Lunar and Planetary Science XXXVII (2006) 1676.pdf

NI IN IMPACTITE SULPHIDES IN THE LAPPAJÄRVI, SÄÄKSJÄRVI, SUVASVESI S, 1,2 AND PAASSELKÄ METEORITE CRATERS IN FINLAND. D. D. BADJUKOV AND J. 2 1 RAITALA ; V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry RAS, 119991, 19, Kosygin str., Moscow, Russia ([email protected]), 2University of Oulu, P.O. Box 3000, FIN-90401, Oulu, Finland ([email protected])

Introduction: The craters are situated in Bravoite is present also in strongly re- the central part of Finland and were formed crystallized impact melt rocks of the in crystalline rocks. The melt rocks at these Paasselkä impact crater. Finnish meteorite craters are enriched in According to morphologic and siderophile elements and other meteoritic composition features, a fraction of sulphides components [1,2]. Contents of a meteoritic and metal in Lappajärvi and Sääksjärvi matter are around 2 – 0.1 % of a nominal CI impactites are a shock re-worked meteorite component and the distributions are matter, that experienced shock-induced heterogeneous on a fine scale [3,4]. melting or, less likely, are condensates of Sulphides in the impact melt rocks are main impact generated vapour cloud [5]. carriers of siderophile elements, especially Other fraction of sulphides and metal for Ni and Co. with low Ni and Co contents has terrestrial The studied impactites: The Lappajärvi origin and formed by shock melting of a melt rocks contain pyrrhotite droplets and target. The reduced from target rocks and oxide-silicate globules (d < 2 mm) rich in Ni Fe-sulphide metal suggests to be slightly rimmed by pyrrhotite and occasionally with enriched in Ni and Co due to presence of pentlandite and chalcopyrite. Sääksjärvi disseminated meteorite matter in an impact impact melt rocks contain Fe-Ni-Co melt. The last fraction of pyrrhotite, monosuphide, millerite (Ni,FeS), pentlandite, chalcopyrite, and other sulphide pentlandite, chalcopyrite, and sphalerite. grains was formed by post-impact The sulphide minerals occur as either hydrothermal activity by mobilization of spherule-like or irregular inclusions. meteorite and terrestrial Ni and Co. Bravoite in the impactites of Suvasvesi South and Paasselkä seems to have originated in similar processes. The Ni-Co- Cu-Zn mineralization observed in the Lappajärvi and Saaksjärvi craters can be characteristic feature of the post-shock hydrothermal activity in impactites enriched in a meteorite matter. References: [1] Muller N. et al., (1990), Fig.1. Fine-grained impact melt rock from the Meteoritics, 25.1-10; [2] Pihlaja P.J., Kujala th Lappajärvi crater. Tiny pyrrhotite and metal H. (2000) 4 Woprkshop of the ESF Impact inclusions (white) are embedded in a silicate matrix Progr., Abstr., 50; [3] Palme H. et al., (1980) consisting of orthopyroxene prismatic grains (very LPSC XI 848-850; [4] Schmidt G. et al., light gray) and a glass (gray). Combined BSE-SE (1997) GCA, 61, 2977-2987: [5] Badjukov image, scale bar =100mm. D. D. et al. (2001). LPSC XXXII, CDROM, #1532. The Suvasvesi South suevite houses . altered impact melt inclusions with euhedral grains of Ni-Co containing pyrite (bravoite).