PGJ/F-130(82)
National Uranium Resource Evaluation NOGALES QUADRANGLE ARIZONA
Bendix Field Engineering Corporation Grand Junction, Colorado
Issue Date April 1982 4 O
SATESO
PREPARED FOR THE U.S. DEPARTMENT OF ENERGY Assistant Secretary for Nuclear Energy
- ~ Grand Junction Area Office, Colorado ARIZONA G LVGU I AL 'I I a "I metadc957793 Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed in this report, or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
This report is a result of work performed by Bendix Field Engineering Corporation, Operating Contractor for the U.S. Department of Energy, as part of the National Uranium Resource Evaluation. NURE is a program of the U.S. Department of Energy's Grand Junction, Colorado, Office to acquire and compile geologic and other information with which to assess the magnitude and distribution of uranium resources and to determine areas favorable for the occurrence of uranium in the United States.
Available from: Technical Library Bendix Field Engineering Corporation P.O. Box 1569 Grand Junction, CO 81502-1569
Telephone: (303) 242-8621, Ext. 278
Price per Microfiche Copy: $6.50 PGJ/F-130(82)
NATIONAL URANIUM RESOURCE EVALUATION NOGALES QUADRANGLE ARIZONA
Robert H. Luning and Lee A. Brouillard
BENDIX FIELD ENGINEERING CORPORATION Grand Junction Operations Grand Junction, Colorado 81502
March 1982
PREPARED FOR THE U.S. DEPARTMENT OF ENERGY GRAND JUNCTION AREA OFFICE UNDER CONTRACT NO. DE-AC07-76GJ01664 This is the final version of the subject-quadrangle evaluation report to be placed on open file. This report has not been edited. In some instances, reductions in the size of favorable areas on Plate 1 are not reflected in the text.
ii CONTENTS
Page
Abstract ...... 1
Introduction ...... 3
Purpose and scope ...... 3
Acknowledgments ...... 3
Procedures...... 3
Geologic setting and history...... 5
Environments favorable for uranium deposits...... 10
Environments unfavorable for uranium deposits...... 10
Precambrian metamorphic rocks: Pinal Schist...... 10
Precambrian intrusive rocks ...... 11
Continental Granodiorite ...... 11
Quartz monzonite intrusive ...... 11
Paleozoic sedimentary rocks ...... 14
Cambrian rocks ...... 14
Bolsa Quartzite ...... 14
Abrigo Formation...... 14
Devonian rocks: Martin Limestone...... 15
Mississippian rocks: Escabrosa Limestone...... 15
Pennsylvanian rocks...... 15
Black Prince Limestone...... 15
Horquilla Limestone ...... 15
Permian rocks: Naco Group ...... 15
Rocks near Laramide intrusives ...... 16
Mesozoic and Cenozoic rocks ...... 16
Baboquivari Mountains and Papago Indian Reservation. . . . . 16
iii CONTENTS (cont.)
Page
Pitoikam Formation, All Molina Formation, and metamorphic rocks of Chutum Vaya...... 16
Intrusives of Jurassic age...... 17
Intrusive rocks of Cretaceous and Tertiary age. . . . . 23
Unnamed rocks west of the Baboquivari Mountains . . . . 23
Atascosa Mountains ...... 24
Montana Peak Formation...... 24
Atascosa Formation...... 25
Pena Blanca Formation ...... 25
Cerro Colorado, San Luis, and Tumacacori Mountains: Volcanic and sedimentary rocks of Tertiary age ...... 26
Sierrita Mountains ...... 26
Ox Frame Volcanics. . . ." ." ." ." ." ." ." ." ." ." ." ." ." 26
Rodolfo Formation . . ." ." ." ." ." ." ." ." ." ." ." ." ." 26
Tascuela Redbeds...... " ." ." ." ." ." ." ." ." ." ." ." ." 27
Stevens Mountains Rhyoll . . . . . 27 . .." .." .." .." .." .." .." . ." Sierrita Granite-Harris Monzonite 27
"" " " . ."." ." ." Whitcomb Quartzite. . . ." ." ." . ."." .." 29
Demetrie Volcanics...... 29
Ruby Star Granodiorite. . ." ." ." ." ." ." ." ." ." ." ." ." ." ." ." ." 29
Helmet Fanglomerate . . ." ." ." ." ." ." ." ." ." ." ." ." ." ." ." ." 30
Santa Rita Mountains ...... " 30
Mount Wrightson Formatic in . . ". ". ". ". ". ". ". ". ". ". ". ". ". . 30
Piper Gulch Monzonite . ." ." ." ." ." ." ." ." ." ." ." ." ." ." ." ." 30
"" "" " . ." Squaw Gulch Granite . . ." ." ." . ."." .". .".". 31
Fort Crittenden Formatic n . . ".".".".".".". .".".". . . . 34
iv CONTENTS (cont.)
Page
Salero Formation ...... 35
Josephine Canyon Diorite...... 0 . . 35
Madera Canyon Granodiorite...... 0.0. . 36
Elephant Head Quartz Monzonite...... 36 . . 0.0. . Gringo Gulch Volcanics...... 37 . . 0. 0. . Grosvenor Hills Volcanics ...... 37
Gravels of Nogales...... 0.0. . 38
Whetstone Mountains: Paleocene intrusive rocks. . . 0. 0. . 38
Patagonia Mountains: Paleocene intrusive rocks. . . .0 .0.0.0 38
Huachuca Mountains ...... 0 .0 .0.0 39
Huachuca Quartz Monzonite ...... 0 .0 .0.0 39
Lower member of Canelo Hills Volcanics...... 0. a. . 39
Bisbee Group...... 39 . .0 .0.9.0 Unevaluated environments...... 40 . . 0. 0. . Precambrian intrusive rocks: Sierrita Mountains. . . 40
Continental Granodiorite ...... 40 .. a..0. Unnamed intrusive rocks...... 41 . .0 .0 .0.0 Mesozoic and Cenozoic rocks ...... 41
. .0 .0.0.0 Baboquivari Mountains and Papago Indian Reservation. 41
. .a .f.0.a Mulberry Wash Formation ...... 41
. .0 .e.0.0 Chiuli Shaik Formation...... 43
Sedimentary, volcanic, and intrusive rocks of Tertiary age...... 43
Cobre Ridge, Oro Blanco, and Pajarito Mountains. . . 43
Cobre Ridge tuff...... 43
v CONTENTS (cont.)
Page
Pajarito Lavas...... 44
Oro Blanco Conglomerate ...... 48
Cerro Colorado, Las Guijas, San Luis, Tumacacori, and Oro Blanco Mountains ...... 49
Volcanic and sedimentary rocks of Mesozoic age. . . .0.0.0 49
Laramide intrusives ...... " ." ." ." ." ." ." ." 49
Sierrita Mountains ...... 50
Sierrita Granite...... " ." ." ." 50
Harris Ranch Monzonite...... 51
Angelica Arkose ...... " ." ." ." 51
Red Boy Rhyolite...... 51
Igneous complex ...... 51
Formation of Tinaja Peak...... 51
Santa Rita Mountains . . 0 . 0 . 0 0 0 . 0 0 0 0 0 . ." ." ." ." 52
Middle member of the Mount Wrightson Formation. . ." ." ." ." 52
Gardner Canyon Formation...... 52
Temporal Formation...... 52
Bathtub Formation ...... 52
Bisbee Group...... 52
Fort Crittenden Formation ...... 53
Intrusive igneous rocks ...... 53
Whetstone Mountains...... 0. 53
Bisbee(?) Formation . .0 ...... ".". ". ". . 53
Extrusive igneous and sedimentary rocks 54
Patagonia Mountains...... " ." ." ." ." ." ." ." ." ." ." 54
Siliceous volcanic rocks...... " ." ." ." ." ." ." ." ." ." ." 54
vi CONTENTS (cont.)
Page
Quartz Monzonite of Mount Benedict...... 54
Granite of Comoro Canyon...... 55
Bisbee Formation...... 55
Huachuca and Mustang Mountains ...... 55
Volcanic and sedimentary rocks of the Mustang Mountains...... 55
Canelo Hills Volcanics...... 55
Siliceous volcanic rocks...... 56
Intrusive crystalline rocks ...... 56
Morita Formation...... 56
Dragoon Mountains: Stronghold Granite ...... 56
Tertiary basins ...... 57
Quaternary deposits ...... 57
Interpretation of aerial radiometric data...... 57
Recommendations to improve evaluation...... 58
Precambrian intrusive rocks ...... 58
Whetstone Mountains...... 58
Huachuca Mountains ...... 58
Sierrita Mountains: Continental Granodiorite. 59
Mesozoic and Cenozoic rocks ...... 59
Sierrita Mountains: Sierrita Granite and Harris Ranch Monzonite...... 59
Santa Rita Mountains ...... 0.0.0 . ." ." 59
Middle member of the Mount Wrightson Formation...... " 59
Squaw Gulch Granite ...... " ." 59
Huachuca Mountains: Morita Formation...... " ." 59
vii CONTENTS (cont.)
Page
Patagonia Mountains: Intrusives of Jurassic age ...... 59
Selected bibliography...... 61
Appendix A. Uranium occurrences ...... In pocket
Appendix B. Tables of chemical analyses ...... In pocket
Appendix C. Uranium-occurrence reports...... In pocket
Appendix D. Petrographic reports...... In pocket
viii ILLUSTRATIONS
Page
Figure 1. Nogales Quadrangle location map...... " 4
-2a. Generalized Paleozoic and Precambrian stratigraphic column ...... " 6
2b. Generalized Cenozoic and Mesozoic stratigraphic column . . ." 7
3. Index map of physiographic features...... " 9
4. Radiometric measurement locations near the Blue Jay occurrence (oversized) ...... In packet
5. Radiometric measurement locations near the Duranium occurrence (oversized) ...... In packet
6. Radiometric measurement locations near the Black Dike occurrence (oversized) ...... In packet
Table 1. Major oxide analyses of the quartz monzonite intrusive . . . 12
2. Radiometric data for the quartz monzonite intrusive. . . 13
3. Chemical and radiometric data...... 13
4. Field gamma-ray spectrometric data for the Baboquivari Mountains and Papago Indian Reservation...... 18
5. Radiometric data for Sierrita Granite and Harris Ranch Monzoni te...... 28
6. Partial whole-rock analysis of a sheared zone and vein in the Squaw Gulch Granite ...... 32
7a. Data, radioactive veinlets in the Squaw Gulch Granite. . . . 33
7b. Data, nonradioactive veinlets in the Squaw Gulch Granite .-. 33
7c. Radiometric data, altered rock, Squaw Gulch Granite. . . 34
8. Field radiometric data for the Black Dike occurrence . . . . 42
9. Selected uranium values, agpaitic coefficients, and emission spectrometry results for samples taken in the Cobre Ridge, Oro Blanco, and Pajarito Mountains . . 45
ix ILLUSTRATIONS (cont.)
Plate 1. Areas favorable for uranium deposits
2. Uranium occurrences
3. Interpretation of aerial radiometric data
4. Interpretation of data from hydrogeochemical and stream- sediment reconnaissance
5. Location map of geochemical samples
6. Drainage
7. Geologic map
8. Chart showing exposed formations and lithologic correlations between mountain ranges in the Nogales Quadrangle
9. Structure map
10. Location map of field radiometric measurements
11. Geologic-map index
12. Generalized land status
13. Culture
Plates.in accompanying packet
x ABSTRACT
Literature research, surface geologic investigations, rock sampling, and radiometric surveys were conducted in the Nogales Quadrangle, Arizona, to identify environments and to delineate areas favorable for uranium deposits according to criteria formulated during the National Uranium Resource Evaluation program. The studies were augmented by aerial radiometric and hydrogeochemical and stream-sediment surveys.
No favorable environments were identified. Environments that do display favorable characteristics include magmatic-hydrothermal and authigenic environments in Precambrian and Jurassic intrusives, as well as in certain Mesozoic and Cenozoic igneous and sedimentary rocks.
1
INTRODUCTION
PURPOSE AND SCOPE
The Nogales Quadrangle, Arizona (Fig. 1), was evaluated to identify geologic environments and delineate areas that exhibit characteristics favorable for the occurrence of uranium deposits. Favorable environments could contain uranium deposits of at least 100 tons (90 metric tons) U308 in rocks with an average grade not less than 100 parts per million (ppm) U308 . The categorization of an environment as favorable is based on the similarity of its geologic characteristics to the National Uranium Resource Evaluation (NURE) recognition criteria described in Mickle and Mathews (eds., 1978). The study was conducted by Bendix Field Engineering Corporation (BFEC) for the NURE program, managed by the Grand Junction Office of the U.S. Department of Energy (DOE).
