Award Date

5-1-2019

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geoscience

First Committee Member

Rodney Metcalf

Second Committee Member

Brenda Buck

Third Committee Member

Jean Cline

Fourth Committee Member

Barbara Luke

Number of Pages

187

Abstract

The term “asbestos” applies to six types of fibrous amphiboles or chrysotile with specific morphologies that are commercially mined and processed. Inhaling asbestos fibers is known to cause many negative health effects, including mesothelioma, several different cancers, various respiratory diseases and non-respiratory diseases, and fatalities. The recent years, several cases of non-occupational exposure to asbestos fibers raised an awareness of environmental exposure to naturally occurring asbestos (NOA) which refers to asbestiform minerals that fall out of the regulatory definition of asbestos.

There are two sources of NOA in the area, Wilson Ridge pluton, AZ, and Boulder City pluton, NV which have similar protolith, tectonic and alteration history. In AZ, I have observed NaFe3+-amphiboles and some Ca-rich actinolite associate with Na-rich albite and Fe3+ -rich hematite. In NV, amphibole was dominated by actinolite, and albite, K-feldspar, magnetite, calcite, and epidote were also observed. Fluid inclusions sampled from NV rocks contain halite crystals which indicate a higher salinity of NV fluid than AZ fluid. I concluded that the ionic ratio of Na/Ca and Fe3+ /Fe2+control the resulted minerals instead of the absolute abundance of specific ions.

Observations of these mineral assemblages and associated minerals suggest several generations of alterations including Na metasomatism. Amphibole asbestos precipitated with two different mechanisms. “Neocrystallized” asbestos formed in open spaces as wildly recognized, or formed within other non-amphibole minerals. I also recognized “recrystallized” asbestos utilized he term “asbestos” applies to six types of fibrous amphiboles or chrysotile with specific morphologies that are commercially mined and processed. Inhaling asbestos fibers is known to cause many negative health effects, including mesothelioma, several different cancers, various respiratory diseases and non-respiratory diseases, and fatalities. The recent years, several cases of non-occupational exposure to asbestos fibers raised an awareness of environmental exposure to naturally occurring asbestos (NOA) which refers to asbestiform minerals that fall out of the regulatory definition of asbestos.

There are two sources of NOA in the area, Wilson Ridge pluton, AZ, and Boulder City pluton, NV which have similar protolith, tectonic and alteration history. In AZ, I have observed NaFe3+-amphiboles and some Ca-rich actinolite associate with Na-rich albite and Fe3+ -rich hematite. In NV, amphibole was dominated by actinolite, and albite, K-feldspar, magnetite, calcite, and epidote were also observed. Fluid inclusions sampled from NV rocks contain halite crystals which indicate a higher salinity of NV fluid than AZ fluid. I concluded that the ionic ratio of Na/Ca and Fe3+ /Fe2+control the resulted minerals instead of the absolute abundance of specific ions.

Observations of these mineral assemblages and associated minerals suggest several generations of alterations including Na metasomatism. Amphibole asbestos precipitated with two different mechanisms. “Neocrystallized” asbestos formed in open spaces as wildly recognized, or formed within other non-amphibole minerals. I also recognized “recrystallized” asbestos utilizedpre-existing magmatic hornblende structure and replaced by fibrous amphibole.

If the hydrothermal alteration of preexisting amphibole to form fibrous amphibole is a common phenomenon, amphibole-bearing rocks can be more abundant than we may think. The background levels of NOA might be an explanation to idiopathy for lung diseases or undiagnosed mesothelioma. Understanding the petrogenesis of NOA is important to predict its occurrence in order to protect public health near those deposits.

Keywords

Amphibole; Asbestos; Boulder City pluton; Hydrothermal alteration; Las Vegas; Naturally occurring

Disciplines

Geochemistry | Geology

Language

English


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