广西佛子冲铅锌多金属矿田热水沉积—叠生改造成矿与找矿模式

【作者】 杨斌；

【导师】 郑明华； 骆良羽；

【作者基本信息】 成都理工大学 ， 矿物学、岩石学、矿床学， 2002， 博士

【摘要】 本文的重要发现之一，是博白-岑溪断裂带早古生代区域性热水沉积成矿活动。在此基础上，作者提出了佛子冲矿田热水沉积-叠生改造成矿模式。 博白-岑溪断裂带在早古生代为一同生断裂系统，在拉张环境下沿断裂带形成了一地堑型断陷盆地。同生断裂活动导致了沉积相的显著变化，沿断裂形成的斜坡上发育有大量的重力流沉积和重力滑动构造，并伴有火山活动。佛子冲、东桃、下水、文龙径、鸡笼顶等一系列铅锌多金属矿床沿该断裂带分布，这些矿床虽然在成矿规模、赋矿层位和矿石矿物组成等方面存在一些差异，但均产于下古生界地层中；主要矿体呈层状、似层状产出，与地层产状大体一致；直接赋矿围岩为层状绿色岩或重晶石岩；矿石中保留有典型的同生沉积组构。因此，从成矿系列的角度可将其归为一类。 作为典型矿例的佛子冲矿田主要产于下志留统细碎屑岩夹碳酸盐岩地层中，作者首次在矿田内发现了两种不同矿石类型：一类矿石具有典型的同生沉积特征，称之为热水沉积型矿石，矿石产于层状、似层状矿体中。主要矿物组合为浅色闪锌矿-方铅矿-透辉石(绿帘石、绿泥石)，其中浅色闪锌矿和透辉石为该类矿石的标型矿物。矿石中发育典型的纹层状构造、软沉积滑动变形构造、同生角砾构造等反映同生沉积特征的矿石构造；另一类矿石具有明显的后生成矿特点，称之为叠生改造型矿石，矿石产于脉状、囊状、透镜状及似层状矿体中，与燕山期岩浆岩及断裂裂隙构造关系密切。主要矿物组合为铁闪锌矿-方铅矿-磁黄铁矿(黄铁矿)-黄铜矿或铁闪锌矿-方铅矿-黄铁矿-钙铁辉石，其中铁闪锌矿和钙铁辉石为该类矿石标型矿物。主要矿石构造为块状构造、脉状构造、晶洞状构造、聚晶镶嵌构造等。局部见有该类矿石穿切热水沉积型矿石现象。作者将本区成矿过程划分出两个成矿期，即早志留世热水沉积成矿期和燕山期岩浆—热液叠生改造成矿期。 作者首次提出赋矿的绿色岩建造概念。其中层状绿色岩是佛子冲矿田层状、似层状矿体的直接赋矿围岩，这种层状绿色岩一直被视为矽卡岩。但这种岩石与传统意义上的接触交代矽卡岩有明显区别，主要表现在：①层状绿色岩产状与地层一致，其中发育典型的同生沉积组构；②层状绿色岩主要矿物成份为透辉石，次为绿帘石、绿泥石、方解石等，这些矿物与铅锌硫化物紧密共生，共同构成矿体，其分布并不局限于岩体接触带，也不因为距某种岩体的远近而出现分带现象。此类绿色岩是一类区域性展布的特殊类型的喷流岩。 地球化学研究显示，佛子冲矿田硫同位素5伦％值主要集中分布在0～＋5之间，与世界其它地区志留系海相硫化物矿床的6吨陆值大体一致。硫的初始来源主要为海水硫和地层硫。佛子冲矿田矿石铅同位素组成稳定，主要来自基底地层沉积物。碳、氧同位素显示，佛子冲矿田赋矿层位中的碳酸盐岩地层与正常的海相沉积碳酸盐岩不同，其成因与热水沉积活动有关。热水沉积型矿石与叠生改造型矿石在硫、铅、碳、氧同位素组成上十分接近，表明两期成矿作用在物源方面具有继承性。流体包裹体分析表明：包裹体类型主要为单 L相和 L—V二相包裹体。均一温度为 ill～35yC，流体盐度 0．7～8．l％NaCI。CaZ“、Mgl”和 SO。’“所占比重较大，F－／CI扎值小于 1，显示出偏酸性特征。物理化学计算表明，铅、锌在流体中迁移的主要形式是氯阴离子络合物。一 佛子冲矿田的形成，经历了两次成矿事件，一是早志留世热水沉积成矿作用，当时矿区所处岩相古地理环境为同生断裂控制的次级断陷盆地环境，位于陆缘斜坡相向深海盆地相的过渡地带。海水深度超过允许成矿流体沸腾深度。成矿处于相对还原环境。成矿流体为一种盆地卤水，当含矿热液喷人海底时，因温度下降、溶液稀释、洲值升高、还原硫浓度增高等，促使铅、锌硫化物及绿色矿物和碳酸盐等分目顺积下来。二是燕山期岩浆一热液叠生改造成矿作用，与燕山期岩浆侵位及伴随的热液活动有关。REE部分熔融模式计算表明，佛子冲矿田岩浆岩是由熔融程度较高的玄武岩熔融体（代表深部来源物质）与熔融程度较低的沉积岩熔融体混合而成。成矿流体为岩浆水和大气水的混合流体，Ph、Zn主要来自热水沉积型矿石和地层沉积物，岩浆主要提供As、Cu、Fe等元素。叠生改造作用以交代和溶解层状矿体的方式，形成Ph． Zn等矿质的再次聚集沉淀。改造成矿事件发生在与热水沉积成矿相同的层位和空问，改造型矿石在很能大程度上是热水沉积型矿石的衍生物。作者认为这是一种非均匀成核条件下，成矿作用的诱导机制或遗传机制的体现。 作者在地、物、化、遥多元信息基础上，建立了成矿预测模型，GIS技术的运用是本论文在成矿预测方面的特色和创新。指出下志留统地层与断裂影响带、岩体接触影响带及Ph、Zn、Ag化探异常的复合地段为最有利成矿地段。更多还原

