Manganiferous Rocks Research Articles

Petrography and geochemistry of manganiferous rocks in the Mankwadzi area in the southern Kibi‐Winneba metavolcanic belt, Ghana: Implications for genesis of Mn formations in the Birimian of West Africa

AbstractManganiferous rocks in the Mankwadzi area in the southernmost portion of the Kibi‐Winneba metavolcanic belt, one of several Mn occurrences in the Paleoproterozoic Birimian of Ghana, are hosted in hornblende schist and amphibolite. These rocks are, in places, intruded by hornblende dyke. In outcrop, the manganiferous rocks appear to be conformable with the host schist and amphibolite, are macroscopically dark, fine‐grained and structurally massive to distinctly banded. Observed alternating light and dark occasionally macro‐folded bands suggest post‐depositional deformation of both light and dark bands. Microscopic observations revealed that the light bands are dominantly Si‐rich and the dark bands mainly of opaque minerals. Whole rock analyses of the manganiferous rocks show high contents of MnO (16.75–27.4 wt%) suggesting that the opaque minerals are likely rich in Mn. The analyzed rock samples show moderate to strong enrichments in light rare earth elements compared to heavy rare earth elements. Whereas the manganiferous rocks show perceptibly negative Eu anomaly, host hornblende schist and hornblende dyke do not. Eu anomaly in amphibolite samples is, however, uncertain as the three samples analyzed gave positive, negative and no Eu anomalies. Based on the field characteristics, microscopic and geochemical features, we suggest that the Mn occurrence in the Mankwadzi area originated via sedimentary deposition and was later modified by metamorphism, hydrothermal and/or supergene processes similar to manganiferous occurrences at Nsuta and Tambao in the Birimian of West Africa.

The Nadeiyakha Ore occurrence (Pai-Khoi, Russia): an example of ferromanganese metasediments in carbonaceous dolomitic shales

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

Geochemistry and formation model of manganiferous rocks in jaspers of the South Urals

Specific features of the geochemistry of manganiferous siliceous rocks confined to Devonian volcanogenic complexes of the Magnitogorsk belt in the South Urals are discussed. It is shown that with respect to the distribution of the major petrogenic and rare earth elements, as well as base and rare metals, manganese rocks are comparable with rocks of the low-temperature hydrothermal sources in active volcanic zones of the World Ocean. Our results agree well with the existing concepts about the hydrothermal-sedimentary origin of manganese deposits in the South Urals and corroborate this hypothesis with new independently obtained data.

Geochemistry of Major Oxides in Host Rocks in Vizianagarm Manganese Ores Belt (A.P.), India

The abundance, distribution trends and significance of the major oxides in the host rocks in Vizianagarm Manganese Ores Belt (A.P.) (between N latitude 18°12' and 18°30' and E longitudes 83°20' and 83°45'), 15 samples of host rocks from different localities of the area under study were collected and analyzed for major oxides. We describe here in major oxides geochemistry of host rocks and manganese ore deposits associated with Precambrian Khondalite and Charnockite in Vizianagarm Manganese Ores Belt (A.P.): 1) Preponderance of SiO2 over Al2O3; 2) Dominance of K2O and CaO over Na2O; 3) Abnormally high concentration of phosphorus and a positive relationship of P2O5 with CaO and Ti contents; 4) Manganese increases with increases of iron, lime and soda and vice versa, 5) CaO increases with the increases of Al2O3, Ti, K2O and vice versa. High P2O5content in these manganese ores appears to be the result of precipitation from secondary manganese rich solutions containing dissolved phosphorus from the P2O5 enriched host rocks. Another source of P2O5 may be the associated granitic and pegmatitic intrusions. Elements like K, Na, Ca, Mg, Co, Ni, Pb and Zn etc. appear to be mostly concentrated in the Mn-minerals viz. psilomelane, cryptomelane, hollandite and pyrolusite and related secondary phases [1] and [2]. Stratigraphically, the study area includes within a thick succession of Precambrian Group belonging to the Khondalite and Charnockite Groups of Dharwar Supergroup, that form a part of Eastern Ghat Complex of India. The manganiferous rocks that have been encountered in the Vizianagarm Manganese Ores Belt (A.P.) India are known as Kodurites.

