Potarite (Pd-Hg) in thermally metamorphosed dunite from the Inazumi-yama ultramafic complex, southwestern Japan; an implication for the behaviour of mercury in PGE mineralization in peridotite

Kanazawa University, Department of Earth Sciences, Kanazawa, Japan

Pd-rich PGM (platinum-group minerals) have been found in sulphide-bearing dunites and harzburgites from the Inazumi-yama ultramafic complex in southwestern Japan. In the dunite, potarite (PdHg (sub 0.85-0.88) ) is the most abundant PGM but other associated PGM include stibiopalladinite (Pd ₅ Sb ₂ ) and rare sperrylite (PtAs ₂ ) and Pd-rich alloys. A Pd telluride has been found in the harzburgite. The PGM are enclosed usually by pentlandite-heazlewoodite composite grains and, rarely, by altered chrome-spinel. These minerals are characteristic of an ultramafic assemblage but they are accompanied by ubiquitous galena and minor sphalerite not usually associated with these ultramafic assemblages. The ultramafic part of this complex has been thermally metamorphosed (olivine-talc zone) within the contact aureole of an adjacent granite. The PGM, sulphides and altered spinel are all intergrown with antigorite and/or chlorite, indicating a metamorphic overprint on the primary igneous mineralogy. The Pd/Pt ratios of 9 suggest a process of hydrothermal concentration for the Pd and it is proposed that the Pd has been remobilized and reconcentrated by hydrothermal solutions derived from the granitic magma which reacted with the Pd concentrated in the primary magmatic sulphides. Mercury may have been leached from surrounding sediments by the hydrothermal solutions. It is possible that potarite and the other PGM formed at temperatures of up to 650 degrees C and are likely to be found in other thermally metamorphosed ultramafic rocks showing a depleted character (spinel Cr/[Cr+Al]>0.7), common in orogenic belts.

This record provided courtesy of AGI/GeoRef.

This article has been cited by other articles:

				A. R. Cabral, G. Beaudoin, R. Kwitko-Ribeiro, B. Lehmann, J. C. Polonia, and M. Choquette PLATINUM PALLADIUM NUGGETS AND MERCURY-RICH PALLADIFEROUS PLATINUM FROM SERRO, MINAS GERAIS, BRAZIL Can Mineral, April 1, 2006; 44(2): 385 - 397. [Abstract] [Full Text] [PDF]

				M. E. Fleet, C. M. De Almeida, and N. Angeli BOTRYOIDAL PLATINUM, PALLADIUM AND POTARITE FROM THE BOM SUCESSO STREAM, MINAS GERAIS, BRAZIL: COMPOSITIONAL ZONING AND ORIGIN Can Mineral, April 1, 2002; 40(2): 341 - 355. [Abstract] [Full Text] [PDF]

				E. H. Nickel AN UNUSUAL OCCURRENCE OF Pd, Pt, Au, Ag AND Hg MINERALS IN THE PILBARA REGION OF WESTERN AUSTRALIA Can Mineral, April 1, 2002; 40(2): 419 - 433. [Abstract] [Full Text] [PDF]

				M. R. Power, M. R. Power, and D. Pirrie Platinum-group element mineralization within ultramafic rocks at Corrycharmaig, Perthshire: implications for the origin of the complex Scottish Journal of Geology, November 1, 2000; 36(2): 143 - 150. [Abstract] [PDF]