BULLETIN 38 Geology and Mineral Resources of Dwyer Quadrangle, Grant, Luna, and Sierra Counties, New Mexico by WOLFGANG E. ELSTON 1957 STATE BUREAU OF MINES AND MINERAL RESOURCES NEW MEXICO INSTITUTE OF MINING & TECHNOLOGY CAMPUS STATION SOCORRO, NEW MEXICO NEW MEXICO INSTITUTE OF MINING & TECHNOLOGY E. J. Workman, President STATE BUREAU OF MINES AND MINERAL RESOURCES Alvin J. Thompson, Director THE REGENTS MEMBERS Ex OFFICIO The Honorable Edwin L. Mechem....................... Governor of New Mexico Mrs. Georgia L. Lusk .........................Superintendent of Public Instruction APPOINTED MEMBERS Robert W. Botts ...................................................................... Albuquerque Holm 0. Bursum, Jr. ........................................................................ Socorro Thomas M. Cramer ........................................................................ Carlsbad John N. Mathews, Jr. ...................................................................... Socorro Richard A. Matuszeski ............................................................ Albuquerque Contents Page ABSTRACT ........................................................................................................ i INTRODUCTION ......................................................................................... 1 Purpose and scope ....................................................................................... 1 Methods of investigation ............................................................................. 1 Previous work .............................................................................................. 1 Geographic features ..................................................................................... 2 Location and accessibility ....................................................................... 2 Physical features ....................................................................................... 2 Climate ....................................................................................................... 3 Acknowledgments ....................................................................................... 3 STRATIGRAPHY ............................................................................................ 4 General statement ........................................................................................ 4 Precambrian era ........................................................................................... 4 Cambro-Ordovician systems ..................................................................... 4 Bliss quartzite ............................................................................................ 4 Ordovician system ....................................................................................... 6 El Paso group .......................................................................................... 6 Montoya group ........................................................................................ 6 Silurian system ............................................................................................... 6 Fusselman limestone ............................................................................... 6 Devonian system ......................................................................................... 7 Percha shale .............................................................................................. 7 Mississippian system .................................................................................... 7 Lake Valley limestone ............................................................................. 7 Pennsylvanian system .................................................................................. 8 Magdalena limestone .............................................................................. 8 Permo-Triassic(?) systems ........................................................................... 8 Abo-Lobo "red beds" ............................................................................. 8 Cretaceous system ....................................................................................... 9 Sarten-Beartooth quartzite ...................................................................... 9 Colorado shale ......................................................................................... 9 Tertiary system .............................................................................................. 9 General statement ................................................................................... 9 Piloncillo sediments .............................................................................. 10 Santa Fe fanglomerates ........................................................................ 11 Quaternary system ..................................................................................... 13 General statement ................................................................................. 13 iii Page Terrace gravels and pediment gravels ................................................ 13 Alluvium ................................................................................................... 14 Talus .............................................................................................. 14 PETROGRAPHY AND STRATIGRAPHY OF TERTIARY VOLCANIC ROCKS .......................................................................................... 15 General statement ............................................................................................ 15 Definitions ......................................................................................................... 15 General statement on field relations ............................................................. 16 Methods of studying volcanic rocks .............................................................. 16 Lower volcanic series ....................................................................................... 17 General statement ........................................................................................ 17 Rubio Peak andesites and latites ............................................................... 17 Sugarlump latite and rhyolite tuffs ............................................................ 23 Kneeling Nun rhyolite tuff ......................................................................... 25 Mimbres Peak formation ............................................................................ 27 Box Canyon rhyolite tuff ............................................................................ 29 Rustler Canyon basalt ................................................................................. 30 Caballo Blanco rhyolite tuff ........................................................................ 30 Upper volcanic series ....................................................................................... 31 General statement ........................................................................................ 31 Razorback andesite and rhyolite ................................................................ 32 Bear Springs basalt ....................................................................................... 34 Swartz rhyolite .............................................................................................. 36 Volcanic rocks of uncertain age ..................................................................... 36 General statement ........................................................................................ 36 White Eagle rhyolite .................................................................................... 36 Faywood rhyolite ......................................................................................... 37 Pollack rhyolite ............................................................................................. 37 Minor dikes ................................................................................................... 37 HYPABYSSAL INTRUSIVE ROCKS ............................................................ 39 Cooks Peak granodiorite porphyry ................................................................ 39 Vista monzonite or granodiorite porphyry ................................................... 39 PETROLOGY AND PETROGENESIS ......................................................... 40 Chemical petrology .......................................................................................... 40 Basalts and olivine andesites ...................................................................... 40 Pyroxene andesites and amphibole latites ............................................... 42 Rhyolites ........................................................................................................ 45 Intrusive rocks .............................................................................................. 45 Special problems of rhyolites ......................................................................... 46 Origin and alteration of rhyolitic glasses ................................................. 46 Ignimbrites .................................................................................................... 49 Petrogenesis ....................................................................................................... 51 General statement ........................................................................................ 51 Lower volcanic series .................................................................................