Analogue Geothermal Systems In Mexico: Insights Into The Deep Part Of Los Humeros Geothermal Field From The Las Minas Mining Area (Eastern Mexico)

This study is part of the H2020-GEMex Project, a collaboration between Europe and Mexico for investigating super-hot geothermal systems. The novelty of this work is in its integrated methodological approach which bridges the past to the present and contributes to the reconstruction of conceptual models of deep geothermal systems, thus favoring appropriate strategies for deep exploration. The Las Minas mining area (Veracruz State) where Cu-Fe-Au ore-deposits have been historically exploited, is considered as an exhumed Neogene geothermal system analogous to the deeper part of the Los Humeros geothermal field (Puebla State). We used an integrated approach, which involved structural and kinematic, petrological, geochemical, geochronological and fluid inclusion analyses of the pre-volcanic Paleozoic-Cretaceous succession, intruded by Miocene-Pliocene granitoids and mafic dykes. Our emphasis was on the (paleo) fluid-rocks interaction and the related structural control. The results indicate that saline and hypersaline fluids (up to 70 wt. % NaCl equiv.) of magmatic derivation and aqueous-carbonic fluids issued during metamorphic or metasomatic reactions with T up to 600-650°C were channeled along and in the intersection between the NW- and NE-trending faults and their damage zones. The faults are characterized by strike-slip to oblique-slip/normal movements. Fluids were also stored in carbonate rock-volumes at the contact with the granitoids. The distribution of the ore-deposits and hydrothermal alteration related to the interaction of geothermal fluids and hosting rocks indicates the importance of conduits (such as fractures and faults) in the reservoirs. Hence, understanding the relationships between ore-deposits, hydrothermal alteration and structures can increase our knowledge of the present geothermal fluids' deep circulation in the Los Humeros geothermal field.