Banded Ores Research Articles

Mossbauer studies of the iron ore band associated with the meta-acidic intrusive of Chamoli, Garhwal Himalaya

A 1 m thick iron ore band, associated with the meta-acidic intrusive of the carbonate suite of Chamoli (Garhwal Himalaya), has been studied. Microscopic observations, chemical and Mossbauer analyses were performed on three samples obtained from the top, middle and bottom parts of this ore band. Magnetite, haematite and stilpnomelane are common in all three samples. The middle part of the ore band is rich in magnetite, whereas the top part contains largely haematite. Magnetite and haematite from the middle part contain less impurities than those from the margins, whereas stilpnomelane from top and bottom is purer than that from the middle portion. These variations have been correlated with the differential stresses and remobilisation within the band caused by the minor movements of rocks along the upper surface of the ore band.

Die Flu�spat- und Bleiglanzvererzung in Karbonatgesteinen der Sierra de Baza, S�dspanien

The triassic sediments of the Sierra de Baza contain deposits of galena and fluorspar, partly under exploitation. After a survey of stratigraphy and tectonics of the mineralised series follows a description of the occurring ore types including stratiform banded “Zebra ores” and homogeneous vein fillings. The banded ores, because of their structures and textures, are regarded as synsedimentary formations, while the vein ore is presumed to be a product of mobilisation of the primary mineralisation.

Infrared Spectra of {Y3}[Mgy M 2-y](M 3-ySiy)O12 Garnets (M=Al3+, Fe 3+, Ga3+, y=0. 0 to 2. 0)

IR spectra in the region from 1200 to 200 cm-i of the garnet selid solutions 1{Ys}[MgvMa, ](MsntvSiy)Ois (M=AIS, FeS, GaS, y=O. O te 2, 0) have been studied systematically and strongly localized group vibration of isolated tetrahedren er octahedren was feund. The spectra assigried to stretching vibratiofi, y3, of tetrahedra, AIOt, FeOa, and GaO4, splitted intothree bands in y=O, O co ositi n Qf each s 1id sdut n 3 bands f A10'degenerqted into two bands at y l O.5, but those of FeOi or GaO' degenerated into oRe band at y 41.5 (Tables 1, 2 and 3, Fig.1, 2 and 3). ys bands shifted toward lower frequency with increasing y value for AIO' (substituting octahedral AIS by Mgg) but not remarkably for FeO4 or GaO4 (substituting octahedral Feg or GaS by Mg) (Fig.4). From these results and the report of McDevitt, it is concluded that the frequency of ys vibration of tetrahedron is affected by the ionic radius, that is, ionic field strength of neighbeuring dodecahedral and octahedral cations. The similar frequency shifts were also evident in the case of ys bands of SiO' (Fig.5). The difference of degeneration tendeney of v3 bands between AIO' and FeOt or GaOd suggests that the bonding character of FeO, or GaOA differs from that of AIO': the interaction of FeO' or GaO' with the garnet lattice seems to be small comparing with that ef AIO'. The bands assigned to stretching vibration of oetahedron were 520, 474, and 438 cmmi for AIO6, 382 and 362 cm-i for FeOs, 466, 400, and 342 cm-i for GaOs, and 400. v350 cm'i for MgO6, respectively.

The Precambrian Banded Iron-Formations of the Soviet Union

The Precambrian iron-formations in the European part of the Soviet Union occur mainly along a trend which can be followed between the Azov Sea coastal region in the south and Kola Peninsula in the north. The deposits of Krivoy Rog and Kremenchug, within the Ukrainian Shield, and those of the Kursk magnetic anomalies (Voronezh plate) form a gigantic metallogenic province. Precambrian banded ores also occur in the Urals and the Asiatic part of the Soviet Union in the cores of Caledonian and Hercynian orogenic belts.Lithologically the iron-formations consist of intercalated, rather continuous bands of silica and iron oxides, or in rare cases, of iron carbonates (carbonate facies). Separate bands range in thickness from a fraction of a millimeter to several centimeters. The bands in turn are composed of microbands. The average iron content of the iron-formations is about 35 percent. The iron-formations are part of a marine geosynclinal sequence and typically are represented by magnetite and hematite facies, the latter being considered by most Russian geologists as the product of sedimentation in relatively deep water far offshore. They are part of the transgressive series. Most of the iron-formations of the Russian platform are thought to be correlative, but the detailed stratigraphy, such as the number of banded ore members, differs from one locality to another. The iron-formation in Krivoy Rog consists of seven members having a total thickness of 1,300 m, whereas that of Kursk consists of five members having a thickness of 500 m.The iron-formations of the Russian platform are underlain by a formation consisting mainly of arkose, phyllite, schist, and quartzite, whereas they are overlain by a succession consisting mainly of carbonaceous shale or schist and dolomite.Reconstruction of the ancient environments in which the iron-formations were formed suggests deposition under both miogeosynclinal and eugeosynclinal conditions. The iron was concentrated in the middle formation of the sequence, corresponding to a sedimentary metallogenic epoch, which probably can be correlated throughout the gigantic metallogenic province of the Russian platform. The major iron-formations in the province are between 2,000 m.y. and 2,600 m.y. old. Some of the smaller iron-formations in other areas are apparently either older or younger than the main ones.Five hypotheses have been proposed to explain the origin of the Precambrian iron-formations and the banding. Among these, hypotheses for a sedimentary origin and a volcanic-sedimentary origin appear to be most realistic and best substantiated.

