Economic Geology 5350

Subject: Magmatic Chromium Deposits

Ore Mineralogy and Tenor

The only economic mineral of chromium is chromite; a variety of the spinel group that has a chemical formula of (Fe,Mg) (Cr, Al, Fe)2O4. Theoretically the mineral contains 68 % Cr2O3 and 32% FeO but Fe+3 may displace some Cr+3 reducing the Cr2O3 content to as little as 40%. To be commercial, ores usually contain a minimum of 45%Cr2O3. There are three types of ore: chemical, refractory, and metallurgical. Metallurgical contains 45-56 Cr2O3 with a high Cr:Fe ratio (2.5 to 4.3); chemical contains >44% Cr2O3 3 with a Cr:Fe ratio of at least 1.5; whereas refractory contains 30-35%Cr2O3, 25-32% Al2O3 with a Cr:Fe ratio of 2-2.5:1 and very low iron content. Common gangue minerals associated with chromite are olivine, orthopyroxene, serpentine, and calcic-plagioclase. Chromite is closely associated with Mg and Ni in ultramafic rocks; peridotite contains 1000-3000 ppm Cr, where 1% is not uncommon. Gabbro however averages 200 ppm Cr.

JD, Is our Cr commercially viable?

Thanks always..

Bernard