Oki C5500-5600-5700-5800-5900-6000-6100 Toner Dolum Teknikleri
GEOLOGY OF THE BUTTE MINING DISTRICT, MONTANA7789' 8251' 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5800 0 6000...
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Butte Granite (Kbg) quartz porphyry dikes (Kqp, Tmqp) Boulder Batholith aplite dikes (Ka) granite cupola carapace B-B’ Section Rhyolite pyroclastics & vent breccia (Tiv, Tvcb, Tvwb) Rhyolite dikes (Tir) Middle Paleocene rhyodacite dike & breccia Trdi Lowland Creek Volcanics Formation Big Butte Vent Complex Sparse py/Gs veins Sericite alteration zone Pre-Main Stage Mineralization Explanation Fault, showing slip direction Main Stage vein or mineralized fault Quaternary & Tertiary sediments (Qal, QTac) Rock Types Butte Granite (Kbg) quartz porphyry dikes (Kqp, Tmqp) Boulder Batholith Magnetite vein (Cu) zone Lower quartz latite pyroclastics & sediments (Tlw, Tlat, Tlt) Tlcv Middle Paleocene rhyodacite dike & breccia Trdi Lowland Creek Volcanics Formation ZnS Interior Sericite alteration zone Pre-Main Stage Mineralization Explanation Fault, showing slip direction Main Stage vein or mineralized fault Magnetite vein (Cu) zone A Blue Bird Nettie Orphan Girl Anselmo Stewart Berkeley Pit Anaconda Dome Big Butte Post-Ore Rhyolite Intrusion Limits of Modern Exposure Milwaukee fault No. 15 fault Trdi West Cupola (Inferred) Modoc qtz ppy Cupola (Inferred) Rocker fault 2.5 km 0 1 km Pittsmont Dome Continental fault Klepper fault East Ridge fault East Cupola (Inferred) Rarus fault East fault Middle fault DDH-7 DDH-6 DDH-2 DDH-10 2.5 km 1 km 0 1 km A’ B B’ A to A’ Section B” 2 km 0 0 1 km 1 km Inferred Granite Pre-Main Stage Cupola Inferred Granite Main Stage Cupola Trdi Tmqp Limits of Modern Exposure 1,500 ft. level 2,800 ft. level Kqp Mt zone Cu Ore Front Cu Ore Front DDH-7 (proj.) DDH-1, 1A (proj.) Tailings Tlcv 0.01 Mo Top of Mo 0.02 Mo 0.05 Mo 0.005 Mo 0.03 Mo 0.05 Mo 0.05 Mo 0.05 Mo 0.02 Mo 0.03 Mo 0.03 Mo 0.03 Mo 0.05 Mo 0.03 Mo Rarus fault Middle fault Badger Leonard aplite dikes (Ka) granite cupola carapace West East North South N N3 34 4°W S S3 34 4°E Tmqp Kqp Supergene Mineralization Chalcocite dominant T T r r p p u u DESCRIPTION OF MAP UNITS QUATERNARY and TERTIARY DEPOSITS Recent Alluvium deposits - Clay, silt, sand, and gravel fluvial detritus from eroded local granitic and volcanic rocks. Includes colluvium, lacustrine and terrace deposits. Landslide deposits - Poorly sorted material derived from bedrock and surficial deposits primarily occur as slump blocks and incipient rotational slumps. Older Alluvium and colluvium deposits - Poorly sorted, unconsolidated to moderately indurated, well-rounded, arkosic silt, sand, pebble and cobble detritus locally derived from granitic and volcanic rocks. Basin fill sediments near the town of Rocker are approximately 180 to 300 m thick (Feiveson, 1997; Hammar-Klose, 1997). Recent to Miocene sedimentary rocks contain locally air-fall rhyolite tuffs. Rare fossil camel, rhinoceros, horse, and oreodont teeth and bones are present in deposits south of Silver Bow Creek (Smedes et al., 1973). Locally, includes talus deposits comprised of unsorted cobble to boulder angular rock fragments and debris flow deposits adjacent to the Rocker, Continental, Klepper, and East Ridge faults, and Recent valley fill and alluvial terrace deposits (Pleistocene and Pliocene age; Elliott and McDonald, 2009). TERTIARY VOLCANIC ROCKS Lowland Creek Volcanics Formation - Modified from Smedes, (1962) Big Butte Vent Complex Rhyolite dikes - Light gray to red-brown,porphyritic rhyolite dikes and shallow irregular intrusive bodies contain plagioclase, quartz, and biotite phenocrysts surrounded in an aphanitic groundmass. Dikes south of Big Butte contain lineated flow foliation and chilled margins parallel to intrusive contacts. North of Bull Run Creek a large rhyolite intrudes dacite lavas and may be the base of an extrusive dome. Upper rhyolite pyroclastics - Light gray to reddish, moderately to strongly welded rhyolite pyroclastic rocks (ignimbrite) contain 25 to 35 volume percent crystals of shattered crystals of quartz, oligoclase-andesine, biotite, and minor sanidine in a vitroclastic matrix. Abundant fiammé have an aspect ratio of approximately 6H:1V and are circular in plan view, suggesting simple compaction. The upper rhyolite pyroclastic rocks are petrographically similar to the lower rhyolite pyroclastic rocks (Trpl), but are locally overlying Trpl along a lithic-rich basal vitrophyre, up to 5 m thick. In the north west part of the district, the occurrence of several vitrophyres, up to 5 m thick, suggests multiple cooling units. Pyroclastic breccia - Includes three subunits consisting of angular blocks (<1 m to 30 m in diameter) of granite, aplite, quartz latite ignimbrite, dacite lava, and welded rhyolite tuff surrounded in a poorly welded matrix pyroclastic rhyolite. The matrix contains broken crystal fragments of quartz, plagioclase, sanidine, and biotite. Pyroclastic breccia (<200 m wide) locally occurs at the contact of the lower rhyolite pyroclastic (Trpl) and granite (Kbg). Three subunits are subdivided based on dominant clast lithology. Trpb 1 , dominated by granite and aplite clasts. Trpb 2 , dominated by quartz latite ignimbrite blocks that locally contain distinctive eutaxitic foliation. Trpb 3 , dominated by dacite lava and breccia clasts that contain planar flow aligned plagioclase phenocrysts surrounded in an aphanitic groundmass. The pyroclastic breccia may represent