PHYSICAL AND CHEMICAL PROPERTIES OF CLAY-RICH MINE TAILINGS FROM TONOPAH, NEVADA; EVALUATING RECYCLING POTENTIAL

Mine waste is a well-known source of contamination to, and destruction of, our natural environment. In the United States, it is estimated that 1.6 billion metric tons of mine waste are produced each year alone, which accounts for almost half of all U.S. solid waste. Over time, this waste has accumulated to >50 billion metric tons that are usually found in heaps or dried-out waste streams. However, extraction of Earth’s natural resources is currently necessary for our world and will likely continue to increase as our technology-driven society advances. In recent years, significant effort has been placed on finding alternative uses for these mine-related wastes, including economic mineral recovery, recycling, and reuse.

Tonopah NV has a history of mining dating back to 1900, where a small town of 40 people grew to a population of over 3,000 within 2 years of the discovery of Ag ore. Major mining operations were conducted from 1901 to 1947, with major commodities in Au and Ag, lesser in Pb and Cu, and minor W and As. In total the Tonopah mines produced >5 million tons of ore worth ~$150 million, >$1 billion in today’s market equivalent, with peak production occurring from 1901–1921 where the mines earned $121 million. Ores were milled and processed through cyanide heap leaching, following which a waste stream produced stratified deposits of clay rich tailings.

15 samples were systematically collected from two of these stratified deposits, in addition to two bulk representative samples. The deposits outcrop as a small cliff 2-2.5m high with interbedded units of clay-sandy material, mostly 2.5Y 8/3 or 6/3 in color, with a few cobble stringers present 10YR 6/2. A detailed analysis of the mine waste including mineralogical, chemical, and physical characteristics aims to provide insight into these materials and their potential for recycling. X-Ray diffraction (XRD) will be used for major mineralogical analysis and scanning electron microscopy (SEM) will be used for textural/chemical characterization. Preliminary SEM results indicate the presence of pyrite and barite consistent throughout all 15 units. Pyrite generally forms cubes from ~80-100 µm in size, and barite forms elongated-irregular crystals from ~20-100 µm. Further characteristic analysis will determine the potential of recovery, recycling, or reuse for these deposits.