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Two populations of apatite in S-granites of the Melechov Massif


Václav Procházka, Dobroslav Matějka

Geoscience Research Reports 36, 2003 (GRR for 2002), pages 178–179

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In the Variscan granites of the Melechov Massif s.s. (Moldanubian Batholith, Bohemian Massif), two populations of apatite, magnetic and non-magnetic were found. The majority of apatite in each sample is weakly magnetic (it was caught at l .4 A during separations). This population forms usually hypautomorphic 0.05-0.3 mm large grains, and the non-magnetic grains are irregular and smaller. Contents of Fe, Mn, Mg (by AAS), and Sr, Ba, Y and REE (by ICP-MS) in the apatite concentrates were obtained. The main source of magnetism is MnII; the Mn compound of apatite reaches 1.5 per cent, according to AAS which is in quite a good agreement with EMP analyses in thin sections. The magnetic population crystallized from magma earlier than biotite, and the non-magnetic one appeared probably during albitization. The magmatic apatite has i higher content of REE and its the main reservoir of P in the rocks. The REE content of apatite reflects the content in the whole rock, and it decreases from the less- to the more acid rocks. In the most acid rocks (the Stvořidla type), apatite has higher HREE compound; there is not enough zircon in these rocks and apatite , which sometimes contains exsolved xenotime, is the main reservoir of Y and HREE.