ABSTRACT
The origin of the ore-bearing apatite rock (nelsonite) from the Suwalki anorthosite massif and the Fe-Ti-P-rich monzodiorite (jotunite) from the Sejny massif, both of Proterozoic age and occurring within the ranges of the Mazury crystalline complex in NE Poland, was investigated by means of melt inclusion studies. Melt inclusions in apatite were filled by pyroxene, apatite, calcite, plagioclase, biotite, halite sylvite, plus ore mineral, aqueous solution and gas bubble. At 880°C two melts (silicate and phosphate) were observed in the inclusions. These melts did not homogenise nor change their proportions up to 1080°C. This behavior suggests the formation of nelsonite from an immiscible, two-phase melt. Inclusions in pyroxene from jotunite were filled by an aggregate of pyroxene, feldspar, apatite, carbonate and ore mineral with gas bubble. The homogenisation temperatures were from 1090 to 1180°C; small droplets of carbonate and phosphate melt were visible in the silicate melt at 1000 to 1030°C, homogenising subsequently to one melt phase.
