Major cities are not only the focal point for Australian's work, leisure and homes, they also are the focal point for the flow of resources into the built environment, motor cars and transportation and urban consumables. The steady increases in stock' and waste generation, in line with GDP growth, means that cities will become the mine sites of the future if the inherent value is recovered from these materials at end of life._x000D_
The urban waste stream can be characterised as containing approximately nine per cent hydrocarbon-based materials; 57 per cent biomass-based material; 28 per cent fully mineralised materials that are inert, five per cent metals and less than one per cent of problematic materials that are potentially hazardous and toxic._x000D_
In order to convert these wastes into value added inputs into the economy, a number of technological interventions are required. These urban waste mining techniques' revolve around source separation and material streaming. One issue that needs to be overcome when determining which mining technique to implement, is identifying the option that will deliver optimal value, both from a financial and a sustainability perspective. The difference between embodied energy and calorific value is a case in point._x000D_
Highest net resource value (HNRV) is a concept that can assist in choosing between different resource recovery options. The assessment can be done at a strategic level, or can be used to work out material specific issues. For example, used tyres can be recovered for their energy content at an approximate cost of $120 per tonne, whereas mechanical processing of used tyres can deliver a net benefit of $192._x000D_
FORMAL CITATION:Glover, M and Warnken. M, 2006. Cities as mine sites of the future, in Proceedings Green Processing 2006, pp 173-178 (The Australasian Institute of Mining and Metallurgy: Melbourne).