Differentiation Features of Alkaline Rocks in Ilmen Miaskite Massif: New Mineralogical and Geochemical Data

Abstract

The Ilmen miaskite massif in the Southern Urals remains largely understudied from the mineralogical and geochemical standpoints, and theories of its formation are still debatable. The paper presents the first data on the mineral associations of the miaskite varieties and REE-rich minerals. Microchemical studies determined that the pyroxene–amphibole miaskites are the most promising rock variety for REE mineralization (REE content at ca. 1500 ppm). These rocks show clearly discernible positive Nb anomalies combined with a negative Pb anomaly. The temperatures of feldspar exsolution indicate their following formation sequence within the miaskite varieties (from higher temperature to lower temperature ones): pyroxene–amphibole miaskite → garnet–amphibole miaskite → amphibole miaskite → biotite miaskite