The noble opal of Raduzhnoye deposit: mineralogy and mechanism of formation
V. B. Tishkina, V. A. Pakhomova, S. Yu. Buravleva, O. V. Stepanov.
Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2015. V. 144. N 1. P. 100-114
Comprehensive analysis of geological history of the area, mineralogical and geochemical features of the noble opal mineralization, and host andesites and propylites, has made the base to determine the possible mechanism of the opal mineral-forming in its Raduzhnoe deposit. For the first time there was studied the nature of the background coloring in ordinary and noble opals with identification of «responsible» group of trace elements. As principal elements providing the coloration of opals there were determined Fe, Mn, Ti and Ni, with the clearly established direct dependence between their contents and saturation and intensity of coloration. Besides, there were revealed elements rarely occurring in opals: V, Rb, Sr, Zr, Mg and phosphorus.
Key words: the noble opal, andesite, propylitization, mineral inclusions, trace elements, coloration, IR spectroscopy, X-ray phase analysis, mechanism of formation.