Geochemical Characterization of Boula Ibi Granitoids and Implications in Geodynamic Evolution

Petrographical and geochemical study, consistent with observed field relations show that the Boula Ibi syn- and post-kinematic granitoids in north Cameroon, occurred in banded gneisses. These syn- and post-kinematic granitoids consist of deformed monzonites typified by its granoblastic texture, diorites, syenites, granites and basic xenoliths of dioritic and monzonitic composition. They are calc-alkaline, hyperpotassic, metaluminous to slightly peraluminous and I-Type granitoids. They display high content in Fe2O3 + MgO + CaO (2.16 – 23.24 %) that reveals their intermediate affinity, magnesian and metaluminous character whilst the low A/CNK (< 1.1) content indicates their mantle origin. Harker diagrams and La/Sm vs La define the fractional crystallization and partial melting as the two main processes that led the geodynamic evolution of the Boula Ibi syn- and post-kinematic granitoids. These are consistent with low-content of Cs, Ta, Nb, Tb and Hf, supporting high melting rates ranging between 20 and 40% as well as molar Al2O3/(MgO + FeOt) vs CaO/(MgO + FeOt) plot showing magmatic evolutions from metabasaltic and metagreywackes sources.

Specific features of supercontinent cycles in the metallogeny of tantalum

The metallogeny of tantalum through the geological history has been analyzed. A representative sampling contains mineral deposits of five types: pegmatitic, granitic, alkaligranitic, foidic, and carbonatitic ones. They were formed with a variable intensity during the time range from the Late Mesoarchean to Cenozoic. The most notable resources of tantalum are known in the deposits of the Rodinian cycle, as well as the Pangean and Colombian ones. All these cycles stand out against other ones by a leading role of the deposits associated with alkaline magmas of mantle origin. However, the concentrates of the highest quality to extract tantalum are obtained from the deposits in rare-metal pegmatites and lithium-fluorine granites produced by crustal magmas. Only the pegmatitic deposits are known for the Kenoran cycle in tantalum metallogeny. They contain a maximum amount of such high-quality resources.

Combining multiple isotope and noble gas data with seismic profiles in an interpretation of hydro-geochemical anomalies

Environmental isotopes (δ18O, δD, δ13C, 14C, 87Sr/86Sr), combined with hydrogeochemical data and seismic profile interpretation, have been used in studying regional groundwater flow systems in the Pannonian Basin. An interpretation of seismic profiles indicates the existence of faults systems, some of them being traceable from the Pre-Cenozoic basement up to near-surface Quaternary sediments. The Lakitelek study area shows high He contents (22 to 25 %) of mantle origin, where fault lines might have been reactivated during recent geological times and facilitated the occurrence of mantle-derived He in the groundwater. The Mezőtúr study area, where most H- and O-isotope compositions are shifted from the global meteoric water line, exhibits 7.6 to 10.6 % He of mantle origin,. The deepest sample indicates mixing with formation waters. Here basement faults might not have been reactivated, since they do not seem to have an active role on the groundwater composition and effects of the regional flow system seem to be the dominant factor determining the groundwater isotope compositions.