Mineralogy of low grade metamorphosed manganese sediments of the Urals: Petrological and geological applications

The paper describes mineralogy of the low grade metamorphosed manganese sediments, which occur in sedimentary complexes of the Pai Khoi Ridge and the Polar Urals and volcanosedimentary complexes of the Central and South Urals. The degree of metamorphism of the rocks studied corresponds to PT conditions of the prehnite–pumpellyite (deposits of Pai Khoi and Polar and South Urals) and green schist (deposits of the Central Urals) facies. One hundred and nine minerals were identified in the manganese-bearing rocks on the basis of optical and electron microscopy, X-ray diffraction, and microprobe analysis. According to the variations in the amount of major minerals of the manganese rocks of the Urals, they are subdivided on carbonate (I), oxide–carbonate–silicate (II), and oxide–silicate (III) types. Carbonates, various Mn^2 +-bearing silicates associated with oxides and carbonates, and braunite (Mn^3 +-bearing silicate) are the major Mn hosts in types I, II, and III, respectively. Because of the different oxidation state of Mn, the rocks of types I and II are termed as “reduced” and the rocks of type III, as “oxidized”. The formation of a certain mineralogical type of metamorphic assemblage is controlled by the content of organic matter in the primary sediments. The sequence type I → type II → type III reflects the decrease in the amount of organic matter in metalliferous sediments. Mineralogical data indicate that manganese in the primary sediments accumulated in a silicate form (MnSi gel, glass, etc). During diagenesis, the Mn–Si phase was transformed to neotokite with subsequent formation of caryopilite and further crystallization of pyroxmangite, rhodonite, tephroite, and other silicates due to reactions involving caryopilite. The hydrated Mn-silicates (caryopilite and/or friedelite) and the spatially associated parsettensite, stilpnomelane, and other minerals are the index minerals of the low grade metamorphism. Under PT conditions of prehnite–pumpellyite facies, nearly 70% of silicate minerals are hydrous. The metamorphosed Mn-bearing sediments are characterized by the low-temperature caryopilite (or tephroite-caryopilite-pyroxmangite ± rhodonite) and the high-temperature caryopilite-free (or tephroite-pyroxmangite ± rhodonite) facies. Their PT conditions correspond to zeolite and prehnite-pumpellyite (the low-temperature) and green schist and higher grade (the high-temperature) facies.     

Mineralogy and metamorphism conditions of manganese ore at the South Faizulino deposit, the southern Urals, Russia

The mineralogy of slightly metamorphosed manganese ore at the South Faizulino hydrothermalsedimentary deposit in the southern Urals has been studied; 32 minerals were identified. Quartz, hausmannite, rhodochrosite, tephroite, ribbeite, pyroxmangite, and caryopilite are major minerals; calcite, kutnahorite, alleghanyite, spessartine, rhodonite, clinochlore, and parsettensite are second in abundance. This mineralic composition was formed in the process of gradual burial of ore beneath the sequence of Middle Devonian-Lower Carboniferous rocks. The highest parameters of metamorphism are T ≈ 250°C and P ≈ 2.5 kbar. The relationships between minerals and their assemblages made it possible to reconstruct the succession of ore transformation with gradually increasing temperature and pressure. Manganese accumulated in the initial sediments as oxides and a gel-like Mn-Si phase. Rhodochrosite and neotocite were formed at the diagenetic stage. In the course of a further increase in temperature and pressure, neotocite was replaced with caryopilite; ribbeite, tephroite, pyroxmangite, and other silicates crystallized afterwards. In addition to the PT parameters, the formation of various metamorphic mineral assemblages was controlled by the Mn/(Mn + Si) ratio in ore and X _CO2 in pore solution. The latter parameter was determined by the occurrence of organic matter in the ore-bearing rocks. Ore veinlets as products of local hydrothermal redistribution of Mn, Si, and CO₂ were formed during tectonic deformations in the Middle Carboniferous and Permian.     

印度次大陆中央构造带沉积—变质型锰矿的矿物学和地球化学

对印度中央构造带sauaar带锰矿及其围岩的31个样品进行了显微镜仔细的观察和鉴定,并分析了其主量元素、微量元素和稀土元素的地球化学特征,发现该带的锰矿主要是软锰矿和硬锰矿,锰矿主要富集在锰榴石英岩内.含锰岩系样品具非常高的Mn/Fe比值,说明热液运输和成矿作用期间锰和铁的强烈分异;MnO/TiO2为67.98-1417.52,说明有大量陆源物质经风化、搬运加入并混合沉积而成.用太古界平均澳大利亚页岩（PAAS）标准化后,稀土元素含量中δEu,δCe都有明显的正异常,说明该带锰矿床是在较强氧化海洋环境和有大量陆源物质加入的条件下沉积,并经过热液的变质交代作用而成的沉积一变质型锰矿床.该沉积—变质型锰矿的发现和研究对我国南方扬子克拉通中元古代浅变质岩系的锰矿寻找具有一定的借鉴意义.     