Ferruginous and manganiferous haloes around massive sulphide deposits of the Urals

Proximal brecciform ferruginous and manganiferous rocks related to VMS deposits of the Urals are subdivided into jasperites, gossanites, and umbers, in addition to thin-bedded jaspers and cherts. The coherence of host rock composition and Mn–Fe-fertility of the sediments have been established. Fe-poor pink hematitic and gray sulphidic chert are typical of the felsic class of VMS deposits. In contrast the contents of Fe vary from high to moderate in ferruginous rocks enclosed in basaltic units associate with VMS deposits. Fe- and Mn-rich ferruginous rocks and umbers occur in association with limestones and calcareous sedimentary rocks in both types of volcanic sequences. A common feature of jasperites and umbers is the abundance of replacement textures of hyaloclastites and carbonates by hematite and silica. In addition, replacement of clastic sulphides by hematite and magnetite is a characteristic genetic feature of gossanites. All of these sedimentary rocks are accompanied by pseudomorphs of hematite and quartz formed after bacterial filaments. The abundance of replacement textures are supportive of the halmyrolysis model, in addition to hydrothermal sedimentary and sub-seafloor hydrothermal replacement theories. Study of chemical zonation of altered hyaloclasts shows depletion of their rims, not only in mobile Na, K, Mg, but also in immobile Al, Ti, and REE; whereas Si and Fe are concentrated in situ. The halmyrolysis model presented here, involving organic-rich calcareous hyaloclastic sediments, resolves the problem of subtraction of Al, Ti, REE and other elements, which are commonly immobile under hydrothermal conditions. The evolution of the halmyrolysis process from acidic reducing to alkaline oxidized conditions infers a possible range in transformation from FeII–Mg smectites to Fe-silicates and Fe-Si oxides as precursors of brecciform jasperite and thin-bedded jasper. The higher acidic, initial stage, of gossanite formation seems to be required for oxidation of organic matter and/or pyrite. The acidic condition facilitates the temporal preservation of “immobile” elements (Al, Ti, REE) in “immature”chlorite–hematite gossanites. Another peculiarity of the gossanite-forming processes is the likely sorption of P, U and V by iron hydroxides displacing sulphides. The general evolution of all ferruginous sediments results in complete Fe2+ oxidation and silicification accompanied by subtraction of other elements. The vertical diagenetic differentiation leads to concentration of Mn-carbonates, silicates and oxyhydroxides into the tops of jasperite and gossanite layers. Mn oxyhydroxides scavenge positively charged hydrated cations like Co and Ni. Near-vent bacterial communities may activate the processes of volcanic glass and sulphide degradation. The proposed processes of halmyrolysis followed by silicification, in situ, may resolve the enigma of silica-rich sediment formation in a silica undersaturated ocean. The discrimination between gossanite and jasperite is useful for elaboration of new criteria for local exploration of VMS- and Mn-deposits. Halo dispersion of gossanites covering an area about two to three times that of the massive sulphide deposit is a good vector for ore body discovery. Proximal gossanites can be differentiated from jasperites by presence of relic sulphide clasts or elevated contents of chalcophile elements (Cu, Fe, Zn, Pb, Bi, Te, As, Sb, Ba), noble metals (Au, Ag) and distinct REE patterns with La and Eu positive anomalies. The development of halmyrolysis and biomineralization models merit further elaboration and testing in on-going research, in order to add or revise theories of iron and manganese deposit formation.

