C1vity pmdutmd by the Gnome explofi~n*rrd 8abmQusnt e4hp. Note Bgum rigbtoantsr of rukbk for m8k. myL 70 feet high and more than 150 feet across, Phomph by Lrwrenca Radiation Laborstory. Geologic Studies Project Gnome Eddy County, New Mexico By LEONARD M. GARD; JR. - - - Prepared on behay of the - - U.S. Atomic Energy Commission -@b UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1968 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART- L. UDALL, Secfetary GEOLOGICAL SURVEY William T. Pecora, Director Librnry of Congress cntalog-cord KO.GS 6s-1S6 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Page a stract------------------------------------------- Gnome area-Continued troduction..----.--------------------------------- Properties of the rocks-Continued Purpose of Project Gnome ....................... Minor elements in Salado Formation in the 9 Historical summary of the project- -- ------------- Gnome drift- -- - - -- - - - -- -- - - - -- - - - - - - - - - - Participation by the U.S. Geological Survey ------- Mineralogy and petrography of the Salado For- Purpose of this report- -- .. -- - - --- --- -------- .. --- - mation near the device ohamber -----------. Acknowledgments- - - - - - - - ---- - - - - - - - - - - - - - - - - - - - Halite-----------------------------..--- 7 Methods of study ------- ------------------------ Polyhalite- - - - - - - - - - - - - - - - - - - - - - - - - - - - - lyseology- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Anhydrite---------..------------------- Regional setting ------- - - ---__-------- - ------ ----- Clastic material ----- ---- - - --------- ---- Effects of the nuclear explosion -------- ------------- -- Effect on the shaft-------- - - .. -- -- -- - - - - - --- - - - - - ilrJ Salado Formation ........................... Bffe'ct at the main station ........................ Rustler Formation ------------ -----..---- --- - The reentry drift - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Dewey Lake Redbeds-- - - --- -- ---- --- -- ---- - Venting ------------_------ .---- ---------------- - - The cavity------------------------------------: Gatuna Formation ----------------.--------- 7 - Explosion-induced structure-, - ---- - - - - - - - - - - - - - - - Structure in confined salt .................... Structhre in unconfined salt------------------ Geology of the preshot Gnome drift--------------- pq New minerals formed- - - - - - :- -- - - - -& - - - - - - - - - - - - - A ~ro~ehiesof the rocks- - - .. - -.- . .-- .. .. - .. .. - - Elements introduced- - -- - - - --- - -- - - --- - ---- - - - - - Physical properties- ---- ------ -- --- - - --- - - - -- Detailed description of rocks in the Gnome shaft-- - - - - - Changes in physical properties --------- --- ---- References- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -.. - - - - - - - - 'T d ILLUSTRATIONS P7I d Page LATE 1. Map and geologic sections of preshot underground workings, Project Gnome, Eddy County, New Mexico--- In pocket T 2. Map and geologic sections of postshot underground workings, Project Gnome, Eddy County, New ?IIexico- - - In pocket ~GURE1. Location map of Project Gnome site, Eddy County, N. Mex ............................................. 2. Map showing extent of the Delaware basin in New Mexico and adjacent structural and geographic features--_. 3. Jlap showing location of shaft, ground zero, and U.S. Geological Survey test holes at Project Gnome site- - - - _ fT 4. Geologic sectiorf~betweenDarIsbad Caverns Natianal Tarband Project Gnome she- - - - - - --- - - - - - - -- - - - - - - - _ U 5. Geologic cross section between shaft and cavity, Project Gnome site ----- ----- ......................... --_ 6. Photograph of units 12, 13, and 14 exposed in preshot drift .......................................... _--- 7. Sketches of twinned polyhalite crystal forms........................................................... P"i I 8. Photograph of steam-eroded potholes in unit 10 where shot vented into preshot drift ........................ Y 9. Map of underground workings and cavity ----------.--------------------------------..----------------- 10. Geologic cross section of drilling alcove, showing thrust faults ----..-------------------------------------.- 11. Photographs showing thrust faults, lithification, and brecciation resulting from the Gnome explosion- --- - -- -- - 12. Geologic cmss section through buttonhook reentry drift ----------..-------------------------------------- Mi# 13. Photomicrograph of preshotsalt---------------------------------------------------------------------- 14. Photomicrographs of intrusive breccia resulting from Gnome explosion--- - ------------------------------- - 15. Photograph of hand specimen showing vein of intrusive breccia ........................................... I$ v TABLES TABLE 1. Generalized stratigraphic section of rocks exposed in the Gnome shaft ...................................... 