Hancocks Tailing (Skimps) Heap contains the waste crushings of ore after concentration by crushing and jigging. The concentrated ore from the local process was sent to the Wallaroo Smelters. Mineral waste from any metal concentration processing is called Tailings. There were five large tailings heaps on the Moonta Mine containing approximately 2,000,000 tons of waste. Coarse waste was known as Skimps. Fine waste was called Slimes. There was still some copper in these crushings and in 1900 the "cementation" process was introduced to leach out the copper and precipitate the valuble metal for melting into ingots.
Moonta cementation plant appears to be the first application of acid leaching to mineral extraction in Australia. To enable this process sea water pumped from the coast was acidified with a small amount of sulphuric acid. The acidic leachate was then pumped to the tops of the skimps heaps and directed into soak beds confined by low earth walls, so that leaching could be concentrated on one area at a time. Once the leachate had percolated through the skimps heap, it was ‘pregnant’, that is it contained copper sulphate in solution, and flowed by gravity down channels to precipitating ponds, which were concrete troughs packed with scrap iron. Roughly two tons of iron was consumed to precipitate one ton of copper.
Copper production from the Moonta cementation plant was carried out from 1901 to 1944. Average yearly production of 700 tons of copper was retrieved from cementation process. Thus almost 31,000 tons of copper was retrieved from waste. Wallaroo ore was metallurgically different, and did not respond to oxidation or readily form sulphates in the leach solution.
Skimps are waste material. Particle size is an important condition in the process. The skimps heaps were terraced as part of the copper recovery process. Terracing allowed control of the seawater leachant during pumping and percolation. The top surface of the heap was covered with low earth walls to provide further process control.
Examine some skimps and the condition of Hancock's Heap and answer the following earthscience questions.
-The skimps are roughly comparable to beach sand or fine gravel? Why is it this size?
-Can you still see terraces on the sides of Hancock's Heap? What has happened?
-Approximately what size are the walls on the top of the heap? Why are they this size?
Send your answers to the cache owner. You can log immediately. Don't forget to send your answers.