Mineralogy, geochemistry and petrogenesis of the V-Ti-bearing and chromiferous magnetite deposits hosted by Neoarchaean Channagiri Mafic-Ultramafic Complex, Western Dharwar Craton, India: Implications for emplacement in differentiated pulses

2014 ◽  
Vol 6 (4) ◽  
Author(s):  
Tadasore Devaraju ◽  
Kallada Jayaraj ◽  
Thavaraghatta Sudhakara ◽  
Tuomo Alapieti ◽  
Beate Spiering ◽  
...  
Keyword(s):  
Dharwar Craton ◽  
Coarse Grained ◽  
Trace Element Geochemistry ◽  
Second Phase ◽  
Element Geochemistry ◽  
Silicate Mineral ◽  
Interface Zone ◽  
Fine Grained ◽  
Ultramafic Complex ◽  
Late Stages

AbstractThe Channagiri Mafic-Ultramafic Complex occupies lowermost section of the Neoarchaean Shimoga supracrustal group in the Western Dharwar Craton. It is a segmented body occupying the interdomal troughs of granitoids. The magnetite deposits occur in the northeastern portion; typically occupying the interface zone between gabbro and anorthositic. Mineralogically, the deposits are simple with abundant magnetite and ilmenite. Hogbomite is a consistent minor mineral. Magnetites are typically vanadiferous (0.7–1.25% V2O5). Ilmenite consistently analyses more MgO and MnO than coexisting magnetite. Chlorite, almost the only silicate present; lies in the range of ripidolite, corundophilite and sheridanite. The chromiferous suit occupying eastern side of Hanumalapur block (HPB) contains Fe-Cr-oxide analysing 37.8–11.9% Cr2O3 and 40.5–80% FeOt. In these too, chlorite, typically chromiferous (0.6–1.2% Cr2O3), is the most dominant silicate mineral. Geochemistry of V-Ti-magnetite is dominated by Fe, Ti and V with Al, Si, Mg and Mn contributing most of the remaining. Cr, Ni, Zn, Co, Cu, Ga and Sc dominate trace element geochemistry. The Cr-magnetite is high in Cr2O3 and PGE. Two separate cycles of mafic magmatism are distinguished in the CMUC. The first phase of first cycle, viz., melagabbro-gabbro, emplaced in the southeastern portion, is devoid of magnetite deposits. The second phase, an evolved ferrogabbroic magma emplaced in differentiated pulses, occupying northeastern portion of the complex, consists of melagabbro→gabbro-anorthosite→V-Ti magnetite→ferrogabbro sequence. Increase in oxygen fugacity facilitated deposition of V-Ti magnetite from ferrogabbroic magma pulse emplaced in late stages. The second cycle of chromiferous PGE mineralized suite comprises fine-grained ultramafite→alternation of pyroxinite-picrite→Crmagnetite sequence formed from fractionation of ferropicritic magma. HPB also includes >65m thick sill-like dioritic phase at the base of the ferriferous suit and a sinuous band of coarse-grained ultramafite enclosed within the chromiferous suit; both unrelated to the two mafic magmatic cycles.

Oxygen, carbon and strontium isotope study of the carbonatitic dolomite host of the Bayan Obo Fe-Nb-REE deposit, Inner Mongolia, N China

1997 ◽  
Vol 61 (407) ◽  
pp. 531-541 ◽  
Author(s):  
M. J. Le Bas ◽  
B. Spiro ◽  
Yang Xueming
Keyword(s):  
Sedimentary Rocks ◽  
Coarse Grained ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
Fine Grained ◽  
Dolomite Marble ◽  
Ore Body ◽  
Ore Bodies ◽  
Isotope Study ◽  
Bayan Obo

