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The Sourdough, or Baldface, area is on Baldface Creek, in sees. 35 and 36, T. 40 S., R. 11 W., Curry County, Oreg., 31 miles west of U. S. Highway 199. The chromite occurs in a large body of peridotite near its contact with slates, sandstones, and pyroclastic rocks, which are probably Jurassic. The peridotite is partly saxonite, partly dunite, and is largely serpentinized. It is cut by diorite dikes of both northeasterly and northwesterly strike. The peridotite is also cut by two fissure systems, of which one strikes N. 50° W. and has an average dip of 50° NE. and the other strikes about N. 20° E. and dips 60° SE. Chromite crystals are disseminated through most of the dunite and locally the crystals are aggregated in streaks or layers separated by barren layers. Some layers or lenses of massive chromite range from a few inches to several feet in thickness. Where undisturbed, they strike about northwest and dip about 45° NE. The chromite that might possibly be mined is all in one zone, which has been shown by prospecting to be at least 2,400 feet long and 965 feet deep. The rapid changes in the tenor of the rock makes any estimate of tonnage without systematic sampling and exploration a guess, but the district may contain between 50,000 and 100,000 tons of milling ore. The Briggs Creek chromite deposits are on Chrome Ridge, in sees. 11, 14, and 23, T. 36 S., R. 9 W., Josephine County, Oreg. There was considerable activity in this area during the World War. The known deposits are all in the southern part of~a silllike peridotite mass, which has been intruded into a group of hornblende schists or gneisses and thin-bedded quartzites that may be regionally metamorphosed equivalents of the Jurassic (?) rocks in the Sourdough area. At least 95 percent of the peridotite in the Briggs Creek area is saxonite. The remainder is dunite, which occurs as small clots scattered through the saxonite. The chromite occurs in the dunite. The peridotite has been sheared and displaced along faults that trend N. 20°-45° W. The ore is mainly of the disseminated type, with some fairly high grade streaks, but some consists of pods and masses of chromite along fissures in dunite. No significant trend of the ore bodies has been recognized. The dunitic layers, which contain the disseminated chromite, seem originally to have ex461 462 STRATEGIC MINERALS INVESTIGATIONS, 1940 tended northward but to have been offset by strong northwestsoutheast shearing. The chromic-oxide content of the chromite ranges from about 39 to 55 percent. The deposits are so numerous and widely scattered as to give a misleading impression of their value and size. The high-grade lenses contain considerable ore, but the horizontal and vertical extensions of individual ore masses are small. No large tonnage has been developed of ore assaying as much as 10 to 20 percent of CrgOs, which grade would be required to warrant concentration on a large scale under present conditions.

Chromite deposits in the Sourdough area, Curry County and the Briggs Creek area, Josephine County, Oregon