Julcani Mining District, Peru: A Study of Metal Ratios

Polymetallic sulfide mineralization is present in the Julcani mining district, Peru, as fracture fillings in Tertiary volcanics. Metal contents from ore inventories are used to determine metal ratios throughout the district. The changes in metal ratios are large and systematic, and contours can generally be drawn separating areas of different values. The concave shape of many contours on vertical vein projections is believed to indicate the direction of flow of mineralizing solutions. In the south-east.ern part of the district, Herminia-Lucrecia, ratios change systematically away from an area of more highly fractured and altered intrusive rock, and the ratio changes indicate solution movement with a large lateral component. Metal changes in three other mineralized areas of the district indicate general domal zoning. In general, Pb/Cu increases monotonically away from the central zone, as might be expected from general zoning considerations. It is suggested that this ratio be used mor. e generally as an index for the quantitative description of zoning in ore deposits. The rate of change of particular ratios along various paths can differ, reflecting dif-ferences in depositional factors. Ag/Pb and Ag/Cu have maxima (Herminia), minima (Ag/Cu in Mimosa), or decrease monotonically (.Carmencita). This quantitative characterization of zoning has been applied successfully to mineral exploration in several districts.