Abstract

The paper presents the results of study of metalliferous (ferromanganese and manganese) rocks at the Nadeiyakha ore occurrence (Pai-Khoi) discovered in 2010. The metalliferous deposit represents a stratiform body lying conformably in the Upper Devonian carbonaceous siliceous and clayey–carbonate–siliceous shales. The ore bed occurs 180 m below the regional Famennian manganiferous rock association in Pai-Khoi. Discovery of the Nadeiyakha ore occurrence suggests the existence of an additional age interval of Mn accumulation within the Devonian sequence of this region. The studied metalliferous rocks display structures and textures typical of the metasedimentary rocks. In terms of composition, they are divided into two varieties: (i) ferromanganese (quartz–carbonate) rocks composed of quartz, dolomite, kutnahorite, rhodochrosite, siderite, and calcite; (ii) manganiferous (quartz–rhodochrosite–silicate) rocks composed of quartz, rhodochrosite, tephroite, sonolite, and pyroxmangite. The Nadeiyakha ore occurrence is marked by the abundance of dolomite in the ferromanganese rocks and host shales. In terms of the relationship of indicator elements (Al, Ti, Fe, and Mn), ferromanganese and manganese rocks are comparable with the recent metalliferous and ore-bearing sediments. The carbon isotope composition in carbonates (δ¹³C from –16.4 to –7.8‰ PDB) corresponds to authigenic carbonates related to the involvement of carbon dioxide produced during the microbial decomposition of organic matter at the stage of dia- and/or catagenesis. Geological and petrographic observations show that the ferruginous and manganiferous sediments were deposited synchronously with the terrigenous–carbonate–siliceous sediments. Fe and Mn could be sourced from hydrothermal solutions or interstitial diagenetic waters. The latter version seems to be more probable. Metals were accumulated in a depression-trap characterized by a periodic stagnation of bottom waters. Such sedimentation setting promoted the formation of paragenetic association of ferruginous and manganiferous sediments with the carbonaceous sediments and fostered reductive conditions during the postsedimentary mineral formation. Calcium carbonates contained in the primary rocks were subjected to dolomitization during the dia- or catagenesis. This process was promoted by the mobilization of Mg released during the transformation of clay minerals owing to the montmorillonite–illite transition. Iron and manganese carbonates were formed during the later replacement of oxides of Mn³⁺, Mn⁴⁺, and Fe³⁺. Crystallization of manganese silicates also started at early stages of lithogenesis and terminated during the regional metamorphism of metalliferous rocks.

中文翻译：

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Nadeiyakha矿石的发生（俄罗斯拜伊）：碳质白云岩页岩中的锰铁沉积物的一个例子

摘要

本文介绍了在2010年发现的Nadeiyakha矿床（Pai-Khoi）中的含金属（铁锰和锰）岩石的研究结果。含金属沉积物表示层状体，均匀地分布在上泥盆统碳质硅质岩和粘土质碳酸盐质硅质岩页岩。矿床位于拜科伊地区的Famennian锰铁矿协会以下180 m。Nadeiyakha矿石发生的发现表明该地区的泥盆纪层序中还存在一个额外的锰积累年龄区间。所研究的含金属岩石具有典型的准沉积岩的结构和质地。就组成而言，它们分为两种：（i）锰铁（石英-碳酸盐）岩石，由石英，白云石，库特纳石，菱锰矿，菱铁矿，和方解石；（ii）由石英，菱锰矿，软锰矿，方钠石和火成锰铁矿组成的锰（石英-菱锰矿-硅酸盐）岩石。Nadeiyakha矿石的出现以锰铁岩石和宿主页岩中大量的白云石为标志。就指示元素（Al，Ti，Fe和Mn）的关系而言，铁锰和锰岩可与近期的含金属和含矿沉积物相媲美。碳酸盐中的碳同位素组成（δ 铁锰和锰岩可与最近的含金属和含矿沉积物相媲美。碳酸盐中的碳同位素组成（δ 铁锰和锰岩可与最近的含金属和含矿沉积物相媲美。碳酸盐中的碳同位素组成（δ¹³C从–16.4到–7.8‰（PDB）对应于自生碳酸盐，与渗碳和/或催化作用阶段有机物的微生物分解过程中产生的二氧化碳有关。地质和岩石学观察表明，铁质和锰质沉积物与陆源－碳酸盐－硅质沉积物同步沉积。铁和锰可能来自热液或间质成岩水。后一个版本似乎更有可能。金属聚集在一个以底水周期性停滞为特征的凹陷陷阱中。这种沉积环境促进了铁质和锰质沉积物与碳质沉积物共生联系的形成，并促进了沉积后矿物形成过程中的还原条件。在渗析或催化作用过程中，原生岩石中包含的碳酸钙经历了白云石化作用。由于蒙脱石-伊利石的转变，在粘土矿物转化过程中释放出的镁的动员促进了这一过程。锰氧化物的后期替换过程中形成了碳酸铁锰盐³⁺，Mn ⁴⁺和Fe ³⁺。硅酸锰的结晶也始于成岩的早期阶段，并在含金属岩石的区域变质过程中终止。