New PhD Geology graduate combines new methodologies to advance the knowledge of energy and mineral resources

Monday, 26 de September

Pablo Sanchez was awarded with the PhD degree after defending a thesis that studies how chemical and structural processes are linked to the formation of geothermal systems and gold precipitation.

Earthquakes and volcanoes are two distinctive geological features of Chile. Normally these concepts are linked to natural disasters, but it is also possible to associate them with more positive elements such as geothermal energy and mineral wealth. “The study of active geothermal systems help us to understand the mechanisms by which metals concentrate, especially gold, which is typical of this type of systems” Pablo Sanchez explains, who obtained the highest academic degree on early July after defending his work “Interplay Between brittle deformation, fluid rock interaction and mineralization in hydrothermal systems from the southern Andes”. His study concentrated among the regions of Bio Bio and Los Lagos, where hot and active volcanism manifestations are controlled by the Liquiñe Ofqui fault zone.

ABSTRACT
The interactions between seismic activity, fluid flow and mineral precipitation exerts a first-order control on the strength and permeability of the crust and plays a critical role in promoting the development of hydrothermal systems and the formation of giant ore deposits. However the role of such interactions on the evolution of hydrothermal systems and its transient effects on mineralization is poorly constrained. This thesis contributes to establish the nature of the dynamic interplay between brittle deformation, heat-fluid-rock interaction and mineralization of hydrothermal systems in volcanic arcs. The ideal natural laboratory used to study such interplay was the Andean Cordillera of Central-Southern Chile, where hydrothermal systems occur in close spatial relationship with active volcanism as well as major seismically-active fault systems.
The combination of regional-scale structural analysis of active geothermal areas with geochemical modeling of hot spring in the Villarrica–Chihuio area (39°S–40°S in Chile) unravel the role of crustal deformation in facilitating and inhibiting the development of geothermal systems. Results reveal the presence of two magmatic-tectonic-geothermal domains and indicate that the chemical evolution of hydrothermal fluids in the area is strongly dependent on structurally controlled mechanisms of heat transfer. These provide new insights towards efficient exploration strategies of geothermal resources in Southern Andes.
The high enthalpy, metal-rich active Tolhuaca geothermal system is the case studied in order to (1) address how the interplay between seismic activity, heat-fluid rock interaction, fluid flow and mineral precipitation defines the physicochemical evolution of hydrothermal systems and (2) analyze the transient effects of earthquake-triggered pressure perturbations on metal solubility and mineralizatio. To achieve these, structural and mineralogical analysis at field and drillhole scales were combined with analytical determinations of present and past fluid compositions and temperature, numerical simulations of fluid evolution and rock failure conditions.
On one hand, results obtained reveal that the hydrothermal alteration that modifies the response of rock to deformation, compartmentalize the system and promotes the development of a clay-rich low permeability zone. Moreover, they indicate that the duration and thermal structure of the hydrothermal system are affected by a low-permeability zone. On the other hand a novel and widely applicable approach is developed, which integrates mechanical processes affecting the rock, changes in the thermodynamic conditions and gold solubility of ore-forming fluids during a seismic event. Results reveals the optimum physical and chemical conditions for metal precipitation, in which small pressure changes triggered by transient fault-rupture can drop gold solubility several orders of magnitude. Moreover, these results unveil how hydrothermal systems evolve to maximize efficiency of earthquake-induced gold precipitation.