Epithermal Zeolite Alteration Associated with Siliceous Sinters, Hydrothermal Eruption Breccias, and Gold-Silver Mineralization, Central Taupo Volcanic Zone, New Zealand

2021 ◽  
Author(s):  
Robert L. Brathwaite ◽  
Andrew J. Rae
Keyword(s):  
Late Quaternary ◽  
Close Association ◽  
The United States ◽  
Taupo Volcanic Zone ◽  
Caldera Collapse ◽  
Geothermal Systems ◽  
Volcanic Zone ◽  
Alkali Chloride ◽  
Hydrothermal Eruption ◽  
Gold Silver

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.

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

SEG Discovery ◽  
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.

Gold and silver resources in Taupo Volcanic Zone geothermal systems

Geothermics ◽  
2016 ◽  
Vol 59 ◽  
pp. 205-214 ◽  
Author(s):  
Stuart F. Simmons ◽  
Kevin L. Brown ◽  
Patrick R.L. Browne ◽  
Julie V. Rowland
Keyword(s):  
Taupo Volcanic Zone ◽  
Geothermal Systems ◽  
Volcanic Zone

Diagenetic transformations (opal-A to quartz) of low- and mid-temperature microbial textures in siliceous hot-spring deposits, Taupo Volcanic Zone, New Zealand

2003 ◽  
Vol 40 (11) ◽  
pp. 1679-1696 ◽  
Author(s):  
Bridget Y Lynne ◽  
Kathleen A Campbell
Keyword(s):  
New Zealand ◽  
Low Temperature ◽  
Hot Spring ◽  
Morphological Changes ◽  
Taupo Volcanic Zone ◽  
Volcanic Zone ◽  
Alkali Chloride ◽  
Silica Phase ◽  
Outflow Channels ◽  
Geologic Record

Silica sinter is a subaerial hot-spring deposit formed upon cooling (<100 °C) of discharging alkali-chloride waters. Silica deposition traps and fossilizes living microbes in low-temperature (<35 °C) to mid-temperature (~35–59 °C) apron–terrace outflow channels and pools, which record distinctive macrotextures and microtextures along a thermal gradient. Sinters from four geothermal fields, Orakei Korako, northern Waiotapu, Te Kopia, and Umukuri, within the Taupo Volcanic Zone, New Zealand, were sampled from two common microbe-rich microfacies (low-temperature palisade, mid-temperature bubble mat) through a range of ages (modern to ~40 000 years BP). We observed morphologic changes in microbial silicification and stepwise transitions in silica phase mineralogy throughout diagenesis (opal-A to quartz). X-ray powder diffractometry analysis of Taupo Volcanic Zone sinter samples revealed that mode of microbial fossilization is controlled by silica phase mineralogy, which also determines the preservation potential of environmentally significant and measurable filament parameters. Typical low-temperature palisade microfacies display thick sheaths (>3 µm diameter) and coarse tubular filament moulds >5 µm in diameter, whereas mid-temperature bubble mat microfacies characteristically consist of thin sheaths (~1 µm diameter) with fine moulds < 3 µm in diameter. Upon diagenesis and silica phase transformation to opal-CT, the two subenvironments cannot be distinguished based on filament diameter alone. This study of recurring microfacies in sinters of different ages allowed us to systematically track the transformation of mineralogical and morphological changes in biotic–abiotic depositional elements during diagenesis of silica sinter, and therefore enhance the paleoenvironmental, paleobiological, and paleohydrologic utility of hydrothermal deposits in the geologic record.

