Summary of Precambrian geology and geochronology of northeastern New Mexico
— James M. Robertson, J. F. Callender, and D. G. Brookins

The Precambrian of northeastern New Mexico received little detailed geologic attention until 1974, when the Pecos Mine in western San Miguel County was re-interpreted as a volcanogenic massive sulfide deposit (Giles, 1974). This hypothesis stimulated new industrial and academic interest in Precambrian lithology, stratigraphy, structure and mineralization in the Sangre de Cristo Mountains and elsewhere in New Mexico and Colorado (c.f., Giles, 1976).

 

In northeastern New Mexico, Precambrian exposures are restricted to the Sangre de Cristo Mountains of western Colfax, Mora and San Miguel Counties and easternmost Santa Fe County (Fig. 1). Within this north-trending mountain belt are two geographically distinct Precambrian terrains: a northern, generally granitic region in the Costilla Lake-Cimarron Range Moreno Valley area, and a southern, predominantly metasedimentary and amphibolitic belt in the Pecos River-Las Vegas Range area.

 

The geologic map which accompanies this report (Fig. 1) is mainly compiled from the following sources: McKinlay (1956 (Costilla Lake area), Clark and Read (1972) (Eagle Nest area), Smith and Ray (1943) and Wanek and others (1964 (Cimarron Range), Montgomery (1963) (upper Pecos River area), Budding (in preparation) and Schowalter (1969) (Mora area), and Dane and Bachman (1965). Much of the following discussion is also based upon the work of these authors.