Geological research in prospecting for diamond deposits

Abstract

Introduction: Among more than 5000 kimberlite diatremes and dykes on the Earth, at least 500 original diamond-bearing structures were found. The effectiveness of the Schlich-mineralogical method of prospecting for new diamond deposits is complicated in the areas with thick sedimentary strata. Therefore, the need for the use of a combination of geological and geophysical research becomes the most important factor when solving forecasting and prospecting problems. Methodology and research efforts: The Schlich-mineralogical method is not very effective in the forecasting of and prospecting for new kimberlite fields and pipes as it is impossible to perform detailed paleogeographic reconstructions due to the insufficient and fragmentary initial geological information. The study of kimberlite magmatism usually requires the use of tectonic and geophysical data on the structure of the section-composing strata and their mineralogical and petrophysical characteristics as well as a comprehensive study of pipe kimberlites and the deep rock xenoliths contained in them. Tectonic, geophysical, space, and historical-mineragenic are the main types of research needed for the geological study of diamond-promising areas. The main geological and tectonic research methods are regional geological and geophysical works. They include a wide range of seismic, gravimetric, magnetometric, and electrical exploration works as well as crosshole tests with various approaches and variations depending on the specific structure of the promising areas. Their methodology involving the use of a large amount of data, including the author’s data, and is based on the diamond potential of the Siberian and East European platforms. These are the leading methods for covered areas where scattering halos of kimberlite minerals have been repeatedly redeposited and detached from their primary sources. Results and discussion: We studied the tectonic history of diamond-bearing magmatism by eight main productive Paleogene and Neogene epochs: Pre-Riphean, Riphean, Early Paleozoic (Caledonian), Middle Devonian – Early Carboniferous (Early Hercynian), Middle Carboniferous – Middle Triassic (Late Hercynian), Late Triassic – Jurassic (Cimmerian), Cretaceous (Early Alpine), and Paleogene – Neogene (Late Alpine). Kimberlite fields with or without diamond-bearing diatremes, dykes, veins, and subtabular deposits are associated with thermoblemes. These fields, which are of all ages on ancient platforms, are affected by lineament rifts of Riphean and Phanerozoic aulacogenes. Kimberlite bodies are inclined towards low-amplitude tectonic disturbances, including those in the peripheral parts of aulacogens. Analysis of the factual data allowed recommending a prospecting strategy for primary diamond deposits at the level of kimberlite fields for both the Siberian and East European platforms as well as other ancient platforms of the world. The standard rational geological and geophysical complex should be used only within the orthocratons. The goal of the system for forecasting geological and geophysical research is to determine the thermoblemes within any given orthocratons which are preliminarily determined based on the maps of gravitational and magnetic fields. The geological and geophysical data is studied in order to discover the signs of lineament rifts crossing thermoblemes. In case of a positive result, structural mapping of the thermobleme area will be required using structural drilling, GIS, and shallow seismic exploration, which will allow mapping the disturbances as well. The obtained structural map will allow outlining the kimberlite field, and in the future its structural elements will become the basis for the selection of specific promising areas for prospecting for kimberlite bodies. Conclusion: The areas of kimberlite magmatism should be considered the most realistic sites for the assessment of the diamond potential of new areas. They are complex radial ring structures of “local” genesis consistently located at the intersection nodes of riftogens that are inherently developing along the elements of planetary and regional radial concentric systems. Such areas emerged due to the relatively small mantle diapirs whose place of penetration into the earth’s crust was prepared by all the previous tectonic events. Magmatic and fluid eliminations of these formations predetermined the exposure of kimberlites with diamonds to the earth’s surface. It is recommended to prospect for kimberlite and lamproite fields only within the areas where they are localised in the sections with a standard set of structural factors. The latter are determined by regional geological studies. The use of space, historical-mineragenic, and geophysical research is highly important in this case.