The results of the examination of the chemical composition and Sr isotopic ratios in brines of Cl-Ca, Cl-Ca-Na, and Cl-Na types from the Tunguska basin with the total salinity within the range of 87-626 g/1 are discussed. The pH is 2.9 to 7.7, and the Sr isotope ratios are 0.70825 ± 5 to 0.72010 ± 11. It is shown that the examined brines strongly differ drastically in their composition from the marine brine formed at the stage of halite precipitation. Based on their composition in terms of a number of indicative indices, we differentiated the brines into infiltrational and sedimentational, with a wide range of mixing between sedimentational and infiltrational (fresh and saline) waters. The sedimentational brines are strongly altered, which is evident from their higher Ca, Sr, Br, and radiogenic 87Sr contents. Sr isotope composition shows that all the brines interact at a various extent with aluminosilicate minerals of the terrigenous or basement rocks, which has led to an enrichment of brines in radiogenic Sr by 2-100%. Two groups of brines have been discriminated by type of strontium alteration: (1) brines altered in sulfate-carbonate rocks with a low 87Sr content and (2) brines altered in aluminosilicate rocks with a high 87Sr content.
|Number of pages||14|
|Publication status||Published - Nov 2000|
ASJC Scopus subject areas
- Geochemistry and Petrology