研究生知识库

位于扬子地块西南缘的川滇黔接壤铅锌矿集区是我国重要的Pb、Zn、Ag、Ge等生产基地之一，滇东北铅锌成矿区是该矿集区的重要组成部分，分布于其中的毛坪铅锌矿床是矿集区内探明规模第二的超大型铅锌矿床，Pb+Zn储量超过300万吨。毛坪超大型铅锌矿床具有许多独特的地质特征，如规模大、品位高、伴生元素多、矿体延深大等，倍受国内外矿床学家关注。虽然前人对该矿床成矿地质条件、矿床地质特征、矿床地球化学和成矿预测进行过研究，但有关成矿动力学背景、矿床成因类型、成矿物质来源、成矿流体来源与演化以及峨眉山玄武岩与成矿的关系等方面还存许多争论，严重影响成矿模型的建立和成矿预测的深入开展。本文以毛坪超大型铅锌矿床规模最大、揭露最好、正在开采的Ⅰ号矿体群为主要研究对象，在深入细致的野外地质观测和室内岩矿鉴定基础上，利用先进的分析测试技术，进行了较为系统的脉石矿物方解石REE、矿石矿物原位微量元素和矿床C-O-S-Pb-Zn-Cd同位素地球化学研究，以此厘定了矿床成因类型，重点从成矿物质来源、成矿流体来源与演化以及峨眉山玄武岩与成矿的关系等方面探讨了矿床成因，初步建立了矿床成因模式。论文取得的主要认识如下：（1）毛坪超大型铅锌矿床Ⅰ号矿体群赋存于上泥盆统宰格组（D3zg）粗晶白云岩中，Ⅱ号矿体群赋存于下石炭统摆佐组（C1b）及中石炭统威宁组（C2w）白云岩中；矿床明显受构造控制，且构造具有分级控矿特征，区域构造控制矿床所在的矿带分布、矿区构造控制矿床分布、层间构造控制矿体分布；矿区广泛发育的峨眉山玄武岩在成矿过程中起“遮挡层”作用，为铅锌矿成矿作用，尤其是高品位铅锌矿成矿作用，营造良好的成矿环境；矿石的矿物成分相对简单，矿石矿物主要为方铅矿、闪锌矿和黄铁矿，脉石矿物主要为方解石和白云石；矿区除广泛发育白云岩化和方解石化外，其他围岩蚀变相对较弱；矿石品位特高，出矿Pb+Zn平均超过20wt%；伴生元素除Ag外，Ge、Cd等分散元素也达到综合利用要求。矿床这些地质特征与川滇黔铅锌矿集区目前探明规模最大、Pb+Zn储量近800万吨的云南会泽超大型铅锌矿床相似，暗示本区深部和外围具有良好的找矿潜力。（2）矿床脉石矿物方解石的REE含量、配分模式和相关参数明显不同于赋矿围岩，暗示成矿流体具有多源性；从成矿早阶段到晚阶段，方解石δEu逐渐降低，表明成矿环境由相对氧化渐变为相对还原。矿石矿物闪锌矿以富集Cd、Ge，贫Fe、Mn、In、Co和Sn为特征，在矿床成因类型闪锌矿微量元素判别图中，本区样品绝大部分位于MVT型铅锌矿床区域；通过与国内外典型MVT型铅锌矿床成矿背景、成矿条件和矿床地质-地球化学特征等方面对比，厘定该矿床为MVT型铅锌矿床。（3）矿床矿石矿物的S同位素组成总体与赋矿地层中的蒸发膏盐层的S同位素组成相近，指示成矿流体中的S主要来自海相硫酸盐的热化学还原作用；脉石矿物方解石C-O同位素组成主要位于海相碳酸盐岩溶解作用区域，少量靠近地幔包体范围，暗示成矿流体中的CO2主要是由海相碳酸盐岩溶解作用提供，少量深源流体可能参加了成矿作用；矿石矿物的Pb同位素组成相对均一，明显的壳源特征，示踪成矿物质主要来源于区域基底岩石，如会理群或昆阳群等，不排除少量成矿物质由盖层提供；矿石矿物闪锌矿的Zn和Cd同位素组成也相对均一，暗示成矿物质为相对单一来源或是在成矿过程中发生过同位素均一化作用的多个来源。矿床地质、脉石矿物方解石REE及C-O同位素组成、矿石矿物S-Zn-Cd同位素组成均证实，流体混合作用是本区铅锌成矿的重要机制。（4）综合所获得的毛坪超大型铅锌矿床各种地质-地球化学资料，初步建立了矿床成因模式：大规模流体运移，淋滤区域基底岩石中的成矿物质，形成富含Pb、Zn等成矿元素的成矿流体；成矿流体沿主干断裂向上运移，受到峨眉玄武岩的“遮挡”被迫折返，向次级断裂或碳酸盐岩地层的层间断裂运移和聚集；成矿流体运移和聚集过程中，与富含还原硫的流体混合，成矿元素沉淀形成铅锌矿床。

Located in the southwestern margin of Yangtze block，Sichuan-Yunnan-Guizhou border lead-zinc ore concentration area is one of the important production bases of Pb，Zn，Ag and Ge in China. The lead-zinc metallogenic area in northeastern Yunnan is an important part of the ore concentration area. The Maoping lead-zinc deposit is the second largest proved lead-zinc deposit in the ore concentration area. The reserves of lead and zinc exceed 3 million tons. Maoping super-large lead-zinc deposit has many unique geological characteristics，such as large scale，high grade，many associated elements，deep ore body，etc. It has attracted much attention of ore deposit scientists at home and abroad. Although predecessors have studied the metallogenic geological conditions，geological characteristics，geochemistry and metallogenic prediction of the deposit，there are still many controversies about the metallogenic dynamic background，genetic types，source of mineralizing materials，source and evolution of metallogenic fluids and the relationship between Emeishan basalt and metallogenic prediction，which seriously affect the establishment of metallogenic model and It seriously affects the establishment of metallogenic model and the further development of metallogenic prediction.On the basis of in-depth and detailed field geological observation and laboratory rock and mineral identification，a systematic study on REE of gangue mineral calcite，in-situ trace elements of ore minerals and C-O-S-Pb-Zn-Cd isotope geochemistry of ore deposits has been carried out by using advanced analytical and testing techniques.Based on this，the genetic types of the deposit are determined，and the genesis of the deposit is discussed in terms of the source of ore-forming materials，the source and evolution of ore-forming fluids，and the relationship between Emeishan basalt and mineralization，and the genetic model of the deposit is preliminarily established. The main understandings obtained in this paper are as follows:（1）The No.1 orebody group of Maoping super-large lead-zinc deposit occurs in coarse-grained dolomite of the Upper Devonian Zaige Formation（D3zg），and the No.2 orebody group occurs in dolomite of the Lower Carboniferous Pengzou Formation（C1b） and the Middle Carboniferous Weining Formation（C2w）.The deposit is obviously controlled by structure，and the structure is characterized by grading ore-controlling which the regional structure controls the distribution of ore