the collapse of previously erupted surface rocks into the vent. Lower rhyolite pyroclastics - Light gray to reddish-brown, moderately to strongly welded rhyolite pyroclastic rocks (ignimbrite) contain 25 to 35 volume percent crystals of shattered oligoclase-andesine, quartz, biotite and sanidine in a vitroclastic matrix. The ignimbrite is intercalated locally with thin (<10 m thick) breccia lenses. Abundant (up to 20 vol. %.) cognate clasts of rhyolite and lesser amounts of partially flattened fiammé (2H:1V to 1.5V aspect ratio) are orientated parallel to the near vertical fabric. This steeply dipping foliation becomes highly contorted, locally. The rhyolite pyroclastic rocks at Big Butte have a 40 Ar/ 39 Ar age of 52.9 ± 0.14 Ma (Dudás et al., 2010). Extrusive Dacite lava - Brown to purplish red dacite lava (<120 m) consisting of abundant flow-aligned plagioclase phenocrysts (20 vol. %), biotite-rich glomerocrysts, orthopyroxene, hornblende, quartz and trace amounts of apatite and opaques are surrounded in an aphanitic groundmass (70 vol. %). There is no age determination for these dacites at Butte, but Dudás et al. (2010) suggest an age of 52.4 Ma based on a dacite sample southwest of Butte. Volcanic breccia - Light-gray, brown to purplish red breccia consists of a lower matrix- supported part and an upper clast-supported part. The lower discontinuous part (up to 50 m thick) contains subangular (less than 1 m diameter) ash-flow tuff and dacite lava fragments (60 vol. %) supported by a light-brown to very pale orange devitrified ash matrix. This lower sequence may represent a volcanic debris flow or lahar. The upper part (up to 120 m thick) of the breccia unit is dominantly framework-supported angular porphyritic dacite lava boulders (90 vol. %) up to 2 m in diameter that are enclosed in a lavender-gray dacite lava matrix. The upper breccia sequence is an autobrecciated lava along the base of the overlying dacite lava (Tll). Quartz latite ash-flow tuff - Light gray, reddish-brown and olive, poorly to strongly welded quartz latite ignimbrite contains shattered plagioclase, biotite, and hornblende crystals in a vitroclastic matrix. Eutaxitic textures are defined by conspicuous fiammé. Normal grading of lithic fragments occurs as repeated distinct zones upward in the section and correlates to 13 thin cooling units marked by distinct welding breaks. Locally, the ignimbrite is up to 300 m thick. In general, hornblende crystal abundance increases slightly from 1 to 5 vol. % upwards in the section. A vitrophyre up to 30 cm thick locally marks the basal contact. This ignimbrite has a 40 Ar/ 39 Ar age of 52.9 ± 0.14 Ma (Dudás et al., 2010) Rhyolitic air-fall tuff and base surge deposits - Light gray, unwelded laminated and cross-bedded crystal-poor ash air-fall and base surge deposit (<50 m) with up to 15 vol. % lithic fragments. This upper unit is interpreted to be the base surge and airfall deposits precursor to the overlying quartz latite ignimbrite. Volcaniclastic sedimentary deposits - Fluvial mudstone, siltstone, sandstone, and pebble conglomerate sedimentary sequences containing reworked volcaniclastic sedimentary rocks. Laminated micaceous mudstones and siltstones grade upward into coarse-grained and rippled arkosic and tuffaceous sandstones. Cross-bedding, ripples and petrified logs indicate a SSW-NNE bi-directional fluvial flow-direction. This sedimentary unit (<50 m) was deposited on an irregular erosional surface, locally marked by deeply weathered granite (grus) surrounding intensely weathered boulders of granite and aplite. Intrusive Rhyodacite dike of Rampart Mountain - Gray, porphyritic rock contains phenocrysts of plagioclase, quartz, and biotite and rare 2 cm orthoclase set in a fine-grained aplitic groundmass (Meyer et al., 1968). From east to west, this dike transects the district for >7 km at depth. Normal displacement along the Continental fault has exposed this dike on Rampart Mountain and further east in a I-15 roadcut. In the hanging wall of the Continental fault, at approximately the 2,000 foot level, a breccia at the apex of the dike, known as the Mountain View breccia, continues upward ~100 m, but is not exposed at surface (Meyer, et al., 1968). Available 40 Ar/ 39 Ar and 206 Pb/ 238 U monazite ages suggest emplacement at ~59 Ma (Dilles et al., 2004). T Tr rp pb b 3 3 T Tr rp pb b 2 2 T Tr rp pb b 1 1 Q Q a a l l Q Q T T a a c c Q Q l l s s T T i i r r T T l l a a t t T T l l t t T T l l w w T T l l l l b b T T l l l l T T r r d d i i T Tr rp pb b 1 1 T Tr rp pb b 2 2 T Tr rp pb b 3 3 LATE CRETACEOUS PLUTONIC ROCKS Boulder Batholith Modoc quartz porphyry plug, irregular intrusions and breccia - Light gray to grayish-green, porphyritic rock contains phenocrysts of plagioclase, rounded embayed quartz, sparse large (6 to 25 mm) K-feldspar, and biotite, in a very fine-grained groundmass of quartz and K-feldspar (64 Ma; Dilles et al., 2004). The Modoc quartz porphyry forms an irregular shaped plug that reaches a maximum width of ~300 m on the 2800 foot level of the Leonard mine (Meyer et al., 1968). Contacts are sinuous with moderate fragmentation of the granite (Meyer et al., 1968). Breccia fragments contain older quartz-molybdenite veinlets characteristic of the deep porphyry Cu-Mo zone. Quartz porphyry dikes - Light colored, porphyritic rock (3 to 20 m wide) contains ca. 50 vol. % aplitic groundmass and 50 vol. % phenocrysts of euhedral plagioclase, rounded quartz eyes, orthoclase and biotite phenocrysts enclosed