Zircon U-Pb Geochronology of a Manganese-rich Supracrustal Succession in Northeast Brazil: Adding a New Piece to the Paleoproterozoic Manganese Mineralization Puzzle

A vast accumulation of manganese occurred in the Paleoproterozoic and it is closely related to the Paleoproterozoic Great Oxidation Event. Although the largest Mn deposits are located in the African continent, relevant deposits that potentially correlate with the African ones are found in South America, specifically in the Brazilian territory. The Borborema Province in Northeast Brazil hosts several Mn-rich meta-sedimentary sequences, containing up to 40 wt.% MnO. These sequences are composed of oxidized and manganese silicate lenses that alternate with spessartite-quartzite layers. This succession is hosted by graphite-bearing pelitic gneisses, is metamorphosed to the amphibolite facies, and is intruded by granitic bodies. Although some preliminary studies report Palaeoproterozoic ages for these meta-sedimentary sequences, the age at which the Mn-rich sequences were deposited has not yet been determined. We investigate in this study the Lagoa do Riacho Manganese Deposit, a representative member of the Northern Borborema Province Mn-rich sequences. Not only was the age of the Mn-rich protolith deposition determined by LA-SF-ICP-MS zircon U-Pb geochronology, but also the timing of the metamorphic reworking of the Mn-rich succession was inferred. The youngest detrital zircon population from a meter-sized bed of spessartite-quartzite interlayered with an oxidized manganese ore from drillhole Ocr-1 yielded a maximum depositional age close to 2130 Ma. Similarly, a gneiss hosting the manganese mineralization at the base of drillhole Ocr-1 also yielded a maximum depositional age in the Rhyacian, close to 2156 Ma. We infer from the U-Pb dating of metamorphic overgrowths on zircon from the Mn-bearing sequences and host rocks and the U-Pb crystallization age of an intrusive leucocratic granite that the minimum age of the Mn-rich succession to be 2023-2106 Ma. The metamorphic reworking of the Mn-rich succession is time-equivalent to the Transamazonian/Eburnean orogeny. Thus, these constraints point to a Rhyacian age (ca. 2100-2200 Ma) for the deposition of the Mn-rich protolith, chrono-correlated with other world-class manganese deposits, such as those from the Franceville Basin in Gabon.

Exploration for Fe-Mn Oxides Using Geochemical Signatures in Soil: A Case Study of Part of Northwestern Nigeria

Part of northwestern Nigeria was investigated with the aim of delineating concealed mineralization using geochemical signatures in soils. To achieve this, 30 selected soil samples were analysed geochemically. The result of the elemental analysis was subjected to Principal Component Analysis (PCA) and isograde plotting, while selected elements were correlated. From the geochemical result, most of the analysed elements have anomalous value in the southern part of the area, while the least values are in the southwestern. From the PCA analysis, six factor groups were distinct. The factor groups were interpreted geochemical to fingerprint mineralization in the area. The result of correlation analysis shows that Fe is negatively correlated with most of the correlated elements. The study concluded that the central part of the study area is mineralized with both manganite and goethite. In addition, manganese mineralization is indicated by elemental association: Zn+As+Be+Bi+Co+Nb+Ni+CsP+Al+Ca+Cd+Li+K, while iron mineralization is indicated with Zr+Th+Pd+Mo+V+Sn+Cr+Ce+InSc+P+Pb association.

Exploring Microbial Biosignatures in Mn-Deposits of Deep Biosphere: A Preliminary Cross-Disciplinary Approach to Investigate Geomicrobiological Interactions in a Cave in Central Italy

The terrestrial subsurface offers privileged sites both to search for microbial life and to observe still mostly unknown characteristic lithologies. In particular, caves represent natural laboratories to investigate unique minerogenetic processes and biotic interactions, connected to these phenomena. Manganese mineralization in cave environments provides a window to understand the complex Mn cycle and the development of microbial communities in special conditions, such as low constant temperature, absence of light and, in particular, low-energy environments. In the current study, we isolated and characterized Mn-samples taken from the cave “Grotta Grande dei Cervi,” L’Aquila, Central Italy, and we used a multidisciplinary approach to characterize them, with the purpose of understanding the biogeochemical processes in extreme environments. A chemical characterization of the samples was done by EDS; further investigations are underway with other multidisciplinary methodologies to understand whether the Mn laminae are related to biological processes. SEM investigations revealed microbial imprints, showing cell-like structures and suggesting that the cell-like shapes occur within internal laminae. A culture-independent approach was used to assess the possibility that biotic factors may be involved in the production of these mineralizations and to investigate the nature of the microbial community in these materials. A molecular approach was the first step to investigate the role of microorganisms in forming manganese oxides associated with water bearing rocks. DNA from the black deposits was extracted and sequence analyses of specimens were performed. Our data support the hypothesis that microorganisms may contribute to the mineralizations of manganese in this environment, providing new encouraging insight into the role of microorganisms in the Mn cycle and the processes of energy acquisition in unfavorable conditions, with relevant implications for astrobiology.