Manganese deposits: Communication 2. Major epochs and phases of manganese accumulation in the Earth’s history

Accumulation of manganiferous rocks in the history of the Earth’s lithosphere evolution began not later than the end of the Middle Archean. Primary manganese sediments were accumulated at that time in shallow-water sedimentation basins with the active participation of organic matter. The concentration of Mn in the primary sediments usually did not reach economic values. The formation of genuine manganese ores is related to later processes of the transformation of primary ores—diagenesis, catagenesis, metamorphism, and retrograde diagenesis. Types of basins of manganese ore sedimentation and character of processes of the formation of manganese sediments during the Earth’s shell evolution changed appreciably and correlated with the general evolution of paleocontinents. Major periods, epochs, and phases of manganese ore genesis are defined. At the early stages of lithosphere formation (Archean-Proterozoic), manganese was deposited in basins commonly confined to the central part of Western Gondwana and western part of Eastern Gondwana, as well as the western part of the Ur paleocontinent. Basins of manganese ore sedimentation were characterized by the ferruginous-siliceous, carbonaceous-clayey, and carbonaceous-carbonate-clayey composition. The Early-Middle Paleozoic epoch of manganiferous sediment accumulation was characterized by the presence of several small sedimentation basins with active manifestation of volcanic and hydrothermal activity. Since the formation of Pangea in the Late Paleozoic until its breakup, accumulation of Mn was closely associated with processes of diagenesis and active participation of the oxidized organic matter.

TEXTURE AND COMPOSITION OF GARNET AS A GUIDE TO CONTAMINATION OF GRANITOID PLUTONS: AN EXAMPLE FROM THE GOVERNOR LAKE AREA, MEGUMA TERRANE, NOVA SCOTIA

The Governor Lake area, Meguma terrane, Nova Scotia, is underlain mainly by ca. 373 Ma granitoid rocks of the Trafalgar plutonic suite that intruded metasedimentary rocks of the Goldenville and Halifax groups. Garnet is abundant in the Beaverbank Formation of the Goldenville Group and its enclaves in the granitoid rocks. Single crystals of garnet, locally up to 3 cm in diameter, are also present in the Twin Lakes granodiorite and Bog Island Lake tonalite. On the basis of petrographic examination and electron-microprobe data, we have identified four different types of garnet. Type-1 garnet, generally associated with coticule xenoliths, forms small spessartine-rich (Sps 19–74 ) grains concentrated in irregular to planar aggregates. Crystals range from homogeneous (type 1A) to zoned toward a Mn-enriched rim (type 1B). Type-2 garnet is restricted to metasedimentary host rocks, where it forms small, spessartine-rich (Sps 22–71 ) grains zoned from a Mn-rich core to a Mn-poor rim. Type-3 garnet contains abundant metamorphic inclusions ( e.g. , sillimanite) and commonly has an inclusion-rich core with an inclusion-poor rim. Type-3A crystals have a Mn-rich core (Sps 21–52 ), whereas type-3B crystals have a Mn-rich rim (Sps 15–21 ). Type-4 garnet forms large, subhedral to euhedral crystals with abundant inclusions ( e.g. , apatite, plagioclase) of probable igneous origin. Type-4A garnet is spessartine-poor (Sps 4–11 ) and weakly zoned, whereas zoning in type-4B crystals suggests that a Mn-poor core (Sps 8–16 ) was partially resorbed and overgrown by a Mn-rich rim (Sps 11–26 ). Of the various types of garnet identified in the granitic samples, types 1A and 3B are interpreted as orthoxenocrysts, type 1B, as paraxenocrysts, type 3A, as having an orthoxenocrystic core overgrown by an orthomagmatic or paraxenocrystic rim, and types 4A and 4B, as orthomagmatic. The presence of Mn-rich xenocrystic garnet suggests that the Twin Lakes and Bog Island Lake plutons were contaminated by manganiferous rocks, probably derived from the Beaverbank Formation. Incorporation and assimilation of Mn-rich material may also have led to crystallization of orthomagmatic garnet in the granitic magmas.

Specific features and composition of the Akkermanov manganese deposit

New data on the Akkermanov deposit characterized by specific structure and composition of primary (carbonate) and secondary (manganese oxide) ores are presented. Distribution of mineralization in host rocks and weathering crusts is considered. It is shown that manganiferous carbonate rocks, which host orebodies, formed in a marine basin with well-aerated bottom waters. Oxide ores are mainly composed of crystalline pyrolusite produced by multiple processes of the oxidation of manganese compounds. In this respect, the Akkermanov deposit differs drastically from all manganese deposits developed in Russia and Ukraine.

