h evsky and others– BEDROCK GEOLOGIC MAP OF THE DELTA MINERAL BELT, BEDROCK GEOLOGIC MAP OF THE DELTA MINERAL BELT, TOK MINING DISTRICT, ALASKA DISTRICT, TOK MINING BELT, MINERAL THE DELTA OF BEDROCK GEOLOGIC MAP TOK MINING DISTRICT, ALASKA by Samuel S. Dashevsky, Carl F. Schaefer, and Edward N. Hunter –Alaska Division of Geological & Geophysical Surveys Professional Report 122 PROFESSIONAL REPORT 122 State of Alaska Department of Natural Resources DIVISION OF GEOLOGICAL & GEOPHYSICAL SURVEYS Rodney A. Combellick, Acting Director 2003 BEDROCK GEOLOGIC MAP OF THE DELTA MINERAL BELT, TOK MINING DISTRICT, ALASKA by Samuel S. Dashevsky, Carl F. Schaefer, and Edward N. Hunter Professional Report 122 Division of Geological & Geophysical Surveys Fairbanks, Alaska 2003 i STATE OF ALASKA Frank H. Murkowski, Governor DEPARTMENT OF NATURAL RESOURCES Tom Irwin, Commissioner DIVISION OF GEOLOGICAL & GEOPHYSICAL SURVEYS Rodney A. Combellick, Acting Director DGGS publications may be inspected at the following locations. Address mail orders to the Fairbanks office. Alaska Division of Geological University of Alaska Anchorage & Geophysical Surveys Library ATTN: Geologic Communications 3211 Providence Drive 794 University Avenue, Suite 200 Anchorage, Alaska 99508 Fairbanks, Alaska 99709-3645 Elmer E. Rasmuson Library Alaska Resource Library University of Alaska Fairbanks 3150 C Street, Suite 100 Fairbanks, Alaska 99775-1005 Anchorage, Alaska 99503 Alaska State Library State Office Building, 8th Floor 333 Willoughby Avenue Juneau, Alaska 99811-0571 This publication was released by the Department of Natural Resources, Division of Geological & Geophysical Surveys, produced at a cost of $16 per copy, and printed in Anchorage, Alaska. Publication of this report is required by Alaska Statute 41 “to determine the potential of Alaska land for production of metals, minerals, fuels, and geothermal resources; the location and supplies of groundwater and construction materials; the potential geologic hazards to buildings, roads, bridges, and other installations and structures; and shall conduct such other surveys and investigations as will advance knowledge of the geol- ogy of Alaska.” NOTE: Mention of any company or brand name does not constitute endorsement by any branch or employee of the State of Alaska. ii CONTENTS Introduction ....................................................................................................................................................... 1 Previous studies ................................................................................................................................................. 2 Exploration history ............................................................................................................................................ 3 Regional geology ............................................................................................................................................... 3 Structural geology.............................................................................................................................................. 5 Local geology .................................................................................................................................................... 7 Lithologic unit descriptions ............................................................................................................................... 9 Macomb Belt .............................................................................................................................................. 9 Jarvis Belt ................................................................................................................................................... 9 Tushtena Pass unit ............................................................................................................................... 9 Lagoon unit ......................................................................................................................................... 11 Tiger unit ............................................................................................................................................. 12 Drum unit ............................................................................................................................................ 12 Tok River unit ...................................................................................................................................... 13 Hayes Glacier Belt ...................................................................................................................................... 13 Intrusive rocks ............................................................................................................................................ 14 Gabbroic intrusives ............................................................................................................................. 14 Granite ................................................................................................................................................. 14 Alkalic mafic dikes and associated plutonic rocks ............................................................................. 14 Economic geology ............................................................................................................................................. 14 Lagoon unit massive sulfide ....................................................................................................................... 15 DW-LP Deposit ................................................................................................................................... 18 PP2 Deposit ......................................................................................................................................... 18 Drum unit massive sulfides ........................................................................................................................ 18 DD Deposits ........................................................................................................................................ 18 Lithochemistry and protolith determination ...................................................................................................... 19 Methodology............................................................................................................................................... 19 Interpretation .............................................................................................................................................. 19 Protolith classification ................................................................................................................................ 19 Sample screening methodology ........................................................................................................... 20 Regional correlation .......................................................................................................................................... 20 Acknowledgments ............................................................................................................................................. 26 Bibliography ...................................................................................................................................................... 26 Appendix I—Chronology of exploration .......................................................................................................... 31 Appendix II—Igneous protolith discrimination plots ....................................................................................... 33 Appendix III—Tables of mineral deposits, prospects, and occurrences and tables of geochemical data with sample descriptions ............................................................................................... 37 Table 1. Mineral deposits, prospects, and occurrences (p. 39–43) Table 2. Inferred resource of massive-sulfide deposits (p. 45) Table 3. Sample rock types and location coordinates (p. 47–71) Table 4. Fire assay gold and inductively coupled plasma (ICP) analyses (p. 73–89) Table 5. Whole-rock major oxide XRF analyses (p. 91–106) Table 6. Trace element x-ray fluorescence analyses (p. 107–122) FIGURES Figure 1. Location map of Delta mineral belt area in the eastern Alaska Range ........................................ 2 2. Regional bedrock geology of the eastern Alaska Range showing the principal terranes, major schist belts, and intrusions of the Yukon–Tanana terrane ................................................. 4 iii 3. Simplified bedrock geology of the Delta mineral belt showing schist unit subdivisions of the Jarvis belt and locations of mineral resources .............................................. 6 4. Tectonic classification of metaplutonic and metavolcanic rocks from the Jarvis schist belt ........................................................................................................................... 7 5. Longitudinal schematic section, looking northeast, showing the DW-LP and PP2 massive-sulfide horizons.............................................................................................................. 16 6. Three-dimensional rendering of modeled DW-LP and PP2 massive-sulfide sheets intersected by drilling .................................................................................................................. 16 7. Protolith classification