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Yogo Gulch, Yogo District, Little Belt Mts, Judith Basin Co., Montana, USA

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Latitude & Longitude (WGS84): 46° 52' 35'' North , 110° 18' 27'' West
Latitude & Longitude (decimal): 46.87639,-110.30750
GeoHash:G#: c83d9vsdb
Locality type:Gulch
Köppen climate type:BSk : Cold semi-arid (steppe) climate


A gemstone deposit located on the eastern flank of the Little Belt Mountains, about 95 km southeast of Great Falls.

An ultramafic lamprophyre (ouachitite?) dike has been mined for xenolithic sapphires of gem quality ("Yogo sapphires"). The sapphires are usually small, but free of zoning and inclusions.

This lamprophyre is very close to a carbonatite in composition. It shows phlogopite and clinopyroxene megacrysts in a matrix of phlogopite, clinopyroxene, calcite, analcime, magnetite and apatite.
The rock contains ocelli composed of calcite, dolomite, ankerite, baryte, analcime, pyrite and amphibole.

It also contains xenoliths :
- Pyrope-cpx-plagioclase granulites (12-20 kb / 850°C)
- Sapphire-pyroxene-plagioclase assemblage
- Pyroxene-phlogopite-sapphire assemblage

Select Mineral List Type

Standard Detailed Strunz Dana Chemical Elements

Mineral List


16 valid minerals.

Detailed Mineral List:

Aegirine
Formula: NaFe3+Si2O6
Reference: Canadian Mineralogist Vol. 26, pp. 81-88 (1988)
'Albite-Anorthite Series'
Description: In pyrope-cpx-plagioclase granulite xenolith.
Reference: http://www.eos.ubc.ca/personal/groat/sapphires.htm
'Amphibole Supergroup'
Formula: AX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
Reference: http://www.eos.ubc.ca/personal/groat/sapphires.htm
Analcime
Formula: Na(AlSi2O6) · H2O
Reference: http://www.eos.ubc.ca/personal/groat/sapphires.htm; Canadian Mineralogist Vol. 26, pp. 81-88 (1988)
Ankerite
Formula: Ca(Fe2+,Mg)(CO3)2
Reference: http://www.eos.ubc.ca/personal/groat/sapphires.htm
'Apatite'
Reference: http://www.eos.ubc.ca/personal/groat/sapphires.htm; Canadian Mineralogist Vol. 26, pp. 81-88 (1988)
Augite
Formula: (CaxMgyFez)(Mgy1Fez1)Si2O6
Reference: http://www.eos.ubc.ca/personal/groat/sapphires.htm
Baryte
Formula: BaSO4
Reference: http://www.eos.ubc.ca/personal/groat/sapphires.htm
Calcite
Formula: CaCO3
Reference: http://www.eos.ubc.ca/personal/groat/sapphires.htm; Canadian Mineralogist Vol. 26, pp. 81-88 (1988)
'Chlorite Group'
Reference: Canadian Mineralogist Vol. 26, pp. 81-88 (1988)
Corundum
Formula: Al2O3
Reference: If there is sapphire there must be corundum.
Corundum var: Sapphire
Formula: Al2O3
Habit: up to 15mm
Colour: Bright blue
Description: Blue (Fe2+/Ti4+ charge transfer) or purple (Cr). Xenolithic.
Reference: http://www.eos.ubc.ca/personal/groat/sapphires.htm; USGS Bull. 259
Diopside
Formula: CaMgSi2O6
Reference: http://www.eos.ubc.ca/personal/groat/sapphires.htm; Canadian Mineralogist Vol. 26, pp. 81-88 (1988)
Dolomite
Formula: CaMg(CO3)2
Reference: http://www.eos.ubc.ca/personal/groat/sapphires.htm
Hematite
Formula: Fe2O3
Reference: Canadian Mineralogist Vol. 26, pp. 81-88 (1988)
Magnetite
Formula: Fe2+Fe3+2O4
Description: With Al-rich rims. Rims pleonaste.
Reference: http://www.eos.ubc.ca/personal/groat/sapphires.htm; Canadian Mineralogist Vol. 26, pp. 81-88 (1988)
Phlogopite
Formula: KMg3(AlSi3O10)(OH)2
Description: Mg-rich core. Fe/Ba-rich rims.
Reference: http://www.eos.ubc.ca/personal/groat/sapphires.htm; Canadian Mineralogist Vol. 26, pp. 81-88 (1988)
Pyrite
Formula: FeS2
Reference: http://www.eos.ubc.ca/personal/groat/sapphires.htm
Pyrope
Formula: Mg3Al2(SiO4)3
Description: In pyrope-cpx-plagioclase granulite xenolith.
Reference: http://www.eos.ubc.ca/personal/groat/sapphires.htm
'Serpentine Subgroup'
Formula: D3[Si2O5](OH)4 D= Mg, Fe, Ni, Mn, Al, Zn
Reference: Canadian Mineralogist Vol. 26, pp. 81-88 (1988)
Spinel
Formula: MgAl2O4
Description: Rims sapphire. Mixture of Al-rich material with the Yogo magma.
Reference: http://www.eos.ubc.ca/personal/groat/sapphires.htm
Spinel var: Pleonaste
Formula: (Mg,Fe)Al2O4
Description: Rims sapphire. Mixture of Al-rich material with the Yogo magma.
Reference: http://www.eos.ubc.ca/personal/groat/sapphires.htm
Zircon
Formula: Zr(SiO4)
Reference: Canadian Mineralogist Vol. 26, pp. 81-88 (1988)

