碳酸盐矿物的阴极发光性与其Fe,Mn含量的关系

根据不同地区和时代84件碳酸盐样品的阴极发光和Fe,Mn元素分析,在本次研究使用的仪器和实验条件下,方解石和白云石的阴极发光性与其Fe,Mn含量之间存在如下关系:Mn<40μg/g(ppm)时,其阴极发光性主要受Mn的绝对含量控制,当Mn<20μg/g时,不具阴极发光;Fe>5000μg/g时,其阴极发光性与Fe的绝对含关系更为密切,当Fe>10000μg/g时,不具阴极发光;Mn>40μg/g,Fe<5000μg/g时,其阴极发光性受Fe/Mn比值的显著控制,此时当Fe/Mn<7时,具强的阴极发光,30>Fe/Mn>7时,具中等强度的阴极发光,Fe/Mn>30时,具弱的阴极发光。两个热液碳酸岩中单晶白云石样品的阴极发光性和稀土元素含量间的关系说明,碳酸盐矿物的阴极发光性可能还与某些稀土元素的存在有关,它们可能是某些样品具低激活电压和长发光余辉的原因。     

碳酸盐岩中方解石胶结物的阴极发光环带与微量元素构成的关系——以塔河油田奥陶系碳酸盐岩为例

对塔河油田奥陶系碳酸盐岩中方解石胶结物的阴极发光性和微量元素构成研究发现,一些与大气水成岩环境有关的方解石胶结物显示出亮、暗相间阴极发光环带,微量元素含量与阴极发光环带之间具有良好的对应关系,亮带具有较高的Mn、Fe含量,暗带则具有较高的Sr、Na含量,显示方解石胶结过程中大气水作用强度的变化。这些碳酸盐矿物的阴极发光环带受元素构成变化控制,并反映成岩流体中元素含量的变化和/或结晶速率的变化,这在一定程度上与大气水环境相对开放的成岩条件有关。相对晚期的环带发光较亮,并具有较高的Mn和较低的Sr、Na含量,显示与加里东—海西期构造运动有关的古岩溶过程中大气水作用逐渐加强的总体成岩趋势。     

佛罗里达大陆架更新世双矿物鲕粒的阴极发光性

在东佛罗里达外大陆架大约40m的海底，发现一种被钻孔和包壳的晚更新世鲕粒灰岩。鲕粒的包壳主要由两种矿物组成，通常情况下，内是放射状排殊镁方解石，而外层则是同心环状排列的文石。多数鲕粒的核心是磨圆的隐晶质颗粒，但也有一部分英颗粒和各种骨粒组成。鲕粒由块状方解石胶结物不完全胶结，部分粒间孔由微晶充填。放射壳层由具亮的阴极发光性的镁方解石组成，含大约12mol％的MбCO3和1000ppm的锶。在放射壳层中，铁和锰含量的一般变化范围分别为500－1000ppm和100－250ppm。同习环状壳层由不具阴极发光的文石组成，含大约11500ppm的锶和小于0．5mol％的MбCO3.心环状壳层中铁的含量范围一般为150－400ppm，而锰通常小于100ppm的检测限。作为次要伴生颗粒的棘皮动物碎片山镁方解石组成，具亮的阴极发光性。一些鲕粒的核心和块状方解石胶结物的薄外缘具阴极发光。微晶基质和大片的块状方解石胶结物不具阴极发兴。在鲕粒中，未见显示重结晶作用的结构迹象。这些鲕粒灰岩经历了大气淡水成岩作用阶段，但鲕粒壳层却未受其影响。我们认为，镁方解石层普在缺氧的海水中遭受成岩蚀变，这是一个尚未被人们认识的过程。在该过程中，镁推动而锰加入，但没有明显的结构蚀变，也没有发生矿物的稳定化作用，因此，我们认为其阴极发光性可能是海底的成岩蚀变造成的。     

