BENEFICIATING AND SMELTING CARTER CREEK, MONT., IRON ORE
By Wesley T. Holmes II, W. Floyd Holbrook, and Lloyd H . Banning
...... • • • • • • report of investigations 5922
UNITED STATES DEPARTMENT OF THE INTERIOR Stewart L. Udall, Secretary
BUREAU OF MINES Marling J. Ankeny, Director Precambrian Geology anc Bedded Iron Deposits of tht Southwestern Ruby Rang~, . M ontar;ia
U '~S ·~ GEOLOGICAL SURVEY PROFESSIONAi PAPEll f .'4 '115; 24 PRECAMBRIAN GEOLOOY AND B&ODED IRON DEPOSITS. RUBY RANGE. MON'l'ANA folds that were subsequently deformed oo one or mon, Tyldal. 1976b: RuppeL 1982) &Del will bereviowed ooly eet.o of croHfolds tMcLelland and Isachsen, 1980). brie.fly h...,. At the beeu,ning of Paleozoic time, the Ruby Range area was st.ill an upland. By mid.Cambrian time, bow· PROTEROZOIC over, the entire resion was covered by• shallow marine se.a t.hat persisted. with some break,. Into MNOtoic The geologic record of the approximetely 2 billion time. In the vicinity of tbe prNent Ruby Ran,e. Palto, yean of Precambrian time that followed the major :roic etrata accumulated to an agsrecate thlclmeaa of """ifflY of the Late Archean is extremel,y sparM. about 5,000 ~ tTylldal, 1976b). In the nonhern part of by documenta loot.opic evidence developed Oileu.i (19661 the range. tbe11 strata are woll p,.oerved in down· a regional thermal rise in Precambrian terranea of dropped fault blocks (Tyodal, 1976"1. but they have been aoutbweotern Montana west of tbe OaDatin Rlver about stripped complet.ol,y from t.he cryat.aliine basement in 1.650 m.y. ago. It la probablo that thi1 also mazb tbe the south,...tan, Ruby ftan,e. dme of widespread ,.trograde metamorphism of older Secl.imentat.lon. in ·part in noomarlne cont!Mntal Precambrian rocks of the Ruby Range and the emplace, basins of linutad extent. cont.lnued through the ment of tourmaline-bearing zoned pegmatites. The only Meeozoic .and into Cenoo.oic U- in much of aouth· other roclt·lonnlnr evento known during Proterozoic western Mootana. In the vicinity of tha Ruby Range, tim4' were the emplacement of diabue dikes about Paleozoic strata on, unconformably overlain by tha COD· 1.425 m.y. ago and tho format.ion of talc depoelts. glomeratic Beaverbeed Group. This daat.lc cwpooit 1'bia moaaer record of events ie ,um.med up as follows, mazka the eazly stages of uplift of basement blocks on old11t to youngHt: newly formed northeast-trending fault.o. CootinlMd I. Following doae of the Lato Archeu, orogeny. the movement on t.be&e faults and on rejuvenated ,.clon remaiMd structurally qujMcent for approx· nortbwui-trending faults produced intermoat1De im.ataly years. 1 billion basina, which became olt.oe of accumulation for thick 2. Sometime late in the Early Proterotolc &Del claatic dtpOSlta of Eoceoe and youngw age. Uplift. of culminating about 1,650 m.y. the roclts of ago, the buement blocks culminated. in • rep,nal - in lat<, Ruby Ranp .,.. wen, subjected to a gswal rise Tertiary U- {Ruppel. 1982). in tampecature. This ....ulted ·in eneoalve retro- The final rteerded 11.ruetural eV11Dt in the aoutlnrui- a:rade met.amcrph.ilm and emplaoament of ecattered ern Ruby Ranp was movemoat oo tbe rejuvenated small bodies of permatita, ~zoned.No firm Stone Creek fault and Corter Creek fault, which pro- qu.antit.at.ive data on, available ta indicate tba duced a 600-~ vorucal offOK in a bull& flow of Pliocae te~prenure coaditlons dllrinr this eveot. age. The S'WOKWltar Buin. on tbe doorndropped - 3. Immediately preceding tand poelibl,y in part con- of tbe fault. wu later covered to a aballow depth witb temporaneous with) diabue dike inlnlsioa at about claatlc m.ai.iala: depoaita, together with the 1,425 m.y., the Precambrian crystalline rocks we,. alluvium along aomet- 9tl'eaml, coostilate the youngeat offeet on steeply dipping nonh....t-treD
