Example of a structurally controlled copper deposit from the Hercynian western High Atlas (Morocco): the High Seksaoua mining district

Abstract

The mineralized district of the High Seksaoua (Western High Atlas, Morocco) is characterized by a lithological succession marked by an alternation of schists and limestones attributed to the Cambrian and affected by at least five deformational events. The copper mineralization herein analysed is systematically localized close to a dolomite/black schist level in which a top-to-the-NNW d6collement-type tectonics (Dd) has been identified. We demonstrate that the economic mineralization is a syn-tectonic stockwork formed in response of this top-to-the-NNW shearing event (Dd). This tectonic event can be reasonably correlated with the late Hercynian tectonics responsible, in the same area, for the Tichka granite emplacement at c. 291 ± 5 Ma, also under the control of a NW-SE shortening direction. Indeed, the Tichka granite represents a good candidate to explain the origin of the mineralized fluid. Such an hypothesis is confirmed by the Permo-Triassic age (c. 270 Ma) given by 4°Ar/39Ar dating realized on white micas related to the stockwork formation (this study). This important result questions the syn-genetic interpretation accepted until now for this mineralization and allows us to propose a new model of formation for this kind of deposit that could contribute to exploration programmes.

Structural Control of Ore Deposits: The Role of Pre-Existing Structures on the Formation of Mineralised Vein Systems

“…The economic mineralisation is a syntectonic stockwork (Figure 9c,d) formed in response to this top-to-the-N-NW shearing event that only affects the black schist layers (Figure 9). We suggest that vein formation is a brittle response, within competent dolomite levels, of the ductile deformation that affects the black schist ( Figure 9a) [51], as described in the conceptual model of the Figure 1b.…”

“…The existence of stratiform masses of pyrite first suggests that this deposit can be a VHMS (Figure 9a) [49]. However, copper mineralisation, the first economic goal, is absent from the stratiform pyrite levels but systematically localised close to the dolomite/black schist contact in which a top-to-the-N-NW décollement-type tectonics [50,51] has been identified ( Figure 9b). The economic mineralisation is a syntectonic stockwork (Figure 9c,d) formed in response to this top-to-the-N-NW shearing event that only affects the black schist layers (Figure 9).…”

Cu–Au vein mineralization related to the Talat n’Imjjad shear zone (western High Atlas, Morocco): geological setting, ore mineralogy, and geochemical evolution

“…These smaller faults and fractures are probably related and induced by the kinematic and operation of the conjugate system formed by Erdouz and Al Medinet faults. The CuBi-Au and polymetallic mineralization described in this contribution is located at the intersections of these faults (Badra 1993;Chauvet et al 2002;Alansari et al 2009;Bouabdellah et al 2009;Ilmen 2011;Baidada 2012;Ilmen et al 2013aIlmen et al , 2013bIlmen et al , 2014.…”

The Bouznika Cambrian barite deposit (Morocco), an early mineralization on the Iapetus margin

“…The association of these elements reflect the selective leaching of K-feldspar. On a regional scale, the Bouznika deposit shares many similarities with the Talmakent deposit in the Seksaoua area of the Western Upper Atlas Mountains (Rchid et al, 1996;Azza, 1998;Gaouzi et al, 2001;Chauvet et al, 2002;Barbanson et al, 2003), where a barite horizon is hosted by a bimodal plutonic and volcanic complex at the Georgian-Acadian transition. The 70-m thick volcanic assemblage includes lapilli tuffs and carbonate units.…”

“…This suggests mud flow deposition and localized reworking of the sediments by streams. Thin sections reveal fresh oligoclase phenocrysts exhibiting oriented trachytic texture in a glassy, chlorite-rich Jaillard, 1993;Rchid et al, 1996;Gaouzi et al, 2001;Chauvet et al, 2002;Barbanson et al, 2003 matrix. Sericite accompanied by apatite and epidote are present as accessory minerals.…”