Molybdenum fertility indicators, granite zircon chemistry, and U-Pb geochronology of the Manjo pluton, southwestern Cameroon

Abstract

Due to an increasing interest in mineral prospection, Manjo granites which are orogenic have been studied in terms of the geochemistry of whole rock and isotopes of interest found in the associated zircons. This was done to define and situate these rock unit within the context of the regional belt that is Pan African in age, establish the source of Manjo granites and their evolution during the Pan-African orogeny. More so, this study sheds more light on the controversy around the orogenic statues of granites in this section of the geological region, examines their potential for hosting molybdenum, establishes their link with other rocks within this part of the region and how they relate to the Mo-U-bearing biotite-granite in its Ekomedion neighborhood. Sixty-six zircon grains gotten from the granites and their trace elements and Lu-Hf isotopic signatures were examined. The zircon grains' ages were gotten by mass spectrometric method using the U-Pb systematics by laser ablation.The zircons ratios of U to Th varry between 0.2–2.3 relating to sources that are originally magmatic and totally different from those related to souces related to hydrothermalism and metamorphism. The granites were emplaced within the 585±17–616±12 Ma age bracket. Zircons in this study similar to the nearby Ekomedion U-Mo-bearing two mica granites and other felsic massifs found within the shear zones of central Africa (CASC)point to the fact that the Manjo granites were formed at low oxygen fugacity (log ƒO₂; -15.848 to -4.515, and log ƒO₂@FMQ; -17.409 to -3.677). More so, samples plot mainly outside the defined fertile fields on plots of Eu/Eu* Vs (Ce/Nd)/Y, 10000 × (Eu/Eu*)/Y Vs (Ce/Nd)/Y and Eu/Eu* Vs Dy/Yb. The above points support dominantly plagioclase fractionation in a reduced and less hydrous melt system pointing to a low Mo fertility potential of this pluton emplaced at an average Ti-in-zircon temperature of 861± 56°C. The apparent εHf(t) values for CMR-01 zircon grains range between -15.84 and -1.45 and apparent εHf_(t) values for CMR-02 zircon grains vary from -25.02 to -12.39. On spidergraphs, the grainites are depleted in HREE and enriched in LREE . These plots together with εHf_(t) values and other indications point to the fact that the granites were derived through partial melting of quartzo-feldspathic crustal magmatic sources. More so, the data showing a new age here show clear signs of post collisional Pan-African magmatism at ∼ 585±17 Ma in the context of a pre-drift Gondwana evolution.