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The Arizona Geological Survey is not responsible for the accuracy of the records, information, or opinions that may be contained in the files. The Survey collects, catalogs, and archives data on mineral properties regardless of its views of the veracity or accuracy of those data. Igneous Rocks and Related Mineral Deposits of the Barker Quadrangle, Little Belt Mountains, .. Montana By IRVING J. WITKIND
GEOLOGICAL SURVEY PROFESSIONAL PAPER 752
A laccolithic complex in central Montana is examined in detail with special attention given to the igneous rocks) the intrusions) and the related silver-lead-zinc deposits
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1973 UNITED STATES DEPARTMENT OF THE INTERIOR
ROGERS C. B. MORTON, Secretary
GEOLOGICAL SURVEY
V. E. McKelvey, Director
Library of Congress catalog-card No. 72-600361
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 Price: Paper cover.-U-OO..dc>maa~~re- Stock No. 2401-00312 /.5S- 58 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA
rangle, Montana: U.S. Geol. Survey Geol. Atlas, Folio in the northern part of the Barker quadrangle, Little 55, 9 p., 4 maps. Belt Mountains, Montana, in Geological Survey research --- 1899b, Description of the Little Belt Mountains quad 1965; U.S. Geol. Survey Prof. Paper 525- C, p. C20-C24. rangle, Montana: U.S. Geol. Survey Geol. Atlas, Folio --- 1969, C1inopyroxenes from acidic, intermediate, and 56, 11 p., 4 maps. basic rocks, Little Belt Mountains, Montana: Am. - - - 1899c, Laccoliths and bysmaliths [abs.]: Science, new Mineralogist, v. 54, nos. 7-8, p. 1118-1138. ser., v. 10, p. 25- 26. --- 1970, Composite dikes in the Little Belt Mountains, CONTENTS - -- 1900, Geology of the Little Belt Mountains, Montana, central Montana, in Geological Survey research 1970: with notes on the mineral deposits of the Neihart, U.S. Geol. Survey Prof. Paper 700- C, p. C82-C88. Barker, Yogo, and other districts; accompanied by a --- 1971, Geologic map of the Barker quadrangle, Judith Page Page report on the petrography of the igneous rocks of the Basin and Cascade counties, Montana: U.S. Geol. Survey Abstract ______1 The intrusions-Continued district, by L. V. Pirsson: U.S. Geol. Survey 20th Ann. Geol. Quad. Map GQ- 898. Introduction ______2 Descriptions of laccoliths- Continued Rept. (1898- 99), pt. 3, p 257-581. Witkind, I. J., Kleinkopf, M. D., and Keefer, W. R., 1970, Previous and present work ______3 Planoconvex laccoliths-Continued Westgate, L. G., 1920, Deposits of iron ore near Stanford, Geologic and gravity evidence for a buried pluton, Little Acknowledgments ______3 Taylor Mountain laccolith ______31 Montana : U.S. Geol. Survey Bull. 715-F, p. 85-92 Belt Mountains, central Montana, in Geological Survey Geographic and geologic setting ______3 Laccolith (?) underlying the Limestone [1921] . research 1970: U.S. Geol. Survey Prof. Paper 700-B, p. Igneous rocks ______5 Butte dome ______31 Witkind, I. J., 1964, Geology of the Abajo Mountains area, B63- B65. Felsic rocks ______5 Dry Wolf laccolith ______31 San Juan County, Utah: U.S. Geol. Survey Prof. Paper Woodward, G. E., and Luff, Paul, 1945, Gold, silver, copper, Old felsic rocks ______5 SatelIitic laccoliths ______31 453, 110 p. lead, and zinc in Montana, in Minerals yearbook, 1943: Porphyry of Clendennin Mountain ______5 Clendennin-Peterson laccolith ______31 --- 1965, Relation of laccolithic intrusion to faulting U.S. Bur. Mines, p. 381-407. Wolf Porphyry ______9 Clendennin fault ______32 Young felsic rocks ______9 Peterson fault ______32 Rhyolite of Granite Mountain ______9 Otter laccolith ______33 Porphyry of Galena Creek ______9 Asymmetric laccoliths ______33 Snow Creek ( ?) Porphyry ______9 Barker laccolith ______33 Chemistry of the felsic rocks ______11 Mixes Baldy-Anderson Peak laccolith __ 34 Intermediate rocks ______11 Bysmalith ______35 Quartz monzonite of Hughesville ______11 Granite Mountain bysmalith ______35 Barker Porphyry ______16 Buried pluton ______36 Chemistry of the intermediate rocks ______16 Indurated alluvium ______37 Mafic rocks ______16 Emplacement sequence of the intrusions ______41 Shonkinite ______19 First intrusive episode ______42 Plagioclase shonkinite ______19 Second intrusive episode ______42 Syenite ______19 Formation of indurated alluvium ______42 Minette-kersantite ______19 Third intrusive episode ______42 Vogesite ______21 Radiometric ages of the intrusions ______42 Chemistry of the mafic rocks ______23 Mineral deposits ______43 Composite dikes ______24 Barker mining district ______43 Similarities of clinopyroxenes ______24 Fissure veins in the stock ______45 The intrusions ______24 Fissure veins beyond the stock ______49 Stock ______25 Contact-replacement deposits ______50 25 Tenor ______Hughesville stock ______50 Laccoliths ______27 Age of the ores ______51 Planoconvex laccoliths __ _ . __ __ . ______28 Localization ______52 Tongue-shaped satellitic laccoliths ______28 San Miguel district ______52 Asymmetric laccoliths ______28 Ore potential ______54 28 Sulfide veins ______Descriptions of laccoliths ______54 Planoconvex laccoliths ______28 Buried mineralized pluton ______56 Butcherknife Mountain laccolith ______28 References cited ______57
ILLUSTRATIONS
Page FIGURE 1. Index map of part of Montana and the study area ______2 2. Map showing pattern of intrusions in the Barker quadrangle ______4 3. Generalized section of sedimentary rocks exposed in the Barker quadrangle ______8 4. Photographs of the felsic igneous rocks ______10 5. Triangular diagram showing some chemical char acteristics of old and young felsic rocks .______11 6. Geologic map of the Hughesville stock and adjacent intrusions ______14 7. Photographs of the intermediate and mafic igneous rocks ______17 8. Silica variation diagrams for intermediate rocks from intrusions in the Barker quadrangle ______18
