GEOCHEMISTRY OF THE GASQUET MOUNTAIN NI-CO LATERITE FROM NORTHERN CALIFORNIA

Several Ni-Co laterite deposits occur in the Klamath Mountains in northern California and southern Oregon. These deposits developed from in-situ weathering of alpine-type ultramafic rocks at higher latitudes than is typical for most laterites (±26 degrees from the equator). Using hand held XRF, micro XRF, and LA-ICP-MS techniques on laterites, hand samples and bulk powders from the laterite profile at Gasquet Mountain in northern California, we have delineated elemental enrichment and depletion at micro and macro scale. Depletion of Si and Mg and enrichment of Fe, Ni, and Co is observed at increasing depth at both hand specimen and outcrop-scales. This reflects the supergene weathering process that enriches Ni-Co occurrence out of a serpentinized peridotite. Mineral delineation is critical in the description of Ni-Co laterites, because the enrichment of nickel and cobalt in hydrous-Mg silicates, oxides, or clay minerals has implication on ore processing and commodity recovery. Within the Gasquet Mountain profile Ni is concentrated in the saprolite containing clays and hydrous Mg-silicate minerals. Implementation of a variety of analytical techniques on a sample suite offers an efficient method of understanding the chemistry of Ni-Co laterite development and mineral paragenesis at the Gasquet Mountain deposit.