GSA Annual Meeting in Indianapolis, Indiana, USA - 2018

Paper No. 24-6
Presentation Time: 9:00 AM-5:30 PM


RENKES, Natalie, BUCK, Brenda J. and METCALF, Rodney V., Department of Geoscience, University of Nevada Las Vegas, 4505 S Maryland Parkway, Las Vegas, NV 89154

The presence of naturally-occurring amphibole asbestos (NOA) has gained a great deal of attention from scientists, health and regulatory agencies, and citizens living in impacted areas. It is commonly believed that fibrous amphibole asbestos can only form through neocrystallization. A recent study found that in southern Nevada, NOA occurs as a result of hydrothermal alteration of granitic rock producing fibrous amphibole asbestos both as cross-cutting neocrystallized veins and via recrystallization of original magmatic hornblende crystals. This study aims to measure the maximum length, average width, and calculate a mean aspect ratio of both recrystallized and neocrystallized fibers to see if the morphologies are similar. The morphology of asbestos fibers is an important characteristic that strongly affects toxicity: longer and thinner fibers are believed to be significantly more toxic than shorter and wider fibers. Samples were collected from corresponding units in McCullough Range, NV and Wilson Ridge, AZ. Neocrystallized and recrystallized fibers will be identified using a petrographic microscope. The identified fibers in polished thin section will be extracted from their corresponding billet using a 0.015” diameter motorized drill. Samples will then be prepared for the scanning electron microscope (SEM) with energy dispersive x-ray analysis (EDS), which will measure fiber morphology and verify that amphibole fibers are present. Amphibole mineralogy will be accurately identified using wavelength dispersive spectroscopy (WDS) and electron probe microanalysis (EPMA) on polished thin sections. We hypothesize that there will be no significant difference in the aspect ratios, average width, and maximum length of neocrystallized and recrystallized fibers having similar mineralogy and chemistry. If so, then both formation processes can produce fibers that are likely similar in toxicity. Because hydrothermal alteration and recrystallization of primary minerals is a very common geologic process, this finding may significantly increase the number and distribution of rocks and soils that contain NOA. Therefore, many more people than we currently recognize may be unknowingly exposed to hazardous fibrous amphibole fibers.