Approximately 2 man-years were spent in literature research, fieldwork, and report preparation. The project started March 1, 1980, and ended February 1, 1981.
ACKNOWLEDGMENTS
Appreciation is-expressed to Robert B. Scarborough of the Arizona Bureau of Geology and Mineral Technology in Tucson. He was very helpful in providing geologic information and in discussing evaluation problems.
Charles F. Barter, Senior Geologist of the Twin Buttes Mine, kindly helped us in the sampling and evaluation of the various units exposed in the mine. Also, Addison Smith, Mining Director, and Max Norris, Chairman of the Papago Tribe, graciously gave us permission to enter the Papago Indian Reservation portion of the Nogales Quadrangle. Thin-section analyses and mineral identification were performed by Michael L. Dixon, Petrology Laboratory, BFEC.
PROCEDURES
A workplan was devised on the basis of literature study. Field study priorities were assigned to geologic units on the basis of their apparent favorabilities so that the allotted time could most completely accommodate the evaluation work. A number of low-priority geologic environments, which could not be evaluated during the field studies because of time constraints or limited accessibility, were described from available literature.
During the field work, some uranium occurrences reported in U.S. Atomic Energy Commission (AEC) Preliminary Reconnaissance Reports (PRRs), Raw Materials Evaluation (RME) reports, and Trace Element Memorandum (TEM) reports and other published reports were examined. Samples at representative occurrences were collected for analysis of uranium and other selected elements. On the basis of these examinations, Uranium Occurrence Reports (UORs) were prepared (App. C).
3 NOON"
1140 120 1100 K38 5
--.- .- .. - 37* 37 ------
I'So Aco av
ARIZONA NEW IM EXICO
340 ------340
0AJO TUCSON SILVER33 CITY
C 32UU0i .,... 32 ! LUKEVILLL NOGALES DOUGLAS
USA MEXICO
31 5 3I0 1120 1100 108
Figure 1. Nogales Quadrangle location map.
4 In order to provide background geochemical values, a limited number of samples of country rock were taken, during the first phase of the fieldwork, from selected areas where no anomalous radioactivity was detected. Petrographic work and major-oxide analyses were performed by BFEC Laboratories in Grand Junction, Colorado. Total uranium (U308 ) contents were determined by fluorimetric analysis. Fifty-eight thin sections were made for the determination of mineral compositions.
Second-phase field studies consisted of geologic investigations and traverses with hand-held scintillometers (Mt. Sopris, model SC-132) to obtain gross gamma-ray counts; a number of traverses were made with portable gamma- ray spectrometers (Scintrex GAD-6 and geoMetrics GR-410) to obtain potassium and equivalent uranium and thorium contents. Areas within the Papago Indian Reservation were evaluated by means of scintillometer and gamma-ray spectrometer traverses. No rock samples were collected during the second phase because time constraints precluded the completion of analytical work.
Data derived from airborne radiometric and magnetic surveys (ARMS), flown by Texas Instruments, Inc., during 1975 and 1978, were analyzed and interpreted. Time restrictions prevented the ground checking of apparent radiometric anomalies except in selected instances.
A hydrogeochemical and stream-sediment reconnaissance (HSSR) sampling program was completed by Savannah River Laboratories (SRL) in April 1980. The results of this program were not received in time to be interpreted for this evaluation. Subsurface environments remain largely unevaluated because of the lack of drilling data.
GEOLOGIC SETTING AND HISTORY
The Nogales Quadrangle is in southeastern Arizona between latitudes 310 N. and 320 N. and longitudes 1100 W. and 1120 W. (Fig. 1). The quadrangle lies partly in Mexico. Only the portion within the United States, an area of about 12,650 km 2, was evaluated during this project. The study area lies within the mountain and desert regions of the southern Basin and Range physiographic province. The area is characterized by subparallel north- to northwest-trending mountain ranges separated by broad alluvium-filled basins.
Rocks ranging from Precambrian to Quaternary in age are exposed along fault-controlled, tilted mountain blocks (P1. 7). Precambrian granitic, schistose, and gneissic rocks crop out in isolated areas in the eastern portion of the quadrangle. Geochronologic studies indicate that the granitic rocks range in age from 1,400-1,450 m.y. old (Silver, 1978).
Paleozoic rocks represent relatively stable cratonic conditions in the area (Peirce, 1976). A thickness of nearly 3 km of predominantly carbonate shelf accumulation is present. Limestone, dolomite, and lesser amounts of shale, sandstone, siltstone, quartzite, and minor conglomerate make up the section (Fig. 2a).
Mesozoic and Cenozoic rocks are predominantly silicic to intermediate volcanics and volcaniclastics (Fig. 2b). Triassic, Jurassic, Cretaceous, and Tertiary intrusives are found throughout the quadrangle.
5 ERA- SYSTEM GROUPIFORMATION ICK- LTH- DESCRIPTION THEM ESSm OLOGY
Limestone and dolomite; some scarce Rainvalley 0-122 sandstone IT I I
Concha Limestone 0-174 Cherty limestone
46-355 Quartzite, sandstone, dolomite, and Scherrer "- - - siltstone
NACO PERMIAN Epitaph 262-524 Dolomite, limestone, marl, siltstone, and Dolomite -2gypsum beds locally
Colina 55-320 Limestone Limestone
- - - . Marl, shale, siltstone, sandstone, Earp 122-375 limestone, and chert-pebble conglomerate
V N HLimestone, ua - :marl, cherty and silty 0 Horquilla 81 -305 limestone W J1 Q PENNSYL- CL VANIAN Black Prince 45-85 Limestone and chert-pebble conglomerate Limestone
SISPP Liesabosna 142-191 Limestone, cherty limestone, and dolomite
DEVONIAN Martin 63-122 Limestone, dolomite, siltstone, and sandstone
Abrigo 244-287 -- 1 Shale, limestone, dolomite and quartzite
CAMBRIAN 1-______
Bolsa 72-145 Quartzite and sandstone Quartzite ~j. Inrsv / Intrusive Alaskite, quartz monzonite, granodiorite, igneous rocks* -I and diorite PRECAMBRIAN ~'%t "1 Pinal schist / Schist and gneiss
0 l l Favorable for uranium deposition Figure 2a. Generalized Paleozoic and Precambrian stratigraphic column.
6 ERA- SYS- ROCK TYPE OR THICK- LITH- DESCRIPTION THEM TEM SERIES FORMATIONt NESSm OLOGY HOLOCENE OQ@o 0- nTER-Pediment, terrace,___-_ Gravel, sand, and silt; mudstone and CEN- -deposits; lacustrine 830 0:O marl associated with lacustrine deposits PLIOCENE deposits locally 00:0 .o*. V.' nsO Epiclastic volcanic conglomerate, Volcaniclastics.Y228 0 Io tuffaceous sandstone, gravel, sand, 0o ,,.," andsilt MIOCENE rocks -
o.oY Rhyolitic and rhyodacitic flows and O Volcanic and tuffs; andesite flows, dacite tuff; N4 volcaniclastic 940 . Y A- conglomerate, agglomerate, and sand- oOLIGOCENE rocks - .o stone; intrusive monzonite, rhyolite, -o*o rhyodacite, and granodiorite
+\ --- Intrusive igneous rocks: quartz mon- Igneous +. zonite, diorite, rhyodacite, latite, and complex + ~ rhyolite; extrusive igneous rocks: quartz latite and rhyolitic tuffs and flows PALEOCENE - --
Gringo 480 ~Y Rhyolitic to dacitic tuff; intrusive Volcanics rhyolite; andesitic lava; sandstone
Intrusive Quartz monzonite, granodiorite, \ ^ \+ monzonite, diorite, quartz diorite, igneous 7 " rocks monzongranite, quartz latite, and A+ rhyolite
' UPPER Predominantly Rhyolitic tuffs and flows; andesitic volcanic and and dacitic breccias and flows; vol- volcaniclastic 5000 YQ Y canic and arkosic conglomerate; rocks; sub- tuffaceous sandtone; basal shale 0 ordiante ter- A W present locally I I restrial clastics I G' V. - 4 I- W Subaerial clastic 2680 Conglomerate, sandstone, siltstone, and marine rocks shale, mudstone, and limestone - V- D ... --e-
LOWER Predominantly volcanic and Y A volcaniclastic Rhyolitic tuff; latitic and rhyolitic (,) 1950 breccia and conglomerate; orthoquart- rocks; sub- Y-- - -' 0 Y. o 0 ordinate ter- zite; andesitic flows locally N 0 restrial clastics W) Intrusive 2 igneous rocks; includes Squaw Gulch Granitic to quartz monzonitic plutons Granite*GranwG*ulnd and and associated dikes MIDDLE Sierrita 4 AND Granite* LOWER Predominantly4 .Y volcanic and 2x volcaniclandI Rhyolitic to andesitic tuffs and flows, ocansiastic 4080 .. , - volcanic conglomerates and breccias; ordinate ter- Ay Y shale and arkose restrial clastics _ _ O.O Y A \..\ \- intrusive igneous rocks; includes \ /\-/fir /\, C-) Monzonitic to quartz monzonitic Quartz Monzonite \ -, / \ -I intrusives UPPER of Harris Ranch* AND 1 \ - \ \ 1 MIDDLE Volcanic and o - - Rhyolitic to andesitic flows and I- volcaniclastic 2590 -* breccias; rhyolitic and latitic tuff, rocks e. tuffaceous sandstone, and conglomerate L I .L 1 'Favorable for uranium deposition tDetailed information about names and descriptions on Plate 9
Figure 2b. Generalized Cenozoic and Mesozoic stratigraphic column. 7 In Triassic and Early Jurassic time, the area experienced at least two periods of volcanic activity apparently separated by a period of plutonism (Hayes and Drewes, 1978). Middle Jurassic plutonic activity emplaced granite and quartz monzonite extensively. Jurassic granitic rocks are characterized by moderate to intense fracturing and alteration and seem to act as preferred sites for uranium deposition.
In Early Cretaceous time, a brief period of localized volcanism in the central portion of the quadrangle was followed by transgression of the sea from the south and southwest (Hayes and Drewes, 1978). The Bisbee Group, a lower conglomerate overlain by a sequence of sandstone, siltstone, and interbedded limestone and shale, was deposited. Then, during Late Cretaceous, uplift and erosion caused deposition of fluvial sediment in valley areas. This was followed by a widespread period of volcanism and a subsequent episode of plutonism.
Activity during early to middle Cenozoic time was mainly volcanic and plutonic. Extensive igneous intrusions produced stocks, plugs, and dikes during the Paleocene (Marvin and others, 1973). Associated local volcanism also occurred at this time in the Santa Rita, Sierrita, and Whetstone Mountains (Fig. 3 and P1. 8). Igneous activity subsided during the Eocene. Radiometric age dates indicate a widespread igneous event during the late Oligocene and early Miocene (28-23 m.y.) (Marvin and others, 1973). During early to middle Tertiary time, final cooling of intrusive igneous bodies occurred. In some areas, mylonitic fabrics were developed within the intrusives by means of dislocation with overlying rocks. These fabrics are characteristic in the development of metatmorphic core complexes and have been recognized in the Pozo Verde, Coyote, and Alvarez Mountains (Fig. 3; Coney and Reynolds, 1980).
Sediments interbedded with variable amounts of volcanics were deposited in basins that began to develop in Oligocene time. The extent of these basins cannot yet be reconstructed, but they are considered more extensive than the late Cenozoic basins that began forming during middle Miocene time, about 13-10 m.y. ago (Scarborough and Wilt, 1979). The younger basins are the result of the block faulting associated with the Basin and Range disturbance. Gravel, sand, and silt fill the younger basins. Lacustrine sediments, Pliocene in age, are found with the younger basin-fill deposits in the San Pedro Valley (Gray, 1965).
The structural complexity of the Nogales Quadrangle (P1. 9) is the result of at least three periods of severe and diverse kinds of regional deformation and local disturbances (Drewes, 1978a). During the Precambrian, major north-, northwest-, and northeast-trending faults were formed (Drewes, 1978a; Peirce, 1976). Some of the faults in this system were activated or reactivated during the Triassic, Jurassic, and Early Cretaceous; and some were reactivated during the Cenozoic (Drewes, 1978a). These faults were probably the conduits for many of the subsequently emplaced intrusives and for the mineralizing fluids in the area, inasmuch as most of the exposed plutons and stocks are elongated in directions similar to those of the faults.
