In:
Mineralogical Magazine, Mineralogical Society, Vol. 65, No. 3 ( 2001-06), p. 397-406
Abstract:
Electron microprobe analyses of prehnites from the Way Linggo low-sulphidation epithermal Au-Ag deposit of southern Sumatra, show that the mole fraction of octahedral Fe 3+ , expressed as Fe 3+ /(Fe 3+ +Al VI ), ranges from 0.0 to ~0.6, the higher values being among the most iron-rich reported for prehnite in a hydrothermal environment. Prehnites from a diabase sill in the Heber geothermal field of California have mole fractions of octahedral Fe 3+ ranging from 0.03 to 0.3. The Way Linggo prehnites formed below 220°C, some 20–30°C lower than those at the Heber field; the lower crystallization temperatures perhaps enhanced the opportunity for Fe 3+ to substitute in octahedral sites. In both occurrences, prehnite predates late-stage calcite, consistent with the need for waters depositing prehnite to have a CO 2 〈 0.01 moles. At higher CO 2 activities the stability field of calcite would swamp the range of a Ca 2+ / a H + values appropriate for crystallizing prehnite. Consequently, the presence of prehnite in a hydrothermal environment primarily indicates that degassing of the hydrothermal fluid in CO 2 occurred prior to deposition.
Type of Medium:
Online Resource
ISSN:
0026-461X
,
1471-8022
DOI:
10.1180/002646101300119475
Language:
English
Publisher:
Mineralogical Society
Publication Date:
2001
detail.hit.zdb_id:
2034522-7
detail.hit.zdb_id:
206325-6
SSG:
13
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