New insights on secondary minerals from Italian sulfuric acid caves

Abstract

Abstract:Sulfuric acid minerals are important clues to identify the speleogenetic phases of hypogene caves. Italy hosts ~25% of the known worldwide sulfuric acid speleogenetic (SAS) systems, including the famous well-studied Frasassi, Monte Cucco, and Acquasanta Terme caves. Nevertheless, other underground environments have been analyzed, and interesting mineralogical assemblages were found associated with peculiar geomorphological features such as cupolas, replacement pockets, feeders, sulfuric notches, and sub-horizontal levels.In this paper, we focused on 15 cave systems located along the Apennine Chain, in Apulia, in Sicily, and in Sardinia, where copious SAS minerals were observed. Some of the studied systems (e.g., Porretta Terme, Capo Palinuro, Cassano allo Ionio, Cerchiara di Calabria, Santa Cesarea Terme) are still active, and mainly used as spas for human treatments.The most interesting and diversified mineralogical associations have been documented in Monte Cucco (Umbria) and Cavallone-Bove (Abruzzo) caves, in which the common gypsum is associated with alunite-jarosite minerals, but also with baryte, celestine, fluorite, and authigenic rutile-ilmenite-titanite. In addition, the core of alunite and jarosite, from these two systems, results enriched in PO 4 3-, clearly suggesting hypogene hydrothermal origin. Santa Cesarea Terme, Capo Palinuro, and Acqua Mintina caves show important native sulfur deposits, which abundantly cover walls, ceilings, and speleothems. Abundant copiapite, pickeringite, tamarugite, hexahydrate assemblages have been observed in the Calabrian systems; their association with pyrite and hematite would suggest they formed in very acidic conditions with pH ranging between 0 and 4.

Geomicrobiology of a seawater-influenced active sulfuric acid cave

“…Specific inner morphologies and mineralogy associated with sulfuric acid speleogenesis have been previously reported in Santa Cesarea Terme caves by D’Angeli et al [17]. In particular, abundant microbial biofilms/deposits were visible in the water pool and on the walls and ceilings of the inner zone of Fetida Cave (FC), suggesting that the development of resident microbial communities was closely related to the rising sulfidic fluids and H 2 S degassing.…”

“…Fetida Cave hosts a peculiar type of vermiculation that has been previously named “biovermiculation” [12, 16], because of their possible biological origin and the inclusion of highly diversified and active microbial populations [20]. The biovermiculations typically develop in sulfidic caves and present complex and highly diversified geometric forms resembling carbonic-acid caves vermiculations, although they lack significant clay content [17, 20, 73]. Instead, the mineralogy of vermiculations from FC showed the abundance of quartz, in addition to either Mg and Fe-rich minerals, in brown vermiculations, or K- and Al-rich minerals in grey vermiculations.…”

“…Italy hosts 25% of all the known sulfuric acid caves worldwide, most of which are located along the Apennine chain [17]. Many of these are still active systems, in which rising sulfidic waters interact with fresh waters.…”

“…They can exhibit different morphologies (i.e. dots, dendritic), colors (red, brown, grey, black) and dimensions [17]. Although the origin of vermiculations was initially associated with specific climatic and environmental conditions [27], some studies also suggested that biological activity could support their formation on the walls of sulfidic caves.…”

“…These are distinguished from the more well-known calcite moonmilk deposits, which consists of microscopic crystals of different carbonate minerals (95%) with minor amounts of sulfates, silicates and phosphates (5%) [30, 31] or pure sulfates. Calcite moonmilk formation is often related to biological processes leading to either direct precipitation of calcite by microorganisms or mineral precipitation on microbial surfaces, functioning as nucleation sites [17, 32]. On the other hand, the microbial communities within gypsum moonmilk deposits, despite their abundance in sulfidic caves, have never been explored thus far.…”