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滇东北毛坪铅锌矿床Ⅰ号矿群蚀变—矿化分带模式研究
【作者】 魏爱英；
【导师】 薛传东；
【作者基本信息】 昆明理工大学 ， 矿产普查与勘探， 2011， 硕士
【摘要】 昭通毛坪铅锌矿区是滇东北富铅锌多金属成矿带上又一个具有超大型成矿潜力的矿集区,过去对其矿床研究程度弱,特别是成因矿物学工作鲜有开展。本论文以毛坪铅锌矿区赋存于猫猫山倒转背斜西翼上泥盆统宰格组(D3zg2)中晶白云岩层间断裂带内的Ⅰ#矿群滇东北铅锌矿富集区毛坪铅锌矿为研究对象,系统开展了矿区立体蚀变填图和岩相学研究,在详细研究矿区地质和矿床地质特征的基础上,重点研究了毛坪铅锌矿床Ⅰ号矿群(群)的矿化-蚀变分带特征,建立了蚀变矿化分带模式,并结合流体包裹体分析以及同位素示踪,探讨了矿床的成因。论文主要取的一下成果和认识：(1)按照矿(化)体、脉体穿插关系、矿物组合以及矿石结构构造特征,区内成岩成矿过程包括沉积成岩期、油气期、热液成矿期和表生氧化期。热液成矿期可划分为五个阶段,其中Ⅱ、Ⅲ阶段是主要的铅锌成矿阶段。在矿体及蚀变围岩中大量固体沥青的发现,既指示成岩期后和热液期前发生过有机质的裂解迹象,也反映热液成矿作用过程中存在有机质的混入,氢氧同位素结果佐证了这一推断。(2)自矿体中心向外围、自下而上,蚀变呈现硅化→碳酸盐化+硅化+泥化→碳酸盐化的显著分带现象,矿化具有致密块状高品位矿石→致密块状黄铁矿外壳→浸染状、脉状、斑块状低品位矿石→星点状黄铁矿外壳的分带特点,矿物组合标志为黄铁矿+白铁矿+毒砂+黄铜矿、黄铁矿+方铅矿++伊利石、黄铁矿+石英+菱铁矿和白云石+方解石。(3)水平分带上,北东端的富铅矿带指示矿体的尖灭。元素垂向分带上,Pb位于中下部,Zn靠前,指示存在流体的叠加作用。条带状矿石也是流体叠加的又一证据。Ⅱ、Ⅲ阶段的矿化元素在670～784m附近发生叠加,在784m以上以Ⅱ阶段矿化为主。(4)黄铁矿外壳是早期流体的产物。富矿石都被致密块状的黄铁外壳所包裹,低品位矿石都被星点状的黄铁外壳所包裹,在透镜状矿体的侧部以及中上部,致密块状黄铁矿壳会出现在富矿体的内部,且黄铁矿矿的五角十二面体晶形在富矿部位较多。硫化物矿物种类自矿体中心向两侧和上部逐渐变少,矿石构造类型自下往上变得简单。(5)白云石、石英、黄铁矿的环带结构仅出现在富矿体的边部以及中上部,在下部不出现,是流体前锋的标志,对找矿具有指导意义。(6)流体具有多个活动中心,且沿断裂、裂隙带通道自南往北东向向上运移,断裂和地层是成矿控制的关键因素。成矿流体演化上,存在温度和压力明显降低,盐度和密度增大的趋势(不显著)。同一阶段的流体在垂向上,自下往上盐度、密度降低,但压力、温度增大。其中,Ⅱ阶段为中-高温高压低盐、低密度的流体；Ⅲ阶段为中温低压低盐、低密度流体。结合黄铁矿、白云石的特殊晶形分析,指示晶体析出的放热效应对流体性质的影响不可忽略。石英歪晶也显示流体单向供给以及在局部发生过循环流动。(7)成矿时代为燕山期。成矿物质来源于上地壳基底建造,也存在上泥盆统碳酸岩盐地层的贡献。成矿流体为大气水、热卤水、有机水和变质水的混合流体,说明有机质的参与以及流体淋滤循环对成矿有一定的作用,而峨眉山玄武岩的喷发活动的成矿意义不大。(8)本次建立的蚀变矿化分带模式有助于成矿流体运聚和富集成矿的深入研究,对深部寻找盲矿体有指示意义。根据目前毛坪矿区Ⅰ号矿群的揭露情况来看,其深部仍有很大的找矿前景。
【Abstract】 Maoping in the Zhaotong area is a potentially large scale ore deposit in the Pb-Zn polymetallic metallogenic belt in northeast Yunnan. In the past, researches are weak on its ore deposit, especially on the field of mineralogy. This project is based on the Maoping Pb-Zn ore deposit (situated in the Upper Devonian dolomite in Maomaoshan). Alteration zonation mapping and petrology was studied, with emphasis on the metallogenesis and alteration of the numberⅠgroup. As a result, alteration zonation pattern was established. Causes of the metallogenesis were also discussed based on the combination of fluid inclusion and isotope studies. The main conclusions are listed as follows:(1) According to the occurrence of the ore, crosscutting relationship of the veins and ore mineral textures, the metallogenesis can be divided to different stages, including diagenesis of ore-forming process, gas phase, hydrothermal mineralization and supergene oxidation of the period. Mineralization-alternation exist in five stages:Ⅰ,Ⅱ,Ⅲ,ⅣandⅤ.Ⅱ,Ⅲstage is the major lead-zinc mineralization stage. Altered wall rock in the ore body and the discovery of a large number of solid bitumen, both direct and hydrothermal diagenesis period of the decomposition of organic matter occurred before the signs, and also reflect the existence of hydrothermal mineralization process of organic matter mixed.