Laramide orogenic events spanned a time between 90 and 53 m.y. ago in southeastern Arizona (Drewes, 1978b). A compressive northeast-southwest- oriented stress field produced thrust faults and folds of local and regional scale. Intrusive and extrusive magmatic activity accompanied orogeny.
8 li2* o 1120 ,QO DRAG 32 2c ET01TO TNS. 0 CO UN A NSJ
NTAINSJ 00\ 4 Cj
A NRESERVAON c 4? SONOITA AREZ .J &VVALLEY MOUNTAINS
31*3 30' 012* I
VERD Z) 0(2-. -.4 4 MTS 4; i
P44,9, q4 9C110SARAFAEL 440 VALLEY 31020' floo
0 5 10 15 20 miles
Figure 3. Index map of physiographic features. The final tectonic event to affect the area, the Basin and Range disturbance, superimposed high-angle normal faults on previously developed structural features. Fault blocks subsided as much as some 2000 m (Scarborough and Peirce, 1978), thereby producing the basins that border the major mountain ranges in the quadrangle. This final event has shaped the present physiographic character of the area.
ENVIRONMENTS FAVORABLE FOR URANIUM DEPOSITS
No favorable environments have been identified in the Nogales Quadrangle, although there are some that possess favorable characteristics similar to those in areas that contain uranium deposits. These environments failed to meet the criteria for uranium deposits containing at least 90 metric tons at a grade of not less than 100 ppm U308 , however. Also, one or more characteristics considered critical for the occurrence of specific types of uranium deposits are lacking or are not apparent. These environments are discussed under "Environments Unfavorable for Uranium Deposits."
ENVIRONMENTS UNFAVORABLE FOR URANIUM DEPOSITS
All environments in Precambrian rocks failed to meet the recognition criteria for plutonic igneous environments (Classes 310 through 380, Mathews, 1978a). Paleozoic, Mesozoic, and Cenozoic sedimentary rocks failed to meet the criteria for all classes of favorable sedimentary environments (Classes 110 through 230, Jones, 1978; Class 240, Austin and D'Andrea, 1978). Mesozoic and Cenozoic intrusive and extrusive rocks failed to meet the recognition criteria for plutonic igneous environments (Classes 310 through 380) and volcanogenic environments (Classes 510 through 540, Pilcher, 1978).
Many, but not all, of the Mesozoic and Cenozoic units that are discussed in this section have each been defined only in one mountain range. This circumstance justifies discussion of those units by principal mountain ranges (P1. 8).
PRECAMBRIAN METAMORPHIC ROCKS: PINAL SCHIST
The Pinal Schist crops out in small, widely scattered areas in the Santa Rita Mountains, Whetstone Mountains, Mule Mountains, and Dragoon Mountains. The Pinal consists of metamorphosed sedimentary and volcanic rocks. The schist is unfavorable for vein-type deposits in metamorphic rocks (Class 720, Mathews, 1978b) because the environment occurs in a mobile-belt terrane; reductants required to precipitate uranium, such as sulfides, hematite, and graphite, are not known to occur; feldspathization, silicification, or hematitic alteration are not evident.
Muscovite-quartz, chlorite-muscovite-quartz, and biotite schists predominate. The schist ranges in texture from aphanitic to coarsely crystalline. Its overall color is light greenish gray, commonly with satiny
10 luster. Most of the Pinal consists of quartz and sericite or muscovite, and accessory tourmaline, hornblende, biotite, magnetite, and chlorite.
PRECAMBRIAN INTRUSIVE ROCKS
Continental Granodiorite
The Continental Granodiorite, of Precambrian age, is a coarse-grained, porphyritic rock. It has abundant biotite and chlorite. It is exposed along the northwestern and southwestern flanks of the Santa Rita Mountains. It is unfavorable for all classes of uranium occurrences associated with plutonic environments (Class 310 and 380) because of its intermediate lithology, lack of sodic ferromagnesian minerals, and apparent lack of fluorite. Miarolitic cavities, indicative of a volatile-rich pluton, were not found. Also, the intrusive has a low silica content, its agpaitic coefficient is less than one, and its magnesium and calcium oxide contents are commonly high (Drewes, 1976b)--unfavorable criteria for uranium occurrences in plutonic environments. Furthermore, equivalent uranium contents are low (MGG 158, 159, App. B1).
The granodiorite contains aplitic, alaskitic, and fine-grained quartz monzonitic bodies, which are volumetrically small, irregular in plan, and commonly lenticular or tabular. Favorable mineralogical aspects of the small bodies are the presence of two-mica aplites, sodic plagioclase, and accessory allanite, a radioactive mineral.
Quartz Monzonite Intrusive
An unnamed Precambrian pluton in the northern foothills of the Whetstone Mountains is unfavorable for authigenic (Class 360, Mathews, 1978a) uranium occurrences because it fails to meet the minimum tonnage and grade requirements. The intrusive meets many of the recognition criteria, however. It is of granitic to quartz monzonitic composition; it is partly porphyritic; and it is also, in part, a leucocratic two-mica granite. Alaskitic phases, aplite dikes, and pegmatitic segregations are commonly found. The silica content is high and the magnesium and calcium contents are low. Metamict fluorite is present and the fluorine content of the intrusive is anomalously high. There are shear zones present, and some show evidence of shattering; they have localized hematitic and limonitic staining, and the iron oxides are anomalously radioactive. Argillic and sericitic alteration is common along the shear zones. The pluton has eight reported uranium occurrences, and sparse amounts of a yellow, possibly radioactive mineral were found at one of these occurrences.
The intrusive is a product of late-stage magmatic differentiation: porphyritic textures are common; it is a quartz monzonite; muscovite and biotite are present; the muscovite is more abundant than the biotite. Table 1 highlights the favorable chemical aspects of the host rock; they are suggestive of a uraniferous pluton.
Alaskite, aplite dikes, and very coarse-grained quartz and feldspar masses in the pluton are indicative of its late-stage magmatic evolution.
11 TABLE 1. MAJOR OXIDE ANALYSES OF THE QUARTZ MONZONITE INTRUSIVE
Sample A12 03 CaO F K20 MgO Na20 SiO2 Fe No. (%) (%) (ppm) (%) (%) (%) (%) (%)
MGG 002 13.02 0.12 1121 6.13 0.24 1.90 81.80 0.52
MGG 005 12.92 0.61 994 5.30 0.40 2.04 79.38 0.84
MGG 010 13.98 0.28 1068 4.02 0.12 3.31 82.26 0.42
MGG 016 12.26 0.29 2759 4.40 0.33 0.14 83.68 0.52
Thin-section studies (MGG 001, 003, 004, 007, 008, 009, 014, and 019, App. D) show minor to moderate argillization and sericitization. Although these types of alteration are not specific evidences of favorability, there is distinct limonitic staining and argillic alteration of feldspars along fracture zones as shown in thin section MGG 009 (App. D). Accessory minerals, such as apatite and zircon, are present. Traces of fluorite were also found-- further evidence of a late-stage quartz monzonite differentiate.
Green to white fluorite occurs to the south of the pluton in a shear-type fissure vein in Pinal Schist. This vein is genetically related to the intrusive because granitic to quartz monzonitic fragments containing fluorite were found in it.
Shear zones, possible channelways for uranium, vary in width from several centimeters to about a meter, but they are not particularly apparent on the surface because of extensive alluvial cover and grus. One such set of shear zones trends N. 600 W., parallel to the contact between the pluton and the Bisbee Formation. Another set trends N. 600 E. These two sets might intersect at depth. Shear-zone intersections could be favorable structural sites for secondary uranium enrichment. Whether or not there are such intersections could not be ascertained. Some shattering of the host rock adjacent to and within the sheared zones is evident.
Hematitic material is locally abundant along some of these shear zones. Some hematitic areas are radioactive (MGG 320, 321, 322, Table 2). However, background radiometric data from unmineralized surficial exposures indicate low equivalent-uranium values (MGG 423, 424, Table 2). Also, scintillometer traverses over country rock indicated no significant changes in background radioactivity.
There are eight reported uranium occurrences in the pluton, all related to shear zones. No uranium minerals were recognized in place. Coatings of a yellow, radioactive mineral resembling secondary uranium minerals were noted in pebble-sized fragments of granite on a dump by the collapsed adit of the First Chance uranium occurrence (UOR-15, App. B). The mineral was not identified, however. The presence of uraniferous material in place was demonstrated analytically (Table 3). The shear zones within the quartz monzonite pluton have low Th/U ratios, which suggests uranium enrichment of
12 TABLE 2. RADIOMETRIC DATA FOR THE QUARTZ MONZONITE INTRUSIVE
K eU eTh eTh/ Sample No. (%) (ppm) (ppm) eU
MGG 320 7.09 24 31 1.3
MGG 321 3.69 48 11 0.2
MGG 322 8.71 41 25 0.6
MGG 423 6.00 4 4 1.0
MGG 424 6.00 5 25 5.0
the zones. The large difference between chemical- and equivalent-uranium values for MGG 006 and MGG 012 probably reflects strong surface leaching along the shears.
The depths and widths of the possibly favorable zones are difficult to measure. Authigenic uranium occurrences are commonly shallow because of their postmagmatic redistribution. They are commonly concentrated at the water table. The water table is estimated to be 100 m (300 ft) below the surface, but, in such an arid area, the depth may be quite variable.
Anticipated ore grades are speculative; they may range from 0.04 percent uranium to 0.07 percent uranium, using the analyses of samples MGG 011 and MGG 017 (Table 3).
TABLE 3. CHEMICAL AND RADIOMETRIC DATA
cU 3 08 eU eTh eTh/ Sample No. (ppm) (ppm) (ppm) eU
MGG 006 6 212 14 0.06
MGG 011 750 644 22 0.03
MGG 012 14 190 15 0.07
MGG 013 53 65 2 0.03
MGG 017 444 328 8 0.02
13 The evidence indicates that the uranium came from the pluton itself. Postmagmatic processes may have removed the labile uranium and concentrated it in shear zones. It is not known, however, under what conditions the uranium precipitated.
PALEOZOIC SEDIMENTARY ROCKS
Paleozoic-aged rocks (Fig. 2b; P1. 7; P1. 8) were evaluated principally from available literature. Low priority for field evaluation was assigned to the units because no reported uranium ocurrences or airborne radiometric anomalies are known to be associated with them.
Limestone portions of the Abrigo Formation, Martin Formation, Escabrosa Limestone, Black Prince Limestone, Horquilla Limestone, Earp Formation, Colina Limestone, Epitaph Dolomite, Scherrer Formation, Concha Limestone, and Rainvalley Formation failed to meet recognition criteria for uraniferous limestone deposits (Class 230). Unfavorable characteristics include deposition in an agitated, open, marine environment; reductants to trap uranium-mineral solutions, such as carbonaceous material or sulfide minerals, are lacking.
Shales within the Abrigo and Earp Formations are unfavorable for uranium deposits in marine black shales (Class 130) because of a lack of any type of reducing mechanism for uranium solutions, such as pyritic, bituminous, or phosphate-rich layers.
The Bolsa Quartzite and sandstone portions of the Epitaph Dolomite and Abrigo, Earp, Scherrer, and Rainvalley Formations are unfavorable for sandstone-type deposits (Class 240). Unfavorable characteristics include lack of a reductant for uranium within the lithologies, such as carbonaceous matter or sulfide minerals, and deposition in an open-marine or near-shore environment which formed non-channelled sandstone bodies. A short description of the Paleozoic units is given below.
Cambrian Rocks
Bolsa Quartzite. The basal formation of the Paleozoic sequence is the Bolsa Quartzite. The Bolsa rests disconformably on Precambrian intrusives and the Pinal Schist. The formation consists almost entirely of resistant beds of dark-weathering silica-cemented orthoquartzite, but local pebble or cobble conglomerates occur at the base (Hayes, 1978). The lower part of the Bolsa is commonly slightly feldspathic, the upper part nonfeldspathic (Hayes, 1978). Interbeds of siltstone or shale are present in the upper part of the formation at some localities. Small- and medium-scale planar cross-laminations are abundant in the formation, particularly in the lower part (Hayes, 1978).
Abrigo Formation. The Abrigo lies conformably on the Bolsa Quartzite. Interbedded shaly layers in the quartzite at the top of the Bolsa become predominant at the Abrigo-Bolsa contact. Above this transition zone, limestone, dolomite, and shale are predominant (Creasey, 1967). In places, the mottled character of the rock may be the result of inclusions of
14 carbonaceous material, but it is generally caused by silty or micaceous material irregularly deposited in the limestone beds (Gilluly, 1956). Toward the top of the Abrigo, dolomite and limestone become increasingly sandy (Creasey, 1967; Gilluly, 1956).
