Mapping lithology and hydrothermal alteration in geothermal systems using portable X-ray fluorescence (pXRF): A case study from the Tauhara geothermal system, Taupo Volcanic Zone

Abstract In the central Taupo Volcanic Zone, extensive zeolite (mordenite ± clinoptilolite) alteration occurs in late Quaternary rhyolitic vitric tuffs that were deposited in a lake formed by caldera collapse following the ~290 Ka Ohakuri ignimbrite eruptions. Glass shards in lacustrine vitric tuffs of the Ngakuru Formation and in the underlying Ohakuri Formation ignimbrite are replaced by mordenite ± clinoptilolite, along with hydrothermal adularia, opal-A, opal-CT, and cristobalite. This mineral assemblage is also found in the outer alteration zones of the nearby Ohakuri and Tahunaatara epithermal gold prospects. Evaluation of whole-rock chemical analyses indicates that the zeolitized vitric tuffs show a slight gain in K, and Na, Ca loss relative to unaltered Ohakuri Formation pumice, which is reflected in the presence of hydrothermal adularia in the alteration assemblage. The mordenite ± clinoptilolite alteration is associated with siliceous sinters and hydrothermal eruption breccias that were formed in recently active (39–1.5 Ka) geothermal systems. By analogy with geothermal systems elsewhere in the Taupo Volcanic Zone at Wairakei and Ohaaki, the mordenite ± clinoptilolite alteration was formed from dilute alkali-chloride aqueous liquid at 60° to 150°C. Based on the close association of the mordenite ± clinoptilolite alteration with siliceous sinters and hydrothermal eruption breccias in the central Taupo Volcanic Zone, it is classified as shallow, low-temperature, epithermal alteration. Mordenite ± clinoptilolite alteration has also been identified in Quaternary rhyolitic caldera settings in Japan and the United States, where it is termed “caldera-type zeolitization.” In exploration for epithermal Au-Ag deposits in rifted arc settings, such alteration may be overlooked, given its subtle appearance and distal location relative to veins that mark upflow areas.

Download Full-text

Sulfur in New Zealand geothermal systems: insights from stable isotope and trace element analyses of anhydrite from Rotokawa and Ngatamariki geothermal fields, Taupo Volcanic Zone

New Zealand Journal of Geology and Geophysics ◽

10.1080/00288306.2020.1851265 ◽

2020 ◽

pp. 1-17

Author(s):

Isabelle Chambefort

Keyword(s):

New Zealand ◽

Stable Isotope ◽

Trace Element ◽

Taupo Volcanic Zone ◽

Geothermal Systems ◽

Volcanic Zone ◽

Geothermal Fields

Download Full-text

3-D interpretative modelling applied to the geology of the Kawerau geothermal system, Taupo Volcanic Zone, New Zealand

Geothermics ◽

10.1016/j.geothermics.2014.03.002 ◽

2014 ◽

Vol 51 ◽

pp. 344-350 ◽

Cited By ~ 5

Author(s):

S.D. Milicich ◽

C. Bardsley ◽

G. Bignall ◽

C.J.N. Wilson

Keyword(s):

New Zealand ◽

Taupo Volcanic Zone ◽

Geothermal System ◽

Volcanic Zone

Download Full-text

The Hydrothermal Alteration of the Cordón de Inacaliri Volcanic Complex in the Framework of the Hidden Geothermal Systems within the Pabelloncito Graben (Northern Chile)

Minerals ◽

10.3390/min11111279 ◽

2021 ◽

Vol 11 (11) ◽

pp. 1279

Author(s):

Santiago Nicolás Maza ◽

Gilda Collo ◽

Diego Morata ◽

Carolina Cuña-Rodriguez ◽

Marco Taussi ◽

...

