Measurement of radon concentration in old metalliferous mines in San Luis, Argentina

ANJOS, R.; RIZZOTTO M.; H. VELASCO; VALLADARES, D.

Barcelona

Conferencia; International Conference on Radioecology & Environmental Radioactivity; 2014

NRPA - Noruega

The analysis of temporal and spatial variations on the flow of soil gases across the soil-airinterface can be a useful tool to study geodynamical processes occurring in the rock mass dueto earthquakes, volcano and seismic activities, tremors, shocks, and coal or rock bursts. Oneof these gases is the alpha radioactive 222Rn (half-life 3.82 days), commonly known as justradon. The generation of radon depends on the uranium concentration and the nature of theparent mineral. However, variations in the radon flux are only caused by physical factors, andthen radon concentration measurements could give valuable information on distribution anddynamics of airflows inside of underground environments, like caves.In caves with two or more entrances at different levels, the air movement inside the caveoccurs due to differences between external and internal air densities caused by varyingexternal temperatures, since the air temperature in caves is usually nearly constant. This is atemperature-induced effect named ?chimney-effect?. The chimney-effect occurs when thepressure exerted at the entrance of a mine, by the column of air inside, differs from thepressure of external air. When the interior air is colder than the outside air, the pressureexerted by the tunnel air will be greater than the pressure outside and the air blows outthrough the lower entrance. When the outside conditions are colder than inside, the airmovement is from the lower entry to the upper. Chimney-effect airflow reverses its direction seasonally and might reverse daily at some times of the year. The seasonal pattern of radonconcentration produced by chimney-effect airflow depends on the configuration andconnection of underground cavities, passages, fissures and fracture system (Atkinson et al,1983).In this study, we summarize our results on radon levels measured in two tourism mines in SanLuis (Argentina), La Carolina gold mine (32o 48' 0" S, 66o 60' 0" W) and Los Cóndorestungsten mine (32o 33' 25" S, 65o 15' 20" W). La Carolina mine is currently a horizontal excavation into the side of a mountain, with only a main adit. Los Cóndores mine is also ahorizontal excavation into the side of a mountain, but has a vertical output (shaft) at the end ofthe main gallery (Da Silva et al., 2011; Valladares et al., 2014).