deposits and the interlayer structure controls the distribution of orebody.Emeishan basalt，widely developed in the mining area，acts as a "shielding layer" in the mineralization process，creating a favorable metallogenic environment for lead-zinc deposits，especially for high-grade lead-zinc deposits.The mineral composition of the ore is relatively simple，the ore minerals are mainly galena，sphalerite and pyrite，and the gangue minerals are mainly calcite and dolomite; besides dolomitization and calcification，the wall rock alteration in the mining area is relatively weak; The grade of ore is very high，the average lead + zinc of ore is more than 20 wt%. Besides Ag，dispersed elements such as Ge and Cd also meet the requirements of comprehensive utilization.These geological characteristics of the deposit are similar to those of Huize super-large lead-zinc deposit in Yunnan Province，which is the largest lead-zinc deposit in Sichuan-Yunnan-Guizhou ore concentration area with nearly 8 million tons of Pb+Zn reserves，suggesting that the deep and peripheral parts of the area have good prospecting potential.（2）The REE content，distribution pattern and related parameters of calcite in gangue mineral of the deposit are obviously different from those of host rocks，suggesting that ore-forming fluids have multiple origins. From early to late stages of mineralization，δEu of calcite gradually decreases，indicating that the metallogenic environment changes from relative oxidation to relative reduction. The ore mineral sphalerite is characterized by enrichment of Cd，Ge and depletion of Fe，Mn，In，Co and Sn.In the trace element discriminant map of sphalerite，most of the samples in this area are located in MVT type lead-zinc deposit area. By comparing with the typical MVT type lead-zinc deposits at home and abroad in metallogenic background，metallogenic conditions and geological-geochemical characteristics of the deposit，it is determined that the deposit is MVT type lead-zinc deposit.（3）The sulfur isotopic compositions of ore minerals in the deposit are generally similar to those of evaporative gypsum layers in ore-hosting strata，indicating that sulfur in ore-forming fluids is mainly derived from thermochemical reduction of marine sulfate; the C-O isotopic compositions of gangue minerals are mainly located in the dissolution zone of marine carbonate rocks and a small amount close to the scope of mantle inclusions，It is suggested that CO2 in ore-forming fluids is mainly supplied by dissolution of marine carbonate rocks，and a small amount of deep-source fluids may participate in mineralization. The Pb isotopic composition of ore minerals is relatively homogeneous，with obvious crustal characteristics，the results show that the ore-forming materials mainly come from the regional basement rocks，such as Huili Group or Kunyang Group，and a small amount of ore-forming materials are supplied by the caprock. The zinc and cadmium isotopic compositions of sphalerite are also relatively homogeneous，suggesting that the ore-forming materials are relatively single sources or multiple sources of isotope homogenization occurred during the mineralization process. The deposit geology，REE and C-O isotopic compositions of gangue minerals and S-Zn-Cd isotopic compositions of ore minerals all confirm that fluid mixing is an important mechanism of lead-zinc mineralization in this area.（4）Based on the geological and geochemical data of the Maoping super-large lead-zinc deposit，the genetic model of the deposit has been preliminarily established: large-scale fluid migration，leaching of mineralizing materials from the basement rocks in the region，forming ore-forming fluids rich in Pb，Zn and other metallogenic elements; The ore-forming fluids migrate upward along the main faults and are forced to return under the "shield" of Emei basalt，migrating and gathering towards secondary faults or interlayer faults of carbonate strata. During the migration and accumulation of ore-forming fluids，they are mixed with fluids rich in reducing sulfur，and the ore-forming elements precipitate to form lead-zinc deposits.