Hypogene porphyry Cu deposits, unaffected by supergene enrichment, are generally perceived as relatively low-grade orebodies, in keeping with a current average production grade of 0.53% Cu. Nonetheless, all or large parts of some deposits exceed 1% Cu, and smaller deposit components can be much higher in grade, locally >6% Cu. In view of the major economic and environmental benefits afforded by high grades, we briefly review geologic features and factors conducive to development of >1% hypogene Cu ore in porphyry Cu systems. Intense quartz veinlet stockworks, magmatic-hydrothermal breccias, vuggy residual quartz or vein systems in telescoped lithocaps, proximal skarns, carbonate-replacement mantos and pipes, low-permeability barriers, and reactive mafic host rocks—either alone or in various combinations—are identified as particularly favorable features because they enhance rock permeability and/or reactivity; most of them may be taken into account when planning and conducting exploration programs, thereby maximizing the chances of high-grade porphyry Cu discoveries.

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