List of minerals arranged by Strunz 10th Edition classification

Group 2 - Sulphides and Sulfosalts
Pyrite2.EB.05aFeS2
Group 4 - Oxides and Hydroxides
'Corundum'4.CB.05Al2O3
var: Sapphire4.CB.05Al2O3
'Hematite'4.CB.05Fe2O3
'Magnetite'4.BB.05Fe2+Fe3+2O4
Spinel4.BB.05MgAl2O4
var: Pleonaste4.BB.05(Mg,Fe)Al2O4
Group 5 - Nitrates and Carbonates
'Ankerite'5.AB.10Ca(Fe2+,Mg)(CO3)2
'Calcite'5.AB.05CaCO3
'Dolomite'5.AB.10CaMg(CO3)2
Group 7 - Sulphates, Chromates, Molybdates and Tungstates
'Baryte'7.AD.35BaSO4
Group 9 - Silicates
'Aegirine'9.DA.25NaFe3+Si2O6
'Analcime'9.GB.05Na(AlSi2O6) · H2O
'Augite'9.DA.15(CaxMgyFez)(Mgy1Fez1)Si2O6
'Diopside'9.DA.15CaMgSi2O6
'Phlogopite'9.EC.20KMg3(AlSi3O10)(OH)2
Pyrope9.AD.25Mg3Al2(SiO4)3
Zircon9.AD.30Zr(SiO4)
Unclassified Minerals, Rocks, etc.
'Albite-Anorthite Series'-
'Amphibole Supergroup'-AX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
'Apatite'-
'Chlorite Group'-
Serpentine Subgroup-D3[Si2O5](OH)4 D= Mg, Fe, Ni, Mn, Al, Zn