in a fine-grained groundmass of quartz and orthoclase (66 Ma; Lund et al., 2002). Aplite, granoaplite, and pegmatite dikes and irregular intrusions - Light colored to pink dikes consisting of orthoclase, quartz, oligoclase-andesine and trace amounts of biotite, contain local occurrences of pyrite, chalcopyrite, magnetite, albitic plagioclase and very rare pyrrhotite in quartz in the core zones (Meyer et al., 1968; Smedes et al., 1962). Black tourmaline and molybdenite also occur in miarolitic cavities and are most abundant in the deepest plutonic exposures along East Ridge. Granoaplite dikes (described as a granite-aplite hybrid rock; Roberts, 1975) contain phenocrysts of plagioclase, biotite, hornblende and rounded quartz eyes entrained in fine-grained aplitic quartz and alkali feldspar groundmass (76 Ma; Lund et al., 2002). Most dikes are gently-dipping and make up parallel sheeted sets. Aplite dikes are cm- to m-thick and typically have sharp contacts with the granite. Aplite dikes locally exceed 20 m thickness and commonly zone inward to pegmatitic cores (Meyer et al., 1968). Most granoaplite dikes occur as massive gently dipping planar sheets that exceed 20 m in thickness. Contacts are gradational with the granite. Sheeted aplite dikes are abundant in the western and eastern parts of the Butte district and intrude parallel to subhorizontal joint sets observed throughout the Butte district. Mafic enclaves - Dark-green to black ellipsoidal nodules (15 to 50 cm dia.) containing crystals of plagioclase, hornblende, biotite, quartz, magnetite and minor apatite. South and adjacent to Bull Run Creek, abundant nodules occur in a linear collection (~15 by 400 meters). At this location nodules are surrounded by fine-grained granite (Kbg). Elsewhere, isolated nodules occur throughout the district. Enclaves cut by aplite dikes. Butte Granite - Gray, medium- to coarse-grained equigranular rock consists of plagioclase (35-40 vol. %), orthoclase (20-25 vol. %), quartz (15-25 vol. %), and about 20 vol. % biotite, hornblende, magnetite, titanite, ilmenite, and apatite (76.5 Ma; Meyer et al., 1968; Martin et al., 1999; Martin and Dilles, 2000, Lund et al., 2002). The granite has distinctive euhedral poikilitic K-feldspar megacrysts up to 3 cm in length (Smedes et al., 1962; Meyer et al., 1968). Occasional mafic enclaves and aplite dikes are present throughout the granite (Houston, 2001). Contact - showing dip; dashed where approximately located; and dotted where concealed Fault - showing dip; dashed where approximately located; dotted where concealed; Names shown on principal faults Vein or mineralized fault - showing dip; dotted where concealed; Names shown on principal veins Strike and dip of beds - shown in all bedded units including sedimentary rocks and sedimentary interbeds within lava flows Strike and dip of compaction foliation structure Strike and dip of rheomorphic foliation Strike and dip of joint Bidirectional paleoflow indicator Anaconda/ARCO Deep Drill Hole Locality Productive Mine Shaft Open-pit outline: Berkeley Pit and Continental Pit Waste rock Tailings pond Historic landfill References 1. Dilles, J., 1998, 2002, 2012, 1:24,000, this study. 2. Dilles, J., Stein, H., and Martin, M., and Rusk B., 2004, Re-Os and U-Pb ages for the Butte Copper District, Montana: IAVCEI Meeting, Púcon, Chile. 3. Dresser, H., 2000, Stereo Picture Guidebook to Big Butte Volcanics: Tobacco Root Geological Society, Annual Meeting, Butte, MT, August 3-6, 73 p. 4. Duaime, T., Kennelly, P., and Thale, P., 2004, Butte, Montana: Richest Hill on Earth, 100 years of underground mining, Montana Bureau of Mines and Geology: Miscellaneous Contribution 19, 1 sheet, 1:9,000. 5. Dudás, F., Ispolatov, V., Harlan, S., and Snee, L., 2010, 40 Ar/ 39 Ar Geochronology and Geochemical Reconnaissance of the Eocene Lowland Creek Volcanic Field, west-central Montana: The Journal of Geology, v. 118, No. 3, p. 295-304. 6. Elliott, C. and McDonald, C., 2009, Geologic map and geohazard assessment of Silver Bow County, Montana: Open-File Report 585, Montana Bureau of Mines and Geology, 81 p., 3 plates. 7. Feiveson, D., 1997, Seismic reflection investigation to support the existence of a normal fault in Rocker, Montana: Unpublished Senior thesis, Northfield, Minnesota, Department of Geology, Carleton College, 4 p. 8. Hammar-Klose, E., 1997, A high-resolution seismic reflection at Rocker Timber Treatment and Framing Plant site, Rocker, Montana: The College of Wooster, Keck Research Symposium in Geology, 10th, Wooster, Ohio, April 1997, p. 302–305. 9. Houston, R., 1998, 1999, mapped at 1:12,000 and 1:24,000, compiled at 1:24,000; this study. 10. Houston, R., 2001, Geology and structural history of the Butte district, Montana: Unpublished M.Sc. thesis, Corvallis, Oregon, Oregon State University, 45 p., 10 plates. 11. Lewis, R., 1998, Geologic map of the Butte 1° x 2° quadrangle, Southwestern Montana: Montana Bureau of Mines and Geology, Open File report 363, scale 1:100,000, 1 sheet, 17 p. 12. Lund, K. Aleinikoff, J., Kunk, M., Unruh, D., Zeihen, G., Hodges, W., Du Bray, E., and O‘Neill, J., 2002, SHRIMP U-Pb and 40Ar/39Ar age contrasts for relating plutonism and mineralization in the Boulder Batholith region, Montana: Economic Geology, v. 97, p. 241-267. 13. Martin, M. and Dilles, J., 2000, Timing and duration of the Butte porphyry system: Tobacco Root Geological Society, Annual Meeting, Butte, Montana, August 3-6, 2000, p. 1. 