2. Detailed stratigraphic section of Salado Formation along drift from device chamber to shaft- - - - - - - - - - - - - - - - - - 3. Physical properties of rock samples from Gnome shaft ................................................... 4. Physical properties of rock samples from Gnome shaft, as determined by static method ---------------------- 5. Measured velocities and calculated elastic moduli for rock salt near the position of the Gnome explosion- - - - - - - 6. Physical properties of samples of halite from unit 10, Salado Formation .................................... 7. Description and stratigraphic position of samples of Salado Formation analyzed by semiquantitative spectro- graphic methods ................................................................................. 8. Summary of semiquantitative spectrographic analyses of evaporite rocks (Salado Formation) from Gnome drift- 9. Approximate size and heavjr-mineral composition of clastic material in units 11-13 of the Salado Formation in Gnome drift------------------------------------i----------------------------------------------- 10. Semiquantitative spectrographic analysis of insoluble residue of vein material resulting from the Gnome explosion- F1 d GEOLOGIC STUDIES, PROJECT GNOME, EDDY COUNTY, NEW MEXICO ABSTRACT -halite, grades upward into pure halfte, and ends with a cl&- bearing halite at the base of the next higher polyhalite. For Project Gnome, part of the Plowshare Program to de Comparison of preahot and post8hot velocities in the salt velop peaceful uses for nuclear energy, a nuclear device wns near the shotpoint indicated that rock fracturing caused by the 10, lM1, detonated December underground in mksalt of the explosion was detectable from changes in elastic moduli, but Permian Salado Formation southemt of Carlsbad, N. Mex. compaction was not. No change in density of the rock could The Geological Survey's investigations on behalf of the L1.S. be detected. Atomic Energy Commission provided basic geologic and geo- The erplosion formed a cavity about 70 feet high and more_ - - physical information needed to deflne preshot and postshot than 150 feet actom. Postshot mining exploration revealed geo- geologic and hydrologic ccmditions at and near the site. This logically interesting phenomena that resulted from the erplo- report describes the geology lob the site, some physical and sion. Intrusive breccia veins associated wtth compler thrust chemical properties of the rocks, and the known effwts of the faulting were formed adjacent to the cavfty. The brecda 1s nuclear detonation on the rocks of the site. composed of blocks of granulated and pla8Ucally deformed salt Geologic strata at the Gnome site consist of evaporite and in a matrix of black melted salt The black color of the mamx chstic rocks of the Salsdo and Rustler Formations and Dewey is'due to the presence of laurionite, galena, and carboa These Lake Redbeds, all of Late Perminn age, the unconformably materiab, nat present in the preshot rocks, were created by overlying Gatuna Formation of Pleistocene(?) age, and a the shot Lead from near the device combined with water and Cover of alluvial and eolian sands. A11 rocks, except where dis- chlorine from salt to form laurionite and with sulfur from polp- torted by solution collapse, are nearly flat lying. halite to form galena. The carbon probably was derired from The evaporite deposits are easily dissolved and either are organic material present in the device chamber at shot time. missing at the surface or only partially crop out in southeastern Lateral displacement of an instrument in a drill hole 100 feet New Mexico; thus the sinking of n 1,200-foot shaft at Project from the shotpoint was about 16 feet Strata 200 feet above the Gnome provided an excellent opportunity to study these for- shotpoint were permanently displaced upward 5 feet, and a mations in detail. The strata were measured, samtpled, and bed 55 feet below the shotpoint was displaced downward more photographed while the shaft was being sunk. than 10 feet. The upper onethird of the Salado is exposed in the shaft and consists of 490 feet of bedded halite containing a few inter- INTRODUCTION stratified beds of clayey halite, anhydrite, polyhalite, and clay. PURPOSE OF PROJECT GNOXE The halite is overlain by a leached member comprised of 58 feet of clay, silt, gypsum, and anhydrite, much of which is a Project Gnome Fas a multiple-objective experiment mbbb sohrticm bmxia. conducted.'by the E.S. Atomic Energy Commission as The Rustler