The Bamun plateau, located at an average elevation of 1200 m, is one of the main units of the western Cameroon highlands. It is an important unit of the Cameroon Volcanic Line (CVL). Within this mega structure, the Bamun plateau lies between longitudes 10˚40' - 10˚56'E and latitudes 5˚36' and 6˚N and covers an average surface area of 900 km² (Figure 1). The CVL has been described as a succession of horst and grabens that stretches from the Pagalu Island in the Gulf of Guinea to the Lake Chad. Most of the horsts are represented by plateaux, among which the most prominent are the Adamawa plateau and the West Cameroonian plateau where the study area is located. Flood basalts outcrop for more than half of each plateau and their emplacement was favoured by reactivations of the Pan African structures marked by N30˚E deformation that is the major evolutionary character of the CVL [2]. Basaltic lavas of the plateaux (51 to 11 Ma) bear the signatures of an old volcanic activity as shown by their significant weathering to form deep ferrallitic soils [3] [4] [5] [6] [7].

The geomorphology of the Bamun plateau (Figure 2) is dotted with clumps of all kinds of scope and size variables such as the Mbam Mountain (1921 m), Nkogham (1724 m), the Batpit Mountain (2097 m) and about fourthing hills in the southern area. Thus, the eastern and northern borders are raised and overlooking the region by an escarpment of aboout 700 m to 1000 m. In the western part, the bamun plateau end with the Noun plain by an escarpment of 200 m to 300 m in altitude. In the north, it extends to the high grass fields at the foot of the Bamenda area that overlooks the ndop pool creating a steep slope of about 500 m. The remaining 20% is covered by rhyolites and slag from central volcanism. Volcanic ash from explosive and phreatomagmatic strombolian dynamics have developed some 40 cones that are often breached and about 12 explosion craters and maars, which lie on an orthogneissic basement.

On the geological point of view, the Bamun Plateau belongs to the western basement complex of the Cameroon Volcanic Line, which forms part of the Pan-African mobile belt situated between the West African Craton and the north of the Congo craton. The basement rocks comprise of Precambrian granito-gneissic bedrock outcrops mainly in the North of the study area. The substratum is made up of gneiss with alternating dark and light bands [8] [9]. Another variety of rocks mapped in the area is mylonite made of granite with biotite as the dominant mafic minerals, consisting of fine-grained leucocratic gneiss consisting of 70% of quartz, 25% of microcline and 5% of biotite. This forms a major topographic feature and structural unit marker in the area.

The fissural basalts or plateaus basalts cover more than half of the surface area of the plateau. There are in fact transitional basalts that outcrop in the western part (Bangouren) while alkaline basalts outcrop in the East around Foumban and Koutaba [7]. The flood basalts of the Bamun plateau with ⁴⁰K/⁴⁰Ar ages of 51 and 46 Ma respectively would represent the oldest dated lavas from the CVL. Ten geological features were identified in the area (Figure 3).

The data used in this study included: 1) Landsat 8 OLI_TIRS images (Path 186 and Row 056) acquired on December 15, 2013, free of cloud and downloaded from the USGS Earth Explorer website. Map projection: UTM_Zone 32; Datum: WGS84;

2) SRTM satellite image of 2014 covering the explored area; 3) the geological informations was gotting from Dumort [10], the geological map of Wum-Banyo [11] and the geological map of the area at the scale of 1/500,000 [12]; and 4) topographic map of 1/200,000 scale covering the study area. The main characteristics of the Landsat satellite images used in this study are presented in Table 1. The softwares used for processing and analysis of the different maps and images are: ArcGIS 10.2, Qgis 3.4, ENVI 5.3; PC geomatica 2016 and Rockworks.

The goal was to detect all linear structures that can significantly influence the fracturation of the study area. All applied filters were intended to enhance certain features of the image. The different results presented in Figure 7 raise the distribution of the lineaments in the study area.

Data compiled from field observations were collected and presented in Table 3. In fact, the high relief form a backbone of the highlands from the Gulf of Guinea to the Tibesti through northern Cameroon along an axis called N30˚E line of Cameroon. However, the highlands of Adamawa have an orientation N73˚E derived from the Pernambuco fracture in Brazil. According to the data compiled, there are four major structural directions in Cameroon with predominance of directions N20˚E to N60˚E, which are the main [22] results of plate movement. Although the movement of plates does not seem better followed by lack of measuring instrument. Cameroon recorded frequent seismic movement of scale, size and variable location. Thus, there was an earthquake in 1987 in Magba, site of

the Mape dam, located on the Foumban Pan-African fault (N58˚E). In 1990, another earthquake was recorded at Ndu in the North West another locality of the high western lands.

Physically, Bamun centre consists of a set of granite plateaux, tectonized and deeply dissected. There are the most brittled structures shown in mylonite and orthogneiss outcrops in Foumban, Foumbot, Koutaba and Bagourain. They are generally in a plane E-W in the sub vertical direction. The N30˚E and N120˚E management is predominant. Like all other structural elements faults are common in mylonite. They are macroscopically expressed in the mylonite of Foumban in vertical form. These are rich in mylonite parallel cracks, more or less parallel to the layering. Two main fracture directions (N140˚E and N55˚E) are identified. We can also distinguish in this series: fractures diaclases and the vein injections joints. They are subvertical with a major direction in the range of N30˚E and N120˚ E. The vein injections are granitic fillings visible on the mylonite Foumban. These subvertical orientation veins E-W, NNE-SSW intersect them (Figure 8).

