Chemical evolution and origin of the Luumäki gem beryl pegmatite (SE Finland)

Granitic pegmatites are important hosts for economically important rare-element and gemstone deposits. However, the magmatic and hydrothermal processes responsible for enrichment of rare-elements and formation of gem bearing miarolitic pockets in granitic pegmatites are not fully understood yet. This project investigates the chemical evolution of the miarolitic Luumäki gem beryl pegmatite (SE Finland) combining field geology, mineral chemistry, fluid inclusion studies, and geochemical modeling. Based on field mapping and analysis of drill cores, the geometry, mineral assemblages and zoning of the Luumäki gem beryl pegmatite (Karelia Beryl Mine) has been established. Key mineral (feldspars, micas, beryl) major and trace elements composition has been used to trace the chemical evolution of the formation processes. Trace element data from fluid inclusion studies sheds new insight on the role and origin of aqueous and aqueous – carbonic fluids commonly found in pegmatites, yet not adequately explained. Thus, this study contributes to improved understanding of the processes that govern formation of granitic pegmatites, and constrains the role of magmatic-hydrothermal fluids in development of miarolitic pockets with economic gemstone mineralization.