III U.S. GOVERNMENT PRINTING OFFICE , 1973 0-496-189 IV CONTENTS REFERENCES CITED 57 Page FIGURE 9. Triangular diagram comparing some chemical characteristics of the intermediate rocks from the REFERENCES CITED Kinney, D. M., Izett, G. A., King, R. U., and Taylor, R. B., Barker quadrangle with comparable rocks --______18 American Geological Institute [Howell, J. V., chm.], 1960, 1968, The Poison Ridge volcanic center and related 10. Photomicrographs of xenoliths and xenocrysts in lamprophyres ______22 Glossary of geology and related sciences with supple mineralization, Grand and Jackson Counties, Colorado: 11. Triangular diagram showing some chemical characteristics of the mafic rocks ______23 ment [2d ed.]: Natl. Acad. ScL-Natl. Research Council U.S. Geol. Survey Circ. 594, 8 p. 12. Map showing the Annie E dike intruding the quartz monzonite of Hughesville ______25 Pub. 501, 325 p. Kleinkopf, M. D., Witkind, 1. J., and Keefer, W. R., 1972, 13. Map showing the distribution and shape of the various intrusions as shown by structure contours Billings, M. P., 1942, Structural geology: New York, Prentice Aeromagnetic, Bouguer gravity, and generalized geologic drawn on the top of the Madison Group in the Barker quadrangle ______26 Hall Inc., 473 p. map of the central part of the Little Belt Mountains, 14. Diagrams showing the relations between parent stock and tonguelike satellitic laccoliths ______27 Catanzaro, E. J., 1967, Correlation of some Precambrian Montana: U.S. Geol. Survey Geophys. Inv. Map GP-837. 15. Equal-area stereographic net plot showing joint pattern in the Hughesville stock ______27 rocks and metamorphic events in parts of Wyoming and Knechtel, M. M., 1944, Oil and gas possibilities of the plains 16. Diagrams showing three types of laccoliths ______29 Montana: Mountain Geologist, v. 4, no. 1, p. 9-21. adjacent to the Little Rocky Mountains, Montana: U.S. 17. Diagrams showing four ways an asymmetric laccolith might develop ______30 Catanzaro, E. J., and Kulp, J. L., 1964, Discordant zircons Geol. Survey Oil and Gas Inv. Prelim. Map 4. 18. Photograph of the compound dome underlain by the Taylor Mountain laccolith and the Granite Moun- from the Little Belt (Montana), Beartooth (Montana), Larsen, E. S., Jr., 1940, Petrographic province of central tain bysmalith ______32 and Santa Catalina (Arizona) Mountains: Geochim. et Montana: Geol. Soc. America Bull., v. 51, no. 6, p. 887- 19. Sections showing one possible explanation for the structural relations between the Taylor Mountain Cosmochim. Acta, v. 28, no. 1, p. 87-124. 948. laccolith and the Granite Mountain bysmalith ______34 Creasey, S. C., 1966, Hydrothermal alteration, in Titley, S. R., Macknight, J. A., 1892, Mines of Montana-Their history 20. Photograph of the Clendennin-Peterson anticline ___ . ______36 and Hicks, C. L., eds., Geology of the porphyry copper and development to date: Helena, Mont., C. K. Wells 21. Geologic map of the proximal end of the C'lendennin-Peterson laccolith showing relations between the deposits, southwestern North America: Tucson, Ariz., Co., 138 p. Clendennin and Peterson faults and the laccolith ______38 Arizona Univ. Press, p. 51-74. Marvin, R. F., Witkind, 1. J., Keefer, W. R., and Mehnert, Photograph of the Barker laccolith ______39 22. Cross, Whitman, 1894, The laccolithic mountain groups of H. H., 1973, Early Tertiary intrusions in the Little 23. Geologic map of the west flank of the Granite Mountain bysmalith ______40 Colorado, Utah, and Arizona: U.S. Geol. Survey 14th Belt Mountains, Montana: Geol. Soc. America Bull. (in 24. Map showing sample localities for radiometric age determinations of various intrusions in the Barker Ann. Rept., pt. 2 (1892-93), p. 157-241. press) . quadrangle ______44 Gerry, C. N ., 1930, Gold, silver, copper, lead, and zinc in Peacock; M. A., 1931, Classification of igneous rock series: 25. Map showing location of mines in and near the Barker mining district ______46 Montana, in Mineral resources of the United States, Jour. Geology, v. 39, no. 1, p. 54-67. 26. Sketch showing the pattern and trend of major veins in the Danny T tunnel of the Liberty mine ______47 1927, pt. I, Metals: U.S. Bur. Mines, p. 745- 782. Pirsson, L. V., 1898, Dynamic and structural geology [chap. 27. Photographs of ore from a crustified vein ______48 Gerry, C. N., and Miller, T. H., 1932, Gold, silver, copper, VI] in Weed, W. H., and Pirsson, L. V., Geology and 28. Sketch maps of the McVeda mine along the southeast flank of the Clendennin-Peterson laccolith ______50 lead, and zinc in Montana, in Mineral resources of the mineral resources of the Judith Mountains of Montana: 29. Idealized sketches suggesting how sulfide ores may have been localized in the Hughesville stock ______53 United States, 1929, pt. I, Metals: U.S. Bur. Mines, p. U.S. Geol. Survey 18th Ann Rept. (1896-97), pt. 3, p. 30. Map showing location of mines and prospects in the San Miguel area ______54 831-876. 576-587. 31. Gravity contour map of the buried mineralized pluton ______54 Gilbert, G. K., 1880, Report on the geology of the Henry --- 1900, Petrography of the igneous rocks of the Little Mountains, [Utah] [2d ed.] : U.S. Geog. and Geol. Survey Belt Mountains, Montana, in Weed, W . H., Geology of Rocky Mtn. Region (Powell), 170 p. the Little Belt Mountains, Montana, with notes on the TABLES Godoard, E. N., 1950, Structure of the Judith Mountains, mineral deposits of the Neihart, Barker, Yogo, and other Montana [abs.]: Geol. Soc. America Bull., v. 61, no. 12, districts : U.S. Geol. Survey 20th Ann. Rept. (1898-99), pt. 2, p. 1465. pt. 3, p. 463-581. Page Harker, Alfred, 1909, The natural history of igneous rocks: --- 1905, The petrographic province of central Montana: TABLE 1. The petrography and chemical composition of old and young felsic rocks from the Barker quadrangle London, Methuen & Co., 384 p. Am Jour. ScL, 4th ser., v. 20, p. 35-49. and of a similar rock from Wolf Butte, Little Belt Mountains ______6 Howe, Ernest, 1901, Experiments illustrating intrusion and Pratt, W. P., and Jones, W. R., 1961, Trap-door intrusion of The petrography and chemical composition of intermediate rocks from the Barker and Neihart quad- 2. erosion, in Jagger, T. A., Jr., The laccoliths of the the Cameron Creek laccolith, near Silver City, New rangles, Little Belt Mountains, and of a similar rock from the Stanford-Hobson area ______12 Mexico, in Short 'papers in the geologic and hydrologic Lamprophyre terminology ______19 Black Hills, chap. 5 of General geology, ore and phos 3. phate deposits, Philippines: U.S. Geol. Survey 21st Ann. sciences: U.S. Geol. Survey Prof. Paper 424-C, p. C164- The petrography and chemical composition of mafic rocks from the Barker quadrangle, Little Belt Moun- 4. Rept., (1899-1900), pt. 3, p. 291-303. C167. tains and of similar rocks from the