CONTACT INFORMATION Mining Records Curator Arizona Geological Survey 416 W. Congress St., Suite 100 Tucson, Arizona 85701 602-771-1601 http://www.azgs.az.gov [email protected] The following file is part of the Grover Heinrichs Mining Collection ACCESS STATEMENT These digitized collections are accessible for purposes of education and research. We have indicated what we know about copyright and rights of privacy, publicity, or trademark. Due to the nature of archival collections, we are not always able to identify this information. We are eager to hear from any rights owners, so that we may obtain accurate information. Upon request, we will remove material from public view while we address a rights issue. CONSTRAINTS STATEMENT The Arizona Geological Survey does not claim to control all rights for all materials in its collection. These rights include, but are not limited to: copyright, privacy rights, and cultural protection rights. The User hereby assumes all responsibility for obtaining any rights to use the material in excess of “fair use.” The Survey makes no intellectual property claims to the products created by individual authors in the manuscript collections, except when the author deeded those rights to the Survey or when those authors were employed by the State of Arizona and created intellectual products as a function of their official duties. The Survey does maintain property rights to the physical and digital representations of the works. QUALITY STATEMENT 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. STATE OF MONTANA J. Hugo Aronson, Go1;errwr MEMOIR 36 October 1957 BUREAU OF MINES AND GEOLOGY E. G. Koch, I>i:reeWr THE MONTANA BUREAU OF MINES AND GEOLOGY IS A PUBLIC SERVICE AGENCY FOR THE STA'l'E OF MONTANA. ITS PURPOSE IS TO ASSIST IN DEVELOPING THE STATE'S MINERAL RESOURCES. IT CONDUCTS FIELD STUDIES OF MONTANA GEOLOGY AND MINERAL DEPOSITS, INCLUDING METALS, OIL AND GAS, COAL, OTHER NONMETALLIC MIN· ERALS, AND GROUND·WATER. IT ALSO CARRIES OUT RE. BEDROCK GEOLOGY OF THE NORTH END SEARCH IN MINERAL BENEFICIATION, EXTRACTIVE METAL­ LURGY, AND ECONOMIC PROBLEMS CONNECTED WITH THE MINERAL INDUSTRY IN MONTANA. THE RESULTS OF THESE OF THE TOBACCO ROOT MOUNTAINS STUDIES ARE PUBLISHED IN REPORTS SUCH AS THIS. FOR FURTHER INFORMATION, ADDRESS THE DIRECTOR. MONTANA BUREAU OF MINES AND GEOLOGY, MONTANA MADISON COUNTY, MONTANA SCHOOL OF MINES, BUTTE. By ROLLAND R. REID ILLUSTRATIONS Plate Page 1. Geologic map of the north end of the Tobacco Root Mountains, Madison Cou n ty, Montana _________________________________ _____ _________________ ___________ _____ ___ _____ _____ - _ ________ In pocket 2. General view of the topography of the Tobacco Root Mountains ___ ____ ______________ Frontispiece 3. A, View of characteristic planar foliation in Pony metamorphics. B, View of minor folding in Pony metamorphics. C, view of boudinage-like structure in Pony gneiss. D, View of large garnets in amphibolite __ ______ ____ _ 2 4. A, View of metabasalt in contact with gneiss. B, View of large metabasalt boudin­ age. C, View of bending in foliation in ampr.ibolite. D, View of strong jointing in gran od iori te ____ ____ ________ ____ _____ ________ ________ _____________ ______ ____ ____________ _____ _ ____________ _ _ 6 5. Aerial view of Madison limestone offset by Pony fault __ ______________ ______ _ 6. Aerial view showing trace of the Mammoth fault ________________________________ _ _ ____ ______ ____________ ____ 18 7. Aerial view showing trace of the Bismark fault ___ _____________ _____ _______________ __ _________________ ____ ____ ________ 18 8. A, View looking southeast along the trace of Hollowtop fault. B, View of large microcline porphyroblast in Pony Metamorphics. C, View of the hornblende-plagio­ clase swirled gneiss in amphibolite. D, View showing enrichment of dark minerals along a quartzofeldspathic layer in amphibolite _ _____ ______________ _____ __ _____________________________ _ 18 Figure 1. Index map showing location of area mapped __ _______________ ________ ____ ________________ ___ ____ ___ ___ ______________ 2 2. Sketch of gneiss cut by metabasalt and pegmatite ________ ~___ __ __ _ ___ _____________________________ _________ 8 3. Sketch of xenoliths in Tobacco Root bathol ith - _ ----________ ____________ ___ ____ ______ ______________ ____ __ _______ 9 4. Cross-section at the Pony-Cherry Creek con tact on Spring Branch Creek ________________________________ 14 5. Recumbent isoclinal folding near axis of Noble Peak anticline ________________ _________ _______ __________ 15 6. Sketch of partly concordant structure of pegmatite II ___ _____________________________________ ______ _____ _____ 21 I ." . I vi CONTENTS Foreword ____ __________ ______ _________________________________________ ___ iii Structural geology _____ ________________________ ___________________ 13 ~ Abstract _____ _________________ __ __ _______ __ _______________________ ______ 1 General setting __________ ______________________________________ 13 '" ~ ..: Introduction ___ _______ ______________ ________________________________ __ 1 Metamorphic rock structure ____ ______________________ 13 ..:l il< ~ Purpose of report _________ ___________ _____ ___________________ 1 Pony-Cherry Creek structure _____________ ___ ____ 13 '" 0 z Geo graphy ___________ _____________________ ______________________ -- 1 Pony-Cherry Creek contact relations ________ 14 ~ (5 ~ Topo gra phy ___________ ___________________________ ____ ____ ____ 1 The Noble Peak anticline ________ ___ _________________ 15 fiI ~ U1 Z The Belle Creek syncline _________________________ __ _16 t-4 Transportation and accessibility ________________ 2 ~ E-< Igneous rock structure ___________ __ __ _____________ ________ 16 Z Clima te ---- ________ _______ _________ _________________ ___ ________ ____ 2 P Bath 0 1i th ________________ ________________________________________ 16 0 Working conditions _____________________ _______ ___________ ___ 2 -"" Stocks _________________________ ___________________________ ___ ______ 16 E-< 0 Previous Work ________________ _____ _______ __ __________________ 2 0""; ~ gj Sills ____________ ___________ _________________________________________ 16 o ~ Ackno w ledgmen ts ____________________ ________ ______ __________ 2 U 0.0 Dikes ________________________________________ __ ________ ____ ________ 17 U _S ~.!<: Rock types _____________________________ _________ __________ ___ _________ 3 >:Q 0 Sedimentary rock structure ____________________________ 17 0.3 E-< ..c:' General remarks ___________________ _____ ______________________ 3 Faul ts ______________________________ __________________________________ 1 7 0. ~ ro II: '-' E-< 0.0 Metamorphic rocks _____________________________________ 3 0 Description of faults _________________________________ 17 ~+-' 0] Pony metamorphics ___________ _______ __________________ 3 0. Displacement along faults ______________ __ __________ 19 >-< II: 0; p.. -,... Cherry Creek metamorphics ______________________ 4 Relation of faulting to ore deposits _________ 20 ~ ;;; ~ :;:s Conclusions ___________________ ________________ ___________________ ----- 20 c.!J (1) Metabasal t sills and dikes _________________________ 5 0 ::l p..-g' 0:0 Distinction between Pony and Cherry Origin of the metamorphic rocks _____________ 20 E-< 0 Creek metamorphics __________________ __ ________ 6 ~~ Pony-Cherry Creek age relations _______________ 21 II: 0.0 E-< >= Metamorphic pegmatites ______ ________ ______________ 7 ro Structural control of batholithic emplace- ~ ~ 0 0 ment and ore deposition ____________________ 21 >< Earlier ideas on the age of C!l ~~ metamorphic rocks ____________________ ____ ___ ___ 8 0 ~ Geologic his tory ____ __________________________________________ 21 ..:l >-< 0 ;> fiI Igneous rocks ___________________________________________________ 8 C!l ~ Suggestions for prospecting ___________ _______________ ___ 22 0 ~ Granodiorite __________ _______________________________ __ _____ 8 z ~ Magn eti te ____ ________________ ___ __________________________ _________ 22 ..: ~ tfJ Z fiI A pli te and pegma ti te ________________ ____ ______________ 10 ~ Sill imani te _____ _______ ____________ _________________________ ____ __ 22 Z c.!J ~ Andesite _______ ______ ______________ ___________________ ___ _______ 10 .,. Talc ____ __ ________________________________________________ ------------- 23 0 ;:J Lati te ________________________________ ____________________________ 11 ..: P e gmati tes ________________________________________ _______________ _24 fiI ~ __ ______________________________________________ 11 ~ Basalt Metalliferous deposits ____________________ __________ ______ 24 ~ ..: Age of igneous rocks ____________ __ ______________________ 11 z . Glos sary ______ _________________________ _______________________ ---------- 25 ..: J Eo< Sedimentary rocks ___________________________________________ 11 Z Bibliography _________________ ______ _______________________________ 25 0 :<1 r~ Pal eo zo i c ________________ __ ________________ ___ _______ _____ _______ 11 Appendix, Representative Lower Pony- Tertiary ___ _________ _________ ________ ______________________ __ __ _12 Upper Cherry Creek section __ ___________ 27 v STATE OF MONTANA BUREAU OF MINES AND GEOLOGY E. G. Koch, Director MEMOIR NO. 36 BEDROCK