РЕДКОЗЕМЕЛЬНЫЕ И СТРОНЦИЕВЫЕ АЛЮМОФОСФАТЫ В ХРУСТАЛЕНОСНЫХ ЖИЛАХ МЕСТОРОЖДЕНИЯ ПИРАМИДА (ПРИПОЛЯРНЫЙ УРАЛ)

Abstract

Alumophosphates of REE and strontium occurring in the rock-crystal Pyramida field have rather complicated polycomponent compositions and structures. They are developed in selvages of hydrothermal rock crystal veins located in tourmalinites - rocks composed of thin needle-shaped tourmaline. Yellow sharply rhombohedric crystals of alumophosphates, up to 0/2 mm in size, have heterogeneous structure with a seed core and an outer zone. The cores of these crystals are represented by isomorphic compounds of REE, Sr, Ca alumophosphates with an admixture of S and Fe: florencite (68-16 %moi>-swanbergite (71-22)-crandallite (32-13 %moi). External zone of the crystal is sharply differing in compositions though represented by isomorphic compounds of Sr and Ca too: gojazitc (40-68) and crandallite (32-60 %moi). Formation of alumophosphates took place within two stages of mineralization process. At the start of the early stage there was mainly crystallization a REE phase with admixture of Fc, Ca and Sr, up to its end the amount of Sr and sulfur has significantly increased; crystallization of the Sr-Ca phase was typical for the second stage. This sequence of the mineral-forming process has reflected the consecutive precipitation of cations with the greater atomic radius (Ca and Sr). The changes of compositions and structure was accompanied by transformation of the crystal forms. According to existing classifications (Fleischer, Mandarine, 1995) florencite and swanbergite are considered as related to mineral series, but the carried out researches made evidence of existing the uniform group of alumophosphate-sulfates. Minerals of similar composition arc known as the satellites of diamonds at the Urals, in Africa and Brazil.