Mn Ore Deposits Research Articles

Precipitation mechanism of Mn ore deposits in the Datangpo Formation, Nanhua Basin, South China

During the interglacial period of the Cryogenian glaciation, the extensive “Datangpo-type” manganese ores were deposited in the Nanhua Basin. However, there has been significant controversy over the precipitation mechanism of manganese for decades. Based on iron and nitrogen isotope data from the manganese ores of the Datangpo Formation in Chongqing (South China), combined with previous research, we propose that the manganese ores of the Datangpo Formation precipitated directly in an anoxic bottom-water environment in the form of rhodochrosite. The δ56Fe values in the Bijiashan manganese ore (δ56Fe = −0.19 ± 0.13 ‰) are close to those of modern marine hydrothermal iron, and there is a strong positive correlation between the δ56Fe value and iron concentration (R2 = 0.81), indicating that the precipitation of manganese ore could be mainly affected by hydrothermal input. After comprehensively comparing the δ56Fe values of the whole rock and pyrite in the manganese ore of the Datangpo Formation, we believe that iron from hydrothermal sources directly and quantitatively combined with sulfides to form pyrite. Additionally, the bottom seawater of the basin was mainly anoxic. The nitrogen isotope composition indicates the presence of a stable nitrate reservoir in the ocean at that time, and manganese ore deposition may have been influenced by the input of high-salinity water from the open ocean. Due to the supply of NO3- from the open ocean to the graben basin, the δ15N in manganese ore is significantly higher than that in black shale. The input from the open ocean led to an increase in alkalinity in the bottom water of the basin, which favored the precipitation of rhodochrosite. Considering that the oxidation potential required for manganese oxidation precipitation is higher than that required for iron oxidation precipitation, it is most reasonable to conclude that under alkaline anoxic conditions in the bottom water layer, Mn2+ directly precipitated in the form of rhodochrosite.

Microbial contribution to the formation of the Carboniferous sedimentary manganese deposits in northwestern China

There is an increasing consensus that microbes play a critical role in the genesis of sedimentary manganese (Mn) carbonate deposits. However, compelling evidence for the microbial involvement during sedimentary Mn metallogenesis remains insufficient, and the specific effects of microbial mediation need to be further elucidated. To advance our understanding of the microbial Mn metallogenesis, multi-scale petrographic observations and high-resolution mineralogical analyses (mainly based on Fourier transform infrared spectrometer and Raman spectroscopy) were conducted on the Carboniferous black shale-hosted Malkansu and limestone-hosted Zhaosu Mn ore deposits in northwestern China. Results show that the Mn ore samples are characterized by finely laminated texture with μm-scale cyclic variations of microbe-associated minerals including rhodochrosite, apatite, quartz, and organic matter as well. These features indicate the ubiquity of microbial mats during Mn mineralization. Microbial involvement is also supported by Mn carbonate aggregates with variable morphologies (filamentous with pearl necklace-like inner forms resembling vermiform morphologies and spheroidal, coccoid-like forms), as well as the annular organic matter that resembles bacterial cells. The cyclic occurrence of trace amounts of remnant Mn oxides verify that primary Mn accumulation took place under oxic bottom waters. The negative co-variation between Mn carbonates and organic matter on Raman profiles suggests that the former was formed during diagenesis via organic matter decomposition coupled with Mn oxide reduction. Combined with previous experimental simulations and natural observations, a two-step microbially mediated Mn metallogenic model is tentatively proposed for the studied Mn deposits: (1) Mn(II)-oxidizing bacteria effectively catalyzed the deposition of considerable Mn oxides under oxygenated bottom water columns, a process that was simultaneously sustained by oxygenic microbial mats such as cyanobacteria; (2) Buried Mn oxides were reduced by highly reactive organic matter sourced from dead biomats of Mn(II)-oxidizing bacteria and benthic phototrophs, a process mediated by Mn(IV)-reducing bacteria which not only promoted the reaction rate but also served as nucleation sites for Mn carbonate minerals. This model can also help to explain the occurrence of diverse authigenic accessory minerals (e.g., quartz, apatite, and talc) and remarkable enrichments of several specific elements (e.g., Co, Ce, and Mo) in the studied Mn ores, which were closely linked to the decomposed cells and extracellular polymeric substance (EPS). By comparing with previous microbial investigations on Mn deposits over geological history, we further highlight the fundamental role of microorganisms in regulating the formation of economic Mn carbonate deposits.