PHANEROZOIC IRON
The post-Proterozoic history of oouthwestlnl Mon· At previoualy described. banded iroo-form.atlon WU tan.a is complex and bu been ably documented in many deposited in at lout two and probably eeveral atzat.i• swdiee {for example, Klopper, 1950: Scholten, 1968: a:raphic levala in the initial sedimentary sequea,,e that MINERAL RESOURCES 25 now makes up the Christensen Ranch Metasedimentary chemistry of the iron-formation of the Carter Creek Suite. The principal deposits, however, are believed to deposit is the low content of manganese and the represent a single stratigraphic unit that generally relatively high phosphorous. ranges in true thickness from about 40 ft to 100 ft. The Beneficiation tests were run on bulk samples by the major area of economic interest and possible develop- U.S. Bureau of Mines, using magnetic separation. The ment, known as the "Carter Creek deposit," is a fold results on three runs, using ball-mill grinding (pre- belt approximately 2.5 mi long and several hundred feet sumably to -100 mesh) and wet magnetic separation, wide between the Hoffman Gulch and Carter Creek are summarized as follows (from Holmes and others, faults, mainly in secs. 3, 9, and 10, T. 8 S., R. 7 W. 1962, p. 10): Elsewhere, particularly in the structural block between Test number ...... 1 2 3 the Carter Creek and Stone Creek faults, iron-formation Quantity, tons ...... 22 34.7 72.7 probably at the same initial stratigraphic position can Initial Fe content, percent ...... 31.5 31.9 31.9 be traced continuously in belts several miles long, but Fe recovery, percent ...... 88.1 85.9 84.0 these lack the structural duplication necessary to pro- Concentrate: duce volumes of iron-formation worthy of serious Fe, percent ...... 55.9 57.5 61.1 Si0 , percent ...... 7.15 16.6 12.6 economic consideration. 2 The distribution and structure of the iron-formation The concentrate assays compare unfavorably with those that makes up the Carter Creek deposit are shown in of pelletized concentrates now being used in iron and figure 6, which is based on the previously published steel plants in the United States, which typically con- detailed map of the area (James and Wier, 1972b). The tain 63-64 percent Fe and about 5 percent Si02. Addi· general structure of this belt is that of an overturned tional laboratory-scale tests on concentrate by the U.S. sequence tightly compressed into a number of Bureau of Mines, involving regrinding to -325 mesh and northeast· to east-trending, northwest· to north-dipping reprocessing, resulted in a product containing 69.8 per- isoclines. In a few places, however, notably in sec. 9, the cent Fe, at 97.2 percent recovery. In appraising the iron-formation is contained in open gentle folds that are results of these beneficiation tests, it is to be noted that approximately co-axial (but not co-planar) with the specularite, a significant constituent in some parts of isoclines. the iron-formation, cannot generally be recovered by The iron-formation is bounded on the north and north· magnetic methods alone. west by stratigraphically lower mica schist and quartz· Exploration of the Carter Creek deposit, which had 1te and on the south and southeast by a thin bed of mica been known to geologists since 1948 (Heinrich, 1960), ~chist that gives way to epidote-diopside-hornblende began in 1956 (DeMunck, 1956) and has continued in· pieiss containing distinctive widely spaced thin layers termittently since that time. Most of it has been done >r laminae of pink calcite marble. Both upper and lower under the auspices of the Minerals Engineering Com· :ontacts of the iron-formation are relatively abrupt, pany, and (later) Steel Alberta, Ltd., of Canada. Early md there is little