These things are employed, heavy earth moving machinery well hole drills etc for extraction of mineral.

The option that describes the use of heavy earthmoving machinery and well hole drills for mineral extraction is mechanized open-cast mining.

Mechanized open-cast mining involves the use of heavy earthmoving machinery such as excavators, shovels, draglines, bulldozers, and dump trucks for the extraction of minerals from the surface of the earth. Well hole drills are also used to create blast holes for blasting activities in the mining process.

Option A, manual mining, involves the use of manual labor to extract minerals from the earth. This method is labor-intensive and time-consuming and is usually used for small-scale mining operations.

Option C, horizon, and option D, slicing, are not related to the extraction of minerals from the earth.

Therefore, the correct answer is option B, mechanized open-cast mining.