Bingham, UT (n = 3) Superior, AZ (n = >200) Bisbee, AZ (n = 5)
% specular hematite (grain size m) 20-30% (300-600) > 75% (300-600, up to 2000 common) > 75% (300-2000 )
% pyrite (grain size m) > 40% (200-1000) < 10% (200-1000) < 10% (200-1000)
% chalcopyrite (grain size m) > 40% (500-1200) < 10% (500-1200) < 10% (500-1200)
paragenesis hematite pyrite chalcopyrite hematite pyrite chalcopyrite bornite hematite pyrite chalcopyrite bornite
sieve texture pyrite common common common
inclusions in pyrite quartz, specularite, anhydrite quartz, specularite, anhydrite, chalcopyrite, (bornite) quartz, specularite, anhydrite
magnetite, sphalerite, galena none none none
rhythmic layering present present unknown
typical Cu grade (%) 2.5 - 4 4 - 6 no assay
typical Au grade (ppm) > 1 1 no assay
typical Ag grade (ppm) 5 - 15 10 - 30 no assay
non-opaque gangue talc ± quartz none ± local quartz quartz, carbonate, chlorite
zoning in massive sulfide barren core, high-grade near contacts with hematite-ores barren core in large bodies, bornite-rich core in smaller bodies, chalcopyrite peripheral barren core in large bodies, highest grade near core of smaller bodies
proximity to porphyry-hosted ore < 300 m > 300 m < 2,000 m
alteration of feldspathic rocks argillic (Rubright and Hart, 1968) kaolinite, sericite, zunyite kaolinite, pyrophyllite, sericite
temporal/spatial relationship to "prograde" skarn cross-cuts skarn/ peripheral cross-cuts skarn no prograde skarn described in district
host rock thinly-bedded silty limestone clean, sparry dolostone argillaceous "limestone"
direct replacement of carbonate likely yes yes
  • Table 1. Characteristics of hematite-chalcopyrite replacement ores.