Paper No. 254-3
Presentation Time: 2:15 PM
LEGACY GOLD MINES PROVIDE AN OPPORTUNITY TO PRODUCE METALS DURING RECLAMATION – AN EXAMPLE FROM THE GOLD-PYRITE BELT OF VIRGINIA
Unreclaimed abandoned hard rock mine sites pose environmental and public safety hazards but are increasingly viewed as potential sources of metals and critical minerals. The Gold-pyrite belt of Virginia, USA, hosted hundreds of mines that were active in the 19th and 20th centuries; all were abandoned before implementation of modern reclamation laws. These sites continue to contaminate waterways and cause problems for landowners and developers. The densest concentration of abandoned gold mines is in western Goochland County, where Ordovician-age gold-bearing quartzite and schist of the uppermost Chopawamsic Formation are folded into an asymmetric synform. One of these, the Moss Mine, originally operated from 1836 – 1838 and from 1893-1936. Development included two inclined shafts, drifts at several levels, a jaw crusher, stamp mills, and gravity separation equipment. Final processing of the ore involved amalgamation of fine gold using mercury, much of which ended up in tailings, where it remained for decades. In the 1990s, waste piles were subject to rudimentary reclamation efforts, during which the material was spread over an acre or more. One small mining operation is now reclaiming the site and recovering gold, lead, and mercury. Reprocessing of the old tailings begins with a reverse helix trommel to wash the soil and separate it from rock. The slurry from the trommel goes to a sluice to separate the larger particles of dense metals, then to gravity separation jigs. Rock goes to an impact crusher, from which fines go to the gravity separation jigs; coarser material is returned to the crusher. The jigs catch gold, lead, and mercury along with other dense fines; this material is then pumped to a wave table that further concentrates the metals. Mercury is retorted from the concentrate, then condensed and sent to a recycling facility. In addition to the environmental benefit of removing mercury, fine gold amalgamated with mercury is being recovered. The potential for recovery of valuable metals may provide adequate incentive for private industry to reclaim some sites, but the need is much greater than current industry interest. A comprehensive inventory of legacy sites, mapping and analysis of associated waste, cooperation of regulators, and additional financial incentives would facilitate remediation efforts.