Stanford-Hobson area . ______20 Hunt, C. B., 1946, Guidebook to the geology and geography of Robertson, A. F., and Roby, R. N., 1951, Mines and mineral 5. Chemical analyses of the mafic margin, transitional zone, and felsic interior of the Maytee composite dike ______-______24 the Henry Mountain region: Utah Geol. Soc. Guidebook, deposits (except fuels), Judith Basin County, Montana: no. 1, 51 p. U.S. Bur. Mines Inf. Cire. 7602, 51 p. 6. Tabular summary of known and inferred crosscutting relations in the Barker quadrangle ______41 --- 1953, Geology and geography of the Henry Moun Schafer, P . A., 1935, Geology and ore deposits of the Neihart 7. Radiometric ages of various intrusions in the Barker quadrangle ______45 Production data for the Block P mine ______51 tains region, Utah: U.S. Geol. Survey Prof. Paper 228, mining district, Cascade County, Montana: Montana 8. Bur. Mines and Geology Mem. 13, 62 p. 9. Production data for the Liberty mine ______52 234 p. [1954]. --- 1956, Cenozoic geology of the Colorado Plateau: U .S. Spiroff, Kiril, 1938, Geological observations of the Block P Geol. Survey Prof. Paper 279, 99 p. mine, Hughesville, Montana: Econ. Geology, v. 33, no. 5, p. 554-567. Iddings, J. P., 1898, Bysmaliths: Jour. Geology, v. 6, p. 704- --- 1939, Some of the common minerals found in the 710. Neihart and Hughesville mining districts, Montana: Johannsen, Albert, 1939, A descriptive petrography of the Rocks and Minerals, v. 14, no. 4, p. 109- 111. igneous rocks, v. 1 [2d ed.]: Chicago, Chicago Univ. Taylor, J. H., 1935, A contact metamorphic zone from the Press, 318 p. Little Belt Mountains, Montana: Am. Mineralogist, v. Johnson, A. C., 1964, The geology of the Big Ben area, 20, no. 2, p. 120-128. Cascade County, Montana: Michigan Univ. unpub. Ph.D. --- 1938, The contact zone of Sheep Creek, Little Belt thesis, 104 p. Mountains, Montana: Geol. Mag., v. 75, no. 5, p. 219- Keefer, W. R., 1969, Preliminary geologic map of the 226. Neihart (7 'h') quadrangle, Cascade and Judith Basin Vine, J . D., 1956, Geology of the Stanford-Hobson area, Counties, Montana: U.S. Geol. Survey open-file map. central Montana: U.S. Geol. Survey Bull. 1027-J, p. --- 1973, Geologic map of the west half of the Neihart 405-470. 15-minute quadrangle, Montana: U.S. Geol. Survey Weed, W. H., 1899a, Description of the Fort Benton quad- Misc. Geol. Inv. Map 1-726 (in press).
------...... 56 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA reportedly contained "good ore" and was about 3 in the Precambrian crystalline rocks. Still farther to feet wide (Roy Thorson, miner, Barker, Mont., oral the northeast the pluton is exposed in the open pit of commun:, 1966). Apparently there was considerable the Silv,er Dyke mine, a once famous producer of diffi-culty in bringing sufficient ore to the surface silver, lead, and zinc. In the pit parts of the pluton through the one available shaft. As a result the gov are seen to be a breccia tightly 'cemented by sulfides. IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE ernment concluded that the mine was a marginal Northeast of the Silver Dyke mine and along the producer and ordered it closed (Woodward and Luff, trend of the buried pluton, small stringers of galena BARKER QUADRANGLE, LITTLE BELT MOUNTAINS, MONTANA 1945, p. 401). and pyrite cut the Precambrian rocks. And still far Since then, intermittent mining in the Block P ther to the northeast, also along the axis of the bur By IRVING J. WITKIND and Liberty mines has resulted in the production of ied pluton, is the San Miguel district (see section on minor amounts of ore. "San Miguel District") in which stringers and lenses of galena are in the Precambrian .crystalline rocks. ABSTRACT Under current economic conditions the sulfide At its inferred northeast end is the Hughesville veins do not seem to offer much chance of successful The Barker quadrangle is astride the north flank of the rangle consists of a parent stock (the Hughesville stock) exploitation 'except by small-scale low-overhead op stock. Little Belt Mountains, one of several laccolithic and volcanic encircled by three laccoliths, which radiate from the stock groups that rise above the broad plains of central Montana. much like spokes from the hub of a wheel. erations. Several factors suggest that the pluton merits in The northern third of the quadrangle includes pediments and Radiometric (potassium-argon) ages that were determined vestigation. (1) The potassium-argon data (fig. 24) sedimentary rocks which slope gently northward from the BURIED MINERALIZED PLUTON for both mineral separates and whole rock from various of indicate that the intrusions, and by implication the mountains; the remainder of the quadrangle is a mountainous The general size and shape of the buried pluton is the intrusions indicate that the intrusions were emplaced related mineral deposits, were emplaced in the early terrain of domelike heights separated by long, narrow, sinu during early Tertiary, most likely the Eocene. expressed by a large northeast-trending gravity ous valleys. Tertiary, a time during which many of the large ore Silver-lead sulfide ore deposits in the quadrangle were anomaly whkh extends from Neihart to near Barker deposits in the western United States were formed. Precambrian paragneiss and orthogneiss are exposed in the mined from about 1879 to 1943. In 1968, all the mines were (fig. 31). A part of the south flank of the pluton is southwest corner of the quadrangle, and comparable rocks closed, and many were flooded. Two mining districts are in (2) The ore deposits in both quadrangles are spa probably underlie the remainder of the quadrangle. This exposed beneath Precambrian rocks in the Carpen tially related to felsic rocks, quartz rhyolite porphy the mapped area: the Barker mining district centered about Precambrian basement is overlain unconformably by a sedi the Hughesville stock near the middle of the quadrangle and ter Creek-Snow Creek area near Neihart. Farther to ries and quartz monzonite. These are quartzose host mentary mantle some 4,800 feet thick. the northeast the axis of the pluton is fo1lowed by a the San Miguel mining district centered about a group of rocks that have been repeatedly dted as being favor Both the Precambrian crystalline rocks and the sedimen small mines and prospects in Precambrian crystalline rocks zone