Page 153 - Geochemical Remote Sensing of The Sub-Surface

130 M.Zhang

100
#
v

76

60

32
25 oo-
: I '/ /

//"5,
I !
100 200 400 600 800 1000
(C ~ )
Fig. 4-7. Thermal stability of some simple carbonates and bicarbonates.

TABLE 4-II

Speciation of CO2 (ppm) in soils from two areas in China

Form of CO2 Humid area Arid area
Background Anomaly 1 Anomaly 2 Anomaly 1 Anomaly 2

Adsorbed 84 168 48 126 126
Boil 100~ 14 152 92 364 334
Total 98 320 140 490 460
% adsorbed 86 52 34 26 27

Formation of carbon dioxide dispersion patterns

The most likely source of most of the anomalous CO2 detected in these studies is the
volatile fraction associated with the emplacement of mineralisation. These volatiles are
rich in CO2, which can migrate along fractures above the main mineralisation. Some of
this CO2 may form carbonates, while some may pass directly into circulating
groundwater. Some carbonates may hydrolyse at a later stage, releasing CO/ into
solution. Where circulating groundwater brings dissolved CO2 near to the surface, some
CO2 exists as bicarbonates of low thermal stability, whilst some is adsorbed onto the