Abstract. Between 1969 and 1981 open pit methods were used to recover the molybdenum ore producing some 317.5 million metric tons of mined rock from the Questa molybdenum mine, which went into nine rock piles. The mine is located in the Sangre de Cristo Mountains of Taos County in northern New Mexico. As part of a multi-disciplinary study to determine the effects of weathering on the long-term stability of the rock piles, we are searching for areas where weathering is occurring within the rock piles. Pyrite oxidation is a weathering process that typically generates large amounts of heat, making it a good candidate for detection by infrared thermography. We conducted surveys of surface temperatures on two rock piles during February and May 2004 using the FLIR SC 3000 infrared thermal camera.Thermal imaging of the rock piles revealed at one rock pile, a "heat vent" of roughly 40 m by 30 m that had the same maximum temperature of 18°C during February and May 2004. The maximum temperature of this heat vent was much larger than the ambient temperature in February (0-2°C) and May (4-6°C). During the February survey, the heat vent had little or no snow cover and appeared to be very wet, whereas the area surrounding the heat vent was snowcovered and frozen at the same time. The heat vent is likely the result of pyrite oxidation within the rock pile. Thermal imaging results from a second rock pile indicate that it is less likely to have a heat vent because the differences between the ambient and maximum surface temperature were much less significant. The small temperature difference could be explained by spatial variations in emissivity from local variations in rock thermal properties or moisture content or by a relatively small heat flux out of the rock pile.
Abstract. Rarely do rock pile characterization methods allow for examination and sampling of the interior of large rock piles in-situ. The regrading of the Goathill North (GHN) rock pile at the Questa mine provided a unique opportunity to examine and sample the interior of a large rock pile through the construction of trenches cut into the rock pile as earth-moving progressed. Maps of each bench were created to document the different stratigraphic units, including the thickness, dip, and extent of the units. Units were defined based on grain size, color, and other physical properties. Units were correlated between benches and downward through the series of successively excavated trenches. Typically, paste pH increased with distance from the outer, oxidized zone (west) towards the interior units (east) of the GHN rock pile. The outer zone was oxidized (weathered) based upon the white and yellow coloring, low paste pH, presence of jarosite and gypsum, and absence of calcite. However, the oxidation/reduction (weathering) state in the interior zone is not yet determined. The base of the rock pile closest to the bedrock/colluvium surface represents the oldest part of the rock pile since it was laid down first. Portions of the base appeared to be nearly or as oxidized (weathered) as the outer, oxidized zone, suggesting that air and water flow along the basal interface occurred and possibly was an active weathering zone. Analyses of samples from unweathered, unoxidized drill core samples and from the GHN rock pile are similar in clay mineralogy as determined by XRD and electron microprobe analyses, which suggests that the majority of clay minerals in the GHN samples were derived from the original, pre-mined hydrothermal alteration and not post-mining weathering. Additional
Modeling studies and experimental work have demonstrated that soil physical properties have a significant effect on most sensors for the detection of buried land mines. Where a modeling approach allows for testing the effects of a wide range of soil variables, most experimental work is limited to either field soils with poorly known properties or oversimplified conditions. With this in mind, we have constructed an outdoor test site with full control of soil water content and continuous monitoring of important soil properties and environmental conditions. In three wooden frames of 2 × 2 × 1 meter, filled with different soil types (sand, loam, and clay), we buried low-metal anti-tank and antipersonnel land mine simulants. Time domain reflectometry sensors and thermistors measure soil water content and temperature, respectively, at different depths above and below the land mines as well as in homogeneous soil away from the land mines. The test site has been in operation for two years, during which time the soils have evolved to reflect real field soil conditions. In this contribution we compare visual observations as well as ground-penetrating radar and thermal infrared measurements at this site taken immediately after construction in early 2004 with measurements taken in early 2006. ADD CONCLUSIONS
Rarely do rock pile characterization methods allow for examination and sampling of the undisturbed interior of large rock piles in-situ. The regrading of the Goathill North (GHN) rock pile at the Molycorp Questa mine, New Mexico provided a unique opportunity to examine and sample the undisturbed, interior of a large rock pile through the construction of trenches cut into the rock pile as earth-moving progressed. Weekly during the regrading of the GHN rock pile, contractors excavated a trench to allow for sampling of rock pile material. Trenches typically had four benches, which were 1.5 m wide and did not exceed 1.2 m in height, to give an overall slope of 1.4 horizontal to 1.0 vertical within the trench. Each trench extended for a length sufficient to explore site conditions, maintain the regraded 2:1 slope, and ensure personnel safety. Once excavated, trench walls and benches were surveyed using a differential global positioning system. For every trench, maps and logs of each bench were created to describe the different "mine soil" units, including the thickness, dip and extent of the units. Units were defined based on color, grain size, stratigraphic position, and other physical properties that could be determined in the field. Units were correlated between benches and to both sides of each trench, and several units were correlated downward through the series of successively excavated trenches. The field sampling crew began sampling within each of the identified units after the unit boundaries were identified and mapped. The following in situ measurements were taken along either the horizontal or vertical surfaces of each exposed bench and along the base of the trench: sand cone (density), tensiometer (matric suction), gravimetric moisture content, grain size, infiltration, and nuclear gauge measurements (density, moisture content). Gravimetric water content samples were collected at the locations selected for the measurement of matric suction and infiltration tests. Samples were collected from each defined unit for geochemical, geotechnical (including shear box tests, slake durability tests), biological, and electron microprobe analyses. Channel sampling for pyrite reserve modeling was performed in short 1.5-m long horizontal slots using a rock hammer to chip material to be placed into a sample bag. Additional material from selected layers was collected for potential weathering-cell tests in the future. Typically, paste pH increases with distance from the outer, oxidized zone (west) towards the interior, unoxidized zone (east) of the GHN rock pile.
Hydrometer analyses are performed when it is necessary to know fine particle size distribution. A glass bulb is inserted into a solution of dispersing agent and soil sample, which measures the relative density of the fluid surrounding the tip of the bulb. In conducting hydrometer analyses on rock pile samples from Questa mine, it is noticed that samples can drastically vary in behavior due to physical and chemical properties. A possible problem that could arise is the need to change the amount of dispersing agent in order to keep particles from flocculating. Early tests indicate that certain samples need more than the usual amount of dispersing agent, but that too much in turn causes additional problems.The hydrometer method is used on fine particles because it is much easier, faster, and as accurate when compared to dry sieving. Possible problems that exist are statistical variation (inherent in sample preparation/choice) and how to determine whether to use 50 or 100 grams of sample without actually performing a dry sieve analysis, thus negating the need for the hydrometer.Chemical composition also causes variations in particle surface forces. A phenomenon known as flocculation (clumping) was observed during certain samples' tests, indicating the clay particles are attracted to each other. Intuitively the larger, clumped particle will now settle faster, negating Stoke's Law, and invalidating the hydrometer analysis. We endeavor to determine ideal calgon and sample concentrations to be used for each test based on properties of the sample and if statistical variation is significant.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.