Mineral formation and redox-sensitive trace elements in a near-surface hydrothermal alteration system |
| |
| Institution: | 1. Hong Kong Geological Survey, Geotechnical Engineering Office, Civil Engineering and Development Department, 101 Princess Margaret Road, Kowloon, Hong Kong, China;2. Department of Earth and Planetary Sciences, Birkbeck, University of London, Malet Street, London WC1E 7HX, UK;3. Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK |
| |
| Abstract: | A recent hydrothermal mudpool at the southwestern slope of the Rincón de la Vieja volcano in Northwest Costa Rica exhibits an argillic alteration system formed by intense interaction of sulfuric acidic fluids with wall rock materials. Detailed mineralogical analysis revealed an assemblage with kaolinite, alunite, and opal-C as the major mineral phases. Electron paramagnetic resonance spectroscopy (EPR) showed 3 different redox-sensitive cations associated with the mineral phases, Cu+ is structure-bound in opal-C, whereas VO2+ and Fe3+ are located in the kaolinte structure. The location of the redox-sensitive cations in different minerals of the assemblage is indicative of different chemical conditions. The formation of the alteration products can be described schematically as a 2-step process. In a first step alunite and opal-C were precipitated in a fluid with slightly reducing conditions and a low chloride availability. The second step is characterized by a decrease in K+ activity and subsequent formation of kaolinite under weakly oxidizing to oxidizing redox conditions as indicated by structure-bound VO2+ and Fe3+.The detection of paramagnetic trace elements structure-bound in mineral phases by EPR provide direct information about the prevailing redox conditions during alteration and can, therefore, be used as additional insight into the genesis of the hydrothermal, near-surface system. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
