Abstract

The Troodos massif is a well-developed ophiolite complex comprising a sequence of basaltic volcanic rocks overlying a plutonic complex of upper gabbros and lower peridotites containing podiform chromite deposits. The chromitiferous rocks range from disseminations and minor segregations of chromite in dunite to orebodies of economic size and grade composed of nearly pure chromitite. They display both primary textures, such as chromite net and occluded silicate texture of cumulate magmatic origin, and schlieren structures produced by deformation. Dendritic texture in nodular chromite is interpreted as a product of crystallization of a magma that was supersaturated and/or supercooled with respect to chromium. Unusual orbicular structures are thought to have formed by mechanical accretion of previously settled chromite grains around a nucleus of dunite.Chromite deposits occur mainly as isolated pods and layers either in the dunite near the harzburgite contact or in the harzburgite within dunite lenses or enclosed in a narrow dunitic envelope. Deposits show a wide range of reciprocal Cr-Al variation and have low iron oxidation values typical of "alpine" chromitites. The areal distribution of chemically and texturally different deposits of variable size and grade conforms to no recognizable pattern. Accessory chromite exhibits a trend of decreasing Cr and increasing Fe in the passage from dunite, through wehrlite, to picrite.It is concluded that the plutonic complex evolved as a differentiated body of magmatic cumulates laid down upon a basement of depleted mantle harzburgite. The chromitites originated as isolated magmatic segregation ore deposits near the base of the cumulate dunite during episodic crystallization at localized centers within the magma. Postcumulus mobilization and accompanying penetrative deformation of the lower ultramafic rocks caused the tectonic overprint of schlieren structures on earlier magmatic textures, and associated large-scale rock flowage resulted in deep infolding between lithologic units; outliers of chromite-bearing dunite were formed in this way.

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