Geochemical model of a magmatic–hydrothermal system at the Lastarria volcano, northern Chile

Abstract

Lastarria volcano (25°10′S, 68°31′W; 5,697 m above sea level), located in the Central Andes Volcanic Zone (northern Chile), is characterized by four distinct fumarolic fields with outlet temperatures ranging between 80°C and 408°C as measured

Hydrothermal alteration, fumarolic deposits and fluids from Lastarria Volcanic Complex: A multidisciplinary study

“…Considering the high Cl/Br and Br/I ratios, and iodine concentration that vary 0.07 and 2.05 ppm (Table 3), similar than Kudryavy volcano, and exceeding those in the arc-related St. Helens volcano (USA; Le Guern, 1988) condensates by more than 3 order of magnitude (0.0005 ppm), could be interpreted that LVC fumaroles present contributions from marine sediments and/or intraporal seawater, added to the original magma during the subduction process, and represented by relative high contents and high log EF i of Br and I. High contributions of sediments during the subduction process have been also observed in LVC fumaroles by Aguilera et al (2012), represented by excess of N 2 , high values of CO 2 / 3 He and δ 13 C-CO 2 values closer to zero.…”

“…Consequently, minerals as potassium alum and hydrohalite, both considered hyper-hydrous mineral, are suitable to appear in fumarolic deposits. Aguilera et al (2012) indicate that a partial decreasing of chlorine contents in fumarolic emissions of LVC could be related to salt deposition/precipitation with decreasing temperatures. Consequently, that process would be reflected by hydrohalite formation, being the water source a shallow aquifer related to the hydrothermal system and/or water vapour from gas fumarole.…”

“…Hydrothermal fluids are originated from the interaction of magmatic fluids with the host rock and/or shallow aquifers at reduced conditions (Giggenbach, 1996), and consequently, incorporation of solutes from the rock/meteoric sources can occur effectively in the magmatic/hydrothermal environments transition zone. In fact, Aguilera et al (2012) have suggested that LVC fumaroles emit a mixing of hydrothermal and deep magmatic fluids, where hydrothermal fluids are mainly originated from discontinuous shallow aquifers. In the case of alkali metals, its behaviour can be considered "normal", with decreasing of log EF i as follow Cs>Rb>K>Na, except in Last_Cond_1 where Rb>Cs.…”

“…Consequently, only high temperature fumaroles are chosen to perform condensates sampling and analysis, with the objective to avoid the meteoric fluids influence (Taran et al, 1995;Zelenzky et al, 2013). According to Aguilera et al (2012), LVC present two types of fumaroles, low (≤96.1 °C) and high (≥120 ºC) temperature, where the hottest fumarolic discharged measured was 408 ºC, lower than typically presented in diverse studies, which cover a range between ~500 and ~1,100 °C (e.g., Tedesco and Toutain, 1991;Symonds et al, 1992;Zelenski et al, 2013). Nevertheless, δ 18 O-δD isotope data from LVC fumarolic discharges (Aguilera et al, 2012) show a very limited contribution of meteoric water, even in low temperature fumaroles, which implies that LVC condensates data can be used confidently, where the addition of solutes from external source can be assumed as negligible.…”

“…Diverse studies have been carried out in the LVC related with fumarolic fluids geochemistry (Aguilera et al, 2008(Aguilera et al, , 2009(Aguilera et al, , 2012, magmatic volatiles (Rodríguez et al, 2013), rock geochemistry (Naranjo, 1992(Naranjo, , 2010Trumbull et al, 1999), eruptive products (Naranjo, 1992(Naranjo, , 2010, and sulphur deposits and flows (Naranjo, 1985(Naranjo, , 1988. However, very few information exist about the mineralogy related to fumarolic deposits and characteristics of the alteration zones.…”