Petrography and geochemistry of biotite gneiss and amphibolite mined as aggregates and the environmental impact of quarrying operations in Logbadjeck, Cameroon

Logbadjeck is situated in the northern edge of the Congo Craton, Nyong Series, Cameroon. This paper presents the petrographic and geochemical characteristics of biotite gneiss and amphibolite mined as aggregates and the environmental impact of quarrying operations in Logbadjeck. Representative rock samples were described under the petrographic microscope. Major, trace, and Rare Earth Elements of these samples were obtained using XRF and ICP–MS respectively. Results show that, biotite gneiss is composed of quartz (40–50%), plagioclase (< 20%), K-feldspar (~ 2%), biotite (20–25%), amphibole (1–2%), and opaque minerals (~ 1%), while amphibolite is made up of amphibole (60–70%), quartz (~ 5%), plagioclase (~ 7%), K-feldspar (~ 6%), biotite (10%), and opaque minerals (~ 2%). These main rock types in Logbadjeck were metamorphosed under the greenschist and amphibolite facies. Biotite gneiss is acidic (SiO2: 64.96–72.87 wt%), tholeiitic, peraluminous, with S-type composition and plots in the igneous protolith. Amphibolite (SiO2: 39.61–48.23 wt%) is ultrabasic to basic, tholeiitic, metaluminous, with I-type composition and also plots in the igneous protolith. These rocks display negative correlations of major oxides versus SiO2. REE patterns show negative Eu anomalies, indicating LREEs enrichment over HREEs and plagioclase fractionation, while multielement normalized diagrams possess K, Sr, P, and Ti negative anomalies pointing a crustal source. Additionally, Th/Nb, La/Nb, Ba/Nb, La/Nb, Nb/U, and La/Sm ratios highlighted crustal contamination or assimilation in the study area. The impact of quarrying operations in Logbadjeck is devastating and the outcomes of this study serves as awareness for environmentalists and legislators in charge of policy formulation.