Sources of Metals and Acidity at the Elizabeth and Ely Mines: Geochemistry and Mineralogy of Solid Mine Waste and the Role of Secondary Minerals in Metal Recycling
Published:January 01, 2001
Jane M. Hammarstrom, Robert R. Seal, II, Andrew P. Ouimette, Scot A. Foster, 2001. "Sources of Metals and Acidity at the Elizabeth and Ely Mines: Geochemistry and Mineralogy of Solid Mine Waste and the Role of Secondary Minerals in Metal Recycling", Part I. Proterozoic Iron and Zinc Deposits of the Adirondack Mountains of New York and the New Jersey Highlands Part II. Environmental Geochemistry and Mining History of Massive Sulfide Deposits in the Vermont Copper Belt, John F. Slack, Jane M. Hammarstrom, Robert R. Seal
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The Elizabeth and Ely mines are developed in pyrrhotite-rich, Besshi-type massive sulfide deposits in the Orange County copper district of east-central Vermont. Mine waste and flotation mill tailings have been exposed to weathering for 50 years or more, resulting in acid mine drainage. The Elizabeth mine became a Superfund site in 2001; the Ely mine is proposed. Geochemical and mineralogical characterization of historical mine waste and modern flotation tailings show that despite differences in mine site history, the mines share many similarities. The Elizabeth site includes metal-rich mine waste piles associated with 19th century copperas (melanterite) production, remnants of copper smelter operations, as well as 1.5 million m3 of pyrrhotite-rich flotation tailings. Total base metal concentrations in the surface material on the historically significant Elizabeth mine wastes are higher (as much as 7,000 ppm) than in oxidized parts of flotation mill tailings piles (1,000 ppm or less). Cu >Zn>Pb throughout historic waste piles; Zn>Cu >Pb throughout much of the flotation tailings piles. Variations in Cu/Zn ratios reflect changes in efficiency of chalcopyrite processing over time. Ely ore was smelted for copper on-site after partial roasting, leaving roast beds, mine waste piles, and slag. Oxidized surface materials at both sites are goethite- and jarosite-rich, and locally hematite-rich in roast bed areas. Fine-grained, unoxidized pyrrhotite- and mica-rich tailings lie within 30 cm of the oxidized tailings surfaces. Highly soluble efflo-rescent sulfate salts (melanterite, rozenite, chalcanthite) form intermittently on historic mine waste piles and locally on flotation tailings surfaces at both mines and contribute metals and acidity to surface runoff during rainstorms and spring snowmelt. Water quality in streams draining both mine sites will improve only if the established cycles of weathering of exposed ore, efflorescent sulfate salt formation and dissolution, and release of metals and acidity to the surface runoff, are broken.
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Part I. Proterozoic Iron and Zinc Deposits of the Adirondack Mountains of New York and the New Jersey Highlands Part II. Environmental Geochemistry and Mining History of Massive Sulfide Deposits in the Vermont Copper Belt
This First day of the field trip visits Proterozoic iron deposits at the Podunk and Skiff Mountain iron mines, in the eastern Adirondack Mountains of New York state. Included are roadcuts to see representative lithologies and structures in the region surrounding the iron deposits. The origin of these iron deposits has been controversial, but studies by Foose and McLelland (1995) and more recently by McLelland et al. (2001b, 2001c) provide strong evidence for a high-temperture, intramagmatic origin related to late stages the Lyon Mountain Granite and correlative intrusions during the latter part of the 1090 to 1030 Ma Ottawan orogeny. The great majority of the deposits consist of low Ti magnetite ore accompanied by apatite and aegerine-augite. The apatite has high concentrations of rare-earth elements (REE) indicating to Foose and McLelland (1995) that the deposits are of Kiruna (REE-Au-U-Cu) type. This is further supported by persistent sodic (i.e., albitic) alteration associated with the ores. Most of the iron ores appear to be undeformed although they may occur in strained host rocks. Deposits are intimately associated with late tectonic to post-tectonic Lyon Mountain Granitic Gneiss that was emplaced at ca. 1055 Ma, during the waning stages of the ca. 1090 to 1030 Ma Ottawan Orogeny.