Ismaila Ahmadou^{1, 2,}, Mana Bouba Christian^{1, 2}, Ipan Antoinette Solange^{1, 3}, Aboubakar Abdoulaye Sahabo^{1, 4}, Sep Nlonngan Jean Paul¹, Yinyang Wanbitching Raoul², Mohamadou Sali⁵, Tchameni Rigobert²

The Biboko locality is located eastward in the central domain of the Pan-African Fold Belt of Central Africa. The task consisted in the cartography of the various types of rocks, to do their petrographic and structural studies with the aim of understanding the geological context of gold which is be exploited in the locality. Weal so brought out the study of environmental impact generated by this exploitation. The main types of rock identified in the locality could be grouped in to two: the metamorphic and plutonic rocks and their associate intrusion. The metamorphic rocks are represented by amphibole-biotite orthogneisses and amphibolites. Their main blade texture is granonematoblastic. The primary assemblage is made up of amphibole, biotite, plagioclase, quartz, zircon and apatite which are in equilibrium in the amphibolite facies. The secondary assemblage is made up of quartz, biotite, chlorite, pyrite, sericites derived from either the alteration or the recristallization of the primary assemblage. The plutonic rocks are slightly deformed and are represented by biotite bearing tonalite, microcline bearing granite, biotite bearing granite, biotite-epidote granite. These rocks have grained-oriented texture made up of quartz + microcline + orthose + plagioclase +/- biotite + accessory minerals. Concerning the structural study of the area, we have four deformationals phases. The first phase D1 is caracterized by subhorizontal shistosity/ foliation. The second phase D2, caracterised by open folds P2, shistosity S2, subvertical to vertical and slightly plonge lineation L2. It is a transpressive deformation with senestral sheared plans. The migmatisation which is the origin of certain plutonic rocks is syn-D1 to syn-D2. The third phase which is not penetrative, is made of folds P3 with straight axes and crenulation S3. The fourth phase is brittle-like and characterized by fractures. The abondances in secondary minerals (microcline, pyrite, chlorite, sericite) in certain facies (microcline bearing granite) is a proof for hydrothermalism. Part of gold found at Biboko could have been derive from altered rocks in the region. This is proved by the presence quartz in intrusion slightly mineralised in pyrite which is associate mineral of gold.

Pétrographie, structural, Biboko, Amphibolites facies, hydrothermalism