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Mallik, A. K.
- Mineralogy, Chemical Characters and Genesis of the Chromite Deposits of Moulabhanja Area, Dhenkanal District, Orissa
Authors
1 Department of Geological Sciences, Jadavpur University, Calcutta, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 12, No 2 (1971), Pagination: 135-141Abstract
Pockets of 'sack-form' chromite deposit occur at the intersection of dykes of olivine gabbro near Moulabhanja hills in the Dhenkanal district of Orissa. The dykes intruded the Precambrian granite-gneiss belonging to the Eastern Ghat orogenic belt. Chromite also occurs as minor accessory in olivine gabbro; and in this respect differs in its mode of occurrence from chromite deposits associated with the dunite-peridotite of the Iron ore orogenic cycle. The close association of chromite with olivine gabbro, the paragenetic sequence of the minerals in the rock, and the mineralogy, texture and chemical nature of the ore, suggest that the chromite melt was separated from the basic (olivine gabbro) magma as an immiscible liquid fraction and crystallized earlier than the silicate minerals.- Petrology of the Basic Intrusive Rocks Around the Moulabhanja Hills in the Dhenkanal District of Orissa
Authors
1 Department of Geological Sciences, Jadavpur University, Calcutta, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 14, No 1 (1973), Pagination: 47-59Abstract
The Moulabhanja hills and the adjoining areas are underlain by Precambrian granite gneiss which is intersected by a variety of gabbroic dykes and stocks. Mineral assemblages and textural relationships point recognition of four types of gabbroic rocks which also represent critical stages of fractional crystallization, e,g., (i) olivine gabbro with essential olivine, pigeonite augite and bytownite (ii) hypersthene gabbro with essential hypersthene, augite and labradorite (iii) doleritic gabbro with essential augite and labradorite, and (iv) normal gabbro with augite and less calcic labradorite.
The chemical and normative mineral composition of the basic magma is tholeiitic. The magma seemingly differentiated into different types of gabbroic rocks by fractional crystallization and gradual enrichment in iron. Two analyses of the olivine gabbro lie on the transitional zone between tholeiitic and calc-alkali suite. The closing temperature ofcrystallization of the basic magma and the corresponding oxygen fugacity are estimated to be 600°C and 18.4 (-Log10 FO2) respectively.