碳酸盐矿物阴极发光性的控制因素分析

碳酸盐矿物的阴极发光性主要受其Mn^2＋和Fe^2＋含量,以及Mn^2＋／Fe^2＋值的综合控制,但Mn^2＋／Fe^2＋值的控制作用强一些。研究中充填裂缝的方解石胶结物样品主要采自北京西山寒武系和奥陶系的碳酸盐岩地层中。此外,还从北京石花洞中采集了现代溶洞的石笋样品。样品的阴极发光强度可分为不发光、暗、中等和亮,阴极发光颜色也相应地分为不发光、橙红色、橙黄色和亮黄色。通过对野外露头样品进行电子探针研究,测定其中的Mn^2＋和F^2＋’的含量,并结合样品的阴极发光颜色和强度,得出Mn^2＋含量要在0．01％以上,Fe^2＋含量至少在0．8％以下,Mn^2＋／Fe^2＋在0．05以上,方解石胶结物才能发光。经研究发现,充填裂缝中方解石胶结物的阴极发光性与Mn^2＋和Fe^2＋含量,以及Mn^2＋／Fe^2＋值之间存在如下关系：不含Mn^2＋,Fe^2＋微量,Mn^2＋／Fe^2＋为0时,不发光;0．05〈Mn^2＋Fe^2＋〈0．2时,发光强度暗,发光颜色为橙红色;0．2〈Mn^2＋／Fe^2＋〈2时,发光强度中等,发光颜色为橙黄色;Mn^2＋／Fe^2＋〉2时,发光强度亮,发光颜色为亮黄色。     

碳酸盐岩中阴极发光的激活作用及发光环带

为了研究碳酸盐的阴极发光特征，在实验室培养了方解石晶体。除Mn^2＋外，不需另加其他微量元素，例激活出与天然碳酸盐类似的阴极发光性。通过阴极发光性的观察，并结合对合成晶体和天然方解石、白云石的Mn、Fe分析，结果表明：1）15－30ppm和30－35ppm的Mn就足以分别激活方解石和白云石的阴极发光。2）阴极发光强度受Mn^2＋的绝对含量控制而不受Fe^2＋／Mn^2＋比率的控制。在Fe的含量较低（＜200ppm）时，上面两个结论成立。3）在合成晶体和天然碳酸盐中常见的阴极发光环带，反映在晶体生长过程中，有含量不同的Mn^2＋进入晶体，其原因有：a）沉淀流体中Mn^2＋含量发生变化；b）晶体生长速率发生变化，这与流体中Mn^2＋含量的多少无关。在过去的阴极发光研究中，对后一过程未给予充分考虑，但它对解释阴极发光特征有着十分重要的意义。例如，在采用岩石的阴极发光性对孔隙流体地球化学历史进行解释时，如不考虑后一过程，就可能得出不尽合理的结果。在对胶结层序的原理进行解释（即将发光颜色或强度类似的胶结物进行对双），尤其需要小心谨慎。只有在证明这种现象主要是由于孔隙流体中的地球化学变化产生的，而不只是由一地晶体生长速率的不同造成时，才可应用这种原理。本文还对鉴别的试验标准进行了讨论。     

阴极发光在湘西北地区二叠—三叠系界线事件及地层对比中应用的尝试

本文对湘西北桑植仁村坪、小埠头和慈利江垭、黄连峪4条剖面的二叠—三叠系界线附近和上二叠统的碳酸盐岩做了系统的阴极发光测试,得出如下共同规律:（1）二叠—三叠系界线上下碳酸盐矿物发光截然不同;（2）不同时代地层阴极发光的颜色和强度有所差异。又通过电子探针、光谱分析和x射线衍射分析,说明阴极发光特征与微量元素的成分及含量有密切关系,因而认为用阴极发光方法可以做为划分、对比地层的辅助手段之一。     

