opencast mining vs excavation

opencast mining and excavation both are nouns.

Word	Noun	Adjective	Verb	Adverb
opencast mining	Yes	No	No	No
excavation	Yes	No	No	No

As nouns, excavation is a hypernym of opencast mining; that is, excavation is a word with a broader meaning than opencast mining:

Other hypernyms of opencast mining include mining.

opencast mining (noun)	excavation (noun)
the mining of ore or coal from an open mine	the act of extracting ores or coal etc from the earth
	the act of digging
	a hole in the ground made by excavating
	the site of an archeological exploration