interbedding with rock above or churn drilling and trenching was followed by core drill- >elow. This overturned stratigraphic succession-older ing. Information on the amount of core drilling done is nica schist and quartzite, iron-formation, and strati· incomplete, but it is known to be in excess of 10,000 ~aphically younger schist and gneiss-is well exposed ft in aggregate. Locations of trenches and of diamond n the NW1/4NE114 sec. 10 (see cross-section A-A', drill holes sunk in the late 1950's are shown on the ig. 6). previously published detailed map of the area (James Physically and chemically, the iron-formation is and Wier, 1972b). unenable to treatment as a low-grade iron ore (taconite). Informal appraisals of reserve tonnage have been }rain sizes are relatively coarse, generally in the range made by a number of investigators; estimates range l. l-1.0 mm, which permits separation of magnetite and from a few tens of millions to several hundred million ;pecularite from gangue minerals without excessively tons. On the basis of surface area of exposure and pro- ine grinding. Bulk chemistry is much like that of other jection to a depth of 300 ft (a possible practical limit \rchean iron-formation of similar mineralogic facies and for open-pit mining), the resources of potential low- 1f the iron-formation of the Mesabi district of Min- grade ore in the Carter Creek deposit, excluding that 1esota, as shown by comparative data in table 6. It dif· contained in isolated minor synclines, are here esti- ers from most commercially processed taconite in the mated to be about 95 million long tons, containing elatively high ratio of ferric to ferrous iron (nearly 3:1; 28-29 percent recoverable (that is, nonsilicate) iron. Of able 2), reflected mineralogically by the presence of tlus, slightly less than two-thirds is in Beaverhead pecularite in addition to magnetite and of riebeckite, County and slightly more than one-third is in Madison he ferri~·ferrous sodic amphibole. Also notable in the County. 28 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA
TABLE 6.-Chemistry of the iron-formation of the Carter Creek A 7 W A 6 W deposit, southwestern Ruby &nge, Mont., compared with other iron· Treas,;re formations 1,,::--~~~chest I
1 2 3 i Beave1rhe adI!, mine Si02 50. 04 49 . 07 50 . 62 i Fe ( total) 31 . 77 31.65 30.84 I
Mn 0. 04 0.42 0.46
P205 .36 . 16 . 09
Samp l e data :
1 . I ron-forma tion of the Ca r ter Creek deposit. Average of analyses 1-4 , table 2.
2 . Ar chean i ron-forma t ion of the Yilgar n block , west ern Australia (Gole and Klein , 1981 , p . 176) .
3 . Biwabik I ron- formation ( Proterozoic), Mesabi district, Minnesota. Recal culated on an H2 0-free and CO 2-free basis from 6 MllfS previously published data by Go l e and Klein I ( 1981 , p. 176 ) . I 6 KILOM ETERS
FIGURE 7.-Location of principal talc mines and proapects in the TALC southern Ruby Range. l, Treasure State; 2, Regal; 3, American Chemet; 4, Sweetwater; 5, Sauerbier; 6, Owens-McGovern; 7, Bozo. Talc seams, veinlets, and lenses occur in dolomite Zobo; 8, Banning-Jones; 9, Smith-Dillon; 10, Crescent. marble throughout the area, and deposits have been mined sporadically for more than 40 years. Locations of larger known deposits that have been explored or with talc formation or whether it was formed earlier is mined in the southern Ruby Range are shown in figure not clear. 