Earth and Planetary Sciences ETDs

Publication Date

Spring 4-20-1978


The Precambrian terrane north of Pecos, New Mexico, contains meta­volcanic and metasedimentary rocks. The subaqueous volcanic rocks are of bimodal composition (basalt-rhyolite). Volcanism was cyclic; three partial or complete cycles are exposed in the study area. A cycle con­sists of basal basalt, overlying rhyolite and a cap of banded iron form­ation. The chemical characteristics of the volcanic rocks are similar to those of several modern island arcs, suggesting the Pecos volcanic sequence may represent a portion of a similar Precambrian system.

Diverse structural elements in the study area. are related to four periods of deformation: 1) a Precambrian compressional event, 2) the in­trusion of the Embudo granite, 3) the formation of the Pecos-Picuris fault and 4) a. late tensional event. Upper greenschist metamorphism occurred during folding.

The massive sulfide ore lenses of the Pecos Mine occur at the con­tact between rhyolite and overlying sedimentary rocks. The ore lenses lie on the flank of a rhyolite agglomerate dome an1d show several pri­mary sedimentary structures. Replacement textures are lacking in the de­posit.

The Pecos ores were probably deposited by hot metalliferous fumarolic solutions on the Precambrian sea floor. The nature and stratigraphic suc­cession of various ore types are related to the declining temperature and density of the ore-bearing solutions. The sulfide ores have been region­ally metamorphosed along with the contemporaneously deposited host rocks.

Weak surficial mineralization in the Jones Mine area southwest of, and possibly on the same time-stratigraphic horizon as the Pecos Mine, may indicate the presence of another massive sulfide deposit. Because massive sulfide deposits in other districts tend to occur in clusters and on the same time-stratigraphic horizon, the Jones Mine area appears to be an excellent exploration target.

Degree Name

Earth and Planetary Sciences

Level of Degree


Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Gary P. Landis

Second Committee Member

Jonathan Ferris Callender

Third Committee Member

Wolfgang Eugene Elston

Fourth Committee Member

Lee Albert Woodward

Fifth Committee Member

Philip J. Sterling

Document Type


Included in

Geology Commons