Browsing by Author "Rytkönen, Jussi"

Critical metals are defined as rare specialty metals (e.g. Be, Sc, Co, Ga, Ge, Nb, REEs, In, Ta) that are critical for the facilitation of the Strategic Energy Technology Plan set by the European Union. These rare metals are typically associated with highly evolved granitic ores. Trioctahedral micas are often one of the main, if not sole, hydrous ferromagnesian phases in these granite-related rare metal deposits. Since many critical metals are readily incorporated in the mica crystal structure, micas are often used as petrogenetic indicators in assessing granite melt evolution. This study is a preliminary investigation in the critical metal distribution of trioctahedral micas in Fennoscandian S-I-A type granites. Ten granite samples (6 A-type, 2 S-type, and 2 I-type samples) were selected for examination that represent three distinct areas within the Fennoscandian shield: the Paleoproterozoic Wiborg rapakivi batholith (A-type) in southeastern Finland, the Paleoproterozoic Västervik metasedimentary formation (S-type) in southeastern Sweden, and the Neoarchean Hattu schist belt (S- and I-type) in eastern Finland. Whole-rock major and trace element chemistry was determined via WD-XRF, mineral major element chemistry via WDS-EPMA, and mineral trace element chemistry via LA-ICP-MS. The A-type granites are predominantly ferroan, alkali-calcic, and metaluminous, whereas the S- and I-type granites are predominantly magnesian, calc-alkalic, and peraluminous. Trioctahedral micas in the A-type granites are characteristically annitic, whereas S- and I-type granites trend progressively towards more phlogopitic compositions. Trace element data indicates that most critical and rare metal abundances (Li, Be, B, Sc, Ga, Ge, Zr, Nb, In, Sn, Ta) tend to increase with progressing fractionation, but largely independent from granite type. Moreover, the absolute differences in abundances are often small, but distinct. However, owing to their more primitive character, I-type granites are typically less fractionated than A- and S-type granites, and thus contain lower amounts of critical and rare metals. Furthermore, it is indicated that the fractionation of the following elements may be correlated: Be & Al, Be & Sc, and In & Sc. Moreover, it is indicated that amphibole and muscovite minerals may incorporate Be, Sc, Zr, and In more readily than trioctahedral micas.