Geochemistry of ore, host rock, and mine waste pile samples of iron oxide-apatite (IOA) deposits of the eastern Adirondack Highlands, New York, in relation to potential rare earth elements resources

The ore from historic iron mines of the eastern Adirondack Highlands, New York, contain abundant quantities of rare earth element (REE)-bearing apatite crystals. These apatite crystals are especially enriched in Y, La, Ce, and Nd. In-ground ore, mine waste piles, and tailings piles that are associated with these mines could contain apatite and other REE-bearing phases at elevated concentrations indicating potential as REE resources. This is the first geochemical database for a regional subset of ore and mine waste products for these mines. Thirty-four ore, twenty-nine mine waste, seven host rock, two pegmatite, and one slag sample were collected from these iron oxide-apatite (IOA) mines in the eastern Adirondack Highlands near Mineville and Ticonderoga, New York. The waste pile samples included 25 samples collected from rubble-sized mine waste piles and four samples from processed tailings piles. Waste pile sampling was accomplished by adapting the sampling strategy outlined by Smith and others (2000, 2006), which included collecting 30 to 50 evenly distributed aliquots (subsamples) from across each waste pile that were composited to form a representative composite sample for the pile. The resulting samples ranged from 12.75 to 32.50 pounds (5.78 to 14.74 kilograms) of material, which were crushed, homogenized, and split prior to geochemical analysis. Major elements were analyzed by wavelength dispersive x-ray fluorescence (WDXRF) and 60-element analyses was completed by inductively coupled plasma-optical emission spectroscopy-mass spectroscopy (ICP-OES-MS). Ore samples were preferably collected in situ from the ore seams, but clasts were collected from waste piles if the ore seam was inaccessible. A wide range in chemical values exists for the ore and waste pile samples. Total REE (lanthanides plus yttrium) varies from 11 to greater than 22,000 parts per million (ppm) for waste piles and 15 to greater than 47,000 ppm for ore samples. All waste pile samples have light REE greater than heavy REE content, with light REE/heavy REE ratio ranging from 1.43 to 35.30, with a median value of 2.14. Ore samples with the highest total REE content have larger negative Eu anomalies, and samples with lower total REE have diminished negative Eu anomalies and more notable negative Ce anomalies. A positive correlation for all samples exists between REE and Th, indicating the potential for radiometric surveys as a tool for vectoring toward higher grade resources.
The elevated REE found in some of these waste piles and ore samples is similar to or higher than grades found in some rare earth mines and advanced exploration projects. However, targeted selection of specific mines and waste piles would be required due to the large range in REE values found in the Adirondack IOA deposits.
References: Smith, K.S., Ramsey, C.A., and Hageman, P.L., 2000, Sampling strategy for the rapid screening of mine-waste dumps on abandoned mine lands, in ICARD 2000—Proceedings from the Fifth International Conference on Acid Rock Drainage, Denver, Colorado, May 21-24, 2000: Society of Mining, Metallurgy, and Exploration, Inc., p. 1453–1461. Smith, K.S., Hageman, P.L., Ramsey, C.A., Wildeman, T.R., and Ranville, J.F., 2006, Reconnaissance sampling and characterization of mine-waste material, in Proceedings of the US Environmental Protection Agency Hard Rock Mining 2006 Conference, Tucson, Arizona, November 14-16, 2006, p. 1–14.