New data on melanostibite, Mn2Fe3+Sb5+O6

AbstractFollowing the identification of a new occurrence of melanostibite from the Apuan Alps, the crystal chemistry of this mineral has been re-examined using specimens from its type locality, Sjögruvan, Örebro County, Sweden, and from the new occurrence, the Scortico–Ravazzone Mn ore deposit, Apuan Alps, Tuscany, Italy. Both specimens were examined through electron microprobe analysis, micro-Raman spectroscopy and single-crystal X-ray diffraction data; Mössbauer spectroscopy was used for the Swedish specimen. Electron microprobe data indicate a close to ideal composition Mn2Fe3+Sb5+O6 for both samples, whereas Mössbauer spectroscopy confirmed the trivalent oxidation state of Fe. Single-crystal X-ray diffraction for the Swedish and Italian specimens points to the acentric nature of melanostibite, space group R3. Refined unit-cell parameters of melanostibite from Scortico–Ravazzone and Sjögruvan are a = 5.2351(3), c = 14.3645(8) Å, V = 340.93(4) Å3, and a = 5.2314(2), c = 14.3518(8) Å, V = 340.15(3) Å3, respectively. Melanostibite is an homeotypic derivative of pyrophanite.

A new metallogenic model for the giant manganese deposits in northeastern Guizhou, China

The recently discovered multiple world-class Nanhuanian manganese (Mn) ore deposits at Datangpo of northeastern Guizhou province in southern China provides substantial amount of Mn that can be economically important for industrial usage. Studies that we previously conducted suggest that these Mn ore deposits are likely manifestations of the deposition of volatile-rich Mn-bearing ore-forming materials originating from deep reservoirs. However, ore-forming structures that transport ore-forming materials, if existed, have not yet been identified. Here, integrated with three-dimensional (3D) geological modeling, aeromagnetic △T data processing and Bouguer gravity anomaly analysis, we found that the intersections of the northwest (NW)-trending early rift basins and the near east–west (EW)-trending Nanhua rift basins overlap with the localities of the giant Mn ore deposits in northeastern Guizhou. In addition, a seismic reflection profiles passing through the Mn mining district reveals an upward-widen, funnel-shaped seismically abnormal structure with a dimension of about 3-km-wide and 45-km-deep. The seismically abnormal structure highly likely represents a deep-seated diapir channel beneath the mining district. Such a structure could contribute to the transportation of Mn-bearing materials that are responsible for the final deposition of Mn ore deposits. This study not only offers a visualization of a deep-seated channel that may be part of ore-guiding structures, but also sheds light on a new metallogenic model of Mn ore deposit.

Development of nickel-rich lithiophorite in khondalite-hosted Mn-ore deposits of South Odisha, India

Development of nickel-rich lithiophorite in khondalite-hosted Mn-ore deposits of South Odisha, India

Features of the content of manganese in natural waters in the south of the Far East (on the example of the Jewish Autonomous Region)

The article provides data on the content of total manganese (Mn) during the 2019 summer in the surface waters of the Bira River and its tributaries, which are located in the North of the Jewish Autonomous Region (JAR), a biogeochemical province in terms of excess iron (Fe) and Mn in the water. The aim of the study was to examine the distribution of Mn and to reveal its concentration in surface watercourses taking into account the geological features and natural conditions of the region. Water samples were taken at 11 stations from the left tributaries of the Bolshaya Bira river. A photometric method with formaldoxime was used to determine the gross Mn content in water in October 2018. The atomic absorption spectrometer “Kvant-2 AT” was used in 2019. Very high concentrations of total Mn were revealed in the waters of rivers in the north-western part of the region in the area of the Mn ore deposit. It has been shown that in the rivers located to the northeast of the deposit, the metal concentration sharply declines. In the eastern swampy part of the region, the Mn content in the river water of the Ikura River sharply increases up to 0.139 mg/dm3. The results of surface water samples from the Bira River basin confirmed the previously identified distribution of Mn levels in the waters of the River and its tributaries in accordance with natural conditions.

