The Role of Mineralogical Research in Mine Site Characterization

English Abstract:

Over the last decade, the GSC, under the Environment and Health Programs, has conducted research into selected ore deposits as a means to: characterize mineralogical and geochemical signatures; provide public geoscience knowledge for decision makers; and promote deeper understanding of mine sites to aid technical reviews of Environmental Impact Assessments for new mine sites. To date, studies have been completed on lode Au deposits in two different geological and geographic environments (Nova Scotia and British Columbia). Currently, studies are near completion on U-REE granitic pegmatites in central (Bancroft) Ontario. U, Th and REEs have been mined in the Bancroft region since the early fifties. Demand for these commodities is increasing and there is renewed interest in re-appraising the region for exploration and development. Several old mine sites were sampled (rock core, tailings, soils, stream/lake sediments, groundwater, radon) for detailed characterization. This presentation will focus on mineralogy and hydrogeology of the Croft Mine that was explored in the early fifties and again in the early seventies. Representative core samples include pegmatite and gneisses (amphibolite, metapelite, quartzofeldspathic). Samples consist of abundant plagioclase and K-feldspar with subordinate quartz, amphibole and biotite. The metapelite contains sillimanite, garnet and allanite. Minor to trace fluor-apatite was detected in one sample and several of them contain minor to trace calcite or dolomite. A variety of oxides (magnetite, hematite, ilmenite) and sulphides (pyrite, pyrrhotite, chalcopyrite) occur in minor to trace amounts. Sediment collected from the outlet of the adit reflects the overall mineralogy of the sampled pegmatite and gneisses. Characterization of the mineralogical signature (ore, gangue, alteration) at this site helps to constrain the mass transfer of U and other species to mine drainage using geochemical inverse modelling.

Although these studies are on abandoned mines, they have provided sites and samples to develop new methods for analytical, geostatistical, hydrogeological, mineralogical and geochemical characterization. Identifying the factors that control geological processes will contribute to the development of models for environmental risk assessment.