CGS LIBRARY RESOURCE SERIES 35 Alkalic Igneous Rocks of Colorado and Their Associated Ore Deposits By james A. Cappa Colorado Geological Survey Department of Natural Resources Denver, Colorado 1998 - I ' - ..... / I / ,/--.1I - , / , / ,/I ...... _I or "blowout" I - \ _ I - \ Tbr Resource Series 35 Alkalic Igneous Rocks of Colorado and Their Associated Ore Deposits By James A. Cappa Colorado Geological Survey Department of Natural Resources Denver, Colorado 1998 CGS LIBRARY Resource Series 35 Contents Preface ......................................................... Vll· · Biotite Latite Porphyry ............... .. 13 Acknowledgements ...................................... vii Hornblende Granodiorite Porphyry ............................. .. 13 I. Survey of Alkalic Igneous Rocks ................ I Structure ........................................... 13 Introduction .............................................. 1 Geochemistry .......................................... 13 Composition .................................................. .1 Economic Geology .................................. 13 Tectonic Setting .............................................. .1 Veins and Fracture Fillings ................. 14 Continental Rift Valley Magmatism .......... 1 Vein mineralogy........................... 14 Oceanic and Continental Zoning ........................................ 16 Intraplate Magmatic Setting ........... 3 Alteration .................................. .. 17 Subduction Related Magmatism .......... 3 Paragenesis ................................ .. 17 Classification ............................................ 3 Vein control ................................. 17 Ore Deposits ............................................. 3 Stockworks ........................................ 17 Niobium and Tantalum ........................ 3 Magma tic Segregations ...................... 18 Rare Earth Elements including Origin and Model of Ore Deposits ..... 18 Yttrium ......................................... 4 Exploration and Production History ........ 19 Zirconium and Hafnium ...................... 4 References ............................................... 2 0 Vermiculite ......................................... .4 Diamonds-Kimberlites and 3. Cripple Creek District ............................ 23 Lamproites .................................. .. 4 Introduction ............................................ 23 Gold .................................................... 5 Geological Setting ...................................23 Molybdenum ....................................... 5 Proterozoic Rocks .............................. 23 Iron ..................................................... 6 Oligocene Volcanic and Titanium ............................................. 6 Volcaniclastic Rocks ..................... 23 Uranium and Thorium ........................ 6 Oligocene Diatreme Complex ............ 23 B . Other .................................................. 6 reccla ......................................... 24 References ................................................. 6 Phonolite ..................................... 26 syemte . ....................................... 26 2. Central Front Range Mineral Belt.. ........... 9 Trachybasalt ................................ 26 Introduction .............................................. 9 Structure ........................................... 27 Geological Setting ..................................... 9 Geochemistry .......................................... 27 Proterozoic Metamorphic Rocks ........ 11 Economic Geology .................................. 27 Proterozoic Quartzite ........................ .11 Vein Deposits .................................... 2 7 Proterozoic Granodiorite ................... .11 Diatreme-Hosted Deposits ................. 29 Proterozoic Granites-Younger. ........... .11 Hydrothermal Breccia Deposits .......... 29 Cretaceous-Tertiary Intrusive Rocks ... 11 Bedded Rock-Hosted Deposits .......... 31 Leucocratic Granodiorite Origin of the Ore Deposits ................ .32 Porphyry .............................. 12 Exploration and Production History ...... .. 32 Alkalic Syenite Porphyry .......... ... 12 References ............................................... 3 3 Quartz Monzonite Porphyry ........ 12 Bostonite Porphyry ..................... 12 4. State Line Kimberlite District ................. 35 Trachytic Granite Porphyry .......... 12 Introduction ............................................ 35 Quartz Bostonite Porphyry .......... 12 Geological Setting .................................. .35 Limburgite Porphyry ................... 12 Gneiss .............................................. 35 iii Resource Series 35 . ...55 Virginia Dale Ring Complex .............. 