7. The two most recently active mines in the region, the Much of the talc that has been tested is of "steatite" Treasure Chest mine and the Beaverhead mine, are just grade, specifications for which, according to Olson outside the area covered by the general geologic map (1976), call for less than 1.5 percent CaO, less than 1.5 (pl. 1). Details on individual deposits are given by Perry percent Fe20 3, less than 4.0 percent AI20 3, and only (1948), Okuma (1971), and Garihan (1973, 1974), and a minute quantities of other impurities. Analyses of comprehensive review of the occurrence and develop- selected samples are given in table 7. ment of talc resources of southwestern Montana is pro- The lithologic control for localization of talc is ab- vided by Olson (1976). solute: all deposits are in dolomite marble. Structural The talc of the area is cryptocrystalline, opaque to control is less certain. Many of the larger deposits (for translucent, and generally white to pale green or olive example, those at the Treasure State and Treasure gray. Contacts with the dolomitic host rock typically are Chest mines, the Beaverhead mine, the American sharp, and bodies tend to be elongate in the plane of Chemet prospect, and the main pit of the Sweetwater bedding in the marble. Impurities generally are scarce, prospect) are in narrow bands of dolomite marble wholly but small flakes of graphite, relict from the replaced enclosed in older quartzofeldspathic gneiss; locally, as marble, are common in a few deposits, and limonite at t he Treasure State and Treasure Chest mines, vir- derived from oxidation of pyrite is a minor additional tually the entire marble unit has been replaced. Some deleterious constituent in some. Other associated of these marble bands are demonstrably synformal, as minerals noted include serpentine (locally abundant), at the American Chemet and Sweetwater deposits; chlorite, quartz, and phlogopite. In a few deposits others may represent structurally emplaced tectonic the host marble is coarsely recrystallized, but whether slices. The Regal (Keystone) deposit, however, is in the this coarsening of grain was penecontemporaneous axial zone of a synform of marble enclosed in schist, and REFERENCES CITED 37
'STRATA OF PALEOZOIC AGE units, are dragfolds that are systematic with respect to the major fold. d previously, the Precambrian rocks of the The central fault block is a lens-shaped mass about ounded on the north and west by strata of 3,500 ft long and 1,200 ft in maximum width that has age. The north boundary is an unconformity; been thrust up from the keel of the main syncline. This recambrian is overlain by the Flathead Sand· mass, cored by peridotite, has the internal form of an ally glauconitic, which is succeeded by the east-southeasterly plunging anticline flanked by a pair 11ale, both of Cambrian age. On the west the of truncated synclines; almost certainly.it originated as ian is in fault contact with massive limestone an anticlinal buckle in the deeply buried axial zone of 1sissippian Madison Group. These strata are the main syncline, moving upward from its original in more detail by Tysdal (1976b). matrix like a squeezed watermelon seed. The iron- formation within the upthrust mass has been greatly thickened by complex folding, evident in most outcrops. STRUCTURE The fault that bounds the central block on the north is exposed in an exploration trench about 700 ft south acipal structural elements of the area consist of the N~ cor. sec. 25; it is a steeply dipping shear zone abrian folds and faults within the block of about 100 ft wide marked by intensely crumpled rock e rocks and faults that displace both Precam· and thin quartz veins. The companion fault that forms ~ and the younger strata of Paleozoic age. The the south boundary is not exposed, but its location is l be described first. tightly controlled by stratigraphic data. These two bounding faults necessarily must terminate to the west, POST-PALEOZOIC FAULTS because they do not cut the stratigraphic units that outline the main syncline. A similar termination by rthern Ruby Range is crossed by a number of merging is inferred for the eastern extension of the it-trending faults of major displacement faults, but the evidence is not definitive. 