4
PRELIMINARY CONCLUSIONS
The Ni-Co-As-Ag ore mineral assemblage at Black Hawk is
remarkably similar in to the typical five-element style of the
Cobalt district in Ontario, Canada. There are notable dif-
ferences, however, in mineral assemblage, texture, and com-
position. As compared to the Cobalt region, Black Hawk is
seemingly deficient in cobalt during arsenide mineralization
and is overall lacking appreciable antimony. This is shown
by the lack of the primary antimony phases breithauptite
and dyscrasite within the main silver aggregates, with only
nickeline observed. The succeeding nickelskutterudite con-
tains appreciable iron and negligible cobalt, showing that
cobalt was not abundant during its precipitation, given the
Figure 3. Reflected photomicrograph from Cobalt-
Gowganda region. FOV 3 mm. Large vein of white native
silver (Ag) heavily included by grey blobs of dyscrasite (Dys)
and exsolution lamella of allargentum (All). Associated
are orange-peach grains of nickeline (Nc), violet-pink
breithauptite (Bhp), and unidentified blue-grey cobalt
arsenides (1,2) in dark quartz matrix
Figure 4. BSE image from Cobalt-Gowganda region.
FOV 2.5 mm. Large grey vein of native silver (Ag). Tiny,
bright white grain of native bismuth (Bi). Included in the
silver, light grey breithauptite (Bhp) and medium grey
nickeline (Nc), scattered throughout. The vein is rimmed by
unidentified cobalt arsenides, first a dark grey (1), sulfur rich
phase, and later a lighter grey sulfur poor phase (2)
Figure 5. Reflected photomicrograph from Black
Hawk District. FOV 3 mm. Massive white native silver
(Ag) aggregates rimmed by massive grey iron-rich
nickelskutterudite (Nskt). Crosscut by dark grey vein of
acanthite (Aca) and pearceite (Pea), with fine orange-pink
lamellae of unidentified nickel-cobalt sulfide (1). All in
dolomitic carbonate breccia
Figure 6. BSE image from Black Hawk District. FOV 2 mm.
White vein of acanthite (Aca), with included light grey
pearceite (Pea) and veinlets of unidentified nickel-cobalt
sulfide (1). Massive white native silver (Ag), bottom right.
Medium grey iron rich nickelskutterudite (Nskt), pervasive.
Dark grey carbonate gangue
PRELIMINARY CONCLUSIONS
The Ni-Co-As-Ag ore mineral assemblage at Black Hawk is
remarkably similar in to the typical five-element style of the
Cobalt district in Ontario, Canada. There are notable dif-
ferences, however, in mineral assemblage, texture, and com-
position. As compared to the Cobalt region, Black Hawk is
seemingly deficient in cobalt during arsenide mineralization
and is overall lacking appreciable antimony. This is shown
by the lack of the primary antimony phases breithauptite
and dyscrasite within the main silver aggregates, with only
nickeline observed. The succeeding nickelskutterudite con-
tains appreciable iron and negligible cobalt, showing that
cobalt was not abundant during its precipitation, given the
Figure 3. Reflected photomicrograph from Cobalt-
Gowganda region. FOV 3 mm. Large vein of white native
silver (Ag) heavily included by grey blobs of dyscrasite (Dys)
and exsolution lamella of allargentum (All). Associated
are orange-peach grains of nickeline (Nc), violet-pink
breithauptite (Bhp), and unidentified blue-grey cobalt
arsenides (1,2) in dark quartz matrix
Figure 4. BSE image from Cobalt-Gowganda region.
FOV 2.5 mm. Large grey vein of native silver (Ag). Tiny,
bright white grain of native bismuth (Bi). Included in the
silver, light grey breithauptite (Bhp) and medium grey
nickeline (Nc), scattered throughout. The vein is rimmed by
unidentified cobalt arsenides, first a dark grey (1), sulfur rich
phase, and later a lighter grey sulfur poor phase (2)
Figure 5. Reflected photomicrograph from Black
Hawk District. FOV 3 mm. Massive white native silver
(Ag) aggregates rimmed by massive grey iron-rich
nickelskutterudite (Nskt). Crosscut by dark grey vein of
acanthite (Aca) and pearceite (Pea), with fine orange-pink
lamellae of unidentified nickel-cobalt sulfide (1). All in
dolomitic carbonate breccia
Figure 6. BSE image from Black Hawk District. FOV 2 mm.
White vein of acanthite (Aca), with included light grey
pearceite (Pea) and veinlets of unidentified nickel-cobalt
sulfide (1). Massive white native silver (Ag), bottom right.
Medium grey iron rich nickelskutterudite (Nskt), pervasive.
Dark grey carbonate gangue