Crystal forms and surface textures of alluvial diamonds from the Western Region of the Central African Republic

Abstract

Abstract. The most common crystal forms of the diamonds from the alluvial deposits in the Western Region of the Central African Republic were examined by scanning electron microscope (SEM) in an attempt to determine their geological history. The marks observed are related to two distinct periods in the geological history of the diamonds: the magmatic episode and their hydraulic transport. The effects of significant magmatic corrosion undergone by the diamonds during their ascent from the upper mantle are shown by the predominance of rhombododecahedral forms over octahedral forms and the frequent occurrence on the crystal faces of pyramidal depressions with triangular (1 1 1) or square (1 0 0) bases, as well as of V-shaped figures (1 1 1) or stepped figures (on the faces around the ternary axes). Some impact marks probably occurred during the explosive episode of kimberlite extrusion. Other impact marks, the marks of general wear, and the high proportion of gemstone-quality diamonds indicate the lengthy transport. They thus also indicate that the diamonds have undergone a prolonged geological history after the erosion of the kimberlite. This

The influence of volcanological and sedimentological processes on diamond grade distribution in kimberlites: examples from the EKATI Diamond Mine, NWT, Canada

“…Sedimentary transport also affects the quality of the diamonds due to preferential breakage of low-quality diamonds (boart) and diamonds with flaws or inclusions due to attrition (Gurney 1989;Censier and Tourenq 1995). However, the influences of volcanic processes on diamond size distribution in primary and resedimented kimberlitic volcaniclastic deposits have not often been documented.…”

Overview of Diamond Resources in Africa

“…The carbonado diamonds on the other hand are significantly larger averaging 2.4 ct/stn. They represent about 15% of the diamond production, a percentage that is similar to CAR diamonds (Censier and Tourenq, 1995). Recently, the largest carbonado recovered at Mobilong was 15.12 ct. No primary source(s) have yet been discovered for Cameroon's diamonds, and the diamond distribution along the Cameroon-CAR border and the similarities to the CAR stones may suggest a common source.…”

Coherence of Bangui Magnetic Anomaly with Topographic and Gravity Contrasts across Central African Republic

“…The alluvium and colluvium from the Pleistocene (Qp) valleys with modern sediments of Holocene (Qe) form the basin of the modern Aouk river and its tributaries which create a natural border between CAR and Chad, Figure 3. The formations in the alluvial deposits also include notable intrusions of diamonds formed as a result of the ascent of the upper mantle and related magmatic processes during the geological history of CAR [59][60][61][62]. The geological development with favourable environmental setting of CAR situated in the equatorial, humid tropical and subequatorial climate resulted in its diverse natural resources.…”