Impact of hydrothermal alteration processes on element mobility and potential environmental implications at the Sousaki solfataric field (Corinthia - Greece)

<p>Tompaso geothermal system is a typical volcanic arc geothermal system in North Sulawesi, Indonesia. Although situated close to the Tondano caldera, subsurface lithologies and structures do not show any evidence for caldera-related features and the system is inferred to be related to the andesitic Soputan volcano. The subsurface geology of Tompaso consists of Tuff B unit, Rhyolite unit, Andesite B unit, Pitchstone unit, Pyroclastic Breccia unit,Andesite A unit, Pumice unit, and Tuff A unit, respectively, from the oldest penetrated unit. The silicic Pitchstone and Rhyolite units are presumed to be sourced from the same magma chamber. Petrological and mineralogical observations using binocular and petrographic microscopy, short-wave infrared (SWIR) analysis, and back-scattered electron (BSE) imaging combined with energy dispersive X-ray spectroscopy (EDS) have been applied to cuttings and limited core material from three boreholes: LHD-26, LHD-27, and LHD-32. Age dating has not been undertaken and, thus, conclusions on correlations between subsurface geology inferred here with surface formation groupings from previous works cannot be drawn. Tompaso geothermal system is characterised primarily by variations in the fracturing within the reservoir. Secondary mineralogy and the structure of present-day temperature of the system suggest that the movement of hydrothermal fluids at Tompaso is controlled by faults: the Soputan, Tempang, and A-A’ faults, the last defined for the first time in this thesis. Soputan Fault controls the outflow of the system. On the other hand, the influence of Tempang and A-A’ faults is dominant only in the upper portion of the system. The A-A’ fault likely acts as a channel for cooler meteoric surface water, while the Tempang Fault is inferred to have experienced self-sealing and appears to be an impermeable structure in the system. The self-sealing process of the Tempang Fault and/or the introduction of meteoric water through the A-A’ fault may be related to the cooling of the northern and western part of the system. The challenges in identifying protoliths in active geothermal areas is addressed here through studies of the influence of andesite textures on the preferences of hydrothermal alteration processes. Wairakei andesites were chosen for comparison to Tompaso andesites, especially because of its different geological setting and geothermal reservoir structure. The results suggest that mineral composition and arrangement affect the preference of hydrothermal alteration on andesites.</p>

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Geology and Geothermal Setting of Tompaso Geothermal System, Indonesia, with Comparisons of Andesite Alteration Patterns with Wairakei, New Zealand

10.26686/wgtn.17014589 ◽

2021 ◽

Author(s):

◽

Kartika Palupi Savitri

Keyword(s):

Hydrothermal Alteration ◽

Short Wave ◽

Age Dating ◽

Core Material ◽

Geothermal System ◽

Scattered Electron ◽

Subsurface Geology ◽

North Sulawesi ◽

Alteration Processes ◽

First Time

<p>Tompaso geothermal system is a typical volcanic arc geothermal system in North Sulawesi, Indonesia. Although situated close to the Tondano caldera, subsurface lithologies and structures do not show any evidence for caldera-related features and the system is inferred to be related to the andesitic Soputan volcano. The subsurface geology of Tompaso consists of Tuff B unit, Rhyolite unit, Andesite B unit, Pitchstone unit, Pyroclastic Breccia unit,Andesite A unit, Pumice unit, and Tuff A unit, respectively, from the oldest penetrated unit. The silicic Pitchstone and Rhyolite units are presumed to be sourced from the same magma chamber. Petrological and mineralogical observations using binocular and petrographic microscopy, short-wave infrared (SWIR) analysis, and back-scattered electron (BSE) imaging combined with energy dispersive X-ray spectroscopy (EDS) have been applied to cuttings and limited core material from three boreholes: LHD-26, LHD-27, and LHD-32. Age dating has not been undertaken and, thus, conclusions on correlations between subsurface geology inferred here with surface formation groupings from previous works cannot be drawn. Tompaso geothermal system is characterised primarily by variations in the fracturing within the reservoir. Secondary mineralogy and the structure of present-day temperature of the system suggest that the movement of hydrothermal fluids at Tompaso is controlled by faults: the Soputan, Tempang, and A-A’ faults, the last defined for the first time in this thesis. Soputan Fault controls the outflow of the system. On the other hand, the influence of Tempang and A-A’ faults is dominant only in the upper portion of the system. The A-A’ fault likely acts as a channel for cooler meteoric surface water, while the Tempang Fault is inferred to have experienced self-sealing and appears to be an impermeable structure in the system. The self-sealing process of the Tempang Fault and/or the introduction of meteoric water through the A-A’ fault may be related to the cooling of the northern and western part of the system. The challenges in identifying protoliths in active geothermal areas is addressed here through studies of the influence of andesite textures on the preferences of hydrothermal alteration processes. Wairakei andesites were chosen for comparison to Tompaso andesites, especially because of its different geological setting and geothermal reservoir structure. The results suggest that mineral composition and arrangement affect the preference of hydrothermal alteration on andesites.</p>

