Bulletin 139 2019 INTERPRETATIONS OF NEW AND PREVIOUS LEAD ISOTOPIC DATA FOR LATE CRETACEOUS TO EOCENE SATELLITE INTRUSIONS, BUTTE GRANITE, VOLCANIC ROCKS, AND BASE METAL VEINS OF THE BOULDER BATHOLITH, SOUTHWESTERN MONTANA Stanley L. Korzeb Montana Bureau of Mines and Geology, Butte, Montana Cover photo: Kirk Waren, MBMG, Rampart Mountain. Bulletin 139 2019 INTERPRETATIONS OF NEW AND PREVIOUS LEAD ISOTOPIC DATA FOR LATE CRETACEOUS TO EOCENE SATELLITE INTRUSIONS, BUTTE GRANITE, VOLCANIC ROCKS, AND BASE METAL VEINS OF THE BOULDER BATHOLITH, SOUTHWESTERN MONTANA Stanley L. Korzeb Montana Bureau of Mines and Geology, Butte, Montana CONTENTS Abstract .............................................................................................................................................. 1 Introduction ......................................................................................................................................... 2 Geologic Setting ................................................................................................................................. 3 Previous Investigations ....................................................................................................................... 5 Analytical Procedures ......................................................................................................................... 6 Results ................................................................................................................................................ 7 Discussion .......................................................................................................................................... 9 Base Metal Veins .........................................................................................................................13 Satellite Plutons and Intrusions ...................................................................................................14 Lowland Creek Volcanic Field ....................................................................................................14 Elkhorn Mountains Volcanic Field ................................................................................................17 Stream Sediments .......................................................................................................................17 Big Belt Mountains ....................................................................................................................18 Belt Supergroup Formations and Sulfi de Veins ...........................................................................19 Magma Source ...........................................................................................................................23 Ore Deposit Genesis ...................................................................................................................27 Conclusion ........................................................................................................................................ 29 Acknowledgments ............................................................................................................................ 29 References ....................................................................................................................................... 30 Appendix A ........................................................................................................................................ 33 Appendix B ....................................................................................................................................... 35 Appendix C ....................................................................................................................................... 36 Appendix D ....................................................................................................................................... 37 Appendix E ....................................................................................................................................... 38 Appendix F ....................................................................................................................................... 40 FIGURES Figure 1. Geologic map of Boulder Batholith showing mining districts and approximate locations for base metal vein galena samples ............................................................................................... 4 Figure 2. Covariant diagram of 206Pb/204Pb vs. 207Pb/204Pb plot for base metal vein and breccia pipe galena lead isotope ratios generated by this investigation ............................................................. 7 Figure 3. Covariant diagram of 206Pb/204Pb vs. 207Pb/204Pb plot for Boulder Batholith intrusions published by Doe and others (1968) with added data generated by this investigation .................. 8 Figure 4. Covariant diagram of 206Pb/204Pb vs. 207Pb/204Pb plot for Lowland Creek volcanic rocks published by Dudás and others (2010) with added data generated by this investigation. ..............8 Figure 5. Covariant diagram of 206Pb/204Pb vs. 207Pb/204Pb plot for Elkhorn Mountains volcanic rocks published by Doe and others (1968) with added data generated by this investigation .................. 9 Figure 6. Covariant diagram of 206Pb/204Pb vs. 207Pb/204Pb plot for Basin Mining district stream sediment samples published by Uhruh and others (2000) ........................................................... 10 Figure 7. Covariant diagram of 206Pb/204Pb vs. 207Pb/204Pb plot for the Big Belt Mountains published by du Bray and others (2017) ........................................................................................................11 Figure 8. Covariant diagram of 206Pb/204Pb vs. 207Pb/204Pb plot for the Belt Supergroup formations and sulfi de veins published by Zartman (1992)...............................................................................11 Figure 9. Covariant diagram for 208Pb/204Pb vs. 206Pb/204Pb plot for base metal vein and breccia pipe galena lead isotope data generated by this investigation............................................................... 13 Figure 10. Covariant diagram for 208Pb/204Pb vs. 206Pb/204Pb plot for Boulder Batholith intrusions published by Doe and others (1968) with additional data generated by this investigation .............15 Figure 11. Covariant diagram for 208Pb/204Pb vs. 206Pb/204Pb plot for Lowland Creek volcanic rocks published by Dudás and others (2010) with additional data generated by this investigation ......... 16 Figure 12. Covariant diagram for 208Pb/204Pb vs. 206Pb/204Pb plot for Elkhorn Mountains volcanic rocks published by Doe and others (1968) with additional data generated by this investigation ... 17 Figure 13. Covariant diagram for 208Pb/204Pb vs. 206Pb/204Pb plot for stream sediment samples from the Basin mining district (Uhruh and others, 2000) ........................................................................ 18 Figure 14. Covariant diagram for 208Pb/204Pb vs. 206Pb/204Pb plot for the Big Belt Mountains, data published by du Bray and others (2017) ........................................................................................19 Figure 15. Covariant diagram for 208Pb/204Pb vs. 206Pb/204Pb plot for the Belt Supergroup formations and hosted sufi de veins, data published by Zartman (1992).......................................................... 20 Figure 16. Lead isotope ratios generated by this investigation for galena samples from base metal veins and galena from Montana Tunnels breccia pipe plotted on Stacey and Kramers (1975) model lead isotope growth curves for 206Pb/204Pb vs. 207Pb/204Pb (below) and 206Pb/204Pb vs. 208Pb/204Pb ratios ............................................................................................................................................... 21 Figure 17. Lead isotope ratios for Boulder Batholith intrusions from data published by Doe and others (1968) with additional data generated by this investigation (red points) plotted on Stacey and Kramers (1975) model lead isotope growth curves for 206Pb/204Pb vs. 207Pb/204Pb (below) and 206Pb/204Pb vs. 208Pb/204Pb ratios. ..................................................................................................... 22 Figure 18. Lead isotope ratios for Lowland Creek volcanic rocks from data published by Dudás and others (2010) with additional data generated by this investigation (red points) plotted on Stacey and Kramers (1975) model lead isotope growth curves for 206Pb/204Pb vs. 207Pb/204Pb (below) and 206Pb/204Pb vs. 208Pb/204Pb ratios ...................................................................................................... 23 Figure 19. Lead isotope ratios for Elkhorn Mountains volcanic rocks from data published by Doe and others (1968) with additional data generated by this investigation (red points) plotted on Stacey and Kramers (1975) model lead isotope growth curves for 206Pb/204Pb vs. 207Pb/204Pb (below) and 206Pb/204Pb vs. 208Pb/204Pb ratios ...................................................................................................... 24 Figure 20. Lead isotope ratios for stream sediments from the Basin mining district from data published by Uhruh and others (2000) plotted on Stacey and Kramers (1975) model lead isotope growth curves for 206Pb/204Pb vs. 207Pb/204Pb (below) and 208Pb/204Pb vs. 206Pb/204Pb ratios ................................... 25 Figure 21. Lead isotope ratios for