚三叠世岩浆活动的产物.石英闪长玢岩和石英二长斑岩岩石地球化学特征显示,为准铝-弱过铝质的高钾钙碱性系列I型花岗岩,稀土元素配分曲线均表现为轻稀土元素富集,重稀土元素相对亏损,具弱的负Eu异常,富集Rb、Ba等大离子亲石元素,亏损Ta、Nb、Ti等高场强元素.综合岩相学、岩石化学、锆石Hf同位素和全岩Sr-Pb同位素等特征,认为松诺含矿斑岩体形成于印支期甘孜-理塘洋壳向西俯冲的岩浆弧环境,岩浆源区为俯冲流体交代的岩石圈富集地幔,岩浆上升过程经历了壳源沉积物质混染.矿区具备弧环境斑岩型铜多金属矿床的成矿条件,且蚀变矿化强烈,找矿前景良好,值得进一步深入研究和开展勘查工作.
三维地质模型是三维成矿预测最重要的数据基础之一,其准确性对于深部预测靶区的圈定具有十分重要的意义.然而,三维地质模型存在一定程度的不确定性,其不确定性主要是受到地质体与地质结构自身的复杂性,数据密度、误差和建模方法等多方面影响.本文以长江中下游成矿带钟姑矿田为例,基于隐式三维地质建模及蒙特卡洛模拟方法,对控制剖面中地质界线产状引起的三维地质模型的不确定性开展定量分析,并度量和评价其对三维成矿预测结果的影响.研究结果显示,深部地质界线的产状倾角及倾向变化会导致三维地质模型产生不同程度的不确定性.通过扰动策略,能够有效开展相关的不确定性分析和度量工作;三维地质模型的不确定性会在一定程度上影响三维成矿预测结果,但三维成矿预测方法具有一定的鲁棒性,基于预测结果圈定的找矿靶区位置相对稳定.对于具有较高不确定性的深部预测靶区,进一步工作可通过降低三维地质模型的不确定性或增加其他预测信息等方式,提高预测结果的确定性,以降低找矿勘探风险.
