Following the extraction of gold, there are two byproducts remaining;
-Waste Rock: A rock containing little to no targeted minerals, economically useless.
-Tailings: The slurry which remains after the gold has been extracted from the crushed ore.
These, like most chemical reaction byproducts, are unwanted, and need to be 'dumped'.
Waste Rock
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| Fig. 2 - Diavik Waste Rock Pile, mneuner |
Depending on the current price of gold, any ore that has been mined gets tested to see its gold content. If it meets the requirement, it goes on to be processed and have the gold extracted. As this rock may still contain smaller traces of gold, it isn't destroyed, and could potentially be reprocessed if the price of gold increased making it economically viable to extract it (e.g.
Von Ketelhodt, 2009). Therefore, waste rock needs to be kept in some place, most commonly close to the mines (see fig. 2).
Tailings
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| Fig. 3 - Geomembrane lined tailings storage, Jon Engels |
Following the extraction of gold using cyanide, what remains in the slurry is known as tailings. This mixture is often around 30% solids, which are silt/sand size. These often dumped in tailing ponds or inpoundments. When dumped, the slurry will separate; the silt and sands will fall to the bottom. Prior to complete separation, the overall pond will be very porous, and the water will seep out into the ground. This will decrease over time as the silt settles decreasing permeability (e.g.
Vicks, 1990;
Vermeulen, 2001). This is a problem as this water is mixing with the local groundwater, and any chemicals present are being dispersed into the environment (see fig. 3).
