Rusty plate leads to new technique

Watching river water corrode an old tin-plated cooking utensil has provided the inspiration for Australian scientist Dr William Baker to develop a new technique for the exploration of mineral deposits.

A geochemist with the Tasmanian department of mines, Baker said it had always been difficult to determine the mineral content of Tasmania’s rugged west coast because high rainfall led to rapid leaching of the clay subsoil and fast-flowing rivers left little in the way of silt deposits.

“I noticed a corrosive ring around the plate after it had been used for washing dishes on one of our field studies,” he said.

This led to speculation about how minerals might be associated with organic matter in soil and water, and has resulted in the past twelve months in the development of the Huminex system, a project Baker began about 1979.

The Huminex system determines the exact association of minerals with organic matter in the topsoil and in river water and can be used to provide information on areas which may have been ignored in the past because of their supposedly low mineral content.

To find mineral deposits, geochemists divide soils into three layers. Horizon A contains the top soil, Horizon B the clay strata and Horizon C the bedrock. Normally, major mineral deposits are discovered by examining the clay content of Horizon B.

But in the past, when soils were affected by heavy rainfall and rapid leaching of minerals occurred, Horizon B provided erratic results and scientists were obliged to examine Horizon C — a costly and time- consuming process. Only shallow sampling

“To reach the bedrock involved hand or machine augering to depths of more than one metre,” Baker said. “Using the Huminex system involves only shallow sampling (about 10 cm — 4 inches) of Horizon A to obtain the soil organic matter.”

He said his method was quick, did not disturb the environment and was a fraction the cost of the old method. Tests had shown it to be as effect ive as Horizon C procedures.

The Huminex system would now be used for a regional reappraisal of mineral distribution in western Tasmania. Baker said it was now economically viable, for example, for the department of mines to use the system to look for large low grade deposits of gold (8 g per tonne) given the price of the metal on world markets.

He had extended the soil sampling technique to determine the mineral content of rivers in the area.

“The closer the proximity of the river to an orebody the greater the concentration of minerals in the water,” he said.” In the past this has been worked out by examining stream sediment which has not always proved very satisfactory for the fast-flowing rivers of Tasmania’s west coast.”

He believed the Huminex system had potential application in heavily vegetated areas such as the tropics, where the topsoil was rich in organic matter.

“It is often difficult to go into these areas without disturbing the environment,” he said. “Using this method, a couple of people can obtain samples and the mineral- rich areas can be identified later.”