L2 - The subsurface environment, crustal fluid and resource deposits Flashcards
what are the 3 key subsurface properties in forming a resource deposit
Temperature
Pressure
Porosity
what is the role of a geyser in a hydrothermal system
it is part of a hydrothermal system where water is enriched with elements at the source and transported upwards
what happens to temperature with depth in the subsurface
T increases w depth
what is a geothermal gradient and does it vary?
the rate of temperature change with depth, and it varies across different tectonic settings worldwide
what is the lithostatic gradient in terms of pressure
it is the overburden pressure caused by the weight of overlying rock, with an average rock density of 2.5 g/cm3 = 25 kPa/m
how does hydrostatic pressure differ from lithostatic pressure
hydrostatic pressure is the pressure in fluid-filled rocks, with a fluid density of 1 g/cm3 - 10 kPa/m, this is lower than lithostatic pressure
define porosity in the context of a subsurface rock
porosity is the space within a rock that can store fluid like water, oil or gas
what is permeability
the ability of a rock to allow fluids to flow through, dependent on the connectivity of the pore network
how does brittle deformation contribute to resource deposits
brittle deformation results in faults and fractures - this allows fluid flow
what is ductile deformation
results in fold which limits flow
how do fluids move through earths crust
driven by gravity, tectonic forces (orogeny), thermal gradients or seismic activity
what are the main types of fluids in the Earth’s crust
Magmas, aqueous fluids, regional metamorphic fluids, connate water, seawater, meteoric water and hydrocarbon fluids
what are the 3 main classifications of resource deposits
igneous
hydrothermal
sedimentary-superficial deposits
