Copper inclusions in sheet silicates from porphyry Cu deposits
Economic geologists have studied the Cu contents of biotite for at least a quarter of a century as potential guides for exploration and as clues to the genesis of porphyry copper deposits1–12. These earlier studies used bulk analytical techniques, and a common, although cautious, assumption was that Cu substituted for Fe in the octahedral sites of the biotite. Here we report data from high-resolution and X-ray analytical transmission electron microscopy which demonstrate that anomalous Cu in biotite is present primarily as submicrometre inclusions of pure native Cu in the interlayer regions of the mica. The inclusions occur with greatest density and size in mixed-layer sheet silicate domains which form by alteration of biotite and chlorite. Less abundant and smaller Cu inclusions are associated with biotites that show subtle alteration only on the high-resolution transmission electron microscopy scale. The association of Cu inclusions with alteration domains, coupled with mass-balance considerations, suggests that these sheet silicates act as Cu sinks, and not as sources for primary mineralization.
Mineral properties and their contributions to particle toxicity.
It has been recognized since at least as early as the mid-1500s that inhaled minerals (i.e., inorganic particles) can pose a risk. Extensive research has focused on the biological mechanisms responsible for asbestos- and silica-induced diseases, but much less attention has been paid to the mineralogical properties and geochemical mechanisms that might influence a mineral's biological activity. Several important mineralogical characteristics control a mineral's reactivity in geochemical reactions and are likely to determine its biological reactivity. In addition to the traditionally considered variables of particle size and shape, mineralogical characteristics such as dissolution behavior, ion exchange, sorptive properties, and the nature of the mineral surface (e.g., surface reactivity) play important roles in determining the toxicity and carcinogenicity of a particle. Ultimately, a mineral's species (which provides direct information on a mineral's structure and composition) is probably one of the most significant yet most neglected factors that must be considered in studies of toxicity and carcinogenicity. ImagesFigure 4.
Vermiculite, hydrobiotite, and biotite in the Rainy Creek igneous complex near Libby, Montana
Abstract Vermiculite and hydrobiotite both occur as alteration products of biotite pyroxenite near Libby, Montana. Hydrothermal and weathering studies and new chemical analyses by C. O. Ingamells suggest that the vermiculite is a product of leaching of biotite by ground waters; the hydrobiotite may be a higher temperature alteration product.