Massive replacement bodies in dolostone
of the C-bed orebody at
Superior contain siliceous, sulfide-rich
cores and hematite margins. The sulfide cores are zoned outward
from (1) central bornite-pyrite white mica chalcocite (with
local shale altered to zunyite-kaolinite-quartz), (2) intermediate
bornite-chalcopyrite-quartz-sericite chlorite chalcocite, and
(3) outer pyrite-chalcopyrite-quartz-chlorite. The outer sulfide
zone is in sharp contact with marginal hematite-quartz pyrite
chalcopyrite which lacks aluminum-bearing phases (with local
shale containing quartz-illite-chlorite). Porphyry dikes within
the marginal hematite zone are altered to quartz-sericite-pyrite-chlorite.
Outside the replacement bodies, quartz-dolomite hematite sphalerite
veinlets cut dolostone. Ores at Superior formed by intial
replacement of carbonate by hematite-quartz which armored fresh
ore fluid from carbonate and allowed it to deposit Cu-Fe sulfides
at higher acidities and sulfidation states. Replacement of hematite
by sulfides neutralized and oxidized the solution and consumed
sulfur, forming a residual fluid that deposited hematite at the
margins of the orebody. Depletion of sulfur in solution led to
cyclic saturation/undersaturation with respect to chalcopyrite,
forming rhythmic mm-scale hematite / chalcopyrite layers parallel
to the massive sulfide / hematite contact.
Key Words:
high-sulfidation, carbonate, porphyry, sulfide, replacement
