Mn Oxide Ore Research Articles

CO<sub>2</sub> hypogene speleogenesis in an endogenic travertine system, Mesa del Oro, New Mexico, USA

The Mesa del Oro travertine, deposited by upwelling CO2-rich spring waters, is a large and thick mantle of calcite overlying soft Triassic Chinle Formation mudstones in western central New Mexico, USA. The travertine contains a system of small caves known as the Pronoun Cave Complex. Whut Cave is the largest known cave in the complex. While the travertine hydrologic system is no longer active, there is ample evidence that Whut Cave was formed by hypogene speleogenesis. The Whut Cave entrance is a small roughly circular shaft that descends ~four meters and intersects a linear fissure-controlled passage. Mn-oxide was once mined below the entrance, leaving a five-meter-deep pit that represents the path of upwelling waters that were likely charged with CO2 and supersaturated with CaCO3 once reaching the surface. The roomiest part of the cave is immediately adjacent to the entrance, defining where most of the upwelling of groundwater and gases took place. Gypsum and other sulfates were only noted microscopically. A sample of travertine at the surface near the entrance yielded a uranium-series age beyond the limit of the method and a δ234U age of 735 ± 109 ka BP (before present). A piece of breccia vein in the mine dump associated with the Mn-oxide ore, and a rill of a drape-like crust on the cave wall, both interpreted to be products of hypogene speleogenesis and representing the oldest speleogenetic material, yielded δ234U ages of 848 ± 110 and 723 ± 109 ka BP. Altogether, materials interpreted to be speleogenetic yielded ages of ~900 – 300 ka BP. Although the cave is dry and hydrologically inactive today, cave development by CO2 hypogene speleogenesis was coeval with endogenic travertine deposition and nearby volcanism. Our interpretation suggests that all these events are linked.

Unravelling the Temporal and Chemical Evolution of a Mineralizing Fluid in Karst-Hosted Deposits: A Record from Goethite in the High Atlas Foreland (Morocco)

Timing and duration of ore deposit formation are crucial to understanding the mineralization process. To address this, the geochronological (U-Th)/He method, geochemical and H- and O-isotope compositions of pure goethite formed in the Imini karst-hosted Mn district (High Atlas, Morocco) were examined in detail. Two main generations of cavity-filling and fracture-filling goethite are identified, and both precipitated prior to the massive Mn oxide ore. The δD and δ18O values reveal that the mineralizing fluid of cavity and fracture-filling goethite is meteoric-derived but enriched in 18O due to fluid–rock interactions with the host rock dolostone or mixing with O2-rich surface water resident in an open karst system. The cavity-filling goethite precipitated between 95 to 80 Ma, whereas fracture-filling goethite formed between 80 to 50 Ma. Ore deposition occurred discontinuously during the early Atlas doming associated with one or more early compressional events in the Atlas tectonism. The increase in δD values and depletion in U content result from a change in the mineralizing fluid within the karst system. At about 50 Ma, the fluid is notably enriched in U, Cu and trace metals.

Degradation performance of high-concentration coking wastewater by manganese oxide ore acidic oxidation.

The degradation of coking wastewater using a manganese oxide ore acidic oxidation was investigated. This work was performed in three stages. Firstly, the advantageous degradation conditions were measured by the degradation tests, and under the optimal conditions percentage degradation was obtained of 91.6% chemical oxygen demand measured by potassium dichromate oxidation (CODcr), 94.7% total nitrogen (TN), 98.3% phenols, 98.2% fatty acid, 89.5% tar, and 98.9% sulphide for the oxidized effluent, simultaneously cogenerating a Mn2+concentration of 46.2 g/L for Mn-electrolytic stock solution. Secondly, the transformation analysis of the special chemical group of coking wastewater contaminants illustrated that the employment of manganese oxide ore generated the degradation of low and high molecular weight organics, especially causing polymers to break down into oligomers. Thirdly, the electrochemical characteristics of the interface between wastewater and ore revealed that the contaminant degradation of coking wastewater greatly depended on the oxidation capacity of the surface oxide species, involving a simple answer to the MnO2 oxidation for small-molecule organic materials and a strengthening response to the MnO·OH oxidation for high-weight molecule organic substances. The treatment of coking wastewater using the Mn-oxide ore acidic oxidation process is an effective and value-added method, which is particularly applicable to high-concentration coking wastewater.