List of minerals arranged by Dana 8th Edition classification

Group 2 - SULFIDES
AmBnXp, with (m+n):p = 1:2
Pyrite2.12.1.1FeS2
Group 4 - SIMPLE OXIDES
A2X3
Corundum4.3.1.1Al2O3
Hematite4.3.1.2Fe2O3
Group 7 - MULTIPLE OXIDES
AB2X4
Magnetite7.2.2.3Fe2+Fe3+2O4
Spinel7.2.1.1MgAl2O4
Group 14 - ANHYDROUS NORMAL CARBONATES
A(XO3)
Calcite14.1.1.1CaCO3
AB(XO3)2
Ankerite14.2.1.2Ca(Fe2+,Mg)(CO3)2
Dolomite14.2.1.1CaMg(CO3)2
Group 28 - ANHYDROUS ACID AND NORMAL SULFATES
AXO4
Baryte28.3.1.1BaSO4
Group 51 - NESOSILICATES Insular SiO4 Groups Only
Insular SiO4 Groups Only with cations in [6] and >[6] coordination
Pyrope51.4.3a.1Mg3Al2(SiO4)3
Insular SiO4 Groups Only with cations in >[6] coordination
Zircon51.5.2.1Zr(SiO4)
Group 65 - INOSILICATES Single-Width,Unbranched Chains,(W=1)
Single-Width Unbranched Chains, W=1 with chains P=2
Aegirine65.1.3c.2NaFe3+Si2O6
Augite65.1.3a.3(CaxMgyFez)(Mgy1Fez1)Si2O6
Diopside65.1.3a.1CaMgSi2O6
Group 71 - PHYLLOSILICATES Sheets of Six-Membered Rings
Sheets of 6-membered rings with 2:1 layers
Phlogopite71.2.2b.1KMg3(AlSi3O10)(OH)2
Group 77 - TECTOSILICATES Zeolites
Zeolite group - True zeolites
Analcime77.1.1.1Na(AlSi2O6) · H2O
Unclassified Minerals, Rocks, etc.
'Albite-Anorthite Series'-
'Amphibole Supergroup'-AX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
'Apatite'-
'Chlorite Group'-
Corundum
var: Sapphire
-Al2O3
'Serpentine Subgroup'-D3[Si2O5](OH)4 D= Mg, Fe, Ni, Mn, Al, Zn
Spinel
var: Pleonaste
-(Mg,Fe)Al2O4