Geochemical signatures of manganese ores around Barbil, Noamundi-Koira basin, Singhbhum Craton, Eastern India

ABSTRACT Palaeoproterozoic Noamundi – Koira Basin (NKB), on the western margin of the >3.0 Ga old Singhbhum Granitoid Complex, forms a horseshoe-shaped synclinorium. Volcanic rocks belonging to Bonai volcanic suite (BVS) occur outside and all-around the NKB that consists of three distinct but conformable stratigraphic units viz; Lower Shale Formation, Middle Banded Hematite Quartzite (BHQ) and/or Banded Hematite Jasper (BHJ) and Upper Shale Formation. The layered, lensoid, lateritoid, and vein type Mn-ore bodies are associated with the Upper Shale Formation. Compositions of the Mn ores widely variable values, SiO2 (1.00%- 16.40%), Al2O3 (1.62%-17.20%), Fe2O3 (10.55%-63.28%), MnO (31.75% −75.72%), Ni (25–260 ppm), Co (78–350 ppm), Zn (82–509 ppm) and Cr (13–187 ppm) clearly reflect their submarine hydrothermal source. Litho-stratigraphic considerations also lead to suggest that BHJ/BHQ and Mn-ore deposits of NKB are genetically related to the BVS. It is suggested that manganese and iron ores were deposited in a (? Forearc) basin associated with the mature island arc or active continental margin setting. FeO and MnO were added to the basin by hydrothermal solutes produced during the Bonai volcanism. BHQ/BHJ precipitation took place under a low redox potential while Mn-ore deposition is a consequence of the high redox potential.

Manganiakasakaite-(La) and Ferriakasakaite-(Ce), Two New Epidote Supergroup Minerals from Piedmont, Italy

Two new monoclinic (P21/m) epidote supergroup minerals manganiakasakaite-(La) and ferriakasakaite-(Ce) were found in the small Mn ore deposit of Monte Maniglia, Bellino, Varaita Valley, Cuneo Province, Piedmont, Italy. Manganiakasakaite-(La) occurs as subhedral grains embedded in pyroxmangite. Its empirical formula is A(1)(Ca0.62Mn2+0.38) A(2)(La0.52Nd0.08Pr0.07Ce0.07Y0.01Ca0.25) M(1)(Mn3+0.52Fe3+0.28Al0.18V3+0.01) M(2)Al1.00 M(3)(Mn2+0.60Mn3+0.27Mg0.13) T(1−3)(Si2.99Al0.01) O12 (OH), corresponding to the end-member formula CaLaMn3+AlMn2+(Si2O7)(SiO4)O(OH). Unit-cell parameters are a = 8.9057(10), b = 5.7294(6), c = 10.1134(11) Å, β = 113.713(5)°, V = 472.46(9) Å3, Z = 2. The crystal structure of manganiakasakaite-(La) was refined to a final R1 = 0.0262 for 2119 reflections with Fo > 4σ(Fo) and 125 refined parameters. Ferriakasakaite-(Ce) occurs as small homogeneous domains within strongly inhomogeneous prismatic crystals, where other epidote supergroup minerals coexist [manganiandrosite-(Ce), “androsite-(Ce)”, and epidote]. Associated minerals are calcite and hematite. Its empirical formula is A(1)(Ca0.64Mn2+0.36) A(2)(Ce0.37La0.17Nd0.06Pr0.03Ca0.35□0.02) M(1)(Fe3+0.61Al0.39) M(2)Al1.00 M(3)(Mn2+0.64Mn3+0.33Fe3+0.02Mg0.01) T(1−3)Si3.01 O12 (OH), the end-member formula being CaCeFe3+AlMn2+(Si2O7)(SiO4)O(OH). Unit-cell parameters are a = 8.9033(3), b = 5.7066(2), c = 10.1363(3) Å, β = 114.222(2)°, V = 469.66(3) Å3, Z = 2. The crystal structure of ferriakasakaite-(Ce) was refined to a final R1 = 0.0196 for 1960 unique reflections with Fo > 4σ(Fo) and 124 refined parameters.

