Page 59 - Geochemical Remote Sensing of The Sub-Surface

36 O.F. Putikov and B. Wen

vf is 10 .9 v0. In the general case a one dimensional equation can be written,

O 2C OC -~j'~c(~,n)~n OC
D~- V ~ - kzqmaxCe = 0 (2.13)
Oz 2 ~g Oz Ot

Under boundary and initial conditions,

Clz=o -Co, (2.14)

(V~yyC- D OC ] ~ C]z=H
- - (2.15)
Oz ) z=,-,

C],_ ~ - 0 (2.16)

The equation is solved by means of iteration and fully-implicit finite difference in the
following scheme (Wen, 1997b),

_(0.25c+0.5s)Ci'+l,,+(1.O+s+~qmax~e , ~=, ~ )C~i~,+~ +(0.25C--0.5S)C++,'m =

(0.25C + 0.5slC'_ , +(1.0--SIC' + (--0.25C + 0.5S)C:'+,

where, c = verrAt/Az, s = DAt/(Az) 2.

Figure 2-15 shows that with parameters Co = 1 1/m ~, Vef f • 10 .5 m/s, D = 10 -7 m2/s,
q,,,,x = 1 1/m ~, [3 = 10 .6 m3/s, the concentration front extends with constant speed and
keeps its distribution shape for a certain time. In this case concentration distribution is
also (as in Fig. 2-14) stabilised with time without diffusion.

Partial extraction of metals (CHIM)

In the CHIM method of prospecting a direct current is introduced into the ground by
means of a current electrode and an element collection electrode. This facilitates the
extraction and accumulation of ions of the metals in zones near electrodes. The
subsequent analysis of the extracted metals yields information about their distribution in
the rocks in the zone of investigation.