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Formula: PtS
Sulphide of platinum, paramorph
of braggite
Crystal System: Tetragonal
Specific gravity: 9.5 measured, 10.2 calculated
Hardness: 4 to 5
Colour: Steel-grey to silvery white
Luminescence: Not fluorescent under UV
Environments
Plutonic igneous environments
Placer deposits
Cooperite is a significant platinum ore mineral, found in
ultramafics, gabbros,
dunites and chromitites,
typically layered, in massive chalcopyrite –
pyrrhotite orebodies and in alluvial placers.
Associated minerals include braggite,
vysotskite, sperrylite,
moncheite, platarsite,
laurite, malanite,
hollingworthite, platinum,
platinum - iron alloys and many other
platinum group mineral species,
chalcopyrite, bornite,
cubanite, pentlandite,
pyrrhotite, pyrite and
chromite
HOM).
Localities
At the Darya River sediments, Sakha Republic, Russia, Idiomorphic crystals up to 3.5 mm in size of
iron - platinum alloy,
cooperite and mertieite-II were found in a heavy-mineral
concentrate from the stream sediments. Platinum -
iron crystals display cubic and thin platy habits; occasionally they are twinned. Some
of the iron - platinum alloy
samples have large (about 100 μm wide) cooperite overgrowth rims or are covered by a
gold - silver alloy. Cooperite
also occurs as large euhedral crystals (up to 3 mm across, partly twinned).
Crystals of mertieite-II are speckled with μm-sized (2−5 μm) inclusions of
sperrylite and intergrown with minerals of
cooperite-braggite solid solution, a
platinum - palladium -
mercury alloy, keithconnite and
a gold - silver alloy
(MM 68.6.871–885).
At the Freetown layered complex, Western Area, Sierra Leone, heavy mineral concentrates from rivers and river terraces
have been examined for their platinum group mineral content. The
alluvial platinum group minerals are 0.1 to 1.5 mm in size and
include copper-bearing
isoferroplatinum,
tulameenite and hongshiite,
and cooperite – vysotskite,
laurite, erlichmanite, an
osmium - iridium alloy, an
osmium - ruthenium alloy and
native copper.
Cooperite in the fresh rocks is rare in the alluvium whilst
platinum - iron alloys become more
abundant. Oxidised platinum group minerals are a feature only of the
weathering process and disordering of the platinum -
iron develops during weathering.
Palladium is much less abundant in the alluvial suite than in the
primary minerals whereas
copper, present as copper sulphides
in the fresh rocks, occurs in the alluvium as a minor component of the
platinum - iron alloys and as
hongshiite
(MM 82.S1.S223–S246).
There are two co-type localities, Mokopane, Mogalakwena, Mogalakwena Local Municipality, Waterberg District
Municipality, Limpopo, South Africa, and the Rustenburg Town & Townlands Farm, Rustenburg, Rustenburg Local
Municipality, Bojanala Platinum District Municipality, North West, South Africa.
At the type localities, cooperite occurs as silvery white metallic to steel grey metallic material in
norite. Associated minerals include
vysotskite, tulameenite,
sperrylite, pyrrhotite,
platinum, pentlandite,
millerite, mackinawite,
kotulskite, keithconnite,
isoferroplatinum, gold,
daomanite, cubanite,
chalcopyrite and braggite
(Mindat).
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