Bobrov O.B. MATERIAL COMPOSITION OF DIAMOND-BEARING TERRACES OF THE SOUTH-WESTERN PART OF THE LEONE-LIBERIA SHIELD (SIERRA LEONE)
UDC 549.2+622.037 (664)
MATERIAL COMPOSITION OF DIAMOND-BEARING TERRACES OF THE SOUTH-WESTERN PART OF THE LEONE-LIBERIA SHIELD (SIERRA LEONE)
Bobrov O.B. 1, Fedorishin Yu.I. 2, Kakaranza S.D. 1, Klochkov S.V. 1, Stepanyuk L.M. 3, Kurylo S.І. 3, Iaskevich T.B. 3
1 Expert Advice of the Union of Geologists of Ukraine
26/2, Kyrylivska Str., Kyiv, Ukraine, 04070
2 Institute of Geology and Geochemistry of Combustible Minerals of the NAS of Ukraine
3a, Naukova Str., Lviv, Ukraine, 79060
3 M.P. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation of the NAS of Ukraine
34, Acad. Palladin Ave., Kyiv, Ukraine, 03142
E-mail: firstname.lastname@example.org, iaskevych@ukr,net
Mineralogical journal 2019, 41 (4): 22-30
In the traditional diamond-bearing areas of Sierra Leone, where diamonds have long been mined from alluvial deposits of buried and Neogene-Quaternary sediments of the Leone-Liberia Shield sedimentary cover in technically accessible depth areas, there is an old and still unsolved problem of finding and identifying high terraces of large river systems. The latter are intermediate collectors of diamonds and an important source of their production. However, their identification is connected with the difficulties of the absence in most individuals, communes and even geological prospecting companies of the necessary equipment, forecasting technologies and knowledge regarding the procedure for geological and geophysical study of the territories of their possible location. During the course of geological exploration, we first predicted and then searched a number of plots, as a result of which distribution areas were mapped with a geomorphological map of 1 : 50.000 scale. Given the rarity of the description of such geological objects, this article offers the first results of their geological and petrographic description. The productive layers of these terraces are represented by a conglomerate-pebble with gravel-psammite filler. The structure is psammite, uniformly coarsely rough, with a basal pore, colloidal or sideronitic type of cement. The mineral composition of the debris (%): rhyolite, basic rocks, quartz — 50—60, microcline — 40—50, kaolin — 2—4, chlorite and opal-shaped quartz — about 1. The presence among the fragments of various rocks and minerals of varying degrees of roughening (especially of acute-angled fragments of rhyolite, microcline and quartz, unchanged by clay minerals) indicates the presence of not only long-range (quartz), but also local material. Studied the chemical composition of minerals. The results indicate that detrital material of various collectors is combined in space, which significantly increases the prospects for their industrial development and use for exploratory purposes (primarily for diagnosing types of near-worn rocks that are still unknown in prospecting areas).
Keywords: Sierra Leone, terraces, paleo channels of river systems, diamonds, conglomerates, gravelites.
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