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Journal Articles Mineralium Deposita Year : 2012

First evidence of epithermal gold occurrences in the SE Afar Rift, Republic of Djibouti

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Abstract

The geology of the Republic of Djibouti, in the SE Afar Triangle, is characterized by intense tectonic and bimodal volcanic activity that began as early as 25-30 Ma. Each magmatic event was accompanied by hydrothermal activity. Mineralization generally occurs as gold-silver bearing chalcedony veins and is associated with felsic volcanism. Eighty samples from mineralized hydrothermal chalcedony, quartz ± carbonate veins and breccias were studied from ten sites representing four major volcanic events that range in age from early Miocene to the present. The most recent veins are controlled by fractures at the edges of grabens established during the last 4 Myr. Gold in excess of 200 ppb is present in 30% of the samples, with values up to 16 ppm. Mineralogical compositions allowed us to identify different types of mineralization corresponding to different depths in the hydrothermal system: (1) surface and subsurface mineralization characterized by carbonate chimneys, gypsum, silica cap and quartz ± carbonate veins that are depleted in metals and Au; (2) shallow banded chalcedony ± adularia veins related to boiling that contain up to 16 ppm Au, occurring as native gold and electrum with pyrite, and tetradymite; (3) quartz veins with sulfides, and (4) epidote alteration in the deepest hydrothermal zones. Samples in which pyrite is enriched in As tend to have a high Au content. The association with bimodal volcanism, the occurrence of adularia and the native Au and electrum in banded chalcedony veins are typical of epithermal systems and confirm that this type of mineralization can occur in a young intracontinental rift system.

Dates and versions

insu-00681697 , version 1 (22-03-2012)

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N. Moussa, Yves Fouquet, Bernard Le Gall, A.M. Caminiti, Joël Rolet, et al.. First evidence of epithermal gold occurrences in the SE Afar Rift, Republic of Djibouti. Mineralium Deposita, 2012, 47 (5), pp.563-576. ⟨10.1007/s00126-011-0397-9⟩. ⟨insu-00681697⟩
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