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Dicaperl Perlite Mine, near Socorro, Socorro County, NM Gabriel Graf 1, Sam Pierce 1, Pedram Rostami 2 1. New Mexico Tech, Earth and Environmental Science Dept, 801 Leroy Pl., Socorro, NM 87801 2. New Mexico Tech, Mineral Engineering Dept, 801 Leroy Pl., Socorro, NM 87801 Introduction Commercial perlite is a water-rich (2-5 wt.% H2O), volcanic glass of normal rock density that expands or “pops” when heated in a furnace (Chamberlin and Barker, 1996). One of the largest producers of perlite in New Mexico is the Dicaperl Perlite Mine, located 6 km southwest of the town of Socorro in central New Mexico. The mine is currently producing 150,000 tons of raw ore per year. This ore is then shipped to a plant where it is expanded (popped). The value of the expanded perlite is ten times that of the raw ore, but is expensive to ship and large amounts of natural gas are needed to expand the ore. Perlite has a variety of uses, including ceiling tiles, horticulture, filtration in food industry, and acoustic walls and tiles (Kogel et al, 2006). Geology This perlite deposit is a small dome of rhyolitic volcanic glass that has been hydrated over time to produce perlite. The alteration to perlite occurred at lowtemperatures, as was noted by (Chamberlin and Barker, 1996) because of the observation of concentric fractures, which requires a roughly spherical hydration geometry. The deposit formed from the fast, low temperature hydration of a body of obsidian. 40Ar/39Ar geochronology of sanadine crystals produces an age of 7.85 0.04 Ma (Chamberlin and Barker, 1996). This age date represents the youngest of a series of lava flows and domes that where then covered by sediments. The small dome was uplifted along a Quaternary fault zone and sufficiently exhumed by erosion to allow open-pit mining of this now uniformly hydrated microvesicular glass (Chamberlin and Barker, 1996). The most interesting feature about this deposit is the lack of the common crystalline core. The reason for the lack of the core is a debated issue, but has been suggested that the termination of the lava dome at its conduit allowed the dome to super cool with out the 1 formation of a crystalline core. The deposit has a maximum extent of 840 m and is exposed over a topographical interval of 135 m (Chamberlin and Barker, 1996). Mining Methods This mine employs the method of open-pit mining (figure 1), where perlite is mined by scraping the deposit with a bulldozer and grader type machine. It is then dumped into a grizzly, which passes the material through a jaw crusher and then onto a conveyor belt (Figure 2). The conveyer belt takes the ore to the mill (figure 3), where the ore is milled and sorted into 20 various sizes for consumers. The ore is dried to remove the moisture and lessen the weight. The mine is currently expanding the open pit operations by stripping the overburden from the west pit wall. This expansion will lead to another 30-40 years of mine life, with many more years possible from future expansions. Shipping The raw ore is shipped by rail and secondarily truck. The perlite ore is shipped in 100 ton sealed railcars (Figure 4) to keep it from becoming wet and heavy. On average, forty-to-fifty of the 100-ton sealed cars are shipped per week. The perlite is usually shipped while unexpanded to cut down on shipping costs. Since perlite expands 40-50 times in size, it becomes uneconomical to ship from Socorro as expanded perlite. The material is shipped to a processing plant in Oklahoma where it is “popped” at a temperature between 1100-1500 C. The final product is then shipped to consumers around the United States. Environmental Issues The main environmental issue at the mine is fugitive dust. The mine currently has a permit that specifies the allowance of dust emissions. However, the health issues associated with airborne silica are minor due to the low levels of crystalline silica in the ore. Silicosis and other silica related issues are caused by crystalline silica damaging the human lungs. The residents of Socorro are not prone to these harmful health issues because of the low amounts of crystalline silica in the deposit. The only harmful health 2 risk may be to workers who work at the mine for decades, and are exposed to the material everyday. The environmental dust issues are controlled by laborers and application of dihydrogen monoxide in sufficient quantities (?). Conclusions The Dicaperl perlite mine produces the largest amount of raw perlite in the state on New Mexico. The rhyolitic lava dome formed 7.85 0.04 Ma and has since been exhumed by faulting. This exhumation led to the mining of this uniformly hydrated glass near Socorro. This ore is then shipped to a processing plant in Oklahoma, where the raw ore is heated to produce the perlite product that consumers’ desire. The health risks to the residents of Socorro are extremely limited because of the low levels of crystalline silica that is present in the deposit. This mine will be located at the outskirts of the town of Socorro for decades to come, with no harm to any residents. Socorro’s world renowned perlite will also be enjoyed by consumers for decades. Figure 1. Open-pit that is currently mined at the Decaperl Perlite Mine, Socorro, NM (Photograph by Gabriel Graf) 3 Figure 2. Grizzly, jaw-crusher and conveyer belt that sends raw ore to the mill for processing (Photograph by Gabriel Graf) 4 Figure 3. Mill were raw ore is crushed and sorted in 20 various sizes (Photograph by Gabriel Graf) Figure 4. 100-ton railroad car in which the raw ore is shipped to a processing plant (photograph by Gabriel Graf) 5 References Chamberlin, R.N. and Barker, J.M. (1996); Genetic Aspects of Commercial Perlite Deposits in New Mexico, New Mexico Bureau of Mines and Mineral Resources, Bulletin 154, Geology of Industrial Minerals 31st Forum Chamberlin, R.N. and Barker, J.M. (2007); Industrial Minerals Class Field Trip, March 23, 2007; Dicaperl Perlite Mine, Socorro, Socorro County, NM Kogel, J.E., Trivedi, N.C., Barker, J.M. and Krukowski, S.T., (2006): Industrial minerals & rocks; 7th edition, Society of Mining, Metallurgy and Exploration, Inc. (SME), Littleton, Colorado 6