A rock magnetic fingerprint of hydrothermal alteration in volcanic rocks - An example from the Los Azufres Geothermal Field, Mexico

Magnetic Signature and Element Content of Upflow and Outflow Hotspring in Arjuno–Welirang Geothermal System

“…The details data is listed in Table 1.. In some cases, the presence of Fe, Si and Mg elements can be used to indicate the presence of geothermal alteration and is associated with low-frequency magnetic susceptibility, as shown in the core sample of Los Azufres geothermal area [17]. In this study, there is no Mg element found.…”

“…From the magnetic susceptibility range of the two hot springs, it shows that the susceptibility is consistent, it would be because the hot springs are located in the same mountain system, the Arjuno-Welirang system, with the same bedrock called the Young Anjasmoro rock formation, Qpva (Figure 1). The range of magnetic susceptibility is greater than the range with two cores in the Los Azufres geothermal area [17].…”

“…The same result was reported by Pandarinath et al (2014), who studied earlier core samples taken from a geothermal area. These results show the increase in Fe-Mg silicate is directly proportional to the value of lf [17]. This study only uses Fe-Si without involving Mg because Mg elements were not found.…”

“…Magnetic susceptibility can be useful during the initial stages of geothermal exploration in identifying hydrothermally altered rock and zones of hydrothermal alteration both at the surface and from drilled wells in a geothermal system. The study indicates a decrease in lf values with depth in the two geothermal wells corresponding with: (1) an increase in the reservoir temperature and hydrothermal alteration and (2) a decrease in the concentration of Fe-Mg silicate and opaque minerals [17]. In this study, measurements of magnetic susceptibility and morphology of magnetic minerals, as well as geochemical tests conducted to identify the magnetic characteristics of the depositional environment in the form of hot springs with upflow and outflow characteristics.…”

High Remanent Magnetization Measured in Hydrothermally Altered Lavas

“…Evidence of how hydrothermal alteration influences magnetic properties of volcanic rocks mainly comes from mid‐ocean ridge basalts (Wang et al., 2020; Xu et al., 1997), seafloor hydrothermal systems (Fujii et al., 2015, 2018), geothermal fields (Pandarinath et al., 2019), and mineralized porphyry systems (Byrne et al., 2019). All these studies associate hydrothermal alteration with reduced magnetization.…”