Using a Field Spectrometer for Chromite Exploration

Chromites are the main source of the metal chromium, which is used to strengthen steel and make it hard, tough, and chemically resistant. There are many types of chromite, including ultramafic parts of layered mafic intrusions and serpentines and other metamorphic rocks formed by altering ultrabasic rocks. Due to its high crystallization temperature, this mineral can often be found in the lower parts of magma bodies due to fractional crystallization.

Occurrences include:
• South Africa (the world’s largest chromite miner)
• United States
• Canada
• Philippines
• Turkey
• Russia

By using a field portable UV-Vis-NIR spectrometer, geologists can identify and distinguish Chromite in mineral assemblages associated with olivine, magnetite, serpentine and corundum (Figure 1).

It is found in two deposit types: stratiform (layered) and podiform (pod shaped). The largest deposit being currently mined is in the Bushveld complex in South Africa. Chromite forms a series with magnesiochromite and hercynite also dimorphous with donathite. Some Mg is always present substituting for Fe+2 and some Al + Fe+3 may substitute for chromium. There is extensive solid solution between chromite and magnesiochromite, MgCr2O4. Occurs chiefly in ultramafic igneous rocks and is a common constituent of peridotites and other ultrabasic rocks and of serpentines derived from them. Chromites have distinct absorption features at 490, 590, 690, 940, 1300, 1750, 2000 and 2300 nm (Figure 2).

Spectral Evolution’s field portable NIR spectrometers are designed to resist the most demanding conditions of the mining environment. Combined with the EZ-ID™ mineral identification software and spectral library builder, geologists can now measure and identify minerals on site, within seconds. They can identify different mineral phases, create alteration maps, and accurately identify mineral pathfinders for vectoring to ore deposits. More ground can be covered rapidly, and core logging can be accelerated thanks to the short data acquisition time of Spectral Evolution’s spectrometers. High-capacity batteries allow for hours of continuous and reliable operation in the field.