Evaluation of Platinum Group Elements (PGE) Potentials of Ultramafic Rocks of the Paleoproterozoic Nyong Series, Southeast Cameroon
International Journal of Mining Science
Meta-ultramafic rocks from the Paleoproterozoic Nyong Series (SE Cameroon) were investigated in this study. The aim was to study trace and rare earth elements (REEs) patterns in these rocks. A layered sequence exposed on a cliff face was mapped. Samples from the various horizons were collected and subsequently analysed in the laboratory for their petro graphic and whole rock chemical compositions (but only the results of trace and rare earth elements are presented in this study). All the
... dy). All the samples from the study area define a light trend on a (Nb/Th) vs (Th/Yb) plot, and have low ( Nb/Th) average ratio of 0.6 and elevated (Th/Yb) average ratio of 1.0 These two characteristics, i.e. ( Nb/Th) < 1 and (Th/Yb) >1, are generally accepted to be the product of crustal contamination of mantle-derived magmas. Relative to the primitive mantle, the rocks show relative enrichment of LILEs (such as Sc, Rb, Ba, Th and U) with very steep slopes and depletion of HFSE (such as Ta and Nb) which also show very steep and gentle slopes respectively. They are further characterized by distinct troughs such as Ta-Nb and Sr-Nb. These features are characteristics of tholeiitic basalts produced at destructive plate margins or within plate tholeiites contaminated by continental crust. The samples are enriched in LREEs (LREE/HREE >1). Average Eu* and Ce* values in the samples are 0.72 and 1.87 respectively while average La/Yb N is 0.79. Primitive mantle normalised REE plots of the ultramafic rocks are characterized by four distinct types of patterns based on their shapes and Eu anomalies (Eu*). Type 1 samples are characterised by steep LREE patterns, slightly positive Eu* and flat HREE patterns. Type 2 exhibit LREE patterns with high peak values for La and Pr, Vshape Ce anomaly, a very gentle HREE pattern and a moderate negative Eu*. Type 3 samples show a steep LREE patterns, strong negative Eu* and flat HREE patterns whereas Type 4 samples display flat and very steep LREE patterns, a very strong negative Eu* and a very flat HREE patterns. Generally, all the four types are characterized by enrichment in LREEs and depletion in HREEs and a negative Eu and Ce anomalies except the type 1. Negative Eu anomaly are all features that suggest removal of plagioclase component from the basic magma or may be due to the magma that might segregated at depth where plagioclase is not stable and thus could not have fractionated.