Metamorphosed manganese mineralisation from the RHV-1 borehole near Rudňany (northern Gemeric Unit, Western Carpathians, Slovakia) occurs in the form of synsedimentary Mn nodules up to 1 cm in size with Mn³⁺/Fe³⁺-rich aureoles hosted in quartz–muscovite phyllites. These nodules show internal zoning with compact yellowish spessartine-rich cores, transitional quartz–spessartine rims, and outer reddish aureoles enriched in epidote, piemontite, hematite, Mn-rich calcite, fluorapatite, and clinochlore. Spessartine represents the dominant Mn-bearing phase (78.9–90.5 mol. % Sps), formed during the Variscan prograde metamorphism under low-temperature greenschist-facies conditions (~350–450 °C). The surrounding aureole comprises of epidote and piemontite with variable Mn³⁺/Fe³⁺ substitutions, recording metamorphic reactions under oxidising conditions and elevated fO₂, with hematite acting as the red coloration cause. Fluorapatite occurs as an important accessory phase in two generations: early As-poor fluorapatite enclosed in later As-enriched fluorapatite rims (up to 0.29 apfu As⁵⁺) formed during recrystallisation and fluid (re)mobilisation, possibly enhanced by Alpine tectonometamorphism. Quartz, muscovite, albite, and titanite represent phases inherited from the host phyllites. The studied mineral assemblage reflects a polyphase evolution of Mn mineralisation derived from volcaniclastic-sedimentary precursors deposited in an Early Paleozoic basin. Subsequent Variscan metamorphism produced spessartine nodules and aureoles, while Alpine metamorphism caused recrystallisation, quartz veinlet formation, and As⁵⁺ (re)mobilisation in outer fluorapatite zones. Compared to other occurrences in the northern Gemeric Unit (e.g., Poráč), the Rudňany assemblage is prominent for its dominance of spessartine and epidote–piemontite aureoles and a different protolith composition.