NATURE OF PHOSPHATE DISTRIBUTION WITHIN THE GOLDEN WEATHERING CRUSTS OF THE TOMSK REGION

Abstract

The relevance of the research. In the Tomsk region, the weathering crusts are very widespread, their gold content has been established, but a detailed study of the mineral composition has not previously been carried out. The relevance of the research is caused by the need to identify the conditions for formation of weathering crusts and to establish the patterns of accumulation of a wide range of minerals in them. The main aim of the research is to study the morphological and chemical features, paragenetic associations and distribution of minerals of the phosphate group, division into primary, transformed, and newly formed, the use of phosphates as minerals-indicators of the conditions for the formation of weathering crusts and their relationship with the distribution of gold. The object: residual and redeposited weathering crusts of the Tomsk region and the minerals of the phosphate group contained in them. Methods. The crystal morphological features of minerals of the phosphate group, their paragenetic associations were studied microscopically using an OLYMPUS SZX10 stereomicroscope, the chemical composition of minerals was determined using a HORIBA Scientific XGT-7200 X-ray fluorescence microscope and a TESCAN VEGA 3 SBU X-50 X-50 EDS Max OXFORD scanning electron microscope. Results. In the weathering crusts of the Tomsk region, phosphates of the apatite group, rare earth elements, and aluminophosphates of the crandallite group have been found. Phosphate minerals are divided into groups: primary terrigenous phosphates, stable in weathering crusts and released during the destruction of bedrock (monazite, xenotime, apatite), hypergene-transformed, altered during weathering (monazite), and secondary (monazite, cularite, flitorensite, crandallite, goyacite, gorseixite, plumbogumite). Established in different zones of the weathering crust, phosphate associations for the most part represent links in the successive transformation of minerals from calcium and rare-earth phosphates to aluminum, indicating an increase in the acidity of the mineral formation environment. In the upper part of the hydrolysis zone of the residual weathering crust, the greatest accumulation of gold is noted.

Keywords

• phosphates
• weathering crust
• mineralogical analysis
• scanning electron microscopy
• kolyvan-tomsk folded zone
• tomsk region