pig iron vs mine pig

pig iron and mine pig both are nouns.

Word	Noun	Adjective	Verb	Adverb
pig iron	Yes	No	No	No
mine pig	Yes	No	No	No

As nouns, mine pig is a hyponym of pig iron; that is, mine pig is a word with a more specific, narrower meaning than pig iron:

Other hyponyms of pig iron include basic iron, cinder pig, spiegel, spiegel iron, spiegeleisen.

pig iron (noun)	mine pig (noun)
crude iron tapped from a blast furnace	pig iron made entirely from ore