Chapter 14 Oxygen and carbon dioxide in soil air

Abstract

This chapter discusses oxygen and carbon dioxide content in soli air. Interstitial air in soils, overburden or porous rocks forms an intermediate reservoir of oxygen between buried sulfides and the free atmosphere. The oxidation may be entirely chemical or may be enhanced by the microbial action of bacteria such as Thiobacillus thiooxidans. The oxidation of sulfides leads to the production of sulfuric acid, which is neutralized by available carbonates with the release of gaseous carbon dioxide into the subsurface surroundings and ultimately into the atmosphere. Thus the oxidation of a sulfide ore body will lead to consumption of molecular oxygen and probable production of gaseous carbon dioxide. A porous overburden will form a buffer in which restricted diffusion, dispersion and replenishment will accentuate and retain anomalous gaseous activity. The concentrations of oxygen and carbon dioxide in soil air reveal the position of concealed mineralization, even through considerable thicknesses of overburden. Surveys can be conducted using any one of several proven field and laboratory methods. The equipment required is, for the most part, inexpensive and readily available.