AbstractThe large Fe-Nb-REE deposit at Bayan Obo is hosted by a dolomite marble within the thrust complex of marbles, quartzites and slates that belongs to the Bayan Obo Formation of mid-Proterozoic age. The dolomite is either a dolomitized sedimentary limestone subsequently mineralized and tectonically thrust and folded, or a dolomite (or dolomitized) carbonatite intrusion with late-stage recrystallization and mineralization that has been subsequently tectonically deformed.O and C isotope data indicate that the sedimentary limestones and dolomites of the Bayan Obo Formation, which occur in the thrust stack together with quartzites and slates, have values of δO c. +20 per mil (SMOW) and δC c. zero. In contrast, the coarser grained facies of the large (0.5 × 10 km) dolomite marble which hosts the REE ore body has δO per mil values between +8 and +12 and δC values between −5 and −3, whereas the finer-grained recrystallized and REE-mineralized dolomite marble which occurs close to the ore bodies has δO between +12 to +16 and δC between −4 and zero. 87Sr/86Sr data confirm this distinction: >0.710 for the sedimentary rocks and <0.704 for the coarse- and fine-grained dolomite marbles.These data are taken to indicate that the large and coarse-grained dolomite was an igneous carbonatite (as borne out by its fenitic contact rocks and trace element geochemistry), and that the finer grained dolomite recrystallized under the influence of mineralizing solutions which entrained groundwater. The stratiform features in the coarse-grained dolomite that are evident in the field are interpreted as tectonic layering.

Microstructural Refinement in a Commercial Aluminum Alloy Processed by ECAP Using a Die Channel Angle of 110 Degrees

2015 ◽  
Vol 1114 ◽  
pp. 3-8
Author(s):  
Nicolae Şerban ◽  
Doina Răducanu ◽  
Nicolae Ghiban ◽  
Vasile Dănuţ Cojocaru
Keyword(s):  
Grain Refinement ◽  
Cross Section ◽  
High Strength ◽  
Secondary Phase ◽  
Coarse Grained ◽  
Metallographic Analysis ◽  
Second Phase ◽  
Channel Angle ◽  
Ambient Temperatures ◽  
Fine Grained

The properties of ultra-fine grained materials are superior to those of corresponding conventional coarse grained materials, being significantly improved as a result of grain refinement. Equal channel angular pressing (ECAP) is an efficient method for modifying the microstructure by refining grain size via severe plastic deformation (SPD) in producing ultra-fine grained materials (UFG) and nanomaterials (NM). The grain sizes produced by ECAP processing are typically in the submicrometer range and this leads to high strength at ambient temperatures. ECAP is performed by pressing test samples through a die containing two channels, equal in cross-section and intersecting at a certain angle. The billet experiences simple shear deformation at the intersection, without any precipitous change in the cross-section area because the die prevents lateral expansion and therefore the billet can be pressed more than once and it can be rotated around its pressing axis during subsequent passes. After ECAP significant grain refinement occurs together with dislocation strengthening, resulting in a considerable enhancement in the strength of the alloys. A commercial AlMgSi alloy (AA6063) was investigated in this study. The specimens were processed for a number of passes up to nine, using a die channel angle of 110°, applying the ECAP route BC. After ECAP, samples were cut from each specimen and prepared for metallographic analysis. The microstructure of the ECAP-ed and as-received material was investigated using optical (OLYMPUS – BX60M) and SEM microscopy (TESCAN VEGA II – XMU). It was determined that for the as-received material the microstructure shows a rough appearance, with large grains of dendritic or seaweed aspect and with a secondary phase at grain boundaries (continuous casting structure). For the ECAP processed samples, the microstructure shows a finished aspect, with refined, elongated grains, also with crumbled and uniformly distributed second phase particles after a typical ECAP texture.

Microstructure, Texture and Recrystallisation Mechanisms of an Al-20%Sn Deformation Processed Metal-Metal Composite

2012 ◽  
Vol 715-716 ◽  
pp. 522-527 ◽  
Author(s):  
Rafael Schouwenaars ◽  
Hugo A. Duran ◽  
Víctor H. Jacobo ◽  
Armando Ortiz
Keyword(s):  
Phase Distribution ◽  
Rolling Texture ◽  
Coarse Grained ◽  
Al Alloy ◽  
Second Phase ◽  
Metal Composite ◽  
Fine Grained ◽  
Texture Change ◽  
Metal Metal ◽  
Cold Rolled

