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Fluids and hydrothermal alteration assemblages in a Devonian gold-bearing hot-spring system, Rhynie, Scotland

Published online by Cambridge University Press:  26 July 2007

M. Baron ,
S. Hillier ,
C. M. Rice ,
K. Czapnik  and
J. Parnell
M. Baron
Affiliation:
Department of Geology & Petroleum Geology, University of Aberdeen, Aberdeen, AB24 3UE, UK. e-mail: [email protected]
S. Hillier
Affiliation:
Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen AB15 8QH, UK.
C. M. Rice
Affiliation:
Department of Geology & Petroleum Geology, University of Aberdeen, Aberdeen, AB24 3UE, UK. e-mail: [email protected]
K. Czapnik
Affiliation:
Department of Geology & Petroleum Geology, University of Aberdeen, Aberdeen, AB24 3UE, UK. e-mail: [email protected]
J. Parnell
Affiliation:
Department of Geology & Petroleum Geology, University of Aberdeen, Aberdeen, AB24 3UE, UK. e-mail: [email protected]
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Abstract

Hydrothermal alteration at Rhynie, Aberdeenshire, Scotland, is concentrated along a fault zone, which juxtaposes surface deposits and the mineralised feeder zone to the Rhynie hotspring system. Mineralisation consists of breccias and veins filled with quartz, chert, calcite, K-feldspar and pyrite. Associated pervasive alteration comprises a high-temperature K-feldsparquartz-illite facies (formed at 250–350°C), a medium-temperature mixed layered illite/smectitequartz-K-feldspar-chlorite-calcite facies (formed at 150–200°C) and a low-temperature mixed layered illite/smectite-chlorite-calcite facies (formed at 100 to +150°C). The fluids responsible for mineralisation were mainly moderate- to high-temperature (Th =91–360°C), low-salinity (<0·2 to 2·9 wt.% NaCl eq.) H2O-NaCl-heated meteoric fluids comparable to modern and ancient hot-spring systems. The migration of these fluids was mainly restricted to a major fault zone bounding the Devonian basin. Fluids responsible for mineralisation, alteration and cementation elsewhere in the basin were low-temperature (Th 57 to 161°C), low- to high-salinity (<0·2 to 18 wt.% NaCl eq.) H2O-NaCl fluids, which resemble basinal brines.

Keywords

Epithermal gold mineralisationfluid inclusionshot springssiliceous sintersX-ray diffraction
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 94 , Issue 4 , December 2003 , pp. 309 - 324
Copyright
Royal Society of Edinburgh 2003

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