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Hydrothermal Alteration of Basaltic Rocks at Eruptive Vents on Mount Cameroon Volcano, West Africa

International Journal of Geosciences 2018年第9期9卷 513-527页

作者： Akumbom Vishiti Taboko Armstrong Elisha Mutum Shemang Jacques Etame Cheo Emmanuel Suh Department of Civil Engineering The University Institute of Technology (IUT) University of Douala Douala Cameroon Economic Geology Unit Department of Geology University of Buea Buea Cameroon Department of Earth and Environmental Science Botswana International University of Science and Technology Palapye Botswana Laboratory of Geosciences Natural Resources and Environment Department of Earth Science University of Douala Douala Came-roon Department of Geology Mining and Environmental Science The University of Bamenda Bambili Cameroon

The study of changes in rocks due to interaction with hydrothermal fluids at active volcanoes provides insights into wall rock alteration associated with ore deposits formed in the geological past. Therefore, the nature of mineral alteration and chemical changes experienced by wall rocks can be investigated at eruptive sites on active volcanoes and the results used to better constrain ore-forming processes. In this study, we investigated the alteration at eruptive sites at Mount Cameroon volcano. These eruptive vents lie along NE-SW-trending fissures that define the Mount Cameroon rift. The vents are surrounded by cones composed largely of pyroclastic materials and to a lesser extent lava. fumaroles (volcanic gases) rising through the vents during and after the 1999 eruption have resulted in the alteration of the pyroclastic robble along the fissures and the inner walls of the cones. Consequently, altered basaltic materials are covered with thin films of reddish, yellowish to whitish secondary minerals. These coatings result from an interaction between the surfaces of the basaltic glass with volcanically-derived acidic fluids. Petrographic investigations and XRD analysis of the basalts have identified primary mineral phases, such as olivine, pyroxene (mainly augite) and feldspars. Alteration products revealed include ubiquitous silica as well as gypsum, magnetite, feldspar, alunite and jarosite. Jarosite occurrence indicates that SO2 is the primary volcanically-derived acid source involved in coating formation. High contents of sulfur identified in the basalts indicate that melts at Mount Cameroon can be sulfur saturated as backed by previous melt inclusion data. Whole rock geochemical analysis shows a gain in silica in the altered samples and this ties with the mass balance calculations although minor gains of Al2O3, , MgO, MnO, CaO and K2O are shown by some samples.

关键词： Mount Cameroon 1999 Eruption fumarole Wall Rock Alteration Mass Bal-ance

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