Abstract

Vein-scale metal ratio configurations of the Coco-Luz Angelica area of the Quiruvilca Cu-Pb-Zn-Ag lode district tend to reflect local zoning about vein intersections. These vein intersections commonly contain greater relative amounts of early-stage pyrite, suggesting that metal ratio work in combination with detailed mapping of mineral abundances along strike of a vein could significantly assist in the evaluation of the exploration potential.The vein-scale metal zoning appears to document the parallel evolution of fluid-controlling structures which developed synchronously with the evolving hydrothermal system. For example, the wider middle portion of the cymoid-curved Coco vein dominantly contains paragenetically early pyritic mineralization, whereas the thinner distal ends dominantly contain paragenetically later sphalerite-galena mineralization; this is an evolution seen in other vein districts such as Freeland-Lamartine, Colorado.The configurations of individual metal ratios are quite varied; hence interpretation should be based on the metal ratios as a group, along with considerations of geology and structure. Only ratios derived from ore or near-ore blocks appear to be valid; waste blocks seem to produce spurious results. Scales should be ore block or larger; smaller scales appear to generate too much noise to discern significant patterns.District-scale metal ratios of base metal lode deposits show considerable variation in absolute value and range. However, the consistent zonation patterns seen in these deposits (inner copper zones, outer zinc-lead-silver zones) are permissive evidence for an underlying fundamental control, here proposed as the progressive cooling of hot metal-bearing fluids by distal ground water.

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