Structural Control and Alteration at Beowawe KGRA, Nevada

Abstract

The Beowawe geothermal system in northern Nevada is a structurally controlled, water dominated resource with a measured temperature of 212°C (414°F). Surface expression of the system consists of a large, active opaline sinter terrace what is present along a Tertiary to Quaternary normal fault escarpment. The thermal system appears to be controlled by the subsurface intersections of the east-northeast trending, north dipping Malais fault with a pre-existing northwest trending fault which dips south and has 884 m of vertical displacement. Surface alteration associated with the geothermal system is vertically zoned along the Malpais escarpment with, from base to top: hematite stained, argillized rock along the fault trace; silicification and quartz veining; and argillic, acid leach zone at the top. Subsurface alteration generally increases with depth in the volcanic rocks and is most intense in basaltic-andesite lava flows which are capped by tuffaceous sedimentary rock.