Al-Sn alloys for tribological applications are industrially important alloys which have attracted little attention over their history. Being cold rolled directly from thin cast slabs and consisting of two ductile phases, their processing and physical behaviour are distinct from classical Al-Alloys. During cold rolling, the coarse-grained, random texture of the slab is transformed into the classical rolling texture of a fine-grained Al-alloy, with elongated Al-grains delimited by thin Sn-ribbons. During annealing at 300°C, the interior of the Al-grains recrystallises rapidly while the liquid Sn-phase migrates toward Al-grain triple lines to form a reticular structure. A weak texture, dominated by Goss and P is produced. Grain growth within the original cold-rolled grains is fast, but once the recrystallised grain size reaches the length scale of the second-phase distribution, it slows down and both phases coarsen simultaneously, accompanied by a significant texture change.

scholarly journals Lithosphere tearing along STEP faults and synkinematic formation of lherzolite and wehrlite in the shallow subcontinental mantle

Solid Earth ◽  
2019 ◽  
Vol 10 (4) ◽  
pp. 1099-1121 ◽  
Author(s):  
Károly Hidas ◽  
Carlos J. Garrido ◽  
Guillermo Booth-Rea ◽  
Claudio Marchesi ◽  
Jean-Louis Bodinier ◽  
...  
Keyword(s):  
Grain Size ◽  
Lithospheric Mantle ◽  
Volcanic Field ◽  
Mantle Xenoliths ◽  
Coarse Grained ◽  
Fault System ◽  
Mantle Flow ◽  
Second Phase ◽  
Fine Grained ◽  
Wide Range

Abstract. Subduction-transform edge propagator (STEP) faults are the locus of continual lithospheric tearing at slab edges, resulting in sharp changes in the lithospheric and crustal thickness and triggering lateral and/or near-vertical mantle flow. However, the mechanisms at the lithospheric mantle scale are still poorly understood. Here, we present the microstructural study of olivine-rich lherzolite, harzburgite and wehrlite mantle xenoliths from the Oran volcanic field (Tell Atlas, northwest Algeria). This alkali volcanic field occurs along a major STEP fault responsible for the Miocene westward slab retreat in the westernmost Mediterranean. Mantle xenoliths provide a unique opportunity to investigate the microstructures in the mantle section of a STEP fault system. The microstructures of mantle xenoliths show a variable grain size ranging from coarse granular to fine-grained equigranular textures uncorrelated with lithology. The major element composition of the mantle peridotites provides temperature estimates in a wide range (790–1165 ∘C) but in general, the coarse-grained and fine-grained peridotites suggest deeper and shallower provenance depth, respectively. Olivine grain size in the fine-grained peridotites depends on the size and volume fraction of the pyroxene grains, which is consistent with pinning of olivine grain growth by pyroxenes as second-phase particles. In the coarse-grained peridotites, well-developed olivine crystal-preferred orientation (CPO) is characterized by orthorhombic and [100]-fiber symmetries, and orthopyroxene has a coherent CPO with that of olivine, suggesting their coeval deformation by dislocation creep at high temperature. In the fine-grained microstructures, along with the weakening of the fabric strength, olivine CPO symmetry exhibits a shift towards [010] fiber and the [010] and [001] axes of orthopyroxene are generally distributed subparallel to those of olivine. These data are consistent with deformation of olivine in the presence of low amounts of melts and the precipitation of orthopyroxenes from a melt phase. The bulk CPO of clinopyroxene mimics that of orthopyroxene via a topotaxial relationship of the two pyroxenes. This observation points to a melt-related origin of most clinopyroxenes in the Oran mantle xenoliths. The textural and geochemical record of the peridotites are consistent with interaction of a refractory harzburgite protolith with a high-Mg no. melt at depth (resulting in the formation of coarse-grained clinopyroxene-rich lherzolite and wehrlite) and with a low-Mg no. evolved melt in the shallow subcontinental lithospheric mantle (forming fine-grained harzburgite). We propose that pervasive melt–peridotite reaction – promoted by lateral and/or near-vertical mantle flow associated with lithospheric tearing – resulted in the synkinematic crystallization of secondary lherzolite and wehrlite and had a key effect on grain size reduction during the operation of the Tell–Rif STEP fault. Melt–rock reaction and secondary formation of lherzolite and wehrlite may be widespread in other STEP fault systems worldwide.