From source to surface: Tracking magmatic boron and chlorine input into the geothermal systems of the Taupo Volcanic Zone, New Zealand

2017 ◽  
Vol 346 ◽  
pp. 141-150 ◽  
Author(s):  
Florence Bégué ◽  
Chad D. Deering ◽  
Darren M. Gravley ◽  
Isabelle Chambefort ◽  
Ben M. Kennedy
Keyword(s):  
New Zealand ◽  
Taupo Volcanic Zone ◽  
Geothermal Systems ◽  
Volcanic Zone ◽  
Surface Tracking

Stratigraphy, chronology, styles and dynamics of late Quaternary eruptions from Taupo volcano, New Zealand

1993 ◽  
Vol 343 (1668) ◽  
pp. 205-306 ◽  
Keyword(s):  
New Zealand ◽  
Fractal Dimensionality ◽  
Pyroclastic Flows ◽  
Taupo Volcanic Zone ◽  
Caldera Collapse ◽  
Volcanic Zone ◽  
Oruanui Eruption ◽  
Self Similar ◽  
Taupo Volcano ◽  
Fall Deposits

Taupo volcano is the southerly of two dormant caldera volcanoes in the rhyolite-dominated central portion of the Taupo Volcanic Zone in the North Island of New Zealand. Taupo has an average magma output rate of 0.2 m 3 s -1 over the past 65 000 years, and is one of the most frequently active and productive rhyolite volcanoes known. The structure of the modern ‘inverse’ volcano was formed largely by caldera collapse associated with the voluminous 22 600 14 C years BP Oruanui eruption, and has been little modified since except for collapse following the 1850 14 C years BP eruption. The products of 28 eruptions (labelled T, f2, A, ..., Z), all of which post-date the Oruanui eruption, are defined and described here. Twenty-seven of these eruptions are represented by pyroclastic deposits (of which three were accompanied by a mappable lava extrusion), and one eruption (Z) solely by evidence for a lava extrusion. The deposits of seven eruptions (B, C, E, S, V, X and Y) largely correspond to previously defined tephra formations (Karapiti, Poronui, Opepe, Waimihia, Whakaipo, Mapara and Taupo, respectively). The previously defined Motutere and Hinemaiaia Tephras are reinterpreted to represent the products of 12 eruptions (G to R), while the remaining eight deposits and one eruption are newly recognized. Eruption T occurred at ca . 17200 14 C or 20500 calibrated years BP and eruption Z about 1740 calibrated years BP. Eruption volumes vary by more than three orders of magnitude between 0.01 and more than 44 km 3 , and repose periods by more than two orders of magnitude from ca . 20 to 6000 years. The eruption deposits reflect great variations in parameters such as volume, the dispersal characteristics of the fall deposits, the presence or absence of intraeruptive time breaks, the formation of pyroclastic flows, the degree of magmawater interaction, the vesiculation state of the magma on fragmentation and the relative proportions of juvenile obsidian versus foreign lithologies in the lithic fractions. All but seven fall deposits are plinian in dispersal; two (Y1 and probably W) are sub-plinian, one (Y5) has been termed ‘ultraplinian’, while 4/ and A are too poorly preserved for their dispersal to be assessed. The lengths of repose periods in the post-Oruanui sequence range are not randomly distributed but show self-similar properties (fractal dimensionality); repose intervals ( r , in years) of not more than 350 years follow n = 53.5r-0'21, and those of not less than 350 years follow n = 2096 r -0-83 , where n is the number of eruptions. The shorter repose periods may reflect triggering processes, such as regional extension, affecting magma bodies during their viable lifetimes, while longer repose intervals (i.e. not less than 350 years) may reflect an episodicity of major rifting events or the production of magma bodies below the volcano. Bulk volumes ( v , in km 3 ) of the eruption products also show self-similar properties (fractal dimensionality), with n = 6.17 v -0.46 . However, there are then apparently random relationships between eruption volumes and the preceding or succeeding repose period such that prediction of the time and size of the next eruption is impossible. The post-Oruanui activity at Taupo represents ‘noise’ superimposed on the more uniform, longer term activity in the central Taupo Volcanic Zone, where large (greater than 100 km 3 ) eruptions, such as the Oruanui, occur at more evenly spaced intervals of one per 40-60000 years.

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