of quartz rhyolite porphyry dikes (Snow Creek able for the deposition of ore. (3) Sulfide minerali tary rocks have been warped, broken, intruded, and elevated exposed along the south edge. Most of the ore produced has Porphyry) which intrude the Precambrian crystal zation of varying degrees of intensity is scattered by a host of large and small igneous masses. The igneous come from the Barker district. Tenor of the mined ore lines. I interpret these dikes to be offshoots from the rocks which form these bodies have been subdivided, on the probably averaged 25 ounces of silver and 30 percent lead erratically along the length of the pluton from N ei basis of their contained silica, into felsic, intermediate, and per ton. crest of the buried pluton. And in the Barker area hart to Barker. mafic groups. All the major plutons are formed of either The stock is intensely fractured. Two conjugate fracture the small fel'sic dikes (porphyry of Galena Creek) felsic or intermediate rocks; the mafic rocks constitute only systems were noted: the first fracture system consists of a that cut the stock are interpreted to be apophyses Although certain segments of the pluton are more a small fraction of the total volume of igneous rock emplaced. vertical joint set that trends N. 62° E. and a second set that promising than others, it seems to me that the area The felsic rocks, mainly rhyolite and granite porphyries, from the northwestern flank of the pluton. The col trends N. 40 ° W. and dips about 80° southwestward; the have been divided into old and young groups. The inter linearity between these intrusions and the gravity most worthy of test by deep drilling is the Hughes second fracture system consists of a joint set that trends mediate rocks are chiefly quartz latite porphyries, which anomaly can hardly be fortuitous. I believe that ville stock. This conclusion is suggested by the fol northerly and a second set that trends easterly. Both dikes lowing factors: (1) In other laccolithic complexes in locally grade into latite porphyries or quartz rhyolite por and veins follow the fractures. these relations indicate that the pluton is a north phyries. There is also some syenite. The mafic rocks consist east-trending ovoid body at least 11 miJes long and the western United States, the ore deposits are spa of medium- to coarse-grained shonkinite and fine-grained Ore has been produced from fissure veins in and near the some 4 miles wide. tially related to stocks. (2) The known major ore lamprophyres, which include such varied types as minette, stock and from contact-replacement deposits along the margin deposits in this quadrangle are localized in the kersantite, and vogesite. Several composite dikes character of the stock. Although the ore deposits are considerably All offshoots or exposures of the pluton are com ized by mafic margins (kersantite) and felsic interiors younger than the stock, they nevertheless are localized in Hughesville stock; other likely as-yet-undiscovered and near it. Such localization may be due to a master posed of felsic rock. The general composition of the ore deposits may be similarly localized. (3) The (quartz rhyolite porphyry) imply that two magmas of pluton is probably well represented by the outcrops diverse composition coexisted in the ,area and were emplaced conduit which, somewhat like an inverted funnel, guided the quartz-molybdenite veinlets and the few scheelite almost synchronously. various magmas and ore solutions repeatedly toward the along Carpenter Creek. In that area, the deroofed blebs imply geochemkal leakage from more exten same site. part of the pluton is a compound mass composed of Eleven major plutons are recognized; these are: one stock, sive deposits at depth. In the past, minor amounts of eight laccoliths, a bysmalith, and a buried ovoid pluton which The fissure veins are crustified, and three major para four quartz rhyolite porphyries similar in mineral molybdenum in the surface rocks have indicated trends northeast, extending from near Neihart, Mont., to genetic stages are recognizable. During the first stage, quartz, pyrite, and some sphalerite were deposited on the fissure ogy and chemi'cal composition (Johnson, 1964). richer deposits of copper and molybdenum at depth near Barker. Significant deposits of silver, lead, and zinc have These units have been mapped as the Snow Creek been mined from the pluton, and it seems likely that com walls. During the second stage, argentiferous galena and (Kinney and others, 1968). (4) Major volumes of sphalerite were deposited; and during the third stage, the Porphyry (Keefer, 1969, 197~). parable deposits are still concealed in the pluton. Molybdenite, mineralizing fluids are implied by the amount pyrite, and quartz fill fractures in both the exposed part of remaining voids were filled with gangue minerals such as Mineralized exposures are along the axis of the (20-30 percent) of rock that has been hydrother the pluton and the surrounding Precambrian crystalline rocks. barite and rhodochrosite. Although most of the ore minerals were deposited in an environment marked by intermediate pluton. At its southwest end near Neihart, veins of mally altered. Such extensive alteration implies a The height of the range and the configuration of each argentiferous galena and sphalerite have been individual mountain are the direct results of the emplace (mesothermal) temperature, a few (molybdenite, scheelite, large source of heat and mineralizing solutions at wurtzite) may have formed under high-temperature (hypo mined. About 2 miles to the northeast in the Carpen depth. (5) A favorable structure is 'suggested by thE ment of one or more of these intrusions. A few of the major intrusions are well exposed owing to the removal of their thermal) conditions. Tenuous evidence suggests that some ter Creek-Snow Creek area, molybdenite and pyrite large volumes of mineralizing solutions which have sedimentary cover, but elsewhere erosion has not been as ore minerals were deposited before the formation of the fill fractures in the Snow Creek Porphyry as well as been channeled through the stock. extensive and only parts of the underlying intrusion are dikes that cut the stock, whereas the major veins were visible. In general, the structural framework of the quad- formed after the dikes were consolidated and fractured.
