Preliminary geological and radiometric studies of granitoids of Zing-Monkin area, Adamawa Massif, Ne Nigeria

Zing-Monkin area is part of a large basement complex of the Adamawa Massif in eastern Nigeria characterised by extensive exposures of granitoids. Field mapping and radiometric survey of the area at a scale of1:50,000 shows that the area is underlain by moderately radioactive biotite-hornblende-granodiorite, migmatites, equigranular granites, porphyritic granites, and highly radioactive fine-grained granite with subordinate pegmatites. Composed of hornblende, plagioclase, biotite, perthitic microcline, quartz with accessory apatite, sphene, and zircon,these rock units host enclaves of various shape and are separated from one another mostly by gradational contacts. The paucity of foliation, the mafic hornblende-bearing enclaves and the gradational contact relation between the rock units have led to a conclusion that the granitoids are probably I-type, genetically related to a common source by fractional crystallisation of hornblende, plagioclase, biotite, microcline and accessory apatite, sphene and zircon. The distribution of enclaves throughout the granodiorite unit, their sub-rounded shape and diffused contacts are consistent with their igneous texture that the enclaves are syngenetic probably representing remnants of pre-existing rocks from which the granitoids were derived. The enhanced radiometric counts in fine-grained granite and pegmatite may be related to uranium occurrences ofmagmatic/hydrothermal nature around Mika, Jada and Nyaza