UNITED STATES MINERAL RESOURCES 



CHROMIUM 



By T. p. Thayer 



CONTENTS 



Page 



Abstract of conclusions 111 



Introduction 111 



Exploitation 112 



Geologic environment 112 



Mineralogy of chromite and chromite ores 112 



Primary chromite deposits 112 



Stratiform deposits 113 



Podiform deposits 115 



Disrupted stratiform deposits 115 



Genesis of primary chromite deposits 116 



Secondary deposits and associated metals 116 



Resources 116 



Identified resources 116 



Hypothetical and speculative resources 119 



Exploration for chromite deposits 119 



Problems for research 120 



References cited 120 



FIGURE 



13. 



Graph showing world production and U.S. con- 

 sumption and production of chromite ore and 

 relation of price to domestic production from 

 1900 to 1970 



TABLE 



24. 



Estimated world reserves and resources of chro- 

 mite ore by type and country 



ABSTRACT OF CONCLUSIONS 



113 



Page 

 117 



Although world reserves are large and resources of chro- 

 mite ore are ample for the foreseeable future, domestic re- 

 sources (excluding the national stockpile) are low grade and 

 represent only about a 4- to 5-year supply. The outlook for 

 substantially increasing domestic resources, even at several 

 times present world prices, is not favorable. The thicker, 



minable parts of the Stillwater Complex in Montana, the 

 principal domestic source, are complexly faulted and sheared 

 off at depth. Although many podiform deposits must occur 

 in serpentine along the Appalachian Mountains and Pacific 

 Coast, most would be too small to mine at depths of 100 feet 

 or more, even if means were available to locate them. A few 

 relatively large podiform deposits probably are concealed 

 at minable depths and might meet national needs for a few 

 months at most. 



The principal North American resources other than those 

 in the Stillwater Complex are in a similar complex in Mani- 

 toba and very large low-grade deposits in Greenland. Metal- 

 lurgical research to improve recovery of chromium from the 

 low-grade "ores" and acquisition of more information on 

 the Greenland deposits are needed. The only minable chro- 

 mite reserves in the Western Hemisphere are a few million 

 tons in Brazil and perhaps some in Cuba. 



INTRODUCTION 



Chromium is one of the most important and indis- 

 pensable industrial metals. It is best known as a 

 silvery white, hard, and bright metal plating on steel 

 or other material used for decoration or protection 

 from corrosion. Such coatings, however, rarely ex- 

 ceed 0.00002 inch in thickness and use only relatively 

 minor amounts of the metal. Over the 5 years 1966- 

 70, the United States consumed an average of 430,000 

 tons of chromium annually; about 67 percent was 

 used in ferroalloys, about 18 percent in high-tem- 

 perature furnace linings, and 15 percent in chemicals, 

 including plating. In relatively small amounts, 

 chromium hardens and toughens steel and increases 

 its resistance to corrosion, especially at high tem- 

 peratures. Most stainless steel contains about 18 per- 

 cent chromium, and some cutting tools and wear- 

 resisting alloys contain as much as 33 percent. The 

 mineral chromite has some unique refractory uses. 

 Although there are substitutes for chromium in 

 many uses, such as titanium or aluminum for stain- 

 less steel and magnesite for chromite in refractories, 

 no adequate substitutes have been, or are likely to be, 

 found for chromium in some applications. 



U.S. GEOL. SURVEY PROF. PAPER 820 



111 



