Compositionally zoned dikes of the Questa mine area, northern New Mexico: Magma mixing and the post-26 Ma evolution of the Questa magmatic system
— David M. Jones

Mid-Tertiary compositionally zoned dikes are present in a 2 km by 4 km, east-west-trending dike swarm at the Questa mine, northern New Mexico. Dike emplacement occurred after deposition of the 26 Ma Amalia Tuff and prior to emplacement of molybdenum-bearing granites. Zoning consists of phenocryst-poor "mafic" dike margins which grade continuously inwards to phenocryst-rich "felsic" cores. Geochemical analysis and petrologic modeling reveal systematic intra-dike mineralogic and chemical zoning which originated through the mixing and cointrusion of andesite and rhyolite magmas. The Amalia Tuff and the younger molybdenumbearing granites are plausibly related through the mixing event which formed the zoned dikes and subsequent crystal fractionation.