List of minerals for each chemical element

HHydrogen
H Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
H AnalcimeNa(AlSi2O6) · H2O
H PhlogopiteKMg3(AlSi3O10)(OH)2
H Serpentine SubgroupD3[Si2O5](OH)4 D= Mg, Fe, Ni, Mn, Al, Zn
CCarbon
C AnkeriteCa(Fe2+,Mg)(CO3)2
C CalciteCaCO3
C DolomiteCaMg(CO3)2
OOxygen
O AegirineNaFe3+Si2O6
O Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
O AnalcimeNa(AlSi2O6) · H2O
O AnkeriteCa(Fe2+,Mg)(CO3)2
O Augite(CaxMgyFez)(Mgy1Fez1)Si2O6
O BaryteBaSO4
O CalciteCaCO3
O CorundumAl2O3
O DiopsideCaMgSi2O6
O DolomiteCaMg(CO3)2
O HematiteFe2O3
O MagnetiteFe2+Fe23+O4
O PhlogopiteKMg3(AlSi3O10)(OH)2
O Spinel (var: Pleonaste)(Mg,Fe)Al2O4
O PyropeMg3Al2(SiO4)3
O Corundum (var: Sapphire)Al2O3
O Serpentine SubgroupD3[Si2O5](OH)4 D= Mg, Fe, Ni, Mn, Al, Zn
O SpinelMgAl2O4
O ZirconZr(SiO4)
FFluorine
F Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
NaSodium
Na AegirineNaFe3+Si2O6
Na AnalcimeNa(AlSi2O6) · H2O
MgMagnesium
Mg AnkeriteCa(Fe2+,Mg)(CO3)2
Mg Augite(CaxMgyFez)(Mgy1Fez1)Si2O6
Mg DiopsideCaMgSi2O6
Mg DolomiteCaMg(CO3)2
Mg PhlogopiteKMg3(AlSi3O10)(OH)2
Mg Spinel (var: Pleonaste)(Mg,Fe)Al2O4
Mg PyropeMg3Al2(SiO4)3
Mg Serpentine SubgroupD3[Si2O5](OH)4 D= Mg, Fe, Ni, Mn, Al, Zn
Mg SpinelMgAl2O4
AlAluminium
Al Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
Al AnalcimeNa(AlSi2O6) · H2O
Al CorundumAl2O3
Al PhlogopiteKMg3(AlSi3O10)(OH)2
Al Spinel (var: Pleonaste)(Mg,Fe)Al2O4
Al PyropeMg3Al2(SiO4)3
Al Corundum (var: Sapphire)Al2O3
Al Serpentine SubgroupD3[Si2O5](OH)4 D= Mg, Fe, Ni, Mn, Al, Zn
Al SpinelMgAl2O4
SiSilicon
Si AegirineNaFe3+Si2O6
Si Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
Si AnalcimeNa(AlSi2O6) · H2O
Si Augite(CaxMgyFez)(Mgy1Fez1)Si2O6
Si DiopsideCaMgSi2O6
Si PhlogopiteKMg3(AlSi3O10)(OH)2
Si PyropeMg3Al2(SiO4)3
Si Serpentine SubgroupD3[Si2O5](OH)4 D= Mg, Fe, Ni, Mn, Al, Zn
Si ZirconZr(SiO4)
SSulfur
S BaryteBaSO4
S PyriteFeS2
ClChlorine
Cl Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
KPotassium
K PhlogopiteKMg3(AlSi3O10)(OH)2
CaCalcium
Ca AnkeriteCa(Fe2+,Mg)(CO3)2
Ca Augite(CaxMgyFez)(Mgy1Fez1)Si2O6
Ca CalciteCaCO3
Ca DiopsideCaMgSi2O6
Ca DolomiteCaMg(CO3)2
TiTitanium
Ti Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
MnManganese
Mn Serpentine SubgroupD3[Si2O5](OH)4 D= Mg, Fe, Ni, Mn, Al, Zn
FeIron
Fe AegirineNaFe3+Si2O6
Fe AnkeriteCa(Fe2+,Mg)(CO3)2
Fe Augite(CaxMgyFez)(Mgy1Fez1)Si2O6
Fe HematiteFe2O3
Fe MagnetiteFe2+Fe23+O4
Fe Spinel (var: Pleonaste)(Mg,Fe)Al2O4
Fe PyriteFeS2
Fe Serpentine SubgroupD3[Si2O5](OH)4 D= Mg, Fe, Ni, Mn, Al, Zn
NiNickel
Ni Serpentine SubgroupD3[Si2O5](OH)4 D= Mg, Fe, Ni, Mn, Al, Zn
ZnZinc
Zn Serpentine SubgroupD3[Si2O5](OH)4 D= Mg, Fe, Ni, Mn, Al, Zn
ZrZirconium
Zr ZirconZr(SiO4)
BaBarium
Ba BaryteBaSO4

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org

Permian - Devonian
251.902 - 419.2 Ma



ID: 3190586
Paleozoic sedimentary rocks

Age: Phanerozoic (251.902 - 419.2 Ma)

Lithology: Sedimentary rocks

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

Visean
330.9 - 346.7 Ma



ID: 2721726
Mission Canyon Formation: locally includes Big Snowy Formation in south-central Montana

Age: Mississippian (330.9 - 346.7 Ma)

Stratigraphic Name: Mission Canyon Formation; Big Snowy Formation

Description: Gray, massive limestone with chert beds and nodules, and solution breccia zones. Shallow marine. Thickness as much as 520 m (1,706 ft). In south-central Montana - Big Snowy Formation: Olive gray, thick-bedded limestone, yellowish gray siltstone, dark gray shale, and yellowish brown, thin bedded siltstone and mudstone. Nearshore marine. Thickness 120 m (394 ft).

Comments: Original map source: Vuke, S.M., Porter, K.W., Lonn, J.D., and Lopez, D.A., 2007, Geologic Map of Montana - Compact Disc: Montana Bureau of Mines and Geology: Geologic Map 62-C, 73 p., 2 sheets, scale 1:500,000. This map was digitized in 2012 as a result of a contract betwe

Lithology: Major:{limestone}, Minor:{siltstone,shale,mudstone}, Incidental:{chert}

Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. [133]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License

References

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Year (asc) Year (desc) Author (A-Z) Author (Z-A)
- USGS Bull 269
- Canadian Mineralogist (1988): 26: 81-88.

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