Although previous work indicated that there may exist a striking relationship between the mineral content of plants and that of the underlying soils and rocks it was thought advisable to re-examine the problem, employing different collectors and analytical methods. Furthermore, if this work were ever to have an economic application, it would be necessary to develop simpler and more direct methods of collecting, sampling, and analyzing.
This paper outlines some of the analytical methods employed and describes a dithi-zone method which seems eminently suitable for both copper and zinc analyses.
Evidence shows that twigs, rather than leaves or needles or even fruit, are probably more satisfactory as indicators of variations in the metal content of soils and rocks. Twigs are easier to collect, to sample, and to ash; indeed, satisfactory results have been obtained from 1- and 2-gram samples. If the evidence is substantiated it may be possible to carry on biogeochemical prospecting in winter.
Numerous analyses of samples from the Britannia and Sullivan mines are tabulated, and their significance is discussed. The results are compared with those obtained previously.
In some areas the zinc-copper ratios may, in biogeochemical prospecting, be more significant than the absolute amounts of zinc and copper present in the trees and lesser plants, particularly when the absolute amounts of copper and zinc are low.