Mineralogy and geochemistry of the Au-Ag ore deposits of the South Korean Peninsula

Pyrite and arsenopyrite are the predominant ore minerals in the Korean Au-Ag deposits of this study. The X _Ni ^py , X _Co ^py , X _Ni ^apy , and X _Co ^apy values range between 100 and 3,000 ppm, 200 and 6,000 ppm, 200 and 8,200 ppm, and 100 and 10,200 ppm, respectively. Most X _Ni ^py /X _Co ^py values fall in the field lower than values varying 0.16–1.30. Arsenopyrite also tends to prefer cobalt rather than nickel showing X _Ni ^apy /X _Co ^apy values between 0.20 and 1.40. The concentrations of minor elements in ores and gangue minerals vary 1–55 ppm Au and 1–1,120 ppm Ag for the former and 4–57 ppm Ni and 2–45 ppm Co for the latter. The Au/Ag ratio in ore has a good correlation to the Ni/Co ratio of arsenopyrite to gangue. The (Ni/Co)_py-(Ni/Co)_gangue and (Ni/Co)_apy-(Ni/Co)_gangue diagrams revealed that the values from the Korean Au-Ag deposits plot in the field lower than 900 °C which is the lowermost temperature determined by previous partitioning experiments.     

Listvenite-related gold deposits of the South Urals (Russia): A review

The Urals is a complex fold belt, which underwent long geological evolution. The formation of most gold deposits in the Urals is related to the collision stage. In this paper, we review some relatively small listvenite-related gold deposits, which are confined to the large Main Uralian fault zone and some smaller faults within the Magnitogorsk zone. The Mechnikovskoe, Altyn-Tash, and Ganeevskoe deposits are studied in detail in this contribution. They comprise the ore clusters along with other numerous small gold deposits, and constituted the sources for the gold placers exploited in historical time. The gold is hosted by metasomatites (listvenites, beresites) and quartz veins with economic gold grades (up to 20 g/t Au). Listvenites are developed after serpentinites and composed of quartz, fuchsite, and carbonates (magnesite, dolomite) ± albite. Volcanic and volcanoclastic rocks are altered to beresites, consisting of sericite, carbonates (dolomite, ankerite), quartz and albite. Pyrite and chalcopyrite are major ore minerals associated with gold; pyrrhotite, Ni sulfides, galena, sphalerite, arsenopyrite and Au-Ag tellurides are subordinate and rare. Gold in these deposits is mostly high-fineness (>900‰). The lower fineness (∼800‰) is typical of gold in assemblage with polymetallic sulfides and tellurides. The ores have been formed from the NaCl–CO₂–H₂O ± CH₄ fluids of low (∼2 wt% NaCl-equiv.) to moderate (8–16 wt% NaCl-equiv.) salinity at temperatures of 210–330 °C. The oxygen isotopic composition of quartz (δ¹⁸O) varies from 14.7 to 15.4‰ (Mechnikovskoe deposit), 13.2 to 13.6‰ (Altyn-Tash deposit) and 12.0 to 12.7‰ (Ganeevskoe deposit). The oxygen isotopic composition of albite from altered rocks of the Ganeevskoe deposit is 10.1‰. The calculated δ¹⁸O_H2O values of the fluid in equilibrium with quartz are in a range of 5.7–6.3, 4.2–4.6 and 6.3–6.7‰ respectively, and most likely indicate a magmatic fluid source.     

Mineralogy and genesis of the metamorphosed manganese silicate rocks (gondite) of Gowari Wadhona,Madhya Pradesh,India

