GEOCHEMISTRY OF RARE EARTH ELEMENTS IN THE ZONE OF INTERFORMATIONAL CONTACT IN THE MALDYNYRD RANGE (NEAR-POLAR URALS)

Abstract

Metamorphic rocks-hydrolysates, which are strongly enriched in Al and Fe (sericite, pyrophyllite, chloritoid, diaspore, and hematite schists), are developed in the interformational contact zone between Precambrian pre-Uralide and Paleozoic Uralide complexes in the Maldynyrd Range (Near-Polar Urals). These rocks have various origins. Some of them are metamorphosed Cambrian weathering crusts (Ti-rich hematite schists, as well as pyrophyllite and chloritoid schists in many localities) or products of their redeposition (Al'kesvozh Sequence, ∈3-O1al). Others are products of Late Paleozoic fault-zone metasomatism (sericitolites, diasporites?, and some boron-rich chloritoid schists). By Ti index (TI), the following two series of metamorphic rocks can be distinguished: low-titanium aporhyolites and high-titanium rocks. The latter are genetically related to metamafic rocks and ancient weathering crust upon them. The greisenized aporhyolitic rocks compose thick zones of REE accumulation. Microprobe analysis shows that REE are concentrated in phosphates, arsenates, silicates, and molybdate-tungstates. Some of these phases could be considered new minerals.