Molybdenum-isotope signals and cerium anomalies in Palaeoproterozoic manganese ore survive high-grade metamorphism

Molybdenum (Mo) and its isotopes have been used to retrieve palaeoenvironmental information on the ocean–atmosphere system through geological time. Their application has so far been restricted to rocks least affected by severe metamorphism and deformation, which may erase or alter palaeoenvironmental signals. Environmental Mo-isotope signatures can be retrieved if the more manganese (Mn)-enriched rocks are isotopically depleted and the maximum range of δ98Mo values is close to the ~2.7‰ Mo-isotope fractionation known from Mo sorption onto Mn oxides at low temperature. Here, we show that the Morro da Mina Mn-ore deposit in Minas Gerais, Brazil, contains Mn-silicate–carbonate ore and associated graphitic schist that likely preserve δ98Mo of Palaeoproterozoic seawater, despite a metamorphic overprint of at least 600 °C. The extent of Mo-isotope fractionation between the Mn-silicate–carbonate ore and the graphitic schist is similar to modern Mn-oxide precipitates and seawater. Differences in δ98Mo signals are broadly reflected in cerium (Ce) anomalies, which suggest an oxic–anoxic-stratified Palaeoproterozoic ocean.

Microbial metallogenesis of Cryogenian manganese ore deposits in South China

The Datangpo Formation manganese deposits (DFMnD) in South China formed during the interglacial stage between the Sturtian and Marinoan glaciations of the Cryogenian period. These black shale-hosted deposits are composed of massive Mn-carbonates with microscopic laminae/laminations and cherty veins. To date, it has been thought that the DFMnD formed through inorganic processes, which were controlled by redox changes in the post-Sturtian Nanhua Rift Basin, South China. However, in this study, systematic petrographic, mineralogical, and geochemical analyses indicate a microbially mediated origin of the Mn ore deposits. Mineralized microbial woven micro-textures (observed at the μm scale) and microbial fossils are common in the laminated Mn-carbonate ores. We infer that microbial enzyme activity formed poorly crystallized Mn oxide/hydroxides and carbonaceous material, which transformed to rhodochrosite, kutnohorite, ankerite/dolomite, framboidal pyrite, and apatite via diagenesis. Some micro-scale quartz and K-feldspar may be detrital but most appears to have formed during diagenesis or through hydrothermal activity. A micro-mineralogical profile determined by 2500 spectra via high-resolution in situ micro-Raman spectroscopy also revealed cyclic laminations of Ca-rhodochrosite as microbialite (ankerite/dolomite) and quartz, indicating a mineralized biomat system. Ca-rhodochrosite transformed to kutnohorite under elevated temperatures, as indicated by the maturation level of organic matter (determined via Raman spectroscopy). Alternating micro-laminae denote cyclic changes in microbial groups (Mn- and Fe-oxidizing microbes versus cyanobacteria) during the formation of the Mn ore deposits. Our proposed model for the microbially mediated metallogenesis of Mn-carbonate deposits begins with enzymatic multi-copper oxidase processes associated with autotrophic microbial activity under obligatory oxic conditions, which results in the precipitation of Mn bio-oxides. Following their burial in organic-rich sediments, the Mn(IV) oxides and hydroxides are reduced, producing soluble Mn(II) via processes mediated by heterotrophic microbes under suboxic conditions, which in turn form the Mn-carbonates. This microbial metallogenesis model for the Cryogenian DFMnD in South China is similar to that proposed for the Jurassic Úrkút Mn deposit in Hungary, indicating that a two-step microbially mediated process of Mn ore formation might be common throughout geological history.

Application of remotely sensed ASTER data in detecting alteration hosting Cu, Ag and Au bearing mineralized zones in Taghdout area, Central Anti-Atlas of Morocco

We conduct a remote sensing investigation to identify alteration zones hosting Cu, Au and Ag mineralization in the Taghdout area, Anti-Atlas. Mineralization occurs in Neoproterozoic rocks exposed along east-trending faults associated with the Major Accident Fault. Remote sensing is applied to delineate Neoproterozoic rocks including ophiolitic suites of the ophiolitic Complex and volcanosedimentary units of the Ouarzazate Group. Band ratios, principle component analysis and filter algorithms identify hydrothermal alteration zones containing ferric iron oxide, ferrous iron oxide, chlorite and carbonate. Phyllic, argillic, propylitic and silicic hypogene alteration zones host Cu, Ag, Au, Mn and Fe ore deposits. Remote sensing analysis identifies the spatial distribution of these ore zones and highlights regional structures that concentrate mineralizing hydrothermal alteration fluid flow. Ground truth verification demonstrates that ASTER provides reliable identification of hydrothermally altered rock units. Image analysis is a robust tool for targeting ore deposits in similar desert terrain ophiolitic complexes.