Selective extraction performance of Ni, Cu, Co, and Mn adopted by a coupled leaching of low-grade Ni-sulfide ore and polymetallic Mn-oxide ore in sulphuric acid solutions

The coupled leaching of ocean polymetallic nodule and low-grade nickel sulphide ore in sulphuric acid solution was investigated, especially in performance on selective extraction of Ni, Cu, Co, and Mn. This work can be divided into three parts. First, the advantageous selective metal extraction conditions, parallel to the optimal coupled leaching conditions, were measured by coupled leaching tests which adopted the Ni, Mn, Cu, Co, and Fe dissolution efficiency. Under the optimal conditions, the extraction ratios of Ni, Mn, Cu, Co, and Fe are 96.8%, 97.3%, 92.2%, 97.9%, and 28.9%, respectively. Second, electrochemical tests revealed that multi-metal simultaneous extraction from two ores depends on the reduction-oxidation dissolution of a corrosion cell of the nodule cathode and the sulphide ore anode. The results showed that acidity and Fe3+ ion affected dissolution of both ores significantly; high valence manganese oxide reduction takes precedence which is in control of the Ni, Mn, Cu, and Co dissolution of the nodule; Ni, Cu, and Co extraction from the nickel ore is a course of sulphide minerals oxidative conversion which significantly affected by Fe2+-containing sulphide oxidation. Third, the separation performance of iron substance in the solution was determined by the transformation of minerals phases of the leached residues, showing that Fe-bearing minerals dissolved to Fe3+ ion then precipitated as iron vitriol or oxide during the selectively coupled leaching. The selectively coupled leaching of low-grade multi-metallic sulphide ore and oxide ore mainly rests with the transformation of Fe-containing species in the system.

Mineralogical Characterization of Manganese Oxide Minerals of the Devonian Xialei Manganese Deposit

The Guangxi Zhuang Autonomous Region is an important manganese ore district in Southwest China, with manganese ore resource reserves accounting for 23% of the total manganese ore resource reserves in China. The Xialei manganese deposit (Daxin County, Guangxi) is the first super-large manganese deposit discovered in China. The Mn oxide in the supergene oxidation zone of the Xialei deposit was characterized using scanning electron microscopy (SEM), energy spectrometer (EDS), transmission electron microscopy (TEM, HRTEM), and X-ray diffraction analysis (XRD). The Mn oxides have a gray-black/steel-gray color, a semi-metallic-earthy luster, and appear as oolitic, pisolitic, banded, massive, and cellular textures. Scanning electron microscopy images show that the manganese oxide minerals are present as fine-spherical particles with an earthy surface. TEM and HRTEM indicate the presence of oriented bundled and staggered nanorods, and nanopores between the crystals. The Mn oxide ore can be classified into two textural types: (1) oolitic and pisolitic (often with annuli) Mn oxide, and (2) massive Mn oxide. Pyrolusite, cryptomelane, and hollandite are the main Mn oxide minerals. The potassium contents of cryptomelane and pyrolusite are discussed. The unit cell parameters of pyrolusite are refined.

