In the West Tintic Mining District Proterozoic quartzites and slates have been thrust over folded Paleozoic limestones and dolomites. Five types of igneous rocks have been intruded in sequence of four stages: (1) monzonite stock simultaneous with monzonite porphyry dikes, (2) granite porphyry stocks with (3) granite cores, (4) aplite dikes.
Contact metamorphism is prominent adjacent to the larger intrusions and is considered to have been accomplished by end-stage liquids with little addition. Pyrometasomatic veins and mesothermal deposits were next formed and were followed by the formation of low-temperature quartz-barite veins and replacements. The entire sequence of events is established by field and laboratory evidence.
It is believed that here is represented the history of a cooling differentiating magma and the deposition of hydrothermal minerals of progressively lower temperature of formation.