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Behaviour of ThSiO4 during hydrothermal alteration of raremetal rich lithologies from peralkaline rocks

Mineralogical Magazine ◽

10.1180/minmag.2016.080.138 ◽

2017 ◽

Vol 81 (4) ◽

pp. 873-893 ◽

Cited By ~ 2

Author(s):

R. Macdonald ◽

B. Bagiński ◽

P. M. Kartashov ◽

D. Zozulya

Keyword(s):

Low Temperature ◽

Hydrothermal Alteration ◽

Late Stage ◽

Great Majority ◽

Hydrothermal Fluids ◽

Element Mobility ◽

Limited Mobility ◽

Fluid Infiltration ◽

Geochemical Indicators ◽

Structural Formulae

AbstractThe behaviour of ThSiO4 during low-temperature alteration has significance for element mobility and redistribution. Here we describe five types of alteration of ThSiO4 by hydrothermal fluids: (1) primary ThSiO4 associated with chevkinite-(Ce) in a quartz-epidote metasomatite; (2) during alteration of monazite-(Ce) in a quartzolite; (3) during alteration of fergusonite-(Y) in a quartz-epidote metasomatite; (4) following exsolution from chevkinite-(Ce); and (5) associated with cerite-(Ce) and with ilmenite and bastnäsite-(Ce) in late-stage veinlets in a syenitic pegmatite and a metasomatite. The great majority of crystals have been strongly altered compositionally, with variable degrees of replacement of formula elements by non-formula elements, such as Ca, Fe, P and REE. The most reliable geochemical indicators of hydrothermal alteration are low analytical totals and non-stoichiometric structural formulae. The alteration is variably ascribed to dissolution-reprecipitation and pervasive fluid infiltration along cracks. Thorium appears to have shown limited mobility in these samples.

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Lithofacies from the 1963-1967 Surtsey eruption in SUSTAIN drill cores SE-2a, SE-2b and SE-03

Surtsey research ◽

10.33112/surtsey.14.2 ◽

2020 ◽

Vol 14 ◽

pp. 19-32

Author(s):

Jocelyn McPhie ◽

James D.L. White ◽

Carolyn Gorny ◽

Marie D. Jackson ◽

Magnús Tumi Gudmundsson ◽

...

Keyword(s):

Hydrothermal Alteration ◽

Sedimentary Facies ◽

Drill Hole ◽

Explosive Eruptions ◽

Volcanic System ◽

Sea Floor ◽

Alteration Processes ◽

Lapilli Tuff ◽

Drill Holes ◽

Drill Cores

Surtsey was drilled in 2017 in the context of the Surtsey Underwater volcanic System for Thermophiles, Alteration processes and INnovative Concretes (SUSTAIN) project. Vertical drill holes, SE-02a and SE02b (drilled to 191.64 m), and angled drill SE-03 (drilled to 354.05 m), intersected armoured lapilli tuff and lapilli tuff generated mainly by explosive eruptions at Surtur from November 1963 to January 1964. The top ~20 m of lapilli tuff was erupted from Surtungur. Intervals of coherent basalt in SE-02b (15.7 to 17 m and <15 cm at the end) and in SE-03 (<1 m at ~60 m and ~238 m, and 10 m near the base) are probably intrusions that may have fed the small lavas erupted at Surtur ~2.5 years later. Although collared only a few m from the 1979 drill hole, neither SE-02a nor SE-02b intersected the 13-m-thick interval of basalt found in the 1979 drill hole. The 2017 drill cores are entirely lithified and variably altered, reflecting the effects of hydrothermal alteration and cement deposition on the originally fresh, unconsolidated ash and lapilli. Drill hole SE-03 was drilled on an azimuth of 264o and at 55o from horizontal, obliquely crossing the crater- and conduit-fill of Surtur. Although the exact trajectory of SE-03 is unknown (the drill hole was not surveyed), the drill hole ended at a vertical depth of ~100 m below the pre-eruption sea floor, however, sedimentary facies known to underlie the sea floor nearby were not intersected. Surtur eruptions therefore excavated the pre-eruption sea floor to a depth of several tens of m.

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