Geology and magnetic character of the Basement Complex rocks in Garun Kurama area, north central Nigeria

Abstract

The volume magnetic susceptibility of the granitic gneiss and garnetiferous migmatite in Garum Kurama area was studied in situ, using Bartington MS2 magnetic susceptibility meter and its MS2D probe. The granitic gneiss is foliated and its constituent minerals include quartz, biotite, microcline, plagioclase feldspar and hornblende. The migmatite is gneissic in places and is strongly foliated. Its constituent minerals include quartz, orthoclase feldspar, biotite, hornblende and garnet. The magnetic susceptibility readings were taken along six E-W profiles at approximately 400m station interval. The coordinates of the stations were obtained with a Garmin 12 Global Positioning System (GPS). The resultant magnetic susceptibility map was then compared with the total intensity aeromagnetic map of the area in a Geographical Information System (GIS) environment using ILWIS and ARCVIEW softwares. The anomalies on both maps coincide. The magnetic susceptibilities are very low. They ranged from -0.09 to 1.88 cgs units. This suggests that both the granitic gneiss and migmatite are paramagnetic. However, they contain two narrow zones of diamagnetic rocks located N and NW of the Garun Kurama settlement. These diamagnetic zones are probably underlain by quartzitic veinstones which may contain gem-quality quartz crystals or topaz. The parent rocks that were regionally metamorphosed to get the granitic gneiss and migmatite were probably richer in felsic minerals than mafic minerals. One can also conclude that the Bartington MS2 magnetic susceptibility meter can effectively be used to map materials that exhibit different kinds of magnetic behavior, since magnetic susceptibility is an intrinsic property of all materials in the natural environment.