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The Chromite Deposits of Selukwe, Rhodesia

By
P. Cotterill
P. Cotterill
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Published:
January 01, 1969

Abstract

The rock types and the structure of the Selukwe area are briefly described. The chromiferous peridotite intrusions were involved in an orogeny, metasomatized, and partly eroded before Bulawayan sediments were deposited. In a subsequent late Bulawayan orogeny a large nappe formed and the peridotites were further sheared and metasomatized. The Pre-Shamvaian rocks in the Selukwe district lie in the eroded remnant of the inverted lower limb of the nappe.

Chromite deposits formed by magmatic segregation as cumulate layers on definite horizons in the differentiating ultrabasic intrusion. Thick layers accumulated in down-warps of the chamber floor. Primary magmatic textures and structures occur in the chromite layers. Two types of chromite ore grain are recognized—"main crop" forming the bulk of the ore similar in form to some varieties of "Alpine" type ore grains; and "second crop" grains similar in habit to "Stratiform" type grains.

At least twice after accumulation, metasomatism of sheared chromite and peridotite has modified the chemical constitution of the chromite ores and of the peridotites.

Typical chromitites are rich in Cr and Mg and poor in Fe, Al, and Mn. A few are rich in Cr, Fe, Al, and Mn, and poor in Mg.

The Selukwe deposits show primary characteristics of both Alpine and Stratiform type deposits.

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Contents

Society of Exploration Geophysicists Geophysical Monograph Series

Magmatic Ore Deposits

H. D. B. Wilson
H. D. B. Wilson
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Society of Economic Geologists
Volume
4
ISBN electronic:
9781934969991
Publication date:
January 01, 1969

GeoRef

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