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U.S. Geological Survey Scientific Investigations Report 2012–5157

Podiform Chromite Deposits—Database and Grade and Tonnage Models

By Dan L. Mosier, Donald A. Singer, Barry C. Moring, and John P. Galloway

Thumbnail of and link to report PDF (3.4 MB)Abstract

Chromite ((Mg, Fe++)(Cr, Al, Fe+++)2O4) is the only source for the metallic element chromium, which is used in the metallurgical, chemical, and refractory industries. Podiform chromite deposits are small magmatic chromite bodies formed in the ultramafic section of an ophiolite complex in the oceanic crust. These deposits have been found in midoceanic ridge, off-ridge, and suprasubduction tectonic settings. Most podiform chromite deposits are found in dunite or peridotite near the contact of the cumulate and tectonite zones in ophiolites. We have identified 1,124 individual podiform chromite deposits, based on a 100-meter spatial rule, and have compiled them in a database. Of these, 619 deposits have been used to create three new grade and tonnage models for podiform chromite deposits. The major podiform chromite model has a median tonnage of 11,000 metric tons and a mean grade of 45 percent Cr2O3. The minor podiform chromite model has a median tonnage of 100 metric tons and a mean grade of 43 percent Cr2O3. The banded podiform chromite model has a median tonnage of 650 metric tons and a mean grade of 42 percent Cr2O3. Observed frequency distributions are also given for grades of rhodium, iridium, ruthenium, palladium, and platinum. In resource assessment applications, both major and minor podiform chromite models may be used for any ophiolite complex regardless of its tectonic setting or ophiolite zone. Expected sizes of undiscovered podiform chromite deposits, with respect to degree of deformation or ore-forming process, may determine which model is appropriate. The banded podiform chromite model may be applicable for ophiolites in both suprasubduction and midoceanic ridge settings.

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Contact Information, Western Mineral and Environmental Resources Science Center, Menlo Park Office
U.S. Geological Survey
345 Middlefield Road, MS 901
Menlo Park, CA 94025-3591
http://minerals.usgs.gov/west/

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Suggested citation:

Mosier, D.L., Singer, D.A., Moring, B.C., and Galloway, J.P., 2012, Podiform chromite deposits—database and grade and tonnage models: U.S. Geological Survey Scientific Investigations Report 2012–5157, 45 p. and database. (Available at http://pubs.usgs.gov/sir/2012/5157/.)



Contents

Abstract

Introduction

Podiform Chromite Deposits

Rules Used

Classification of Podiform Chromite Subtypes

Preliminary Analysis

Conclusions

Explanation of Data Fields

Location Maps

Acknowledgments

References

Appendixes A and B

database


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