Major, trace and rare earth element (REE) geochemistry of the Oligocene stratiform manganese oxide-hydroxide deposits in the Nikopol, Ukraine

The Nikopol manganese deposit is situated in the west and north of Nikopol, Ukraine and one of the world's largest deposits among the sedimentary manganese deposits. The Nikopol Oligocene basin consists of two structural stages, Precambrian crystalline basement rocks and sedimentary cover rocks (Cretaceous to Quaternary). Nikopol Ore horizon is traced in a thickness varying from several cm to 4.5 m and a single stratum from the west to the eastwards to about 250 km. Nikopol manganese ore horizon was separated to three different units; carbonate ore, mixed carbonate-oxide ore, and oxide ore. The main minerals of supergene oxidation zone in Nikopol manganese deposits are: manganite, pyrolusite, todorokite, cryptomelane, birnessite, rancieite. The manganese oxide-hydroxide ores were analyzed for major oxides using ICP-AES and, trace and rare earth elements (REE) using ICP-MS. The mean major oxide contents of the manganese ores are 40.7 wt% MnO, 4.1 wt% Fe2O3, 15.6 wt% SiO2, 4.17 wt% for Al2O3, and 7.1 wt% for CaO. The average Mn/Fe, Co/Ni, Co/Zn, and Zr/Hf ratios in the Nikopol manganese deposit are 25, 0.54, 1.15, and57, respectively. The total REE contents are between 60 and 197 ppm, with a mean of 108 ppm. The PAAS-normalized REE patterns of the Nikopol manganese oxide ores have similar trends and show MREE (middle rare earth element) and HREEs (heavy rare earth element) enrichments. The Ce/Ce* values of manganese oxide-hydroxide ores collected from the study area vary from 0.88 to 1.43, with the mean of 1.16. Most of manganese samples have positive Ce anomalies except for a few samples, indicating that ore-forming rocks were primarily marine chemical or biogenic deposit. The Eu/ Eu* anomalies of the manganese oxide-hydroxide ores are close to 1 with a range of 0.68 to 1.12 (mean: 0.96). The Y concentrations vary from 9.1 to 47.1 ppm, with an average of 18.2 ppm and show negative Y anomalies, except for three samples. The Pb isotope ratios are 19.0 for 206Pb/204Pb, 15.7 for 207Pb/204Pb and 39.4 for 208Pb/204Pb isotopes. All these data indicate that the Nikopol manganese oxide-hydroxide ores formed rapidly within oxic/suboxic seawater as reflected by Ce anomalies close to 1 in compared to similar environments, low-oxygen fugacity in source of the hydrothermal fluids, volcanogenic input or hydrothermal contributions to seawater, and high Co, Ni, Cu, Sr, Ba and As and low V, Rb, Nb, Hf, U, Th, Pb and Zn values. Also, our results point out that the metals were transported from both a hydrothermal source in deeper water (chemical discrimination diagrams) and terrestrial sources (Pb isotopic data). The metals formed to the Mn-oxide ores syngenetically likely came from water depths deeper than the area where the carbonate-ore deposits formed.

Orthovanadate wakefieldite-(Ce) in symplectites replacing vanadium-bearing omphacite in the ultra-oxidized manganese deposit of Praborna (Aosta Valley, Western Italian Alps)