Mineralization age and metallogenic environment of Daotuo manganese deposits in Guizhou: Evidence from Re-Os isotopes

The Neoproterozoic is a critical interval in Earth’s history, having witnessed the breakup of supercontinent Rodinia, global glaciations (or the snowball Earth), and the evolution of multicellular organisms. It is proposed that the breakup of Rodinia might have triggered the snowball Earth, while the termination of the Neoproterozoic global glaciations might have triggered the evolution of life in the Ediacaran Period. Two snowball Earth events, the Sturtian (717–663 Ma) and the Marinoan (654–635 Ma) glaciations, were separated by an interglacial interval of ~10 million years (663–654 Ma). In South China, the Sturtian and Marinoan glacial deposits are represented by the Jiangkou and Nantuo Formations. The interglacial Datangpo Formation is characterized by widespread manganese (Mn) ore deposits, such the Datangpo and Xixibao in Guizhou, Minle in Hunan, and Xiushan in Chongqing, representing the most important metallogenic period of Mn in China. The Daotuo Mn ore, a superlarge-scale deposit (approximately 200 million tons), was first discovered in 2010 in northeastern Guizhou. It is hosted in a fault-bound depression system between the Yangtze block and the Jiangnan orogenic belt. The Mn ores were discovered in black shale of the Member I of the Datangpo Formation, and occur as rhodochrosite (MnCO3). In order to constrain the age of Mn ores, here we report Re-Os isochron age of the ore-bearing black shale from the Member I of the Datangpo Formation. The Re-Os isochron age of the Member I black shale is 660.6±7.5 Ma, consistent with the zircon U-Pb age of the tuff layer from the base of the Datangpo Formation and other Re-Os isochron ages from other localities (such as Canada, Australia, Scotland, and Mongolia). Furthermore, the initial value of 187Os/188Os from the Re-Os isochron age is 0.781, suggesting predominantly terrestrial input. Based on previous research, it is shown that during the Sturtian glaciation, under the influence of sea ice cover barrier and atmospheric material exchange, the hypoxic water led to the formation of iron and sulfide rich environments on the seafloor near hydrothermal vents, giving rise to a large number of rift basins rich in Mn2+. After the glaciation and water and atmospheric exchange of material recovery, the glacier meltwater carries the terrigenous material into the rift basin containing Mn2+, accompanied by the melting of the land glacier and the rapid increase of the atmospheric oxygen content. The surface water body of the rift basin is rapidly oxidized, and the oxidation degree is higher than the ocean area. Mn2+ are also oxidized to MnO2 and precipitate back into the environment, where they buried with organic matter, undergo diagenesis, and eventually form rhodochrosite.

Manganese mineralogy and diagenesis in the sedimentary rock record

Oxidation of manganese (II) to manganese (III,IV) demands oxidants with very high redox potentials; consequently, manganese oxides are both excellent proxies for molecular oxygen and highly favorable electron acceptors when oxygen is absent. The first of these features results in manganese-enriched sedimentary rocks (manganese deposits, commonly Mn ore deposits), which generally correspond to the availability of molecular oxygen in Earth surface environments. And yet because manganese reduction is promoted by a variety of chemical species, these ancient manganese deposits are often significantly more reduced than modern environmental manganese-rich sediments. We document the impacts of manganese reduction and the mineral phases that form stable manganese deposits from seven sedimentary examples spanning from modern surface environments to rocks over 2billion years old. Integrating redox and coordination information from synchrotron X-ray absorption spectroscopy and X-ray microprobe imaging with scanning electron microscopy and energy and wavelength-dispersive spectroscopy, we find that unlike the Mn(IV)-dominated modern manganese deposits, three manganese minerals dominate these representative ancient deposits: kutnohorite (CaMn(CO3)2), rhodochrosite (MnCO3), and braunite (Mn(III)6Mn(II)O8SiO4). Pairing these mineral and textural observations with previous studies of manganese geochemistry, we develop a paragenetic model of post-depositional manganese mineralization with kutnohorite and calcian rhodochrosite as the earliest diagenetic mineral phases, rhodochrosite and braunite forming secondarily, and later alteration forming Mn-silicates.

