Page 50 - Geochemical Remote Sensing of The Sub-Surface

Geoelectrochemistry and stream dispersion 27

Vm~t~m/year
10 7 L
10 6 .
105
10 4
103
102
10
1
10 -!
10 .2
10 -3
10 .4
10 -s i i i i
0.01 0.1 1 10 100 r, lxm

Fig. 2-7. Dependence of the maximum speed of the gas bubbles in the porous rock model Vmax on
radius r of the rock particles.

where, Vomax is the estimated speed of bubbles in free liquid when these bubbles have the
maximum speed in a porous system of particles of radius r.
If we take P = 103 kg/m 3, 90 - 0 kg/m 3, g = 9.8 m/s 2, r I = 10 .3 kg/(m• we obtain,

Vma x - - 7.9 x 103 r 2

where, [r] = m, [Vmax]-" m/S, or,

Vma x -- 2.49 x 10 zz r 2

where, [r] = m, [Vmax] ---- m/year
For comparison we extrapolate the experimental data by the equation to those in a
porous system of particles of very small radius (Fig. 2-7), for instance, r = l~tm. Then
the maximum speed of the front of the bubbles may be Vmax -- 2.49 X 10 -I m/year. When
r- 0.1 ~tm, then Vma x = 2.49 x 10 .3 m/year.
For prospecting, the requirements for bubble-facilitated transport of metals are that:
(1) the ore bodies or oil and gas reservoirs contain heavy metals of higher concentrations
than the surrounding rocks; (2) the metals may transform into mobile forms of metals in
the vicinity of prospection targets; and (3) the metals may be captured by gaseous
bubbles and be transported upwards through the overlying rocks. First consider ore
deposits in which metal concentrations are raised to some degree. Transfer of these