14. Martin, M., Dilles, J., and Proffett, J.M, 1999, U-Pb geochronologic constraints for the Butte porphyry system [abs.]: Geological Society of America Abstracts with Programs, v. 31, no. 7, p. A380. 15. Meyer, C., Shea, E., Goddard, C., Jr., and Staff, 1968, Ore deposits at Butte, Montana, in Ridge, J., ed., Ore deposits of the United States, 1933-67, v. 2: New York, American Institute of Mining, Metallurgical, and Petroleum Engineers, p. 1373-1416. 16. Proffett, J.M., Jr., 1973, Structure of the Butte district, Montana: in Miller, R., ed., Guidebook for the Butte field meeting of the Society of Economic Geologists, The Anaconda Company, Butte, Montana, p. G-1 to G-12, plus figures. 17. Proffett, J.M., Burns, G., and Anaconda staff, 1982, Geologic map of the Butte district, Montana: Anaconda Archives, American Heritage Museum, Laramie, Wyoming, scale 1:12,000. 18. Reed, M., 1979 a and b, written communication. 19. Roberts, S., 1975, Early hydrothermal alteration and mineralization in the Butte district, Montana: Ph.D. thesis, Cambridge, Mass., Harvard University, 173 p. 20. Sales, R., 1914, Ore deposits at Butte, Montana: American Institute of Mining and Metallurgical Engineers Transactions, v. 46, p. 4-106. 21. Smedes, H., 1962, Lowland Creek Volcanics, an Upper Oligocene formation near Butte, Montana: Journal of Geology, v. 70, p. 255-266. 22. Smedes, H., 1967, Preliminary geologic map of the northeast quarter of Butte South Quadrangle, Montana: U.S. Geological Survey, Open File Map, 1:24,000. 23. Smedes, H., 1968, Preliminary geologic map of part of the Butte North Quadrangle, Silver Bow, Deer Lodge and Jefferson Counties, Montana: U.S. Geological Survey Open-File Report, Scale 1:48,000. 24. Smedes, H., Klepper, M., Pinckney, D., Becraft, G., and Ruppel, E., 1962, Preliminary geologic map of the Elk Park Quadrangle, Jefferson and Silver Bow Counties, Montana: U.S. Geological Survey map MF-246, Scale 1:24,000. 25. Smedes, H., Klepper, M., and Tilling, R., 1973, The Boulder Batholith, Montana: in Miller, R., ed., Guidebook for the Butte field meeting of the Society of Economic Geologists, The Anaconda Company, Butte, Montana, p. E-1 to E-16. 26. Smedes, H., Klepper, M., and Tilling, R., 1988, Preliminary map of plutonic units of the Boulder Batholith, southwestern Montana: Montana Bureau of Mines and Geology, Open-File Report 88-283, Scale 1:200,000 (& digital reprinted USGS Data Series 454, 2009). 27. Weed, W.H., 1912, Geology and ore deposits of the Butte district, Montana: U.S. Geological Survey Professional Paper 74, 262 p. Acknowledgments This research was supported by grants from the Tobacco Root Geological Society to Houston, and by NSF grants EAR-9614683 and EAR-0001230 to Dilles and Cyrus Field of Oregon State University. We greatly thank the many geologists who contributed scientific research to advance the knowledge of the geology of the Butte deposit over the last 140 years, and we acknowledge the research sponsorship until 1986 by the Anaconda Company and its successor the Atlantic Richfield Company. Steve Czehura of Montana Resources Inc. kindly provided many informative discussions as well as unpublished data of the Butte district, including geologic maps made by George Burns and John Proffett. Review of an earlier version by Professors Cyrus Field, Edward Taylor and Robert Yeats, when it was part of a M.Sc. thesis by Houston, is greatly appre- ciated. We gratefully acknowledge two Economic Geology reviewers John Proffett and David Cooke, who reviewed the map as part of the formal review process of the manuscript (Houston and Dilles, 2013). Finally, the senior author is indebted to the residents of the study area who freely gave their permission to traverse their properties. K K a a K K q q p p K K b b g g K K m m e e T T m m q q p p D U 78 85 D U 64 25 15 10 75 DDH-8 25 9 1, 9, and 23 9, 17, and 23 9, 17, 16, 1, 27, 24, 22, 15, 26, 4, 11, 20 and 18 Complied by R.A. Houston Index Map showing credit for geologic mapping noted by reference number Montana Bureau of Mines and Geology Open File MBMG 627 GEOLOGY OF THE BUTTE MINING DISTRICT, MONTANA Robert A. Houston 1 and John H. Dilles 2 2013 1 Oregon Department of Geology and Mineral Industries, Albany, Oregon 2 Oregon State University, Corvallis, Oregon This map supplements Houston and Dilles, 2013, Structural Geologic Evolution of the Butte District, Montana: Economic Geology, v. 108, no. 6, p. 1397-1424. Q Q T T a a c c T T r r p p l l T T l l l l T T l l t t T T l l w w K K a a K K q q p p K K b b g g T T r r d d i i K K m m e e T T l l l l b b T T r r p p u u T T i i r r Q Q a a l l T T l l a a t t T T m m q q p p Q Q l l s s Main Stage Mineralization Eocene Late Cretaceous QUATERNARY Paleocene CRETACEOUS TERTIARY Recent Recent to Miocene Pre-Main Stage Mineralization CORRELATION OF MAP AND CROSS SECTION UNITS T T r r p p l l Maps may be obtained from: Publications Office Montana Bureau of Mines and Geology 1300 West Park Street Butte, Montana 59701-8997 Phone: (406) 496-4167 Fax: (406) 496-4451 http://www.mbmg.mtech.edu Open File MBMG 627, Plate 1 of 1 Geology of the Butte mining district, MT, 2013 MONTANA BUREAU OF MINES AND GEOLOGY A Department of Montana Tech of The University of Montana A A’ ’ A A B B B B’ ’ B B’ ’’ ’
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MONTANA
BUTTE DISTRICT LOCATION
GEOLOGY OF THE BUTTE MINING DISTRICT, MONTANA
Base map modified from four U.S. Geological Survey 7.5 minute topographic quadrangles;Butte North (1989), Butte South (1989), Elk Park Pass (1985), and Homestake (1978).