The use of magnetic susceptibility and trace element geochemistry for the correlation of fine-grained siliciclastic sequences: a Late Llandovery example from northwest England

1999 ◽  
Vol 136 (4) ◽  
pp. 423-436 ◽  
Author(s):  
L. T. P. ENGLISH
Keyword(s):  
Magnetic Susceptibility ◽  
Bottom Water ◽  
Sediment Accumulation ◽  
Clay Mineralogy ◽  
Manganese Carbonate ◽  
Trace Element Geochemistry ◽  
Accumulation Rates ◽  
Element Geochemistry ◽  
Fine Grained ◽  
Water Oxygen

High-resolution lithological and magnetic susceptibility logs were made of two sections of the Upper Llandovery Browgill Formation in northwest England: Stockdale Beck, the type section of the Browgill Formation, and Spengill. The Browgill Formation is composed of fine-grained deep marine siliciclastics, which can be divided broadly into two facies: a homogeneous grey mudstone, deposited under oxygenated bottom-water conditions, and subordinate beds of laminated, graptolite-bearing black mudstone deposited under low bottom-water oxygen levels. The latter facies is often partially or fully diagenetically altered to chlorite nodules, occasionally with manganese carbonate nucleii. Magnetic susceptibility logs are shown to reflect variations in the illite–chlorite ratio of the clay mineralogy. Chlorite is a paramagnetic mineral, so the bands of chlorite nodules produce magnetic susceptibility highs. Correlation demonstrates that diagenetically altered beds of laminated black mudstone are continuous between the two sections, now situated 32 km apart. This lateral continuity would favour pelagic fallout in preference to gravity flow as a depositional model for both facies. A correlated sequence within the turriculatus Biozone is 3.8 times thicker at Spengill than at Stockdale Beck, probably reflecting variations in sediment accumulation rates. Correlation also identifies significant non-sequences in both sections: at least 47% of the turriculatus Biozone (including maximus Sub-biozone) is missing at Stockdale Beck and at least 77% of the crispus Biozone is missing at Spengill. The identification of non-sequences may be of value for refining graptolite biostratigraphy.

scholarly journals Lithosphere tearing along STEP faults and synkinematic formation of lherzolite and wehrlite in the shallow subcontinental mantle

2019 ◽  
Author(s):  
Károly Hidas ◽  
Carlos J. Garrido ◽  
Guillermo Booth-Rea ◽  
Claudio Marchesi ◽  
Jean-Louis Bodinier ◽  
...  
Keyword(s):  
Grain Size ◽  
Lithospheric Mantle ◽  
Volcanic Field ◽  
Mantle Xenoliths ◽  
Coarse Grained ◽  
Fault System ◽  
Mantle Flow ◽  
Second Phase ◽  
Fine Grained ◽  
Wide Range