贵州省松桃大塘坡组含锰岩系的形成环境分析

贵州黔东断裂坳陷带是我国重要的锰矿成矿区,发育了新元古代大塘坡早期富锰黑色页岩。一般认为,锰矿是氧化环境下沉积的MnO2在早成岩过程中与有机质之间发生氧化—还原反应形成的;但最近研究显示,也有可能直接从缺氧海水中沉淀而成。本文对贵州省松桃县西溪堡锰矿区大塘坡组一段含锰岩系和大塘坡锰矿区铁矿坪锰矿床的大塘坡组一段含锰岩系中的样品,采用总有机碳、总硫、显微镜薄片鉴定、扫描电镜、电感耦合等离子体质谱等研究方法,探讨了大塘坡组一段的沉积环境,为锰矿成因提供新的线索。本研究分别提取和测试了碳酸盐矿物和残余物(主要为粘土矿物)微量元素、稀土元素的含量后发现,去除碳酸盐矿物后余样Sr/Ba比值为0.06～0.19、B/Ga比值为1.44～5.01,碳酸盐矿物成分中Y/Ho比值为16.18～29.78,均指示锰矿层沉积于Sturtian冰期后冰川消融而成的淡水—半咸水的环境。锰矿的稀土总量高,类似于大洋铁锰氧化壳的“帽型”稀土元素配分模式,具有Ce/Ce^*正异常;氧化还原敏感元素双原子比U/Th比值为0.16～0.35、V/Cr比值主要为0.35～5.84、Ni/Co比值介于0....     

海拉尔盆地贝尔凹陷含片钠铝石沉凝灰岩的成岩作用

以海拉尔盆地贝尔凹陷大磨拐河组-伊敏组的含片钠铝石火山碎屑岩为研究对象,采用偏光显微镜、扫描电镜及配套能谱、茜素红 S染色、阴极发光和X 射线衍射分析等技术手段,对研究样品的岩石类型、自生矿物种类及共生序列进行了详细研究。贝尔凹陷发育片钠铝石的宿主岩石类型为沉凝灰岩,自生矿物以发育片钠铝石、铁白云石和菱铁矿三种碳酸盐矿物为主,片钠铝石含量高达25%。成岩共生序列为菱铁矿Ⅰ→高岭石、石英次生加大→片钠铝石→微晶石英→方解石→铁白云石→菱铁矿Ⅱ→沥青。不同于国内外其它地区发现片钠铝石的主要产状为充填孔隙,本区内发育的片钠铝石以交代长石、石英、岩屑颗粒和高岭石基质为赋存特征,表明沉凝灰岩中的长石、岩屑、高岭石基质可以为其提供金属离子物质来源,并在CO2参与下,与成岩流体反应生成片钠铝石。大量碳酸盐矿物（15-44%）的发育证明了火山碎屑岩具有较高的CO2矿物捕获能力。     

四川盆地东北部三叠系飞仙关组碳酸盐岩成岩作用和白云岩成因的研究现状和存在问题

四川盆地东北部三叠系飞仙关组是我国重要的天然气储集层，优质储层形成机制直接与碳酸盐岩成岩作用、尤其是白云岩化作用相关，但飞仙关组碳酸盐岩在锰含量、锶含量、阴极发光性等特征上反映其成岩过程与经典成岩理论相悖；碳酸盐岩的锶同位素组成和锰、锶含量的关系也表明与大气水有关的成岩过程和作为重要储集岩的结晶白云岩的形成机制无关，传统的白云岩化机制难以解释结晶白云岩的成因。具有海源色彩的高锶、低锰成岩流体在很大程度上控制了飞仙关组碳酸盐的成岩作用，其来源与成因值得进一步关注，控制其运移、封存和发生水—岩反应的时空机制有待回答。整个海相三叠纪时间段盆地尺度碳酸盐岩和蒸发岩的沉积地球化学研究、尤其是不同结构组分碳酸盐的锶同位素组成、锶和锰含量研究（包括碳酸盐岩中不同结构组分的阴极发光性研究），可为四川盆地东北部飞仙关组碳酸盐岩成岩作用（尤其是白云岩化作用和作为重要储集岩的结晶白云岩的成因研究），天青石矿床成因研究和四川盆地三叠系深层富钾、锶、硼、溴卤水的成因研究提供重要的线索。     

