Origin of potassium-bearing tourmalines of the Kumdy-Kolsky deposit (Kokchetav massif, Northern Kazakhstan): Study of Mineral inclusions

Abstract

Research subject. Mineral inclusions in potassium-bearing tourmaline crystals of the Kumdy-Kol microdiamond deposit. Aim. To reconstruct PT conditions for the origin of potassium-bearing tourmalines. Materials and methods. Mineral analysis and element mapping were performed using an X-ray spectral microanalyzer. Raman spectroscopy was used to detect the C and SiO2 polymorphs. Results. For the first time, diamond inclusions were identified in tourmalines with the potassium content ranging from 1.0 to 1.6 wt %. In addition, diamond-bearing zircon was detected in tourmaline crystals, with the K2O content below the detection limit. Previously, diamond inclusions had been exclusively identified only within the most potassium-rich cores of tourmaline crystals, which were approved as a new end member referred to as maruyamaite. Similar to the previous studies, the Kfs inclusions were recognized in both marumaite crystals and tourmaline crystals, with a variable content of potassium. Conclusions. The obtained findings indicate that high-pressure conditions may not be necessary for the formation of potassium-rich tourmaline. The chemical composition of the fluid is most likely to be the main factor controlling the appearance of tourmalines with an unusual composition.