gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1987.051.363.09 Mineralogy Deerite from Papua New Guinea Worthing M. A. * Department of Geology, U.P.N.G., Box 320 University P.O., Port Moresby, Papua New Guinea

Present address: Department of Earth Sciences, The University of Leeds, Leeds, LS2 9JT, U.K.

 12 1987 51 363 689 693 10 10 1986 26 1 1987 Copyright © 1987, The Mineralogical Society 1987 Abstract

Deerite in two meta-ironstones from Papua New Guinea coexists with quartz-albite-riebeckite-dannemorite-magnetite-spessartine-stilpnomelane-apatite-Ca/Mn carbonates and quartz-albite-crossite-ilmenite-spessartine-stilpnomelane-apatite respectively. Geochemical comparisons in the system FeO-MnO-MgO suggest that the P.N.G. deerites most closely resemble Franciscan types. However, the metamorphic assemblages more closely resemble Alpine types indicating metamorphism close to the lower P-T limit of deerite stability. Consistent differences in whole-rock and internal oxidation ratios between the two specimens suggest that fo2 may be important in determining deerite chemistry. A redox equation is suggested linking changes in deerite internal oxidation ratio with variable OH content.

 Keywords deerite Papua New Guinea oxygen fugacity