A Consideration of Geological Settings for and the Structural Morphology of Terrestrial Hydrothermal Systems

Abstract

The minerals and mining industry has developed detailed data on the geometry, controls, and duration of hydrothermal systems for more than 100 years. These data provide a valuable base for understanding active geothermal systems and resource trends (fairways). It provides insight into the tectonic settings, structural controls and geometry of geothermal resources with dynamic fluid flow. These data combined with data developed by the geothermal exploration community show a spectrum of terrestrial hydrothermal resources with two end members; those directly deriving thermal energy from young hot pluton and subvolcanic rocks and those deriving thermal energy from deep crustal temperature gradient by fluid up-flow. Those associated with cooling felsic plutons have the potential of residing in expansive 3-dimentional fracture networks or within fractured subvolcanic rock. Geothermal cells hosted by vertically dilated structures are typically not as large as those associated with cooling plutons, though they can be locally numerous, forming in clusters of dilation structures. The geometry of the geothermal cells at depth provide constraints on exploration and development strategies. Deeper fluid sources and flow-path structures also significantly constrain all deep resource exploration. Not included in this discussion are static traps containing hot water (e.g. the Pannonian Basin of Eastern Hungary), basin sediment hosted hot water (e.g. the Texas Gulf Coast, U.S.A.) or EGS (hot rock with limited permeability).