Heap leaching is a low capital cost alternative to conventional processing techniques for gold recovery from areas that contain small gold particles in a porous host rock._x000D_
For successful heap leaching the ores to be leached must maintain good permeability after being stacked into heaps so that the leach solutions can percolate evenly through them._x000D_
The presence of clays, slimes or excessive amounts of fines can hamper the flow of leach solutions causing channelling and producing dormant or unleached areas within the heaps. This results in unreasonably long leach periods and poor extractions. In extreme cases the clays or fines completely seal ore heaps, causing leach solutions to run off the sides of t'he heaps rather than penetrate the ore._x000D_
The Northern Queensland Company uses the Agglomeration Heap Leach technique (AHL) to overcome the difficulties associated with clays or fines. This technique involves cementing the fines, by using readily available binders, into a rigid, porous network that greatly enhances uniform flow of cyanide leach solutions through the ore heaps.