Abstract. Subduction-Transform Edge Propagator (STEP) faults are the locus of continual lithospheric tearing at slab edges, resulting in sharp changes in the lithospheric and crustal thickness and triggering lateral and/or near-vertical mantle flow. However, the mechanisms at the lithospheric mantle scale are still poorly understood. Here, we present the microstructural study of olivine-rich lherzolite, harzburgite and wehrlite mantle xenoliths from the Oran volcanic field (Tell Atlas, NW Algeria). This alkali volcanic field occurs along a major STEP fault responsible for the Miocene westward slab retreat in the westernmost Mediterranean. Mantle xenoliths provide a unique opportunity to investigate the microstructures in the mantle section of a STEP fault system. The microstructures of mantle xenoliths show a variable grain size ranging from coarse granular to fine-grained equigranular textures uncorrelated with modal variations. The major element composition of the mantle peridotites provides temperature estimates in a wide range (790–1165 °C) but in general, the coarse-grained and fine-grained peridotites suggest deeper and shallower provenance depth, respectively. Olivine grain size in the fine-grained peridotites depends on the size and volume fraction of the pyroxene grains, which is consistent with pinning of olivine grain growth by pyroxenes as second phase particles. In the coarse-grained peridotites, well-developed olivine crystal preferred orientation (CPO) is characterized by orthorhombic and [100]-fiber symmetries, and orthopyroxene has a coherent CPO with that of olivine, suggesting their coeval deformation by dislocation creep at high-temperature. In the fine-grained microstructures, along with the weakening of the fabric strength, olivine CPO symmetry exhibits a shift towards [010]-fiber and the [010]- and [001]-axes of orthopyroxene are generally distributed subparallel to those of olivine. These data are consistent with deformation of olivine in the presence of low amounts of melts and the precipitation of orthopyroxenes from a melt phase. The bulk CPO of clinopyroxene mimics that of orthopyroxene via a topotaxial relationship of the two pyroxenes. This observation points to a melt-related origin of most clinopyroxenes in the Oran mantle xenoliths. The textural and geochemical record of the peridotites are consistent with interaction of a refractory harzburgite protolith with a high-Mg# melt at depth (resulting in the formation of coarse-grained clinopyroxene-rich lherzolite and wehrlite), and with a low-Mg# evolved melt in the shallow subcontinental lithospheric mantle (forming fine-grained harzburgite). We propose that pervasive melt-peridotite reaction – promoted by lateral and/or near-vertical mantle flow associated with lithospheric tearing – resulted in the synkinematic crystallization of secondary lherzolite and wehrlite and played a key effect on grain size reduction during the operation of the Rif-Tell STEP fault. Melt-rock reaction and secondary formation of lherzolite and wehrlite may be widespread in other STEP fault systems worldwide.

scholarly journals Kivilompolo Mo mineralization in the Peräpohja belt revisited: Trace element geochemistry and Re-Os dating of molybdenite

2020 ◽  
Vol 92 (2) ◽  
pp. 131-150
Author(s):  
Jukka-Pekka Ranta ◽  
◽  
Eero Hanski ◽  
Holly Stein ◽  
Matthew Goode ◽  
...  
Keyword(s):  
Uranium Mineralization ◽  
Coarse Grained ◽  
Geochemical Data ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
Zircon Age ◽  
Porphyritic Granite ◽  
Quartz Veins ◽  
Nappe Complex ◽  
Magmatic Fluids

The Kivilompolo molybdenite occurrence is located in the northern part of the Peräpoh jabelt, within the lithodemic Ylitornio nappe complex. It is hosted within a deformed porphyritic granite belonging to the pre-orogenic 1.99 Ga Kierovaara suite. The minerali-zation occurs mostly as coarse-grained molybdenite flakes in boudinaged quartz veins, with minor chalcopyrite, pyrite, magnetite, and ilmenite. In this study, we report new geochemical data from the host-rock granite and Re-Os dating results of molybdenite from the mineralization. For the whole-rock geochemistry, the mineralized granite is similar to the Kierovaara suite granites analyzed in previous studies. Also, the ca. 2.0 Ga Re-Os age for molybdenite is equal, within error, to the U-Pb zircon age of the Kierovaara suite granite. In addition, similar molybdenite and uraninite ages have been reported from the Rompas-Rajapalot Au-Co occurrence located 30 km NE of Kivilompolo. We propose that the magmatism at around 2.0 Ga ago initiated the hydrothermal circulation that was responsible for the formation of the molybdenite mineralization at Kivilompolo and the primary uranium mineralization associated with the Rompas-Rajapalot Au-Co occurrence or at least, the magmas provided heating, and in addition potentially saline magmatic fluids and metals from a large, cooling magmatic-hydrothermal system.

