Kaolin occurrence and formation in the Tobeatic shear zone

Abstract

Kaolin is found along the south-eastern contact of the South Mountain Batholith and the Meguma metasediments, 21 km along length on strike of the Tobeatic shear zone and on trend with regional folds and faults. The Meguma Terrane, along with the exotic terrane of Avalonia, accreted to ancestral North America (Laurentia) during the Middle Devonian Acadian Orogeny, causing voluminous felsic magmatism. The region remained periodically active throughout the final event of the Appalachian orogen, the Late Carboniferous-Permian Alleghanian orogeny (~310 - 260 Ma). The shear zones are inferred to have been active during the igneous emplacement SMB and remained pathways for late-stage mineralizing fluids during uplift. Kaolin is found associated with several types of mineralization, including base metals (Zn, Sn), Cu and aluminum-phosphate-sulfate minerals (APS). Using optical and SEM petrography, geochemical analysis, including ¹⁸O values, the kaolin is characterized, according to morphology, fabric and texture, growth mechanics and formation, as well as mineral and textural associations. Two chemically different types of kaolin are identified. 𝛿 ¹⁸O values provide additional constraints on the sources of the oxidizing fluids, having a significant contribution of meteoric fluids. Relative chronology of formation is inferred, based on types of alteration and temporal events, with quartz and kaolin not forming synchronously along the Tobeatic shear zone.