Page 87 - Geochemical Remote Sensing of The Sub-Surface

64 O.F. Putikov and B. Wen

mineral " low ] r mineral
Chalcopyrite ]+0,18I -0,53Pyrite
-0,6 Chalconvrite
-1,18Sphalente
- 1,45Chalcopyrite
Pyrite
I,A

J i
~100

g~,V + 1.0 0 - 1.0 q~,V

Fig. 2-42. The CPC polarisation curves of the great polymetallic ore body in Rudny Altay, Russia
(reproduced with permission from Ryss, 1973).

found from comparison of these electrochemical reaction potentials with the standard
values of potentials for minerals (Table 2-II).
The CPC method gives information not simply in the vicinity of a borehole but about
the whole ore body, for example, at a distance 200-300 m from the measurement
borehole. Thus CPC is considered a remote sensing method (Ryss, 1973; Putikov, 1995).
For example, Fig. 2-43 shows two boreholes, 2012 and 2014, originally drilled to check
an electrical survey anomaly. Both intersected only the pyrite ore. However, CPC results
obtained from borehole 2012 show the presence of polymetallic mineralisation. This
polymetallic ore body was subsequently intersected by underground borehole 326, at a
distance of 200 m from borehole 2012.
The limiting current Ilim i of the electrochemical reaction of a mineral i satisfies the
expression,

Ilim i = Si j lim (2.41)

where S~ is the mineral surface on the contact between the electron-conducting ore body
and the ion-conducting host rocks and jlim is the limiting current density of the
electrochemical reaction. For a concentration C~ of the mineral i we can write,

Ci=Si/S0 ' (2.42)