Behavior of TiO2 in Dolerits as a Possible Search Sign for Kimberlites

Abstract

A generalization of studies of the chemical composition of dolerites of the Vilyui-Markha dike swarm (VMDS) in the Eastern part of the Siberian Platform is carried out. This belt stretches along the North-Western side of the Vilyui paleorift system (Eastern part of the Siberian platform) for almost 700 km. The formation of VMDS intrusives took place in the interval of 372 million years. The Devonian kimberlites, which formed three kimberlite fields: Malo-Botuobin, Nakyn, Suldyukar, are confined spatially to the VMDS. One is in the Southern part of the belt, and the last two are in its Central part. The formation of kimberlite pipes according to K-Ar, 40Ar / 39Ar, Rb-Sr dating is close to 362 Ma. When studying dolerites, it was found that near the kimberlites, the proportion of TiO2 increases in the first (almost 2 times - up to 4-5% versus 2.2-2.5%) and a number of heavy rare-earth elements, such as Th, Hf, Y, Nd. An increase in the content of these elements proceeds gradually from the edge of the kimberlite field to kimberlites and reaches a maximum of 7% (a single case) directly near kimberlites. The authors suggest that the latter is indirectly associated with kimberlites. The solubility of titanium in a basite melt sharply increases with increasing pressure. The kimberlite-forming system is long-lived, associated with diapir-like kimberlite protrusion, which subsequently produces kimberlite pipes. Long before the formation of kimberlites around the diapir, possibly located in the lower horizons of the earth’s crust, excessive stress pressures are created. A basite melt, penetrating through these abnormal (relative to pressure) regions, reacts with an increase in the content of titanium and HREE. Outside the kimberlite field contours, the content of the elements in question in dolerite dikes remains normal, i.e. 2-2.5%. Based on the above stated fact and the study of the geochemistry of dolerites of VMDS, the authors suggest the discovery of two more kimberlite fields within the swarm: Tenkelyakh, located 20-30 km North of the famous Nakyn field, and Orto-Kyulunke, whose location is possible in the North of the VMDS. The authors gave the names of the fields by the names of the rivers flowing through this territory.