Manganese silicate rocks, interbanded with manganese oxide orebodies, constitute an important stratigraphic horizon in the Mansar formation of the Sausar Group of Precambrian age in India. The manganese silicate rocks of Gowari Wadhona occupy the westernmost flank of the manganese belt of the Sausar Group. These rocks are constituted of spessartite, calcium-rich rhodonite, quartz, manganoan diopside, blanfordite (manganese bearing member of diopside-acmite series), brown manganese pyroxene (manganese bearing aegirine-augite), winchite (manganese bearing richterite-tremolite), juddite (manganese bearing amphibole with richterite, tremolite, magnesioriebeckite and glaucophane molecules), tirodite (manganese bearing amphibole with richterite, cummingtonite and glaucophane molecules), manganophyllite, alurgite, piedmontite, braunite, hollandite (and other lower oxides of manganese) with minor apatite, plagioclase, calcite, dolomite and microcline. A complete mineralogical account of the manganese-bearing phases has been given in the text. It has been shown that the juxtaposition of manganese silicate rocks with dolomitic marble, regional metamorphism to almandine-amphibolite facies and assimilation of pegmatite veins cutting across the manganese formation, were responsible for the development of these manganese silicate rocks and the unusual chemical composition of some of the constituent minerals. It has been concluded that the manganese silicate rocks of Gowari Wadhona were originally laid down as sediments comprising manganese oxides admixed with clay, silica etc. and were later regionally metamorphosed to almandine-amphibolite facies. All evidences indicate that rhodochrosite was not present in the original sediment and the bulk composition of the sediments was rich in manganese. These rocks agree entirely to the detailed nomenclature of the gondites enunciated by Fermor (1909) and amplified by Roy and Mitra (1964) and Roy (1966).     

Garnierite in nickel deposits of the Urals

Oxide-silicate ore deposits containing approximately 10% of Ni reserves of Russia are located in the Sverdlovsk, Chelyabinsk, and Orenburg districts of the Urals. Garnierite is among the most important industrial minerals of supergene nickel deposits. We studied this mineral in metasomatites and ores of the Cheremshan, Sinar, Elov, Sakhara, and Buruktal deposits based on the chemical, thermal, and X-ray phase analysis data. It is shown for the first time that garnierites of the Ural province are composed of both exogenous and hydrothermal mineral associations. The spatial distribution of minerals suggests that the hydrothermal association is a lateral and vertical (depth) continuation of mineralization in the Uralian supergene deposits. This conclusion widens significantly the scope of prospecting for new mineralized sectors in old deposits and the possibility of discovery of new deposits.     

Supergene sulphides and related minerals in the supergene profiles of VHMS deposits from the South Urals

The mineralogy and structure of the supergene profile in recently-exploited volcaniс hosted massive sulphide (VHMS) deposits of Cyprus, Uralian and Kuroko type in the South Urals, Russia, have been studied. Specific subzones enriched in secondary sulphides and associated minerals have been distinguished in residual pyrite and quartz–pyrite sands at the Gayskoye, Zapadno-Ozernoye, Dzhusinskoye and Alexandrinskoye deposits. Besides minerals which are common to the cementation subzones (covellite, chalcocite and acanthite), non-stoichiometric colloform and framboidal pyrite, pyrite–dzharkenite, pyrrhotite-like and jordanite-like minerals, metacinnabar, sphalerite, selenium-enriched tetrahedrite and unidentified As-, Sb sulphosalts of Pb or Hg and Ag, sulphur-bearing clausthalite, naumannite and tiemannite were also found. Secondary sulphide minerals in VHMS deposits of the South Urals region are characterized by light sulphur isotope compositions (− 8.1 to − 17.2‰). Superposition of the advanced oxidation of colloform pyrite, an enrichment in impurities (sphalerite, galena, and tennantite) from the primary ores, stagnant water conditions, an elevation of the water table during oxidation, and bacterial activity led to supergene concentrations of the base metals as sulphide, selenides or sulphosalts.     

Oxidation gradients in metamorphosed non-carbonatic manganese formations

This paper aims to ascertain the degree of equilibrium attained with respect to oxygen during metamorphism of non-carbonatic manganiferous sediments and the nature of mobility of oxygen in rocks of adjacent beds by measuring the composition of coexisting phases. Through algebraic analysis of the relevant phase equilibria, a difference of ≃17 kcal in in rocks of adjacent beds is obtained. This confirms the immobile nature of oxygen during metamorphism of manganiferous sediments.     

Sulphide neomagmas and highly metamorphosed sulphide deposits

Orebodies that have undergone high grade regional metamorphism sometimes exhibit features which appear to be metamorphic counterparts of certain magmatic-hydrothermal mineralization. These include ore bearing metapegmatites, metahydrothermal veins and metadeuteric veins and vugs. These mineral facies are completely contained within the metamorphosed orebody the ore minerals of which invariably exhibit textures resulting from annealing recrystallization. Intrusive relationships between metapegmatite, metahydrothermal veins, etc., and the orebody are evident. — Experimental work on certain sulphide systems indicates that partial melting may occur at temperatures around 700 °C, i.e., at the sillimanite grade of metamorphism. Thus a sulphide neomagma may develop along the lines of anatexis. — These aspects are considered with respect to the lead—zinc orebody at Broken Hill, New South Wales.