35 Mancos FormatiOn ........... ········ . ...55 Diorite ......................................... 35 Browns Par k Formation .............. Sherman Granite .......................... 36 Tertiary Porphyritic Intrusive Trail Creek Granite ................. 36 andE xtrus1ve. R oc k s .............. · ..... 55 Cap Rock Quartz Monzonite .. 36 Structure ................................. ···· ...... 57 Log Cabin Granite ....................... 36 Hydrothermal Alteration .................. ·57 Phanerozoic Sediments ............... ....... 38 G eoc h em1s. t ry ................................... ...... 57 Structure ........................................... 38 Economic Geology .................................. 57 Geochemistry .......................................... 39 Exploration and Production History ...... .. 58 Economic Geology .................................. 39 References .................... ··························· 58 Origin of Ore Deposits ...................... .42 7. Iron Hill Alkalic Complex ....................... 61 Exploration and Production History ....... .43 Powderhorn District ................ ···· .. · ........ · 61 References ...............................................45 Introduction ............................................ 61 5. La Plata District .................................... .4 7 Geological Setting .......................... · ........ 61 Introduction ........................................ ... 47 Pyroxenite ......................................... 62 Geological Setting ................................... 47 Uncompahgrite ................................. 63 Paleozoic Sedimentary Rocks ............. 49 Nepheline Syenite ............................. 63 Hermosa Formation .................... .49 Carbonatite ....................................... 63 Rico Formation ......................... ... 49 Geochemistry .......................................... 64 Cutler Formation .........................49 Economic Geology .................................. 64 Mesozoic Sedimentary Rocks .......... ... 49 Thorium ............................................ 64 Dolores Formation ...................... 49 Niobium ............................................ 66 Entrada Sandstone ...................... .49 Titanium ........................................... 66 Wanakah Formation .................... 49 Rare-Earth Elements .......................... 66 Junction Creek Sandstone ............ 49 Iron ................................................... 67 Morrison Formation .................... 49 Uranium ........................................... 67 Dakota Sandstone ....................... .49 Vanadium .......................................... 67 Mancos Formation ..................... .. 49 Exploration and Production History ........ 67 Laramide Intrusive Rocks ................ .. 49 References ............................................... 6 7 Porphyritic Rocks ...................... .. 49 8. Silver Cliff and Rosita Hills District ......... 69 Equigranular Rocks .............. ....... 50 Introduction ............................................ 69 Structure ........................................ ... 50 Geological Setting ................................... 69 Geochemistry ......................................... 50 Proterozoic Undifferentiated .............. 69 Economic Geology .................................. 50 Rosita Hills Complex ......................... 70 Quartz-Tell uri de Veins ....................... 50 Rhyolite Flows and Volcaniclastic Telluride Replacement Bodies ............ 51 Rocks, Oligocene .................... 70 Gold-Bearing Exoskarns .................... 53 Rosita Andesite, Oligocene ........... 72 Quartz-Gold-Sulfide Veins and Hornblende Andesite, Miocene .... 72 Replacement Bodies ..................... 53 Rhyodacite of Bald Mountain, Breccias ............................................. 53 Miocene ................................. 72 Copper Porphyry-Type Deposits ........ 53 Rhyolite of Rosita Volcano, Exploration and Production History .... .... 54 Miocene ................................. 72 References ............................................... 54 Bunker Trachyandesite, Miocene .. 72 6. Hahns Peak District ................................ SS Pringle Latite, Miocene ................ 72 Introduction ............................................ 55 Trachyte of Game Ridge, Geological Setting ................................... 55 Miocene ................................. 72 Mesozoic to Cenozoic Rhyolite Porphyry of Antrim Sedimentary Rocks ...................... 55 Lode, Miocene ....................... 72 Morrison Formation ..................... 55 Silver Cliff Complex .......................... 72 Dakota Formation ........................ 55 iv