Volcanic clays in the Cretaceous of southern England and Northern Ireland

Clay Minerals ◽  
1982 ◽  
Vol 17 (1) ◽  
pp. 105-156 ◽  
Author(s):  
C. V. Jeans ◽  
R. J. Merriman ◽  
J. G. Mitchell ◽  
D. J. Bland
Keyword(s):  
Northern Ireland ◽  
Western Europe ◽  
Upper Cretaceous ◽  
Isotope Analysis ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
Southern England ◽  
Fine Grained ◽  
The North ◽  
The North Sea

AbstractThe mineralogy, petrology and trace element geochemistry of volcanogenic glauconites and smectite-rich clays are described and related to clay assemblages in Lower and Upper Cretaceous sediments of southern England and Northern Ireland. Volcanogenic glauconite grains represent argillized lava particles of predominantly mafic composition and may have been derived from submarine basaltic magmatism; they occur in all the sediments examined (Aptian-Senonian), and are particularly abundant in the Cenomanian-Campanian Hibernian Greensand of Antrim. The smectite-rich clays in southern England have developed by the argillization of predominantly acid or alkaline ash during early diagenesis. Three types of volcanogenic deposit are recognized. Primary bentonites are thin ash-falls deposited in quiet, brackish and marine waters (Speeton Clay, Ryazanian; Weald Clay, Barremian). Secondary bentonites are local accumulations of ash transported into the Cretaceous seas by rivers draining ash-blanketed, local land areas (London Platform, Portsdown Axis). These deposits are well-developed in the Sandgate Beds, Folkestone Beds and their contiguous deposits, and the lower part of the Gault (Upper Aptian-Middle Albian). The ash originated from penecontemporaneous, subaerial vulcanism located in the southern part of the North Sea. The most conspicuous phase of activity occurred during late Aptian times and has been dated by 40Ar/39Ar isotope analysis at 112 m.y. Bentonitic clays and marls are widespread accumulations of argillized ash that occur as a fine-grained fringing facies to glauconitic quartz sand facies. They make up the upper part of the Atherfleld Clay (Aptian) and the upper part of the Gault (Upper Albian), and they are associated respectively with the Hythe Beds (Aptian) and the Upper Greensand (Upper Albian). They may also occur in the lower part of the Lower Chalk (Cenomanian). The distribution pattern of these smectite-rich clays in southern England is related to the changing palaeogeography of the area in Cretaceous times, and the general coincidence of extensive glaueonite deposits and smectite-rich clays in the Middle and Upper Cretaceous of western Europe and along the eastern seaboard of North America is briefly discussed.

scholarly journals The Niederschlag fluorite-(barite) deposit, Erzgebirge/Germany—a fluid inclusion and trace element study

2021 ◽  
Author(s):  
Sebastian Haschke ◽  
Jens Gutzmer ◽  
Cora C. Wohlgemuth-Ueberwasser ◽  
Dennis Kraemer ◽  
Mathias Burisch
Keyword(s):  
Fluid Inclusion ◽  
Trace Element ◽  
Fluid Inclusions ◽  
Open Space ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
Fine Grained ◽  
Trace Element Study ◽  
Northern Atlantic ◽  
Homogenization Temperatures

AbstractThe Niederschlag fluorite-barite vein deposit in the Western Erzgebirge, Germany, has been actively mined since 2013. We present the results of a first comprehensive study of the mineralogy, petrography, fluid inclusions, and trace element geochemistry of fluorite related to the Niederschlag deposit. Two different stages of fluorite mineralization are recognized. Stage I fluorite is older, fine-grained, associated with quartz, and forms complex breccia and replacement textures. Conversely, the younger Stage II fluorite is accompanied by barite and often occurs as banded and coarse crystalline open-space infill. Fluid inclusion and REY systematics are distinctly different for these two fluorite stages. Fluid inclusions in fluorite I reveal the presence of a low to medium saline (7–20% eq. w (NaCl+CaCl2)) fluid with homogenization temperatures of 140–180 °C, whereas fluorite II inclusions yield distinctly lower (80–120 °C) homogenization temperatures with at least two high salinity fluids involved (18–27% eq. w (NaCl+CaCl2)). In the absence of geochronological data, the genesis of the earlier generation of fluorite-quartz mineralization remains enigmatic but is tentatively related to Permian magmatism in the Erzgebirge. The younger fluorite-barite mineralization, on the other hand, has similarities to many fluorite-barite-Pb-Zn-Cu vein deposits in Europe that are widely accepted to be related to the Mesozoic opening of the northern Atlantic Ocean.

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