Composition and provenance reconstruction of terrigenous deposits in the North-West of South Africa

Северо-западный регион ЮАР до недавнего времени не являлся промышленно марганценосным. Однако результаты изучения последних лет дают основание думать, что здесь могут быть залежи марганцевых руд. Марганцевое оруденение в этом регионе встречается в виде марганцевых конкреций, порошкообразного марганцевого вада и марганцевых корок в коре выветривания. Марганцевые конкреции приурочены к аллювиальной части «Westwits alluvium» рудного разреза и марганцевый вад накоплялся в карстовых структурах, образовавшихся в результате приповерхностного выветривания, выщелачивания и растворения подстилающих марганценосных неоархейских доломитов. Предполагается два потенциальных источника марганца: первый расположен непосредственно под рудным телом, а второй – на существенном удалении от него. Если первый источник рудного вещества поставлял марганец из подстилающих доломитов в процессе их выветривания, то второй вариант подразумевает существенный перенос металла из неизвестных коренных источников, расположенных на значительном удалении от области рудонакопления. Таким образом, для решения этого вопроса, необходимо провести экспериментальные исследования, изучающие природу, минералогию и источник сноса терригенных отложений «вмещающих материалов» верхнего рудного разреза. Цель работы – уточнить природу марганценосных терригенных залежей «Westwits alluvium» и, что самое важное, определить их коренной источник поступления и собственно минеральный состав. Методики исследования включали: петрографическое описание пород, геохимические анализы методами XRF и SEM, подсчеты объемного состава детритовых минералов и анализ дискриминационных диаграмм. Результаты. В результате проведенных исследований было установлено, что терригенные зёрна в основном представлены кварцем. Содержание полевых шпатов, минералов цемента и глинистых минералов не более 20 %. Использована классификация составов терригенного материала, основанная на подсчете в объемных процентах зерен кварца, полевого шпата, обломочных зерен других пород (вулканических, магматических и метаморфических пород), слюды и др. По этим данным были определены вероятные источники сноса, которыми являются породы Рэнд-Антиклинального хребта, расположенного к югу от изучаемого региона, а также архейские граниты, гнейсы и мафические-ультрамафические породы Каапваальского кратона. Осадконакопление происходило в низменной равнине с тропическим умеренно влажным и субгумидным климатом. Здесь, при повышенном рН воды происходило интенсивное выщелачивание пород и замещение детритовых зерен разного минерального состава диоксидом марганца. Ключевые слова: марганцовистый аллювий, третичный, терригенные отложения, Каапваальский кратон, Южная Африка The North-West region of the Republic of South Africa was previously not considered to constitute of manganese mineralization of industrial value. However, recently published articles indicated the presence of secondary manganese mineralization in the weathering crust, underlain by the manganiferous Neoarchean dolomites. Manganese mineralization in this region occurs in the form of manganese nodules, powdered manganese wad, and manganese crusts. Manganese nodules are confined to the alluvial part of the ore section known as the «Westwits alluvium» and manganese wad is accumulated in karstic structures formed as a result of near-surface weathering, leaching, and dissolution of underlying manganese-bearing Neoarchean dolomites. Two potential sources of manganese are assumed: the first relates to the dolomites which are located directly under the ore body, and the second relates to the source areas of terrigenous deposits. If the first hypothesis suggests that manganese ore substances were supplied from the underlying dolomites during their weathering, the second option then implies a significant transfer of metal from unknown root sources located at a considerable distance from the area of ore accumulation. Thus, it is necessary to conduct petrographic study to reconstruct their source regions and understand the close relations with Mn mineralization. Aim is to clarify the nature of the manganese-bearing terrigenous deposits «Westwits alluvium» and, most importantly, to determine their root source of supply and the actual mineral composition. Methodology of study includes mainly: petrographic study of rocks, geochemical analyses with the use of XRF and SEM methods, modal compositional analysis of the detrital minerals, and analysis of discrimination diagrams. Results. As a result of the conducted research, it was found that terrigenous grains consist mainly of detrital quartz grains. The content of feldspars, cement minerals and clay minerals seldom exceeds 20 %. The classification of terrigenous material based on the calculation of the volumetric percentage of the detrital framework grains: quartz, feldspar, clastic grains of other rocks types (volcanic, igneous and metamorphic rocks), mica, indicated probable source areas of the terrigenous sediments. These include metasedimentary rocks of the Rand Anticline Ridge which is located south of the studied region, and Archean granites, gneisses, and mafic-ultramafic rocks of the Kaapvaal Craton. In the basin of deposition, sedimentation occurred in a lowland plain within tropical region, characterized by moderately humid and sub-humid climatic conditions. These conditions, combined with oxidation and increased pH of the basin waters, contributed to the replacement of detrital grains with manganese dioxide

