The Buena Vista iron ores have a geologic setting and genesis distinct from that usually attributed to contact-metasomatism. The ore is confined to igneous rock with the majority of the magnetite localization controlled by fold axes and fissures in hornblende andesite. No massive replacement bodies occur in sedimentary rock and the alteration preceding and accompanying mineralization affected only the igneous rock.Ore-bearing fluids introduced considerable quantities of iron, chlorine, fluorine, phosphorus, sodium, potassium, and carbon dioxide into the host rock. Vanadium also was introduced and formed the rare spinel type mineral, coulsonite, in association with two varieties of scapolite and various alteration minerals.Regional and local geology suggest that a structural intersection marks the area of mineralization and that structural control strongly influenced ore localization.

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