Devonian Rocks: Martin Limestone
The Martin Limestone, of Late Devonian age, overlies the Abrigo Formation paraconformably. Much of the Martin is limestone, but dolomites and dolomitic limestones are more prevalent in it than the Abrigo below or the Escabrosa Limestone above (Bryant, 1968).
Mississippian Rocks: Escabrosa Limestone
The Escabrosa rests paraconformably on the Martin Limestone (Gilluly, 1956). The formation is typically a coarse-grained limestone, commonly containing a high percentage of crinoidal debris (Bryant, 1968). No sandstone or shale has been found in the formation. Chert is absent in the lower part of the Escabrosa, but a few thin bands occur in the middle and toward the top (Gilluly, 1956).
Pennsylvanian Rocks
Black Prince Limestone. The only exposure of the Black Prince Limestone in the Nogales Quadrangle is in the Whetstone Mountains. Here, the Black Prince lies disconformably on the Escabrosa Limestone. The basal portion of the formation consists of fragments of red chert. Above this is crystalline limestone (Creasey, 1967).
Horguilla Limestone. The Horquilla rests disconformably on the Escabrosa Limestone, except in the Whetstone Mountains, where it rests on the Black Prince Limestone (Creasey, 1967). The formation is predominantly a fossiliferous limestone, having subordinate cherty and silty limestone, marlstones, and siltstones.
Permian Rocks: Naco Group
The Naco Group is composed of, in ascending order, the Earp Formation, Colina Limestone, Epitaph Dolomite, Scherrer Formation, Concha Limestone, and Rainvalley Formation.
The Earp Formation rests conformably of the underlying Horquilla Limestone (Bryant, 1968). The lower portion of the Earp is made up of shales, marlstones, and thin shaly limestone. A unique feature of the Earp is a chert-pebble conglomerate in the middle of the formation. Varying proportions of siltstone, sandstone, or limestone are found in the upper portion, depending on the locality of the section (Creasey, 1967; Bryant, 1968).
15 The Colina Limestone is gradational with the underlying Earp. The Colina is dominantly a thick-bedded to massive limestone.
Conformably overlying the Colina is the Epitaph Dolomite. In the Empire and Whetstone Mountains, the Epitaph consists of a lower massive dolomite, overlain by marlstone, mudstone, and a large proportion of gypsum. The upper part of the Epitaph is composed of dolomite and limestone (Creasey, 1967; Bryant, 1968).
The Scherrer Formation consists mainly of sandstone and siltstone. There are a few limestone beds in its lower part (Bryant, 1968). Its middle portion is commonly composed of dolomite, although limestone may be present at some exposures (Creasey, 1967). The upper part of the Scherrer is composed of sandstone and quartzite.
Overlying the Scherrer is the Concha Limestone. It is composed of thick- bedded to massive, cherty, fossiliferous limestone.
The Rainvalley Formation marks the top of the Naco Group. It is composed predominantly of limestone and dolomite, but there are some beds of sandstone (Bryant, 1968).
Rocks Near Laramide Intrusives
Contact metasomatic deposits of copper and silver, and occurrences of lead, zinc, molybdenum, and tungsten (Keith, 1973; 1975), are present in Paleozoic carbonates near quartz monzonitic and granodioritic plugs and dikes of Laramide age. Skarns and hydrothermal alteration are present. Productive districts include the Twin Buttes area, near the Sierrita Mountains; the Helvetia and Rosemont districts in the Santa Rita Mountains; the Washington Camp-Duquesne area in the Patagonia Mountains; and the Tombstone district in the Tombstone Hills. Although these areas show some favorable characteristics, they are considered unfavorable for contact-metasomatic (Class 340) and magmatic-hydrothermal occurrences (Class 330). The intrusive bodies are not highly silicic or alkalic, and fluorite is not known to be present in any of the deposits. Favorable aspects include moderate to intense hematitic and silicic alteration and sulfide and carbonate minerals near the deposits. Surface radiometric surveys of these areas detected no anomalously high radioactivity, however. Uranium minerals are not known to occur, but some uranium is being recovered from copper-enriched solutions--said to contain about 35 ppm U3 08 -- at the Anamax Twin Buttes Mill (Charles Barter, Senior Geologist, Anamax Twin Buttes Mine, Sahuarita, Arizona, oral comm., 1980). Although some of these deposits may be anomalously uraniferous, it is doubtful they could meet the 90-metric-tons-of-U 308 -at-100-ppm criterion.
MESOZOIC AND CENOZOIC ROCKS
Baboquivari Mountains and Papago Indian Reservation
Pitoikam Formation, Ali Molina Formation, and Metamorphic Rocks of Chutum Vaya. The Pitoikam and Ali Molina Formations are unfavorable for uranium occurrences in sandstone (Class 240) and volcanic (Classes 510 through 540)
16 rocks. These units are unfavorable because no reductant, such as carbonaceous material, is present in the sedimentary portions of the rocks. Favorable characteristics, such as the presence of fluorite, sodic pyroxenes or amphiboles, and alteration products, are lacking. The metamorphic rocks of Chutum Vaya are unfavorable for vein-type deposits in metamorphic rocks because the veins present are small, nonpersistent and are not likely to contain a uranium occurrence large enough to be a deposit.
The Ali Molina Formation, of Jurassic age (P1. 8), is exposed in the northwest portion of the Baboquivari Mountains (Haxel and others, 1980). Its lower part contains porphyritic andesite, latite, quartz latite porphyry, and rhyolite flow breccia. Its upper portion consists of pyroclastic or laharic material and interbedded phyllite and phyllitic conglomerate. Radiometric measurements of rhyolitic and schistose rocks within the unit indicate somewhat elevated uranium content in two of the rhyolite samples (MGG 345, 346; Table 4).
The Pitoikam Formation, of Jurassic age (P1. 8), is exposed in the central portion of the Baboquivari Mountains (Haxel and others, 1980). The Pitoikam Formation is divided into a lower conglomerate member, the middle Contreras Conglomerate Member, and the upper Chiltepines Member. The lower conglomerate member is composed of alternating beds of volcanic conglomerate, sandstone, and siltstone. The Contreras Conglomerate Member is made up of conglomerate, sandstone, and siltstone-sized quartz latite porphyry fragments. The Chiltepines Member is composed of shale, which contains thin beds of arkose, quartzite; and in the basal part, the Chiltepines Member is composed of a volcanic conglomerate (Heindl and Fair, 1965).
The metamorphic rocks of Chutum Vaya (P1. 8) are exposed at the southern end of the Baboquivari Mountains. This unit was apparently derived from the Ali Molina and Pitoikam Formations by a Late Cretaceous metamorphic event (Haxel and others, 1980). Two radiometric readings within the Metamorphic rocks of Chutum Vaya showed somewhat elevated uranium contents. A rhyolite porphyry (MGG 140, App. D; MGG 309, Table 4) with vuggy quartz-filled fractures had an equivalent uranium content of 13 ppm. A phyllite with hematite-stained veins of quartz, malachite, and azurite (Table 4) contained 33 ppm equivalent uranium. None of the other rock types in the unit showed anomalous uranium values (Table 4). Because of the very limited extent of veins present in the unit it is unlikely a deposit of 90 metric tons of 100- ppm U3 08 could be present.
Intrusives of Jurassic Age. Intrusives of Jurassic age (Pl. 8) are exposed in the central and northern Baboquivari Mountains (P1. 7). They are unfavorable for uranium deposits in plutonic igneous rocks (Classes 310 through 380) because they are not known to have favorable features, such as the presence of sodic pyroxenes or amphiboles, miarolitic cavities,.or fluorite.
The rocks do have some favorable characteristics. Most are relatively quartz rich. They range from alkali-feldspathic to granodioritic in composition (Haxel and others, 1980). Petrographic samples of an intrusive at the north end of the Baboquivari Mountains (MGG 077, 081, App. D; P1. 5) show argillic and sericitic alteration, although it should be noted that the
17 TABLE 4. FIELD GAMMA-RAY SPECTROMETRIC DATA FOR THE BABOQUIVARI MOUNTAINS AND PAPAGO INDIAN RESERVATION
Radiometric measurements Sample no. Age Formation* Rock type eK eU eTh eTh (%) (ppm (ppm) /eU
MGG 344 Tertiary Sedimentary, volcanic and Rhyolite 5.65 8 39 4.9 intrusive rocks
348 Tertiary Sedimentary, volcanic and Tuff 3.27 6 26 4.3 intrusive rocks
329 Tertiary Monzogranite of Pan Tak Pegmatite dike 4.31 11 18 1.6
315 Tertiary Porphyry of Tinaja Spring Aplite dike 9.91 11 49 4.5
316 Tertiary Porphyry of Tinaja Spring Monzonite 6.10 6 44 7.3
342 Tertiary Porphyry of Tinaja Spring Granite 8.00 11 47 4.3
300 Tertiary or Cretaceous Granite of Presumido Peak Granite 4.56 5 10 2.0
301 Tertiary or Cretaceous Granite of Presumido Peak Granite 4.25 3 6 2.0
302 Tertiary or Cretaceous Granite of Presumido Peak Granite 5.63 4 11 2.8 303 Tertiary or Cretaceous Granite of Presumido Peak Granite 4.88 4 39. 9.8
304 Tertiary or Cretaceous Granite of Presumido Peak Granite 5.83 7 19 2.7
305 Tertiary or Cretaceous Granite of Presumido Peak Granite 4.95 5 17 3.4
306 Tertary or Cretaceous Granite of Presumido Peak Quartz Diorite 6.07 7 28 4
331 Tertiary or Cretaceous Granite of Presumido Peak Lamprophyre dike 3.37 47 25 0.5 TABLE 4. FIELD GAMMA-RAY SPECTROMETRIC DATA FOR THE BABOQUIVARI MOUNTAINS AND PAPAGO INDIAN RESERVATION (Continued)
Radiometric measurements t Sample no. Age Formation * Rock type eK eU eTh eTh (%) (ppm) (ppm) /eU
MGG 332 Tertiary or Cretaceous Granite of Presumido Peak Granite 4.77 8 13 1.6
333 Tertiary or Cretaceous Granite of Presumido Peak Granite 5.27 5 13 2.6
334 Tertiary or Cretaceous Granite of Presumido Peak Granite 4.39 10 16 1.6
335 Tertiary or Cretaceous Granite of Presumido Peak Granite 4.14 4 8 2
347 Cretaceous or Jurassic Chiuli Shaik Formation Conglomerate 5.87 9. 26 2.9
343 Jurassic Syenogranite of Baboqui- Granite 5.04 6 17 2.8 vari Peak
317 Jurassic Kug Granite 5,92 9 44 4.9 Wongogranite of Pavo 318 Jurassic Monzongranite of Pavo Kug Monzoni te 6.17 9 42 4.7 Wash
319 Jurassic Monzogranite of Pavo Kug Quartz Montonite 7.90 8 35 4.4 Wash
328 Jurassic Monzogranite of Pavo Kug Pegmat ite dike 4.15 8 11 1.4 Kug Wash TABLE 4. FIELD GAMMA-RAY SPECTROMETRIC DATA FOR THE BABOQUIVARI MOUNTAINS AND PAPAGO INDIAN RESERVATION (Continued)
Radiometric measurement st emAneUR eTh eT Sample No. Age Formation* Rock TypeK (ppm) (ppm) /el U
MGG 324 Jurassic Monzongrani te-granodi on te Granite 4.52 5 20 4 of Kitt Peak
327 Jurassic Monzongrani te-granodiorite Granite 4.40 5 25 5 of Kitt Peak
312 Jurassic Mulberry Wash Formation Intermediate 8.14 9 48 5.4 volcanic N\ O 346 Jurassic Ali Molina Formation Intermediate 3.36 8 20 2.5 volcanic
345 Jurassic Ali Molina Formation Rhyolite 9.51 8 23 2.9
349 Jurassic Ali Molina Formation Biotite schist 4.87 7 29 4.1
350 Jurassic Ali Molina Formation Rhyolite 3.94 3 9 3
307 Jurassic Metamorphic rocks of Rhyolite 4.56 5 18 3.6 Chutum Vaya
308 Jurassic Metamorphic rocks.of Rhyolite 6.10 8 43 5.4 Chutum Vaya
309 Jurassic Metamorphic rocks of Rhyolite 6.6 13 42 3.2 Chutum Vaya
310 Jurassic Metamorphic rocks of Rhyolite 3.38 9 28 3.1 Chutum Vaya TABLE 4. FIELD GAMMA-RAY SPECTROMETRIC DATA FOR THE BABOQUIVARI MOUNTAINS AND PAPAGO INDIAN RESERVATION (Continued)
Radiometric measurements) r Sample no. Age Formation* Rock type eK eU eTh eTh (%) (ppm) (ppm) /eU
MGG 311 Jurassic Metamorphic rocks of Copper oxide vein 5.04 33 75 2.3 Chutum Vaya
313 Jurassic Metamorphic rocks of Volcanic breccia 5.47 7 31 4.4 Chutum Vaya
314 Jurassic Metamorphic rocks of Rhyolite 5.34 9 43 4.8 Chutum Vaya
340 Jurassic Metamorphic rocks of Si It stone 3.03 6. 16 2.7 Chutum Vaya
341 Jurassic Metamorphic rocks of Phyllite 2.55 4 11 2.8 Chutum Vaya
336 Tertiary Unnamed Intermediate vol- 3.84 5 24 4.8 canic
337 Tertiary Unnamed Intermediate vol- 3.36 4 21 5.3 cani c
338 Tertiary Unnamed Andesite 4.77 4 14 3.5
339 Mesozoic Unnamed Schist 5.54 8 37 4.6
351 Jurassic Unnamed Quartz diorite 3.94 3 9 3 TABLE 4. FIELD GAMMA-RAY SPECTROMETRIC DATA FOR THE BABOQUIVARI MOUNTAINS AND PAPAGO INDIAN RESERVATION (Continued)
Radiometric measurement s t Sample no. Age Formation* Rock type eK eU eTh eT (%) (ppm) (ppm) /e U
MGG 352 Tertiary or Cretaceous Unnamed Gnessic Granite 4.01 3 12 4
353 Tertiary or Cretaceous Unnamed Gnessic Granite 4.32 3 10 3.3
354 Tertiary or Cretaceous Unnamed Quartz diorite 5.44 4 33 8.3
355 Tertiary Unnamed Dacite 1.90 10 25 2.5
*Formation names used by Haxel and others (1980) tThe statistical uncertainty for eU values less than 10 ppm is as high as 30%; eU values 10 ppm - 20 ppm have uncertainties as high as 20%; eU values greater than 20 ppm have an uncertainty less than 10%. alteration is not pervasive. The rocks are coarse grained and have porphyritic phases with aplite, granophyre, and pegmatite dikes. Uranium contents range from 4 to 12 ppm (MGG 078, 079, 080, 082, 083, App. B; Table 4) for the rocks in the areas examined (P1. 10a; P1. 5). Even though the intrusives show some favorable characteristics, they are not anomalously uraniferous.
