IJG International Journal of Geosciences 2156-8359 Scientific Research Publishing 10.4236/ijg.2020.1112040 IJG-106086 Articles Earth&Environmental Sciences Sedimentological Characterization of Alluvial Gold Deposits of Betrare-Oya and Its Surroundings (Cameroon Eastern Region) Daniel Mackaire Eloung Nna 1 * Paul Desiré Ndjigui 1 Joseph Quentin Yene Atangana 1 Alexis Jacob Nyangono Abolo 2 Constantin Maurice Ndongue 1 Faculty of Mines and Petroleum Industries, University of Maroua-Cameroon, Maroua, Cameroon Department of Earth Sciences, University of Yaounde I-Cameroon, Yaounde, Cameroon 24 12 2020 11 12 783 799 30, August 2020 21, December 2020 24, December 2020 © Copyright 2014 by authors and Scientific Research Publishing Inc. 2014 This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/

Sedimentological methods such as granulometry, morphoscopy and heavy minerals analysis have been carried out to characterize alluvial gold deposits of Betare-Oya and its surroundings, with the aim to determine their origin and conditions in which they are formed and also to determine the mineralogical content of these deposits, their nature and distribution. It came out from this study the following: The alluvial deposits studied are sand, constituting of coarse fraction (grains), medium grains in abundant and fine grains. The average values of sorting index (S0) and coefficient of asymmetry (A) are respectively 2.53 and 0.73. These values indicate that the sand is poorly arranged and poorly sorted with a better classification or arrangement in the coarse fraction (grains). These are sediments that are deposited together by high competent currents. It would therefore probably be torrential deposits and or streams from short transport. Unused grains are dominating (80.5%) which translate a proximal source of the sediments. So it would be probably from the dismantling of the surrounding landforms. The heavy minerals studied revealed the presence of the following minerals; zircon, gold, sphene, green hornblende, tourmaline, rutile, augite, hypersthene, sillimanite, glau-cophane, biotite, staurotide, and the opaque. These minerals belong to the cortege of plutonic and metamorphic rocks from a single proximal distributing province.

Betare-Oya and Its Surroundings Alluvial Gold Deposits Granulometry Morphoscopy Heavy Minerals Polished Sections 1. Introduction

Gold remains one of the world’s economy strategic resource; its exploration, therefore, remains a permanent and decisive activity. In Cameroon, the intensive exploitation of alluvial gold has led to an exhaustion of mineralized deposits in some basins of production. This is the case of the zone of Betare-Oya in the East Region of Cameroon. So it’s crucial for the research of new auriferous indices and most importantly their primary source so as to maintain the activity and increase production for a better contribution of the natural resource to the Gross Domestic Product(GDP) of the country. The characterization of alluvial deposits by the sedimentological methods such as; particle size, morphoscopy and the study of the heavy minerals constitute an approach which adheres or concurs to the exploration of gold. It will lead to the understanding of the sedimentary dynamics responsible for the formation of these deposits and also to know the origin of the mineralization and their distribution.

 2. Geological Setting

The study area, Betare-Oya is found in the East Region of Cameroon. The study area is characterized by two (02) main hydrographic basins namely, Lom basin in the North West and Kadei basin in the South East (Figure 1).

The geological context is that of the Pan-African base of the Cameroon center. The geology of the Betare-Oya area is dominated by volcano-sedimentary rocks of Neoproterozoic in the Lommetamorphise group [1]. In fact, the Lom basin which is the greatest hydrological collector of the area is mainly composed of

metasedimentary rocks grouped into two main structural and sedimentary units. These units include the monocyclic unit which is composed of the volcanoclastic materials of the Lom series, orthogenesis, quartzites and the polygenic conglomerates of Mali [2] [3], the metamorphosed green schist associated with the graben. The polycyclic unit as for it includes the Mica schists, gneisses of the Lom bridge and the myloniteschloritoides-staurolites linked to the structures in horst form [3] [4] (Figure 2). These mylonites are the main characteristics of the presence of the Sanaga Fault (SF) in the Region [2]. These different units are crossed by quartz veins and the Pan-African granitoids (granites, monzoniteetc.) [1] [4]. Structurally, the schists are well folded with an orientation of NE-SW linked to the shear zone system. The alluvial and eluvial deposits are abundant and hence concentrate mineralization [1].

The geology of the Ngoura zone is associated with that of Batouri as described by [5]. In fact, these zones are formed of three (03) types of granitic intrusions in the metamorphic host namely;

· Ancient syntectonic granites with often heterogeneous structures and with a composition often oriented or even gneissic and whose contours are consistent with the host formation.

· Late homogeneous syntectonic granites of compositions close to the previous ones;

· Discordant post-tectonic granites, very homogeneous and more alkaline in composition than the previous two.

