Page 125 - Geochemical Remote Sensing of The Sub-Surface

102 S.M. Hamilton

cells in the Earth were based on a fundamental false premise. The problems stem from
the fact that most authors (e.g., Bolviken and Logn, 1975; Govett, 1976; Sivenas and
Beales, 1982; Smee, 1983; Clark, 1997), inadvertently or otherwise, saw the conductor
itself as the voltaic cell. This led to models involving self-polarising conductors that
generated their own electrical field within the Earth's redox field (Fig. 3-6). When
considering the conductor and the Earth electrolyte as a whole, the result was an
electrolytic cell, not a voltaic cell. Hamilton (1998) provides an in-depth treatment of the
theoretical problems with some of these models.

TABLE 3-II

Electrical conductivities of typical shallow groundwater in glacial terrain (Shoot Zone gold
property, northwestern Ontario) and those of common bedrock materials converted from the usual
resistivity units (from Keller and Frischknecht, 1966)

Conductor n Electrical conductivity (~tS/cm)
Range Mean
Groundwater
Peat 3 297- 347 328
Glaciolacustrine Clay 7 357- 714 508
Sand Aquifer 23 138 - 558 387
Glacial Till 7 254 - 536 417
Crystalline Rock 15 159- 581 370
Bedrock material"
Arsenopyrite 0.33 - 5 1.3
Chalcopyrite 0.011 - 0.67 0.086
Native copper 330 - 8300 1700
Graphite (parallel to cleavage) 100 - 280 167
Galena 0.0011 15 0.13
-
Magnetite 1.9 1.9
Marcasite 0.00067 - 0.10 0.0082
Molybdenite 0.000013 - 0.00083 0.00011
Pyrrhotite 0.63 - 50 5.6
Pyrite 0.00017 - 0.083 0.0037
Pyrolusite 0.0000033 - 0.014 0.00022
Sphalerite ("non-conductive") 0.0000000083 - 0.037 0.000018

* Means for bedrock material are geometric means

There are two models for the development of SP cells around electronically-
conductive mineralisation that are considered here to be theoretically sound. They are