Petrology of Mn carbonate–silicate rocks from the Gangpur Group, India

Metamorphosed Mn carbonate–silicate rocks with or without oxides (assemblage I) and Mn silicate–oxide rocks with minor Mn carbonate (assemblage II) occur as conformable lenses within metapelites and metacherts of the Precambrian Gangpur Group, India. The petrology of the carbonate minerals: rhodochrosite, kutnahorite, and calcite that occur in these two assemblages is reported. Early stabilisation of spessartine, aegirine, quartz, and carbonates (in a wide solid solution range) was followed by pyroxmangite, tephroite, rhodonite through decarbonation reactions. Subsequently, jacobsite, hematite, braunite, hollandite and hausmannite have formed by decarbonation–oxidation processes during prograde metamorphism. Textural characteristics and chemical composition of constituent phases suggest that the mineral assemblages reflect a complex relationship between protolithic composition, variation of X CO 2 (<0.2 to ∼0.3) and oxygen fugacity. A variation of X CO 2 and f O 2 would imply internal buffering of pore fluids through mineral reactions that produced diverse assemblages in the carbonate bearing manganiferous rocks. A minor change in temperature (from around 400 to 450 °C) does not appear to have had any major influence on the formation of different mineral associations.

The mineralogy and petrography of the ferruginous manganese rocks at Mankwadzi, Ghana

Outcrops of a banded ferruginous manganiferous rock occur at Mankwadzi village 8 km west of Winneba, Ghana. The rock has variously been referred to as gondite and banded iron formation. The very fine-grained texture and the intense alteration of the rock make the resolution of its petrographic nature by ordinary transmitted and reflected light microscopy rather difficult. The present investigations provide petrologic and chemical data from microprobe analyses of the minerals within the manganiferous horizons and whole rock analyses of the country rocks. Mineral compositions were calculated and rock classifications determined from the data so obtained. The host rocks appear to have been deposited in a sub-aqueous environment during Birimian times. They include erosion products made up of siliceous material from terrigenous sources and mafic material probably of submarine volcanic origin. Chemically, the rock compositions suggest andesitic and tholeiitic basaltic parentage. The Mn/Fe ratio of 3:1 of the Mn horizons lies within the range (0.1 < Mn/Fe < 10), which is typical of “Sedex” deposits. Also, the contents of transitional metals (notably Co, Ni, and Zn) in the Mn horizons are high and point to probable derivation from marine sources. The Cu content is, however, low. The Fe content is constant in both the host rocks and the Mn horizons, whilst the Mn/Fe ratio rises from an average of less than 0.02 in the host rocks to over 3.00 in the manganiferous horizons indicating that while the Fe may be indigenous, the Mn appears foreign and was probably introduced from external source(s). Although regional metamorphism is up to garnet-amphibolite facies, the effects of retrograde metamorphism are recognised in all the rocks. The presence of pyroxene and pyroxmangite/rhodonite in the manganiferous rocks is enigmatic since these minerals could be either primary igneous precursor minerals or products of a higher temperature metamorphic event distinct from the pervasive regional amphibolite facies conditions. The field relationship between the manganiferous horizons in the quartzites and an adjacent mafic intrusion (now metamorphosed to hornblendite) is intriguing and the arguments for and against possible genetic links between the Mn mineralization and intrusion are discussed. The study thus shows that the mineral occurrence at Mankwadzi is Mn rather than Fe mineralization. This Mn mineralization is of limited area extent and is restricted to the contact between the late mafic intrusion and the quartzites. It also shows that this contact is a probable locus for similar manganese occurrences and should be the target for manganese exploration within the Birimian, especially within the Winneba–Kibi volcanogenic greenstone belt of Ghana.

