SCANNING ELECTRON MICROSCOPY INVESTIGATIONS OF OXIDES AND SULFIDES FROM MINE WASTE IN TONOPAH, NEVADA

By volume, mine waste is the largest solid waste material produced by humans. Mine waste hosts a variety of minerals and elements that are harmful to human health and lead to environmental degradation. Tonopah, Nevada is a former mining town with a legacy of mine waste that has accumulated since the early 1900’s. Studies previously conducted on the mine waste of Tonopah indicated the presence of gold, silver, and pyrite. This study focuses on a more detailed study of the pyrite present, which averages between 3-5% of most of the sample material and is estimated to approach concentrations of 10% in some samples. The characterization of Tonopah’s mine waste and the pyrite associated with it is the first step towards enhancing Tonopah’s economy and decreasing possible health risks of its residents.

Pyrite is often responsible for acidic water generation as a result of rapid oxidation. Acidic water is the driving force in acid rock drainage (ARD), which is considered to be the most harmful environmental issue associated with mine waste. Arsenic has several negative human health impacts and is a common constituent in pyrite. Gold is often associated with the presence of arsenic in pyrite and can be of economic interest if present in large enough concentrations. Thus, characterizing the pyrite in the mine waste of Tonopah allows for the understanding of the environmental and human health impacts as well as the recyclability of the material.

Scanning electron microscopy (SEM) backscatter revealed equant subhedral pyrite crystals of 40-80 µm and pyrite fragments 2-5 µm in diameter which comprise 3-5% of each sample. Most of the pyrite is present within quartz, occurring with deterioration and replacement by Fe-oxides. Elements of environmental concern were found in the form of arsenian pyrite and micrometer scale inclusions of barite and galena. A collection of K-feldspar and elongated Fe-Mn-oxide particles 5-30 µm in length occur together in local clusters that make up 15-20% of each sample. Moving forward, the gold content of the pyrite will be determined using an assortment of analytical techniques. If present in high enough quantities, the gold can be recycled for a profit and give Tonopah the aid necessary for its rejuvenation.