There was a sense of excitement as I found myself negotiating the narrow strip road that passes Lonely Mine, 80 miles north of Bulawayo, in the country of Zimbabwe.

I was born in Zimbabwe and lived in Africa for 34 years prior to locating to the USA for work opportunities. The objective at the Lonely Mine operation is to recover gold left in the mill tailing dumps in the 1930s. Casmyn Mining Zimbabwe (Pvt.) Ltd, a wholly owned subsidiary of Casmyn Corp., listed on the bulletin board of the NASDAQ stock exchange, aims to treat 45,000 tons per month at Lonely Mine. The dump has sufficient reserves for a two and a half year project life. This project is one of two large dump retreatment projects the company has in the area.

 

The process is really very simple and cheap. The production costs are around US$ 200 per ounce of gold.

The most critical part and most scarce resource of the operation is water. Under the heat of the relentless African sun, approximately 75% of all the process water evaporates from the tailings dam before it can be recycled. The makeup water is pumped from the old mine shaft to a plastic lined surface storage dam.

From here, 75 cubic meters per hour of water, at pressures of 36-40 bar are pumped through a 19 mm nozzle to produce a jet stream powerful enough to break down the tailings. The result is a mixture whereby 55% is solids in the form of suspended tailings called pulp, the balance being water. The pulp then gravitates via a system of trenches to a pump where lime is added for pH control before it is pumped to the processing plant.

The plant (designed by RPM Engineering, Pty. Ltd., Bulawayo) is a modular and easy to transport plant consisting of six treatment tanks in series. The first is a conditioning tank where cyanide is added to dissolve the gold. The next five tanks have in them (made from burning coconuts) for the absorption of the dissolved gold. The process is a counter current between the carbon and the pulp. That is to say carbon pumped up the tanks while pulp flows via gravity down the tanks. The processed pulp is then pumped back out to the tailings, leaving the gold behind in the tanks on the carbon. The carbon is removed from the tanks once a day.

A major obstacle to this project would have been the spoiling of some 10 hectares of prime untamed African bush needed for the new tailings site. By coming up with a system whereby the processed pulp is pumped back into the already worked tailings dams, the unspoiled land surrounding the tailings dams is preserved. In effect, the entire dams will be reworked without disturbing the surroundings at all - a strategy for which the locals can thank Ian Saunders, Chief Metallurgist for Casmyn Mining Corporation.

Comparison of Sluicing verses Hauling

A detailed analysis comparing the costs of the traditional haul and dump operation identified the sluicing to have a cost of Z$2.39 per ton verses Z$10.45 per ton for haul and dump. A considerable savings and one of the key factors to producing the gold at such a low cost.

But the advantages of sluicing do not stop here.

Zimbabwe has dry winters with a heavy rainy season in the summer. The results is impassable mud roads. The sluicing method on the other hand will benefit from the additional water.

Another major benefit is eliminating the construction of haul roads, their maintenance and "dead space" they create in the middle of the tailings dams. Using a slope angle of 45 degrees, a 10 meter wide road is needed for the trucks to drive on. By utilizing the sluicing method, the top of the wall need be only four meters wide. The walls for hauling need to be straight, restricting the freedom often desired by those planning the operation. When sluicing, this is not an issue.

24 Hour Standby Equipment

When running 24 hours per day, standby equipment is vital. In a remote location such as the aptly named Lonely Mine, the cost of having standby trucks and excavators would be high. Conversely, the cost of a standby pump is minimal.

Coca-Cola comes to the rescue!

In the bush, finding spares for even the simplest equipment, can be challenging. This was the case with 19 mm nozzles used to form the jet. As engineers relaxed enjoying a true African sunset, downing a cold beer... and Coca-Cola, discussion began to revolve around the almost perfect hydraulic shape of the inside of a coke bottle neck! It was only days before a few Coke bottles, the contents consumed, had been tried. By adding putty to the outside of the neck, the new nozzle fitted perfectly into the housing of the high pressure monitors. The results were astounding! The nozzles work perfectly, once again adding another simultaneous operation to Lonely Mine...consumption of Coca-cola, and generation of nozzles!

And who says Coca-Cola isn’t the real thing.