Manganese oxide mineralisation hosted in Upper Triassic dolostone near Királyszentistván, Hungary

Abstract

A manganese- and iron-bearing mineral assemblage occurring in Upper Triassic dolostone near Királyszentistván (Transdanubian Range, Hungary) was investigated in order to characterise the mineralogical composition and to reveal the textural relations on the micrometre scale, thereby contributing to a better understanding of the geological processes yielding these manganese oxides, partially covered by yellowish-brown goethite, occurring within vugs and cavities con­tain­ing strongly brecciated and pulverulent dolomite. To analyse the detailed mineralogical and textural features of the samples X-ray powder diffraction, scanning electron microscopy (SEM-BSE imaging, SEM-EDX point analysis and ele­mental mapping), micro-XRF elemental mapping, Raman spectroscopy and computed tomography were applied. The in­ves­tigated assemblage consists mainly of tunnel-structured manganese oxides, including romanèchite, todorokite and coronadite-group minerals, associated with goethite. Micrometre-scale observations reveal intimate intergrowths of min­er­al phases and heterogeneous element distributions, indicating multiple stages of mineral precipitation under changing redox and pH conditions. The results demonstrate that integrated mineralogical investigations, particularly high-resolu­tion textural analyses, provide essential constraints on fluid–rock interaction processes and the evolution of mineralising en­vironments. The Királyszentistván occurrence highlights the geological significance of detailed mineralogical studies of seemingly common mineral assemblages in reconstructing local geological and geochemical processes.