Actual Problems of Prediction of Manganese Deposits in the Urals

Based on recent publications and our long-standing investigations, the most reasonable ways were proposed to obtain the manganiferous raw material for the Uralian metallurgic industry, which lost the traditional raw base (Ukrainian and Georgian deposits) after the USSR breakdown. The Urals is region is perspective for the discovery of two types of manganese deposits. (1) Insignificantly metamorphosed siliceous–carbonate ores with silica modulus MSi (i.e., MnO : SiO2) ranging from 1 to 2 and manganese content of 17–20%. The most promising are the areas with different-age, mainly carbonate rocks in the Urals (Northern and Polar) and Pai-Khoi regions. (2) Oxide, mainly pyrolusite–psylomelane ores with Mn content of 30–35% in the Meso–Cenozoic manganese hats developed in the Paleozoic manganiferous (volcanogenic–siliceous and carbonate–siliceous) rocks and noneconomic (small) deposits. The most promising areas are Late Cretaceous and Paleogene peneplains of the Southern Urals (Trans-Uralian and Zilair regions). It is necessary to intensify works on the improvement of concentration technique for manganese ores and to carry out the marketing study of the expediency of replacing imported manganiferous concentrates by those obtained from the Uralian ores.

Meta-evaporite sequence, exhalative chemical sediments and associated rocks in the Proterozoic Willyama Supergroup, South Australia: implications for metallogenesis

The Willyama Supergroup comprises Proterozoic meta-sedimentary and meta-igneous rocks in western New South Wales and eastern South Australia, and contains the giant Broken Hill PbZnAg deposit, in addition to numerous small stratiform, stratabound and vein mineral deposits. New lithological, geochemical and fluid inclusion data from the Olary Block, west of Broken Hill, suggest the presence of former evaporite rocks now metamorphosed to a variety of chemically and mineralogically unusual lithologies. These evaporite rocks overlie relatively oxidised strata, and are in turn overlain by reduced, graphite-bearing pelites. Rocks of sodic composition abound, represented by albite-quartz-rich rocks (+calcite, actinolite, epidote, garnet, clinopyroxene), inferred to represent metamorphosed analcime-rich strata of felsic volcaniclastic provenance, with variable proportions of carbonates; for example calcite, dolomite, trona and shortite. These rocks are interspersed with potassic rocks, possibly also with an evaporitic origin, in addition to “normal” clastic meta-sediments. The presence of halogen-rich minerals in a distinctive mineral assemblage, hypersaline fluid inclusions, pseudomorphic voids and minerals after gypsum and carbonate, in addition to tourmalines with isotopically light boron isotopes is interpreted as evidence for a non-marine evaporite parent rock for portions of the Olary Block. Types of mineral occurrences in the Olary Block form a continuum between chemical sediments formed by the exhalations of hydrothermal fluids to intrasediment deposits, inferred to have been formed due to the chemical changes imposed on these and/or diagenetic fluids during their passage through the sedimentary pile. Disseminated stratabound pyrite (including cobaltian types) and chalcopyrite extend along strike for many kilometres and are interpreted to have formed by a diagenetic mechanism. The presence of massive sulphide-bearing strata, iron formations, barite, tourmalinite and manganiferous rocks are typical of chemical sediments derived from hot spring sources. The Olary Block meta-evaporites have similar whole-rock compositions to Tertiary analcime-rich rocks of the Green River Formation, Wyoming. These new data imply that portions of the adjacent Broken Hill Block may also comprise meta-evaporites, for example the quartz-albite-rich strata of the Thackaringa Group and the calcsilicates of the lower Broken Hill Group, and that the disseminated cobaltian pyrite mineralisation in the Thackaringa Group may not be of exhalative origin.

Chemistry of micas and chlorite in Proterozoic acid metavolcanics and associated rocks from the H�stef�lt area, Norberg ore district, central Sweden

Microprobe analyses are performed on micas (biotite, muscovite and phlogopite) and chlorite from 1.9–1.8 Ga acid K- or Na-rich metavolcanics, cordierit-emica schists and manganiferous rocks from the Hastefalt area in central Sweden. The results indicate that Fe-rich biotites and muscovites containing ≥10 to ≤25% celadonite and/or pyrophyllite are common in the K- and Na-rich metavolcanics. In the cordierite-mica schists the biotites are Mg-rich and the muscovites contain less than 10% celadonite and/or pyrophyllite. The predominant mica in the manganiferous rocks are phlogopite and less frequent rather pure muscovite. The chlorites show a wide range in composition, but principally those occurring in the K- and Na-rich metavolcanics are brunsvigite and diabantite and those in the cordierite-mica schists and the manganiferous rocks are mainly sheridanite and clinochlore. The chlorites of the manganiferous rocks show enrichment in Mn compared to those in other rock types. In general the compositional variations in the micas and less commonly chlorites are strongly controlled by rock type and fluid chemistry, particularly with respect to the ratio of FeO/(FeO+MgO). Estimates of maximum prograde metamorphic temperature, based on phyllosilicates and co-existing cordierite and garnets, indicate a value of up to 500° C.