MVT矿床中与成矿有关热液方解石的地球化学判据——以青海多才玛超大型铅锌矿床为例

碳酸盐矿物是MVT型铅锌矿床最为常见的热液蚀变矿物,记录了成矿流体特征,其元素或同位素组成对示踪和定位矿体具有一定的指示意义,但由于该类矿床中碳酸盐矿物成因多样,单一的岩相学观察往往难以准确识别与成矿有关和无关的方解石,需要辅以地球化学手段来确定方解石成因。本文利用钻孔编录、岩相学观察、C-O-Sr同位素和原位微量与稀土元素组成分析等手段,探讨了青海多才玛超大型MVT铅锌矿床中与成矿有关和无关两期方解石的矿物化学特征。结果表明,多才玛矿床成矿前方解石(Cal1)空间上与矿体无相关关系,遍布于中二叠统九十道班组灰岩内,阴极发光呈暗棕色至棕黄色,无明显生长环带;成矿期方解石(Cal2)主要产于铅锌矿体内及其上盘围岩中,多呈砂糖粒状-皮壳状充填于围岩裂隙和溶孔内,阴极发光呈暗黄色至亮橙色,常发育生长环带。相对于Cal2, Cal1与围岩的C-O-Sr同位素组成更为接近,这表明水岩反应期间,Cal1组成受围岩影响更大,Cal2组成受影响更小;相比于Cal1,Cal2具有较高的Mn、Fe、Zn、Pb含量和U/Th、V/Cr值以及较低的LREE/HREE值、Mg、Sr含量和弱的Ce负异常,指示成矿...     

Effects of Spin Transition and Cation Substitution on the Optical Properties and Iron Partitioning in Carbonate Minerals

The high-pressure behavior of deep carbonate dictates the state and dynamics of oxidized carbon in the Earth’s mantle, playing a vital role in the global carbon cycle and potentially influencing long-term climate change. Optical absorption and Raman spectroscopic measurements were carried out on two natural carbonate samples in diamond-anvil cells up to 60 GPa. Mg-substitution in high-spin siderite FeCO₃ increases the crystal field absorption band position by approximately 1000 cm     

The solubility of rhodochrosite (MnCO3) and siderite (FeCO3) in anaerobic aquatic environments

Natural groundwaters are often reported to be highly supersaturated with the carbonate minerals siderite (FeCO₃) and rhodochrosite (MnCO₃). The kinetics of precipitation and dissolution were determined in the light of new determinations of the solubility products of siderite and rhodochrosite. Laboratory experiments showed that the precipitation kinetics of siderite and rhodochrosite were much slower than that of calcite, and also much slower than their dissolution kinetics. Experiments with supersaturated solutions failed to reach steady state within 474 days in the case of siderite, whereas steady state for rhodochrosite was reached after 140 days. Suspensions of siderite and rhodochrosite crystals reached steady state after 10 and 80 days, respectively. The solubility product of siderite (−log K_S0(FeCO₃)) was 11.03 ± 0.10 for dried crystals and 10.43 ± 0.15 for wet crystals. For rhodochrosite the solubility product (−log K_S0(MnCO₃)) was 11.39 ± 0.14 for dried crystals and 12.51 ± 0.07 for wet crystals. The solubility product determined from supersaturated solutions was −log K_S0(MnCO₃)=11.65 ± 0.14. The observed slow precipitation kinetics of siderite and rhodochrosite might explain the apparent supersaturation that is often reported for anaerobic aquatic environments.     

Arsenic and metal contamination of water resources from mining wastes in Korea

 Water resources near a gold-mine waste site were studied for the distribution and contents of contaminants, and their behavior in the surface and groundwater systems. Arsenic, cadmium, and manganese were identified with levels exceeding the drinking water guidelines of WHO (World Health Organization), and their distribution depended upon the differences in source materials and in spatial pH variations. Originating from arsenopyrite, concentrations of dissolved arsenic were controlled by sorption with amorphous iron (Fe(OH)₃) and carbonate minerals. Cadmium and manganese were derived from the mineral phase including sphalerite (ZnS), otavite (CdCO₃), and rhodochrosite (MnCO₃); their concentrations in water resources were limited by the solubility of mineral phases. All of these processes are significantly pH-dependent, implying that a small decline in pH could result in a drastic increase in contaminant concentrations and become a pollution threat to the water resources of the Gubong area. Received: 13 December 1999 · Accepted: 21 March 2000     

On the distribution of iron and manganese at the sediment/water interface: thermodynamic versus kinetic control

