Page 150 - Geochemical Remote Sensing of The Sub-Surface

Carbon dioxide dispersion halos around mineral deposits 127

Year 1 (30 cm soil sampling depth)
,.., 400
E
Q. 300
200
O" lOO
(,..1
0 , 9 ' 9 . . . .
"~ Year 2 (30 cm soil sampling depth)
n. 250
n. 200
"" 160
, , , , , , ,
A Year 3 (80 cm soil sampling depth)
E 2so
Q" 200
15o
. 100
0 6O
(.) 0

Fig. 4-4. Relation between carbon dioxide in soil and lead-zinc mineralisation at Qixiashan,
China.

DISCUSSION

Speciation of carbon dioxide

What is the parent or form of CO2 detected in these studies? Theoretical
considerations suggest that, of the various carbonates and bicarbonates likely to occur in
rocks and soils,, NaHCO3 releases the most CO2 at relatively low temperatures; at
100~ it liberates 32% of its CO2 content, whereas metal carbonates, CaCO3, K2CO3
and NazCO3 do not begin to break down until much higher temperatures are reached
(Fig. 4-7). The thermal stability of these carbonates was confirmed by laboratory
experiments in which they were boiled in distilled water and the CO2 released into
solution was determined by titration (Table 4-I).