SEM-EDS STUDY OF THE PLATINUM-GROUP MINERALS IN THE PGE MINERALIZED HANUMALAPURA SEGMENT OF THE LAYERED MAFIC-ULTRAMAFIC COMPLEX OF CHANNAGIRI, DAVANGERE DISTRICT, KARNATAKA (original) (raw)
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The Channagiri layered complex is located near the southeastern boundary of the Shimoga Greenstone Belt. It is predominantly an ultramafic complex. While a large part SEM-EDS study of outcrop samples from the PGE mineralized, layered Hanumalapura segment of the Channagiri mafic-ultramafic complex, has revealed that they contain a variety of platinum-group mineral inclusions. Among more than 25 different PGM's distinguished, sperrylite, stibiopalladinite, hollingworthite, keithconnite, mertieite II, laurite, ruarsite together with a suite of Pt and Pd alloys, constitute the more important carriers of PGE in the ore reefs. From the close association of PGM's with chromite-bearing host rocks, it is inferred that crystallization of chromite had the governing control over the concentration of PGE.
Open Geosciences, 2015
The Kondapalli Layered Complex (KLC) is a dismembered mafic-ultramafic layered intrusion, mainly composed of gabbroic and anorthositic rocks with subordinate ultramafics and chromitite. Chromitite occurs as lenses, pods, bands and disseminations. Platinum group of minerals (PGMs) occur as inclusions within chromite and silicates. The study indicates an inhomogeneous distribution of PGMs and distinct dominance of IPGEs over the PPGEs. The average ΣPGE content of chromite of KLC varies from 64 ppb to 576 ppb with Pt ranging from 5 to 495 ppb, Pd 5 to 191 ppb, Ir 3 to 106 ppb, Ru 3 to 376 ppb and Rh 3 to 135 ppb. The PGMs identified in the KLC indicate primary deposition of the IPGE, preceding chromite, indicating its orthomagmatic nature. Most of the PGM grains are usually below 10 μm. The identified PGMs are Laurite (RuS2), irarsite (Ir, As, S), iridosmine (Os, Ir), undetermined Os-Ir sulphide and Ru-Os-Ir-Zn alloys. Chromite also contains inclusions of pentlandite, millerite, chalco...
The Channagiri mafic-ultramafic complex constitutes the main lithounit of Hegdale Gudda Formation of the Shimoga Supracrustal Belt. Mapping at a scale of 1:2000 coupled with detailed petrological examination of the Platinum Group Element (PGE) mineralized 3.5 km x 0.3 km Hanumalapur segment of the complex has revealed that it is composed of outer gabbroic zone and central 100-150 m ultramafic zone. While V-Ti magnetite seams occupy the outer boundary of the ultramafic zone, several small isolated lenses/pods of anorthositic variation occur within the ultramafic zone itself. The complex is affected by penetrative deformation, hydrothermal alteration and low-grade metamorphism, which together have caused complete replacement of olivine and pyroxenes by chlorite, amphibole, epidote and carbonate. The gabbro forming outer zone is in the range of quartz gabbro-melagabbro and is strongly banded/foliated. The ultramafite in the central zone is a complex mix of the dominant fine (chromite-chlorite schist) and subordinate coarse grained units. The magnetite occupying the western interface zone is the typically coarse grained V-Ti variety whereas that on the eastern side includes narrow chromiferous lenses. PGE data obtained for the different units of Hanumalapur segment has revealed that only the central fine-grained ultramafite and the chromiferous lenses in the eastern magnetite seam host PGE mineralization of commercial interest with Pt+Pd values ranging from 1.5 to 6 ppm; the other lithologies of the segment as well as those constituting the remaining segments of Channagiri ultramafic complex and Hegdale Gudda Formation have not yielded positive anomalies of PGEmineralization. The governing control of chromite over the separation of PGE in the very early stages of magmatic crystallization is inferred taking into account the close association of PGE with the chromite-bearing units. The recorded textural relationships suggest that the PGEs remained virtually immobile during later penetrative alterations of the host rock.
2013
Ultramafic rocks comprising dunite, harzburgite, lherzolite, olivine webserite and websterite occur as intrusives in the form of small hillocks at Pindar into the granite-gneisses of Bundelkhand Gneissic Complex (BnGC). The peridotites are dominated by olivine cumulates where chromite and precious metal-bearing sulphides crystallized along with pyroxenes, subsequent to crystallization of olivine into the interstitial spaces of cumulates during cooling. Ultramafic rocks of Pindar are characterized by high MgO (up to 46.0 wt%) and FeO (up to 5.8 wt%); low SiO 2 (40.8 to 48.0 wt%), TiO 2 (0.2 to 0.5 wt%), Al 2 O 3 (∼3.2 wt% av.), CaO (∼2.7 wt% av.) and Cu (11 to 73 μg/g). Cr and Ni values range from 2297 to 3150 μg/g and 2434 to 2767 μg/g, respectively. Distribution of Ir (up to 20 ng/g), Ru (27 to 90 ng/g), Rh (3 to 14 ng/g), Pt (18 to 72 ng/g), Pd (10 to 27 ng/g) and Au (22 to 57 ng/g) indicate platinum group element (PGE) and associated gold mineralization in these ultramafic rocks. A mineral phase representing sperrylite (PtAs 2) was also identified within the sulphides in scanning electron microscopy with energy dispersive spectrometer (SEM-EDS) studies. The primitive mantle-normalized siderophile elements pattern shows platinum group element PGE (PPGE) enrichment (Rh, Pt, Pd). Discrimination diagrams of Pd/Ir vs. Ni/Cu, Pd/Pt vs. Ni/Cu, Cu/Pd vs. Pd, and Cu vs. Pd for the peridotites of Pindar attribute to affinity towards komatiite magma, derived from high degree of partial melting of prolonged depleted mantle, and the sulphur saturation condition incurred during the crystallization of chromite which was favourable for PGE mineralization.
Journal of the Geological Society of India, 2019
The results of SEM-EDS and XRD, indicating the presence of PGE in stratified vanadium bearing magnetite-ilmenite ore, hosted by layered ultramafic-mafic complex in a part of east-central Karbi Anglong district, Assam (NE India) are reported here. The initial XRD data indicate presence of PGE minerals like braggite, laurite and cooperite; the SEM-EDS indicate variable wt. % of PGE and rare metals like 11.58% Re and gold. The highest weight % value is 19.55 Pt; 13.83 Ir; 7.36 Os; 0.95 Pd and 0.45 Ru. Plume model has been cited as the key factor causing high partial melting of the upper mantle in back arc rift environment, producing platinum rich but sulphur poor magma, subsequently acquiring sulphur from pelites of Shillong Group, thereby, gaining PGE.