Piemontite‐bearing rocks from the Olary District, South Australia

Well laminated piemontite‐bearing rocks occur as a local manganiferous unit within a metamorphosed, dominantly albite‐rich volcano‐sedimentary sequence forming part of the Olary Block of the Willyama Orogenic Domain. The fine to medium grained rocks contain piemontite, spessartine‐rich garnet, albite, phengite, manganoan tremolite and phlogopite, quartz and Mn‐bearing hematite. Distinctive mineralogical layering is characteristic and appears to represent original sedimentary bedding. Bulk chemical compositions indicate that the piemontite‐bearing rocks represent a Mn (‐Fe‐Ca‐K)‐enriched variant of the regionally widespread albite‐rich rocks; Piemontite and garnet exhibit wide compositional ranges (Pm3.6–35.1PS2.5–25.1CZ51. 4–75.3 and Sp59.2–82.2 Ad6.6–34.6Gro‐16.7Cto‐10. 7, respectively) and associated tremolite and phlogopite are highly magnesian, with Mn > Fe. The coexisting metamorphic assemblage of piemontite, garnet, tremolite, phlogopite and hematite indicate that during crystallization, oxygen fugacity was above the hematite‐magnetite buffer (10∼22—10∼15 bars). Estimates of metamorphic temperatures are loosely constrained between 400 and 500°C. The manganiferous rocks possibly represent an original exhalative chemical sediment rich in MnO2 and Fe2O3 within reworked felsic‐intermediate (‐alkaline) tuffs. High oxygen fugacity conditions were maintained during metamorphism, resulting in the piemontite‐bearing assemblages.

Estudo mineralógico e textural dos minerais de manganês do depósito de Bandarra, Jacaraci, Bahia

This paper discusses the mineralogy and the mineralogical and textural changes of the Bandarra manganese deposit which is located in the southern part of the State of Bahia. This deposit comprises lenses of manganiferous rocks deposited within the iron formation and associated with the Licinio de Almeida metamorphic complex. The iron formation, with discontinuous manganiferous lenses, belongs to a Precambrian sequence with mica-schists and amphibolites in its basal portion and mica-schists and quartzites at its top. The metamorphism of Bandarra is thought to be of almandine-amphibolite fades. The assemblage of metamorphic minerals in the protore (primary minerals) includes quartz, spessartite, tephroite, alleghanyite, amphibole, mangano-dolomite, magano-micas, jacobsite, hausmannite, bixbyite and hematite. The assemblage of secondary minerals, formed by a supergene process, contains aMnO2 , malachite, cuprite, goethite and lepidocrocite. Both the hematite and hausmannite show two different phases of mineralization. Polished section analyses revealed that hematite and bixbyite are exsolved in jacobsite.

Geologia e gênese dos depósitos de manganês da provincia de Aracoiaba - Pacajús, Ceará