Butte Granite(Kbg)
quartz porphyry dikes(Kqp, Tmqp)
Boulder Batholithaplite dikes(Ka)
granite cupolacarapace
B-B
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ectio
n
Rhyolite pyroclastics & ventbreccia (Tiv, Tvcb, Tvwb)
Rhyolite dikes(Tir)
Middle Paleocenerhyodacite dike & brecciaTrdi
Lowland Creek VolcanicsFormation Big Butte VentComplex Sparse py/Gs veins
Sericite alteration zone
Pre-Main Stage MineralizationExplanationFault, showingslip directionMain Stage vein ormineralized fault
Quaternary &Tertiary sediments(Qal, QTac)
Rock Types
Butte Granite(Kbg)
quartz porphyry dikes(Kqp, Tmqp)
Boulder BatholithMagnetite vein (Cu) zone
Lower quartz latite pyroclastics& sediments (Tlw, Tlat, Tlt)Tlcv
Middle Paleocenerhyodacite dike & brecciaTrdi
Lowland Creek VolcanicsFormation
ZnSInterior
Sericite alteration zone
Pre-Main Stage MineralizationExplanationFault, showingslip directionMain Stage vein ormineralized fault
Magnetite vein (Cu) zone
A
Blue Bird NettieOrphan Girl
Anselmo Stewart
Berkeley Pit
Anaconda DomeBig Butte Post-OreRhyolite Intrusion
Limits ofModernExposure
Milwau
kee fau
lt
No.
15fa
ult
TrdiWest
Cupola(Inferred)
Modoc qtz ppyCupola (Inferred)
Rocker fault
2.5 km
0
1 km
Pittsmont Dome
Continental faultKlepper fault
East
Rid
gefa
ult
EastCupola
(Inferred)
Rarus
fault East fault
Middle fault
DD
H-7
DD
H-6
DD
H-2
DD
H-1
0
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1 km
0
1 km
A’B B’ A to A’
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00
1 km
1 km
Inferred GranitePre-Main Stage
CupolaInferred Granite
Main Stage Cupola
Trdi
TmqpLimits ofModernExposure
1,500 ft. level
2,800 ft. level
Kqp
Mtzone
Cu
Ore
Fron
t
Cu
Ore
Front
DD
H-7
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DD
H-1
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0.01 Mo
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0.02 Mo0.05 Mo 0.005
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0.05M
o0.05 Mo
0.05 Mo
0.02 Mo
0.03 Mo
0.03 Mo 0.03M
o 0.05M
o0.03
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Rarus fault
Middle faultBadger Leonard
aplite dikes(Ka)
granite cupolacarapace
West East
NorthSouthNN3344°W
SS3344°E
Tmqp
Kqp
Supergene MineralizationChalcocite dominant
TTrrppuu
DESCRIPTION OF MAP UNITS
QUATERNARY and TERTIARY DEPOSITS
Recent Alluvium deposits - Clay, silt, sand, and gravel fluvial detritus from eroded localgranitic and volcanic rocks. Includes colluvium, lacustrine and terrace deposits.
Landslide deposits - Poorly sorted material derived from bedrock and surficial depositsprimarily occur as slump blocks and incipient rotational slumps.
Older Alluvium and colluvium deposits - Poorly sorted, unconsolidated to moderatelyindurated, well-rounded, arkosic silt, sand, pebble and cobble detritus locallyderived from granitic and volcanic rocks. Basin fill sediments near the town ofRocker are approximately 180 to 300 m thick (Feiveson, 1997; Hammar-Klose,1997). Recent to Miocene sedimentary rocks contain locally air-fall rhyolite tuffs.Rare fossil camel, rhinoceros, horse, and oreodont teeth and bones are present indeposits south of Silver Bow Creek (Smedes et al., 1973). Locally, includes talusdeposits comprised of unsorted cobble to boulder angular rock fragments and debrisflow deposits adjacent to the Rocker, Continental, Klepper, and East Ridge faults,and Recent valley fill and alluvial terrace deposits (Pleistocene and Pliocene age;Elliott and McDonald, 2009).
TERTIARY VOLCANIC ROCKS
Lowland Creek Volcanics Formation - Modified from Smedes, (1962)
Big Butte Vent ComplexRhyolite dikes - Light gray to red-brown, porphyritic rhyolite dikes and shallow irregular
intrusive bodies contain plagioclase, quartz, and biotite phenocrysts surrounded in anaphanitic groundmass. Dikes south of Big Butte contain lineated flow foliation andchilled margins parallel to intrusive contacts. North of Bull Run Creek a large rhyoliteintrudes dacite lavas and may be the base of an extrusive dome.
Upper rhyolite pyroclastics - Light gray to reddish, moderately to strongly welded rhyolitepyroclastic rocks (ignimbrite) contain 25 to 35 volume percent crystals of shatteredcrystals of quartz, oligoclase-andesine, biotite, and minor sanidine in a vitroclasticmatrix. Abundant fiammé have an aspect ratio of approximately 6H:1V and arecircular in plan view, suggesting simple compaction. The upper rhyolite pyroclasticrocks are petrographically similar to the lower rhyolite pyroclastic rocks (Trpl), but arelocally overlying Trpl along a lithic-rich basal vitrophyre, up to 5 m thick. In the northwest part of the district, the occurrence of several vitrophyres, up to 5 m thick,suggests multiple cooling units.
