1201 The Canadian Mineralogist Vol. 45, pp. 1201-1211 (2007) DOI : 10.2113/gscanmin.45.5.1201 DJERFISHERITE IN THE GULI DUNITE COMPLEX, POLAR SIBERIA: A PRIMARY OR METASOMATIC PHASE? FEDERICA ZACCARINI § AND OSKAR A.R. THALHAMMER Department of Applied Geosciences and Geophysics, University of Leoben, Peter Tunner Strasse 5, A8700 Leoben, Austria FRANCESCO PRINCIVALLE AND DAVIDE LENAZ Dipartimento di Scienze della Terra, University of Trieste, Via Weiss, I34127 Trieste, Italy CHRIS J. STANLEY Mineralogy Department, Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom GIORGIO GARUTI Dipartimento di Scienze della Terra, University of Modena and Reggio Emilia, Via S. Eufemia, 19, I41100 Modena, Italy ABSTRACT The uncommon sulde djersherite, ideally K 6 (Fe,Cu,Ni) 25 S 26 Cl, occurs in the dunite portion of the Guli complex, located in Polar Siberia, Russia. Distinctive features of the Guli complex are its considerable size, ~2000 km 2 , making it the largest duniteclinopyroxenite massif in the world, and its complicated geology. The exposed part is composed predominantly (60%) of variably serpentinized dunite. Melanocratic alkaline rocks cover about 30%, and other rock types, including melilitolite, ijolite, alkaline syenite and carbonatite, occupy less than 10% of the area. The sample with the most abundant djersherite is a coarse- grained phlogopitemagnetite-rich clinopyroxenite. Djersherite most commonly occurs in irregular patches of sulde composed mainly of pyrrhotite accompanied by minor chalcopyrite and rare galena, in a matrix of Ti-bearing andradite, clinopyroxene, phlogopite, plagioclase, apatite and rare zircon, titanite and pyrophanite. It forms crystals generally less than 100 m in size and occurs as irregular single-phase grains or it lls ssures of the silicate matrix and inltrates phlogopite along its cleavage planes. We provide new data on the physical and crystallographic properties of djersherite. Its composition is characterized by an extensive substitution among Fe, Cu and Ni; their reciprocal substitutions are mainly controlled by the nature of the host rock. The djersherite from the Guli complex is Cu-rich and resembles that reported from alkaline rocks. This feature is consistent with the proposal that djersherite in the Guli complex crystallized as a primary mineral, during the late-stage fractionation of a highly alkaline melt portion, derived from successive fractional melting of an ascending mantle plume under metasomatic conditions. Keywords: djersherite, Raman spectroscopy, crystal-structure analysis, Guli dunite complex, mantle, Siberia, Russia. SOMMAIRE La djersherite, de formule idØale K 6 (Fe,Cu,Ni) 25 S 26 Cl, sulfure assez inhabituel, a ØtØ trouvØe dans la dunite du complexe de Guli, situØe en SibØrie polaire, en Russie. Le complexe de Guli se distingue par sa dimension, environ 2000 km 2 , ce qui en fait le massif de duniteclinopyroxØnite le plus grand au monde, et par la complexitØ des relations gØologiques. Les afeurements consistent surtout (60%) de dunite variablement serpentinisØe. Les roches alcalines mØlanocratiques couvrent environ 30%, et les autres variØtØs de roches, y inclus mØlilitolite, ijolite, syØnite alcaline et carbonatite, occupent moins de 10% de la supercie. LØchantillon contenant la plus grande proportion de djersherite est une clinopyroxØnite  phlogopitemagnØtite  gros grains. La djersherite se prØsente surtout en amas irrØguliers de sulfures faits de pyrrhotite avec chalcopyrite accessoire et galLne plus rare, dans une matrice dandradite titanifLre, clinopyroxLne, phlogopite, plagioclase, apatite, et zircon, titanite et pyrophanite plus rares. Elle se prØsente en monocristaux irrØguliers, gØnØralement de moins de 100 m, ou bien elle remplit les ssures dans la matrice silicatØe et sinltre dans la phlogopite le long de clivages. Nous avons effectuØ de nouvelles mesures des propriØtØs § Present address: Instituto Andaluz de Ciencias de la Tierra, University of Granada, CSIC, Campus Fuentenueva, E18200 Granada, Spain. E-mail address: fedezac@tsc4.com, federica.zaccarini@unileoben.ac.at