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This paper discusses the porphyry copper mineralization in A‐type granitoids from the Precambrian shield of the Karbi Hills (Mikir Hills), NE India. The prospective zone lies in the Kuthori‐Bagori of Kaziranga locality of the north Karbi Hills. The host granitoids are characterized by intermediate to high SiO2 (66.30–72.97 wt.%), Na2O (up to 4.90 wt.%), Ba (up to 1,943 ppm), Zr (up to 410 ppm), Y (up to 70 ppm) and Al2O3 (up to 14.77 wt.%) with low concentrations of CaO (up to 1.53 wt.%), and Cu (up to 32.41 ppm) which suggest a consistent granodiorite‐monzogranite host composition, an intraplate emplacement, A‐type chemistry, shoshonitic to high‐K calc‐alkaline and a predominant metaluminous character. Minerals in the investigated granitoids show hypogene alteration features similar to ideal porphyry style mineralization. Remnants of early chalcopyrite‐bornite‐magnetite (Magnetite‐I) veins have been preserved in the distant propylitic zone. The central core zone of potassic alteration shows the dominance of pyrite‐chalcopyrite‐magnetite (Magnetite‐II) assemblages. Mineral chemistry confirms the presence of two types of magnetites: magmatic (Mag‐I) and hydrothermal (Mag‐II). Mag‐I is octahedral, less commonly cubic, or irregular. It has a porous core with trellis‐type ilmenite exsolution lamellae. Mag‐II is non‐porous, devoid of ilmenite exsolution lamellae, has irregular to distinctly octahedral crystal habit and contains micro‐inclusions of pyrite, chalcopyrite, aluminosilicates, manganite and apatite. The progressive chemical purification of igneous magnetite, exacerbated by hydrothermal re‐equilibration, has resulted in a significant reduction in trace element contents such as Ti, Al, Mg, Zn and Cr, and a significant increase in iron content from 89 to ~94 wt.%. A combination of [Ni/(Cr + Mn) vs. Ti + V], and [(Ca + Al + Mn) vs. Ti + V] variation diagrams and upper threshold concentrations for the Kuthori‐Bagori ore effectively separates Mag‐I and Mag‐II. Our field, petrographic and geochemical data indicate that the Kuthori‐Bagori of Kaziranga granitoid of the Karbi Hills (Mikir Hills) in NE India is an ideal location for porphyry copper mineralization.

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.

The Kulamati gabbro-anorthosite complex in the Karbi Hills of the Shillong Plateau, north-east India is a newly discovered stratified Fe-Ti-V-bearing magmatic body that has been classified as a titano-magnetite ore. The host gabbro-anorthosite is found intruded into the Mesoproterozoic Shillong Group. The stratified Fe-Ti-V oxide body consists mostly of magnetite-rich and magnetite-poor layers. The magnetite-rich bands are composed of titanomagnetite, haematite, ilmenite, and coulsonite with minor Alspinel, while the mineral constituents of silicate bands contain plagioclase, clinopyroxene, olivine, apatite, and chlorite. Titaniferous magnetites display a wide variety of subsolvus features, including Al-spinel-magnetite-ulvöspinel exsolutions and crystallographically oriented ilmenite exsolutions, but magnetites are exclusively vanadiferous. Comprehensive chemical analyses show that the ore is rich in TiO 2 (10.98-12.78 wt%) and V 2 O 5 (1.32-1.47 wt%). Ti is attributed by the presence of rutile, titanite, and ilmenite, while V is attributed by coulsonite as a solid solution component in the titanomagnetite. It records moderate to high Al 2 O 3 (4.51-5.46 wt%), with enrichment of FeO and Fe 2 O 3 (26.22-28.32 wt% and 39.34-42.86 wt%, respectively), which can be attributed to the presence of magnetite-spinel-ulvospinel. Higher Fe 2 O 3 and lower FeO are indicative of oxidizing conditions of the ore-forming environment. The rare earth element (REE) patterns have (La/Yb) N and (Ce/Yb) N ratios comparable to an evolved basaltic melt, with light REE being enriched compared to heavy REE and a positive Eu anomaly. The electron probe micro analyser data of magnetite is conformable with the bulk chemistry, and shows consistently high FeO (70.87-88.06 wt%), Cr 2 O 3 (1.02-2.44 wt%), TiO 2 (0.16-6.20 wt%), and V 2 O 3 (1.47-2.26 wt %), with trace amounts of Al, Si, Mg, Mn, and PGE. As per targeted parameters, the ore occurrence distinctly belongs to a stratified Fe-Ti-V class, where alternate thick (>1.0 m) and thin (<20 cm) strata resulted from the late magmatic crystallization of the original tholeiitic composition.