Lyell Collection
Journal of the Geological Society
Lyell Centre  |   Lyell Collection  |   Subscriptions   |   Geological Society  |   Email alerts  |   Online bookshop  |   Help

Keywords:
Author:
Advanced search>>
This Article
Right arrow Full Text (PDF)
Right arrow References
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by BOTTRELL, S. H.
Right arrow Articles by SPIRO, B.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation
Journal of the Geological Society; 1988; v. 145; issue.6; p. 941-949;
DOI: 10.1144/gsjgs.145.6.0941
© 1988 Geological Society of London

Article

A stable isotope study of black shale-hosted gold mineralization in the Dolgellau Gold Belt, North Wales

S. H. BOTTRELL1 & B. SPIRO2

1 Department of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK
2 British Geological Survey, Geochemical Division, 64-78 Gray’s Inn Road, London WC1X 8NG, UK

Isotopic determinations have been made on minerals from mineralized veins (including inclusion fluids), altered wall-rocks and host shales from the Clogau-St Davids gold mine and smaller mines in the Dolgellau Gold Belt. The Clogau Formation shales hosting the mineralization contain calcite (mean {delta}13C –11.5{per thousand}PDB) and graphite (mean {delta}13C –22.2{per thousand}PDB) yielding an equilibrium isotopic exchange temperature of 300-315 ±20 °C, a likely metamorphic temperature. Mineralized vein calcites are isotopically lighter than calcite in the shale with mean {delta}13C of -12.9{per thousand}PDB. Mineralized vein quartz oxygen isotopic compositions (9.6-11.0{per thousand} SMOW) are similar to the host shale quartz (9.4-13.6{per thousand} SMOW). Calcites are always too enriched in 18O to be in equilibrium with quartz in the same sample. It is not possible to distinguish whether this is a primary feature or whether the calcite compositions have been reset subsequent to formation. Chalcopyrite and pyrrhotite in one sample from the Clogau-St Davids mine give an equilibrium formation temperature of 300 ± 50 °C. A relationship exists between the composition of mineralized vein sulphur and that in the host shales, though the ore sulphur is always depeleted in 34S relative to the shale host. This is most probably due to a mixing of shale sulphur with a lighter, introduced component during ore formation. Deuterium/hydrogen ratios in fluid inclusion water may also indicate the introduction of a fluid into the shales during mineralization.

The stable isotope data show that mineralization in the Dolgellau gold belt probably involved the introduction of an externally derived fluid into the shales of the Mawddach Group and that it interacted to a significant extent with the shales. This interaction makes it difficult to be certain of the original isotopic 'signature' of the ore-forming fluid, but is was probably derived from an igneous source, either as a primary magmatic fluid or as the result of fluid interacting with igneous material during metamorphism.




This article has been cited by other articles:


Home page
 Can MineralHome page
N. J. Cook, C. L. Ciobanu, C. J. Stanley, W. H. Paar, and K. Sundblad
COMPOSITIONAL DATA FOR Bi-Pb TELLUROSULFIDES
Can Mineral, 2007; 45: 417 - 435.
[Abstract] [Full Text] [PDF]

Home page
 Geological Society, London, Special PublicationsHome page
D. Lowry, A. J. Boyce, A. E. Fallick, W. E. Stephens, and N. V. Grassineau
Terrane and basement discrimination in northern Britain using sulphur isotopes and mineralogy of ore deposits
Geological Society, London, Special Publications, 2005; 248: 133 - 151.
[Abstract] [PDF]

Home page
 Journal of the Geological SocietyHome page
T. Wagner, T. Wagner, and A. J. Boyce
Sulphur isotope geochemistry of black shale-hosted antimony mineralization, Arnsberg, northern Rhenish Massif, Germany: implications for late-stage fluid flow during the Variscan orogeny
Journal of the Geological Society, 2003; 160: 299 - 308.
[Abstract] [Full Text] [PDF]

Home page
 Exploration and Mining GeologyHome page
I. M. Platten, I. M. PLATTEN, and S. C. DOMINY
The Occurrence of High-grade Gold Pockets in Quartz Reefs at the Gwynfynydd Mine, Wales, United Kingdom: A Geological Explanation for the Nugget Effect
Exploration and Mining Geology, 2001; 10: 249 - 272.
[Abstract] [Full Text] [PDF]