(2) The results indicate that the alternation zonation from the center of ore bodies outward is silicification zone, carbonation+silicification+argillation zone and carbonation zone. As a result, the mineralization zonation changes from massive high grade ore to massive pyrite shell, disseminated-vein-patchy low-grade ore and star-shaped pyrite shell, the mineral composition zonation can be divided into Py +Mrc+(Cpy)+Apy,Py+Gn+Sp+Dol+Ank+Cal+Q+Ill zone, Py+Dol+Ank+Cal +Q+Sd zone and Dol+Cal zone.; Sphalerite has color zonal structure which contain dark red, reddish orange, saffron, buff and light green. From center to edges of the ore bodies and the upper the zoning increased more significant, but that are always occurrence in the form of darker stain. (3) Horizontal band, with the northeastern end of the galena-rich ore bodies pinch out instructions. Elements bring vertical points, pb in the lower part, zn front, indicates the presence of fluid superimposed. Banded ore is another evidence of fluid overlay.Ⅱ,Ⅲstage of mineralization elements in the 670～784m near the superposition of more than 784m to the main mineralization stageⅡ.(4) Py shell is an early product of the fluid. Rich ores are compact blocks of yellow iron shell of the package, low-grade ores are star-shaped yellow iron shell of the package, the ore body in the lens and the upper side, dense block will appear in the high-grade ore shell Py inside the body, and pyrite mine pentagonal dodecahedron crystal form part of the more high-grade ore. Sulfide minerals change from the ore body center to the sides and top of gradually less structural types of ore from the bottom up easier.(5) Q, Dol, Ank, Py structure of the ring occur only in high-grade ore body and the upper edge, does not appear in the lower part is a sign of fluid forward,(6) Fluid occurs with multiple centers, and along faults, fractures from south to northeast with access to the upward migration, fracture and formation is a key factor in controlling mineralization. Evolution of ore-forming fluid, there is significantly lower temperature and pressure, salinity and density of the trend (not significant). The same stage of the fluid in the vertical, since the bottom-up salinity, density decreased, but the pressure and temperature increase. Which,Ⅱstage in-high temperature and high salt, low-density fluid;Ⅲstage in the temperature and low pressure low-salt, low-density fluid. With pyrite, dolomite of the special crystal, indicating that the exothermic effect of precipitation on the crystal properties of the fluid cannot be ignored. Quartz crystal distortion and also showed the supply of fluid in the local one-way circulation occurred.(7) Mineralization occurred during the Yanshanian (Mesozoic) period. Forming materials were derived from the construction of the basement, there is also the Devonian carbonate strata of the contribution of rock salt. Ore-forming fluid of meteoric water and hot brine, the organic mixture of water and deterioration of water flow, indicating the involvement of organic matter and fluid leaching cycle has a definite effect on the mineralization, and the eruption of the Emeishan basalt forming meaningful activities.(8) The established pattern ofalteration and mineralization zoning of Sichuan-Yunnan-Guizhou Pb-Zn ore field can be of universal significance, and can contribute to the genesis of fluid migration and accumulation of ore deposit researches. Under the current reviewed Mining Area No.Ⅰsituation, there is still much space of deeper prospects.