Executive summary

• The Superior, Bingham, Bisbee, and Yauricocha (Perú) carbonate-hosted massive hematite-bearing copper ores show a similarity in the opaque mineralogy, mineral zoning, ore textures, and metal grades.
• The mineral zonation in these deposits probably reflects pH gradients between oxidized, acidic ore fluids and carbonate wall rocks (Friehauf, 1996).
• The differences in non-opaque gangue mineralogy may be due to differences in wall rock composition and the distance from porphyry, both reflected in differences in the degree of saturation of the ore fluid with respect to minerals in the system Al2O3-MgO-SiO2-CO2-H2O.
• The preservation of anhydrite as inclusions within pyrite grains suggests that these ores may have contained significant anhydrite during early stages of their formation which has since been removed, either by later hydrothermal solutions or by deeply-circulating post-mineralization fluids.
• The discovery of massive ores at Bingham with similar copper grades and higher-than-normal gold grades is very encouraging from the perspective of exploration in the greater Bingham area and carbonate-hosted porphyry deposits elsewhere in the world.
• Similarities of Superior massive carbonate-hosted ores with those of major porphyry copper districts like Bingham and Bisbee supports the model that ores of the Superior district are related to a porphyry copper center and should encourage proponents of further exploration in the district.

Purpose and scope

This study was inspired by a visit to the Bingham district (Utah) by the Stanford Ore Deposits Group (ODEX) in August, 1996. My thesis research in the Superior district (Arizona) focused on similar looking rocks. The purpose of this study is simply to convey some of my observations to the geologists at Bingham (Geoff Balantyne and Charles Phillips) and Superior (Scott Manske, Alex Paul, Matt Knight, and Eric Seedorff) which they might find useful enough to incorporate into their exploration models. Copies were also supplied to Marco Einaudi, Guillermo Pareja, Patrick Redmond, and Esra Inan of Stanford University.