|The Tamlalt-Menhouhou Polyphase Gold Deposit (High-Atlas, Morocco): IOCG-type Mineralisation Overprinted by Shear-Zone Related Gold|
Ewan Pelleter, Geological Survey of Canada, Natural Resources Canada, Quebec, Alain Cheilletz, ENS Géologie, Vanduvre-lés-Nancy Cedex, France, Dominique Gasquet, CISM-EDYTEM, Université de Savoie, Le Bourget du Lac cedex, France, Abdellah Mouttaqi, Mohammed Annich and Abdelkhalek El Hakour, ONHYM, Rabat, Maroc.
in - Porter, T.M. (ed.), 2010 - Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective, v. 4, Advances in the Understanding of IOCG Deposits; PGC Publishing, Adelaide. pp. 535-552.
The Tamlalt-Menhouhou gold deposit is hosted by strongly altered Neoproterozoic volcanosedimentary rocks outcropping in the eastern High Atlas of Morocco. Previous studies highlight the polyphase character of the deposit, describing two distinct pulses of auriferous mineralisation telescoped in space: (i) an Ordovician gold mineralisation (448±12 Ma) recorded by hydrothermal zircons and (ii) a regional "shear zone-related" Variscan gold mineralisation (293±7 Ma). The Ordovician mineralising event shares common characteristics with IOCG-like deposits: (i) occurrence of intense and extensive sodic and sodic ± calcic alteration; (ii) a S-poor fluid (iron oxides > sulphides); (iii) mineralisation hosted by hematite breccias or disseminated inside strongly altered rocks; (iv) polymetallic, i.e. Au, Cu, Ni, Co, As, Mo, Ag, ± Bi, Sb and Te enrichment; (v) fluid mixing; and (vi) a genetic link with the Zelmou barite mineralisation, all of which underline a regional-scale hydrothermal event. Ordovician alteration and mineralisation is strongly reworked during the Variscan event. The latter is associated with shear-zone development and with overprinting of former alteration patterns by a strong phyllic and argillic alteration. Gold appears as free particles inside quartz veins located along shear faults, and is interpreted as a remobilisation of the Ordovician gold. Recognition of a possible IOCG-like mineralisation encourages further exploration in the Tamlalt plain (and by extension in Morocco), and/or re-examination of Moroccan precious metal deposits associated with large amounts of iron oxides. Finally, this study of the Tamlalt-Menhouhou gold deposit underlines the potential for Variscan tectonics to remobilise metals within the High Atlas belt.
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