Abstract Because of their unique structure and properties, rare-earth (REE) orthovanadates have been extensively employed for decades in advanced ceramics, in particular in the laser industry in replacement of Nd:YAG. A Ca-bearing REE orthovanadate with the empirical formula (Ce0.279Ca0.271Y0.267Gd0.057Nd0.055Dy0.032Sm0.027La0.020Th0.027Sr0.002)(V0.9085+Cr0.0673+Fe0.0173+As0.0055+)O4⋅nH2O has been found in metacherts from Praborna (Italian Alps) as micrometer-sized euhedral crystals in clinopyroxene + plagioclase symplectites replacing eclogite-facies vanadium-bearing omphacite (Aegirine55–48Jadeite42–33Diopside10–8 with V2O3 ≤ 1.39 wt%). We applied the synchrotron radiation, single crystal, micro-diffraction technique, recently optimized at ID09A beamline (ESRF, France), to determine the crystal structure of this mineral. It is tetragonal and isostructural with zircon, with a = 7.2233(12) Å, c = 6.3949(18) Å, V = 333.66(13) Å3, Z = 4, space group I41/amd, and it has been therefore identified as Ca- and Y-bearing wakefieldite-(Ce) (ideally CeV5+O4). Cell parameters are in agreement with those of synthetic Ce0.7Ca0.3VO4. Raman spectra of the studied wakefieldite-(Ce) are comparable with natural and synthetic wakefieldite-(Ce) spectra and revealed the presence of OH groups and/or water of hydration, which is also suggested by the low totals in microprobe analyses. Mass balance indicates that wakefieldite-(Ce) is a by-product of the omphacite breakdown; omphacite and Mn-rich epidote, a minor reactant, provided vanadium and REE, respectively. Petrological observations and thermodynamic modeling suggest that the mineral, coexisting with hematite, Mn-rich epidote, and braunite, formed during retrogression to greenschistfacies conditions at ultra-oxidized conditions (DFMQ ≥ +16 log units), which are often observed in Mn-oxide ores. Wakefieldite is an effective scavenger of REE in oxidized geological environments at P-T conditions that range from sedimentary to medium-grade metamorphic settings, even where the REE bulk concentration is negligible. Its rarity reflects both the overall low abundance of vanadium and the need for ultra-oxidized conditions that are rarely achieved in metamorphic rocks, where REE phosphates (i.e., monazite, xenotime) are commonly found instead.

Precipitation of Mn Oxides in Quaternary Microbially Induced Sedimentary Structures (MISS), Cape Vani Paleo-Hydrothermal Vent Field, Milos, Greece

Understanding microbial mediation in sediment-hosted Mn deposition has gained importance in low-temperature ore genesis research. Here we report Mn oxide ores dominated by todorokite, vernadite, hollandite, and manjiroite, which cement Quaternary microbially induced sedimentary structures (MISS) developed along bedding planes of shallow-marine to tidal-flat volcaniclastic sandstones/sandy tuffs, Cape Vani paleo-hydrothermal vent field, Milos, Greece. This work aims to decipher the link between biological Mn oxide formation, low-T hydrothermalism, and, growth and preservation of Mn-bearing MISS (MnMISS). Geobiological processes, identified by microtexture petrography, scanning and transmission electron microscopy, lipid biomarkers, bulk- and lipid-specific δ13Corganic composition, and field data, and, low-temperature hydrothermal venting of aqueous Mn2+ in sunlit shallow waters, cooperatively enabled microbially-mediated Mn (II) oxidation and biomineralization. The MnMISS biomarker content and δ13Corg signatures strongly resemble those of modern Mn-rich hydrothermal sediments, Milos coast. Biogenic and syngenetic Mn oxide precipitation established by electron paramagnetic resonance (EPR) spectroscopy and petrography, combined with hydrothermal fluid flow-induced pre-burial curing/diagenesis, may account for today’s crystalline Mn oxide resource. Our data suggests that MISS are not unique to cyanobacteria mats. Furthermore, microbial mats inhabited by aerobic methanotrophs may have contributed significantly to the formation of the MnMISS, thus widening the spectrum of environments responsible for marine Mn biometallogenesis.

Grootfonteinite, Pb3O(CO3)2, a new mineral species from the Kombat Mine, Namibia, merotypically related to hydrocerussite

Grootfonteinite, Pb3O(CO3)(2), is a new Pb oxycarbonate found in a mineralogically complex, banded assemblage from the Mn (-Fe) oxide ore unit of the Kombat mine. Grootfonteinite is named after the ...

