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在蒙大纳州西南的蒙大纳燧道处,有一个总体可采的金-银矿床,正位于一火山角砾岩筒的中心部位.这一火山角砾岩筒是沿着安山岩火山碎屑岩之间的接触带断裂侵位的.计有晚白垩世的EIkhom火山岩,以及一套石英安粗熔灰岩,其中有一部分是属于中始新世的低地湾火山岩.一组走向为北北东的石英安粗斑岩岩墙群是在火山作用减弱阶段中侵入并定位的.有两个最大的岩墙,年代为45至50百万年(中始新世),是在矿化和角砾岩化停止之前侵入火山角砾岩筒的.火山角砾岩筒的面积在地表为1km~2,由钻探得知为陡倾斜向下延伸至少310米.其中主要岩石类型是一种富基质的角砾岩.它的特征是由一种砂粒大小的以石英安粗岩成分的凝灰质基质、以邻接的火山围岩接触后产生与来自晚白垩世Boulder岩基所派生的侵入岩作为碎块物质.下面潜伏有岩基,该岩基被推测为下伏在蒙大纳地区.不同状态的火山围岩的塌陷岩块紧靠着火山角砾岩筒壁和位于火山角砾岩筒里面,由Elkhorn火山岩的物质组成,在它们下沉到火山角砾岩筒里面以后发生了水压角砾化作用.把岩块解释为由火山碎屑岩底面起伏沉积物(由地表凝灰环形成)以及古地表的部分碳化木(下沉到火山角砾岩筒里面)组成.火山角砾岩筒被-北西西走向的斜交滑动断层切割成不等的两部分.在火山角砾岩筒的角砾岩基质里硫化物以浸染状产出.而在更广阔的空间范围内,硫化物则以更为稀疏的呈多方向网脉以及在Elkhorn山火山岩角砾岩块的基质中分布.各种矿化都含有黄铁矿、闪锌矿、方铅矿以及伴生着以锰方解石为脉石的稀有银金矿、菱铁矿和少量的石英.硫化物和脉石矿物的碎块和碎屑粒是常见的,并不证明是多次角砾岩化和矿化交替穿插形成的.在矿带里面有大量的锰方解石和菱铁矿并伴随着普遍的绢云母蚀变,不过只有弱高岭石化和硅化.绢云母化向外超出矿带为绿泥石-蒙脱石-碳酸盐蚀变,这一组合也是火山角砾岩筒里晚期矿脉的内部特征.金赋存在银金矿里面,纯度约550,在黄铁矿和闪锌矿里呈<200μm的包裹体.银金矿和方铅矿包裹体是一同沉淀的.银主要是在方铅矿中呈固溶液.
At Mont-Genesis, Montana, south-west of Montana, there is an entirely recoverable gold-silver deposit, located in the center of a volcanic breccia barrel that is littered with andesitic volcanic debris There is a Late Cretaceous EIkhom volcanic rock and a set of quartz amphibolite, some of which belong to the Lower Eocene volcanic rocks of the Middle Eocene. The north-eastern quartz amphibolite dyke swarm intrudes and positions during volcanism depletion, with two of the largest dikes dating from 45 to 50 million years (mid-Eocene) And brecciated into the volcanic breccia tube prior to the cessation of volcanic breccia tube surface area of 1km ~ 2, known from the drilling down steep slope extending at least 310 meters. The main type of rock is a Matrix-rich breccia that is characterized by a grit-sized tuffaceous matrix of quartz-bearing coarse-grained rock that comes into contact with adjacent volcanic rocks to produce intrusive rocks derived from the Boulder bedrock of the Late Cretaceous As a fragment of material, there is a submerged rock base beneath which it is presumed to land under Montana The collapsed rock mass of the volcanic surrounding rock in various states, immediately after the volcanic breccia barrel wall and inside the volcanic breccia barrel, consists of Elkhorn volcanic rocks that occur after they sink into the volcanic breccia cylinder Hydrodynamic brecciation was interpreted as consisting of undulating sediments (formed by the surface tuff rings) on the bottom of pyroclastic rocks and partially carbonized wood (sunken into the volcanic breccia tubes) of the paleogeographic surface. The volcanic breccia tubes are cut into unequal two sections by a north-west-trending ramp-slip fault that is disseminated within the breccia matrix of a volcanic breccia barrel, while in a broader spatial extent Sulphides are distributed in a more sparse, multi-directional reticulate vein and in the matrix of the Elkhorn volcanic breccia blocks, each of which contains pyrite, sphalerite, galena, Manganese calcite is a rare silver-gold mine, siderite and a small amount of quartz from gangue, and fragments and crumbs of sulfides and gangue minerals are common and do not prove to be multiple brecciated and mineralized alternations Interspersed formed in the mine there is a lot of manganese calcite and siderite and With the widespread alteration of sericite, there is only weak kaolinite and silicification, sericitization outcrops the chlorite-montmorillonite-carbonate alteration, and this assemblage is also a volcanic breccia cylinder The inner features of the late veins, which are present in the silver-gold deposit with a purity of about 550 and inclusions <200μm in pyrite and sphalerite, are precipitated together with silver and gold galena inclusions. Mainly in the galena was solid solution.