nGossan(Geol) Decomposed rock, usually reddish or ferruginous (owing to oxidized pyrites), forming the upper part of a metallic vein. Called also iron hat.
Century Dictionary and Cyclopedia
ngossanIn mining, the ferruginous quartzose material which often forms a large part of the outcrop of a lode in which the metallic contents at depths exist chiefly in the form of sulphids, among which pyrites, a combination of sulphur and iron, is rarely wanting, and is often present in large quantity. These sulphids becoming oxidized, the resulting brown oxid of iron remains mixed with the gangue, of which the larger part is usually quartz; and this dark, rusty-brown material is the gossan of the Cornish miner, a term also in very common use in other mining regions. It is the eisenhut of the German and the chapeau de fer of the French miners; and, indeed, the corresponding term in English, the iron hat, is not unfrequently heard in the United States.
Chambers's Twentieth Century Dictionary
nGossangos′an (prov.) decomposed rock, usually ferruginous, forming the upper part of a metallic vein
What is left is either iron oxide, "gossan," or the oxides of the other metals.