A phosphate-bearing pegmatite from Lutomia and its relationships to other pegmatites of the Góry Sowie Block, southwestern Poland

Abstract

A geochemically primitive, moderately fractionated, LCT pegmatite from Lutomia (Góry Sowie Block, SW Poland) has been characterized in respect of the primary and secondary phosphate assemblages. The pegmatite crystallized from anatectic granitic magmas mobilized by M2-3 metamorphism at ∼370-380 Ma. Three phosphate assemblages had a different origin: (1) the primary, magmatic one [graftonite-(I)-beusite-(I) + triphylite ± sarcopside], (2) a secondary, metasomatic one [Ca-rich graftonite-(II) - Carich beusite-(II) + wolfeite/triploidite/staněkite + hagendorfite/alluaudite + kryzhanovskite ± a Cabearing phosphate close to erromerrillite + fluorapatite], and (3) a secondary, hydrothermal and weathering one [ferrisicklerite ± heterosite + phosphoferrite-kryzhanovskite + ludlamite + vivianite ± hureaulite + earlshannonite-whitmoreite + strunzite-ferrostrunzite + beraunite + dufrénite + jahnsite-(CaMnFe), -(CaMnMn) and -(MnMnMn) + landesite + fairfieldite + Mn2+-bearing hydroxyapatite]. The magmatic assemblage resulted from the breakdown of a primary, high-T, Ca- and Lienriched graftonite-like phase. It was induced by cooling and elevated incompatible Ca, Na, Li and F concentrations. The metasomatic assemblage refects the destabilization of the magmatic phosphates and their Ca- and Nametasomatism by a high-T fluid connected with a PO4-bearing melt, which previously had evolved along with graftonite-(I)-beusite-(I). The assemblage of secondary, hydrothermal and weathering, phosphates was a result of lower T alteration by hydrothermal fluids and meteoric water by both topotactic Fe and Mn oxidation as well gradual hydration and Fe oxidation. Taken together, the Lutomia pegmatite has been compared to the phosphate-bearing pegmatite at Michałkowa and the mixed NYF + LCT, PO4-poor pegmatitic system of Piława Górna.