1976a; Karasevich, 1981). Within the Kelly system is represented by the fault that brings 1 of the Madison Group into juxtaposition with REFERENCES CITED rian crystalline rocks. This structure, labeled hart fault" by Karasevich, is not here exposed, Armstrong, F.C., 1950, Geologic maps of Crystal graphite mine, Beaverhead County, Montana: U.S. Geological Survey Press ing from the relation of the surface trace to Release July 31, 1950. ,by, it dips steeply to the east. Movement is Armstrong, F.C., and Full, R.P., 1946, Geology and ore deposits of le and reverse, and the minimum displacement the Crystal graphite mine: U.S. Geological Survey Preliminary ti thousand feet. The Kephart fault in turn is Report, February 1946. later east-trending fault that is the structural Bastin, E.S., 1912, The graphite deposits of Ceylon and a similar graphite deposit near Dillon, Montana: Economic Geology, v. 7, or the north branch of Taylor Canyon. Move- p. 419-443. this fault is dominantly left lateral, displacing Bayley, R.W., and James, H.L., 1973, Precambrian iron-formations h.art fault trace by about 800 ft, but offset of of the United States: Economic Geology, v. 68, p. 934-969. nbrian-Precambrian unconformity indicates Bielak, J ., 1978, The origin of Cherry Creek amphibolites from the rlical movement, north side down. Poor ex· Winnipeg Creek area of the Ruby Range. southwestern Montana: Missoula, University of Montana, M.S. thesis, 46 p. of the fault, about 900 ft north of the N~ cor. Burger, H.R., Ill, 1967, Bedrock geology of the Sheridan district, indicate a nearly vertical dip. Madison County, Montana: Montana Bureau of Mines and Geology Memoir 44, 22 p. Clabaugh, S.E., and Armstrong, F.C., 1951, Corundum deposits of PRECAMBRIAN STRUCTURES Gallatin and Madison Counties, Montana: U.S. Geological Survey Bulletin 969-B, p. 29-53. 1ajor Precambrian structures of the area are a Cordua, W.S., 1973, Precambrian geology of the southern Tobacco •pen syncline that is clearly outlined by the Root Mountains, Madison County, Montana: Bloomington. In· aphically lower beds of the Christensen Ranch diana University, Ph.D. dissertation. 300 p. limentary Suite, and an upthrust central block Dahl, P.S., 1977, The mineralogy and petrology of Precambrian 1tains the explored iron deposits. The axial plane metamorphic rocks from the Ruby Mountains, southwestern Mon- tana: Bloomington. Indiana University, Ph.D. dissertation. 280 p. 1ajor syncline apparently is about vertical; the __1979 , Comparative geothermometry based on major-element s trends N. 70° W. and the plunge is to the east- and oxygen isotope distributions in Precambrian metamorphic st at about 40 °. Minor structures, most inferred rocks from southwestern Montana: American Mineralogist, v. 64, ap patterns and the located traces of magnetic p. 1280-1293. 38 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA
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Survey Bulletin 1405-1, p. 11-125. .rie, 1955, Chemistry of the Earth's Crust, in Poldevaart, Vitaliano, C.J., Cordua, W.S., Burger, H.R., Hanley, T.B., Hess, D.F., Crust of the Earth: Geological Society of America Special and Root, F.K., 1979, Geology and structure of the southern part , p. 119-144. of the Tobacco Root Mountains, southwestern Montana-Map 1948, A new study of the anthophyllite series: American summary: Geological Society of America Bulletin, v. 90, pt. l, no. gist, v. 33, p. 263-323. 8, p. 712-715. 