Prospecting with plants

One day in the summer of 1959, geologist Helen Cannon was returning home after a day's field work on the Colorado Plateau, USA. Stopping to rest a moment, she let her horse to eat some grass growing along the road. Shortly afterward the animal died. Mrs. Cannon collected some of the grass that caused her horse die and asked a chemist to analyse it. It was found to be rich in selenium, a highly poisonous metallic element. Mrs. Cannon learned why her horse died. But she learned also a more interesting fact, for she knew that selenium usually lies together with uranium. And so a valuable deposit of uranium was found near the place where the grass had grown.

This incident shows that mineral deposits can be found by using plants.

The use of plants in looking for minerals is called botanical prospecting. It can be done by one of three methods. First, analyse the chemical composition of plants to find the minerals. Second, map the places of growth of particular species of plants – indicator plants – that grow only in soil that is rich in this or that mineral. And third, note changes that are made by certain soil minerals in the size or form of plants.

Why not just analyse the soil, then? This method is not always good. One sample of soil may differ fully of the soil over a wide area. A plant, on the other hand, sends roots down into the soil. It absorbs minerals from a large part of ground together with water which contains minerals in solution¹. In this way minerals become concentrated in the plant.

The first who used botanical prospecting was the Russian scientist S.M. Tkalitch in 1938. He used the first and the second methods in looking for deposits of iron-containing minerals in eastern Siberia. He found that grasses growing above iron deposits contain iron.

Today it is common to have a geobotanist, a man trained in both geology and botany, the science of plants, in every geological expedition. Botanical prospecting has been used here in looking for deposits of boron, nickel, cobalt, iron, chromium and molybdenum.

The use of indicator plants is the simplest botanical prospecting method. No chemical analysis is necessary. Nor a detailed knowledge is needed of how various minerals affect the size or form of plants. Where indicator plants are present, a prospector needs only make a map of their distribution to find possible mineral-rich areas.

Since the time when Helen Cannon's horse died from eating selenium containing grass the United States govern ment, too, has begun botanical prospecting studies. Scientists are beginning to understand that this technique can open up to prospectors large areas of the world now hidden² in forests or tropical jungles.

Notes and Commentary

¹ solution - розчин

² hidden - прихований