Diamonds of the Morgogor placer (Anabar, Yakutia)

Abstract

Research subject. The placer diamond deposit of the Morgogor River, Anabar, Yakutia. The geological history of this deposit has not been reliably established, and the root sources remain unknown. Aim. To describe the mineralogical and spectroscopic characteristics of diamonds from the Morgogor river deposit in comparison with the previously studied diamonds from the Ebelyakh river placer. To divide the studied diamonds into genetic groups, presumably reflecting the primary sources of demolition, according to the distribution of A-centers. To assess the stability of mineralogical and spectroscopic features for the identification of genetic groups. Materials and Methods. Data on 1386 diamond crystals mined from 1978 to 2018 were used. Detailed descriptions were made for 1168 of them; IR spectroscopic studies were carried out for 103 diamonds; informative EPR spectra were obtained for 61 diamonds. Results. Using IR spectroscopy data, the Morgogor diamonds were divided into three groups based on the content of A-centers according to the methodology previously developed for the study of Ebelyakh diamonds. The diamonds of the studied groups differed significantly in terms of the habitus and morphology of crystals, the development of plastic deformation processes, the content of inclusions, the presence and diversity of visual luminescence, as well as associations of paramagnetic centers. The difference between the Morgogor and Ebelakh samples consisted in the ratio of the shares of genetic groups, which can be interpreted as the influence of a geographical factor, i.e., location in relation to the sources and directions of demolition at all stages of placer formation. Conclusions. The diamonds of the Morgogor river have the same three primary sources as the diamonds of the Ebelakh river. Statistical separation of crystals by primary sources - genetic groups - is possible based on the distribution of the content of A-centers. This separation forms groups, whose diamonds differ not only in IR characteristics, but also in the morphological features and the nature of luminescence. The statistically significant samples of diamonds from various Anabar placers differ in the ratio of the shares of genetic groups, which reflects their geographical location, adjusted for the directions of demolition in the processes of formation and redeposition of placers. The data obtained can be used to identify the directions of demolition and, ultimately, to search for its primary sources.