Answer:
Potash feldspar: (Microcline) - is a type of orthoclase feldspar (KAlSi3O8) that is light in color- if its bright green its called amazonite. Potash feldspar is a major mineral found in nearly all continental plutonic igneous environments, and is prevalent in metamorphic environments. This means they are probably gathered in a strip-mine/ quarry fashion. Seeing as how its granite its found in.
Unless you were talking about the salt, which is used as a fertilizer, in that case its mined via a shaft that goes down to the deposit layer and the layer is hollowed out using heavy machinery and tnt that makes a series of chambers and columns to hold the hollowed out part up.