1 2 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA SAN MIGUEL DISTRICT 55
Geologic and geophysical evidence both suggest that part rise above the plains of centra,l Montana (fig. 1). 110°35' of the ovoid pluton underlies the stock. The ore potential of The height of the "Little Belts" and the specific the .area rests heavily on (1) the sulfide veins in the stock, and (2) the size, shape, and metal content of this buried structural features within them are directly attrib pluton. utable to one or more of the major intrusions. The e·omposition and form of these intl1usions and of INTRODUCTION their related mineral deposits within the Barker The Little Belt Mountains are one of several Ter quadrangle-astride the north flank of the Little tiary laccolithic and volcanic mountain groups which Belts-are the subjects of this report. 4
III °00' 109°30'
BLAINE I
• 4 7"00' /, JUDITH BASINU ~ca West half of Neihart quadrangle Youo ,>If." '),*Q,~ • Gravity station 2 LiB ~00 ' I 'l. BIG SNOWY Garneill -("'i"/1", _____ "~ 1 MOU NTAINS '-'--J-v--ToS' ---./_J -~ - I --- WHEATLAND ,------, I 8earpaw Mts I • Little Rocky "Mo.ts. --,Ro-'V_,,_'R HighWOOd~ts., MISSOURI \ BARK E R ~Moccasin Mts " • \ OUAOR)NG, LE ~rrudith Mts Little Belt Mts ~ HELENAO .Big Snowy Mts ( Castle Mt5~ • \ • ' Crazy Mts \.~ \ MONTANA '\ ______.1 \ /,j • \.- o 2 MILES I I o 10 20 30 MILES I I I I
FIGURE t.-Part of central Montana showing Barker quadrangle (hachured) and the mapped part of the Neihart quadrangle. 54 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA INTRODUCTION 3
* * *" (Gerry and Miller, 1932, p. 859). Work property strikes about N. 5° W. According to G. VR. The geology of the Barker quadrangle is shown on lished as Geophysical Investigations Map GP-837 stopped shortly thereafter, and since then only McBride (oral commun., 1968), most veins strike U.S. Geological Survey Geologic Quadrangle Map (Kleinkopf and others, 1972). minor amounts of assessment work, chiefly the bull almost due north. Robertson and Roby (1951, p. 40) GQ-898, issued in 1971. Readers will find the map a In an attempt to determine the time and sequence dozing of exploration pits, have been carried on by reported a N. 50 E. trend for a narrow stringer necessary adjunct to this report. of emplacement of the intrusions, potassium-ar'gon the owners, the Faith Mining Co. of Helena, Mont. containing galena that is exposed at the San Marcos E,Ieven large plutons have been mapped in the ages were determined for some 32 samples from the During the summer of 1968, a small prospect pit dug adit. Barker quadrangle. Of these, one is a stock, ei,ght Barker-Neihart area. The pertinent data and the in the Montgomery property along the nose of a The thickness and tenor of the veins are also un are probably laccoliths, one is a bysmalith, and one conc.Iusions resulting from this study have been pub knoll in the NElli. sec. 31 exposed small discrete certain. A sample of ore from the Montgomery prop is a buried ovoid pluton (fig. 2). These have intruded lished (Marvin and others, 1973). pods, seams, and lenses of sulfide minerals, mainly erty contained about 0.10 ounce gold, 19 ounCes sil the Precambrian basement rocks, as well as the MacKnight (1892) described the prominent lead galena. ver, and about 78 percent lead per ton, according to overlying sedimentary units, and have warped and silver mines in the Barker mining district. Robert The distri,ct is near the east edge of the uplifted G. VR. McBride (oral commun., 1968). The carload broken them. As a result, the once nearly horizontal Son and Roby (1951) described the mines and min Precambrian complex of crystalline rocks, and the of silver-lead ore that was shipped in 1927 was re sedimentary strata have been deformed into domes eral deposits of Judith Basin County incLuding the intensely fractured and altered rocks are believed to ported to contain 0.70 ounce gold, 18 ounces of sil and elongate antidines which reflect the underlying Barker mining district. refl'ect the east flank of a buried pluton (see section ver, about 51 percent lead, and 3.0 percent zinc per intrusion. Between these upwarps are oval basins Spiroff (1938) studied and described the now on "Buried Pluton" and fig. 31). The host rock for ton (Robertson and Roby, 1951, p. 40). and plunging synclines. flooded Block P mine, the major producer of lead-sil the ore deposits is chlorite schist, the alteration Galena, ,sphalerite, and pyrite occur as small pods, The ,general format followed in this report is (1) ver ore in the district. He (1939) also described product of hornblende-biotite gneiss. stringers, and disseminations in the schist. Other Ore a description of the different igneous rocks, (2) a some of the common minerals in the N eihart discussion of the forms of the intrusions, and (3) an Very little is known about the veins in the dis minerals found in rock fragments in the mine dumps Hughesville area. examination of the relations of the ore deposits to trict. A mineralized seam that is exposed in the include chalcopyrite, azurite, mala'chite, and Taylor (1935, 1938) reported on specimens from a these igneous bodies. prospect pit which was dug on the Montgomery bornite( ?). contaoct metamorphic zone south of Neihart. ORE POTENTIt&L My work began in the Barker quadrangle in 1963 PREVIOUS AND PRESENT WORK and was completed in 1966. Field compilation was on The ore potential of the Barker quadrangle lies in topographic sheets at a scale of 1: 24,000. A geologic two types of deposits: first, the sulfide veins in the map of the quadrangle at a scale of 1: 62,500 with an stock, and second, disseminated ore minerals that Although the nearby Highwood and Judith Moun expanded explanation was published as U.S. Geologi may be in part of a deeply buried pluton beneath the tains have been studied intensively in recent dec ades, the Little Belt Mountains have been compara cal Survey Geologic Quadrangle Map GQ-898 (Wit Hughesville stock. Geologic and geophysical evidence kind, 1971). both indicate that a large Tertiary pluton underlies tively neglected since the turn of the century. Weed the southwest 'corner of this quadrangle and the (1899a, b) furnished brief descriptions of the geol northwest corner of the Neihart quadrangle (see ogy and structure of the Little Belt Mountains and ACKNOWLEDGMENTS section on "Buried Pluton" and fig. 31). It is the later presented a comprehensive report (1900) northwest flank of this pluton that may extend be whi'ch includes detailed petrographic