Géochimie, Géochronologie et Métallogénie (Au-EGP) des formations lithologiques de Ngaye, Nord-Cameroun

Abstract

The objective of this work is to deepen the understanding of the crustal and geodynamic evolution of the Adamaoua-Yadé domain through the characterisation of geological formations and the assessment of the economic potential in gold and platinum group elements (Au-PGE) in the Ngaye area. To achieve this, several fields of expertise were employed, including petrography, mineralogy, structural geology, geochemistry, metallogeny, and geochronology. The results show that the study area is composed of two lithological groups: an intrusive suite consisting of granodiorites and granites, and a metamorphic suite composed of amphibolites (pyroxene-bearing and garnet–pyroxene-bearing) and gneisses (amphibole biotite and biotite-rich). These rocks typically outcrop as enclaves, blocks, slabs, and domes. The granitoids, with a porphyritic granular texture, exhibit a typical mineral association: Pl+Kfs+Qz+Amp+Bt, while the metamorphic rocks, of amphibolite facies ranging from medium to high grade, show granoblastic textures with parageneses such as: Amp+Pl+Cpx+Bt+Qz+Kfs; Amp+Grt+Pl+Cpx+Bt+Qz; Bt+Qz+Pl+Kfs; and Bt+Amp+Qtz+Pl+Kfs. Structural analysis reveals a polyphase evolution involving three deformation phases (D1, D2, D3). Phase D1 is characterised by foliation S1 and lineation L1. Phase D2 is marked by shear planes C2 and folds P2. Phase D3 corresponds to brittle tectonics, mainly indicated by fractures (joints). From a geochemical perspective, the intrusive rocks are calc-alkaline with metaluminous to peraluminous compositions (A/CNK: 0.87–1.21), mainly I-type, and are derived from partial melting of the upper crust with a mantle contribution. In contrast, the metamorphic rocks display both calc-alkaline and tholeiitic characteristics. The gneisses, in particular, are Mg-rich dioritic magmas (sanukitoids), resulting from the interaction between a mantle peridotite and an incompatible-element-enriched magma, typical of subduction zone environments. Low concentrations of LILEs, HFSEs, and REEs suggest partial melting of a depleted mantle in a continental arc setting. Dating results indicate a Mesoarchaean crust formed at 2997 ± 38 Ma, reworked at 2080 ± 10 Ma and 606 ± 113 Ma, during the Eburnean and Pan-African orogenies, respectively. This crustal evolution is comparable to that of the Nyong complex. From a metallogenic standpoint, palladium (Pd) and platinum (Pt) concentrations in the amphibolites are relatively low, ranging from 0.15 to 21.10 ppb for Pd and from 1.96 to 14 ppb for Pt. These values are consistent with data from the Akom II area (Nyong complex), confirming the geochemical similarity of the samples. In summary, the Ngaye region represents an Archaean core reworked during the Palaeoproterozoic and Neoproterozoic.