METASOMATITES AND RELATED PGE MINERALIZATION OF THE LAYERED LUKKULAISVAARA COMPLEX, OLANGA GROUP OF INTRUSIONS, NORTHERN KARELIA

PGE mineralization of the Lukkulaisvaara massif belongs to the low-sul fide type. The most considerable deposits are confined to the ''pothol e'' structures of the gabbro-norite-I and norite-II zones and have a m etasomatic genesis. The sulfide and PGE mineralization is restricted t o (1) the pothole bottom or underlying rocks, (2) the contacts with fi ne-grained norites and gabbro-norites, and (3) veined facies of the mi neralized pyroxenites and gabbro-norites typical of large microgabbro- norite bodies. According to the assemblage of secondary silicate miner als, talc-anthophyllite-tremolite metasomatites I and amphibole-clinoz oisite-chlorite-quartz metasomatites II are distinguished. The former are characteristic of the veined facies of the ore-bearing rocks. The richest PGE mineralization was discovered in the metasomatized veined facies of the mineralized pyroxenites and gabbro-norites (metasomatite s I), as well as in the metasomatites after leucocratic gabbronorite-a northosites developed on contact with microgabbro-norites (metasomatit es II). These rocks contain more than 40 PGE minerals the Pt + Pd cont ents in the rocks are as high as 70 ppm. Data on gas-liquid and aqueou s inclusions, together with the paragenetic analysis of the secondary minerals indicate that the most active rock alteration occurred at 320 -450 degrees C and 1.5-2.0 kbar in a reduced environment of high salin ity. The Sm-Nd mineral age of the metasomatites is 2423+/-180 Ma, whic h is consistent with the massif age within the analytical error. Howev er, the distinct initial Nd isotope composition of the metasomatites a nd layered-series rocks (epsilon Nd=+0.9 for metasomatites compared to -2.1 for the weakly altered rocks) may indicate that the metasomatic fluids were derived from different sources: one of them being isotopic ally similar to and the other different from the source of the rocks.