Geothermal systems in the Great Basin, western United States: Modern analogues to the roles of magmatism, structure, and regional tectonics in the formation of gold deposits

Western North America produces over one-third of the world’s geothermal
power, and significant increases in power production are expected as additional plants
come on line. Many geothermal systems in western North America derive their heat
from magmas or cooling intrusions that occur in variety of tectonic settings, including
a triple junction, volcanic arc, hot spot, and pull-apart zones in strike-slip systems.
The interior of the Great Basin however, is characterized by widespread amagmatic
geothermal activity that owes its existence to high crustal heat flow and active extensional
tectonics.
Even though magma-heated geothermal fluids have higher concentrations of
some trace metals, including As, Li, B, and Cs, than extensional (amagmatic) fluids,
both fluid types in the Great Basin have recently, or are currently, depositing gold.
Quaternary to Pliocene-aged gold deposits with adjacent high-temperature (≥ 150°C)
active geothermal systems occur at Long Valley, California, and Florida Canyon,
Wind Mountain, Dixie Valley, and other locations in Nevada. Prolonged uplift of mineralized
zones along range-front faults suggests that extensional systems, although
possibly episodic, have lifetimes measured in millions of years. The total known gold
inventory in deposits younger than 7 Ma in the Great Basin exceeds 12 million ounces.
Many Great Basin geothermal systems are aligned along northeast-trending belts
hundreds of kilometers long that are likely related to ongoing northwest-directed
crustal extension. However, the highest-temperature extensional systems and the most
productive young gold deposits are aligned along northwest trends sub-parallel to the
dextral Walker Lane shear zone. A transitional transtensional setting in which rightlateral
fault motion along the Walker Lane splays into extensional northeast-striking
normal fault systems may promote deep fracturing and the circulation and heating of
meteoric fluids to form hydrothermal systems.