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Tracking down ores with trees.

There's gold in them thar trees -- and arsenic, antimony and zinc. Prospectors have long taken clues from plants to hunt down precious oeres. But while fortune hunters and scientists have understood that trees and other plants can take up many metals in the soil, until recently no one had done a controlled study in a natural environment of the relationship between soil minerals and the metal content of trees.

So several years ago three U.S. Geological Survey scientists took 57 pine, spruce and Douglas fir seedlings--each planted in a clay pot with soils containing different combinations of minerals--to a forest in the Rocky Mountains, where they buried the pots to their rims, and left. The minerals added to the soils were representative of four kinds of ore deposits. One group, for example, contained minerals deposited at high temperatures, such as bismuth and tin; another represented gold deposits.

Seven years later Harley King, Gary Curtin and Hansford Shacklette returned to analyze the chemicals in the trees, all of which had grown at expected rates. They found metals from soil minerals in the roots, stems and leaves of most of the trees. Even gold, which was thought to be very insoluble and resistant to chemical reactions, was taken up by some trees, they say.

The USGS researchers conclude that the three species studied showed no great differences in the uptake of metals, although they say in a recent USGS report that the Douglas fir "showed a remarkable ability to concentrate arsenic in leaves and stemps, and lodgepole pine was found to be greatly limited in the absorption of barium."
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Title Annotation:experiment on relationship between soil minerals and metal content of trees
Publication:Science News
Date:Sep 21, 1985
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