Earth and Planetary Sciences ETDs

Publication Date

Spring 5-30-1978

Abstract

The purpose of this thesis is to report and discuss the chemistry and petrology of the axinite and scapolite occurrences in the White Oaks mining district, Lincoln County, New Mexico. Sampling, reconnaissance field geology, chemical analysis of rock samples, petrographic studies, and unit-cell d terminations for axinite and scapolite were completed for this investigation. The data was used to determine the conditions of formation for the axinite and scapolite.

The axinite is found in small pods, or nodules, of marble near the contact with the syenite-monzonite porphyry stock. The variety of axinite is ferroaxinite which occurs with calcite, actinolite, and quartz in these marbles. Chemical analyses showed high concentrations of B2O3 (1.3 percent) in the axinite-bearing marbles suggesting an introduction of boron, possibly in the form of boron-rich fluids from the stock. The axinite-bearing marbles are interpreted as belonging in the albite-epidote-hornfels facies. Temperatures f approximately 300° to 450°c at pressures of 1 kb or less are suggested for the meta­ morphism.

Scapolite occurs in hornfelses and marbles. The major occurrence of scapolite is in the area of a monzonite porphyry dike in the southern part of the study area. The scapolite is most abundant at the dike contact and the amount of scapolite present in the metasedimentary rocks decreases with increasing distance from the dike. The chlorine content of these scapolite-bearing rocks is much greater than that contained in non-scapolitic rocks of the area, indicating that the chlorine was not present in the original sedimentary layers. Chemical analyses showed that the chlorine content of the scapolite-bearing rocks was highest at the dike contact and decreased outward from the contact. The origin of the scapolite is attributed to contact metamorphism involving an introduction of chlorine from the dike. The scapolite-bearing rocks of the major occurrence are indicative of the hornblende-hornfels facies. The mineral assemblage of these rocks includes scapolite, diopside, calcite, and quartz. The variety of scapolite is dipyre as determined by optical data and the unit-cell dimensions. Textural and mineralogical evidence reflect the changes in temperature outward from the dike contact. An initial contact temperature of approximately 6oo0 c is suggested. The maximum temperature obtained in the outermost part of this scapolite occurrence was probably between 500° and 510°c, assuming pressures of 1 kb or less.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Albert Masakiyo Kudo

Second Committee Member

Douglas Gridley Brookins

Third Committee Member

Rodney Charles Ewing

Fourth Committee Member

J. Paul Fitzsimmons

Document Type

Thesis

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