Geowebinar Insights
The physical and chemical conditions for the formation of giant diamonds weighing more than 400 carats are examined based on statistics from De Beers. The main focus is on South African pipes, where more than half of the known Type II crystals have been mined. Diamonds of this type are characterised by the absence of inclusions, low nitrogen content and a high degree of resorption.
Existing hypotheses of their genesis are analysed, including the Moore, Smith, author's and combined fluid concepts. It is shown that Smith's model, associated with iron-nickel melts at depths of up to 700 km, does not explain a number of observed facts, such as the absence of macroscopic iron-nickel inclusions in kimberlites.
Based on fO₂ parameters and data on inclusions in diamonds, the composition of fluids is reconstructed. Type IIa diamonds are associated with more oxidised hydrocarbonate environments, which confirms the fluid nature of their formation. Such conditions promote crystal growth by increasing the volume of the fluid phase in the late stages of crystallisation.
Similar characteristics can be observed in Yakutia diamonds: large, nitrogen-free crystals associated with low-diamond-bearing pipes. The most promising sites in the region are the Novinka, Izopolesnaya, Deimes and Yubileynaya pipes. Preference is given to the model of late magmatic crystallisation from fluids, which explains the morphological and structural features of Clipper Diamonds.
The study focuses on the Bogbasinsky massif of basalt-ultrabasalt composition located in the Ayan district of the Khabarovsk Territory. Comprehensive geological exploration work carried out between 2019 and 2023 included geochemical surveys, aeromagnetic and electrical surveys, and well drilling. The analytical base includes petrographic and mineralogical methods, scanning electron microscopy, and energy dispersive analysis.
It has been established that the massif is composed of pyroxenites, dunites, and pyroxene-amphibole gabbros of Early Cretaceous age and is intruded by Late Granites. The structural features are controlled by regional faults that form the lens-shaped morphology of the massif. Nickel, copper and platinum group mineralisation is associated with serpentinised dunites located in the south-western marginal zone of the massif.
Rare sulphide phases (somonite, chromonite, pentlandite) and non-stoichiometric Cu–Ni–Fe–Co–S compounds have been identified. Microinclusions of platinum group elements, interpreted as zegincite-like phases associated with late-stage magnetite generation, have been discovered for the first time. The mineralisation is considered to be fluid-metasomatic, involving secondary processes of transformation of the original silicates.
The paper discusses the results of a comparative analysis of chromspinelides from phyllite hyperbasites of the northwestern part of the Peredovy Ridge of the Greater Caucasus and the Mayari-Barakoa ophiolite belt (Cuba). The study was based on chromspinels, which are stable indicators of the geodynamic conditions of ultrabasic rock formation, capable of recording both the initial crystallisation parameters and subsequent metamorphic transformations.
It is shown that the Caucasus massifs, despite their close spatial location, are characterised by differences in the composition of chromspinelides. The Kishinsky massif is dominated by alumochromites with relics of chrompicatites, while the Dakhovsky massif is dominated by subferrochromites and chromites. These features are interpreted as the result of formation at different levels of the mantle and the subsequent influence of Late Palaeozoic granitoid melts.
A comparison with the Cuban Mayari-Crystal and MOA-Baracoa massifs suggests similarities in geodynamic conditions and mantle column type. The similarities found confirm the model of fragmentation of a unified mantle system due to tectonic restructuring.
The report is devoted to the use of high-pressure roller presses (HPRP) in the mining industry and presents the experience of BMH Rus, a system integrator and supplier of comprehensive engineering solutions for enrichment plants. The report provides an overview of the company, its partners and completed projects, as well as its areas of supply and expertise in the field of EPC contracts.
The main focus is on HPHP technology, the kinematics of the process and its advantages over traditional grinding methods. Three technological schemes for the use of presses are considered, and the significant reduction in energy consumption and CO₂ emissions when using them is emphasised. The design of the equipment is described in detail, including the hydraulic system, self-aligning tyres, pin armour and innovative slide bearings.
The report provides an overview of the range of roll presses manufactured by Li Jun, a strategic partner of BMH Rus. The production parameters and performance indicators of the equipment are specified. Special attention is paid to the possibilities of laboratory testing, design and integration of equipment into production lines, including the experience of implementation at the Mikhailovsky GOK.
