1 Other Occurrences of Small Deposits, about Which Little Information is Available, and Currently Uneconomic Mineralized Intrusions A large number of mineralized occurrences exist that can- not be included in the main text but are relevant for a variety of reasons. In some cases, they form small deposits that are being mined and are similar to other deposits that are de- scribed in the main text. In other cases, there is a lack of ge- ologic and/or resource information, so that adequate descrip- tion is not possible. Many other examples exist where exploration has been undertaken but the size or grade make the deposit uneconomic at present; nevertheless these occur- rences have yielded useful published geologic information about mineralization processes alluded to in the main text. In- formation on these occurrences is listed here. PGE Occurrences Layered intrusions Munni Munni Complex, Australia: The Munni Munni Com- plex in Australia (Barnes and Hoatson, 1994) is a boat-shaped layered intrusion, 2.9 Ga in age, forming part of a 60-km-long linear belt of intrusions emplaced in granitic rocks of the west Pilbara Craton, Western Australia. In outcrop Munni Munni covers only 16 by 10 km but a large gravity anomaly suggests its preserved area is three times greater, but hidden under sed- imentary rocks. It is divided into a lower keel-shaped ultra- mafic series up to 1,850 m thick, overlain by a gabbroic se- quence at least 3,000 m thick. The ultramafic rocks consist of cycles of olivine-clinopyroxene cumulates devoid of chromite. The top of the ultramafic series is marked by a distinctive 20- to 80-m-thick Porphyritic Websterite zone, carrying PGE min- eralization. This zone is referred to as the Ferguson reef, which extends laterally beyond the limits of the ultramafic se- ries to form a 200-m-thick layer of pyroxenite along the slop- ing sidewalls of the intrusion. The overlying gabbroic rocks show a typical differentiation sequence. The Ferguson reef is a stratiform accumulation of PGE-en- riched disseminated sulfides over an interval of 2 to 10 m within the top 20 m of the Porphyritic Websterite zone along its entire exposed strike length, with maximum total PGE grades up to 8 ppm over 50 cm. The Porphyritic Websterite zone marks a pronounced discontinuity in mineral composi- tion trends within the intrusion, between uniform relatively high Mg number and Cr-rich pyroxenes in the main part of the ultramafic series, to gabbroic cumulates showing a mo- notonous trend of declining Mg number and Cr in pyroxene due to closed system fractionation in a large chamber. Disseminated cumulus sulfides are abundant within an in- terval from 5 m above the gabbro contact to 15 m below it. Two sulfide-bearing layers are present in the area of highest PGE grades. The lower layer has lower PGE-in-sulfide tenors but generally higher grades and is characterized by coinci- dence of peak Cu, Ni, S, and PGE abundances. The second layer is variable in composition, strongly PGE enriched at the base and depleted at the top, and is characterized by system- atic vertical offsets between the peak PGE and Cu abun- dances. These “offset” horizons of sulfides always occur im- mediately above the “coincident” sulfides, where maximum values of the PGE and base metals coincide, and their first appearance in the stratigraphy broadly corresponds to the sudden drop in Cr 2 O 3 content of clinopyroxene within the Porphyritic Websterite zone. Coincident sulfides, and the higher overall PGE grades within the reef, are restricted to a strike extent of about 3 km centered on a dikelike feature in- terpreted as the feeder conduit to the Porphyritic Websterite Supplement to Platinum-Group Element, Chromium, and Vanadium Deposits in Mafic and Ultramafic Rocks R. GRANT CAWTHORN, STEPHEN J. BARNES, CHRISTIAN BALLHAUS, AND KRESHIMIR N. MALITCH APPENDIX ©2005 Society of Economic Geologists, Inc. Economic Geology 100th Anniversary Volume pp. 215–249 TABLE A1. Proportions of Total Reserves of Various Ore Types in the Noril’sk Area Ore type Reserves (%) Average metal contents in ores Total ore Ni Cu PGE Ni (%) Cu (%) PGE (g/t) Massive, Cu-Ni 10.3 41.7 31.8 20.6 3.2 4.6 10.8 Vein/disseminated (Cu-dominant) 7.4 8.1 16.4 13.3 0.9 3.3 9.8 Disseminated (PGE-dominant) 82.3 50.2 50.2 66.1 0.5 0.9 4.3 Low sulfide horizon 0.3 0.2 3–6 Notes: Data compiled from Lyul’ko et al. (2002); ore from the low sulfide horizon has not been adequately evaluated to include in reserves but 90 and 120 Moz of PGE may occur in this setting at Noril’sk and Talnakh and Oktyabr’skoe (combined); Eckstrand (1996) suggested that the Noril’sk-Talnakh region had 555 Mt of ore, which is considered to be an underestimate