Intrusive Rocks of Cretaceous and Tertiary Age. Intrusive rocks of Cretaceous and Tertiary age (P1. 8) are exposed in the Coyote and middle and southern Baboquivari Mountains (Fig. 3; P1. 7). They are unfavorable for uranium deposits in plutonic igneous rocks (Classes 310 through 380) because they lack such favorable features as fluorite or sodic minerals, and very few mineral occurrences of any type are known.
The rocks are mainly leucocratic monzogranites. Biotite, muscovite, and garnet are common (Haxel and others, 1980). In the Coyote and Pozo Verde Mountains (Fig. 3), the intrusives are mylonitically deformed and display characteristics associated with Cordilleran metamorphic core complexes. These mountains are part of a discontinuous belt of metamorphic core complexes that extend through the Cordillera and southern Arizona into Sonora, Mexico (Coney and Reynolds, 1980). Evaluation, by Charles Kluth (Coney and Reynolds, 1980), of the rocks in the Pozo Verde and Coyote Mountains for uranium favorability of the metamorphic core complexes, resulted in Kluth's classifying them as unfavorable because of their low uranium content, their lack of occurrences of metallic minerals, and their low radioactivity.
Radiometric measurements (Table 4) show no highly anomalous uranium contents. A lamprophyre dike within one of the intrusives (MGG 331, Table 4) has slightly elevated uranium content and low thorium content. The high uranium content may be caused by mobilization and reconcentration of uranium from the surrounding granite to the dike as a result of its intrusion.
Unnamed Rocks West of the Baboquivari Mountains. Unnamed rocks west of the Baboquivari Mountains lie within the Papago Indian Reservation. The units are exposed in the Artesa, South Comobabi, and Alvarez Mountains, the Topawa Hills, and the Etoi Ki buttes in the extreme northwestern part of the quadrangle (Fig. 3). The units include sedimentary, volcanic, intrusive, and metamorphic rocks (P1. 7). The sedimentary rocks, which are of Jurassic age, consist mainly of sericitized argillite and sandstone, but there are some interbedded intermediate volcanic rocks.
The sedimentary sequences are not favorable for sandstone-type uranium occurrences (Class 240) because there is no evidence for such reductants as carbonaceous matter or pyrite; there are no scour-and-fill sedimentary structures; and there are no mudstone interbeds.
Dacite and rhyodacite flows, some of which are vesicular, occur at Etoi Ki and vicinity, the Artesa Mountains, and the South Comobabi Mountains. Porphyritic varieties have nonsodic phenocrysts. Such favorable aspects as spherulitic and devitrification textures are locally present. Some of the flows are also strongly silicified, possibly because of magmatic fluids.
23 Associated, moderately to strongly welded tuffaceous units display favorable characteristics similar to those indicated above.
Locally, vesicular andesitic flows and trachyandesites are also found at Etoi Ki south of Sells, and in the South Comobabi Mountains. Some are porphyritic. The porphyritic varieties are nonsodic. The units are altered: plagioclase laths show evidence of sericitization; pyroxene is commonly altered to chlorite, calcite, and hematite.
The volcanic units, comprising dacite, rhyodacite, andesite, and trachyandesite, are not favorable for volcanogenic uranium deposits (Classes 510 through 540) because alkali feldspars, sodic pyroxenes and amphiboles, and fluorite are not known to be present. Also, there is no evidence that the units are subvolcanic or ring-fracture intrusives. Neither is there any evidence of albitization. There are no uranium occurrences or radiometric anomalies associated with the volcanic units. Furthermore, radiometric measurements indicate low equivalent-uranium values (MGG 336, 337, 338, 355, Table 4). The highest value, in a dacite sample, is only 10 ppm eU (MGG 335, Table 4).
The igneous intrusive units range in composition from dioritic to muscovite monzogranitic. Outcrops are found at Topawa Hills and the Artesa Mountains. The intrusives are characterized by fine- to medium-grained textures; some are hypidiomorphic granular. Phenocrysts comprise quartz and feldspar. Muscovite and biotite are found together in some leucocratic units; the former is commonly the more abundant. Apatite and zircon, as accessory minerals, occur in minor amounts. The leucogranitic units may have aplitic and pegmatitic phases. The igneous intrusive rocks are unfavorable for uranium occurrences in and associated with plutonic igneous rocks (Classes 310 through 380) because they lack sodic feldspars, fluorite, sodic ferromagnesium minerals, shear and fracture zones, base-metal deposits, miarolitic cavities, and airborne radiometric anomalies. Ground gamma-ray spectrometric measurements indicate low equivalent-uranium values (MGG 351-354, Table 4). Favorable aspects include the presence of a two-mica granite and its pegmatitic and aplitic phases.
Metamorphic rocks crop out in the Topawa Hills, Artesa Mountains, and Alvarez Mountains. The metamorphic rocks are mainly orthogneiss and schistose units. Microline and oligoclase are the usual phenocrysts. Accessory radioactive allanite, apatite, and zircon are present. Garnetiferous aplite dikes and pegmatite intrude the metamorphosed rocks. The metamorphosed units are not favorable for vein-type uranium deposits in metamorphic rocks (Class 720) because there is no evidence of sulfides; pelitic schists are not known; feldspathization and carbonatization did not occur; radioactivity is low (MGG 339, 352, 353; Table 4); and no airborne radiometric anomalies are present.
Atascosa Mountains
Montana Peak Formation. The Montana Peak Formation, of Oligocene age, (P1. 8) overlies Mesozoic rocks north and northwest of the Pajarito Mountains. The formation is well exposed in Pena Blanca Canyon (Fig. 3). It is unfavorable for volcanogenic uranium occurrences (Classes 510 through 540) because no reductants are present, and no sodic pyroxenes or amphiboles,
24 sulfide minerals, or fluorite have been found or are reported. No uranium occurrences or mineral deposits of any type are found in the unit.
The formation consists mainly of andesitic agglomerates, breccias, and airfall and water-laid tuffs. Numerous ash layers and flows of porphyritic andesite are also present (Nelson, 1963). Numerous veinlets of quartz, chalcedony, opal, and calcite cut the unit (Nelson, 1963). There is no evidence of hydrothermal activity. A tuff, which was measured radiometrically, contained only 7 ppm equivalent uranium (MGG 163, App. B2).
Atascosa Formation. The Atascosa Formation, of Miocene age(?), is exposed principally in the Atascosa Mountains (Fig. 3; P1. 7). The Atascosa is unfavorable for volcanogenic uranium occurrences (Classes 520 through 540) because no evidence of a reducing mechanism was noted; the volcanic rocks are silicic, but do not carry anomalous quantities of lithophile elements; the unit is not associated with any recognized cauldron system; and no mineral deposits of any type are found in the formation.
The following discussion of the Atascosa Formation is based principally on Nelson's (1963) study of the unit in the Pena Blanca Canyon area. The formation consists mainly of lithic and vitric tuffs with interbedded lenses of conglomerate. The whole formation is well indurated, and it has pronounced bedding. In places, it is broken by numerous joints and faults.
The tuffs of the Atascosa Formation are well bedded; they probably were water laid. The tuffs have rhyolitic to quartz latitic compositions and consist mainly of devitrified glass and pumice lapilli. They are commonly argillaceous and contain phenocrysts of orthoclase, sanidine, oligoclase, and quartz. Biotite, magnetite, and glass shards occur in lesser amounts. Secondary minerals include sericite, calcite, opal, and chalcedony. One sample of a vitric tuff (MGG 161, App. B1) within the Atascosa contained 16 ppm equivalent uranium. Although this represents anomalous radioactivity, there were no uranium concentrating mechanisms in the unit.
Pena Blanca Formation. The Pena Blanca Formation (Nelson, 1963), of late Miocene(?) age, is exposed east of the Atascosa and Pajarito Mountains. The formation is unfavorable for volcanogenic (Classes 510 through 540) and sandstone (Class 240) uranium deposits. No reductants, such as pyrite or carbonaceous material, are present in the sediments. There is no source for uranium within the unit: the glass shards present are not devitrified.
The formation consists of a sequence of distinctly bedded conglomerates with interbedded layers of tuff and basalt (Nelson, 1963). Conglomerate beds of the formation are tuffaceous and well consolidated. They consist of a coarse- to fine-grained conglomerate with lenses of arkosic sandstone. Fragments in the conglomerate consist of ignimbrite, andesite, quartz latite, arkose, and rhyolite. Chalcedony can be found in numerous veinlets as veneer and fragments throughout the formation (Nelson, 1963).
Layers of vitric and lithic tuff within the Pena Blanca measure from a few inches to over 6 ft in thickness. The tuff layers are commonly well bedded and lenticular (Nelson, 1963).
25 Cerro Colorado, San Luis, and Tumacacori Mountains: Volcanic and Sedimentary Rocks of Tertiary Age
Volcanic and sedimentary rocks of Miocene and Oligocene(?) age compose a large portion of the Tumacacori and Cerro Colorado Mountains and a small part of the San Luis Mountains (Fig. 3; P1. 7). They are correlative to the Montana Peak, Atascosa, and Pena Blanca Formations discussed previously and are unfavorable for volcanogenic (Classes 510 through 540) and sandstone (Class 240) uranium deposits for the same reasons given for the above.
Sierrita Mountains
Ox Frame Volcanics. The Ox Frame Volcanics, of Triassic age, are exposed in the southern Sierrita Mountains. They consist of generally light-colored silicic rocks, which range in composition from rhyolitic to rhyodacitic, and of dark-colored andesite and dacite. They comprise-ash flows, flow breccias, welded and nonwelded tuffs, and tuff breccias. They are unfavorable for uranium occurrences in volcanogenic environments (Classes 510 through 540) because alkali feldspars are not known; sodic pyroxenes or amphiboles are absent; fluorite, which could indicate volatile-rich magma, is unknown. There are no known uranium occurrences or any airborne radiometric anomalies. There are high silica and potassium contents, but fluorine content appears to be low (MGG 058, App. B1).
