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Platinum-group element mineralization in an As-rich magmatic sulphide system, Talnotry, southwest Scotland

¹ Camborne School of Mines, University of Exeter, Redruth, Cornwall TR15 3SE, UK
² Laboratoire de Géochimie et de Mineralogie, CP160/02 - Université Libre de Bruxelles, 50 Avenue Roosevelt, B-1050 Bruxelles, Belgium
³ Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, UK

View larger version (71K): [in a new window]   FIG. 1. Simplified regional geological map of the Southern Uplands of Scotland.

View larger version (32K): [in a new window]   FIG. 2. Simplified geological map of the area surrounding the Talnotry ore body (after Cook, 1976). As: arsenopyrite trials.

View larger version (58K): [in a new window]   FIG. 3. Schematic log through the mineralized interval largely based on unpublished work presented in Stanley et al.(1987).

View larger version (137K): [in a new window]   FIG. 4. SEM images of ore minerals: (a) ?tellurobismuthite within pentlandite; (b) euhedral cobaltite-gersdorffite grain enclosed within pyrrhotite with hessite grain (hs) and rim (arrowed) at the margin; (c) relict niccolite grain (nc) partially replaced and overgrown by gersdorffite (gf); (d) weathered niccolite (nc) and annabergite (an) with a euhedral gersdorffite (gf1) grain surrounded by a gersdorffite rim (gf2); (e) subhedral niccolite grain enclosing euhedral gersdorffite; (f) euhedral gersdorffite (gf1) and chalcopyrite (ccp) partially rimmed by gersdorffite (gf2).

View larger version (34K): [in a new window]   FIG. 5. Ternary diagram showing restricted composition of PGM- and PGE-bearing gersdorffite grains. Po-ccp (PGE-rich): PGE- or PGM-bearing euhedral gersdorffite within the pyrrhotite-chalcopyrite assemblage: Po-ccp: euhedral gersdorffite within the pyrrhotite-chalcopyrite assemblage; Nc-gf (euhedral): euhedral gersdorffite within the niccolite-gersdorffite assemblage; Nc-gf (rims): gersdorffite rims and overgrowths within the niccolite-gersdorffite assemblage. Temperature data after Klemm (1965).

View larger version (101K): [in a new window]   FIG. 6. (facing page) Representative SEM images of PGM: (a) euhedral sperrylite enclosed within euhedral cobaltian gersdorffite at edge of pyrrhotite grain; (b) euhedral cobaltian gersdorffite grain with Rh-rich zone (arrowed) and anhedral sperrylite inclusion (bright phase); (c) two anhedral sperrylite grains within chalcopyrite; (d) euhedral sperrylite (sp) and gersdorffite (gf) grains within pyrrhotite; (e) large anhedral sperrylite enclosed within amphibole; (f) michenerite (mi) and froodite (fr) within amphibole; (g) thin veins of electrum (el) and chalcopyrite (ccp) cutting gersdorffite; (h) Pd-Bi-Te (?michenerite) (mi) at edge of euhedral niccolite (nc) and gersdorffite (gf).

View larger version (17K): [in a new window]   FIG. 7. Simplified summary of the paragenetic sequence showing evolution of the sulphide liquid. Direct: direct crystallization from an immiscible sulphide liquid; MSS: crystallization and exsolution from a monosulphide solid solution; NiAs: crystallization from a Ni- and As- rich liquid; ISS: crystallization from intermediate solid solution.