957, Bedrock geology of the north end of the Tobacco Weis, P.L., Friedman, lrving, and Gleason, J.D., 1981, The origin of 11ntains, Madison County, Montana: Montana Bureau epigenetic graphite-Evidence from isotopes: Geochimica et and Geology Memoir 36, 25 p. Cosmochimica Acta, v. 45, p. 2325-2332. cMannis, W.J., and Palmquist, J.C., 1975, Precambrian Wier, K.L., 1965, Preliminary geologic map of the Black Butte iron ,f the North Snowy block, Beartooth Mountains, Mon- deposit, Madison County, Montana: U.S. Geological Survey Open· >logical Society of America Special Paper 157, 135 p. File Report, scale 1:9,600. 1, Papike, J.J., and Shaw, K.W., 1969, Exsolution tex- __l 982, Maps showing geology and outcrops of part of the mphiboles as indicators of subsolidus thermal histories: Virginia City and Alder quadrangles, Madison County, Montana: ~cal Society of America Special Publication No. 2, U.S. Geological Survey Miscellaneous Field Studies Map •9. MF-1490, scale 1:12,000. Ir., Wadell, J.S., and Peterson, L.E., 1971, X-ray deter- Winchell, A.N., 1910, Graphite near Dillon, Montana: U.S. Geological of calcite-dolomite-An evaluation: Journal of Sedimen- Survey Bulletin 470, p. 528-532. ology, v. 41, no. 2, p. 483-488. __1911, A theory for the origin of graphite as exemplified in the ~las, and Haering, T.C., 1986, Carbon isotope geochem- graphite deposit near Dillon, Montana: Economic Geology, v. 6, :raphite vein deposits from New Hampshire, U.S.A.: p. 218-230. ca et Cosmochim.ica Acta, v. 50, p. 1239-1247. __1914, Mining districts of the Dillon quadrangle, Montana, and and Thomas, L.C., 1928, Stratigraphic relations of the adjacent areas: U.S. Geological Survey Bulletin 574, 191 p. reek group in the Madison Valley, Montana (abs.]: Wooden, J.L., Vitaliano, C.J., Koehler, S.W., and Ragland, P.C., 1978, l Society of America Bulletin, v. 39, p. 202-203. The late Precambrian mafic dikes in the southern Tobacco Root 1982, Cenozoic block uplifts in east-central Idaho and Mountains, Montana-Geochemistry, Rb-Sr geochronology, and Montana: U.S. Geological Survey Professional Paper relationship to Belt tectonics: Canadian Journal of Earth Sciences, ~- v. 15, p. 467-4'19.
'i:r u.s. GOVERNMENT PRINTING OFFICE: 1989-773-047/06019 PRECAMBRIAN GEOLOGY AND BEDDED IRON DEPOSITS, RUBY RANGE, MONTANA
7(XX)-, t- w I w u.. i ! ~ z 0 4 3 ~ w> ...J w 600) k
1000-, t- w w u.. es ~ z 6500 0 w~ ...J ~ w 60lJ B B' es &amr' ' am~ URE 6.-Geologic map of the Carter Creek iron deposit, Madison and Beaverhead Counties, Mont. Map covers secs. 3, 9, and 10, T. 8 S .. R. 7 w. MINERAL RESOURCES 27 ,....,., , '>,, . 65 5;( -- ; pg~ ;;r4:f' / 15 q, i amllf'. :-· I-'- ~"'i --,... -· 40 ) I ~ " ~ . ~ ~am ,,,...-: ., 'y : '"~ es o5~-f ; if ~5 . pg _,.,-- -~I,-,60 ( 5 ...,.- ~ pg~ / / . ! ~ ~ ~,:; . '),,.!E.. ? 45 / ,zP9j : am~__...?!~,,. i I .1/ ~ / / J' ,, . 75 i .fL-- . / 0 / ~2~r.-{ ' 80 _..L_ i I ?5 . P9 ,- .--?' 70 / _' / ,,.<,.. By -~ 5---' / ,,Y A -_, -~,o 15 . . / 60 so -- '/ am _. ,,r ,.- _. /'// 1f / y ..--:::J;- _, / 20 _: / '/'7 65 / 65 55 ...-:7' '70 ' _,/ --__,,. /' ·-v- 4 3 -- -~ , ,,-, ,• ,,., 32 10 11 I sy / / so ..,.,.. ,,.,,.=/ •A "Y C .....--'- EXPlANATION [See plate l for descriptions and.age relations of rock units] Diabase (Proterozoic) 75..,... / ,,- // es .C enter Pegmatite (Proterozoic(?) and Archean) /:/·· II: 1sec. 10 . _.i:::,..c::______am [ /_5---~-7-e""·;:;.:------t-l-- : Amphibolite (Archean) if Iron- formation (Archean) 65/ I es Strata enclosing iron•formation-Seq·uence is over- turned. so strata bounding main belt of iron-formation on north and northwest are older. those on south and southeast are younger Contact ---- Fault 55 -'-- Strike and dip of layering in metasedimentary rocks 55 --"-- Strike and dip of foliation 20 Minor fold-Showing form in plan view. and bearing 0 500 1000 i500 ::!000 FEET I ~ and plu nge of axis I Bearing an~ plunge of lineation- May be combined 0 100 200 300 400 500 METERS with strike and dip symbol