First 40Ar/39Ar dating of intense Late Palaeogene lateritic weathering in Peninsular India

Lateritic surface processes have shaped large platform and cratons of the tropical belt. Constraining the timing of such processes is crucial to decipher their role in cratonic morphogenesis and their response to long-term climatic change and lithospheric deformation. Weathering histories have been documented for South America, Africa and Australia, but precise time constraints of the lateritic weathering processes in South India are still lacking. We present 40Ar/39Ar ages of supergene cryptomelane (K–Mn oxide) formed in the Sandur Mn ore deposits exposed on the highest lateritic paleolandsurface that once covered the Mysore plateau and the adjacent Deccan Traps. Significant 40Ar/39Ar ages are estimated between ∼36 and ∼26 Ma from well-defined plateaus in step heating 39Ar release spectra and from best-fitted inverse isochrones. These ages constitute firm time constraints that document intense late Eocene–Oligocene lateritic weathering over Peninsular India under the influence of warm and wet climate comparable to that prevailing in tropical humid forests. These results imply that Southern India was weathered between ∼36 and 26 Ma and may have been dissected mostly in the Neogene.

Dolomitization of the Miocene carbonates in Gebel Abu Shaar El Qiblie and Salum area, Egypt: a petrographical and geochemical comparative study

The shallow marine Miocene carbonates of Gebel Abu Shaar El Qiblie and Salum escarpment, Egypt have been extensively dolomitized. Different dolomite textures are identified in the two areas: mimic replacive dolomite with uni- to polymodal size distribution and high preservation of the grain fabrics, non-mimic replacive crystalline dolomite with relatively uniform crystal size distribution, and partial dolomitization with polymodal size distribution and planar crystal boundaries. Minor cavity-filling dolomite cement is also observed. The development of non-planar crystal boundaries, stoichiometric characteristic, Sr content (92–245 ppm), negative δ18O values (−9.34 to 1.59 ‰) of Abu Shaar dolomites and their association with Fe–Mn ore deposits suggest that these dolomites formed from partial recrystallization and modification of early formed normal marine dolomites by the influence of hydrothermal fluid evolved during rifting of Red Sea. However, recrystallization by freshwater-dominated fluid during meteoric water diagenesis can be supposed. Alternatively, the non-stoichiometric composition, δ18O values (2.15–3.19 ‰) of marine signature and Sr content (73–204 ppm) of Salum dolomites indicate that dolomitization was probably mediated by seawater or slightly modified seawater within the subtidal zone during early stage of diagenesis. The δ13C values (–1.03 to 0.7 ‰ for Abu Shaar, and –0.23 to 1.69 ‰ for Salum dolomites) reflect normal marine-derived carbon source and are probably inherited from the precursor marine limestones. The negative values of some Abu Shaar dolomites may be attributed to minimal contribution of carbon derived from soil-derived CO2 or from oxidation of methane derived from deep hydrocarbon reservoir via fractures during rifting of Red Sea.

Hydrothermal origin of manganese in the high-pressure ophiolite metasediments of Praborna ore deposit (Aosta Valley, Western Alps)