Pyroclastic breccia - Includes three subunits consisting of angular blocks (<1 m to 30 m indiameter) of granite, aplite, quartz latite ignimbrite, dacite lava, and welded rhyolitetuff surrounded in a poorly welded matrix pyroclastic rhyolite. The matrix containsbroken crystal fragments of quartz, plagioclase, sanidine, and biotite. Pyroclasticbreccia (<200 m wide) locally occurs at the contact of the lower rhyolite pyroclastic(Trpl) and granite (Kbg). Three subunits are subdivided based on dominant clastlithology. Trpb1, dominated by granite and aplite clasts. Trpb2, dominated by quartzlatite ignimbrite blocks that locally contain distinctive eutaxitic foliation. Trpb3,dominated by dacite lava and breccia clasts that contain planar flow alignedplagioclase phenocrysts surrounded in an aphanitic groundmass. The pyroclasticbreccia may represent the collapse of previously erupted surface rocks into the vent.
Lower rhyolite pyroclastics - Light gray to reddish-brown, moderately to strongly weldedrhyolite pyroclastic rocks (ignimbrite) contain 25 to 35 volume percent crystals ofshattered oligoclase-andesine, quartz, biotite and sanidine in a vitroclastic matrix.The ignimbrite is intercalated locally with thin (<10 m thick) breccia lenses. Abundant(up to 20 vol. %.) cognate clasts of rhyolite and lesser amounts of partially flattenedfiammé (2H:1V to 1.5V aspect ratio) are orientated parallel to the near vertical fabric.This steeply dipping foliation becomes highly contorted, locally. The rhyolitepyroclastic rocks at Big Butte have a 40Ar/39Ar age of 52.9 ± 0.14 Ma (Dudás et al.,2010).
ExtrusiveDacite lava - Brown to purplish red dacite lava (<120 m) consisting of abundant flow-aligned
plagioclase phenocrysts (20 vol. %), biotite-rich glomerocrysts, orthopyroxene,hornblende, quartz and trace amounts of apatite and opaques are surrounded in anaphanitic groundmass (70 vol. %). There is no age determination for these dacitesat Butte, but Dudás et al. (2010) suggest an age of 52.4 Ma based on a dacitesample southwest of Butte.
Volcanic breccia - Light-gray, brown to purplish red breccia consists of a lower matrix-supported part and an upper clast-supported part. The lower discontinuous part (upto 50 m thick) contains subangular (less than 1 m diameter) ash-flow tuff and dacitelava fragments (60 vol. %) supported by a light-brown to very pale orange devitrifiedash matrix. This lower sequence may represent a volcanic debris flow or lahar. Theupper part (up to 120 m thick) of the breccia unit is dominantly framework-supportedangular porphyritic dacite lava boulders (90 vol. %) up to 2 m in diameter that areenclosed in a lavender-gray dacite lava matrix. The upper breccia sequence is anautobrecciated lava along the base of the overlying dacite lava (Tll).
Quartz latite ash-flow tuff - Light gray, reddish-brown and olive, poorly to strongly weldedquartz latite ignimbrite contains shattered plagioclase, biotite, and hornblendecrystals in a vitroclastic matrix. Eutaxitic textures are defined by conspicuous fiammé.Normal grading of lithic fragments occurs as repeated distinct zones upward in thesection and correlates to 13 thin cooling units marked by distinct welding breaks.Locally, the ignimbrite is up to 300 m thick. In general, hornblende crystal abundanceincreases slightly from 1 to 5 vol. % upwards in the section. A vitrophyre up to 30 cmthick locally marks the basal contact. This ignimbrite has a 40Ar/39Ar age of 52.9 ±0.14 Ma (Dudás et al., 2010)
Rhyolitic air-fall tuff and base surge deposits - Light gray, unwelded laminated andcross-bedded crystal-poor ash air-fall and base surge deposit (<50 m) with up to 15vol. % lithic fragments. This upper unit is interpreted to be the base surge and airfalldeposits precursor to the overlying quartz latite ignimbrite.
Volcaniclastic sedimentary deposits - Fluvial mudstone, siltstone, sandstone, andpebble conglomerate sedimentary sequences containing reworked volcaniclasticsedimentary rocks. Laminated micaceous mudstones and siltstones grade upwardinto coarse-grained and rippled arkosic and tuffaceous sandstones. Cross-bedding,ripples and petrified logs indicate a SSW-NNE bi-directional fluvial flow-direction.This sedimentary unit (<50 m) was deposited on an irregular erosional surface, locallymarked by deeply weathered granite (grus) surrounding intensely weatheredboulders of granite and aplite.
IntrusiveRhyodacite dike of Rampart Mountain - Gray, porphyritic rock contains phenocrysts of
plagioclase, quartz, and biotite and rare 2 cm orthoclase set in a fine-grained apliticgroundmass (Meyer et al., 1968). From east to west, this dike transects the districtfor >7 km at depth. Normal displacement along the Continental fault has exposedthis dike on Rampart Mountain and further east in a I-15 roadcut. In the hanging wallof the Continental fault, at approximately the 2,000 foot level, a breccia at the apexof the dike, known as the Mountain View breccia, continues upward ~100 m, but isnot exposed at surface (Meyer, et al., 1968). Available 40Ar/39Ar and 206Pb/238Umonazite ages suggest emplacement at ~59 Ma (Dilles et al., 2004).
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LATE CRETACEOUS PLUTONIC ROCKSBoulder Batholith
Modoc quartz porphyry plug, irregular intrusions and breccia - Light gray to grayish-green,porphyritic rock contains phenocrysts of plagioclase, rounded embayed quartz, sparselarge (6 to 25 mm) K-feldspar, and biotite, in a very fine-grained groundmass of quartzand K-feldspar (64 Ma; Dilles et al., 2004). The Modoc quartz porphyry forms an irregularshaped plug that reaches a maximum width of ~300 m on the 2800 foot level of theLeonard mine (Meyer et al., 1968). Contacts are sinuous with moderate fragmentation ofthe granite (Meyer et al., 1968). Breccia fragments contain older quartz-molybdeniteveinlets characteristic of the deep porphyry Cu-Mo zone.