descriptions of lowe special thanks to Mrs. Gwenllian Vaughan neath the stock. the igneous rocks by L. V. Pirsson. Rhys McBride of Monareh, Mont., for many stimu Schafer (1935) studied the geology and ore depos lating discussions and for guiding me through sev SULFIDE VEINS its of the Neihart mining district. eral mines. Mr. Roy Thorson of Barker, Mont., and Inasmuch as most of the mines were caved or Catanzaro and Kulp (1964) and Catanzaro (1967) Mr. Geor,ge A. Croff of Monarch, Mont., supplied flooded in 1968, it was not possible to determine the briefly described the metamorphic rocks that crop valuable out-of-print maps and much first-hand in thickness and nature of those veins exposed in the out near Neihart. formation on the ore deposits. workings. Many of the mines have been closed for No mention will be made here of the many work Mr. Fred Cornell and Mr. John Hook, District more than half a century, presumably because the ers, beginning with Weed, who have contributed to Rangers in the Lewis and Clark National Forest, veins are so thin that mining them is uneconomic, were helpful in many ways. the knowledge of the stratified rocks of the quadran but other undiscovered veins may still contain siza gle, for these rocks are not discussed in this report. Jon P. Thorson, Benjamin L. Peterson, and ble deposits of ore minerals. One of the last large o v., 1 MILE Thomas E. Redlinger served competently as geologic I I I mines to close was the Block P which ceased opera Previously, I have offered some preliminary views CONTOU R INTERVAL 200 FEET field assistants. tions in 1943. At that time the vein being worked on the structural framework of the Little Belt EXPLANATION Mountains (Witkind, 1965), on the petrographic re FIGURE 31.-The trend, size, and shape of the buried mineral o X ized pluton. Gravity contoured by M. D. Kleinkopf; contour lations suggested by the clinopyroxenes from intru GEOGRAPHIC AND GEOLOGIC SETTING Prospect Abandoned cabin interval is 2 milligals. Geology north of lat 47 °00' by I. J. sive rocks in the quadrangle (1969), on ,composite -< Witkind in 1967; south of it by W. R. Keefer in 1965. Base dikes (1970), and with M. D. Kleinkopf and W. R. Mine tunnel Road The Barker 15-minute quadrangle includes part of Showing direc tion from U.S. Geological Survey, Barker and Neihart quad Keefer (1970), on a buried pluton beneath the Pre the north flank of the Little Belt Mountains, a rangles, 1 :24.000, 1961. Tsc, Snow Cr~ek Porphyry, Th, cambrian complex. Detailed results of ground-grav mountain group that occupies about 1,250 square FIGURE 30.-Mines and prospects in the San Miguel area. quartz monzonite of Hughesville; Tgc, porphyry of Galena Creek (all units of Tertiary age). All mines shown are ity and airborne magnetometer surveys across the miles in parts of Cascade, Judith Basin, Meagher, Base from U .S. Geological Survey, Barker and Mixes Barker and Neihart quadrangles have been pub- and Wheatland Counties. Of the 215 square miles Baldy quadrangles, 1 :24,000, 1961. abandoned. 4 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA SAN MIGUEL DISTRICT 53 4rN0·r04__ 5::...' _,-______-.-_____ ---,______,-1---,10030'
EXPLANATION ,---;r ". - Ti 11 [ij"\ \ '" Inferred pluton
" ~, Tg. c , Ii m ~~· 1 Porphyry of Minette- kersantite Galena Creek vogesite .' / ~ ...... -...... lL.T~ /' Quartz monzonite of Hughesville \ / " LI MESTO NE BUTTE C"'eek - DOME ~~ ( ) Barker '. Porphyry \
T. 16 N . r; Mesozoic and Paleozoic rocks OTTE R LACCO LITH ,1 111 ..... t p£rj " , - Precam brian rocks " \
~ II , l:l, / ,' _", \~ I,/ ", '""-- " ".\ D ~ --U-- T ··.GRANITE MTN FAULT \ HUGHESVILLE - - '" \1\\111111 I '" I, " STOCK , \ .. ' "", " -- , "\ BARKER LAC CO LITH M I XES BALDY- \( "'\ ANDERSON PEAK LAC CO LI TH TAYLOR MOUNTAIN LACCO LITH
T. 15 N.
Brecciated and altered contac t zon e Pre- B elt crystalline roc k s c underlain by f e ls ic pluton B UTCHERK N IFE MOUNTAIN FIGURE 29.-How a master conduit may have repeatedly During the third episode, young salic and fernic magmas, LACCO LI TH guided diverse magmas and ore solutions into the Hughes guided into the master conduit, invade fractures in the ville stock. stock to form felsic, mafic, and composite dikes. Upon The magmas and their related ore solutions were cooling, the sali c pluton expels mineralizing solutions. channeled into an old master conduit which acted some These solutions rise in available fractures to higher and ~ ': . 4 7 °00' L------~~~~------L----~----=-~------~~~~-L-~,~'---~-L-_ what like an inverted funnel. Presumably the radial pat cooler parts of the stock and form veins which locally R. 8 ° 2 3 MILES R. 9 E . tern of laccoliths about the stock (fig. 2) is the result of are adjacent to the dikes but elsewhere cut across them. I I I ascending magma repeatedly using the same parent e, During a renewed surge of localized intense igneous conduit. A, At the conclusion of the second intrusive activity, another pluton is again guided into the master FIGURE 2.-Pattern of intrusions in the Barker quadrangle. U, upthrown side of fault; D, downthrown side. episode, intermediate magma congeals in the throat of conduit. It jostles the stock and reactivates some frac the conduit. This plug, now known as the Hughesville tures. stock, has solidified and been broken by fractures. B, 52 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA GEOGRAPHIC AND GEOLOGIC SETTING 5
TABLE 9.-Production data for the Liberty mine within the margins of the quadrangle (Witkind, the basis of their silica (Si02 ) content as felsic [Modified from data supplied by Mrs. G. VR. McBride, Faith Mining Co.] 1971), about 70 square miles is plains and pediments (>70 percent), intermediate (60-70 percent), or whioch slope gently northward from the mountains. mafic (45-60 percent). The intermediate rocks form Gold Silver Copper Lead Zinc are The remainder of the quadrangle is a mountainous (dry weight) most of the large intrusions. The felsic rocks have Vein Productive years Ounces Pounds terrain of rounded, elongate ranges separated by been divided into (1) those that were likely formed ------I-----.-----.---_,-----~----.----,------.-----.---~----- narrow, sinuous valleys. Pound. Ton. Re- Ounces Re- Ounces Re- Per- Recovered Per- Re- Per- before most of the major intrusions were emplaced-· covered per ton covered per ton covered centage 1 centage covered centage The sedimentary mantle rests on a basement com old felsic rocks, and (2) those that were formed after I--- Liberty ______1900, 1916, 1917, plex of medium- to coarse-grained metamorphic the large intrusions--young felsic rocks. The mafic 192L ______1,151,553 575.8 24.60 0 . 