Keyword(s):

Hydrothermal Alteration ◽

Geothermal Field ◽

Geothermal System ◽

Volcanic Complex ◽

Geothermal Systems ◽

Acid Sulfate ◽

Alteration Zones ◽

Geological Processes ◽

Freshwater Bodies ◽

Hydrothermal Alteration Zones

Detailed mineralogical analyses in areas with surface hydrothermal alteration zones associated with recent volcanism (<1 Ma) in the Central Andean Volcanic Zone could provide key information to unravel the presence of hidden geothermal systems. In the Cordón de Inacaliri Volcanic Complex, a geothermal field with an estimated potential of ~1.08 MWe·km−2 has been recently discovered. In this work, we focus on the hydrothermal alteration zones and discharge products of this area, with the aim to reconstruct the geological processes responsible for the space-time evolution leading to the geothermal records. We identified (1) discharge products associated with acid fluids that could be related to: (i) acid-sulfate alteration with alunite + kaolinite + opal CT + anatase, indicating the presence of a steam-heated blanket with massive fine-grained silica (opal-CT), likely accumulated in mud pots where the intersection of the paleowater table with the surface occurred; (ii) argillic alteration with kaolinite + hematite + halloysite + smectite + I/S + illite in the surrounding of the acid-sulfate alteration; and (2) discharge products associated with neutral-alkaline fluids such as: (i) discontinuous pinnacle-like silica and silica deposits with laterally developed coarse stratification which, together with remaining microorganisms, emphasize a sinter deposit associated with alkaline/freshwater/brackish alkaline-chlorine water bodies and laterally associated with (ii) calcite + aragonite deriving from bicarbonate waters. The scarce presence of relics of sinter deposits, with high degree crystallinity phases and diatom remnants, in addition to alunite + kaolinite + opal CT + anatase assemblages, is consistent with a superimposition of a steam-heated environment to a previous sinter deposit. These characters are also a distinguishing feature of paleosurface deposits associated with the geothermal system of the Cordón de Inacaliri Volcanic Complex. The presence of diatoms in heated freshwater bodies at 5100 m a.s.l. in the Atacama Desert environment could be related with the last documented deglaciation in the area (~20–10 ka), an important factor in the recharge of the hidden geothermal systems of the Pabelloncito graben.

Download Full-text

Determination of Alteration Indexes using a Portable X-ray Fluorescence Analyzer: A Case Study on Hydrothermal Alteration of Limestones from Gangwon Province, South Korea

Journal of the Korean Society of Mineral and Energy Resources Engineers ◽

10.12972/ksmer.2016.53.6.541 ◽

2016 ◽

Vol 53 (6) ◽

pp. 541-554

Author(s):

Sung-Min Kim ◽

Da-Eun Yun ◽

Seong-Jun Cho ◽

Il-Mo Kang ◽

Hyeong-Dong Park

Keyword(s):

South Korea ◽

Hydrothermal Alteration ◽

X Ray ◽

Fluorescence Analyzer

Download Full-text

Precious Metals in Modern Hydrothermal Solutions and Implications for the Formation of Epithermal Ore Deposits

SEG Discovery ◽

10.5382/segnews.2008-72.fea ◽

2008 ◽

pp. 1-12

Author(s):

Stuart F. Simmons ◽

Kevin L. Brown

Keyword(s):

New Zealand ◽

Precious Metals ◽

Ore Deposits ◽

Taupo Volcanic Zone ◽

Geothermal System ◽

Hydrothermal Solutions ◽

Geothermal Systems ◽

Gold Silver ◽

Wide Range ◽

Time Required

ABSTRACT We determined the concentrations of gold, silver, arsenic, antimony, and mercury in deep hydrothermal solutions (~1 km depth, 200° to >300°C) from active geothermal systems in the Taupo Volcanic Zone, New Zealand, and Ladolam, Lihir Island, Papua New Guinea. The wide range of concentrations in the New Zealand systems and the stable isotope signatures at Ladolam confırm that magmas are an important source of high concentrations of gold and silver in hydrothermal solutions. The Rotokawa geothermal system in New Zealand has the highest hydrothermal fluxes of gold (~30–100 kg/yr) and silver (~5000–11,000 kg/yr), which, if they remained constant, could match the metal inventories of the largest ore deposits in the world in <50,000 years. This relatively short time span is comparable to the amount of time required to account for the known gold resource in ores at Ladolam, which has a slightly lower gold flux (~25 kg/yr). The fact that a giant gold deposit exists at Ladolam, rather than at Rotokawa, demonstrates the importance of fluid focusing and effıcient metal deposition in the formation of epithermal gold and silver ore deposits.

Download Full-text