Early fumarolic minerals from the Tajogaite volcanic eruption (La Palma, 2021)

Abstract

This work constitutes the first geochemical, mineralogical and textural analysis of the early fumarolic deposits that appeared in the Tajogaite Volcano (La Palma island, Spain) one month after the official end of the eruptive process. Fourteen fumaroles grouped into 5 study areas have been characterized following a novel methodology that includes on-site microscopic observations and weak samples preservation for their laboratory characterization. Three main mineralogical zones were identified in the fumaroles: 1) sulphur-sulphate; 2) halides; and 3) salammoniac zone. Zones 1 and 2 are included in the S-gas domain and the predominance of sulphur-sulphate minerals or halides in the mineral deposits is dependent on the gas temperature (halides appear in the high temperature fumaroles). Zone 3 overlaps the (HCl-CO) and (HCl) -gas domains. The thermal analysis of the fumaroles provides the sequence of mineral suites according to the vent temperature. Sylvite-halite-tenorite are revealed as typical minerals of high-temperature fumaroles (>530 °C), whilst Ca, Mg and Na sulphates appear in low-temperature fumaroles (<200 °C). Salammoniac-Mascagnite forms in intermediate ranges (170–350 °C). Finally, three different fumarole types are recognized (punctual, diffuse and associated to fissures), establishing different environmental conditions for mineral precipitation. Differences are based on the gas flux mechanism, the gas-rock interaction intensity, temperature and gas concentrations. All these data will serve as a referenced starting point for later studies focused on fumarole evolution and the degassing process of volcanic systems in oceanic volcanic islands framework.