The manganese ore deposit of Praborna crops out in the Zermatt-Saas unit of the Western Alps, in the St. Marcel valley. It represents a Jurassic ophiolitic sedimentary cover subducted at high-pressure conditions during the Alpine orogeny. Major- and trace-element analyses of representative samples of the ore and the host metasediments were collected to geochemically characterise the deposit. Selected phases (piemontite, braunite, garnet, clinopyroxene, white mica and manganiandrosite) were investigated with ion and electron microprobes to link the mineral chemistry to the bulk-rock chemistry. Compared to shales, Praborna is enriched in Mn (up to 38.7 wt% Mn 2 O 3 ) and in many trace elements (Sc, Co, Ni, Cu, Ge, As, Sr, Ag, Sb, Te, Ba, Tl, Pb and Bi). The bulk-rock REE pattern suggests 20 % hydrogenous and 80 % hydrothermal inputs in the proto-ore. Compared to the shale, the hanging-wall Mn-poor schists share with the Mn ore body the enrichment in Sc, Mn, Co, Sr and Te, suggesting a common enrichment process involving these elements. The REE pattern suggests a sedimentary origin for these schists, which were probably composed of clay mixed with components of volcanic origin. In order to confirm the hydrothermal origin of the Praborna Mn ore deposit, we built up a database of more than 5000 data of modern hydrogenous and hydrothermal oceanic Mn deposits worldwide, adding data of oceanic Mn-rich sediments and of the Ligurian Mn ore deposits, which are thought to be the unmetamorphosed geological equivalent of Praborna. The classic ternary Mn–Fe–(Cu + Co + Ni) diagram, the agglomerative hierarchical clustering and the principal-component analysis, which takes into account a larger set of elements, strongly support the hypothesis of an oceanic hydrothermal origin for manganese in the Praborna and in the Ligurian ore deposits.

Geology, ore deposits and hydrothermal venting in Bahía Concepción, Baja California Sur, Mexico

Abstract Bahía Concepción is located in the eastern coast of the Baja California peninsula and it is shaped by northwestern–southeastern normal faults. These are associated with a 12–6 Ma rifting episode, although some have been reactivated since the Pliocene. The most abundant rocks correspond to the arc related Comondú Group, Oligocene to Miocene, which forms a mainly calc‐alkaline volcanic and volcaniclastic sequence. There are less extensive outcrops of sedimentary rocks, lava flows, domes and pyroclastic rocks of Pliocene to Quaternary ages. The Neogene volcanism in the area indicates a shift from a subduction regime to an intraplate volcanism related to continental extension and the opening of an oceanic basin. The Bahía Concepción area contains numerous Mn ore deposits, being the biggest at El Gavilán and Guadalupe. The Mn deposits occur as veins, breccias and stockworks, and are composed by Mn oxides (pyrolusite, coronadite, romanechite), dolomite, quartz and barite. The deposits are hosted in volcanic rocks of the Comondú Group and, locally, in Pliocene sedimentary rocks. Thus, the Mn deposits formed between the Middle Miocene and the Pliocene. The mineralized structures are associated with Miocene northwestern–southeastern fault systems, which are analogous to those associated with the Cu‐Co‐Zn‐Mn deposits of El Boleo. The Bahía Concepción area also bears subaerial and submarine hot springs, which are associated with the same fault systems and host rocks. The submarine and subaerial geothermal manifestations south of the bay are possibly related with recent volcanism. The geothermal manifestations within the bay are intertidal hot springs and shallow submarine diffuse venting areas. Around the submarine vents (5–15 m deep, 87°C), Fe‐oxyhydroxide crusts with pyrite and cinnabar precipitate. In the intertidal vents (62°C), aggregates of opal, calcite, barite and Ba‐rich Mn oxides occur covered by silica‐carbonate stromatolitic sinters. Some 10–30 cm thick crustiform veins formed by chalcedony, calcite and barite are also found close to the vents. The hydrothermal fluids exhibit mixed isotopic compositions between δ18O‐enriched meteoric and local marine water. The precipitation of Ba‐rich Mn oxides around the vent sites could be an active analog for the processes that produced Miocene to Pliocene hydrothermal Mn‐deposits.

Mineralogical and geochemical constraints on environmental impacts from waste rock at Taojiang Mn-ore deposit, central Hunan, China

