Blackbird Cobalt Deposits, Lemhi County, Idaho Page: 8
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In general, cobalt occurs as fine- to coarse-grained lenses, stringers,
and disseminations of' cobaltite along zones of fracturing- and shearing in
both quartzites and schist. In. the southern-and eastern parts of the dis-
trict, cobaltite. is minutely disseminated along, illdefined zones in shattered
quartzite. A few weathered outcrops are spectacoularwith cobalt bloom
(erythrite. or cobalt-chalcanthite), Copper: and gold are present in minor
quantities. The average bobal, content arid the continuity of known 'ore bodies
are apparently low in these areas.
In the central and northern parts of the district cobaltite is usually
found in,and adjacent to zones of horth to northwest fracturing. It is found
disseminated in both the wall rocks arid throu ho t the fr.actu-e zo~s., It
sometimes occurs within: the fracture zones. as -stringers . nr-d"lehses of massive
cobaltite in a quartz gangue, At some places it i's i timately associated with
chalcopyrite, iron sulfides gold, 'nd silver,
Structure typs. - The' deposits-of the Blackbird districthave. been
classified/. into four main types on the' basis -of. structure, as follows:
,l. Uncle Sam t pe: Complex, vein zones along extensive reverse faults,
The ores' in the Bryan Gulch-Chicago-Brown -Bear zone belong to this
..2. Bonadza type: -Zones of small, elongate pods and lenses in schist,
often containing high-razde cobalt, ores.
3. Hawkeye type:. Broad zones of small veins and stringers deposited
along schistose partings.
I+. Haynes Stellite type: Cobalt deposited in silicified: and tourmna-
The first three types, occurring either separately or together, are pre-
dominant in the central part of the district. The Hayrnes Stellite type has
been found only in the southern part 'of 'th& area.
Localization: The. favorable host ro.cks-iappeoar to be the thin-bedded
micaceous quartzites -and sandy 'schists. Mineralization of the Hawkeye type
is also usually best developed in these rocks; hb ver, this type is occasion-
ally found in intensely fractured quartzites. Bonanza-type mineralization
apparently is limited to the micaceous rocks. Haynes Stellite-type mineral-
ization is confined to the less deformed And.mo.r.quartzitic rocks,
The nest intense neralization .in the Blackbird' district is distributed
throughout a triangular zone about 7500 feet long, trending .to the northwest.
It ranges in width from 200 feet on the horth to 1,600 feet on the south at
the base of the triangle. The three .principal.lodes :in this zone are
the Chicago-Brown Bear, the Uncle Sam,: and the Hawkeye. Minor elements of
this system are known as the Bohannon, St. Joe, and Indian. Prior to.ecent
8 See footnote 7.
1322 8 -
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Reed, G. C. & Herdlick, J. A. Blackbird Cobalt Deposits, Lemhi County, Idaho, report, February 1947; [Washington D.C.]. (digital.library.unt.edu/ark:/67531/metadc38467/m1/16/: accessed February 20, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.