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Formula: AuSb2
Antimonide, pyrite group,
gold-bearing mineral
Crystal System: Isometric
Specific gravity: 9.98 measured, 9.91 calculated
Hardness: 3
Streak: Bronze
Colour: White
Environments
Aurostibite occurs in hydrothermal gold -
quartz veins, in portions deficient in
sulphur and containing other antimony
minerals. Associated minerals include gold,
freibergite, stibnite,
jamesonite, chalcostibite,
bournonite, boulangerite,
arsenopyrite, pyrite,
chalcopyrite, sphalerite,
galena and tetrahedrite
(HOM).
Localities
There are two co-type localities, the Giant Yellowknife mine, Yellowknife, North Slave Region, Northwest Territories,
Canada, and the Chesterville Mine, McGarry Township, Timiskaming District, Ontario, Canada.
At the Giant Yellowknife mine, Yellowknife, North Slave Region, Northwest Territories, Canada, the type specimen is a
two-inch fragment of greyish white impure vein quartz containing inclusions of
chloritised and silicified wall-rock heavily mineralised with fine euhedral
arsenopyrite. The walls of narrow vugs in the vein
quartz are coated with minute imperfect rhombohedral crystals of
dolomitic carbonate and thin flakes of
sericite mica. Among the carbonate
crystals in these vugs are scattered grains of hackly gold varying in size from
about 20 microns up to 1 or 2 mm, accompanied by separate grains of aurostibite up to about 350 microns in
size. Some of the gold grains appeared to be thinly coated with tarnished grey
aurostibite.
The quartz contains irregular masses of
bournonite, chalcopyrite,
sphalerite, and bladed and fibrous masses of
jamesonite and
chalcostibite, associated with
arsenopyrite and pyrite
crystals. The wall-rock inclusions appear to be mineralised exclusively with disseminated euhedral crystals of
pyrite and arsenopyrite.
Single grains of gold and aurostibite occur scattered in
quartz and carbonate immediately adjacent to fractures in the clear
quartz.
(AM 37.461-469).
The paragenesis of the Yellowknife ores is postulated as follows, oldest first:
1. A solution rich in sulphur, iron
and arsenic was introduced, from which
arsenopyrite and pyrite formed.
Much of the arsenopyrite was formed before deposition of
pyrite started.
2. A solution rich in sulphur, zinc,
iron and copper, and containing minor
tin was introduced. Sphalerite was
the first mineral to be formed from this solution, followed by
chalcopyrite, pyrrhotite
and stannite.
3. There was, possibly, an early introduction of gold.
4. An antimony-rich solution was introduced, which also contained
sulphur, gold,
silver and lead, and possibly some
copper and iron. Aurostibite and
gold probably formed late in this period, with aurostibite forming
shortly after the gold by reaction with excess
antimony. Native lead and
antimony were probably among the last minerals to form, and indicate an
appreciable deficiency of sulphur during the later stages of mineralisation.
5. Late faulting and circulation of supergene or
hypogene solutions, caused the formation of a second age of
sulphides
(AM 38.506-527).
At the Chesterville Mine, McGarry Township, Timiskaming District, Ontario, Canada, the aurostibite occurs
sparsely as minute grains embedded in clear dark quartz near and attached to
small hackly masses of bright yellow gold. Where
gold is undisturbed below the surface of clear
quartz, coatings of light grey aurostibite and darker grey
freibergite partly occur on some of the extremities of the irregular
gold grains.
A polished section reveals sparse grains of aurostibite up to 250 microns in diameter in clear
quartz closely associated with gold,
freibergite, chalcopyrite,
jamesonite and galena. This
clear quartz has largely absorbed and recrystallised an older, less
transparent, milky-white quartz which is now mineralised with
pyrite, arsenopyrite,
gersdorffite,
chalcopyrite, sphalerite
and tetrahedrite
(AM 37.461-469).
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