Fe-Mn Ores Research Articles

Comparative Effects of Biochar, Slag and Ferrous-Mn Ore on Lead and Cadmium Immobilization in Soil.

A variety of remediation approaches have been applied to the heavy metals-contaminated soils, however, the immobilization of metals in co-contaminated soils still not cleared. Therefore, an incubation study was conducted to evaluate the instantaneous effects of different concentrations of biochar (BC), slag (SL) and Fe-Mn ore (FMO) on immobilization of Pb and Cd through the Toxicity Characteristic Leaching Procedure (TCLP) by following the the European Community Bureau of Reference (BCR), CaCl2 and NH4NO3. The sequential extraction of BCR showed decrease in acid soluble fractions, while the residual proportions of Pb and Cd were enhanced with increasing concentrations of SL and BC. Addition of BC significantly lowered the extractable fractions of both metals by TCLP, NH4NO3 and CaCl2 as compared to SL and FMO. Among all amendments, BC incorporation into co-contaminated soil offered promising results for Pb and Cd immobilization. Overall, all amendments showed positive and long-term impact on the reclamation of co-contaminated soil with heavy metals and could deserve advance monitoring studies on a field scale.

Genetic Aspects of the Noble-Metal Mineralization at the Poperechnoe Deposit, Lesser Khingan, Russia

Bodies of cryptovolcanic rocks (fluidolites) play a significant role in the structure of the Poperechnoe ferromanganese deposit, Lesser Khingan, Russia. Fe-Mn ores in association with fluidolites are localized in ancient carbonate rocks. PGM, gold, and silver minerals up to tenths of a millimeter in size are established in the rocks and ores of the deposit. Characteristic admixtures in the platinum are iron (9-11%), with less common copper, iridium, and osmium. An intergrowth of isoferroplatinum polycrystal with forsterite is observed. There are also individual grains of Os-Ir-Ru-Rh intermetallides. The gold grains (up to 93% Au) are characterized by dendritic and clumpy morphology, frequently showing faceting elements. The grains are frequently rounded and sometimes have an almost perfect spherical shape. Native silver is distributed among the dolomites, as well as in the dolomitic fragments from the fluidolites. Ubiquitous admixtures in the silver are copper, iron, and more rarely zinc; single grains contain admixtures of molybdenum, nickel, gold, and palladium. PGM and high-fineness gold are related to the fluidolites, which are the only magmatic rocks in the studied range of the deposit. Silver, its minerals, low-fineness gold, and sulfides are confined to the rocks and ores subjected to the regional dolomitization, low-temperature hydrothermal reworking, and silicification. Samples contain up to 11.3 g/t platinum, 2.35 g/t gold, 296.2 g/t silver, which allows us to consider the studied object as economically promising for noble metals.

Major and trace metals in suspended and bottom sediments of the Mandovi and Zuari estuaries, western India: distribution, source, and pollution.

Major elements and trace metals in suspended sediments along transect stations of the Mandovi and Zuari estuaries showed three types of distribution: (a) high concentrations of most metals (Al, Fe, Mn, Cr, Pb, Cu, Ni, Zn, Co, Sc, Mo, and U) in the upper estuary and their decreasing concentrations seaward in every season, (b) lower concentrations of some metals (Mg, Cr, Zr, V, Al, Th) in the upper estuary and bay and their increased concentrations in the lower estuary, and (c) higher concentrations of some metals (Cu, Ni, Zn, Pb, and Cr) in the upper estuary and bay and their decreased concentrations in the lower estuary. Mn was the most significant pollutant in both the estuaries. The Zn, Cr, Fe, and Mo in Mandovi during the monsoon and post-monsoon and, Pb, Ni, and Cr in Zuari during the post- and pre-monsoons were in the range "moderately to heavily polluted." The pollution load index of metals was high at upstream stations, with higher values in Mandovi during monsoon and Zuari during the post- and pre-monsoons. Most trace metals were correlated with Fe and Mn indicating their association primarily with Fe-Mn ore material. The principal component analysis indicated natural and anthropogenic inputs and the latter was predominantly related to ore material in both the estuaries. The distribution factor was high for Al, Mg, Zr, Th, and U in <2-μm fraction and Cr, Cu, Ni, Zn, Co, V, Sc, and Zr in 2-4-μm size fraction sediments suggesting two sources of sediments. More than 60% concentrations of all trace metals were associated with <2-μm fraction sediments. The distribution of trace metals along transect was affected by the physico-chemical conditions of the estuary, grain size of sediments, and anthropogenic contribution of metals.

