goldmine vs mine

goldmine and mine both are nouns.

Word	Noun	Adjective	Verb	Adverb
goldmine	Yes	No	No	No
mine	Yes	No	Yes	No

As nouns, mine is a hypernym of goldmine; that is, mine is a word with a broader meaning than goldmine:

goldmine (noun)	mine (noun)
a mine where gold ore is found	explosive device that explodes on contact; designed to destroy vehicles or ships or to kill or maim personnel
a good source of something that is desired	excavation in the earth from which ores and minerals are extracted

goldmine (verb)	mine (verb)
	lay mines
	get from the earth by excavation