Petrogenesis and 40Ar/39Ar dating of hydrothermal romanechite from the sub-aerial fault-related Romanèche Mn deposit (France)

This study discusses the hydrothermal formation of romanechite (Ba0.7Mn4.5O10.1.1H2O) in Romanèche Mn deposit and significance its age by combining ore petrogenesis 40Ar/39Ar ages. Romanechite occurs as a minor phase various manganese types remains poorly studied comparison with other K-bearing oxides (i.e., coronadite group) because scarcity, small grain size, intermixing poor crystallinity. The fault-controlled (Massif Central, Eastern France) investigated herein exhibits well-crystallized late stage massive occurring quartz-barite-fluorite gangue. Petrographical geochemical data support under sub-aerial conditions temperatures close to fluorite precipitation (100–200 °C) characterized Mn-Ba-W-As association. Five out eight samples have produced plateau ages ranging from 25.2 ± 0.3 18.2 0.5 Ma. Despite low K content (0.1–0.6 wt% K), good crystallinity due epithermal likely favours better production and/or retention radiogenic argon than crystallized phases supergene origin. Therefore, dataset identifies period at least c. 7.6 My discontinuous activity, which is consistent graben-related fault reactivation volcanic activity Massif Central. Ultimately, this confirms feasibility dating.