Formation rates of calc-silicate minerals deposited inside drillhole casing, Ngatamariki geothermal field, New Zealand

Journal Article · · American Mineralogist; (USA)

OSTI ID:6956138

Browne, P R.L.; Courtney, S F ^[1]; Wood, C P ^[2]

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1. Univ. of Auckland (New Zealand)
2. New Zealand Geological Survey, Rotorua (New Zealand)

Chips ejected during the initial openings of Ngatamariki well, NM2, in the Taupo Volcanic Zone, New Zealand, consist of euhedral crystals of wairakite, prehnite, Fe-rich epidote, plus rare quartz and pyrite. The shapes of some of the ejecta surfaces show clearly that they formed inside the casing and liner slots of the well during the 472 days it was shut in. The calc-silicates were derived from a depth of 1,580 to 1,600 m where they grew from hot, dilute alkaline chloride water of near-neutral pH and low dissolved CO{sub 2} content. Textural relations and thermodynamic considerations show that, for a time, wairakite, epidote, and prehnite grew together in apparent equilibrium from quartz-saturated water with log(a{sub Ca}2+/a{sup 2}{sub H+}) = 8 and log(a{sub Fe}3+/a{sup 3}{sub H+}) = {minus}8. The approximate minimum growth rates of individual crystals are estimated to be wairakite, 190 {mu}m{sup 3} per day; prehnite, 0.2 to 0.5 {mu}m per day in a direction parallel to the 110 faces, and epidote, 0.2 {mu}m per day in a direction parallel to the 100 faces.

• OSTI ID: 6956138
• Journal Information: American Mineralogist; (USA), Vol. 74:7-8; ISSN 0003-004X
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
GEOTHERMAL WELLS
SCALING
NEW ZEALAND
SILICATE MINERALS
CRYSTAL GROWTH
CALCIUM COMPOUNDS
CARBON DIOXIDE
DEPOSITION
DEPTH
GEOTHERMAL FIELDS
PH VALUE
QUANTITY RATIO
RESERVOIR FLUIDS
SHUTDOWNS
SYNTHESIS
TEXTURE
THERMODYNAMIC PROPERTIES
WELL CASINGS
ALKALINE EARTH METAL COMPOUNDS
AUSTRALASIA
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
DIMENSIONS
FLUIDS
MINERALS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
WELLS
150903* - Geothermal Engineering- Corrosion
Scaling & Materials Development