Gold mineralization in the Ourika Gneiss High Atl

Authors: Ahmed Barakat

Publish Date: 2014/05/11

Volume: 8, Issue: 5, Pages: 3207-3222

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Abstract

The Ourika gold showing lies in the High Atlas of Morocco near Marrakech It is mainly hosted by Precambrian gneiss and basic dykes and is controlled by shear zones Gold mineralization occurs mainly within quartz structures Fracturing and mineralization are interpreted to have occurred in three stages Early and intermediate stages involved the deposition of an arsenopyrite–pyrite–quartz–chlorite assemblage and a chalcopyrite–arsenopyrite–pyrite–quartz–chlorite assemblage respectively Early intermediate stage fluid inclusions belong to the CHON system typical of the retrograde metamorphism that affects the PanAfrican terranes at PT conditions of 140–300 MPa and 240–450 °C and moderate ductile–brittle deformation Deposition of native gold bismuth bismuthinite and galena during the ore stage from lowsalinity aqueous fluids was related to downward penetration of meteoric waters trapped at PT conditions of 20–110 MPa and 170–210 °C Evolving physical conditions and fluid compositions from early to late fluid stages played important roles in oreforming processes Owing to structural observations oreforming fluids could be linked to regional Variscan hydrothermal event Gold crystallised as native particles in microfissures crosscutting earlier sulphides Thus the gold deposition was late and appears as a consequence of deeply penetration of oxidising fluids favoured by microfracturing of the already ore As–Fe–Cu structuresThe research has benefited from collaboration with Christian Marignac MarieChristine Boiron and Michel Cathelineau I would like to acknowledge assistance in the field given by Reminex Companies of Groupe ONA All reviewers are thanked for their helpful comments and suggestions

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