placer vs alluvial deposit

placer and alluvial deposit both are nouns.

Word	Noun	Adjective	Verb	Adverb
placer	Yes	No	No	No
alluvial deposit	Yes	No	No	No

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

placer: an alluvial deposit that contains particles of some valuable mineral
alluvial deposit: clay or silt or gravel carried by rushing streams and deposited where the stream slows down

Other hypernyms of placer include alluvial sediment, alluvion, alluvium.

placer (noun)	alluvial deposit (noun)
an alluvial deposit that contains particles of some valuable mineral	clay or silt or gravel carried by rushing streams and deposited where the stream slows down