Mineral Resources Potential - Geothermal Resources

3.6 Chromite
Metallic Minerals 109
An iron magnesium chromium oxide: (Fe,Mg)CrzOb is an oxide
minerd belonging to the spinel gotip. Magnesium is always
present in variable amounts, also aluminium and iron substitute for
chromim. Chromite is found in peridotite and other layered
ultramafic intrusive mks as well as in metamorphic racks such as
serpentinites. Ore deposits of chromite form as early magmatic
differentiate, It is commonly associatsd with olivine, magnetite,
serpentine, and corundum, The vast Bushveld Igneous Complex of
South Africa is a large layered d c to dtrarnafic igneous body
with some layers, consisting of 90% chromite making the rare rock
type chromitite. Chromite is found in Afghanistan, Iran, Pakistan,
Oman, and Zimbabwe (Boyle, 1987).
Origin
,When dense minerals form early in the crystallisation sequence,
they may sink to nmr the bottom of the magma chamber and
accumulate. This process is called crystal settling. Such settling is
aided by a low viscosity of the magma; so crystal settling is best
developed in basaltic magmas. Chromite is one of the first minerals
to crystallise hm basaltic melts, and may settle out to form dark
bands of nearly pure chromite. Stratiform chromite deposits consist
of laterally persistent chromite-rich layers (a few mm to several m
thick) alternating with silicate layers. The silicate layers include
ulb.amafic and d ~ rocks c such as dunite, peridotite, pyroxenite
vd a variety of others, less commonly gabbroic rocks.
\ Chromite deposits are the end product of the separation of
solid phases (Cr-rich spinets, (Fe, Mg) (Al, Cr. Fe) 204) from a
liquid and their accumulation into chmite-rich layers. The
pmsses involved in the formation of chromite layers are
Mional crystallization and gravity settling. Chromite crystallizes
into mineral grains within the silicate liquid and, because they are