Сomposition and mineralogy of granitoids of the Ob-Zaisan folded region in the context of the prediction of groundwater radioactivity

Abstract

The presented research is carried out in continuation of the works connected with studying the nature of radioactivity of drainage waters of quarries of Novosibirsk region, performed by the Laboratory of Hydrogeology of Sedimentary Basins of Siberia, INGG SB RAS, which showed that the waters of granite quarries are characterized by significantly higher radioactivity, than waters of other host rocks. The results of detailed mineralogical and geochemical studies of granitoids of the Ob-Zaisan region within the Kolyvan-Tom folded system are presented for the first time. The relevance of the present study is determined by the previously obtained data on high concentrations of uranium, thorium, and radon in drainage water of quarries developed in this territory. The granitoids of the Priobsky (Obsky and Novosibirsk massifs) and Barlak complexes were studied. It was established that the rocks of the complexes differ significantly in the spectrum of accessory minerals, which acted as the concentrators of natural radioactive and rare-earth elements: in the Barlak, in addition to apatite, sphene, and zircon, typical for all phases of the intrusion, fluorite, topaz, rutile, and minerals enriched with rare-earth elements are found: monazite, xenotime, bastnesite, parisite, less often uraninite. It was shown that a wide range of mineral-concentrators of radioactive and rare-earth elements determines higher concentrations of radionuclides in groundwater of the Barlak granitoid complex. Maximum uranium concentrations are one order of magnitude and those of thorium are two orders of magnitude higher in the groundwater of the Barlak granitoid complex compared to those of the Priobsky granitoid complex. The following peak concentrations, mg/dm3, were established in the groundwater of the studied granitoid complexes: 238U up to 1.40 and 232Th up to 2.16 · 10–3. One can predict a high background of radionuclides in the groundwater of the Barlak and Priobsky granitoid complexes, within the ranges, mg/dm3: 238U from 0.1 · 10–3 to 1.40 and 232Th from 1 · 10–6 to 2.16 · 10–3. Radon 222Rn activity in the groundwater ranges 1–50 Bq/dm3 in the contact zones of granitoids with different-aged sedimentary rocks to 600–5,000 Bq/dm3 in the areas of granitoids occurrence.

Keywords

• granitoids
• mineral-concentrators of radioactive and rare-earth elements
• groundwater
• radionuclides
• 238u
• 232th
• 222rn
• novosibirsk region
• western siberia