Iron and manganese solubility at the sediment/water interface has been studied at a water depth of 20 m in Kiel Bight, Western Baltic. By means of an in situ bell jar system enclosing 3.14 m² sediment surface and 2094 l water a complete redox turn-over in the bottom water was simulated in an experiment lasting 99 days. The concentration of dissolved Fe in the bell jar water never exceeded 0.041 μmol · dm^?3during the first 50 days of the experiment and then rose abruptly as the Eh fell from +600 to ?200 mV. The concentration of dissolved Fe under oxic and anoxic conditions seems to be limited by equilibria with solid Fe-phases (hydroxides and amorphous sulphide, respectively). In contrast to Fe, manganese was released continuously from the bottom during the first 50 days of the experiment leading to exponentially increasing manganese concentrations in the bell jar water. During this time dissolved O₂ had become ready depleted and pH had dropped from 8.3 to 7.5. Contrary to iron, manganese being solubilized in reduced sediment layers can penetrate oxic strata in metastable form due to slow oxidation kinetics; when the redoxcline moves upwards Mn²⁺ is enriched in bottom waters. The maximum concentration of dissolved Mn under anoxic conditions is controlled by a solid phase with solubility properties similar to MnCO₃ (rhodochrosite). Bottom water enrichment in dissolved Mn²⁺ could be traced to originate from excess solid manganese within the top 3 cm of the sediment.     

The role of carbonate ions in pyrite oxidation in aqueous systems

The mechanism of pyrite oxidation in carbonate-containing alkaline solutions at 80 °C was investigated with the help of rate experiments, thermodynamic modeling and diffuse reflectance infrared spectroscopy (DRIFTS). Pyrite oxidation rate increased with pH and was enhanced by addition of bicarbonate/carbonate ions. The carbonate effect was found to be limited to moderately alkaline conditions (pH 8-11). Metastable Eh-pH diagrams, at 25 °C, indicate that soluble iron-carbonate complexes (FeHCO₃⁻, FeCO₃⁰, Fe(CO₃)(OH)⁻ and FeCO₃²⁻) may coexist with pyrite in the pH range of 6-12.5. Above pH 11 and 13, the Fe(II) and Fe(III) hydroxocomplexes, respectively, become stable, even in the presence of carbonate/bicarbonate ions. Surface-bound carbonate complexes on iron were also identified with DRIFTS as products of pyrite oxidation in addition to iron oxyhydroxides and soluble sulfate species. The conditions under which thermodynamic and DRIFTS analyses indicate the presence of carbonate compounds also correspond to those in which the fastest rate of pyrite oxidation in carbonate solutions was observed. Following the Singer-Stumm model for pyrite oxidation in acidic solutions, it is assumed that Fe(III) is the preferred pyrite oxidant under alkaline conditions. We propose that carbonate ions facilitate the electron transfer from soluble iron(II)-carbonate to O₂, increase the iron solubility, and provide buffered, favorable alkaline conditions at the reaction front, which in turn favors the overall kinetics of pyrite oxidation. Therefore, the electron transfer from sulfur atoms to O₂ is facilitated by the formation of the cycle of Fe(II)-pyrite/Fe(III)-carbonate redox couple at the pyrite surface.     

Cathodoluminescent bimineralic ooids from the Pleistocene of the Florida continental shelf

A bored and encrusted late Pleistocene ooid grainstone was recovered from the seafloor at a depth of approximately 40 m on the outer continental shelf of eastern Florida. Ooid cortices are dominantly bimineralic, generally consisting of inner layers of radial magnesian calcite and outer layers of tangential aragonite. Ooid nuclei are dominantly rounded cryptocrystalline grains, although quartz grains and a variety of skeletal grains also occur as nuclei. Ooids are partially cemented by blocky calcite, and interparticle porosity is partially filled by micrite. Radial cortex layers are composed of brightly cathodoluminescent magnesian calcite having a composition of approximately 12 mol% MgCO₃ and 1000 ppm strontium. The iron and manganese concentrations in radial cortex layers are generally in the range of 500–1000 ppm and 100–250 ppm, respectively. Tangential cortex layers are composed of noncathodoluminescent aragonite containing approximately 11 500 ppm strontium and less than 0.5 mol% MgCO₃. Iron concentrations in tangential cortex layers are generally in the range of 150–400 ppm, and manganese concentrations are generally below the detection limit of 100 ppm. Echinoderm skeletal fragments, which are present as accessory grains, are composed of brightly cathodoluminescent magnesian calcite. Some ooid nuclei and the thin outer edges of some blocky calcite cement are cathodoluminescent; micrite matrix and the bulk of blocky calcite cement are noncathodoluminescent. Ooids do not exhibit textural evidence of recrystallization. The ooid grainstone underwent an episode of meteoric diagenesis. but ooid cortices were not affected by the event. We propose a previously unrecognized process by which the magnesian calcite cortex layers underwent diagenetic alteration in oxygen-depleted seawater. During this diagenesis, magnesium was lost and manganese was incorporated without apparent textural alteration and without mineralogical stabilization. Thus, we Suggest that cathodoluminescence may result from diagenetic alteration on the sea-floor.     

