Hydrothermal Signatures of Geochemical Surface Processes In Los Humeros Geothermal Field: A Preliminary Geochemometric Case Study

Geochemometric mass balance studies in rock outcrop samples collected at the Los Humeros geothermal field (LHGF) were carried out. These geochemometric studies were based on the mineral characterization and whole-rock elemental analyses for determining the mobility of major and trace elements from a perspective of water-rock interaction (WRI) processes. Two extensive events of hydrothermal alteration were identified on the LHGF surface, which was characterized by: (i) a silicification and argillization process (from argillic to advanced argillic); and (ii) an acid-sulphate alteration (alunite and jarosite). According to a geochemometric version of the well-known Gresens-Grant mass balance method, the WRI processes identified at the LHGF cause significant statistical differences among the element mobilities of major and trace elements. This geochemical behaviour evidences a clear enrichment in SiO2, Ti2O, Mo, As, Nb, Pb, S, Th, Mo, Bi, U, and Sr; and depletion in Al2O3, Fe2O3T, MgO, CaO, K2O, Cr, and Zn. The analysis of bivariate geochemical studies indicated that the elements with the highest proportion of enrichment with respect to the SiO2 major compound were Th, Rb, Bi, and Sr, whereas the elements with a high depletion degree with respect to Al2O3 were Cr, Cu, Zn, CaO and Fe2O3T. The spatial distribution of these hydrothermal signatures due to the WRI processes, and evidence at surface conditions, shows a preferred alignment with the NW-SE and the N-S fault systems. The geochemical anomalies were mainly concentrated on the North of the LHGF. This geochemical non-conventional method explores the highest hydrothermal alteration zones which are evidenced by greater permeability areas. Within this investigation framework, it was also developed a low-cost analytical methodology based on energy-dispersive X-ray fluorescence technique, and the use of open-source software applications (e.g., Qgis, R-programming, and UDASys).