Alkaline-ultrabasic rocks of Novobobrovsky ore field (Middle Timan): mineralogy, petrography

Minerals of disintegrated alkaline-ultrabasic dike rocks exposed by wells within the rare-metal–rare earth Novobobrovsky ore field (Middle Timan) were studied. Microprobe studies were conducted in CCU "Geoscience" (Syktyvkar) and the Institute of Experimental Geology, RAS (Chernogolovka). Primary mineral parageneses are difficult to diagnose due to strong secondary alteration of rocks. The primary minerals are phlogopite (XMg = 0.64–0.89) and minerals of the chromespinelides group (the central parts are represented by chrompicotite, and the marginal zones – by ferrichromite); the secondary minerals are represented by the chlorites group (talcochlorite, clinochlorite, pennine). The rock is saturated with numerous xenoliths of quartzite sandstones, and has also undergone fenitization processes, which is why the development of rare metal–rare earth mineralization is observed in the rock: columbite, rutile ↔ Nb-rutile ↔ ilmenorutil, monazite, Th-monazite, more rare phosphates (complex phosphates and hydroaluminophosphates of lead similar in composition to dragmanite, differing by the presence of Mn, Ba, K). The studied primary mineral parageneses are typical for the picrite-lamprophyre Chetlas dike complex developed here; the superimposed rare-metal–rare-earth mineralization is specific for dike rocks developed within the ore fields of the Kosyu ore cluster