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Zusammenfassung Erzkörper, die hochgradiger Regionalmetamorphose unterworfen waren, zeigen manchmal Charakterzüge, welche denjenigen gewisser magmatisch-hydrothermaler Vererzungen gleichgestellt werden können. Diese Beispiele umfassen erzführende Metapegmatite, metahydrothermale Adern und metadeuterische Adern und Drusen. Diese Mineralfolgen sind beschränkt auf den metamorphosierten Erzkörper, dessen Erzmineralien dann jeweils Erzgefüge zeigen, die durch Rekristallisation entstanden sind. Intrusive Beziehungen zwischen den Metapegmatiten, den metahydrothermalen Adern usw. und dem Erzkörper sind offensichtlich. — Experimentelle Untersuchungen gewisser Sulfidsysteme deuten darauf hin, daß partielles Schmelzen bei Temperaturen um 700 °C möglich ist; also in dem Sillimanitbereich der Metamorphose. In dieser Weise ist es möglich, daß ein Sulfidneomagma sich in der Art einer Anatexis entwickeln kann. — Diese Probleme werden in bezug auf den Blei-Zink-Erzkörper in Broken Hill, New South Wales, Australien, diskutiert.

     

Mineralogy and geochemistry of a stratabound manganese deposit in the Tangganshan region of South China

The Tangganshan manganese ore deposit is a typical sedimentary-magmatic hydatopneumatogenic superimposed ore deposit. In this paper this deposit is discussed in more detail from the following aspects: geology, ore mineralogy, and geochemistry. On the basis of its occurrence, mineral assemblage, element geochemistry, isotopic geochemistry, and characteristics of organic matter and fluid inclusions, the Tangganshan manganese ore deposit has proved to be a new-type manganese ore deposit that has been enriched by magmatic-pneumatolic solutions. Most of the ore-forming elements were derived from the ore deposit itself, and the rest from the magmatic-pneumatolitic solutions.     

Types of massive sulphide deposits in the Urals

Massive sulphide deposits in the Urals are found within volcanic and volcanic-sedimentary sequences of Ordovician to Middle Devonian ages. Four types of economic sulphide deposits have been recognized: Cyprus, Besshi, Urals and Baimak. The Cyprus-type copper sulphide deposits are hosted by mafic volcanites that occur in the basal parts of Palaeozoic volcanic sequences. The Besshi-type copper-zinc deposits are located within clastic sedimentary rocks intercalated with basalts and andesites. Zinc-copper deposits of the Urals-type are hosted by bimodal rhyolite-basalt assemblages, which occur at a higher stratigraphic level than those of Cyprus- and Besshi-types. The Baimak-type zinc-copper-barite deposits are associated with intrusive quartz porphyries which occur in the upper parts of bimodal volcanic successions. In addition there are some sulphide deposits of zinc-lead-barite and zinc-copper composition hosted by Ordovician terrigenous sequences which occur within depressions in Precambrian blocks. These types of sulphide deposits have been formed at various stages of divergence and convergence of the Earth's crust during the orogenic history of the Urals. Received: 27 June 1997 / Accepted: 14 May 1998     

Mineralogy, chemistry and genesis of Nishikhal manganese ores of South Orissa, India

Manganese ores of Nishikhal occur as distinctly conformable bands in the khondalite suite of rocks belonging to the Precambrian Eastern Ghats complex of south Orissa, India. Manganese minerals recorded are cryptomelane, romanechite, pyrolusite, with minor amounts of jacobsite, hausmannite, braunite, lithiophorite, birnessite and pyrophanite. Goethite, graphite, hematite and magnetite are the other opaque minerals and quartz, orthoclase, garnet, kaolinite, apatite, collophane, fibrolite, zircon, biotite and muscovite are the gangue minerals associated with these ores. The mineral chemistry of some of the phases, as well as the modes of association of phosphorous in these ores have been established. The occurrence of well-defined bands of manganese ore; co-folding of manganese ore bands and associated metasedimentary country rocks; the min-eral assemblage of spessartite-sillimanite-braunite-jacobsite-hausmannite; the geochemical association of Mn-Ba-Co-Ni-Zn together with the Si versus Al and Na versus Mg plots of the manganese ores suggest that the Nishikhal deposit is a metamorphosed Precambrian lacustrine deposit. Continental weathering appears to be the source for manganese and iron. After deposition and probable diagenesis, the manganese-rich sediments were metamorphosed along with conformable psammitic and pelitic sediments under granulite facies conditions, and subsequently underwent supergene enrichment to produce the present deposit. Received: 14 March 1995 / Accepted: 11 April 1996     

