We should celebrate such rarities:
There are millions of tons (and billions of dollars in value) of recoverable metals, plastics, and other materials currently stored in landfills. The simple reason mining does not occur is economics: for multiple reasons, the costs to mine a solid waste landfill are currently greater than the value of recoverable materials.
The cost of any mining operation includes extraction of the target ore, processing to concentrate the ore (beneficiation), managing the associated wastes, transporting and selling the material, and finally closing and reclaiming the mine. These costs must be lower than the revenues made from selling the mined material. While the mining of solid waste landfills has many environmental benefits, it is subject to the same economic conditions as traditional mining.
Entirely, wholly and exactly spot on.