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

Barrie, C., Boyce, A. , Boyle, A.P., Williams, P.J., Blake, K., Wilkinson, J.J., Lowther, M., MacDermott, P. and Prior, D. (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. (doi: 10.1144/0016-76492008-080)

Abstract

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 δ³⁴S signature between end-member bacteriogenic (–25‰) and hydrothermal (+10‰) sources. Although these results, combined with petrographic observation, allow the determination of a probable growth history, there is no correlation between shifting CPO and δ³⁴S 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 Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Boyce, Professor Adrian and Barrie, Dr Craig
• Authors: Barrie, C., Boyce, A., Boyle, A.P., Williams, P.J., Blake, K., Wilkinson, J.J., Lowther, M., MacDermott, P., and Prior, D.
• Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Journal of the Geological Society
• Publisher: Geological Society of London
• ISSN: 0016-7649
• Published Online: 01 January 2009