Secondary mineralization and hydrothermal alteration in the Reydarfjordur Drill Core, eastern Iceland

Journal Article · Tue Aug 10 04:00:00 EDT 1982 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JB087iB08p06511· OSTI ID:6038600

Mehegan, J M; Robinson, P T; Delany, J R

Deep crustal driling in eastern Iceland has allowed study of a fossil hydrothermal system at a constructive plate margin. The drilled sequence consists of partly to completely altered subaerial lava flows, basaltic dikes, and minor clastic material. Alteration and secondary mineralization are most intense in the flow top breccias where water/rock ratios are presumed to have been the highest. In the upper portion of the cored sequence (to a depth of about 1200 m) alteration is characterized by the deposition of clay minerals +- calcite +- quartz +- laumonite into open spaces such as vugs and vesicles. Low-temperature zeolites, such as stilbite, epistilbite, mordenite, and heulandite, are also present but are restricted to the upper 500 m of the drill core. Below 1200 m, alteration is characterized by the dissolution and replacement of both primary minerals and earlier authigenic minerals, followed by partial filling of dissolution cavities. Early mineral assemblages consist of epidote +- quartz +- prehnite +- albite, and a later superimposed assemblages consists of calcite+laumontite +- anhydrite. Authigenic sphene, pyrite, chalcopryite, pumpellyite, aceinolite, and wairakite also occur sporadically in the cored sequence. Secondary mineral assemblages and temperature measurements of fluid inclusions suggest a maximum temperature of alteration of about 300/sup 0/C. Fluid inclusioncompositions indicate that the geothermal fluid was meteoric water with very low salinities and high calcium activities. Iron activities and oxygen fugacites were highest in the deeper portions of the systems.

• Research Organization: Department of Sciences, University of California, Riverside, California
• OSTI ID: 6038600
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 87:B8; ISSN JGREA
• Country of Publication: United States
• Language: English

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