Mineralogy and 40Ar/39Ar geochronology of supergene Mn-oxides in the Dongxiangqiao deposit, Hunan Province, South China

The Dongxiangqiao Mn deposit in Hunan Province is one of numerous supergene Mn-oxide deposits in central South China. This deposit is derived from chemical weathering of Permian Mn-rich shales and limestones. Mn-oxide samples from the Dongxiangqiao deposit consist mainly of pyrolusite, lithiophorite, and cryptomelane, with minor amounts of hollandite and nsutite. Cobalt and Ni are enriched in lithiophorite and cryptomelane-hollandite. Our studies suggest that Co occurs mainly in the structural and adsorption sites of lithiophorite. Cobalt in lithiophorite accounts for ~80 % of the bulk Mn-oxide ores, thus it can be comprehensively utilized when lithiophorite has been separated by a suitable physical beneficiation process. Four cryptomelane-dominated grains from the saprolite zone yield 40Ar/39Ar plateau ages ranging from 10.3 ± 0.3 to 4.19 ± 0.08 Ma (2σ). This indicates that intense enrichment of supergene Mn-oxides has prevailed at least in the late Miocene and persisted into the Pliocene at Dongxiangqiao. When combined sedimentalogical and thermochronoloical data, our dating results suggest that central South China has a relatively rapid surface uplift rate.

Multivariate analyses and spatial distribution of Manganese minerals in soils close to an abandoned Manganese mine

AbstractFour hundred soil samples were obtained from a 4 km2 area close to the abandoned Kgwakgwe Mn oxide ore mine in order to investigate the environmental association of Mn minerals and concentrations in the soils. Manganese minerals and Mn concentrations in samples were identified by X‐ray diffractometry and atomic absorption spectrometry, respectively, and results statistically analysed. Bixbyte, Mn2O3; braunite, Mn+2MnSiO12; ramsdellite, MnO2; pyrolusite, β‐MnO2 and cryptomelane, K2 − xMn8O16 were identified in soil samples at the study site but none of these minerals found in soil samples from the control site. Manganese concentrations in samples from the study area were significantly higher than those from the control site. Statistical data yielded seven clusters with distribution of the Mn minerals and concentrations as follows: cluster 1 dominated by Mn concentrations in soil, cluster 2 by none of the seven Mn minerals, cluster 3 by pyrolusite, cluster 4 by braunite, cluster 5 by cryptomelane, cluster 6 by bixbyite and cluster 7 by ramsdellite. Very weak associations of these minerals were depicted from their correlations. The clusters had a bearing on the spatial distribution of the different minerals. Comparing results obtained from the control site, and geological materials, to the soils from the study area, it is certain that Mn minerals and high Mn concentrations in soils originated from the surrounding geological materials. The mining activities most possibly have affected Mn concentrations' and minerals' occurrences in the soils at the study area. Copyright © 2009 John Wiley & Sons, Ltd.

Multivariate analysis of selected allied chemical properties of soils close to an abandoned manganese mine

This study aimed at understanding the statistical relationships between base saturation percent (BSP), cation exchange capacity (CEC), pH(water) and electrical conductivity (EC) in soils within close proximity to the abandoned Kgwakgwe Mn oxide ore mine, Botswana. Four hundred soil samples were collected from a 4 km2 area close to the abandoned mine. Soil pH ranged from 2.92 to 7.26 with very acidic soils located close to the mine workings. Electrical conductivity values were low, ranging from 49.1 Scm−1 to 123.5 Scm−1. The BSP in the soil samples varied between 33.77 and 100 with a mean of 82.10 and CEC values % (cmolckg−1) ranged from 1.1 to 29.2, with a mean of 8.2. Relationships between the various parameters were generally poor and negative with the exception of EC/BSP and BSP/CEC which were positive. The statistical data yielded five clusters with distribution of the parameters as follows: cluster one is dominated by pH and EC, cluster two by EC, cluster three by CEC, PBS and EC, cluster four by PBS, and cluster five by none of the four parameters. The PBS and CEC values are closely associated. Comparing results obtained from the control site, it is certain that mining activities have affected the soil PBS, CEC, pH and EC of the study area.

