CHARACTERIZATION OF WEATHERING OF MINE ROCK PILES:EXAMPLE FROM THE QUESTA MINE, NEW MEXICO, USA

摘要

The Questa mine (Chevron Mining Inc. or CMI, formerly Molycorp, Inc.),a porphyry molybdenum deposit in New Mexico, USA, constructed ninemine waste rock piles between 1969 and 1982. The evidence forweathering in the Goathill North (GHN) rock pile includes somecombination of: 1) color changes, 2) bulk texture changes, 3) mineralogychanges, 4) mineral texture changes, and 5) grain texture changes. Clayminerals are abundant and varied in the Questa rock piles, but five lines ofevidence suggest that clays are predominantly from the pre-mininghydrothermal alteration: 1) fresh or lightly tarnished pyrite surrounded byclay minerals, 2) similar types and abundance of clay minerals in theunweathered drill core and rock pile samples from GHN, 3) similarchemical compositions for the clays from unweathered drill core vs.weathered GHN rock pile, 4) textural association between clay and otherminerals, and 5) oxygen and hydrogen isotopic analysis. Predominantweathering reactions in the GHN rock pile are oxidation of pyrite,dissolution of carbonate, and formation of sulfate minerals (gypsum,jarosite, and soluble, efflorescent salts). Waters from the Questa rock pilesyield SO4 (up to 19,000 ppm) and Al (up to 1690 ppm), indicating majorsulfide and subordinate silicate dissolution.