Alunites from the low sulfidation-type epithermal systems of the Tokaj and the high sulfidation-type epithermal systems of the Velence Mountains were compared in terms of mineralogical and genetic aspects Na-enriched (1.14 to 2.35% Na2O) tabular alunites from the advanced argillic alteration zones of the Velence Mountains appear in the cavities formed from leached phenocrysts of andesitic rocks. These magmatic-hydrothermal alunites display compositional zoning due to variation in Na and K content and contain Ca-rich phosphate-sulfates with REE elements in their cores (i.e., woodhouseite series). The source of P is probably magmatic apatite that dissolved during intensive leaching of the host rock by acidic magmatic-hydrothermal fluids. Alunites in the steam-heated alteration zones of the Tokaj Mountains appear in the cavities formed from leached pumice fragments of rhyolite tuff units or in fractures in altered rhyolite domes. Rhombohedral and platy alunites have minor Na content (0.02 to 0.61% Na2O) and display compositional zoning due to the variation in Ba content. However, comb alunites contain more Na (1.55 to 1.82% Na2O) and compositional zoning can be attributed to variation of Na and K content. Alunites from the Velence Mountains have much higher δ34S values (24.2 to 25.3%) compared to alunites from the Tokaj Mountains (4.7 to 8.6‰). The δ18O values for the sulfate site in the alunite structure are between 10.6 and 13.6‰ in both areas. High δ34S values can be attributed to S isotope fractionation during the high temperature magmatic-hydrothermal formation of alunite from the Velence Mountains, which did not occur during formation of low-temperature steam-heated alunites from the Tokaj Mountains.
- Al-sulfate-phosphate minerals
- Stable isotope
ASJC Scopus subject areas