On the growth of colloform textures: a case study of sphalerite from the Galmoy ore body, Ireland

Barrie, Craig D., Boyce, Adrian J., Boyle, Alan P., Williams, Patrick J., Blake, Kevin , Wilkinson, Jamie J., Lowther, Mike, McDermott, Paul, and Prior, David J. (2009) On the growth of colloform textures: a case study of sphalerite from the Galmoy ore body, Ireland. Journal of the Geological Society, 166 (3). pp. 563-582.

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Colloform textures have been described from many of the world's sulphide ore deposits and involve formation of distinct microcrystalline layers. These textures provide information related to sequential stages of ore formation, yet their mechanism of growth is poorly understood. This study has analysed a series of colloform samples from the Galmoy Zn + Pb mine, Ireland. Results indicate that the growth sequence is not always intuitive and layers that appear stratigraphic upon cursory observation may not be. The crystal preferred orientation (CPO) of discrete colloform layers abruptly switches between different orientation axes. Examination of the same layers using in situ laser sulphur isotope analysis reveals equally striking changes in {delta}34S signature between end-member bacteriogenic (–25{per thousand}) and hydrothermal (+10{per thousand}) sources. Although these results, combined with petrographic observation, allow the determination of a probable growth history, there is no correlation between shifting CPO and {delta}34S signature. Trace element analysis reveals changes in trace element sequestration between colloform layers. Cadmium- and chlorine-rich layers correspond to a hydrothermal sulphur source, whereas iron-rich layers correspond to a bacteriogenic sulphur source. In the absence of alternative mechanisms we suggest that the most likely factors influencing CPO changes are temperature and degree of supersaturation during two-fluid mixing.

Item ID: 8054
Item Type: Article (Research - C1)
ISSN: 0016-7649
Keywords: Europe; Western Europe; sulfides; Ireland; mixing; temperature; iron; chlorine; cadmium; trace elements; trace-element analyses; correlation; isotopes; in situ; laser methods; preferred orientation; crystals; mines; ore bodies; sphalerite; case studies; textures; growth
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Date Deposited: 02 Feb 2010 00:54
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040306 Mineralogy and Crystallography @ 100%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840108 Zinc Ore Exploration @ 100%
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