Eh ph Diagrams for mn, fe, co, ni, cu and as Under Seawater Conditions: Application of two new Types of eh ph Diagrams to the Study of Specific Problems in Marine Geochemistry

E_H pH diagrams have been calculated using the PHREEQC programme in order to establish the predominance fields of Mn, Fe, Co, Ni, Cu and As in bottom waters from the Angola Basin. Predominance fields are presented separately for both aquatic species and solid mineral phases in order to simplify interpretation of the data. The diagrams show significant differences from standard E_H pH diagrams for these elements calculated for freshwater at 25 °C and 1 bar which assume an element concentration of 10^-6 M. In particular, our diagrams show that Mn²⁺ and NiCO ₃ ⁰ are the predominant aquatic species for Mn and Ni in bottom seawater and FeOOH, Fe₂O₃, Fe₃O₄, CoFe₂O₄, CuFe₂O₄, CuFeO₂, and Ba₃ (AsO₄)₂ the predominant solid phases for Fe, Co, Cu and As, respectively. Mn and Ni are therefore undersaturated and Fe, Co, Cu and As supersaturated in bottom seawater from the Angola Basin. Neither rhodochrosite (MnCO₃) nor siderite (FeCO₃) can form in this marine environment in equilibrium with seawater. A mixed Mn-Ca carbonate is therefore formed within the pore waters of reducing sediments. The high Ni/Cu ratios in cobalt-rich manganese crusts formed adjacent to the oxygen minimum zone may be explained by the change from Cu²⁺ to CuCl ₃ ^2- as the dominant aquatic species of Cu in seawater at an E_H of +0.48 V.     

A comparison of the early diagenetic environment in intertidal sands and muds of the Manukau Harbour,New Zealand

The early diagenetic environment of intertidal sandy sediments (sands) and muddy sediments (muds) is described and compared from two cores taken from an unpolluted part of the Manukau Harbour, New Zealand. Extraction techniques characterized the form of the trace elements (Fe, Mn, S, C, Pb, Zn, Cu) at different depths in the sediment. Dissolved forms of Fe, Mn, and S were measured in interstitial water. Nonresidual metal concentrations, humic acid, FeS, and FeS₂ are an order of magnitude higher in the muds than in the sands because of dilution by unreactive sand particles. Muds contain a larger proportion of metals in the mobile fractions; exchangeable (Mn), carbonate (Mn, Fe, Zn), and easily-reducible oxide (Fe, Mn, Zn, Pb). This is due to greater surface area (for Mn adsorption); the favorable conditions for MnCO₃, FeCO₃, and FeS precipitation; and higher concentrations of easily reducible iron oxide and humic acid. Therefore, compared to the sands, muds are more important as reservoirs for toxic metals, both in terms of quantity and availability. At either site there was very little difference between the forms of Zn, Pb or Cu identified by sequential extraction as sediments changed from oxic to anoxic conditions. One reason for this is that the amounts and proportions of some of the important components that bind metals, viz., amorphous iron hydrous oxides, humic acids, and FeS₂, do not change much. Other components that do change with redox conditions, for example, manganese phases and FeS, are only minor components of the sediment. Redox conditions, then, have relatively little effect on trace-metal partitioning in the sediment matrix of these unpolluted sediments.     