Rhyolitic flows compose the lower member of the Ox Frame volcanic sequence. Porphyritic textures are common (MGG 059, App. D). Potassium feldspars are commonly composite phenocrysts. Plagioclase is commonly of oligoclase-andesine composition. The feldspars are slightly to moderately argillized and sericitized. Altered andesite and some lenticular rhyolite flows compose the middle member. The upper part of the middle member of the formation consists of andesite flows and dacite with lenses of andesitic tuff, tuff breccia, and andesitic sandstone. Rhyolitic extrusive rocks with intercalated lenses of quartzite are found in the upper member. The rocks are locally flow banded. A favorable mineralogic aspect of the rhyolite is that the feldspar crystals are perthitic orthoclase accompanied by sericitic albite and phenocrystic quartz (Cooper, 1971).
Rodolfo Formation. In ascending order, the Triassic Rodolfo Formation consists of a basal conglomerate, siltstone, sandstone and conglomerate, and an upper volcanic member composed mainly of andesitic breccia. The sedimentary sequence lacks channel-fill or scour features. Moreover, there is no carbonaceous trash, limonitic alteration, or bleaching of the rocks documented in the literature (Cooper, 1971) and is therefore unfavorable for sandstone-type uranium deposits (Class 240). The upper volcanic member is unfavorable for volcanogenic uranium deposits (Classes 510 through 540) because alkali feldspars, sodic pyroxenes or amphiboles, fluorite or sulfides are not present.
The conglomerate consists of chert, quartzite, and limestone pebbles set in a sandy matrix. Coarse-grained sandstone is interbedded with the conglomerate and the overlying beds. Indistinctly bedded, nonfissile siltstone predominates in the middle member of the Rodolfo and is
26 characterized by widely distributed lenses of pebble conglomerate. The volcanic member is a propylitized andesitic breccia and includes a probable extrusive dacitic and rhyolitic rock.
Tascuela Redbeds. The Tascuela Redbeds, of Triassic age, are in the southwestern Sierrita Mountains. The sequence consists of a coarse basal conglomerate, shale and argillite, and sparse beds of sandstone, quartzite, and sandy limestone. The basal conglomerate includes volcanic graywacke and sedimentary rocks. Shale and argillite overlie the basal conglomerate. The red beds have been partially metamorphosed to slate, phyllite, and mica schist (Cooper, 1971). There is no literature documentation of the existence of any precipitant for uranium deposition in the Tascuela Redbed sequence. The Tascuela is therefore unfavorable for sandstone-type uranium deposits (Class 240).
Stevens Mountain Rhyolite. In the western Sierrita Mountains (P1. 13), the Stevens Mountain Rhyolite, of Late Triassic or Early Jurassic age (Cooper, 1971), is exposed at Stevens Mountain, its type locality. The rhyolite is not favorable for volcanogenic uranium deposits (Classes 510 through 540) because it is not alkali rich. The agpaitic coefficient and the fluorine content are low (MGG 153, App. B1); it lacks such sodic ferromagnesian minerals as aegerine, riebeckite, and sodic plagioclases; airborne radiometric data and hand-held scintillometer traverses over outcrops show no anomalous radioactivity; and uranium occurrences are not known.
The Stevens Mountain Rhyolite consists of a basal volcanic conglomerate and overlying rhyolitic crystal tuffs, welded tuffs, and flows. The conglomerate comprises pebbles and cobbles of felsic volcanic rocks in a tuffaceous matrix, which grades upward into overlying crystal tuff. Rhyolitic tuffs and flows are commonly porphyritic; phenocrysts comprise orthoclase, quartz, chalky plagioclase, and altered biotite (Cooper, 1971). Interbedded quartzite occurs locally in the tuffs and flows. Petrographic analysis of Sample MGG 152 (App. D) details the characteristics of the rhyolitic volcanic sequence.
Sierrita Granite-Harris Ranch Monzonite. The Sierrita Granite and part of the Harris Ranch Monzonite, both Jurassic, are unfavorable for magmatic- hydrothermal uranium deposits (Class 330) because the environment fails to meet the tonnage and grade requirements. However, there are many favorable aspects: brecciated veins and vein systems are common; quartz and some chalcedony are found in the veins; fluorite, pitchblende, and some calcite are reported (Bissett, 1958); argillic and iron oxide alteration is common; and some shear zones and veins are anomalously radioactive. There is one uranium occurrence known, as well.
The area has many faults. Veins occupy steep fracture zones. Quartz composes the bulk of the vein material, although it is not the metamict, smoky variety. At the Diamond Head uranium occurrence (UOR-7, App. C), pyrite, fluorite(?), calcite, and chalcopyrite with malachite are found as accessory minerals. Brecciation is common there. Sparse copper carbonate minerals were also found in narrow quartz-hematite veins in the vicinity. Emission
27 spectrographic data (MGG 029, App. B) did not indicate above-average concentrations of elements other than that mentioned above.
The alaskite and granite adjacent to the veins are argillized. Within the strongly jointed country rock itself, feldspars have been slightly to moderately argillized (MGG 027, 030, 070, and 072, App. D).
Anomalous radioactivity is associated with some quartz-hematite veins. They may have sparse copper carbonate minerals associated with them. The radioactivity along them is variable; many of them have no radioactivity at all, whereas some register about twice background value. Because of extensive alluvial mantling of the steep canyon slopes, the better exposed veins are along the dry washes. Gamma-ray spectrometric results are summarized in the following table (Table 5).
TABLE 5. RADIOMETRIC DATA FOR SIERRITA GRANITE AND HARRIS RANCH MONZONITE
K eU eTh eTh/ Sample No. (%) (ppm) (ppm) eU
MGG 069 3.68 8 31 3.9
MGG 092 3.71 6 45 7.5
MGG 073 2.27 58 34 1.7
MGG 089 5.09 90 20 0.2
Samples MGG 069 and 092 represent radiometric data for unmineralized surficial exposures. MGG 073 and 089 are from anomalously radioactive shear zones within the Sierrita Granite.
Of special interest is sample MGG 089, which has a Th/U ratio less than one. It could possibly indicate fractionation of the two elements or perhaps a slight uranium enrichment or a depletion of thorium.
Uranium minerals are present in the area. Yellow coatings occur along the walls of the portal at the Diamond Head uranium occurrence. They were identified as bayleyite. Pitchblende is also reported (Bissett, 1958). Furthermore, a chemical uranium value of 13 ppm cU3O 8 (MGG 029, App. B) reflects the uranium content of the mineralized vein at the Diamond Head. A magmatic-hydrothermal system is invoked because of the presence of pyrite, quartz, chalcedony, hematite, carbonates, and base-metal sulfides.
The granitic host rock has been strongly broken, faulted, and brecciation is common. Therefore, it is possible that much of the uranium has been leached from the surface. The inferred mineral assemblage is bayleyite,
28 autunite, or uranophane. There may be pitchblende at depth. These minerals may occur in an inferred gangue of quartz and calcite with minor base-metal sulfides. Depth is estimated to be 100 m (300 ft) below the surface. This depth projection is based on the exposed strike length of the veins elsewhere in the Basin and Range Province. Expected grades may vary from 500 ppm to about 2,500 ppm uranium (Tilsley, 1978) in hydrothermal deposits.
Whitcomb Quartzite. The Whitcomb Quartzite, a Lower Cretaceous(?) unit, is present in the eastern part of the Sierritas. It is mainly a well-sorted, fine- to medium-grained, indistinctly bedded orthoquartzite. About 25 percent of the Whitcomb consists of a rhyolitic tuff (Cooper, 1971) that overlies the quartzite. The orthoquartzite has about 10 percent sericitized and argillized feldspar grains.
It is possible that some uranium was present in, and subsequently released from, the rhyolitic tuff since it is devitrified. The altered feldspar grains in the orthoquartzite constitute a possible uranium source, as well. Even if uranium had been leached from the possible sources cited, however, it is doubtful, given the orthoquartzite's unfavorable characteristics, that uranium deposits would have been found in the Whitcomb; carbonaceous matter is not known to be present, and the orthoquartzite's differential permeability is low. The unit is therefore classified unfavorable.
Demetrie Volcanics. The Demetrie Volcanics, of Late Cretaceous age (Cooper, 1971), are unfavorable for all classes of volcanogenic uranium deposits (Classes 510 through 540) because they lack soda-rich, highly differentiated units; metamict fluorite is not known to be present; there are neither significant uranium occurrences nor airborne anomalies; and evidence of extensive silicification is also lacking. Hematitic alteration and albitization, which indicates the presence of volatiles, are minor.
The formation comprises a thick sequence of andesitic and dacitic breccias. There is some local conglomerate and rhyolitic tuff (Cooper, 1971). Andesitic breccia is the most widespread rock in the formation. Feldspar phenocrysts are common; they are zoned and range in composition from oligoclase to andesine (MGG 057, App. D). Argillization and sericitization may locally be intense. There are two intercalated rhyolitic tuff members; both consist of ashfall and ash-flow tuffs and contain some disseminated pyrite. This tuff is porphyritic in part. The phenocrysts comprise quartz, plagioclase, sanidine, and locally orthoclase.
Ruby Star Granodiorite. The Ruby Star Granodiorite, of Paleocene age (Cooper, 1973; P1. 7), is extensively exposed in the northern Sierrita Mountains. It is a northwestward-trending batholith of varying textures and includes a quartz monzonite porphyry differentiate. The unit has localized bodies of aplite. The granodiorite is a porphyritic rock with coarse phenocrysts of potassium feldspar. Accessory minerals include apatite, sphene, and zircon.
29 The Ruby Star Granodiorite is not favorable for uranium deposits associated with plutonic igneous rocks (Classes 310 through 380) because sodic pyroxenes or amphiboles are not known to occur; there is no evidence of extensive albitization of hematization; fluorine content is low (MGG 067, App. B1); and there are no sodic plagioclase feldspars present. Furthermore, a subaluminous or peralkaline pluton cannot be demonstrated, as its agpaitic coefficient is less than one. There are no airborne radiometric anomalies over the intrusive and surface radioactivity is not above normal background values (MGG 065, 066, 068, 074, 094, and 123, App. B1).
At the Twin Buttes Mine (P1. 13), a thermal and metasomatic aureole surrounds the quartz monzonite phase of the Ruby Star Granodiorite and extends into Paleozoic and Mesozoic sedimentary sequences (Barter, 1978). Copper is being mined from the altered sedimentary rocks. Uranium is produced as a byproduct from leach solutions. The solutions (reportedly from the copper oxide minerals present in the aureole) carry about 35 ppm uranium. Daily production is about 700 lb U3 08 (Nuclear Fuel, May, 1980). A selected sample of stockpiled copper oxide ore (MGG 124, App. B1) shows a value of only 18 ppm cU 308 . A thin section of very weakly radioactive copper oxide ore (MGG 125, App. D) failed to identify uranium minerals. The uranium may be associated with copper sulfides.
Helmet Fanglomerate. The Helmet Fanglomerate, of Oligocene age, is exposed along the eastern flank of the Sierrita Mountains. According to the literature (Cooper, 1960), it is a coarse, poorly sorted, poorly bedded conglomerate with angular pebbles, cobbles, and boulders in a silty matrix. The fragments are of Paleozoic and Cretaceous(?) rocks. It has intercalated beds of andesitic lava flows, a few rhyolitic tuffs, tuffaceous sediments, and lenses of monolithologic breccias and conglomerates. The Helmet probably formed as fan deposits near the base of a tectonically active mountain mass. It is unfavorable for all classes of uranium deposits in sedimentary and volcanogenic rocks be ause it lacks precipitants.
Santa Rita Mountains
Mount Wrightson Formation. The Mount Wrightson Formation, of Triassic age, underlies the crest of the high central part of the Santa Rita Mountains (Drewes, 1971a). It is informally divided into three members. The upper and lower members of the formation consist of andesitic and dacitic lava flows. These lava flows are not favorable for volcanogenic uranium occurrences (Classes 510 through 540) because neither sodic amphiboles nor pyroxenes are present; plagioclase feldspars are too calcic; fluorite is not known to occur; fluorine content of the intrusive is generally low (MGG 134, 155, App. B1); and the agpaitic coefficient is less than one. There is no evidence of extensive silification or hematitic alteration. Furthermore, miarolitic cavities were not seen. The middle member has some favorable features, but time constraints precluded adequate evaluation of the unit. It is discussed further in "Unevaluated Environments."
