Page 147 - Geochemical Remote Sensing of The Sub-Surface

124 M. Zhang

CASE HISTORIES

The skarn copper deposits at Huaitongshan, Gansu province, which are accompanied
by some minor lead-zinc veins, lie of depths of 5-80 m. The area is arid and the surface
is covered by Quaternary sediments on which a poor sandy and rudaceous soil, 3-50 cm
thick, has developed. A traverse of soil samples revealed CO2 anomalies reaching 285
ppm over the main copper mineralisation, a contrast of about 4.4 (Fig. 4-1). The weaker
anomaly further north is thought to lie over minor lead-zinc veins.
The iron ore deposit at Wang-wang, Shandong province, has been described as a
pneumatolytic high-temperature skarn. The ore minerals are sulphur-rich magnetite and
minor pyrrhotite. The deposit is about 300 m below surface. The Quaternary cover is
130-180 m thick. The area is semi-arid, with soils under cultivation. Along a soil
traverse, a CO2 anomaly reaching 285 ppm occurs over the mineralisation, and against
background levels has a contrast factor of 3.6 (Fig. 4-2). This result is of particular
interest for two reasons: (a) the deposit is not a sulphide ore body, but a high-sulphur
iron deposit; and (b) other methods for detecting concealed mineralisation
(geoelectrochemistry and Hg) did not yield anomalies here.
The Shanbaidu polymetallic deposit, Jiangsu province, lies between 5 and 40 m
below the surface and is overlain by eluvium and alluvium 5-15 m thick. The area is
semi-arid and the soils are cultivated. Soil samples collected at three depths along a

Fig. 4-1. Relation between carbon dioxide in soil and copper mineralisation at Huaitongshan,
Gansu province, China.