. An unusual Fluorbritholite-(Ce)-rich REE deposit in a fenite body of Devonian granites, Central Argentina

LORENZ M; ALTENBERGER, U; TRUMBULL, R.; LÓPEZ DE LUCHI, M.G.,

Bonn

Conferencia; GEOBONN 2018 Living Earth; 2018

Rheinische Friedrich-Wilhelms-Universität Bonn

The middle Devonian Las Chacras-Potrerillos batholith, San Luis province, Central Argentina, is composed of A-type monzonite and granite suites. The REE deposit ?Rodeo de Los Molles? is situated in a fenitized zone in a biotite-monzogranite at the northern margin of the batholith. The fenitization is accompanied by the transformation of monzogranite to alkali-feldspar (±quartz) syenite compositions. REE-rich mineral assemblages occur as isolated patches as well as in vein structures consisting of intergrown britholite group minerals (BGM) with REE carbonates, fluorapatite, allanite, fluorite, titanite, hydrothermal zircon, albite and quartz. The patchy REE mineralizations are located at small syenite bodies enclosed in areas with stronger fenitization. Small and large-scale vein structures are up to 1m thick and cut the fenitization zone. Britholite group minerals are found in unusual high amounts at Rodeo de Los Molles, reaching 80 Vol% within vein structures, whereas in isolated patches britholite is mostly altered to bastnaesite, reaching only 10 Vol%. The later suggests the presence of fluids rich in CO2, leading to the dissolution of britholite and its replacement by REE carbonates