몽골 우기누르 철-망간 부존 지역의 3차원 지질모델과 자력탐사 결과의 비교분석

몽골 우기누르 철-망간 부존 지역의 3차원 지질모델과 자력탐사 결과의 비교분석

자력자료를 이용한 몽골 우기누르 철-망간 분포 특성

한국지질자원연구원은 몽골 광물자원청과 공동으로 우기누르 철-망간 광화대에 대한 공동 연구를 수행하였다. 이의 일환으로 수행된 육상 자력탐사에서 획득한 자료를 바탕으로 3차원 자력 역산을 수행하였으며, 3차원 지질모델링 기술을 이용하여 철-망간 광화대에 대한 3차원 영상화 및 광체 평가를 위한 연구를 수행하였다. 총자력 이상의 분포 특성을 통해 연구지역의 광상에서 지표 노두로부터 수평적으로 연장되는 광체의 부존 가능성을 확인하였다. 또한, Fe 함량과 상관성이 높은 자기감수율 역산 결과를 토대로 연구지역의 제 1광상 및 제 2광상 모두에서 지표에서 드러난 광체가 지하 하부로 연장되어 있는 것으로 해석되어, 지표에 드러나지 않은 광체의 부존 가능성이 높은 것으로 판단된다. 시추 조사를 통해 일부 대표 지역의 광체 품위 자료가 확보되고 이번 연구결과와의 복합 해석을 수행한다면 효과적인 개발 가능성 평가가 가능할 것으로 판단된다. Korea Institute of Geoscience and Mineral Resources (KIGAM) and Mineral Resources Authority of Mongolia (MRAM) performed a joint survey on Ugii Nuur Fe-Mn mineralized area. Following the survey, we carried out magnetic survey and 3D magnetic susceptibility inversion. Based on the inversion results, basic feasibility study and 3D imaging of Fe-Mn mineralized area were performed using 3D geological modeling technique. Using the distribution of total magnetic field data, we were confirmed for the possibility of horizontal extension of ore bodies from surface outcrops. The 3D magnetic susceptibility model, which is highly related with Fe content, analyzed by inversion shows that the ore bodies of Deposit 1 and Deposit 2 are extended to the underground and ore bodies that are not exposed on the surface are largely distributed in the underground. If we perform the integration analysis using this magnetic susceptibility model and the ore grade data analyzed by drilling survey, it is possible to carry out the effective potential evaluation of Ugii Nuur Fe-Mn ore deposit.

Boron-polymetallic metallogeny of the north and northeast of the Sino-Korean Craton

Based on published data and original investigations, it has been shown that the combination of widely known Ag, Fe, and Fe-Mn ore deposits, as well as boron and Pb-Zn world-class deposits, is typical for metallogenic zones in the north and northeast of the Sino-Korean Craton. The ore genesis was spatially inherited and lasted from the Archean to Mesozoic. The Archean metallogenic zones are related to the protocontinental margin terranes of the craton basement and they comprise banded iron ore and Cu-Zn sulfide deposits. The proterozoic-Early Paleozoic metallogenic zones are related to rift basins, where the ore-bearing Archean folded basement is overlain by volcanic and sedimentary complexes. The Proterozoic metallogenic zones host quartz veins and schistosity zone-related Au deposits, banded iron and Cu-Zn ore deposits, large sedimentary-metamorphogenic borate and magnesite deposits, Cu-W deposits in tourmalinites, exhalation-sedimentary Pb-Zn ore deposits, and large polygenic REE-Fe-Nb ore deposits. The Riphean-Cambrian terrigenous-carbonate strata are represented by stratiform Pb-Zn and fluorite deposits. Mesozoic metallogenic zones related to volcano-plutonic complexes of intraplate series coincide with zones where the folded basement is made of Precambrian ore-bearing series. Gold deposits are typical of all the metallogenic zones, but most of them are related to Mesozoic volcano-plutonic complexes.

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.