Piper Gulch Monzonite. The Triassic Piper Gulch Monzonite intrudes the Mount Wrightson Formation and, in turn, is extensively intruded by the Squaw
30 Gulch granite and by some even younger rocks (Drewes, 1971). The monzonite is not favorable for uranium occurrences in and related to plutonic igneous rocks (Classes 310 through 380) because it has a low silica content (less than 60 percent); its agpaitic coefficient is less than one; weight percentages of lime and magnesia are relatively high; the plagioclase feldspars are too calcic; and there are no sodic ferromagnesian minerals present. Moreover, miarolitic cavities and fluorite are not present.
The unit varies in composition from monzonitic to granitic (MGG 095 and 096, App. D). It has a hypidiomorphic texture. There has been moderate to intense argillization and sericitization. Accessory minerals include apatite, zircon, and sphene.
Squaw Gulch Granite. The Jurassic Squaw Gulch Granite intrusive is in the southern Santa Rita Mountains (Pl. 9). The pluton is unfavorable for magmatic-hydrothermal uranium occurrences associated with plutonic rocks (Class 330) because it fails to meet tonnage and grade requirements. Nevertheless, favorable characteristics include: the epizonal intrusive is alaskitic to quartz monzonitic in composition; there are small masses of aplite; sericitic, argillic, and hematitic alteration is present; silica weight percentages are high; magnesium and calcium oxide contents are low; there are high sodium and potassium contents; and the thorium-to-uranium ratios are less than one. Part of an airborne radiometric anomaly occurs over the intrusive. There are uranium occurrences, and anomalously high radioactivity is found over scattered areas. Brecciated veins that contain lead, copper, gold, and silver are found near the area of the airborne radiometric anomaly.
The Squaw Gulch Granite is a leucocratic rock of granitic to quartz monzonitic composition. The mineral constituents are potassium feldspar, quartz, and plagioclase. The plagioclase feldspars are albite. They have been altered to clay minerals and sericite, which obscures any evidence of albitization (Drewes, 1976b). The pluton appears to be a late-stage differentiate, probably epizonal in origin, as there are small masses of aplite contained in the unit; these masses commonly fill dilation fractures and may represent expansion fractures caused by deroofing of the pluton. The pluton is also characterized by sharp, steep contacts. Roof pendants and xenoliths are found locally.
Chemically, the Squaw Gulch granite has favorable characteristics: the silica content is about 74 percent; sodium and potassium oxide values are relatively high; magnesium and calcium oxide contents are low (Drewes, 1976b).
In the highly sheared and altered zone, sodium oxide has apparently been leached (Table 6, MGG 143). Fluorine is not enriched in the altered granite, but some enrichment was noted in the vein (Table 6, MGG 146). The hydrothermal solutions that formed the vein may have effectively transported uranium as a UF6 complex. No fluorite was observed in the veins.
Anomalous radioactivity is found in the immediate vicinity of the Blue Jay Mine -(UOR-27, App. A) in the southern part of the intrusive. This radioactivity is associated with closely spaced, steeply dipping quartz- hematite veins that strike roughly east-west. This east-west alignment of
31 TABLE 6. PARTIAL WHOLE-ROCK ANALYSIS OF A SHEARED ZONE AND VEIN IN THE SQUAW GULCH GRANITE
Na2 0 K20 A1 2 03 Si0 2 F Sample No. (%) (%) (%) (%) (ppm)
MGG 143 0.23 5.62 14.88 70.76 425
MGG 146 0.16 4.11 9.04 77.30 957
veins occurs also in younger units surrounding the intrusive. Magmatic- hydrothermal uranium veins are commonly restricted to fractures of a single orientation; so it is unlikely that either veins or trends, other than those of east-west orientation in this area, are particularly uraniferous. The veinlets, which are commonly quite resistant to erosion, are between 1 and 3.5 cm in width and can be traced on the surface for 30 to 40 m. Near some of the quartz-hematite veinlets, the altered granite has been locally replaced by gossanlike hematitic masses. Such masses could be uranium-ore guides. An occasional cavity after pyrite(?) was noted in the veinlets, but no sulfides were found.
Radioactivity of the veinlets ranges from 5 to 9 times the background radioactivity. It occurs sporadically. Some of the veinlets have no anomalous radioactivity. Radiometric data for the Squaw Gulch area are summarized in Tables 7a, 7b, and 7c; (see Fig. 4). The results in Table 7a indicate a very low Th/U ratio (0.1-0.8) for veinlets that have the highest radioactivity. This indicates that thorium and uranium could have been fractionated.
Table 7b summarizes the results of analyses of samples of those veinlets that have little or no radioactivity. The Th/U ratios are greater than one. Perhaps there was some leaching of uranium or partial fractionation of thorium and uranium.
Table 7c summarizes radiometric data for the unmineralized altered host rock. Higher Th/U ratios are indicated, varying from 3 to 5.
Autunite was reported at the Blue Jay occurrence (Miller, 1956; PRR-A-101), but no uranium minerals have been observed in the area. Some concentration of uranium in shear zones is indicated by the chemical uranium contents of samples MGG 143 and 146, which have 94 ppm cU3 08 and 15 ppm cU3 08 , respectively (Table 6).
Although no evidence was seen of sulfides, there are copper and lead deposits in the area. Some of the deposits are enriched in gold and silver. Uraninite or pitchblende is reported from the Happy Jack Mine (Schrader, 1915) where it is associated mainly with lead-silver ore. Such ores occupy steep to
32 TABLE 7a. DATA, RADIOACTIVE VEINLETS IN THE SQUAW GULCH GRANITE
K eU eTh eTh/ Sample No. (%) (ppm) (ppm) eU
MGG 385 8.13 60 51 0.8
MGG 388 4.89 47 31 0.7
MGG 389 6.95 72 48 0.7
MGG 390 21.84 649 77 0.1
MGG 391 8.46 139 60 0.4
MGG 393 8.28 161 60 0.4
MGG 396 8.27 89 54 0.6
MGG 397 7.61 139 73 0.5
TABLE 7b. DATA, NONRADIOACTIVE VEINLETS IN THE SQUAW GULCH GRANITE
K eU eTh eTh/ Sample No. (%) (ppm) (ppm) eU
MGG 384 7.15 19 64 3.4
MGG 394 6.04 24 52 2.2
MGG 395 5.84 35 43 1.2
MGG 400 2.78 9 28 3.1
MGG 402 5.73 13 43 3.3
MGG 403 6.70 24 44 1.8
33 TABLE 7c. RADIOMETRIC DATA, ALTERED ROCK, SQUAW GULCH GRANITE
K eU eTh eTh/ Sample No. (%) (ppm) (ppm) eU
MGG 386 6.56 19 54 2.8
MGG 397 4.44 12 33 2.8
MGG 392 5.50 12 41 3.4
MGG 398 4.02 9 37 4.1
MGG 399 4.37 6 32 5.3
MGG 401 5.12 12 35 2.9
MGG 404 5.64 11 37 3.4
MGG 405 5.45 10 43 4.3
MGG 406 6.79 16 34 2.1
vertical fault or fracture zones. Uranium minerals can be encountered at shallow depths as lenticular or pod-shaped masses (about 100 m [300 ft] from the present erosion surface), if the shear zones persist in strength at depth.
Because of the hydrothermal environment, the probable uranium-ore minerals, should they exist, are uraninite and pitchblende. Ore-grade concentrations of uranium minerals should be spotty and should occur in distinct areas along the veins because uranium-rich fluids commonly are concentrated along dilated zones.
Fort Crittenden Formation. Scattered exposures of rocks assigned to the upper red conglomerate and tuff members of the Fort Crittenden Formation (Drewes, 1971) occur along the western slopes of the Santa Rita Mountains. The Duranium occurrence (UOR-32, App. A) is in this sedimentary sequence. Because some uraniferous rock was produced from the Duranium, the unit was studied in this area.
The Fort Crittenden is unfavorable for sandstone-type uranium deposits (Class 240) because neither interstitial carbonaceous material nor pyrite was found, and none has been documented (MGG 051, App. B1). There is no evidence of channel-fill sediments. Also, such indicator trace elements as molybdenum, arsenic, cobalt, nickel, and zinc are either absent or present in insignificant quantities.
34 The sequence exposed near the Duranium occurrence, which appears to be structurally controlled, consists of conglomerate, reddish shale, silicified sandstone, and sedimentary breccia. Gamma-ray spectrometric surface measurements in the vicinity of the Duranium occurrence (Fig. 5) indicate equivalent-uranium values that range from only 3 ppm eU3 08 to 13 ppm eU3 08 (MGG 376 to 382, App. B2). Also, selected radiometric traverses with hand-held scintillometers across exposed rock failed to record significant deviations from normal background radioactivity.
There are, however, some favorable aspects. Lithologies vary from arkosic conglomerate to arkosic sandstone with interstitial conglomeratic beds; finer grained sediments, siltstones, and shale or mudstone are present as well. There is weak to moderate iron oxide staining of the arkose, especially at the Duranium occurrence. Feldspars are moderately argillized.
The Fort Crittenden Formation is also unfavorable for magmatic- hydrothermal uranium deposits (Class 330) because, even though permeable channel-ways (faults) are present and may be locally brecciated, smoky quartz, base-metal sulfides, and dark fluorite were not found. There is no evidence of any veins or vein systems. Also, there are no base-metal deposits evident within the Fort Crittenden. Emission spectrograpic data (MGG 036, 053, App. B1) indicate low values for such indicator elements as uranium, silver, titanium, molybdenum, magnanese, tin, arsenic, and zirconium. There is, however, moderate to strong argillization, and there are varying degrees of chloritization and limonitic alteration along sheared zones.
It is possible that the source of the uranium found at the Duranium occurrence in the Fort Crittenden is the Elephant Head quartz monzonite: airborne radiometric data indicate a distinct northwest-trending anomalous zone partly over this intrusive (P1. 3) and well into the alluvial cover.
Salero Formation. The Salero Formation, of Late Cretaceous age, is found in the western Santa Rita Mountains, Patagonia Mountains, and San Cayetano Mountains (P1. 7). It consists mainly of dacitic volcanic rocks in the Santa Rita Mountains. The sequence is not favorable for volcanogenic uranium deposits (Classes 510 through 540) because neither sodic minerals nor metamict fluorite are known to occur; the agpaitic coefficient is less than one. Although the volcanic members of the Salero are commonly porphyritic and include welded and silicic tuffs, their silica content is less than 70 percent; glass fragments and lithophysae are not present. A value of only 4
ppm eU3 08 (MGG 119, App. B1) was indicated for a tuffaceous sandstone.
The sedimentary members of the Salero comprise argillized arkosic sandstones and conglomerates. They lack precipitants for uranium except in a localized occurrence of fossil plant fragments in siltstone beds of an arkose member in the Santa Rita Mountains (Drewes, 1971).
Josephine Canyon Diorite. The Josephine Canyon Diorite, of Late Cretaceous age, is exposed in the San Cayetano and Santa Rita Mountains as two major stocks (Drewes, 1976b). The unit is unfavorable for all classes of uranium deposits associated with plutonic igneous rocks (Classes 310 through 380) because sodic ferromagnesian minerals and fluorite are not present;
35 silica content is low; agpaitic coefficients are less than one; and no anomalous radioactivity is associated with the unit.
The Josephine Canyon Diorite consists of three phases: diorite, quartz diorite, and quartz monzonite. In addition to the common rock-forming minerals, disseminated allanite and pyrite are present in the diorite (Drewes, 1976b).
Some differentiation of the parent magma is noted. The quartz monzonite represents a later and more silicic phase of the stocks. However, no increase in radioactivity is noted in the quartz monzonite when compared to the diorite.
Some hydrothermal activity is associated with the intrusion of the stocks. Base-metal sulfide deposits and pyritiferous quartz veins transect the stock, locally (Drewes, 1976b). No anomalous radioactivity is associated with the deposits or veins.
Madera Canyon Granodiorite. The Madera Canyon granodiorite stock, consisting of three rock types, is of Late Cretaceous age (Drewes, 1976b). The intrusive is composed of quartz, oligoclase, andesine, perthite, biotite, and some hornblende. Sphene, magnetite, zircon, apatite, and allanite occur as accessory minerals. It is unfavorable for uranium occurrences associated with plutonic igneous rocks (Classes 310 through 380) because its composition is intermediate; porphyritic textures are common; it lacks sodic ferromagnesian minerals; plagioclase feldspars are not sodic; fluorite is not known; and the agpaitic coefficient is less than one. A nonporphyritic granodiorite is the most widespread rock type. It has a hypidiomorphic- granular texture. Porphyritic granodiorite and a melanocratic granodiorite containing abundant hornblende and andesine constitute the other two rock types.