Potential low-grade iron ore deposits in metamorphosed banded iron formations, Northern Province, South Africa

Exploitation of low-grade iron ore would be quite unique in a South African context as South Africa is well endowed with high-grade iron ore resources. Low-grade iron ore, defined as containing between 20 and 47% iron, is thought to be the primary iron-bearing lithology from which most high-grade ore deposits formed, through different processes of enrichment. The low-grade iron ores in the Northern Province represent meta-banded iron formations (BIFs), with an average iron content of about 36%. The main iron-bearing mineral is magnetite. The Northern Province ores have to be milled to sizes smaller than 150 μm in order to liberate the iron minerals from the host rock, and beneficiation is accomplished through a series of magnetic separation processes. Irrespective of the in situ quality of the ore, final concentrates of exceptionally good quality with more than 69% iron and very low contaminant levels can be produced. This, combined with mass yields of between 40 and 50% and iron recoveries greater than 80%, are excellent for this type of iron ore deposit. The beneficiation products are suitable for use in iron- and steel-making processes. Received: 4 July 1996 / Accepted: 7 January 1997     

Mineralogy of metamorphosed carbonatite of the Vesely occurrence, Northern Transbaikal region, Russia

Metamorphism of carbonatite is exemplified in the Vesely occurrence. According to available data, the age of the carbonatite is 596 ± 3.5Ma, whereas metamorphism is dated at 550 ± 14 Ma. The rocks at the Vesely occurrence were metamorphosed under conditions of greenschist facies (epidote-muscovite-chlorite subfacies) under elevated pressure. Microthermometry of fluid inclusions in minerals indicates that the temperature of metamorphism is 377−450°C and the pressure estimated from phengite geobarometer is 6−8 kbar. The low-grade metamorphism led to the partial recrystallization of carbonates and apatite with removal of trace elements. This process resulted in a change of the oxygen isotopic composition of the studied minerals. Metamorphism was accompanied by formation of talc, phengite, chlorite, quartz, tremolite-actinolite, and anthophyllite, which are not typical of carbonatite. The data obtained show that the metamorphism exerted an effect on the mineralogical, isotopic, geochemical, and technological properties of the carbonatite. The effect of metamorphism should be taken into account in determination of the nature of ore mineralization and estimation of ore quality and perspective of the occurrence.     

The South Faizuly manganese deposit in the southern Urals: Geology,petrography, and formation conditions

The South Faizuly manganese deposit hosted in cherty rocks of the Magnitogorsk paleovolcanic belt has been studied. The geology, mineralogy, and chemistry of ores and host silicites (jasperites, jaspers, and cherty siltstones) are characterized. The deposit was formed in the following four consecutive stages: (1) sedimentation and diagenesis of ore-bearing sediments in the Middle Devonian, (2) metagenesis of Mn-bearing rocks in the Middle Devonian-Early Carboniferous, (3) hydrothermal-metasomatic stringer ore mineralization during tectonic deformation of volcanosedimentary rocks in the Middle Carboniferous-Permian, and (4) supergene alteration and partial denudation of the deposit in the Mesozoic-Quaternary. Models of Mn-bearing rock deposition in the proximal and distal zones of the hydrothermal solution discharge area are considered.Translated from Litologiya i Poleznye Iskopaemye, No. 1, 2005, pp. 35–55.Original Russian Text Copyright 2005 by Brusnitsyn, Zhukov.     

New iron resources of the South Urals

An area with brick-red loose and viscous sandy-clayey rocks and brown ores with an average Fe content of 19.84% and possible resources of 1 billion tons of metal was determined. Mn and Ti are the main alloying components; Ni, Co, Cr, V, and Zr are additional; and goethite (FeOOH) is an ore mineral.     

Mineralogy of manganese oxides from Groote Eylandt

The manganese ores on Groote Eylandt occur in a flat-lying horizon in a series of Lower Cretaceous sands and clays which overly unconformably the Middle Proterozoic sandstone basement. The ore horizon exhibits a variety of textural and compositional ore types. Textural types include pisolites and concretions, either free or cemented into massive, bouldery or pebbly horizons. Compositional variations result from varying degrees of admixture of the manganese materials with the sands and clays of the formation. — The ore minerals are pyrolusite and cryptomelane, with minor amounts of lithiophorite, psilomelane, nsutite and todorokite. Gangue minerals include kaolinite, quartz and goethite. — Mineralogical studies indicate that three microtypes of cryptomelane occur. Low levels of cobalt, nickel and zinc in certain of the ore types are associated with the mineral lithiophorite.