Banded sulphide ores: The experimental production of monomineralic sulphide bands in sediments

Banded sulphide ores of the McArthur River type are characterized by large numbers of conformable, monomineralic sulphide bands. These appear to have formed prior to consolidation of the host sediments. This paper describes a series of laboratory experiments designed to test the possibility that the bands could have been generated by the migration of metal, sulphide, and possibly carbonate ions through unconsolidated sedimentary materials or slowly settling suspensions. It is concluded that ionic migration processes probably occur during the formation of these banded sulphide ores, in conjunction with the deposition of metalliferous mud layers.

The Older Ortho-gneisses of Carn Chuinneag and Inchbae

A study of the ortho-gncisses in the Carn Chuinneag-Inchbae complex indicates that the main acid gneisses represent original pre-tectonic orthoclase granites. The earlier basic rocks have recrystallized to amphibolites characterized by a highly aluminous hornblende. The intermediate rocks of the complex are believed to have formed by a process of hybridization. The acid gneisses have been reclassified and mapped as separate divisions. The Lochan a'Chairn subdivision has been recognized. An analysis of the riebeckite from the riebeckite gneissic granite shows it to be similar to riebeckites from Nigeria and to contain more of the arfvedsonite component than riebeckite proper. An examination of the spread of albitization into the surrounding rocks from the garneti-ferous albite gneiss, and an analysis of the garnet, indicate that the emplacement of this gneiss, probably with the magnetite-cassiterite ore bands which are confined to it, took place late in the igneous cycle.

Iron formations in the southeastern United States; Discussion of Paleozoic banded iron-formations by J. E. O'Rourke (1961)

Discussion of GeoScience Abstracts 3-2780. Although early geological reports corroberate O9Rourke in emphasizing similarities between Precambrian banded Fe formation and Fe ores found in the southern Appalachians, this view has little basis in fact. Examples of Appalachian Fe deposits mentioned by O9Rourke as being comparable with Precambrian formations do not resemble one another in mineralogy, lithology, texture, or in any other diagnostic feature except that they both contain Fe. Ages and correlation of formations as given by O9Rourke are criticized in some detail.

GEOLOGICAL STRUCTURE OF THE SOUTH KHINGAN MANGANESE DEPOSIT AND ESSENTIAL COMPOSITION OF ITS ORES

The South Khingan manganese deposits are geologically a part of the Malyy Khingan manganeseiron ore district. The geological sequence of the region consists of Precambrian and Lower Cambrian sedimentary, sedimentary metamorphic, extrusive and intrusive rocks. The lower series are exposed in anticlines intruded by granites. The manganese ores are confined to the base of the ferruginous quartzite ore horizon, which is located in the middle part of the Lower Cambrian ore-bearing series. The latter lies transgressively but without apparent disconformity, on the eroded surface of Upper Sinian dolomites. The manganese ores are paragenetically associated with banded ferruginous quartzites and siliceous-argillaceous slates which contain variable amounts of dolomite.of chemical or clastic origin. The banded ore structure is characterized by rhythmic interbedding of ore and barren bands from 0. 10 to 10 cm thick. The essential ore-body minerals are braunite, hematite, hausmannite, magnetite, rhodochrosite, chalcedo...

Manganese silicate minerals from Chikla, Bhandara District, India

SummaryBlanfordite (a manganiferous aegirine), rhodonite, alurgite, manganophyllite, and piemontite are deseribed from a pegmatite that cuts a manganese ore band in the Sitasaongi mine, Chikla, Bhandara district, India. In addition, rhodonite and piemontite are described from gneiss and schist areas. Chemical analyses and optical properties of all these minerals are given and their possible origin suggested.

Contribution to studies of origin of Precambrian banded iron ores

The geochemical environment favorable for the formation of Precambrian banded iron ores is reconstructed and illustrated with results of experiments with the leaching of iron oxide and silica at different temperatures, at different pH ranges, and in the presence of certain elements in solution.It is suggested that the intermittent banding of silica and hematite in Precambrian banded ores is caused principally by the selective weathering of Precambrian soil. Due to the seasonal changes of temperature, amount of precipitation, and the alternately higher and lower pH range of the leaching solution, the Precambrian soil yielded alternately solutions carrying to the basin of deposition almost exclusively silica during the warm season and chiefly iron oxide during the cool period of the year.

Manganese amphiboles from Chikla, Bhandara district, India

The four amphiboles described in this paper were collected during the summer of 1950 from the Sitasaongi mine. This mine, which produces high-grade manganese ore, is situated in the Chikla area, Bhandara district, India. The ore band is 8 to 18 feet thick and is strongly folded and faulted at many places (fig. 1). The most common rock types in the area are: calc-granulites, calc-gneisses, mica-schists, quartzites, gondite (quartz-spessartine-rock), injection gneisses, and pegmatites. The pegmatites are the youngest and cut through the manganese-ore band as well as the country-rocks. All are of Archaean age.

Banded hematite ores; discussion

Shows in what respects the views differ on the origin of banded hematite ores expressed by himself and W. G. Woolnough in recent papers in Economic Geology vol. 36, nos. 4 and 5 and summarizes the conditions under which laterite forms.

Societies and Academies

Societies and Academies