Potassium basalts and picrobasalts from the devonian kimberlite fields of Western Yakutia, Russia, and their relations to kimberlite magmatism

Basic explosion pipes occur along with basic dikes, sills, and chonoliths within the Vilyui—Markha basic dike belt in the northwestern marginal part of the Vilyui Rift, characterized by widespread basaltic magmatism. The explosion pipes are of interest for exploration geology owing to their specific composition and tectonic setting, similar in many respects to the structural localization of kimberlite bodies in the sedimentary cover of the Siberian Platform. The basic explosion pipes from the Mirny district were referred to as tholeiitic and alkali-basaltic petrochemical rock series. Peculiar potassic and ultrapotassic rocks—potassium olivine basalts and picrobasalts—were identified in the alkali-basaltic series. These rocks were regarded as related to the deepest sources among basalts and were recommended for use as a prospecting guide for primary diamond sources. Our investigations allowed us to interpret the elevated K and Mg contents in basic fragments from some explosion pipes and associated intrusive bodies as a result of low-temperature metasomatic alteration. The explosion breccias and metasomatically altered basic rocks probably mark areas favorable for explosion activity and intrusion of both basic and kimberlitic rocks.