04 15.859 27 . 5 2.824 0.3 295.239 25 . 6 108,952 9.5 Emerald ______1921, 1924, 1927 __ 812,254 406.2 8.96 .02 10,128 24 . 9 884 .1 296,260 36.5 61,952 7.6 crystalline rocks that have been mapped as nine dis rocks make up small lamprophyric plugs, dikes, and August No. 2 ______1921-1924, 1926, 1933.1935 ____ _ 558.719 279.2 10.44 . 04 6.444 23.1 346 231,482 4l.4 23,278 4.2 tinct units (Witkind, 1971). Of these, three are re sills which are considered to be younger than the Danny T ______1923, 1936-1947, 1950, 1951, garded as paragneiss and six as orthogneiss. Al large intrusions and so may be correlative in age 1953,1958 ___ __ 496,261 24S.3 5.90 .02 4,331 17.4 353 91,550 lS.5 49,527 10.0 MarceUine ______1939, 1941. 1963, though exposed only over about 20 square miles in with the young felsic rocks. This age relation is sug 1964 ______359.S31 179. 9 3.S0 .02 3.522 19. 6 377 104,415 29.0 27,220 1916 . ______7.6 gested by several composite dikes which imply that Queen of the Hills __ 88,349 44.2 .40 .01 1,648 37.3 ------22,355 25 . 3 17 .432 19. 7 the southwest corner of the quadrangle, they proba ---- TotaL ______------salic and femic magmas coexisted and were emplaced 3,466,967 1,733. 6 54.1 ------41,932 ------4.784 ------1.041,301 ------288,361 ------bly underlie the entire report area. All nine units ------almost synchronously. The mafic rocks constitute Metal content; weighted average ______------0.03 ------24.2 ------30.0 ------8.3 are more or less foliate as a result of repeated com pression. Dips of the foliation are generally north only an infinitesimal fraction of the total volume of 1 Based on incomplete data. ward, suggesting that these units form the north emplaced igneous rock. flank of the eastward-trending anticlinorium as Samples of all rock types have been analyzed probably was differential becruuse some parts were magma of this episode. T:here is some geologic and noted by Catanzaro and Kulp (1964, p. 89). chemircally and the data have been processed by com more severely affected than others. geophysical evidence that the felsic pluton which These Precambrian crystalline rocks are the prod puter through the U.S. Geological Survey's C.I.P.W. was formed at this time extends as an ovoid mass ucts of medium- to high-grade regional metamor Rock Norm Program to obtain a calculated mineral LOCALIZATION beneath the Precambrian crystrullines from near phism, and they are probably best grouped in the am composition--the norm-of the rock. The actual The Hughesville stock has been the center of re Neihart to near Barker (see section on "Buried Plu mineral composition-the mode--has been deter ton" and fig. 31). phibolite facies. The paragneisses have been derived peated igneous and hydrothermal activity. At least from impure arkosic sandstone and other fine mined for the more significant rock types by mineral three intrusive episodes, each more intense than the Evidence for the fourth intrusive episode is grained clastic rocks; the orthogneisses from both point ,counts made on representative thin sections. preceding one, can be recognized on the basis of largely radiometric and has been presented else small and large igneous intrusions. These data are presented in various tables through geologic evidence, and a fourth is implied by the where (Marvin and others, 1973). In brief, the po out the report. During the Precambrian the gneisses underwent radiometric data (p. 43). This has led me to pro tassium-argon data imply that another young felsic pose that a master conduit--now occupied by the pluton is concealed beneath the stock. Clear geologic at least two metamorphic episodes (Catanzaro and FELSIC ROCKS (More than 70 percent silica) Hughesville stock-has acted much like an inverted evidence of such a pluton is lacking, Kulp, 1964; Catanzaro, 1967) and were further al funnel (fig. 29). Successive diverse magmas as well tered when they were lifted and baked by the em In the field the felsic rocks appear as light-gray to as mineralizing fluids from crystallizing magmas at SAN MIGUEL DISTRICT placement of a ,compound rhyolitic pliuton either in light-tan porphyries marked by sparse to many depth have been repeatedly channeled into the con The San Miguel district is centered on a group the Late Cretaceous (Catanzaro and Kulp, 1964) or rounded quartz phenocrysts. By contrast the inter duit and so ,localized in the stock. of abandoned mines in the N1f2 sec. 31, T. 15 N., R. 9 in the early Tertiary (Marvin and others, 1973). mediate rocks are 'gray porphyries speckled with The consolidated sedimentary rocks that overrlie phenocry,sts of tabular white feldspar and black nee During the first intrusive episode, salk magma E. (unsurveyed). The district, about 3112 miles south the Precambrian ,gneisses range in age from Middle dles of hornblende and biotite. Quartz phenocrysts rose in the conduit to form first the Clendennin-Pe of Barker, is along the west valley walrl of the Dry Cambrian (Flathead Sandstone) to Early Creta are rare in the intermediate rocks. terson laccolith and then the Mixes Baldy-Ander,son Fork Belt Creek and is aocessible by way of moun ceous (Kootenai Formation) and include rocks as Peak laccolith (p. 42). tain roads (fig. 30). signable to six systems (fig. 3). The sequence is bro OLD FELSIC ROCKS The ore deposits in the district were discovered Subsequently, magma of intermediate composi ken by six unconformities, of which two (post Two large intrusions are composed of old felsic about 1881 (Robertson and Roby, 1951, p. 39), At tion, using the same conduit, flushed out the salic Cambrian-pre-Upper Devonian, and post-Pennsyl rocks: the Clendennin-Peterson la'ccolith formed by that time considerable exploratory work was done, magma as it formed the Barker laccolith (p. 42). A vanian-pre-J urassirc) represent maj or gaps in the the porphyry of Clendennin Mountain, and the but it is unknown whether any ore was shipped. more basic phase of this magma, again using the sedimentary record. Mixes Baldy-Anderson Peak laccolith formed by the same conduit, formed the Otter laccolith, the sill MacKnight, writing in 1892 (p. 108), commented on Wolf Porphyry (fig. 2). Although both porphyries the activity in the Dry Fork Mining Co.'s mines and northeast of Irene Peak; and when it finally crystal IGNEOUS ROCKS are similar mineralogically and chemically (table 1), rlized in the conduit, it