The copper history in the Anti Atlas belt, from Panafrican to Variscan orogeny, a persistence of tectonic controls: an overview of Bou Azzer-El Graara inlier
Résumé
The Anti-Atlas belt is well known for its numerous copper deposits.
It displays also a complex geological, metallogenic and
tectonic history which is challenging for mining companies in order
to better understand and prospect these Cu-deposits. In the
Bou Azzer-El Graara inlier, these deposits are hosted as well within
the Precambrian basement as within the Neoproterozoic to Paleozoic
cover. This study based on mapping, structural, mineralogy,
textures and micro-textures observations present a synthesis of
Cu-deposits at this inlier scale In this Neoproterozoic to Paleozoic
sedimentary cover, two types of mineralizations are distinguished:
one is related to local folds and faults and another one associated
with a deformation localized in specific stratigraphic levels at the
base of the cover. Geological and mineralogical studies showed
that both Cu-ores types are controlled by the same hydrothermal
event associated to the Variscan orogeny. In the Precambrian
basement, massive copper sulfides lenses are present at the intersection
between regional pyritic beds or black shales and brittle
faults potentially associated with the late Panafrican deformation.
Another kind of Cu-deposits is spatially associated with Panafrican
shear zones, which showed ductile and brittle deformations. These
mineralizations seem to be linked to the late brittle deformation
that re-used the ductile shear zones inherited from the Panafrican
orogeny. During the Variscan compression, the reactivation, of
basement-inherited Panafrican structures controlled the deformation
responsible of mineralization in the cover. In summary, copper
mineralizations are closely associated with a brittle deformation,
posterior to the ductile Panafrican deformation in the basement
and synchronous with the Variscan orogeny in the cover. The metallogenic
history of copper in the Bou Azer-El Graara inlier can
be depicted through, at least, two models: (i) a two-stage model,
with a first late Panafrican hydrothermal event, responsible for the
basement-hosted Cu-bodies and a second Variscan event, yielding
Cu-deposits hosted in the cover. (ii) A single metallogenic phase,
during Variscan deformation, that mineralized both the basement
and the cover. Works in progress try to assess the relevance of
these models at the Anti-Atlas scale.