placer mining vs mining

placer mining and mining both are nouns.

Word	Noun	Adjective	Verb	Adverb
placer mining	Yes	No	No	No
mining	Yes	No	No	No

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

placer mining: mining valuable minerals from a placer by washing or dredging
mining: the act of extracting ores or coal etc from the earth

Other hypernyms of placer mining include excavation.

placer mining (noun)	mining (noun)
mining valuable minerals from a placer by washing or dredging	the act of extracting ores or coal etc from the earth
	laying explosive mines in concealed places to destroy enemy personnel and equipment