CHEMICAL COMPOSITION OF THE SMALL WATERCOURSES OF THE KUGDA MASSIF AND ITS MARGIN (EASTERN SIBERIA)

Abstract

Relevance. The extensive development of the Arctic territories and global climate change issues have attracted Geosciences researchers’ attention to exploring the environmental characteristics of the Russian Arctic and subarctic territories over the past few decades. The outcrops of intrusive massifs in the northern part of Eastern Siberia are of interest due to the prospects for mineral deposits. At the same time, the terrestrial water systems of this region remain poorly studied. Inaccessible location and a virtual absence of infrastructure is the main account. Research of the water chemistry of intrusive massifs is challenging for explaining their formation mechanisms in the Arctic territories and improving hydrogeochemical exploration methods. The aim and object. The research object is the small watercourses draining the Kugda ultramafic alkaline intrusive massif and its carbonate margin located in the western part of the Anabar Plateau. The study aims to investigate the water chemistry and carry out a comparative analysis with the large rivers of the region as well as reveal the consistencies of the chemical composition formation. Methods. During the fieldwork in July–August 2020, three samples from small watercourses draining ultramafic alkaline massif and its carbonate margin were taken. The carbonate system components were determined by potentiometric titration. The anionic composition was determined by ion chromatography. Dissolved organic carbon was measured by the high-temperature catalytic oxidation method. Elemental analysis of water was carried out by ICP-AES and ICP-MS methods. Samples for elemental analysis were filtered through a polyethersulfone membrane of 0,45 µm mesh into analytical pure 15 mL tubes with 0,45 mL of high purity HNO3 for conservation. Results and conclusions. The cationic content of the studied waters of the ultramafic alkaline massif and its margin reflects the rock composition adequately. At the same time, their anionic composition is controlled by a complex set of factors, both geochemical (rock composition and interaction with organic matter) and hydrological (recharging features). The small watercourse chemical composition draining the Kugda massif and its margin compared to the medium and large rivers of the region revealed the domination of magnesium in the cationic composition and increase in the proportion of potassium in contrast with sodium. The anionic composition of the small watercourses is relatively homogeneous; bicarbonate is sharply dominant, in contrast to large rivers, where the proportion of sulfate and chloride ions increases. The concentrations of trace elements in the surface waters draining the massif and its margin show that the composition of the studied waters can be used as an indicator of ore mineralization. The studied waters are enriched with such ore elements as Ni, Zn, Rb. According to the water migration coefficient values, Ni, Cu, Zn, Rb, Ag, Pb are readily removed from the rocks. Abundancies of trace elements in small watercourses draining alkaline rocks make the geochemical signature which could be classified as copper-nickel mineralization of the Kugda massif.

Keywords

• trace elements
• surface water
• water migration coefficient
• ore mineralization
• anabar plateau
• arctic
• kugda
• polar siberia