Moreover, we note the presence of primary gold mineralization linked to siliceous appearances of vein appearance in shales and quartzites or then in the disseminated form in the plutonic massifs [5].

3. Methodology of Investigation 3.1. Sampling

The alluvial deposits studied are surface sediments of the rivers distributed in the 11 sectors which are: Lom sector (LM), Mali (ML), Nakoyo (NY), Bangbel (BL), Sarambi (SB), Boyo (BY), Tourake (TK), Wantamo (WM), in the North West zone of the study area and Woumbou (WB), Ouaden (OD) and Rigue (RG) in the South-East zone (Figure 1).

A total of 11 samples corresponding to the 11 sectors were taken from the flats (right bank and left bank) and from the beds of the rivers between 1 and 8m of depth; these are gravel levels. After washing the samples with the use of a washed pan, these samples were the subject of particle size, morphoscopic and mineralogical analyses.

 3.2. Study of Particle Size

The sediments were sieved by agitation according to the conventional procedure [6], on an AFNOR column of 9 sieves with decreasing mesh, from top to bottom having the following meshes; 4, 2, 0.5, 0.4, 0.315, 0.2, 0.1, 0.08, and 0.05 mm. The sieving process was carried out for 15 minutes continuously with a constant amplitude of agitation. The rejects collected in each sieve were weighed on an electronic balance with a precision of 0.01 g. According to the Folk and Ward method [7], these data makes it possible to plot histograms and cumulative curves, to calculate the particle size parameters such as the Mode (Mo), Median (Md) and the quartiles (Q1, Q2 and Q3) and the sedimentological parameters such asymmetry coefficient noted A (or Skewness noted Sk). These parameters make it possible to characterize the feeling and the processes of transport and sedimentation [8].

These parameters also make it possible to define the mode of transport of the sediments as well as the of deposit midium resulting from the diagrams of Visher [9] and Moiola and Weiser [10]. In fact, numerous studies have shown that the Md-So diagrams applied to sands, permit to determine their deposit environment [11] [12] .

3.3. Morphoscopic Study

The morphoscopic analysis of the quartz grains was carried out with a binocular microscope at a magnification of 40. The counting was carried out on 100 grains per sample. The objective was to trace their conditions of transport. The surface appearance and the shape of a quartz grain closely linked to their environments and modes of transport [13], thus proposes the classification of all quartz grains into three (03) categories; the unused corresponding to sand closer to its source of materials, the shiny foam which characterizes an aquatic transport and the dull circles which indicates transport by wind.

3.4. Mineralogical Study 3.4.1. Heavy Minerals

Heavy minerals act as markers which provide information on the origin of rocks and the conditions of transport [14] [15]. In order to make the identification of heavy minerals, the samples taken underwent physical treatment mainly by the quartering and sieving on approximately 20 g of the collected samples. The particles size cuts adopted in this work and recommended by Berthois and Lucas [16] are distinct into three (03) fractions; 1) 60 µm - 250 µm; 2) 250 µm - 315 µm; 3) 315 µm - 500 µm. These different fractions will undergo treatment with hydrochloric acid (10%) for 15 minutes for the removal of cements and lime tests while organic debris are eliminated with oxygenated water (H2O2) for 10 minutes. The densimetric separation or extraction of heavy minerals is done by immersion of the minerals in bromoform (CHBr3) which is a liquid of density equal to 2.89; minerals with a lower density than that of the bromoform will float on the surface and those with a high density are deposited at the bottom of the separating funnel [17]. Once obtained, the minerals are mounted between thin sections and lamella on a plat of Malassez using Canada balsam. Thus, when the slide is prepared, it is then ready for microscopic examination. Minerals are identified using a polarizing microscope.

3.4.2. Polished Sections

Preparing polished sections is similar to other materials preparation. It therefore includes cutting in reduced dimensions as well as bonding to glass slide, etc. the preparation follows the following steps or stages: After consolidation of the sample by the means of a polymerizable resin, one proceeds to the coating in order to obtain a suitable geometry or to protect the sample. Then a grinding/lappingoperation is carried out in order to eliminate surface damage so as to obtain a flat surface and to prepare it for polishing. And finally, we proceed to polish the surface, which reveals the structures of the sample and obtain a reflecting surface [18] [19]. The sample is thus ready for observation under an optical microscope by reflection.

4. Results and Discussions 4.1. Particle Size Data

The results obtained after sieving (Table 1) make it possible to construct graphs (histograms and cumulative curves) and to calculate the main particle size parameters which are Mode (Mo), Median (Md) and quartiles (Q1, Q2 and Q3), and the sedimentological parameters such as the sorting index (S0), the Krumbein index (QdØ) and the asymmetry coefficient noted A (Skewness noted Sk). All these parameters are listed in Table 2.

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