ISSN:
1432-1866
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
Abstract The chromiferous ultramafic rocks of Sukinda Valley (21°0'–21°5'N:85°43'–86°0'E) of Orissa are intrusive into the Iron-Ore Supergroup (2,950–3,200 Ma) at the eastern periphery of the Indian Precambrian shield. Both laterally and vertically, chromite occurs as persistent layers, lenses or pockets in the serpentinized and silicified dunite-peridotite extending over a strike length of 25 km. The ultramafic rocks and the chromitite layers are cofolded with the Iron-Ore Supergroup into a plunging syncline. Primary layering, ball and pillow structures, cross laminations, graded bedding etc. can also be detected. The different varieties of chromite ore present in the area are massive, banded and spotted, laminated and friable. The grain size of chromite varies between 0.25 and 4 mm, and the fineness of the grain increases from the bottom to the top layers. The cell dimension of chromite (8.23–8.32 Å) decreases with the increase of Al2O3. Cr2O3 in pure chromite varies between 48 to 61 wt. percent, Al2O3 is 7.10–15.09 wt. percent, whereas Fe2O3 is very low (0.03–3.20 wt. percent). The amount of RO to R2O3 varies within a narrow limit of 0.98–1.13, indicating that the chromite is chemically balanced. The FeO to MgO ratio is intermediate between the stratiform and alpine type. Fe3+ and Al3+ increase with respect to Cr3+ and Mg2+ in the upper chromitite layers. TiO2 lacks significant correlation with the major element composition of chromite. It is concluded that the Sukinda Valley chromitites of Orissa are predominantly stratiform in nature and were presumably formed in situ by crystal settling, the layering having been accentuated by the fluctuation of FO2. The geological features suggest a single magmatic cycle.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00204378
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