Petrology and feldspar chemistry of the Penja–Manjo pegmatites in the Pan-African orogenic belt of Cameroon: economic implication

Penja and Manjo pegmatites crosscut the basement of the North Equatorial orogenic belt in Cameroon. We combined field study, pegmatite petrology and feldspar chemistry. Pegmatites occur as N110E, N150E and N160E veins (5–8 m long, 0.4–1.5 m wide) truncating the Precambrian basement and striking N110E–N180E (3–6 m long, 0.3–1.5 m wide) along fractures. They display coarse-grained textures outlined by plagioclase, microcline, quartz, biotite, muscovite and accessories. Two varieties of coarse-grained pegmatites exist, the quartz–plagioclase ± microcline containing SiO 2 (70.18 wt %) and CaO (0.61 wt %) and the quartz–plagioclase–microcline pegmatite which is barren (Ta/Nb > 5), having SiO 2 (68.34 wt %) (Na 2 O + K 2 O) = 9.27 wt %, with low Ta, Nb, Sn, Li and Be, and is similar to S-type, peraluminous, high-K calc-alkaline granite from volcanic arc. The negative Eu anomalies, light rare earth element enrichment over heavy rare earth elements (for the multi-elements and rare earth elements), low K/Rb and Rb/Sr with depleted light field strength elements and P 2 O 5 values between 0.99 and 1.95 wt % in feldspars refer to low evolved and fractionated pegmatites. These pegmatites were originated from a single magmatic melt linked to multiple sources. The low Fe 2 O 3 (~ 1 wt %), the Al 2 O 3 /K 2 O ratios (3.82–3.92), the high K 2 O + Na 2 O (7.44–9.27 wt %) and K 2 O/Na 2 O (~ 1) and the dominance of plagioclase over microcline feldspar underline the suitability of the studied pegmatites for ceramic manufacturing.