formed the Hughesville stock claims 3 miles south of Barker. It seems likely that they differ markedly in texture. (p. 42). Minor amounts of mineralizing fluids pos these are the properties here grouped in the San The rocks that form the various intrusions belong sibly accompanied this activity (fig. 29A). Miguel district. to the Little Belt subprovince, one of Larsen's PORPHYRY OF CLENDENNIN MOUNTAIN The third intrusive episode is represented in and It is certain that mining was adive in the district (1940) divisions of the central Montana petro (Samples 1-5, table 1) near the Hughesville stock by felsi'c, mafic, and com during the late 1920's because at least one carload of graphic province. In the Peacock (1931) classifica Weed (1900, p. 356-358) thought that the Clen posite dikes (fig. 29B). The major sulfide veins silver-lead ore was produced and shipped in 1927 tion, the rocks have an alkali-lime index of 51.2 and dennin-Peterson anticline, 6 miles long and 3112 probably represent mineralizing fluids expelled dur (Gerry, 1930, p. 769). And in 1929, "about 2,000 feet so are just within the alkali ... calcic group. miles wide, resulted from the juxtaposition of sev ing the final stages in the crystallization of the felsic of tunnel work was done at the San Miguel property In this report the i.gneous rocks are grouped on eral igneous bodies. In his opinion, the distal end, at 6 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA BARKER MINING DISTRICT 51
» lOCOaJ~ ~'I""'IQ)~OlO lO ::l lOlO~~~~~~OlOOOOO...... ~ The dominant metal is lead; and galena, its source value, which is supported by the production data .. -'" tOC'¢ C'¢. v g: .9" f~ I 1:- .... mineral, probably contains most of the silver al available for the Liberty mine, indicates that for the a;'" I ~ '" .. though some may be carried by sphalerite and pyr period 1900-64 the produced ore contained a ~ >. ,,'".. ~ ~ '"E- !:. s" 0 -'"0'" ite. Silver minerals are rare in the district. Polished weighted average of 24 ounces of silver and 30 per ~ Il< Po >. .'l ",'Q; '" .. ~ ... ::::;. w :5 ... 0: ;§ - sections of ore show no silver minerals; this lack cent lead per ton (table 9). These va;lues, I believe, .a.~ '" ~. Po .. » ~ ..., .. .!:S '; Q ::i ~ w .~ '"... Ei= implies silver either is very finely admixed or is more closely approximate the tenor of veins in the .. 0 .9 ~ '"~ '" ..... oS U ~ Il< " .0 'carried in solid solution by the other Ore minerals. district. ~ '"'c -,;""'" ~ ~ ~ ~ 0 '" ""'al "C\1Na.i .. :- ..lC ~ b'o~;";: <:> ~...,~r ·~ '" Minor amounts of gold have been produced. No 0 til 0 .. .- 0 " ... 0 ..., AGE OF THE ORES ... :a ...- t ;:l .8 0" u ",.0 •... O'..c Z gold minerals were found in the polished sections, ... c;y ~ It seems likely that ther.e have been at least two ~ 0 and here too, I suspect that the gold is carried by .!!l'" ...'" episodes of sulfide ore mineralization: one older than :~ "g ~OOlO~~C'¢~lO~~~~~~ ~ other minerals, possibly the pyrite. 5 '1""'1 C'¢~~ ~ lO ~ '"<::l I "" 1:-'" 0> the young felsic dikes, and a second younger than .; I ... .. ~w " " ",. "" ! ~ c ... 'C- "0 the dikes. This is suggested by field relations: a dike '"" :§ ~ » ~ ,,~ Any estimate concerning the tenor of the ores pro "<:l i u .E ~ .. !:. S ..., -'"0'" duced from the fissure veins in the stock is based on of the porphyry of Galena Creek, exposed near the <::l '8 ~~\Or.o 0 '<:II~r.olO LQ " Po .'l ",'Q; "0 " l""'4~lOOeo~c.o'l""'l'<:ll.'I""'IOOO ~ til ~" '" I .. :.e ~ ><" :5 '" ;;. ;§ .a...-. ~ the production records ·of the two major mines in Sinclair mine (S of fig. 25), contains fragments of '" C!l" Po .. x- t!~CN to '1""'1 V ~ ""~ '"Z <::l ==,;; ~ '0 ~ » '"E- oS .- " the area: the Block P and the Liberty. It is regretta galena (as well as xenoliths of the stock). The impli ... :::: I '0 I 0 I .S a=... .. ~ "<:l 0 Il< I ,.0 <::l j:Q » "to S] ble that the information is contradictory. As an ex cation is that some .galena was inexistence prior to ;:! ~ ..., ""'c ~ ~ § .. "<:tI~ CQ '<:II ~'I""'I~¢ 0 'Q; '" ,,~ "" '"~ '".. "":.21 :- COC'¢Q)~OlO'I""'IC'¢~~~'I""'IO~...... 00 ample, MacKnight (1892) reported that in the early the time the young felsic dikes were emplaced. But ... ~ ~.- Sot '".. ~C'¢ '1""'1 ~~ '1""'1 ~ "a Il< 0 " ..., o 1:-'" 0> II to 0 .... 1890's the Block P produced ore that contained val other veins are younger than these dikes, inasmuch ... til I ".- .~... 0-" <::l " ",.0 Z >; c;y ~ ~ ues of 40-65 ounces ·of si·lver and 40-48 percent lead as several dikes are cut by the veins. The sulfide vein ..!l'" I I ~ I per ton. The production data for the mine for the that cuts the Annie E composite dike is an example ~'" t oS .s E » ~ ""'" ~ of this group (fig. 12). 0 '" B~ -~ .~ ~ g.:;"" . period 1915-48 (table 8), however, inditeate a much '" 0.'l 'il a ~ ~= '0 .. '" -< -;~ ~ :- ~ ... .'l'- » A to ~ ... '" lower tenor. Of the 406,000 tons of ore produced, the .'lEi" -to" .. I believe that most of the ores were formed during ..lC ",' .- .. ...,Po .a" '" ..., ~ ~ ... ~ '" '" " '" 'c '" ~ .- 0 A=Q:j",""'" 0 weighted average values recovered were close to ~~ ::'!,.o ..cC!l fi;" :9"" ,,"- Z 6112 this younger episode of mineralization, likely from ...... ~'" C!l ~ -< -< <:><::l C!l ounces of silver and 5 percent lead per ton. ~ mineralizing solutions expelled during the crystalli ..."'!< :::ltj'" ~ ~lO~g~'I""'Ioo~~~~~~~ ~ '"0 ~ . zatiOn of the salic magma responsible for the felsite ~5 '" 0" ~ . There seems to have been some drastic variations ...... ,-." '" 00 '1""'1'<:11'1""'1 'I""'ICQ"dI 0':1 ~j:Q ... ,, '" .. " 1:-.... 0> ~~ » ~S:o .. "" 'So ~ N .~j in metals produced from time to time (table 8). Al dikes. The time of emplacement of the high-tempera ;:!~ » C" Q),g ,.0"-" cd:'= t: t-: a 0- --- !:. 8" .,,~ ! ;;. » »"',.0 c.~ ~~"' ~ ture minerals is uncertain. ::l ..c " ,!t:~'O 12:,"'''' . N LOCN c.loo'l""'lOCOLO 1""'4 though in several periods, the recovered values were '"Eo 0;-; 0'~1l 'I""'Ir.o~'I""'ItO'o:t't-.l.QooO')eoeooo 0':1 O ~ 0"" C'3~~ o ...... ~...., . . ~'" ... e- l Ei~ ... ~~ 0 Po .., "''''Po -.:t't-:~2° 'I""'I~~ ~~ Q) as high as 31 ounces of silver and 29 percent lead Some evidence indicates that parts of the stock <::l~ " Il< ..c .. C'\I...-I,.Q ... <-.... 0> .s '" .'l E- :'=C\1'1j gsco ...... c to: ~Il< .. '"0 ~:a.g~ "-'" :::l ~ ...... 0 ~;.:s oS 0 ~ ].a:§ 'per ton, during other periods the values dipped to as were broken after the veins were formed. For exam 0 ... Il< § aSffi~ 0 ~ g'!3 1: E·S;:c S ~;i ~ ~ ~~ ~ C!l'" ~ ~~~ 000 '<:lltO