The mineralogy and geochemistry of the waste rocks distributed at Taojiang Mn-ore deposit, central Hunan province, China, were studied using X-ray powder diffraction (XRD), electron microprobe analysis (EMPA) fitted with energy dispersive spectrometer (EDS) and inductively coupled plasma mass spectrum (atomic emission spectra) ICP-MS (AES), with the aim of predicting the environmental impacts of weathering of the waste rocks. The mineralogical results from microscope observation and XRD and EMPA studies show that the waste rock is composed of black shale and minor Mn carbonates. The oxidation of sulfide minerals such as galena, pyrite and chalcopyrite is accompanied by decomposition of Mn carbonates and K-feldspar during exposure to atmospheric O2. The geochemical characteristics of major, rare earth elements (REE) and trace elements of the waste rocks also show that the waste rock can be divided into black shale and Mn carbonate, and both of them are currently under chemical weathering. The major alkalies and alkaline elements (Ca, Mg, Na, K, Rb, Sr and Cs) and major elements (Fe, S and P) and heavy metals (Sc, V, Cr, Th, U, Sn, Co, Ni, Cu, Zn, Pb, Mo, Cd, Sb, an Tl) are being released during weathering. The mobility of alkalis and alkaline elements Ca, Mg, Na, K, Rb, Sr and Cs is controlled by decomposition of Mn carbonates. The dispersion of Cr, Sc and Th (U) might be related to weathering of K-feldspar, and the release of the heavy metals Co, Ni, Cu, Zn, Pb, Mo, Cd Sb and Tl is dominated by the breaking of sulfide minerals. The REE of the waste rocks and surrounding soils and the spidery distribution patterns of heavy metals in the waste rocks, the surrounding soils and the surface waters show that weathering of the waste rocks and bedrock might be the sources of heavy metal contamination for the surrounding soils and surface water system for the mining area. This is predicted by the mass-balance calculation by using Zr as an immobile element. Therefore, it is urgently necessary take measures to treat the waste rocks distributed throughout the area for the local environmental protection.

Environmental impacts from mining at Taojiang Mn ore deposit, central Hunan, China

Tyndrum was an industrial mining area from 1741 until the 1920s where the main ores extracted were lead sulphide (galena) and zinc sulphide (sphalarite). Situated in central Scotland, the now deserted site is identified as a highly polluted, barren area where the original waste residues from the mine, an ore processing and a smelting site are clearly evident. Previous studies have suggested that high levels of lead and zinc contaminants are still dispersed from this former mine site, both atmospherically and through fluvial transport. For example, high concentrations of Pb, identified by its isotopic signature as originating in Tyndmm, have been found in sediments in Loch Tay, 25 km east of this area. This paper presents the results of a study of the occurrence and magnitude of airborne contamination by dispersion from the former mine site using measurements of metal concentrations in tree bark. These naturally occurring 'bio monitors', which accumulate airborne materials including heavy metals, have become an effective alternative to the more costly air-filter system, which is restricted in scope and coverage. Bark samples were acquired from Scots pine (Pinus sylvestfis) trees, which are abundant around the derelict mine site. Suitable locations were chosen to investigate atmospheric transport and deposition of contaminants within the area. Bark samples were taken on two sides of each tree, selecting Northwest (NW) and Southeast (SE) facing aspects. Trees of about the same age were selected and samples of bark were carefully removed at an average height of about 2.0 m above the ground. Concentrations of Pb and Zn were determined by atomic absorption spectrometry. The results demonstrate that Scots pine bark is an effective bio-monitor for the dispersal of airborne pollution. Elevated levels of Pb and Zn were observed in the bark facing the waste dump and dissimilar levels were recorded between samples from the northwesterly and southwesterly sides. This indicates that contaminant metals within the area are actively being transported atmospherically, with a major influence by wind direction. Overall, the results have proven to be consistent with and correspond to the implications that waste from this abandoned mining site continues to represent a significant environmental problem, especially in the Tyndrum area.

Health status of inhabitants of a region of the Northwest Peloponnese, Greece, having drunk Mn-contaminated water some years ago

This study has been conducted in a region of the Northwest Peloponnese, characterized by moderate to high levels ofMn in soils and water. The studied region includes 3 small towns: Andravida, Lechaina and Varda. Signs of Mn intoxication were observed in 1986 in Varda and even more in Andravida, a village located on an Mn-ore deposit, and were due to very high levels of Mn in the drinking water. After changing the source of water supply, no more neurological disturbances were observed. Although the inhabitants of Lechaina were drinking an Mn-contaminated water due not only to a source containing 60 μg Mn/I but also to an old and corroded water network built 40 years ago, no neurological disturbances have been observed neither before nor after changing the source of water supply. The only actual problem seems to be the presence of characteristic black spots on the teeth enamel. These teeth have been analyzed for their manganese and other trace elements content in order to find a relationship between the environmental manganese and the health status of the population.