Abstract
A geophysical investigation of suspected base metal mineralization commenced at Riruwai, in Doguwa Local Government Area of Kano State. The Survey is a ground follow – up to the 1976 airborne magnetic survey with the objective of ground truthing the results of the preliminary interpretation of the airborne survey.Earlier works by Geological survey of Nigeria Published in Bulletin 33 revealed the occurrence of Cassiterite, Wolframite, from the quartz-greisens veins in the biotite – granites, but columbite occurs as a primary accessory constituent in the granite. The heavy mineral residues from the biotite – granites also contain appreciable amounts of thorite, monazite and Zircon. Very Low Frequency-Electromagnetic (VLF-EM) and magnetic methods were implored in this survey. The aim of the investigation is to identify structural features or lineaments like faults, joints, veins, sills, contact zones and etc which are host to base metal ores.Correlation between EM and magnetic anomalies could be very attractive because most massive Sulphides, except a few do contain elements of magnetic materials in them e.g. Magnetite and Pyrrhotite.Riruwai is located in Doguwa Local Government Area of Kano State. It is bounded by latitude 10042’13 – 10045’00”N and longitude 8045’00” – 8047’39” E covering an area of 109km2. Riruwai town can be reached by road either on Kaduna – Kano dual carriage way, through Kwanar Dangora Junction or on Kaduna – Jos highway through Unguwar Bawa Junction. The site of the detailed investigation is called Kaffo, located 10km east of Riruwai town.The absence of settlement in Kaffo make the area highly inaccessible, except for minor foot path across steep hills and rivers, there are no motorable road that can lead to the area from Riruwai.The area was described by Jacobson and Macleod in 1977 as a ring complex, which composed of elliptical multiphase granitic massif bodies that intruded into Pan – African basement. It is part of Nigerian younger granite province that comprises mainly of granitoids and volcanic sequence.The basin is completely surrounded by high and rugged hills mainly volcanic rocks. Dutsen Shettu (1,358m) and Ginshi (1,345m) are the highest summits.The drainage pattern is dendritic with River Kano and Kaffo as the main sources of drainage. There are many seasonal rivers running down the hills to the lowland which remain flooded in the rainy season. Riruwai is primarily a mining community. Mechanized mining once flourished in Riruwai but now abandoned.Minerals mined include Cassiterite, Columbite, Wolframite and Sphalerite. Vegetation is of Sudan Savannah type, characterized by shrubs in the relatively flat land to light forest in the valleys and around the hills. Riruwai is characterized by two main climatic seasons – Rainy season (April – October) and dry season from (December – April)The field procedure involves profiling along straight line Traverses approximately normal to the geologic strike. Fifty-one N-S traverses each 2.5km long with a separation of 50m made up the whole area of investigation. Stations were marked at 10m, giving a total of 12,000 stations occupied for each of the method used.Field data normally suffered from geologic and non-geologic noise. These noises were observed as spikes and micro anomalies in the data and therefore needed to be removed and or filtered.Both the EM and magnetic data are presented in form of Profiles and maps. Profiles give location, attitude and depth of target, while maps give information on location, geometry, strike and strike length of target.The Geosystem Winglink software was used to generate both EM and Magnetic maps used for interpretation.From the results and analysis of the models, maps and profiles, it was found out that most mineralized linear features are near surface. Mineralization was identified by anomalies trending in two major directions, the NW-SE and the NE-SW. These anomalous zones could be structurally controlled. The NE-SW features are major. The deeper and probably the oldest linear features are the N-S trends which are not mineralized.Some of the conductors (mineralized bodies) do have sufficient lateral extent, spreading to hundredth of meters in width and are having high amplitude. Drilling is therefore recommended at some locations to serve as a test check to the interpretation. These locations are as follows:1. Traverse 26, station 78.5: Longitude 8° 13′ 38.4107″E, Latitude 10° 43′ 14.3199″N, Striking NW-SE2. Traverse 26, station 225.5:L0ngitude 8° 13′ 38.2967″E, Latitude 10° 42′ 26.2558″N, Striking NW-SE3. Traverse 30.5, station 113.5: Longitude 8° 13′ 23.5069″E, Latitude 10° 43′ 00.6387″N, Striking NW-SE4. Traverse 46, Station 58.5: Longitude 8° 12′ 35.2677″N, Latitude 10° 42′ 50.4679″N, Striking NE-SW
