Chromite placer occurrences of the Volga-Ural basin – genesis, sources and industrial potential

Chromium is a strategic metal, but more than a half of Russia’s needs are met by imports, so new deposits of chromites, including unconventional placer deposits, are of industrial and scientific interest. Previous studies and current works of the authors of the article have established the chromite placer metal content of Permian-Jurassic deposits of the Volga-Ural basin, which has industrial and potential significance: within the Lukoyanovsky placer area (Nizhny Novgorod region), the industrial chromite content of Jurassic coastal-marine titanium-zirconium placers has been established; in the south-west of Bashkiria, chromite-bearing sands (Sabantuy occurrence) with increased contents, but not yet clear industrial potential. The study of the typomorphism of chromites indicate their close relationship with the chrome spinel of ophiolite associations. The assumed overthrust structure of chromite-bearing hyperbasites of the Urals suggests a wide distribution of chromite-bearing sands within the Upper Permian-Jurassic Volga-Ural paleobasin, in which the increased content of chromites was controlled by hydro- and lithodynamic conditions favorable for placer formation. Questions of the genesis of chromite placer occurrences in the Ural part of the East European Platform, their distribution and primary sources need further study.

Diamondiferous alluvial deposits of the Longatshimo Valley, Kasai Province, southern DRC: a sedimentary and economic model of a central African diamond placer

The Kasai alluvial field in southern Democratic Republic of Congo (DRC) is part of central Africa’s largest diamond placer that has produced more than 200 million carats, mainly derived from Quaternary deposits. A small part of these deposits, along and within the Longatshimo River, is the subject of this study providing a glimpse into the alluvial history of the Kasai diamond placer. This work documents their sedimentological and diamond mineralization attributes, as well as their emplacement processes, which can inform future exploration models. The key controls of this placer formation, notably Quaternary climatic variations, fluvial landscape evolution and bedrock conditions are also evaluated. A consequence of the interplay among these processes is that diamond supply (from Cretaceous alluvial sources), recycling and concentration were most pronounced and consistent, in the Late Quaternary. Alluvial diamond mineralization in this central African region thus evolved differently to those in southern Africa. Based on exploration results in the Longatshimo Valley, diamond concentration improves but diamond size diminishes with decreasing deposit age, and thus the modern river sediments contain the highest abundance but smallest diamonds. This is opposite to the grade and diamond size trend that characterises southern African fluvial diamond placers. The Longatshimo River study offers insight into the Kasai alluvial field, and its placer model is expected to be applicable to the exploration of other central African diamond placers.

Reconstruction of the Ancient River Network and Prospects of the Placer Gold Mineralization on the Southern Part of the Miass Intermountain Depression (South Urals)

We conducted the reconstruction of the ancient river network of the basins of the right tributaries of the Uy River Shartymka and Kiruda located in the southern part of the Miass intermountain depression within the Shartymskiy graben and its southern periphery. The sequence of placer formation from Cretaceous and Miocene karst-alluvial placers (Shartymsky graben) to the Eopleistocene and Neopleistocene has been established. In the valleys of the Shartymka and Kiruda rivers, areas of inherited development have been identified. This increased the reliability of estimation of the placer gold forecast resources. The most promising areas are recommended for geological exploration licensing.

Development of a method for forecasting the potential of placers by formalizing the factors of placer formation based on loparite placers of the Lovozero massif

Within the Northern periphery of the Lovozero massif (Kola Peninsula), the authors have identified the main formation factors of proximal (near drift) rare-metal loparite placers. They have performed the formalization (numerical evaluation) of factors; developed multiplicative indicators that reflect the placer potential of territories; and assessed the effectiveness of the developed indicators on the reference objects of the Northern periphery of the massif. The developed method allows automating the process of forecasting of placer parameters.