Occurrences of precious metals and uranium along the Rio Grande rift in northern New Mexico
Virginia T. McLemore and Robert M. North
Silver and gold occur in at least minor concentrations (above 1 ppm Au and 14 ppm Ag) in 25 mining districts within and adjacent to the Rio Grande rift in Colfax, Taos, Rio Arriba, Sandoval, Santa Fe, and Torrance Counties in northern New Mexico (Fig. I , Table 1). No platinum or platinum-group metals are known to occur in the area. Uranium occurs in 15 of these districts and in four additional areas (Fig. 1, Table 1). Uranium also occurs in Precambrian pegmatites in the Tusas and Sangre de Cristo Mountains, and in Jurassic and Cretaceous sediments in the eastern San Juan Basin, Chama Basin, and near San Ysidro. These occurrences are not discussed in this report, but they are described elsewhere by Hilpert (1969), Chenoweth (1974a, 1974b, 1979), and McLemore (1983).
Gold, silver, and/or uranium occurrences are found in eight types of deposits (Table 1), many of which are genetically related to the formation of the Rio Grande rift. Gold occurs in late Tertiary to Recent placers in eight districts within basins of the Rio Grande rift and surrounding areas. Gold, silver, and uranium are associated with three types of Tertiary-age deposits: (I) hydrothermal gold—silver vein and breccia deposits, (2) base-metal veins, and (3) replacement deposits in limestones. Silver and rarely gold are found in barite—fluorite—lead vein deposits in three areas along or near the Rio Grande rift in northern New Mexico. Silver, uranium, vanadium, and rarely gold also occur in stratabound sedimentary copper deposits and probably formed prior to the Rio Grande rift. Mineral deposits in Precambrian rocks also contain gold, silver, and/or uranium mineralization and are occasionally associated with younger mineralization.
Production of gold and silver from placer deposits, deposits of Tertiary age, and deposits in Precambrian rocks has been moderate (Table 2). Except for La Bajada mine, uranium and vanadium production has been insignificant (Table 2).
- McLemore, Virginia T.; North, Robert M., 1984, Occurrences of precious metals and uranium along the Rio Grande rift in northern New Mexico, in: Rio Grande rift--Northern New Mexico, Baldridge, W. S.; Dickerson, P. W.; Riecker, R. E.; Zidek, J., New Mexico Geological Society, Guidebook, 35th Field Conference, pp. 205-212.