Stillwater 2

7/29/2019 Stillwater 2

1/64

SAMPLEPREFIX

ROCK TYPES LOCALITIES DESCRIPTION

CZA, STx Anorthosite,dunite,harzburgite,gabbro,granophyre,norite, troctolite

Mouat Mine,Picket Pin,various others

Mafic cumulatesfrom StillwaterComplex, MO

STILLWATER COMPLEX, MONTANA


2/64


3/64


4/64


5/64

NoriteStillwater Complex , Nye County, MONTANA


6/64

Norite from other localities


7/64

STILLWATER CHROMITITEChromitites are intrusive igneous rocks dominated by the mineralchromite (FeCr2O4 - iron chromium oxide). The mineral chromite

has a metallic luster, a blackish color, and is moderately heavy for

its size. Chromitite rocks are typically masses of granularchromite. The Stillwater Complex has economic concentrations ofchromitite, but Cr mining was only done in the mid-20th century.Today, the chromitites are not the targets of active mining. Thechromitite shown below is not from the J-M Reef.


8/64

STILLWATER SULFIDIC SERPENTINITEHeres an altered pegmatitic dunite very richly infused with intercumulate Pt/Pd-richchalcopyrite & pyrrhotite. Dunites are >90% olivine peridotites (ultramafic, intrusiveigneous rocks). During metamorphism, olivine typically converts to serpentine, ifwater is present. The resulting rock is serpentinite. In the sample below, theblackish areas are serpentine masses (formerly large olivine crystals). Some

magnetite is also mixed in with the serpentine.This ore sample grades to about 2.5 ounces of Pd-Pt per ton of rock, with a Pd-Pt ratioof about 3:1.Locality: 55W15100 D1 area (5500 elevation above sea level & 15,100 west of shaft),Stillwater Mine, underground & west of the Stillwater River, southwestern StillwaterCounty, Beartooth Moutains, southern Montana, USA.


9/64

Sulfidic serpentinite (above & below) from the Johns-Manville Reef,Lower Banded Series, Stillwater Complex (Neoarchean, 2.71 b.y.) inthe Stillwater Mine, Beartooth Mountains, Montana, USA.Black: serpentine mixed with a little magnetite (formerly dunite).Metallic-lustered areas: Pt/Pd-rich chalcopyrite & pyrrhotite.

Above: field of view ~9.5 cm across. Below: field of view ~4.1 cmacross.


10/64

STILLWATER SULFIDIC TREMOLITITEAn exceedingly rare rock in the J-M Reef is tremolitite. Tremolitite is a rock

dominated by tremolite (Ca2Mg5Si8O22(OH)2), a whitish amphibole that typically forms

needle-like crystals. This was originally a dunite, composed of olivine crystals.Metamorphic alteration has transformed the olivine into tremolite. This rock is from avery localized alteration spot in the J-M Reef. Typically, dunites get altered toserpentinites (serpentine with a little magnetite), and this tremolitite was observed tobe in close association with such rocks.This ore sample grades out to ~2.0 ounces of Pd & Pt per ton of rock. The Pd-Pt ratio isabout 3:1.Locality: 41W1500 stope (4100 elevation above sea level & 1500 west of shaft),Stillwater Mine, underground & west of the Stillwater River, southwestern Stillwater

County, Beartooth Mountains, southern Montana, USA.


11/64

Sulfidic tremolitite (above & below; field of view ~3.0 cm across)from the Johns-Manville Reef, Lower Banded Seriers, StillwaterComplex (Neoarchean, 2.71 b.y.) in the Stillwater Mine, BeartoothMountains, Montana, USA.White = tremolite. Yellowish-gold colored masses = chalcopyrite.

Silvery-bronze colored masses = pyrrhotite.


12/64

Bronzitite, thin section of a rock made of olivine and pyroxene, mostlybronzite. Photomicrograph, viewed with polarized light.
http://en.wikipedia.org/wiki/Polarized_lighthttp://en.wikipedia.org/wiki/Polarized_light


13/64

Chromitite and bronzite from Stillwater Igneous Complex
http://en.wikipedia.org/wiki/Chromititehttp://en.wikipedia.org/wiki/Bronzitehttp://en.wikipedia.org/wiki/Bronzitehttp://en.wikipedia.org/wiki/Chromitite


14/64


15/64


16/64


17/64


18/64


19/64


20/64


21/64


22/64


23/64


24/64


25/64


26/64


27/64


28/64


29/64


30/64


31/64


32/64


33/64


34/64


35/64


36/64


37/64


38/64


39/64


40/64


41/64


42/64


43/64


44/64


45/64


46/64


47/64


48/64


49/64


50/64


51/64


52/64


53/64


54/64


55/64


56/64


57/64


58/64


59/64


60/64

Braggite (silver area near center) in sulfidic serpentinite from theJohns-Manville Reef Lower Banded Seriers Stillwater Complex


61/64

Johns-Manville Reef, Lower Banded Seriers, Stillwater Complex(Neoarchean, 2.71 b.y.) in the Stillwater Mine, Beartooth Mountains,Montana, USA. Field of view: 1.7 cm across.Silvery = braggite. Brownish bronze = Pt/Pd-rich pyrrhotite.Yellow brassy = Pt/Pd-rich chalcopyrite. Dull greenish gray =serpentinite host rock (formerly a dunite).

STILLWATER MASSIVE SULFIDE


62/64

Platinum- and palladium-bearing pyrrhotite & chalcopyrite in the Stillwater Complexusually occur as intercumulate fills between crystals of plagioclase or pyroxene orolivine/serpentine. Occasionally, these sulfide minerals occur in a massive state.Below is the front & back of a fragment of massive sulfide from the Stillwater ComplexsJ-M Reef. The yellowish-gold colored material is Pt/Pd-rich chalcopyrite, and the

brownish-gold colored material is Pt/Pd-rich pyrrhotite. There are other mineralspresent, including bornite (Cu5FeS4) (see multicolored areas in 2nd pic below), and small

patches of some silvery-colored mineral (what?). Several rare sulfide and element andelement-alloy minerals have been reported from the Stillwater, includinghollingworthite ((Rh,Pt,Pd)AsS), gold (Au), tetraferroplatinum (PtFe),palladobismutharsenide (Pd2(Bi,As)), braggite ((Pt,Pd,Ni)S), keithconnite (Pd3-xTe),

moncheite (Pt(Te,Bi)2), vysotskite ((Pd,Ni)S), etc.

Locality: 46W500 stope (4600 elevation above sea level & 500 west of shaft), StillwaterMine, underground & west of the Stillwater River, southwestern Stillwater Coutny,Beartooth Mountains, southern Montana, USA.

Massive sulfide (above & below; 4.6 cm across) - front & back of apiece of Pt/Pd rich massive sulfide from the Johns Manville Reef


63/64

piece of Pt/Pd-rich massive sulfide from the Johns-Manville Reef,Lower Banded Seriers, Stillwater Complex (Neoarchean, 2.71 b.y.) inthe Stillwater Mine, Beartooth Mountains, Montana, USA.


64/64

Stillwater 2

Documents

Transcript of Stillwater 2