Richard Maxwell Pearl
Turquoise deposits of Colorado
Economic Geology and the Bulletin of the Society of Economic Geologists (May 1941), 36(3):335-344

Abstract:
Colorado ranks as the second state in the production of turquois, which comes from near the towns of Villagrove, Manassa, Leadville, and Creede.The deposits occur in weathered acid igneous rocks rich in alkalic feldspar. The turquois is found as veins and nodules in faults, fissures, and cavities. The Hall mine near Villagrove is in felsite porphyry, an Oligocene volcanic flow locally cut by quartz latite. The King mine near Manassa is also in felsite porphyry, probably an extrusive member of the Miocene Santa Fe formation, which is locally cut by felsite, possibly trachyte. The Turquois Chief mine near Leadville is in the Algonkian Silver Plume granite. Turquois is found near Creede in a stream bed, but the source is unknown.The three lode deposits were formed by circulating meteoric waters that leached and concentrated the constituents of turquois from the surficial rocks and precipitated them from cold solution in fracture and shear zones. The phosphorus was probably derived from apatite; the copper, from copper ores; and the aluminum, from the alteration of feldspar; iron and silica are impurities.