Quartz porphyry dikes - Light colored, porphyritic rock (3 to 20 m wide) contains ca. 50 vol. %aplitic groundmass and 50 vol. % phenocrysts of euhedral plagioclase, rounded quartzeyes, orthoclase and biotite phenocrysts enclosed in a fine-grained groundmass ofquartz and orthoclase (66 Ma; Lund et al., 2002).
Aplite, granoaplite, and pegmatite dikes and irregular intrusions - Light colored to pinkdikes consisting of orthoclase, quartz, oligoclase-andesine and trace amounts of biotite,contain local occurrences of pyrite, chalcopyrite, magnetite, albitic plagioclase and veryrare pyrrhotite in quartz in the core zones (Meyer et al., 1968; Smedes et al., 1962).Black tourmaline and molybdenite also occur in miarolitic cavities and are most abundantin the deepest plutonic exposures along East Ridge. Granoaplite dikes (described as agranite-aplite hybrid rock; Roberts, 1975) contain phenocrysts of plagioclase, biotite,hornblende and rounded quartz eyes entrained in fine-grained aplitic quartz and alkalifeldspar groundmass (76 Ma; Lund et al., 2002). Most dikes are gently-dipping andmake up parallel sheeted sets. Aplite dikes are cm- to m-thick and typically have sharpcontacts with the granite. Aplite dikes locally exceed 20 m thickness and commonly zoneinward to pegmatitic cores (Meyer et al., 1968). Most granoaplite dikes occur as massivegently dipping planar sheets that exceed 20 m in thickness. Contacts are gradationalwith the granite. Sheeted aplite dikes are abundant in the western and eastern parts ofthe Butte district and intrude parallel to subhorizontal joint sets observed throughout theButte district.
Mafic enclaves - Dark-green to black ellipsoidal nodules (15 to 50 cm dia.) containing crystals ofplagioclase, hornblende, biotite, quartz, magnetite and minor apatite. South and adjacentto Bull Run Creek, abundant nodules occur in a linear collection (~15 by 400 meters). Atthis location nodules are surrounded by fine-grained granite (Kbg). Elsewhere, isolatednodules occur throughout the district. Enclaves cut by aplite dikes.
Butte Granite - Gray, medium- to coarse-grained equigranular rock consists of plagioclase(35-40 vol. %), orthoclase (20-25 vol. %), quartz (15-25 vol. %), and about 20 vol. %biotite, hornblende, magnetite, titanite, ilmenite, and apatite (76.5 Ma; Meyer et al.,1968; Martin et al., 1999; Martin and Dilles, 2000, Lund et al., 2002). The granitehas distinctive euhedral poikilitic K-feldspar megacrysts up to 3 cm in length (Smedes etal., 1962; Meyer et al., 1968). Occasional mafic enclaves and aplite dikes are presentthroughout the granite (Houston, 2001).
Contact - showing dip; dashed where approximately located; anddotted where concealed
Fault - showing dip; dashed where approximately located;dotted where concealed; Names shown on principal faults
Vein or mineralized fault - showing dip; dotted where concealed;Names shown on principal veins
Strike and dip of beds - shown in all bedded units includingsedimentary rocks and sedimentary interbeds within lava flows
Strike and dip of compaction foliation structure
Strike and dip of rheomorphic foliation
Strike and dip of joint
Bidirectional paleoflow indicator
Anaconda/ARCO Deep Drill Hole Locality
Productive Mine Shaft
Open-pit outline: Berkeley Pit and Continental Pit
Waste rock Tailings pond Historic landfill
References1. Dilles, J., 1998, 2002, 2012, 1:24,000, this study.2. Dilles, J., Stein, H., and Martin, M., and Rusk B., 2004, Re-Os and U-Pb ages for the Butte
Copper District, Montana: IAVCEI Meeting, Púcon, Chile.3. Dresser, H., 2000, Stereo Picture Guidebook to Big Butte Volcanics: Tobacco Root Geological
Society, Annual Meeting, Butte, MT, August 3-6, 73 p.4. Duaime, T., Kennelly, P., and Thale, P., 2004, Butte, Montana: Richest Hill on Earth, 100 years
of underground mining, Montana Bureau of Mines and Geology: MiscellaneousContribution 19, 1 sheet, 1:9,000.
5. Dudás, F., Ispolatov, V., Harlan, S., and Snee, L., 2010, 40Ar/39Ar Geochronology andGeochemical Reconnaissance of the Eocene Lowland Creek Volcanic Field, west-centralMontana: The Journal of Geology, v. 118, No. 3, p. 295-304.
6. Elliott, C. and McDonald, C., 2009, Geologic map and geohazard assessment of Silver BowCounty, Montana: Open-File Report 585, Montana Bureau of Mines and Geology, 81 p.,3 plates.
7. Feiveson, D., 1997, Seismic reflection investigation to support the existence of a normal fault inRocker, Montana: Unpublished Senior thesis, Northfield, Minnesota, Department ofGeology, Carleton College, 4 p.
8. Hammar-Klose, E., 1997, A high-resolution seismic reflection at Rocker Timber Treatmentand Framing Plant site, Rocker, Montana: The College of Wooster, Keck ResearchSymposium in Geology, 10th, Wooster, Ohio, April 1997, p. 302–305.
9. Houston, R., 1998, 1999, mapped at 1:12,000 and 1:24,000, compiled at 1:24,000; this study.10. Houston, R., 2001, Geology and structural history of the Butte district, Montana: Unpublished
M.Sc. thesis, Corvallis, Oregon, Oregon State University, 45 p., 10 plates.11. Lewis, R., 1998, Geologic map of the Butte 1° x 2° quadrangle, Southwestern Montana:
Montana Bureau of Mines and Geology, Open File report 363, scale 1:100,000, 1 sheet,17 p.
