Paper Number: 1953
Main types of Platinum-Group Element Mineralization in the Fedorovatundra layered intrusion, Kola Peninsula, Russia
Groshev, N.Yu., Subbotin., V.V., Korchagin, A.U.
Geological Institute KSC RAS, Apatity, Russia, email: nikolaygroshev@gmail.com
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The 2526 to 2485 Ma Fedorovatundra layered mafic intrusion in the central part of the Kola Peninsula, Russia, is the western massif of the Fedorova-Pana Complex (2526-2446 Ma), which is situated along the northern contact of the Early Proterozoic Imandra-Varzuga rift and Archean granite gneiss. The Fedorovatundra intrusion is approximately 4 km thick and has two major parts: (1) located at the bottom of the intrusion, the Taxitic series (10 to 900 m); and (2) composing the main volume of the massif, the Layered series (4000 m). The Taxitic series is distinctive, due to its predominant variable-textured often quartz-saturated norites and gabbronorites (with minor leucogabbro, melanorite and olivine-gabbronorite) and abundant pyroxenite (with occasional harzburgite xenoliths). Medium to coarse-grained mottled or massive leucocratic gabbronorite and leucogabbro prevails in the Layered series with mesocratic gabbronorite, pyroxenite and troctolite as subordinate rocks.
Depending on its localization, geochemical features, mineral composition and economic value, platinum-group element (PGE) mineralization of the Fedorovatundra intrusion is divided into ‘marginal’ (basal, contact) and ‘reef’ types. ‘Marginal’ type of mineralization is presented by irregular disseminated interstitial sulfides (1-2 vol. %) of pentlandite-pyrrhotite-chalcopyrite association (Cu/Ni = 1.8) in the Taxitic series. Less sulfides occur as uniformly disseminated aggregates, thin massive lenses and nests. PGE and base metals are concentrated in several ore horizons of in a 3.5 km long complicated structure. Thickness of ore horizons varies generally within 10–150 m, but it can rise up to 280 m in overthickened lenses. In the most common ore-bearing rock (taxitic gabbronorite) the average Pt + Pd content is 1.6 ppm (Pd/Pt 4.5). The pyroxenite xenoliths occurring within the Taxitic series are practically barren of sulfide and can dilute higher PGE and base metal grades in the gabbronorite matrix. This ‘Marginal’ mineralization the forms the largest Fennoscandian PGE deposit with several hundred tons of contained precious metals.
PGE mineralization of a ‘reef’ type was found in rhythmically layered olivine-bearing horizons in the lower and middle parts of the Layered series. The ‘reef’ PGE mineralization is closely associated with finely disseminated (up 0.5 vol. %) pentlandite, pyrrhotite and chalcopyrite (Cu/Ni 2.4). Thickness of mineralized horizon varies from 1 to 3 m and is continuous for over 500 m (with estimations up to 3 km). In the lower mineralized horizon the average Pt + Pd content is 1.4 ppm (Pd/Pt 1.5), and that in the middle part is 0.4 ppm (Pd/Pt 0.8).
The most common PGE-bearing minerals of ‘marginal’ mineralization are merenskyite, moncheite, kotulskite, sobolevskite, and michenerite; less common are sperrylite, stillwaterite and vysotskite-braggite. ‘Reef’ type mineralization includes the same minerals, but it is substantially more enriched in PGE arsenides and sulfides.
A two-stage process is postulated for the genesis of the PGE mineralization of the Fedorovatundra massif. This involves the intrusion of sulfur-saturated PGE-enriched gabbronorite magma of the Taxitic series (2493-2485 Ma, ‘marginal’ PGE mineralization) into already solidified mafic and ultramafic rocks of the Layered series (2526-2507 Ma, PGE reef as a marker) [1, 2].
The work was supported by RFBR (16-05-00367, 15-35-20501).
References:
[1] Groshev N et al. (2009) Dokl Earth Sci 427(2): 1012-1016
[2] Schissel D et al. (2002) Econ Geol 97: 1657-1677