Setting of a magmatic sulfide occurrence in a dismembered ophiolite, southwestern Oregon

Al Introduction Al Regional geology Al Previous work A3 Sulfide occurrence A3 Lithology A4 Pyroxene cumulates A4 Metagabbroic sequence A6 Mineral and rock analyses A8 Geothermometry and metamorphism A15 Summary and discussion A16 References cited A21 FIGURES 1. Index map and generalized geologic setting of the Illinois River sulfide occurrence A2 2. Geology of the Illinois River sulfide occurrence A4 3. Photomicrographs of sulfides in pyroxenite A7 4. Plot of pyroxene compositions in the Ca-Mg-Fe ternary All 5. Chondrite-normalized plot of PGM and Au contents after recalculation to 100 percent sulfides A20 6. Composition of sulfides from cumulus pyroxenite plotted on the Fe-Ni-S diagram A21 TABLES 1. Modal compositions of rock units A6 2 11. Electron microprobe analyses of: 2. Clinopyroxene A9 3. Orthopyroxene A10 4. Olivine A12 5. Plagioclase A13 6. Amphibole A14 7. Cordierite A15 8. Pentlandite A15 9. Pyrrhotite A16 10. Chalcopyrite A17 11. Pyrite A18 12-13. Compositions of five sulfide-bearing samples: 12. Whole-rock analyses A19 13. Analyses recalculated to 100 percent sulfide A19 14. Metal-metal and metal-sulfur ratios from recalculated 100 percent sulfide compositions A20

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