Occurence of ore metals in some terrestrial geothermal systems

Conference · Wed Feb 01 00:00:00 EST 1984 · Prepr., Soc. Min. Eng. AIME; (United States)

OSTI ID:6165905

Browne, P

Drilling programs and the study of active geothermal systems have shown that the reservoir rocks in many fields contain minor quantities of base and precious metals. Commonly, base-metal sulfides occur in the subsurface but, where present, Au, Ag, Hg, As, Tl and Sb rich precipitates deposit near, or at, the surface. Although in some fields (Geysers, Larderello, Tongonan) some of the ore minerals (and others) are relict, there is evidence that they are now depositing in a few systems. Recent work on active hydrothermal systems in New Zealand shows that: (1) Sphalerite, galena, chalcopyrite (forming veins and disseminated discrete crystals) plus rare pentlandite, cobaltite and arsenopyrite, occur at Broadlands, NZ. Rare quantities of base-metal sulfides also occur in cores and cuttings from the geothermal fields of Waiotapu, Kawerau, Tauhara, and Ngawha. Further, Kakimoto (1983) has identified cassiterite, native silver, and trace gold in cores from Tauhara, in the south-eastern part of the Wairakei field. Bore temperatures at the depths from which these minerals were recovered are mostly between 220/sup 0/ and 300/sup 0/C, but at Broadlands are locally as low as 120/sup 0/C. The host rocks are Quaternary calc-alkali, silicic lavas and pyroclastic rocks, andesites, dacite and deep Mesozoic greywackes and argillites; however, there is no obvious relationship between mineralization and stratigraphy, permeability or well output. The deposition of amorphous precious metal precipitates (Au, Ag, Hg, As, Sb, Tl) from hot springs and well discharges has taken place at Broadlands, Waiotapu and Rotokawa; it also occurs at Kawerau. Water discharging from Frying Pan Lake, Waimangu, is presently depositing siliceous sinter containing up to 4.1% tungsten.

• Research Organization: Geothermal Institute, University of Auckland
• OSTI ID: 6165905
• Report Number(s): CONF-840218-
• Journal Information: Prepr., Soc. Min. Eng. AIME; (United States), Vol. 84-73; Conference: 113. annual meeting of the American Institute of Mining, Metallurgical and Petroleum Engineers, Los Angeles, CA, USA, 26 Feb 1984
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
HYDROTHERMAL SYSTEMS
GEOCHEMISTRY
NEW ZEALAND
GEOTHERMAL FIELDS
PHILIPPINES
CHEMICAL COMPOSITION
GEOTHERMAL FLUIDS
MESOZOIC ERA
ORES
QUATERNARY PERIOD
RESERVOIR ROCK
TERTIARY PERIOD
ASIA
AUSTRALASIA
CENOZOIC ERA
CHEMISTRY
DEVELOPING COUNTRIES
ENERGY SYSTEMS
FLUIDS
GEOLOGIC AGES
GEOTHERMAL SYSTEMS
ISLANDS
150302* - Geothermal Exploration & Exploration Technology- Geochemical Techniques & Surveys