In this study, mineralogical and geochemical characteristics of weathered pyroxenites boulders of Mamb, Ngong and Nkolmbong areas (Pan-African Yaoundé group) are determined in order to understand the mineralisation processes of Ni, Co, Cr and Cu during the early stage of weathering of ultramafic rocks. These pyroxenites are intruded in micaschist at Mamb and Ngong or in migmatitic gneiss at Nkolmbong. Fresh samples are made up of clinopyroxene, orthopyroxene, amphibole and accessory biotite, plagioclase, chlorite and sulphides. Their peculiar chemical features include high Ni (58–194 ppm), Co (46–137 ppm), Cr (875–3017 ppm), Zn (37–185 ppm) and Cu (27–159 ppm) contents. REE contents vary in a large range (ΣREE ̴ 59–478 ppm) with LREE-enrichment (LREE/HREE ̴ 3–6) and negative Ce and Eu anomalies. The thin (≤ 10 cm) weathered rims comprise alternating black streaks and red beds made up of kaolinite, gibbsite, goethite, hematite, halloysite and maghemite. The alteration intensity is marked by a decrease of the rock density and an increase of its porosity and Chemical Index of Alteration (CIA) values. The supergene alteration of fresh pyroxenites boulders yields Ni-, Co-, Cu-poor, but Cr-slightly enriched weathered rims. Conversely, the lateritization of pyroxenite boulders having previously undergone a hydrothermal alteration into chlorite-rich rocks leads to the formation of clay-, Ni-, Co-, and Cu-rich cortices. These cortices are peeled off during weathering and got mixed with the soils formed under and around the boulders. So, the current weathered rims are probably related to the recent climatic variations and the soils are the host of potential concentration in Ni, Co, Cu and Cr.

在这项研究中，确定了Mamb，Ngong和Nkolmbong地区（Pan-AfricanYaoundé组）的风化辉石岩的矿物学和地球化学特征，以了解Ni，Co，Cr和Cu在风化早期的成矿过程。超镁铁质岩石。这些辉绿岩侵入Mamb和Ngong的云母片岩中，或Nkolmbong的多片性片麻岩中。新鲜样品由斜发rox，邻苯二酚，斜闪石和辅助黑云母，斜长石，绿泥石和硫化物组成。它们独特的化学特征包括高含量的镍（58–194 ppm），钴（46–137 ppm），铬（875–3017 ppm），锌（37–185 ppm）和铜（27–159 ppm）。稀土元素含量在较大范围内变化（ΣREE̴59–478 ppm），其中LREE富集（LREE / HREE̴3–6）且Ce和Eu异常为负。薄的（≤10 cm）风化轮辋包括交替的黑色条纹和由高岭石，菱铁矿，针铁矿，赤铁矿，埃洛石和磁赤铁矿组成的红色床层。蚀变强度的特征在于岩石密度的降低以及其孔隙度和化学变化指数（CIA）值的增加。新鲜的辉石岩巨石的超基因改变会产生贫镍，富钴，贫铜，但含铬量略高的风化轮辋。相反，以前经历了水热蚀变的辉石岩巨石的红土化过程变成富含绿泥石的岩石，导致形成了富含粘土，镍，钴和铜的皮质。这些皮质在风化过程中被剥落，并与巨石下面和周围形成的土壤混合。所以，