Mining stockpiles are precisely what they sound like — a surplus of mined material, either accumulated on the surface or dug and piled for future use. They originate from a variety of factors, including supply temporarily outstripping demand, production without immediate access to a treatment plant or the acquisition of a previously mined project. Although they don't always contain mineable or renewable resources, there are many benefits to production when they do.
Aside from being one of the most efficient ways to restart a project, stockpiles are an incredibly effective way to store large quantities of material , and tend to exist in one of three forms.
The most generic stockpiles are made by standard bucket loading and dumping techniques. Ramp stockpiles, meanwhile, are constructed and piled high using a narrow ramp, making them optimal for storing very large volumes of material in a limited area. Finally, bin stockpiles store minerals in a row of three-sided bins, enclosed inside hard walls to keep types of material separate from one another.
For further details see:
How Investors and Mining Companies Benefit from Stockpile Projects