Page 44 - Geochemical Remote Sensing of The Sub-Surface

Geoelectrochemistry and stream dispersion 21

Pb, ~tg/ml

20

~ h = 0 m

5 l

o
5
0
'l
01 - , h=2.5m

>

A B

~ 1

Fig. 2-3. Jet halo of lead for the A-B segment of Fig. 2-2 at the surface (h = 0 m), at depths 0.5,
1.0 and 2.5 m, and a schematic depth section of the halo of the mobile forms of lead: 1- halo of
the mobile forms of lead; 2- streams of lead migration (reproduced with permission from Ryss et
al., 1987b).

structure, representing a stream of migrating metals (Fig. 2-3). Shigaev (1997) studied
the structure of the stream of Mn in an oil field to depth of 140-160 m.
The principal difference between jet halos and diffusion halos is the vertical
prolongation of the former. The two important factors determining this vertical
prolongation are temperature and pressure in the Earth's crust. The numerical solution of
the differential diffusion equation for the concentration of a mobile form of metal in a
non-isothermal rock shows that even a localised temperature gradient results in vertical
prolongation of halos. The pressure gradient influences the migration of gases of the
least density, which perhaps migrate in the form of bubbles. A physico-chemical model
of jet halos formed by bubble-facilitated transport of metals is proposed and illustrated in
Fig. 2-4. In this model the following conditions need to be satisfied: