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.