ЗВ’ЯЗОК НАКОПИЧЕННЯ ТОНКОГО ЗОЛОТА З ЛІТОЛОГІЧНИМИ ОСОБЛИВОСТЯМИ СУЧАСНИХ ДОННИХ ВІДКЛАДІВ ПІВНІЧНО-ЗАХІДНОГО ШЕЛЬФУ ЧОРНОГО МОРЯ

Abstract

Purpose. The presence of fine gold is a characteristic feature of the shelf depositsof the Black Sea. Moreover, fine gold is accumulating in different terrigenousmineralogical provinces of the shelf and is not connected to any distinct source. Fine gold has a polygenetic character and its distribution in the sediments is highly uneven. For these reasons, identification of distinct patterns of fine gold accumulation is complicated. The aim of the article is characterization of lithological control of fine gold accumulation in recent sediments in the Northwestern Black Sea shelf. Data & Methods. Results of the study of lithological features and concentration of free gold in the sediments in the area of Dnieper depression, in the vicinity of the Tendra spit, Zhebriiany bay and Zmeinyi Island, within the Northwestern Black Sea shelf were used. The samples of bottom sediments were obtained in the course of the survey, carried out by the Laboratory of Marine Geology and Geochemistry of Odesa I.I. Mechnikov National University. Concentrates for the determination of concentrations of gold and other heavy minerals were obtained by gravity separation on a spiral sluice. The results of grain size and mineralogical analyses, as well as determinations of gold concentration by amalgamation method and assay tests were processed statistically. Results. The increased content of gold is often found in multy-component, nongraded recent sediments of the shelf, namely muddy and sandy shell deposits. The accumulation of fine gold is confined to very fine sand fraction of the recent sediments in the Dnieper depression. There is a highly negative correlation between gold content and psephites can be observed. Psephites are represented exclusively by shelly material in these sediments. This negative relationship is quite natural, because there is no genetic relationship between biogenic psephites and predominantly terrigenous fine gold. Positive correlation between gold and very fine sand in the sediments indicate that the determining factor is the hydrodynamic regime for the accumulation of fine gold in marine sediments. Fine gold tends to accumulate in sediments with a high content of heavy minerals near Tendra spit. Here, the accumulation of gold is directly related to the formation of coastal marine titanium-zirconium placers, evidenced by positive correlations between gold and zircon, ilmenite and anatase. Maximum gold content occurs in well-graded fine sand sediments in Zhebriiany bay and Zmeinyi island area. The correlation of fine gold accumulation with lithological characteristics of bottom sediments is expressed in different ways within different areas of the Northwestern Black Sea shelf and in different facial environment.