Environmental association of iron minerals and iron concentrations in soils close to an abandoned manganese mine – a multivariate analytical approach

Environmental association of iron (Fe) minerals and Fe concentrations in soils close to the Kgwakgwe Mn oxide ore abandoned mine, Botswana are investigated in this study. Four hundred soil samples were obtained from a 4 km 2 area close to the abandoned mine. The Fe minerals in the soil samples were identified by x-ray diffractometry and the Fe concentrations by atomic absorption spectrophotometry. Results were processed using the statistical package for social science (SPSS). Iron minerals namely hematite and goethite were found in soils from the study area but only hematite in soils from the control site. Also Fe concentrations in soils from the study area were significantly higher than those from the control site. The correlations depicted very weak associations of these parameters. Hematite contributed significantly in the formation of the five clusters, goethite's contribution was for three of the clusters, and Fe concentrations in soils were for two of the clusters. At Kgwakgwe, exposed surfaces of mine workings, ferruginous shale and country rocks through wind erosion release particulate air matter, rich in Fe into the atmosphere which are transported over short distances and deposited on soils. Through chemical alteration processes, hematite is hydrated to goethite and neomineralization of goethite from the ferruginous shale occurs in the surrounding soils. Journal of Applied Sciences and Environmental Management Vol. 10(1) 2006: 31-36

Total organic carbon in soils and its relation with manganese concentrations in soils and vegetation close to an abandoned manganese mine

This study aimed at quantifying the total organic carbon (TOC) present in soils within the proximity of the Kgwakgwe Mn oxide ore abandoned mine, Botswana, and establish its relationship with Mn concentrations in soils and vegetation based on multivariate and Geographical Information Systems (GIS) analytical techniques. Four hundred soil samples and 200 vegetation set samples were obtained from a 4 km2 area close to the abandoned mine. The TOC in soil samples were determined using a carbon/hydrogen/moisture determinator, and Mn concentrations in soils and vegetation by atomic absorption spectrophotometry. Results were processed using the statistical package for social science (SPSS), GIS, and Remote Sensing (RS) techniques with the Integrated Land and Water Information System (ILWIS), Geosoft Oasis Montaj and ArcGIS software packages. The values for TOC in the soil samples from the study area ranged from 0 wt % to 7.91 wt %, with a mean of 1.90 wt %, and at the control area, from 4.07 wt % to 4.86 wt %. The range of concentrations of Mn in soils was from 36 mg/g to 24908 mg/g and for Mn concentrations in the vegetation samples from 26 mg/g to 3611 mg/g with a mean of 598 mg/g. Results of correlation coefficients depicted very weak negative association except Mn in soils/Mn in leaves which was weak but positive. The statistical data yielded four clusters as follows: cluster one consisted mainly of Mn in leaves, cluster two was constituted of Mn in soils, and cluster four had TOC. Cluster three was dominated by the three parameters but with negative t statistic. The spatial presentation of data presented revealed little or no vegetation in the south eastern area and those close to the mine workings, and some significant vegetation in the north western part of the study area. The low TOC in the soils is associated to low vegetation cover which is considered to have been influenced by the soil clay fraction mineralogy and high concentrations of Mn.

Using GIS to understand the environmental chemistry of manganese contaminated soils, Kgwakgwe area, Botswana