First find of cerianite in zircons from metasomatites of the Terskii greenstone belt, Baltic shield

) is one of the most scarce rareearth minerals. Because of difficulties in discovery andidentification of this mineral, E.I. Semenov proposedconsidering cerianite as an object of nano (not micro)mineralogy [1]. Since its discovery in the 1950s, nomore than 20 reliable finds of this mineral (mainly inthe form of microscopic grains and microinclusions inother minerals) have been documented. Cerianite wasdiscovered for the first time in Sudbury (Canada) inthe carbonate dikes cutting across nepheline syenites[2]. In addition to Ce, cerianite contains isomorphicadmixtures of other LREE (La, Pr, Nd). Significantamounts of Th and other elements (Xe, Cs, Pb, Rh)were found in cerianite from pegmatites of East Antarctica [3]. Supergene cerianite occurs as a weatheringproduct of bastnaesite [1] and fluocerite [4], as well asin the weathering crust of different compositions [1,5–7]. In the oceanic Fe–Mn ores, cerianite isobserved as submicron films on apatite [8]. The formation of cerianite in granites is considered to berelated to hydrothermal alteration, accompanied byfluid leaching of Ce from monazite [9]. Cerianite associates with minerals and ores of noble metals: Au, Pt(Sukhoi Log deposit [10]); Au, Pd, and REE (oremanifestations of the Polar Urals [11] and others]).Overgrowths of cerianite of a few microns thick ondiamond phase were found in the carbonado fromBrasilia [12].Cerianite is a sensitive indicator of conditions ofmineral formation, because Ce is the only compatibleREE, which in natural conditions can occur not onlyin trivalent but also in tetravalent form. Cerianite isformed only in strongly oxidizing conditions, mainlyin alkaline solutions (fluids) [13].Submicron inclusions of cerianite were found by usin the zircon from twomica garnet–chlorite–quartz–plagioclase metasomatite (sample 2508) in the Terskiigreenstone belt in the southern framing of the Imandra–Varzuga structure (southeastern part of the KolaPeninsula). Complex isotopic–geochemical study ofzircons from metasomatites of the Terskii greenstonebelt allowed us to distinguish two stages of metamorphism (2680 and 2025 Ma) and two stages of metasomatism (2600 and 1800 Ma) [14]. Practically all zircons of different ages were completely or partiallymetasomatized, which caused their enrichment inREE (especially LREE), Th, U, Sr, and Ba, and formation of flat REEs with a reduced Ce anomaly.The structural features, majorelement composition of the zircons, and the composition of foreignmineral inclusions, if present, were studied in theregime of compositional contrast on a JEOL JSM6460LV scanning electron microscope equipped withan Oxford INCA detector at the St. Petersburg MiningInstitute. U–Pb dating of zircons from metasomatiteswas conducted on a SHRIMPII ion microprobe atthe Center for Isotopic Research, Karpinskii AllRussia Research Institute of Geology. The REE and traceelement composition of zircons was analyzed at thesame grains and points as U–Pb dating, on a CamecaIMS4f ion microprobe at the Yaroslavl Branch of thePhysicoTechnical Institute of the Russian Academyof Sciences.Zircon containing cerianite differs in the heterogeneous structure. Its weakly altered right upper part(point 2.1 in Fig. 1) retains traces of faceting and primary growth zoning. At the final stage of the Svecofennian metasomatism, most zircon was transformed with the formation of “patches” of irregularreniform shape, which form a band up to 100 µm insize with a characteristic dark tint in backscatteredelectrons (BSE) (point 2.2 and inset

Scientific substantiation of ecological technology for the recovery of oceanic Fe-Mn ores

Scientific substantiation of ecological technology for the recovery of oceanic Fe-Mn ores

Manganese and ferromanganese ores from different tectonic settings in the NW Himalayas, Pakistan