【Abstract】 The Fozichong lead-zinc polymetallic orefield is one of the large-scale deposits in Guangxi Province. In the previous studies, the orefield was regarded either as a group of typical skam or as magmatic hydrothermal deposits.One of the most important discoveries in this study is the regional exhalative sedimentary mineralization along the Bobai-Chenxi faulted zone in early Palaeozoic, based on which, the metallogenic model of diplogenesis is developed for the Fozichong orefield.According to regional data, the Bobai-Chenxi fault zone was a syngenetic system in early Palaeozoic. Activities of the fault zone led to the change of sedimentary facies, and a large number of grativity sedimentation and grativity sliding structures were developed along the slope contolled by the fault zone, with volcanic activities. There are a series of lead-zinc polymetallic deposits, such as Fozichong, Dongtao, Xiashui, Wenlongjing and Jilongding distributed along the fault zone. These deposits have some similiar features: 〢ll of them are bounded in the strata of lower Palaeozoic group; ㎝ain orebodies occur as stratiform or stratoid form with occurrence consistent with that of host strata; ㏒tratiform skam or baritic rock are the direct country rock of orebodies; ㏕ypical syngenetic sedimentary fabric preserved in the ore. These deposits may be included in the same metallogenic series.Fozichong orefield occurs in lower Silurian which is composed of fine clasolite and carbonate. Two kinds of ore have been identified. The first type is characterized by syngenetic sedimentation, which is called as hot-water sedimentary ore. The ore emerges in bedded orebodies which have stable thickness. The ore’s mineral component is simple, and its main association of minerals are leucocratic sphalerite-galenite梔iopsite (epidot, chlorite). Leucoratic sphalerite and diopsite are the guide minerals in the ore. There are typical laminated structure,soft sedimentary-slipping deformed structure, syngenetic brecciated structure in the ore which are the mirror of syngenetic sedimentation. The other type of ore has the charactristic of epigenetic mineralization,which is called as telescoped ore. The ore occurs in vein, pocket, lensoid and bedd. The ore minerals are mainly composed of marmatlte, galenit, pyrrhotite(pyrite), chalcopyrite, or marmatite, galenite, pyrite and hedenbergite. Marmatite and hedenbergite are the indicated minerals of the ore. The main ore structure include massive % vein> drusy structure, etc. The second type ore penetrates last type ore in some areas. Therefore, two mineralization periods ore divided, which can be called as hot-water sedimention period and telescoping period.Stratiform green-rock is the direct country rock of bedded orebodies. The rock was called as skam in the past. The green-rock has following features: ㏕he stratiform green-rock’s mode of occurrence is conformable with that of the strata, and there are typical syngenetic sedimentary structure in the rock; (2)The stratiform green-rock is constituted mainly by bistagite without zonal distribution around magmatic rocks. The auther regards the stratiform green-rock as a kind of exhalative sedimentary rock which is different from contact-metasomatic skarn.In terms of sulphur isotope result from sphalerite, galenite > pyrite and chalcopyrite, the 8 34S%o value obtained in Fozichong orefield ranges mainly between 0~+5, which is coincident with the average 5 34S%o value of submarine stratabound sulphide deposits in Silurian strate distributed over other areas of the world. The initial sulphur in Fozichong orefield is mostly derived from marine sulfate and strata sediment. The lead isotope compsition of ore suggested that the lead should mainly be derived from old sequence at depth.Carbon and oxygen isotope data show that the carbonatite layer in Fozichong ledge is different from the normal marine sedimentary carbonatite, infering that its formation has relation with hot-water sedimentary activity. Isotope compositions of sulphur, lead, oxygen and carb更多还原