This study aimed at establishing the spatial distribution of manganese (Mn) and iron (Fe) within the periphery of a manganese oxide (Mn oxide) ore abandoned mine. Four hundred soil samples were obtained from a 4 km 2 area close to the Kgwakgwe Mn oxide ore abandoned mine, Kanye, South eastern Botswana. The determination of Fe and Mn concentrations after acid digestion of samples was performed on a Varian Spectra AA-220 FS atomic absorption spectrometer (Varian, Australia) equipped with a deuterium background correction. Laboratory results were processed using Geographical Information Systems (GIS), and Remote Sensing (RS) techniques with the integrated Land and Water Information System (ILWIS), Geosoft Oasis Montaj and ArcGIS software packages. Microsoft Excel was used for statistical and graphical presentation of data analyses. The range of concentration levels of Fe in soils was from 1116 µg g -1 to 870766 µg g -1 with a mean of 17593 µg g -1 and for Mn in soils was 35 µg g -1 to 24907 µg g -1 with a mean of 1088 µg g -1 . The gridded soil maps for Fe and Mn show anomalies in different parts of the study area. Where Mn is high, the Fe is low and vice versa. Manganese was high at the mine workings and in the northwestern part of the study area. Iron on the other hand is very low in the mine working area and is high on the northern part of the study area. Suggestions are advanced for the Mn interplay in the soils and environment around the Kgwakgwe abandoned Mn oxides ore mine. Journal of Applied Sciences and Environmental Management Vol 9(2) 2005: 37-42

THE MANGANESE FORMATION OF THE NEOPROTEROZOIC PENGANGA GROUP, INDIA—REVISION OF AN ENIGMA—A DISCUSSION

Sir : Gutzmer and Beukes (1998) have revised the sedimentary-diagenetic mode of origin suggested earlier for the todorokite-rich (with birnessite, manganite, braunite, and bixbyite) manganese deposits of the Penganga Group, India (Roy, 1981; Roy et al., 1990; Bandopadhyay, 1996), concluding that these Mn oxide deposits were entirely derived by supergene alteration of a Mn carbonate protolith which they discovered in one deep quarry section (near Nipani) below the Mn oxide ore horizon. I congratulate the authors for this discovery of the Mn carbonate horizon that eluded us in spite of thorough search (Roy et al., 1990) during the 1980s, that perhaps was limited by the depth-extension, at that time, of the section by mining operations. Credit must also go to these authors for the very detailed characterization of these Mn carbonates including stable isotope and REE geochemistry. I have, however, strong misgivings on several conclusions drawn in this paper. In a 40-km-long belt of Mn oxide deposits, this study was confined to only two spots (p. 1091) near Nipani (Mn carbonate rock) and Jamdapur (supergene ore) and yet a generalization is made that the entire Mn oxide ore horizon was formed by supergene alteration of a Mn carbonate protore rejecting our conclusion (Roy et al., 1990), based on studies over the entire ore belt, that the Mn oxide ores are sedimentary-diagenetic in character. Our studies showed that the …

Geology, mineralogy, and geochemistry of the Middle Proterozoic Wafangzi ferromanganese deposit, Liaoning Province, China

Wafangzi is the largest ferromanganese-ore deposit in north China, consisting of southeastern and northwestern regions containing 11 ore blocks (districts). Middle Proterozoic and Cambrian sedimentary rocks occur in the mine area, and Jurassic–Cretaceous intrusive igneous rocks subjected the ores to local metamorphism. The ore-bearing sequence is located in the upper part of the Middle Proterozoic Tieling Formation, which is composed of three ore beds and associated rocks. The ore-bearing sequence and the ores display lithological and mineralogical changes from manganite ore and red and dark-brown mudstone in the southeast to rhodochrosite ore and black shale and silty dolostone in the northwest. The industrial type of Wafangzi ores is ferromanganese containing 16 to 33% Mn, 15 to 20% Fe, and Mn/Fe ratios of 1 to 2. Genetic types include primary sedimentary and diagenetic type which includes manganite and rhodochrosite ores; contact metamorphic type, which includes bixbyite–braunite ore, Mn silicate–Mn oxide ore, and pyrosmalite–rhodochrosite ore; and secondary oxidized type, which includes pyrolusite ore and psilomelane–vernadite–goethite ore. Mean contents of Co, Ni, and Zn in rhodochrosite ore are two to four times higher than those of the other ores. Strontium and Ba contents in manganite ores are 16 to 27 times higher than in the rhodochrosite ores, indicating that Sr and Ba probably occur in barite in manganite ores. The mean total REE content of the various ore types is 129 ppm, LREE/HREE is 6.5, La/Yb is 12.3, Eu/Sm is 0.18, and Sm/Nd is 0.22, comparable with those of continental and subcontinental crust. Chondrite-normalized REE patterns of the various ore types have small negative Eu anomalies, whereas the shale-normalized REE curves have weak negative Eu anomalies. Organic carbon contents in rhodochrosite ores range from 1.18 to 1.77%, whereas contents in the host rocks range from 0.58 to 0.88%. The H/C vs. O/C diagram shows that organic matter in ores experienced catagenesis and metagenesis. The mean δ 13 C PDB of the rhodochrosite ore is −6.5‰ (range −3.9 to −10.5‰), and δ 18 O PDB is −7.2‰ (range −4.7 to −9.4‰). The following conclusions are made: (1) The source of the ore components is mainly terrigenous, derived from the weathering of continental crust; (2) both manganite and rhodochrosite ores are of primary sedimentary origin, and precipitated in a shallow-marine basin; (3) the presence of bacterial textures in the black matrix of spheroidal rhodochrosite ore and C isotope data indicate that microbial activity played a role in formation of the ores; (4) some evidence indicates that hydrothermal solutions contributed to the ores, such as the presence of adularia in manganite ore and pyrosmalite in rhodochrosite ore. Hydrothermal fluids were generated by igneous intrusions.