12. Lund, K. Aleinikoff, J., Kunk, M., Unruh, D., Zeihen, G., Hodges, W., Du Bray, E., andO‘Neill, J., 2002, SHRIMP U-Pb and 40Ar/39Ar age contrasts for relating plutonism andmineralization in the Boulder Batholith region, Montana: Economic Geology, v. 97,p. 241-267.
13. Martin, M. and Dilles, J., 2000, Timing and duration of the Butte porphyry system: TobaccoRoot Geological Society, Annual Meeting, Butte, Montana, August 3-6, 2000, p. 1.
14. Martin, M., Dilles, J., and Proffett, J.M, 1999, U-Pb geochronologic constraints for the Butteporphyry system [abs.]: Geological Society of America Abstracts with Programs, v. 31,no. 7, p. A380.
15. Meyer, C., Shea, E., Goddard, C., Jr., and Staff, 1968, Ore deposits at Butte, Montana, inRidge, J., ed., Ore deposits of the United States, 1933-67, v. 2: New York, AmericanInstitute of Mining, Metallurgical, and Petroleum Engineers, p. 1373-1416.
16. Proffett, J.M., Jr., 1973, Structure of the Butte district, Montana: in Miller, R., ed., Guidebookfor the Butte field meeting of the Society of Economic Geologists, The AnacondaCompany, Butte, Montana, p. G-1 to G-12, plus figures.
17. Proffett, J.M., Burns, G., and Anaconda staff, 1982, Geologic map of the Butte district,Montana: Anaconda Archives, American Heritage Museum, Laramie, Wyoming, scale1:12,000.
18. Reed, M., 1979 a and b, written communication.19. Roberts, S., 1975, Early hydrothermal alteration and mineralization in the Butte district,
Montana: Ph.D. thesis, Cambridge, Mass., Harvard University, 173 p.20. Sales, R., 1914, Ore deposits at Butte, Montana: American Institute of Mining and
Metallurgical Engineers Transactions, v. 46, p. 4-106.21. Smedes, H., 1962, Lowland Creek Volcanics, an Upper Oligocene formation near Butte,
Montana: Journal of Geology, v. 70, p. 255-266.22. Smedes, H., 1967, Preliminary geologic map of the northeast quarter of Butte South
Quadrangle, Montana: U.S. Geological Survey, Open File Map, 1:24,000.23. Smedes, H., 1968, Preliminary geologic map of part of the Butte North Quadrangle, Silver
Bow, Deer Lodge and Jefferson Counties, Montana: U.S. Geological Survey Open-FileReport, Scale 1:48,000.
24. Smedes, H., Klepper, M., Pinckney, D., Becraft, G., and Ruppel, E., 1962, Preliminarygeologic map of the Elk Park Quadrangle, Jefferson and Silver Bow Counties, Montana:U.S. Geological Survey map MF-246, Scale 1:24,000.
25. Smedes, H., Klepper, M., and Tilling, R., 1973, The Boulder Batholith, Montana: in Miller, R.,ed., Guidebook for the Butte field meeting of the Society of Economic Geologists, TheAnaconda Company, Butte, Montana, p. E-1 to E-16.
26. Smedes, H., Klepper, M., and Tilling, R., 1988, Preliminary map of plutonic units of theBoulder Batholith, southwestern Montana: Montana Bureau of Mines and Geology,Open-File Report 88-283, Scale 1:200,000 (& digital reprinted USGS Data Series 454,2009).
27. Weed, W.H., 1912, Geology and ore deposits of the Butte district, Montana: U.S. GeologicalSurvey Professional Paper 74, 262 p.
AcknowledgmentsThis research was supported by grants from the Tobacco Root Geological Society toHouston, and by NSF grants EAR-9614683 and EAR-0001230 to Dilles and Cyrus Field of OregonState University. We greatly thank the many geologists who contributed scientific research toadvance the knowledge of the geology of the Butte deposit over the last 140 years, and weacknowledge the research sponsorship until 1986 by the Anaconda Company and its successorthe Atlantic Richfield Company. Steve Czehura of Montana Resources Inc. kindly provided manyinformative discussions as well as unpublished data of the Butte district, including geologic mapsmade by George Burns and John Proffett. Review of an earlier version by Professors Cyrus Field,Edward Taylor and Robert Yeats, when it was part of a M.Sc. thesis by Houston, is greatly appre-ciated. We gratefully acknowledge two Economic Geology reviewers John Proffett and DavidCooke, who reviewed the map as part of the formal review process of the manuscript (Houstonand Dilles, 2013). Finally, the senior author is indebted to the residents of the study area whofreely gave their permission to traverse their properties.
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4, 11, 20 and 18Complied byR.A. Houston
Index Map showing credit for geologicmapping noted by reference number
Montana Bureau of Mines and GeologyOpen File MBMG 627
GEOLOGY OF THE BUTTE MINING DISTRICT,MONTANA
Robert A. Houston1 and John H. Dilles2
2013
1Oregon Department of Geology and Mineral Industries, Albany, Oregon2Oregon State University, Corvallis, Oregon
This map supplements Houston and Dilles, 2013, StructuralGeologic Evolution of the Butte District, Montana: Economic
Geology, v. 108, no. 6, p. 1397-1424.
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Main Stage Mineralization
Eocene
LateCretaceous
QUATERNARY
Paleocene
CRETACEOUS
TERTIARY
RecentRecent toMiocene
Pre-Main Stage Mineralization
CORRELATION OF MAP AND CROSS SECTION UNITS
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Maps may be obtained from:Publications Office
Montana Bureau of Mines and Geology1300 West Park Street
Butte, Montana 59701-8997Phone: (406) 496-4167 Fax: (406) 496-4451
http://www.mbmg.mtech.edu
Open File MBMG 627, Plate 1 of 1Geology of the Butte mining district, MT, 2013
MONTANA BUREAU OF MINES AND GEOLOGYA Department of Montana Tech of The University of Montana
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