Page 152 - Geochemical Remote Sensing of The Sub-Surface

Carbon dioxide dispersion halos around mineral deposits 129

Fig. 4-6. Relation between carbon dioxide in soil and lithogeochemical halos at Xuanchengshan
cupriferous pyrite deposit, Anhui province, China.

Some CO2 could also be present in soils in an adsorbed form, having previously been
transported in solution. This hypothesis was investigated using five soil samples, of
which three were from a humid area and two were from as arid area (Table 4-1I). A
sample from a background site in the humid area was found to contain 84 ppm CO2 in
the adsorbed form, compared with only 14% that was released by boiling; thus 86% of
the CO2 was in the adsorbed form. In anomalous samples from the same area, 34% and
52% of the CO2 was in the adsorbed form. In the arid area, however, the two anomalous
samples contained only 26% and 27% of their CO2 in the adsorbed form.
These experiments suggest that in arid areas, CO2 related to mineral deposits occurs
in soils mainly as salts of bicarbonates (which break down upon gentle heating). In
humid areas, by contrast, CO2 related to mineral deposits coexists as bicarbonates and
adsorbed CO2.