Abstract
Historic lead and zinc (Pb-Zn) mining in southeast Missouri’s “Old Lead Belt” has left large chat piles dominating the landscape where prior to 1972 mining was the major industry of the region. As a result of variable beneficiation methods over the history of mining activity, these piles remain with large quantities of unrecovered Pb and Zn and to a lesser extent cadmium (Cd). Quantifying the residual content of trace metals in chat piles is problematic because of the extensive field effort that must go into collecting elevation points for volumetric analysis. This investigation demonstrates that publicly available lidar point data from the U.S. Geological Survey 3D Elevation Program (3DEP) can be used to effectively calculate chat pile volumes as a method of more accurately estimating the total residual trace metal content in these mining wastes. Five chat piles located in St. Francois County, Missouri, were quantified for residual trace metal content. Utilizing lidar point cloud data collected in 2011 and existing trace metal concentration data obtained during remedial investigations, residual content of these chat piles ranged from 9247 to 88,579 metric tons Pb, 1925 to 52,306 metric tons Zn, and 51 to 1107 metric tons Cd. Development of new beneficiation methods for recovering these constituents from chat piles would need to achieve current Federal soil screening standards. To achieve this for the five chat piles investigated, 42 to 72% of residual Pb would require mitigation to the 1200 mg/kg Federal non-playground standard, 88 to 98% of residual Zn would require mitigation to the Ecological Soil Screening level (ESSL) for plant life, and 70% to 98% of Cd would require mitigation to achieve the ESSL. Achieving these goals through an existing or future beneficiation method(s) would remediate chat to a trace metal concentration level that would support its use as a safe agricultural soil amendment.
Highlights
Lead and zinc have been important resources of human existence for thousands of years, but the global industrial revolution of the last 250 years has been the driving factor in its increased production and resulting waste load
Estimating the quantity of material remaining in a chat pile can involve extensive field labor that generally includes topographically measuring elevation using a survey-grade Global Navigation Satellite System (GNSS) and Real Time Kinematics (RTK)
Lidar sensors use the GNSS and RTK systems, but collection error is substantially reduced by employing an Inertial Measuring Unit to correct for sensor movement
Summary
Lead and zinc have been important resources of human existence for thousands of years, but the global industrial revolution of the last 250 years has been the driving factor in its increased production and resulting waste load. The piles of gangue and processing waste from beneficiation used to extract the Pb and Zn sulfides from host rock currently exist in every region where there has been a history of mining activity. These piles have risen more than 100 m above the surrounding landscape representing landmarks of a region’s mining history. Remediation is often limited to slope stabilization and vegetation or gravel cover to reduce contaminant transport [6] While this has substantially mitigated much of the erosion and wind-blown transport of the finer Pb-laden material from these piles, the problem of residual trace metals remains
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