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Formation of coagulated colloidal silica in high-temperature mineralizing fluids

Published online by Cambridge University Press:  05 July 2018

B. J. Williamson ,
J. J. Wilkinson ,
P. F. Luckham  and
C. J. Stanley
B. J. Williamson*
Affiliation:
Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, UK
J. J. Wilkinson
Affiliation:
Department of Earth Science and Engineering, Imperial College, Prince Consort Road, London SW7 2BP, UK
P. F. Luckham
Affiliation:
Department of Chemical Engineering, Imperial College, Prince Consort Road, London SW7 2BY, UK
C. J. Stanley
Affiliation:
Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, UK
*
*E-mail: [email protected]
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Abstract

Recent experimental studies have suggested that colloidal silica can form in high-T (300 to >700°C) hydrothermal fluids (Wilkinson et al., 1996). Natural evidence in support of this was found by Williamson et al. (1997) who proposed a colloidal (gel) silica origin for <50 μm irregularly-shaped inclusions of quartz contained in greisen topaz from southwest England. Confocal and microprobe studies, presented here, strengthen this argument although rather than forming a gel in the hydrothermal fluid, it is suggested that the colloidal silica aggregated as a viscous coagulated colloid, with much of its volume (<10 to 30 vol.%) consisting of metal (mainly Fe) -rich particles. This is evident from the largely solid nature of metal-rich shrinkage bubbles contained at the margins of the inclusions of quartz which shows that the material forming the inclusions contained much less liquid than would be expected in a silica gel. These findings may have important implications for models of ore formation since the precipitation of a coagulated colloid could inhibit hydrothermal fluid transport and cause co-deposition of silica and entrained ore-forming elements. The mode of formation of the colloidal silica and further implications of the study are discussed.

Keywords

silicacolloidhydrothermalore genesissupercritical fluids
Type
Research Article
Information
Mineralogical Magazine , Volume 66 , Issue 4 , August 2002 , pp. 547 - 553
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2002

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