Earth and Planetary Sciences ETDs

Publication Date

6-23-1972

Abstract

The mapped area is in Sandoval County, New Mexico, 4 miles east of La Ventana. Precambrian rocks in the core of the Nacimiento uplift in this area consist mainly of quartz monzonite gneiss which has been intruded by granite. Hornblende schist xenoliths, zones of sheared quartz-plagioclase schistose gneiss, and mafic and leucocratic dike rocks are less abundant. Strata totaling 6200 feet, ranging from the Pennsylvanian Madera Formation through the Cretaceous Mancos Formation, are exposed in the area. Overlying the marine Madera Formation is 3400 feet of continental, marginal marine, and evaporite deposits consisting in ascending order of the Permian Abo, Yeso, Glotieta, and Bernal Formations, the Triassic Chinle Formation, and the Jurassic Entrada Todilto, and Morrison Formations. Cretaceous rocks are represented by the marginal marine Dakota Formation and marine Mancos Formation, totaling 2400 feet. Younger Cretaceous rocks lie west of the mapped area. At least 7500 feet of structural relief exists between the Nacimiento uplift and the San Juan Basin in the vicinity of this report. Four parallel, north-trending structural elements contribute varying amounts to the total structural relief: 1. a synclinal bend, 2. the Pajarito fault, 3. other synthetic faults, and 4. an anticlinal bend. The Pajarito fault is nearly vertical in this area. The uplift developed as a result of vertical forces acting on basement rocks. It was initiated as a west-facing monocline with stratified rocks draped over a bulge in basement rocks. Subsequent deformation resulted in the Pajarito fault along the center of the monocline. The Pajarito fault formed as a curved upthrust, concave down, as did the Nacimiento fault to the north of this area. At the present level of erosion the Pajarito fault is vertical, but the Nacimiento fault is in places flat-lying; this is because the Pajarito fault is seen at a lower structural level than the Nacimiento fault. The Pajarito fault formed east of the Nacimiento fault, higher on the monocline, and its upper curved segment has been eroded. Deposits of economic importance in the area include uranium, gypsum, gravel, and copper. The San Miguel mine is of the "sedimentary copper" type with chalcocite, malachite, azurite and chrysocolla mineralization which is localized around fossil carbonaceous wood fragments in a paleo-channel complex in the Triassic Agua Zarca Sandstone. The source of the copper was probably an eroded copper-bearing mass in the Uncompahgre Highlands about 100 miles to the northeast where conditions favored lateral migration of Cu ions away from the source area. Transport to the site of deposition occurred mainly in the form of soluble sulfates. At the end of the sedimentation process copper was distributed irregularly throughout the enclosing rock. Concentration into a mineable orebody took place late in the sedimentation process or during diagenesis with carbonaceous material serving as foci for the precipitation of chalcocite.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Lee A. Woodward

Second Committee Member

J. Paul Fitzsimmons

Third Committee Member

Albert Masakiyo Kudo

Language

English

Document Type

Thesis

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