The inventor is aware of a variety of apparatus and processes that have been used for extracting heavy particles, such as gold, platinum, lead and the like, from ore, gravel or sand, earth, including placer ore for example in respect of alluvial gold, and the like. Such apparatus and methods suffer from certain problems including an inability to deal with a broad range of particle sizes and a failure to recover fine particles. This reduces the efficiency and hence the profitability of such recovery systems.
Another disadvantage is that certain recovery systems involve the use of large quantities of water. Such large quantities of water are not always available at a site where, for example, gold-bearing placer ore is found and processed. Even in localities where large quantities of water are available, such usage can impact negatively on the environment, and hence large holding ponds or holding tanks are required.
Another disadvantage of conventional placer ore recovery systems is that a surge is created in water flowing through the system with each new load of gravel that is added to the system. This results in loss of fine gold particles.
Further disadvantages of for example existing gold recovery systems include an extended clean-up time and a large volume of concentrate which add significantly to the cost of operations; the large size of equipment; high capital cost and difficulty of transporting such equipment.
The inventor is also aware of the apparatus and process disclosed in his U.S. Pat. No. 5,108,584, which was granted and published on 28 Apr. 1992. This patent describes an outer and inner barrel arrangement. The inner drum has an upper fragmentation section, an intermediate trommel section and a lower discharge section. A spray of water is directed into the inner barrel. The ore is separated into large tailings that are discharged from the lower end of the inner drum and fine, light tailings from the outer drum. Heavy, fine portions of the material are carried by a spiral on the inside surface of the outer drum and discharged into the upper end of a sluice box from the upper end of the outer drum. The sluice box includes the plurality of landings upon which heavy material, such as gold, collect. The outer drum may be vibrated to assist in the recovery process.