Earth and Planetary Sciences ETDs

Publication Date

7-1971

Abstract

The mapped area is in Sandoval and Rio Arriba Counties, New Mexico, 3 mi southeast of Cuba and includes the eastern margin of the San Juan Basin and the western margin of the Nacimiento Mountains. The emphasis of this report is on the stratigraphy, structure, and ore deposits of this area.

The Precambrian quartz monzonite basement rock is non-conformably overlain by approximately 6000 ft of sedimentary rocks, which range in age from Pennsylvanian to Cretaceous. The Pennsylvanian Madera Formation is predominantly marine limestone and is overlain by the clastic Permian Abo and Yeso Formations. A maximum of 1050 ft of Triassic Chile Formation is overlain by the Jurassic Entrada, Todilto, and Morrison formations which are in turn overlain by 2800 ft of Cretaceous sedimentary rocks which include the Naturita formation, Mancos shale, Mesaverde Group, and part of the Lewis Shale. Younger strata of Cretaceous and Tertiary age are present to the west, but were not mapped. In the south-eastern part of the area the Abo Formation is capped by the Quaternary Bandelier Tuff.

The north-trending Nacimiento upthrust dips 70⁰-85⁰ E. and is exposed at a deep structural and stratigraphic level within the area. The Nacimiento fault separates the steeply westward-dipping to overturned beds of the San Juan Basin on the west from the Nacimiento uplift on the east. A maximum of 7400 ft of structural relief exists between the uplift and the basin. The maximum vertical displacement on the Nacimiento fault is 5500 ft and the uplift has yielded to the west a maximum of 700 ft in this area.

The Trail Creek fault divides the uplift within the mapped area into two major blocks, the northern block being structurally lower. The east-trending, high-angle Cajete, Blue Bird, campfire and San Pablo faults on the western margin of uplift show only dip-slip movement and segment the northern block into parts that have been uplifted different amounts.

The sedimentary copper deposits within the Agua Zarca member of the Chinle Formation include the Eureka, Copper Glance-Cuprite, Cliff, and Blue Bird workings. Primary copper sulfide minerals were deposited in, and adjacent to, carbonaceous fossil wood and formed from copper-bearing ground-water which passed through porous and permeable zones during or shortly after deposition of the Agua Zarca. The copper sulfide minerals later were oxidized, and copper, in the form of malachite, azurite, and chrysocolla, is disseminated in the adjacent host sandstone and conglomerate.

Cross-bedding in the Agua Zarca at the Eureka and Copper Glance-Cuprite workings indicate paleocurrents flowed to the southwest. The mean vector azimuth of the long axes of fossil wood fragments at Eureka mine is perpendicular to the paleocurrent direction; thus, the fragments if deposited as wood in fluvial environments are good paleocurrent indicators.

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

Fourth Committee Member

Sherman Alexander Wengerd

Language

English

Document Type

Thesis

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