Basically, the need for blending and storage often requires formation of intermediate stockpiles at mine or processing plant. In this way, the handling and blending of gold ores may need initial storage and accumulation of as-received ore into classified lots at the processing plant, continuing with crushing and sampling and return to the storage place for blending into several stockpiles before taking the material and feed it to the process. It has been noted in several gold mines that the physical properties of the gold ore may affect the way in which it must be prepared and stored. For example, if the content of clay is high, the material tends to be wet and sticky and this produce problems in storage bins and the potential segregation of fine and coarse particles. If the gold is associated with any special fraction size, the plant should expect any problems such as abrupt change in gold grade and ore hardness distribution.
In order to avoid problems, most gold operations perform some degree of blending to get a uniform feed to the mill. It is possible to find some exceptions if the gold ore processing plant are regulated to optimum levels for particular gold ore types or when the ore extracted does not present a high level of variability in gold content, hardness or mineralogical distribution. However, it is important to adopt a blending strategy in order to get an ore with uniform properties. The ideal case is to process a material very close to the ore type evaluated in the testing program for the feasibility study.
If the ore maintains uniformity, the plant operation is smooth out and plant capacity is close to the maximum level. It has been reported that some gold operations experimented problems when individual ore had a high content of compounds such as oxide copper minerals, arsenopyrite, clays, carbonaceous matter or organic matter. The presence of excessive content of clays may cause excessive frothing in a gold flotation circuit and a high concentration of organic matter may cause fouling and poisoning of the cyanidation process with preg-robbing materials.
Other important consideration for blending is when the material is excessively hard, slimy or sandy. For example a hard gold ore limits the capacity of the grinding circuit and it is possible to experiment liberation problems. A sandy or coarser gold ore can produce problems of settling out in tanks or piping systems. The presence of slimes affects flotation and leaching circuits by reducing the metallurgical efficiency of the process. The flotation plant has problems with concentrate grade and dewatering operations due to slimes are difficult to depress, settle, and filter. For these reason it is important to adopt a blending strategy.