Page 149 - Geochemical Remote Sensing of The Sub-Surface

126 M.Zhang
c02[ 30 cm soil sampling depth
(ppm) ]
400 l
300 ]
200 I

C02 60 cm soil sampling depth
(ppm)
400
300
200
100
0
C02 100 cm soil sampling depth
(ppm)
400
300
200
100
0

Fig. 4-3. Relation between carbon dioxide in soil and polymetallic mineralisation at Shanbaidu,
Jiangsu province, China.

The Xuanchengshan cupriferous pyrite deposit, Anhui province, occurs in the
cataclastic zones between granodiorite and limestone, and is of hydrothermal origin. It is
overlain by 300 m of basic rocks and 10 m of alluvial sediments. Samples from a
traverse at surface above the mineralisation reveal a broad, clear CO2 anomaly with peak
values in excess of 200 ppm CO2 and a contrast factor of 6 (Fig. 4-6). Of the other
elements determined along this traverse, Mo, Sn and W yielded no anomalies, and a Cu
anomaly is confined to a single point. However the pattern for thermally-released Hg
matches that of CO2. The primary halo of CO2 at Xuanchengshan is similar to that at
Qixiashan. The highest concentrations of CO2 occur within the ore body, and the halo
extends outward and upward. Nearer the surface is a second lens enriched in CO2,
related to ore mineral formation and chloritisation. The halo around this extends towards
the surface and its suboutcrop exactly matches the extent of the anomaly on the surface
traverse.