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The nature and significance of sulphate-rich, aluminous efflorescences from the Te Kopia geothermal field, Taupo volcanic zone, New Zealand

R. Martin, K. A. Rodgers and P. R. L. Browne
The nature and significance of sulphate-rich, aluminous efflorescences from the Te Kopia geothermal field, Taupo volcanic zone, New Zealand
Mineralogical Magazine (June 1999) 63 (3): 413-419

Abstract

Alunogen and meta-alunogen are the dominant phases present in transient sulphate efflorescences that are the latest products of the alteration of ignimbrite country rocks in the long-lived Te Kopia geothermal field. Meta-alunogen pseudomorphs alunogen and both species occur as white, fibrous, tangled masses, as prismatic, parallel growths, and as thin, platy, crystals, 8-15 mu m across, that coalesce in an open cellular network. Small (<2 mm diam.) spherical aggregates of radiating, acicular halotrichite (Fe (sub 0.51) Mg (sub 0.49) Al (sub 2) (SO (sub 4) ) (sub 4) .22H (sub 2) O), potash alum, mirabilite, melanterite and tschermigite are present locally. The cations needed to form these minerals derive from the host rocks with the exception of sulphur and ammonia that come from H (sub 2) S and NH (sub 3) gases ascending with steam. The particular efflorescence assemblage reflects the prevailing conditions and ionic activities of a local micro-environment. Kaolinite formed by acid sulphate alteration is now being altered by steam to yield alunogen. In turn, alunogen can react with silica, or co-dissociate with silicic acid, to form kaolinite. The alternating dissolution and reprecipitation of kaolinite and alunogen moves aluminium in and through the surficial environment at Te Kopia.


ISSN: 0026-461X
EISSN: 1471-8022
Coden: MNLMBB
Serial Title: Mineralogical Magazine
Serial Volume: 63
Serial Issue: 3
Title: The nature and significance of sulphate-rich, aluminous efflorescences from the Te Kopia geothermal field, Taupo volcanic zone, New Zealand
Affiliation: University of Auckland, Department of Geology, Auckland, New Zealand
Pages: 413-419
Published: 199906
Text Language: English
Publisher: Mineralogical Society, London, United Kingdom
References: 7
Accession Number: 1999-066045
Categories: General mineralogy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. geol. sketch map
S38°23'60" - S38°23'60", E176°13'00" - E176°13'00"
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute.
Update Code: 199922
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