The lineament and frequency map (Figure 4 & Figure 5) show that the fractures distribution is homogeneous. The lineament number is in the range of 0 and 7. The majority of the fractures are located on the hard rocks which refer to igneous and metamorphic rocks. They are mylonite, gneiss and granite.

The number of lineaments on the map is about 1921 structural elements, ranging in size from 30 m to 5845 m, with an average length of 671 m in the field. The total length of the mapped lineaments is approximately 1289 km. The most important lineament (5845 m length) diagonally is oriented NNE-SSW. In addition to this trend, all others are smaller than 14 km, more than 92% of lineaments are less than 5 km in size, only 1.3% of them are larger than 5 km; small lineaments are thus the most numerous. According to their directions, the lineaments listed are grouped into 18 directional classes of 10 degrees interval. The rosette of their directions (Figure 8) highlights the preferred directions NE-SW, N-S, E-O, NNE-SSW and ENE-WSW.

The orientation of the lineaments is analysed by drawing rose diagrams (Figure 8). Even though these diagrams are not length-weigthted, they can indicate on each occasion what are the most dominant directions of fractures. This analysis is very important for the study of groundwater flow, as in most cases the orientation of the fractures is identical to the orientation of the preferential flow path.

Here the fault rose plot indicates two sets of orientation classes. The main two classes are NE and SW strike, while others have NW and SE strike. The uniformity of fracture orientation becomes an additionnal indication for the hydrogeological regime.

The length of 1921 interpreted lineaments range from 30 m to 5845 m (Figure 9). Fracture dimensions (aperture and apparent aperture) are very difficult to define and the depth of the apertures makes the measurement even more complicated. Nevertheless, length measurements can be taken relatively easily and they are also significant, since a fracture with a greater length affects the groundwater flow in a more dominant way than those of smaller length.

The purpose of the fracture density analysis is to calculate frequency of the fractures per unit area. The map shows the concentration of the lineaments of the Bamoun Plateau (Figure 10). There are essentially three classes (low, average and high). The drainage density represents the precipitation amount which could seep into the basement. Therefore, the higher the drainage density is, the higher the recharging probability is [23]. The map in Figure 10 shows that hight density is observed around the localities of the Khogham, Mbatpit and Mbam massifs on the one hand and Manswen, Njikwop, Mfelap, Foumban, Njindaré, Nkoundem and Ngwen jigoumbé localities on the other hand. Mountains areas and hills have high densities of lineaments which justify the preponderance of perched groundwater and the quality of the water resources. The degree of hydraulic interconection between the above lithologic units as surface water circulates through these discontonuities is verified in the next consideration (degree of fractures intersection). On the other hand very low density is observed in the volcanic rocks (1 km/Sq.Km²), and in areas where combinations of more lithological features dominate. This verifies that these lithologies are affected by tectonic activity. However, low elevation areas which are generally wetted can have aquifer whose management for quality remains complicated.

The density and degree of lineament connection determine the level of anisotropy of groundwater flow in the fractured aquifer, as in an environment with a high degree of interconnection where groundwater flow is steadfast. Fracture intersection density map shows the frequency of intersections per unit area. Therefore, the intersection density maps were used to classify the areas of diverse fracture orientations. If the fractures do not intersect in the aforesaid area, the resultant map will be represented by a plain map with almost no density contours and the fractures will almost be parallel or sub-parallel. The groundwater potential zones map of the study area (Figure 10) indicates areas with very high density of lineaments.

The flow of water is generally from east to west and north to south in the plain of Noun, in front of the rest of the Bamun plateau. Which is justified by the hydraulic activity of network faults and tectonic deformation that have severely affected the region.

The groundwater yield of these crystalline rocks is directly depending on the degree to which the rock has been fractured. Presence of weak planes in the rocks makes them susceptible to develop secondary porosity. Contact zones between crystalline-rock types are also favorable places for the location of wells yielding large volumes of water. Wells that penetrate no fractures will yield little or no water. Wells that penetrate only a few small shallow fractures initially may have an adequate yield; however, after the fractures are drained, well yield can suddenly decrease and the sustained yield may be small. Wells that penetrate only one large fracture have similar yield characteristics. Wells that penetrate several small fractures as well as one large one probably will have a large sustained yield. Wells that penetrate intensely fractured rock will be the most dependable in terms of sustained yield. Steeply inclined fractures are commonly expressed at the land surface as lineaments; and wells drilled along such lineaments or along known fracture traces consistently yield more water than randomly located wells.

Most of the lineament clusters in the central part of the area and are N20˚ - 30˚E and N60˚ - 70˚E trending lineaments. In this study, NE-SW dominates the structural trend followed by NW-SE and N-S. This can be an indication of the directions of groundwater movement in the area. From Table 1 and the geomorphological map (Figure 11) alluvial plain and valley fills have moderate to very good groundwater potential that occur all over the study area. Porosity of the volcanic rocks varies greatly, but it is everywhere more porous than the underlying unweathered bedrock. We can distinguish 13% of the area has good potential around the mountains; about 58% is moderately good which corresponds to high to moderate lineament densities situated at average altitude 1000 m; while about 31% of the area has poor ground water potential corresponding to low lineament density areas. Moreover, this work has helped develop a detailed lineament map that can be used for mining and hydrogical prospecting campaigns.