The manganese deposits of Aracoiaba-Pacajus district are located in northeast of the State of Ceara, Brazil. The protore and the ore of some of the manganese deposits studied occur between belts of manganiferous rocks extending 60 by 15 km. The Precambrian regional rocks consist of gneisses, garnet-sillimanite-quartzites, metabasites and some pegmatites. These are the host rocks of the manganiferous rocks. All these rocks belong stratigraphically and structurally to the Caico Complex and are part of the Jaguaribeana folding belt. The silicatic protore is composed of spessartite, rhodonite, quartz, manganocummingtonite with subordinated amounts of pyrite and pyrrhotite. The granulite facies of the regional metamorphism was superimposed by amphibolite facies. The original sediments which altered to form the protore were deposited in a restrict basin of reducing condition and underwent the action of two different phases of metamorphism. Surface weathering altered the protore forming an ore consisting of an assemblage of manganese oxides such as lithiophorite, pyrolusite, mangano-nsutite and aMnO2 . The ore presents typical depositional and pos-depositional textures, which show that the ore was formed by replacement and cavity filling. The manganese content of the ore varies from 18 to 38%. The reserves of the district are 2.500.000 metric tons, making economic explotation viable with a small, local siderurgical industry in Ceara. The manganese minerals were formed according to the following sequence: spessartite, lithiophorite and/ou cryptomelane, manganite, pyrolusite, mangano-nsutite.

Prospecção magnetométrica de depósitos óxido-silicáticos de manganês com jacobsita, no Ceará

Jacobsita occurs in metamorphic oxide-silicatic manganese protore in Itacima, in the manganese district of Pacatuba, Ceara, Brazil. Precambriam gneisses and schists are the host rocks of the lenses of the manganese protore which was weathered at the surface, forming small ore deposits. All the Precambrian rocks in this area belong to the Maranguabe Metamorphic Complex and are located in the Jaguaribeana folding belt. The assemblage of primary manganese minerals in the protore consists of rhodonite, spessartite, tephroite, jacobsite and hausmannite. Manganese silicates and hausmannite were altered to aMnO2, but the jacobsite shows only incipient alteration. In spite of the presence of two micas in the gneissic country rock, the metamorphism is believed to be of high grade, as evidenced by the assemblage of manganese metamorphic minerals. Probably the regional metamorphic rocks underwent two different phases of metamorphism. The manganese content of the manganiferous rocks varies from 10.0 to 38.0%. The magnetometric anomalies were very useful in establishing the form and dimensions of both the manganese ore and protore. The Mn-deposits of Itacima have very small reserves, consequently their resources have no economic interest.

Manganite formation in the first stage of the lateritic manganese ores in Africa

Lateritic profiles on manganiferous rocks from two areas in central West Africa permit the observation of manganite formation on rocks of different primary nature. In an area of gondites and tephroitites (Ziemougoula, Ivory Coast) manganites are found to replace tephroites and manganocalcites, whereas in a weathered carbonate sequence (Moanda, Gabon) manganite replaces rhodochrosite. In both areas manganite occurrence is limited to a very narrow and basal portion of the altered profile, in conformity with the limited stability field established for this mineral. It is found that manganites of different mineral lineages may be distinguished chemically from one another by variation in the ratio MnO ( CaO + MgO) .

A study of the application of regression analysis for trace element data from stream sediment in New Brunswick

Observed correlations of Zn, Pb, Cu and Mo with Fe and Mn in 1197 samples of stream sediments from a survey area of 1060 km 2 in New Brunswick have been studied with the use of multiple regression analysis. The study showed that up to 70% of Zn variance, 49% of Pb and Cu, and 28% of Mo might be related to the variations of Fe and Mn. Corrected (residual) metal values were obtained by subtracting the predicted values generated by the regression equation from the observed values. Comparison of the observed and residual maps showed no significant differences in geochemical relief indicating that the geochemical anomalies may be associated with the bedrock anomalies. Geological information suggests that most of the anomalies are related to weak base metal mineralization with associated pyrrhotite and pyrite or to base metal occurrences in ferrugenous and manganiferous rocks.

Structure and stratigraphy of the manganese deposits of Visakhapatnam and Srikakulam districts, India

The deposits include bedded oxide ores which are considered primary and syngenetic with the enclosing paragneisses (khondalites), and secondary massive botryoidal ores and irregular replacement bodies generally associated with zones of strong structural disturbance. The manganiferous rocks occupy a definite stratigraphic position in the sequence of aluminous and calcareous sediments from which the khondalite formations of the Eastern Ghats were derived. Kodurites, once interpreted as igneous intrusives with which the manganese ores were considered genetically related, represent hybrid rock types formed as a result of assimilation of manganiferous country rock by granite.