Geology of the Red River district, Taos County, New Mexico
— Thomas T. Roberts, Gary A. Parkison, and Virginia T. McLemore

The Red River district encompasses a belt 15 km long and 6 km wide situated along the southeastern edge of the Questa caldera in the Sangre de Cristo Mountains of northern New Mexico. Caldera formation and associated plutonic activity represent the later stages in the evolution of the Latir volcanic field. Southernmost of the Rocky Mountain volcanic fields, the Latir field was active from 29 to 19 Ma and is located near the intersection between the Jemez lineament and the eastern margin of the Rio Grande rift. Along the southern margin of the caldera are postcaldera plutons which are characteristically rich in molybdenum. The Questa molybdenum mine and precious metal minralization are both products of this period of plutonism. Precious metal veins occupy radial and ring fractures associated with the caldera and normal faults associated with early rift related extension. Alteration in the district occurred in three stages: (1) regional propylitic alteration and smaller areas of intense acid alteration, both associated with molybdenum mineralization; (2) local argillic alteration and silicification along structures, associated with the precious metal mineralizing event; and (3) supergene alteration generated by weathering of the two previous stages. Mineralization occurs as quartzcemented breccia zones and banded, massive or vuggy quartz veins, both of which occupy fault zones. Gangue mineralogy includes quartz, calcite and rare fluorite. Metallic mineralogy consists of pyrite, native gold, sphalerite, galena, chalcopyrite, pyrargyrite and argentite. Homogenization temperatures from two-phase liquid dominant inclusions average 237°C, and salinity averages 1.1 percent equivalent wt. NaCI. Salinity vs. homogenization temperature data are consistent with mixing between fluids of contrasting salinity. These characteristics are similar to epithermal deposits; however, additional geochemical and hydrologic studies are needed to support this origin.