Genesis of secondary Mn-oxide ores in the Úrkút deposit, Hungary

The Urkut Basin of western Hungary is well known for its early Jurassic Mn-carbonate deposit that is related genetically to Jurassic black shale formation. This carbonate deposit has undergone multistage oxidation during the Cretaceous that produced secondary Mn-oxides. Among the geochemical characteristics that distinguish the host sedimentary rocks and Mn-carbonates from the Mn-oxides is an extreme enrichment in Sr (up to 1%) without an observable independent Sr-phase. This enrichment indicates a special process of formation. The δ18O values of these Mn-oxide ores fall between 1.5 and 5.5%. (VSMOW) showing a slight bimodal distribution. This isotopic variability is interpreted as a product of superposing effects of the interaction of surficial and deep-seated magmatic fluids. The δ18OMnO2 values (from 1.5 to 5.5%.), the assumed δ18Owater values and formation temperatures fit well with the MnO2-water fractionation curve based on the data of Yeh et al. (1985) and Hoefs et al. (1987).

Genesis of secondary Mn-oxide ores in the �rk�t deposit, Hungary An oxygen isotope study

Genesis of secondary Mn-oxide ores in the �rk�t deposit, Hungary An oxygen isotope study

Geochemistry and depositional environment of Mn oxide deposits in the Tokoro Belt, northeastern Hokkaido, Japan

Numerous Early Cretaceous Mn oxide and Mn-Fe deposits are distributed in the Tokoro belt, northeastern Hokkaido, Japan. The Mn oxide deposits usually occur in the southwestern part of the belt and within bedded cherts whereas the Mn-Fe deposits are restricted to the northeastern part of the belt and occur between bedded cherts and underlying basaltic pillow lava.The Mn oxide ores are characterized by low Fe/Mn ratios, and the trace element concentrations and rare earth element (REE) patterns are similar to those of the submarine hydrothermal Mn deposits. Distribution patterns of trace elements (Co, Ni, Cu, and Zn) and REE in the Mn oxide ores determine two types of deposits: hydrogenous deposits which have relatively high concentrations, and submarine hydrothermal deposits which have low concentrations.These compositional trends and geologic evidences of the Tokoro Mn deposits suggest that the Fe phases precipitated first closer to their source whereas the Mn phases deposited later at a distance from their source. Some hydrogenous effects on the Mn oxide deposits are due to the adsorption of trace elements from seawater. Trace element concentrations of Tokoro Mn oxide deposits show that they formed within 40 km from their source.