The control of cathodoluminescence in dolomite by iron and manganese

Variations in the cathodoluminescent properties of carbonates are usually attributed to differing proportions of manganese (Mn²⁺) as the most important activator, and iron (Fe²⁺) as the main inhibitor of luminescence. Interactions between manganese and iron concentrations and the luminescent properties of dolomite are demonstrated by petrographic and chemical analyses of 86 samples of dolomite representing a range of depositional environments and ages (Cambrian to Cretaceous) and a wide geographical distribution (North America and Europe). Iron and manganese are positively correlated in the dolomites, with the former showing a greater range of variation. Very small amounts of manganese are sufficient to activate the luminescence and as little as 100 ppm Mn²⁺ is present in highly luminescing samples. The intensity of luminescence is not proportional to the manganese concentration. Iron begins to quench luminescence as its concentration reaches 10,000 ppm. Above that level, luminescence is rapidly lost and total extinction occurs among samples containing more than 15,000 ppm Fe²⁺, regardless of the manganese concentration.     

Verbreitung und Entstehung Mangan-reicher Gesteine im Jura der Nördlichen Kalkalpen

Zusammenfassung Schichtgebundene Mn-Anreicherungen sind in den Nördlichen Kalkalpen nahezu ausschließlich auf feinschichtige Tonmergelsteine (Manganschiefer) des oberen Toarcian und unter-bis mitteljurassische Rotkalke beschränkt.Die primären Mn-Minerale in der Manganschiefer-Fazies sind Mischkarbonate der Reihe CaCO₃–MnCO₃–FeCO₃ und geringe Mengen von Braunit und Pyrolusit. Die Fe-Mineralisation charakterisiert eine Faziesreihe, die von schwach oxidierenden Ablagerungsbedingungen (Goethit, Hämatit) an der Basis der Mn-führenden Serie, zu reduzierenden (Siderit, Chamosit, Pyrit) führt. In den Rotkalken sind Pyrolusit und Goethit bzw. Hämatit in calcitreichen Knollen und Krusten konzentriert.Die chemische Zusammensetzung der Mn-reichen Gesteine ist bei hohen Ca- und SiO₂-Gehalten von korrelierbaren Mn- und Fe-Anteilen in gleicher Größenordnung bestimmt. Gegenüber der durchschnittlichen Zusammensetzung faziell vergleichbarer Schwarz- und Tonschiefer und marin-sedimentärer Mn-bzw. Fe-Lagerstätten sind auch die Spurenelement-Gehalte deutlich erhöht und zumindest im Falle des Co mit den Mn-Gehalten korreliert.Nach ihrer mineralogischen und chemischen Zusammensetzung sind die Manganschiefer zu den vulkanogen-sedimentären Lagerstätten zu rechnen. Unmittelbare Hinweise auf vulkanische Aktivität im oberen Lias sind in Form von Seladonit-führenden Tuffen, die mit Mn-Karbonaten wechsellagern, erstmals in den Nördlichen Kalkalpen aufgefunden worden.

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Distribution and genetic significance of jurassic manganese deposits in the Northern Limestone Alps

Summary In the Northern Limestone Alps strata-bound deposits of manganese are concentrated in laminated marls (manganese shales) of the lower Toarcian and lower to upper Jurassic red limestones.Carbonates of the system CaCO₃–MnCO₃–FeCO₃, and minor quantities of braunite and pyrolusite are the prevailing primary manganese minerals. Characteristically they are associated with sedimentary iron minerals (hematite, goethite, Mn-siderite, chamosite, pyrite) showing a vertical sequence leading from weakly oxidzing to anaerobic conditions. In the red limestones pyrolusite and goethite are concentrated in carbonate-rich nodules and crusts. The manganese shale facies besides its elevated contents of Ca and SiO₂ is characterized by Mn and Fe values which are closely correlated. In contrast to the average composition of comparable black shale and normal marine Mn and Fe deposits the trace element contents, partly correlated with manganese, are raised, as well.According to their mineralogical and chemical composition the manganese shales must be classed with volcanogenic sedimentary deposits. Volcanic activity during manganese deposition in the Northern Limestone Alps could be proved for the first time by celadonite-bearing tuffaceous layers in manganese carbonate sediments.

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