Botanical prospecting for uranium is a method of
finding
uranium deposits either by
observation of plant life growing on the surface, or by geochemical
analysis of plant material.
The history of
uranium prospecting, especially in the
Colorado Plateau of North America, has seen
several methods of identifying likely
ore
body locations. The use of radiation detectors, such as
Geiger counters and
scintillation counter is one such
method. Another method widely used relies on knowledge of the
geologic history of an area, such
as locating a
geologic formation
known to host ore deposits.
United States
During the early efforts to locate uranium deposits in the United
States, the
U.S. Geological Survey conducted studies
of prospecting through botanical surveys. These studies examined
three methods.
Each method begins with the identification of an area of interest.
This area is then gridded off, which allows the prospector to map
samples to specific locations on the ground.
Plant morphology variations
The first method, not widely used in the
Colorado Plateau, looks for physiologic and
morphologic changes in plants growing in or around ore bodies. A
survey of plants in the gridded area is conducted. Comparison of
normal growth habits and rates is done with known normal plants,
and areas with high rates of change in either physiology or
morphology indicate likely spots for further prospecting. This
method is time consuming, and is not useful in all areas.
Deep-rooted plants
The second method uses a survey of deep-rooted plants in an area of
interest. This works because the plant roots carry
uranium to the surface, where it is concentrated in
growing areas of the plant.
Juniper or
saltbrush are usually used, as they are
known
uranium concentrators. Samples of tree
branch tips and leaves are taken from each area in the grid. These
samples are then sent to a laboratory for analysis. Concentrations
of more than 1 part in a million-(> 1 ppm) of
uranium indicate likely areas to investigate
further, through drilling or digging. This method provides
information about likely ore bodies down to a depth of between 50
and 70 feet, and is generally good in areas where mineralized beds
form broad flat benches, so that a grid pattern can be used.
Indicator plant species
The third method looks for concentrations of
indicator plant species in an area of
interest. Some
uranium ore bodies contain
higher concentrations of certain elements, such as
selenium, than the surrounding host rock in which
they are found. Certain plants that concentrate these elements act
as indicator species for likely ore body locations. Mapping these
plants provides information about areas in which further
prospecting should be done. For example, in areas such as the
Colorado Plateau, various species
of
Astragalus are selenium
concentrators (
A. pattersoni, A. preussi, A. thompsonae).
Other indicator plants for
sulfur and
calcium, such as
Eriogonum inflatum and
Oenothera caespitosa help to identify likely
areas also, especially in conjunction with the
selenium indicators.
Other regions
In areas
outside the Colorado Plateau, such
as in South
Australia
or Saskatchewan
, Canada
, other
plants would naturally be used than the ones cited in this
article.
See also
References
Cannon, H. L., 1957, Description of Indicator Plants and Methods of
Botanical Prospecting for Uranium Deposits on the Colorado Plateau,
Geological Survey Bulletin 1030-M.
McKelvey, V. E., 1955, Search for Uranium In the United States,
Geological Survey Bulletin 1030-A.
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