Basically, costs cannot be cut unless costs are known, but there still gold operations lacking detailed, definitive cost data. In this way, optimum cost control needs good organizational systems, log books, time sheets, work orders, maintenance schedules, and other more. They can be tedious, but they are important for detailed and critical cost analysis. Computers have made it easy to organize such information, give detailed breakdown of expenditure and identify the control of high-cost items. Major operating costs categories are usually power, operating and maintenance labor and operating and maintenance supplies. Each of these categories accounts for about a third of total costs.
Power charges are based on a mixture of demand and consumption, and in many places different tariffs apply at different times of day or season of the year. Some penalties are incurred if agreed peak demand is exceeded. Controlling power costs requires minimizing peak demand, taking advantage of differential tariffs where available, maximizing power factor and making the most use of installed horse power. Crushing and grinding are by the far the largest consumers of power in a gold ore processing plant. Phasing start-ups reduces peak demand and running crushers and mills at full power maximizes throughput and makes the most efficient use of installed horsepower. Intermittent activities such as pumping fresh water should be done when low tariffs apply. By considering such small and obvious measures, power costs can be reduced markedly. Even insignificant changes such as employing efficient lamps, add up to savings at the end of the year.
Labor costs are basically a function of plant design. In this way a complex plant on many levels will need more personnel than a simple plant with a spacious layout. There is usually scope for reducing requirements by automating simple control loops and promoting flexible working practices. Maintenance in a gold processing plant is related largely with the replacement of wear items such as crusher bowls and mantles, jaw crusher liners, screens, ball mill liners, pump impellers and linings, flotation cell impeller, etc. Advances in material technology have had an important impact. For example steel screens are being replaced by rubber and polyurethane in many applications. Rubber liners have become universal for fine grinding, hydrocyclones are made or lined with polyurethane and rubber is being utilized on piping systems. There are also low friction materials for lining chutes and special steels, and a variety of ceramics for very high abrasion applications. To consider all these materials, will help to reduce costs.
For supplies, close control of consumption is important. In many gold processing plants, steel balls, liners and chemical reagents are the main consumable. Different liner designs and materials, and also different reagent regimes can all contribute to cost reductions, but these are long term tests that must always consider the metallurgical parameters. Probably, with reagents, the greatest economy comes from close control, making sure the feeders are level and easy to tune and avoiding spillage in mixing and transfer. Plant management must be aware that the same metallurgical performance can be obtained with starvation dosages. This is especially true on silver-gold ores treated by flotation where operators may easily get into a vicious cycle of increasing depressants for non-sulphide gangue and then increasing the dosage of xanthates to compensate any imbalance.
Energy prices have left a mark on the industrial brain and have been the spur behind many advances on gold ore processing. This is clearly seen in the utilization of large equipment such as ball mills, flotation cells or optimized cyanidation circuits. Single high tonnage circuits make for simplicity of operation, needs less labor, and make easier and cheaper to install on-stream analysis and computer control. A very high level of availability is needed due to any breakdown can imply a high loss of production. For this reason, maintenance is an important part of the cost.