In Pakistan manganese and ferromanganese ores have been reported from the Hazara area of North West Frontier Province, Waziristan agencies in the Federally Administered Tribal Areas and the Lasbela-Khuzdar regions of Baluchistan. This study is focused on comparison of mineralogy and geochemistry of the continental ferromanganese ores of Hazara and the ophiolitic manganese ores of the Waziristan area of Pakistan. In the Hazara area, ferromanganese ores occur at Kakul, Galdanian and Chura Gali, near Abbottabad, within the Hazira Formation of the Kalachitta-Margala thrust belt of the NW Himalayas of the Indo-Pakistan Plate. The Cambrian Hazira Formation is composed of reddish-brown ferruginous siltstone, with variable amounts of clay, shale, ferromanganese ores, phosphorite and barite. In Waziristan, manganese ores occur at Shuidar, Mohammad Khel and Saidgi, within the Waziristan ophiolite complex, on the western margin of the Indo-Pakistan Plate in NW Pakistan. These banded and massive ores are hosted by metachert and overlie metavolcanics. The ferromanganese ores of the Hazara area contain variable amount of bixbyite, partridgeite, hollandite, pyrolusite and braunite. Bixbyite and partridgeite are the dominant Mn-bearing phases. Hematite dominates in Fe-rich ores. Gangue minerals are iron-rich clay, alumino-phosphate minerals, apatite, barite and glauconite are present in variable amounts, in both Fe-rich and Mn-rich varieties. The texture of the ore phases indicates greenschist facies metamorphism. The Waziristan ores are composed of braunite, with minor pyrolusite and hollandite. Hematite occurs as an additional minor phase in the Fe-rich ores of the Shuidar area. The only silicate phase in these ores is cryptocrystalline quartz. The chemical composition of the ferromanganese ores in Hazara suggests that the Mn–Fe was contributed by both hydrogenous and hydrothermal sources, while the manganese ores of Waziristan originated only from a hydrothermal source. It is suggested that the Fe–Mn ores of the Hazara area originated from a mixed hydrothermal–hydrogenetic source in shallow water in a ontinental shelf environment due to the transgression and regression of the sea, while the Mn ores of Waziristan were formed at sea-floor spreading centers within the Neo-Tethys Ocean, and were later obducted as part of the Waziristan ophiolite complex.

Sources of manganese deposited as oceanic Fe-Mn ore

The current concepts of two competing sources of manganese deposited as oceanic Fe-Mn ore are reviewed and assessed critically. A new solution of this problem proposed in this paper is a further development of fundamental works by N.M. Strakhov in the light of new facts and with allowance for geological, geochemical, and geohistorical data. It has been concluded that terrigenous material removed from land serves as a main source of manganese fixed in oceanic Fe-Mn ore. The history of sedimentation and nodule formation in the World Ocean lasted for more than two billion years. Manganese has been supplied to recent bottom sediments from both present-day and older sources. The closed geochemical cycle of Mn circulation in the ocean is intimately related to its circulation in the hydrosphere. Seawater is oversaturated with Mn and serves as its immediate source for ore deposition and elevated concentrations in bottom sediments affected by hydrothermal solutions or other manifestations of endogenic activity. Seawater is a repository for Mn, where this element is retained during global cataclysms, which have repeatedly occurred in geological history.

Description and crystal structure of turtmannite, a new mineral with a 68 Å period related to mcgovernite

Jacobsite-rich Fe-Mn ores of probable Dogger age fill paleokarst pockets in the Triassic marbles of the Barrhorn Unit under Pipjigletscher in the Turtmanntal, Valais, Switzerland. These ores and embedding rocks underwent Tertiary metamorphism under upper greenschist facies conditions. Some of these jacobsite ores contain minor amounts of a yellow micaceous mineral, which appears to be a new Mn-Mg silicate-vanadate-arsenate that was named “turtmannite” with respect to the type locality. Turtmannite flakes up to 200 μm in length occur parallel to the main schistosity, or fill thin discordant veinlets. Turtmannite is rhombohedral R3̄c, with a H = 8.259(2) and c H = 204.3(3) Å in the hexagonal setting. The corresponding primitive rhombohedral cell has a R = 68.31 and α R = 6.92°. HRTEM images indicate that turtmannite is perfectly ordered along c. The structure of turtmannite has been solved to a final R1 of 12.4% on a Siemens Smart CCD diffractometer with MoKα X-radiation, and a detector to sample distance extended to 12 cm. The structure consists of 84 oxygen layers stacked along c, with twelve close-packed layers followed by two non-close-packed layers. This sequence is repeated six times. The structure contains eight symmetrically distinct cation layers. Three different occupational variants have been recognized leading to the following hypothetical end-member formulae and approximate abundances: I [IV] Mn 1.5 [IV] Mg 3 [VI] (Mn,Mg) 21 [(V,As)O 4 ] 3 [SiO 4 ] 3 O 5 (OH) 20 , 50% II [IV] Mn 1.5 [VI] (Mn,Mg) 21 [(V,As)O 4 ] 3 [SiO 4 ] 3 [AsO 3 ](OH) 21 33% III [IV] Mn 1.5 [VI] (Mn,Mg) 21 [(V,As)O 4 ] 3 [SiO 4 ] 2 [SiO 3 OH](OH) 25 16% The simplified chemical formula for turtmannite can be written as: (Mn,Mg) 22.5 Mg 3-3x [(V,As)O 4 ] 3 [SiO 4 ] 3 [AsO 3 ] x O 5-5x (OH) 20+x . The unit cell of turtmannite is similar to those of mcgovernite, a Mn-Mg-Zn arsenate from Sterling Hill, New Jersey, and an unnamed “mcgovernite-like” Mn-Mg arsenate from the Kombat Mine, Namibia. The crystal structure of turtmannite is close to the model predicted for mcgovernite by Moore and Araki (1978)

