CHROMIUM 



119 



in the Great Dyke which have been projected to 500 

 feet below the surface but which are known to go 

 much deeper (Stanley, 1961). Eastern Hemisphere 

 reserves outside southern Africa are estimated at 

 55-60 million tons, and conditional resources at 

 about 50 million tons. Even excluding southern 

 Africa, reserves and presumed resources of the East- 

 ern Hemisphere appear to be about triple those of 

 the Western Hemisphere. However, because most of 

 these resources are in podiform or highly deformed 

 stratiform deposits, the uncertainties of supply and 

 costs of production can be expected to mount rapidly 

 as identified resources are depleted. 



HYPOTHETICAL AND SPECULATIVE RESOURCES 



The probability of finding major new chromite dis- 

 tricts is believed to be shrinking rapidly, except pos- 

 sibly in central Asia, where little information is 

 available. In the last 20 years, major high-chromium 

 podiform deposits have been developed in two regions 

 in Iran. The stratiform deposit at Kemi, Finland, 

 with reserves of approximately 33 million tons of 

 crude milling-grade high-iron ore, was discovered in 

 1959 (Kahma and others, 1962) ; it represents a 

 major new district that was discovered under glacial 

 drift. The low-grade but potentially very important 

 chromite deposits at Fiskenaesset in southwestern 

 Greenland were discovered in 1964 during regional 

 geologic mapping (Ghisler and Windley, 1967) . The 

 figures for hypothetical and speculative resources are 

 predicated more on discoveries in known districts 

 than on new districts. The figures for India and Mala- 

 gasy assume that large segments of disrupted strati- 

 form deposits will be found in laterite-covered areas 

 or at depth. 



The universal presence of chromite as an acces- 

 sory mineral in peridotite suggests a possibility of 

 recovering it by large-scale mining of very low-grade 

 rocks, as copper and molybdenum are mined from 

 porphyry-type deposits. The analogy is not apt, how- 

 ever, for several reasons. In rock containing less than 

 about 10 percent CraOs or 20 percent chromite, be- 

 cause the chromite is fine grained and relatively soft, 

 it slimes badly during the grinding necessary to free 

 it from the silicates. Furthermore, flotation processes 

 that work so well with sulfide ores present difficulties 

 for chromite, an oxide (Batty and others, 1947 ; Sulli- 

 van and Stickney, 1960). Concentrates from low- 

 grade disseminated ores normally are considerably 

 lower in chromium and richer in iron than high- 

 grade massive ores (Jackson, 1968, p. 1510) . 



Extensive deposits of iron-rich laterite blanket 

 many peridotites in tropical and subtropical regions 

 of the world. The laterite contains approximately 



40-50 percent iron, 0.5-3 percent chromium, 0.2-2.5 

 percent combined nickel and cobalt, some aluminum, 

 and 10-15 percent combined water (Gross, 1970a, 

 p. 27) . Only relatively small amounts of laterite are 

 used as iron ore, although nickel is recovered from 

 laterite on a large scale by hydrometallurgical proc- 

 esses in New Caledonia and Cuba. Recovery of all the 

 metals presents difficult unsolved metallurgical prob- 

 lems. The laterites of Cuba alone have been estimated 

 at 3 billion tons; at an average of 2 percent CrsOs 

 (1.4 percent Cr), they would contain 42,000,000 tons 

 of chromium metal (Gross, 1970b, p. 250). Estimates 

 of the potential chromium resources in laterite are 

 not included in table 24 because of the low tenor of 

 chromium, scarcity of essential data on tonnages, 

 and the lack of technology for recovery. 



EXPLORATION FOR CHROMITE DEPOSITS 



Restriction of chromite deposits to the lower parts 

 of very distinctive layered complexes and to perido- 

 tite of the alpine type (Thayer, 1971) sharply limits 

 areas for prospecting. By virtue of its resistance to 

 weathering, massive chromite crops out or forms 

 bouldery float and black sand that can be traced 

 readily. In stratiform complexes the layered struc- 

 ture can be used as a guide to concealed deposits and 

 faulted blocks or segments of ore. 



Prospecting for concealed podiform deposits gen- 

 erally has been disappointing. In large peridotite- 

 gabbro complexes, chromite deposits are concen- 

 trated within the peridotite near the gabbro, and 

 thus the peridotite-gabbro contact can be used as a 

 guide to the most promising ground (Flint and 

 others, 1948 ; Rossman and others, 1959) . Under al- 

 most ideal conditions of low relief in central Cuba, 

 gravimeter surveys located some concealed deposits 

 (Hammer and others, 1945) , but in most areas high 

 relief precludes use of this method. Magnetic sur- 

 veys can outline areas of serpentine very accurately, 

 but because most chromite is less magnetic than the 

 host rocks, such surveys do not indicate concealed 

 deposits. The high-iron stratiform deposits at Kemi, 

 Finland, however, were traced under glacial till by a 

 combination of magnetic and gravimetric surveys 

 (Kahma and others, 1962). Seismic methods are not 

 effective because most ore bodies are too small to 

 detect and the host rock commonly is highly frac- 

 tured and sheared. Known geochemical methods are 

 not applicable because of presence of accessory 

 chromite in all peridotite. With the exceptions noted, 

 no substitute for detailed geological mapping and 

 traditional means of underground exploration has 

 been devised for finding concealed podiform chromite 

 deposits. 



