Hydrothermal Vent at Flag Resources (1985) Limited's Cobalt Hill, Mackelcan Township, Wanapitei Anomaly, Sudbury, Ontario
Abstract
The Cobalt Hill property of Flag Resources (1985) Limited is underlain by
extensively brecciated, pyritized and hydrothermally altered quartzites and
arkosic quartzites of the Lorrain Formation. The mineralization potential of
the area was re-evaluated on the basis of drill logs obtained from thirteen
drill holes (DDH 83-21, 83-22, 83-23, 83-23A, 83-24, 81-1, 81-4, 81-5, 81-6,
81-7 and 81, 83-9 & CH-91-2) and on the basis of earlier mineralogical and
fluid inclusion studies of grab samples collected from the area.
The brecciated and hydrothermally altered quartzites at Cobalt Hill
probably represent part of a fossil hydrothermal vent. Brecciated quartzites
show evidence of pervasive silicification, pyritization and locally, chlorite
and carbonate alteration. The abundance of pyrite appears to be proportional
to the extent of brecciation and silicification in the rocks, suggesting that
pyrite was introduced with quartz during hydrothermal alteration. Therefore,
the previously documented small inclusions of Ni-sulfides, chalcopyrite,
pyrrhotite, and gold in pyrite must also have a hydrothermal origin.
Pyrite is generally most abundant at depths of 200-300' and increase in
abundance from east to west. The highest pyrite concentration occurs in the
westernmost drill hole DDH 81-9 between 175 and 325' depth where the pyrite-
rich section is underlain by a ca. 450' thick breccia zone. The increasing
thickness of the breccia zone, coupled with increasing pyrite concentration
and silicification in the form of chert and quartz veins in drill hole 81-9
suggests that mineralization potential of the area increases from east to
west.
As brecciated quartzites were healed with late quartz veins which locally
contain up to 5% fuchsite (Cr-rich muscovite), up to 20% pyrite, minute
inclusions of Ni-Cu sulfides and gold in pyrite, it is suggested, that saline
hydrothermal solutions circulating at Cobalt Hill were in contact with
mineralized mafic or ultramafic rocks at some depth. The intensity of
brecciation, the thickness of the breccia zone, silicification, chlorite
alteration and the greatest abundance of pyrite in hole 81-9 suggests that out
of the thirteen drill holes, 81-9 may be located nearest to the center of the
hydrothermal vent. Whereas the presence of fuchsite in late quartz veins at
depths of 1200-2200' suggests that the mafic/ultramafic source rocks for Cr
must be present at similar or shallower depths.
End of Abstract
-------------------------------------------------------------------------
In her report of March 4th, 2002, Dr. Schandl states that the ubiquitous
presence of nickel-bearing sulfides and chalcopyrite inclusions in pyrite-rich
quartz veins at Cobalt Hill suggests that the fluids that precipitated the
sulfides must have been nickel and copper-rich. The percentage of nickel in
the small nickel bearing sulfide inclusions at Cobalt Hill is as follows;
pentlandite: 41 percent, bravoite: 39-62 percent and gersdorffite: 35-39
percent.
Is is important to emphasize that the previously reported occurrence of
fuchsite in the same quartz plus pyrite veins implies that the source of
metals (including the chromium in fuchsite) is probably a mafic/ultramafic
intrusion at depths of ca. 1200-2200 feet. This suggested depth corresponds to
the depth interval of the fuchsite-bearing quartz veins. As chromium is an
immobile element it is unlikely to have moved far from its source.
Where to drill on Cobalt Hill to intersect the suggested mineralized
mafic/ultramafic intrusion? West of drill hole A81-9, which is the westernmost
drill hole on Cobalt Hill. In her October 3rd report, Dr. Schandl points out
that the increasing thickness of the breccia zone, coupled with increasing
pyrite concentration and silicification in drill hole A81-9, suggests that the
mineralization potential of the area increases from east to west. Accordingly
(pending on precursory essaying and geophysical work), Flag proposes to drill
a 2000 foot deep drill hole west of A81-9 to intersect the indicated
mineralized mafic/ultramafic intrusion.
Flag owns the mineral rights in most of Mackelcan and adjoining Rathbun
Township.
With results from Dr. Schandl's mineralogical studies, over the past
year, and the re-interpretation of drill log summaries, Cobalt Hill has become
a major exploration project for Flag.
Flag holds 70,000 acres in the Wanapitei Anomaly, the adjoining magnetic
and gravity anomaly to the Sudbury Anomaly and its nickel, copper, platinum
group ore deposits. |