ORIGIN AND DISTRIBUTION OF SOME TRACE ELEMENTS IN METAMORPHOSED Fe Mn DEPOSITS, VAL FERRERA, EASTERN SWISS ALPS

Numerous small Fe–Mn deposits occur in Triassic marbles of the Middle Penninic Suretta, Starlera, and Schams nappes in Val Ferrera, eastern Swiss Alps. These deposits are characterized by high contents of Ba, Sb, As, V, Be, W, and rare-earth elements ( REE ), and most likely represent chemical sediments deposited around submarine springs, similar to some modern seafloor metalliferous sediments. Circulation of the hydrothermal fluid within the granite-bearing basement underlying the sedimentary rocks is inferred as the most likely mechanism for the derivation of the Be and W concentrated in the ores. The orebodies studied shared a similar Alpine metamorphic evolution, culminating with blueschist- to greenschist-facies conditions. The chemical and mineralogical composition of the ores strongly influenced the behavior of the minor constituents Ba, Sr, Sb, As, V, Be, W, and REE . During the main deformation (D 1 ), As and V, for example, were incorporated into hematite in Fe-rich ores, whereas in Mn-rich ores they were concentrated into accessory minerals growing in the main schistosity. These syn-D 1 minerals represent important sinks of trace elements released by recrystallization or breakdown of their primary hosts as a result of prograde metamorphism. Post-D 1 mobility of Ba, Sb, As, V, Be, REE and, in some cases, W is recorded by various mineral parageneses that either overgrow the S 1 schistosity or occur in several types of discordant veins. In addition to the chemical and mineralogical controls, the structural position of the deposit influenced the remobilization of trace elements. Element mobility during the Alpine greenschist-facies metamorphism within the Fe–Mn ores involved large-ion lithophile elements (Be, Sr, Ba), high-field-strength elements (Mo, W, Sb, As), and the light REE . The geochemical signature is analogous in many respects to the remobilization observed during subduction-related metamorphism and during metasomatism in the mantle.

The formation of Palæoproterozoic banded iron formations and their associated Fe and Mn deposits, with reference to the Griqualand West deposits, South Africa

This paper models the physico-chemical conditions of a Neoarchæan to Palæoproterozoic marine basin in which the sedimentary sequence of BIF, Fe and Mn ores of the Lake Superior-type formed. The model is based on Eh-pH diagram stability fields for Fe, silica and Mn solubilities (taken from the literature) and on field observations of the lithological sequences. BIF formation took place in epicontinental marine basins with free access to the ocean. The main Fe source for BIF formation was ocean enriched with about 6–10 ppm ferrous Fe of hydrothermal geochemical affinity. Land-derived Fe influxes into the BIF-forming basins certainly contributed, but the lack of clastic sedimentation precludes estimation of element budgets. The main silica source for formation of chert layers is sea water. If silica was precipitated by evaporation, the silica concentration of the BIF-forming sea must have been close to saturation (15–20 ppm). Biogenic silica concentration from a possible silica undersaturated sea may not be excluded. These inferred BIF-forming conditions fit the global occurrence of Lake Superior-type BIF in general, whereas special sedimentary environments were probably responsible for the formation of highly enriched laminated Fe ore at the Maremane Dome and in the Sishen-Kathu mining district in Griqualand West, and for the FeMn ores in the Kalahari field. Formation of laminated Fe ore in the Maremane Dome and in the Sishen-Kathu areas were restricted to local deeps within the BIF basins, caused by karst collapse in the underlying Campbellrand dolomites. In such deeps, increased pH values relative to the normal BIF-forming sea caused sufficiently increased silica solubility, resulting in the almost exclusive sedimentation of colloidal Fe precipitates. In the Kalahari field, the BIF sedimentation pile became silica-depleted when approaching the Mn layers. This was genetically controlled by the increased pH of sea water and increased silica solubility. Under such increased pH conditions, Mn oxides become stable for precipitation if minimum Mn activity is achieved in the sedimentary basin. The sedimentation sequence of low silica BIF - kutnahoritic BIF - jacobsitic BIF - braunitic Mn ore can be explained, using combined Eh-pH diagrams, as reflecting a precipitation path of increasing redox potential in a pH environment slightly above 9. These conditions were achieved by closing the access of the basin to the open ocean, resulting in the reduction of water level by evaporation and thereby increasing salinity and pH. Precipitation of low silica BIF followed and, in the presence of sufficient Mn activity with increasing Eh in the precipitating water stratum, deposition of the Mn mineral associations occurred.