STUDY OF THE MATERIAL COMPOSITION OF THE SAMPLE MANGANESE-CONTAINING ORE DEPOSITS “KARAMOLA”

In this work, the material composition of the ore of the Karamola Deposit is studied. A sample of manganese ore from the Karamola Deposit with a size of 0-120 mm was received for research on the material composition. The manganese mineralization of the sample is represented by the mineral series polyanite-pyrolusite and WADA-psilomelane. Mineral secretions are crystalline earthy structures and mixed formations. Manganese oxides are distributed almost throughout the entire mass of the rock. They are represented by crystallized gel formations, soot, and skeletal structures. Ore gels permeate the rock through cracks, cleavages, leaching voids, pores, cleavage planes and penetrate between the scales of layered minerals and form a variety of forms in the mass of the rock: individual strokes, thread-like cuts, veins, edges, layers, nests. Replacement solutions are siliceous or manganese-siliceous in nature and color the rock in the corresponding color with mineral microparticles: black – manganese, red and red – iron. Rock-forming minerals are mainly represented by quartz. The granulometric composition of an ore sample crushed to the minus 2.0+0 mm class was determined.

The setting and style of manganese mineralization in the Constantiaberg Massif, Cape Peninsula, South Africa

Manganese oxyhydroxide mineralization is widespread in the Constantiaberg Massif. It is largely hosted by west-northwest – east-southeast trending brittle structures in the competent Ordovician arenites of the Peninsula Formation of the Cape Supergroup. Manganese is also found impregnating more porous Peninsula Formation arenites and Quaternary scree. This study proposes that the more significant deposits at Hout Bay and Constantiaberg differ from most of the mineralization in that they are spatially associated with saprolithic dolerite dykes belonging to the 132 Ma False Bay dolerite dyke swarm. It is suggested that this deep weathering may be related to a Miocene palaeo-landsurface, yielding a maximum age for these more important Mn deposits. However, there is evidence for mineralization of different ages through the Quaternary Period. Apart from Mn-mineralization hosted by rare breccias containing hydrothermal quartz, most of the mineralization is supergene, having been leached and transported in reduced acidic groundwater and precipitated at or near a redox front in a near-surface environment.

Multi-Phase Manganese Mineralization in the Noamundi Synclinorium, East Indian Shield

Manganese mineralization associated with phyllites in and around Joda, Odisha belongs to the Iron Ore Group of Noamundi basin and is a part of Jamda-Koira belt of East Indian Shield. The present study area comprises low to medium grade tectonites containing economic resources of both iron and manganese. Present study is concentrated on Manganese mineralization. Field study and petro-mineralogical observations reveal syngenetic character of manganese ores comprising lowT higher oxides viz. pyrolusite, cryptomelane, manganite as major Mn-minerals along with highT lower oxides viz. jacobsite, bixbyite, braunite and hausmannite as minor Mn-minerals. The Mn-ore bodies and associated phyllites have undergone multiple phases of deformation and metamorphism followed by hydrothermal and supergene processes. Four deformational phases have been deciphered during field study. Geochemical analyses of ores and phyllitic host rocks show high values of Al2O3, TiO2, Ba, Co, Ni, Cr, Cu, Sc, V, As, Zn but depletion of Sr, Yb, Sm, Nb. Geochemical data infer ores to be a recycling product originally derived from a mafic crustal source of tholeiitic character. Age data obtained from Sm-Nd ratio of two rock samples are 3.46 Ga and 2.79 Ga. Present work provides a critical assessment on the multiphase mineralization of manganese ores.