India's Mineral Potential: Present Status and Future Trends

This paper outlines the potential of India's mineral resources, which comprise a wide range of deposit types scattered across the subcontinent, within an area of 3,287,590 km2. The geological environment is extremely diverse, ranging from extensive Archean cratonic nuclei, with large areas of high-grade metamorphic rocks of lower-crustal provenance, to Proterozoic sedimentary basins and mobile belts, to Tertiary mountain ranges and Quaternary surficial deposits. The mineral endowment of these disparate regions includes world-class deposits of iron, manganese, and chromium, plus base metals (copper, lead, zinc), precious metals, and a spectrum of nonmetallic resources from bauxite to gemstones. India is a major exporter of Fe ore, Mn ore, chromite, mica, and granite. The Exclusive Economic Zone (EEZ) around the shores of India totals 2,014,900 km2, 61% the size of the landmass, holding additional potential for commodities such as heavy mineral sands (monazite, rutile, and other materials) and Mn and Co-rich ferromanganese nodules and crusts. A selective overview of India's mineral potential is provided with reference to 22 metals and groups of metals and 6 non-metallic commodity groups, excluding fuels. These are Cu, Zn, Pb, and Ag; Fe, Ti, V, and Mn; Cr, Ni, Co, and PGE; Au; Sn, W, and Mo; Nb, Ta, and Li; bauxite; U, Th, and the REE; barite, garnet, and graphite; and diamonds and colored gemstones. The effectiveness of the domestic mineral industry in locating and exploiting these resources varies greatly among commodities. Some sectors where the country was once a noted producer, such as diamonds and gold, have been eclipsed by major discoveries in other lands and by stagnant domestic output. In some cases, such as gold and nickel, known reserves and output are small compared to both the area of prospective terrain and high domestic demand (Table 1). Some indication is provided of likely future trends, in view of the Government of India's current initiatives to entice foreign investment in many sectors. This recently developed open policy extends to exploration and mining ventures, construction of power generation units, and modernization of existing industrial plant, transport, and communications. With an eye on this mineral-economic context, we present a synthesis of the issues faced by the mineral sector as it enters the 21st century.

The Fe [sbnd]Mn ore deposits of Urucum, Brazil: An oxygen isotope study

The Fe Mn ore deposits of Urucum are located close to the Brasilian-Bolivian border. They appear to be considerably younger (Late Proterozoic) than most other banded iron ore formations. The Mn ores occur in three or four well-defined beds. Oxygen isotope determinations have been carried out in Fe-poor and Fe-rich layers and on a few Mn ores. Due to the extremely small grain size, a conventional mineral separation was impossible. However, since the banded iron ores consist of two components only (SiO 2 and Fe 2O 3), a determination of the Fe content allows a calculation of the oxygen isotope composition of the pure end-members. The so calculated δ 18O-values vary between +21.3 and +26.4‰ for quartz and between +0.8 and +6.5‰ for hematite. Isotope equilibrium may have been reached in some but not all samples. Calculated temperatures vary between 250° and 280°C, depending upon which calibration curve is used. Such temperatures are higher than indicated by maximum burial depths. The δ 19O-values appear to reflect diagenetic and burial metamorphic conditions rather than primary conditions.