Elephant Head Quartz Monzonite. The Elephant Head Quartz Monzonite, of Late Cretaceous age (Drewes, 1976b), is not favorable for uranium occurrences of the plutonic environment because the intrusive lacks sodic ferromagnesian minerals; its fluorine content is low; fluorite is not known in it; its agpaitic coefficient is less than one; it is mostly nonporphyritic; and miarolitic cavities were not seen in it. Its equivalent uranium content is low (MGG 055, App. B1).
The quartz monzonite, consisting of coarse- and fine-grained phases, has sharp, discordant contacts, but chilled contact zones and contact metamorphosed aureoles are commonly lacking (Drewes, 1976b). Silica contents are high whereas weight percentages of magnesium and calcium oxides are low. Fluorine content is also low (MGG 054, App. BL). Aplitic masses are known but they are small and tabular. Plagioclase feldspars are commonly altered and may be albitized. Traces of allanite, a radioactive mineral, and monazite occur as sparse accessory minerals in some areas. Evidence presented (Drewes, 1968) implies that the quartz monzonite and the Jurassic Squaw Gulch Granite are consanguineous. Moreover, the Squaw Gulch Granite contains Area C (P1. 1), favorable for magmatic-hydrothermal uranium deposits.
36 Gringo Gulch Volcanics. The Gringo Gulch Volcanics, of Paleocene(?) age, are in the southeastern part of the Santa Rita Mountains. The unit is a sequence of rhyolitic to dacitic pyroclastic rocks and intercalated lava flows, sandstone, and conglomerate (Drewes, 1972a). Published information indicates that the volcanics are unfavorable for all classes of volcanogenic uranium deposits (Classes 520 through 540) because they lack sodic pyroxenes, sodic amphiboles, glass, and miarolitic cavities; fluorite is not known to be present; the area is not taphrogenic; there are no uranium occurrences; and no airborne radiometric anomalies were found. Limited rock sampling indicated no anomalous concentrations of uranium (MGG 117, 118, App. B1).
Dacitic lavas and epiclastic rocks, the latter derived from dacitic volcanics, are part of the lower member of the Gringo Gulch Volcanics. The dacitic lavas are commonly finely porphyritic, and the plagioclase phenocrysts are labradorite in composition. The rocks are commonly argillized and propylitized. A rhyolite flow within the lower unit is porphyritic and has argillized potassium feldspar and albitized(?) plagioclase.
Within the upper member of the sequence, andesitic rocks predominate. A basal bluish-gray tuff is included in this member. Plagioclase feldspars are albitized; some altered biotite may be present. Magnetite and apatite occur as accessory minerals. Porphyritic andesitic lava composes the top unit of the upper member. Augite is the most abundant type of phenocryst, and the lava lacks sodic plagioclase. Secondary minerals include calcite, epidote, chlorite, iron oxide, and clay minerals.
Grosvenor Hills Volcanics. The Grosvenor Hills Volcanics, of Oligocene age (Drewes, 1972a), consist mainly of rhyolite and rhyodacite. There are some pyroclastic units. These rocks are extensively exposed in the Grosvenor Hills and the San Cayetano Mountains, southwest of the Santa Rita Mountains. The sequence is unfavorable for all classes of volcanogenic uranium deposits (Classes 510 through 540) because of its lack of soda-rich, highly differentiated units and its low agpaitic coefficient. The unit, except for the rhyolite member, commonly contains less than 72 weight-percent silica and has low potassium oxide content. Sodic pyroxenes and sodic amphiboles are not known to occur. There are no anomalous concentrations of beryllium or molybdenum (Drewes, 1972). There are no significant uranium occurrences or any airborne radiometric anomalies.
The Grosvenor Hills volcanic sequence is divided into a thin basal gravel and silt member, a moderately thick medial rhyolite member, and a thick capping rhyodacite member (Drewes, 1972a). According to the literature, the gravel and silt member occurs commonly as thin, discontinuous sheets of bedded siltstone, shale, and some limestone. Possible reductants, such as fossil plants, are contained in the limestone and shale. The rhyolite member is composed mainly of tuff and tuff breccia. Favorable aspects include the presence of pumice and vitrophyre fragments as well as some opaline material in this member. Argillic alteration is pervasive. The rhyodacite member consists of abundant agglomerate, which is commonly the basal unit, and lava flows. The agglomerate locally contains blocks of silicified wood. Rhyodacite boulders are common in the agglomerate. Lava flows of rhyodacitic composition are next in abundance to agglomerate, and welded tuff makes up less than 10 percent of the rhyodacite member. A favorable aspect of the
37 welded tuff is that it has a glassy to cryptocrystalline groundmass, although plagioclase feldspar phenocrysts are nonsodic. Most rocks of the rhyodacite member are only weakly altered to clay minerals.
Gravels of Nogales. The Gravels of Nogales (Drewes, 1972a), of Miocene(?) age, are present southwest of the Santa Rita Mountains. The rocks consist of moderately well-indurated tuffaceous sand, silt, grit, and pebble gravel deposited by streams on hills of low topographic relief. The clasts are predominantly rhyolitic and rhyodacitic rocks derived mainly from the Grosvenor Hills Volcanics. The Gravels of Nogales are unfavorable for uranium deposits in sedimentary rocks because of unfavorable source-rock lithologies and absence of precipitants.
Whetstone Mountains: Paleocene Intrusive Rocks
Discontinuous sill-like masses or stocks of granodiorite of Paleocene age crop out along the eastern slopes of the Whetstone Mountains (Creasey, 1967). The granodiorite, porphyritic in part, is medium to coarse grained. It has a hypidiomorphic-granular texture. The unit is not favorable for deposits associated with plutonic igneous rocks (Classes 310 through 380) because its lithology is intermediate; it has a low silica content; its agpaitic coefficient is less than one; its magnesia and lime contents are very high; and its fluorine content is average (MGG 062, App. B1). There is no apparent albitization in the intrusive. Miarolitic cavities, pegmatites, aplite masses, or dikes in the intrusive are not observed. Shear zones, although present, are not anomalously radioactive. Sodic ferromagnesian minerals were not observed. There are no uranium occurrences in the intrusive, nor were any airborne radiometric anomalies detected. Furthermore, equivalent uranium content is very low (MGG 061, App. B1).
Patagonia Mountains: Paleocene Intrusive Rocks
Paleocene intrusive granodiorites (Simons, 1974) extend in a north- northwesterly direction from the United States-Mexico boundary along the Patagonia Mountains (Pl. 6). The units appear, for the most part, unfavorable for uranium occurrences in and related to plutonic rocks (Classes 310 through 380), with the possible exception of the magmatic-hydrothermal environment (Class 330), because of its intermediate lithology (MGG 181, App. D); apparent absence of miarolitic cavities; and the lack of sodic ferromagnesian minerals and metamict fluorite. There are no uranium occurrences, and no anomalous airborne radiometric values occur over the intrusive. The granodiorite.is medium- to coarse-grained equigranular to porphyritic rock. The intrusive contains scattered aplite dikes as irregular bodies. Breccia pipes, as much as several hundred feet across, contain numerous rock fragments altered to quartz, sericite, and minor tourmaline, epidote, and jarosite.
Mineralized shear zones and pervasively altered zones in the granodiorite could have uranium concentrations, because a value of 19 ppm cU3 08 (MGG 130, App. B1) was obtained from a shear zone that has base-metal sulfides. Also, a sample containing 42 ppm eU308 (MGG 182, App. B1) was obtained from a mine dump at the Four Metals Mine. This sample may represent an
38 intensely sericitized, kaolinized granodiorite with minor iron oxides and disseminated pyrite. It seems likely, therefore, that the intrusive carries some anomalous uranium within its sheared zones. Further work, though, is required to corroborate these initial results.
Huachuca Mountains
Huachuca Quartz Monzonite. The Huachuca Quartz Monzonite, of Jurassic(?) age (Hayes and Raup, 1968), is an elongate stock that parallels the trend of the Huachuca Mountains. It is a medium-grained biotite-hornblende quartz monzonite with accessory sphene, apatite, and magnetite; plagioclase is of andesine composition (Weber, 1950). The quartz monzonite is cut by gold- pyrite quartz veins that also contain sparse copper, lead, and zinc minerals. The intrusive is not favorable for orthomagmatic uranium occurrences (Class 310), however, because sodic pyroxenes, sodic amphiboles, fluorite, primary and secondary hematite, and albitized feldspars are not evident. There are neither uranium occurrences in the intrusive nor airborne radiometric anomalies associated with it.
Lower Member of Canelo Hills Volcanics. The lower member of the Canelo Hills Volcanics, of Triassic/Jurassic age, exposed in the Huachuca Mountains (Hayes, 1970), consists predominantly of volcanic sedimentary rock and subordinate amounts of interlayered rhyolitic tuff and lava. This lower member is unfavorable for volcanogenic uranium occurrences (Classes 510 through 540) and for sandstone-type uranium occurrences (Class 240). It is unfavorable for volcanogenic uranium occurrences because of the absence of alkali feldspars, sodic ferromagnesian minerals, fluoride, and sulfides. There are no uranium occurrences and no airborne radiometric anomalies. It is also unfavorable for sandstone-type uranium occurrences because reductants such as carbonaceous matter and favorable depositional characteristics (i.e., scour-and-fill structures) are not present.
The volcanic sedimentary rocks consist of conglomerate, sandstone, and mudstone. The constituents of the conglomerate comprise siliceous volcanic rocks and fragments of Paleozoic rocks. The conglomerate is set in a matrix of tuffaceous sandstone or feldspathic graywacke. The sandstone in the member is also feldspathic graywacke and is cross laminated. Mudstone in the member is mostly silty.
Tuffaceous units are usually welded, fine grained and contain quartz, sanidine, microcline, and biotite. Lithic and vitric fragments are commonly sparse.
Bisbee Group. The Bisbee Group, present in both the Mule and Huachuca Mountains, consists, in ascending order, of the Glance conglomerate, Morita Formation, Mural Limestone, and Cintura Formation. The group was evaluated from the literature (Hayes, 1970). It is unfavorable for sandstone-type uranium deposits (Class 240), except in the Morita Formation, which is discussed under "Unevaluated Environments."
39 The Glance conglomerate is unfavorable because favorable lithologies are not present; there is no evidence of fluvial channeling; and precipitants, such as carbonaceous material or pyrite, are lacking. The unit is an alluvial-fan deposit that accumulated in terranes of large relief. The Glance consists of poorly sorted and poorly rounded cobbles and pebbles set in a matrix of sandy and silty mudstone. Volcanic rocks in the Glance conglomerate in the Huachuca Mountains are lavas of intermediate compositions. They are mostly porphyritic, but vesicular varieties are also present. The lavas are not favorable for volcanogenic uranium occurrences (Classes 510 through 540) because they have low silica contents; they have high magnesium and calcium contents; and they have agpaitic coefficients less than one. Furthermore, sodic ferromagnesian minerals and fluorite are not present.
The Mural Limestone comprises calcareous mudstones, impure fossiliferous limestone, calcareous siltstones, and sandstones. The limestone was deposited in a nearshore marine environment. The upper member of the Mural is, in the Mule Mountains, strongly fetid when freshly broken. There is no evidence of such minerals as hematite, pyrite, or fluorite.
The Cintura Formation is similar to the Morita Formation (see "Unevaluated Environments"). It consists mainly of repeated sequences of sandstone that grade upward into siltstone and mudstone. The sequence is a subaerial, prograding-delta deposit. Possible uranium precipitants are not evident, however.
UNEVALUATED ENVIRONMENTS
The unevaluated units include Precambrian intrusive rocks, various Mesozoic and Cenozoic units, units in the intermontane Tertiary basins; and Quaternary deposits. These units were not evaluated because of inadequate information or time constraints. In some cases, evenly balanced favorable and unfavorable evidence made evaluation of these units indeterminate. The unevaluated units are discussed below.
PRECAMBRIAN INTRUSIVE ROCKS: SIERRITA MOUNTAINS
Continental Granodiorite
The Continental Granodiorite crops out in the northwestern Sierrita Mountains. The granodiorite was studied in detail to determine its favorability for contact-metasomatic uranium deposits (Class 340). There is a uranium occurrence here, and anomalously high radioactivity is noted in metasedimentary rocks near the occurrence. Time constraints dictated that most data collected consist of radiometric measurements. The results were inconclusive, and the unit is, therefore, considered unevaluated. The intrusive has such favorable aspects as shear zones, brecciated textures, fluorite, sulfides, and a sulfide-bearing uranium occurrence--the Black Dike occurrence. The pluton is associated with greenschist-facies metamorphic rocks as well.
40 The Black Dike occurrence (UOR-3, App. C) is in a shear zone in a metagranodiorite. The zone strikes about N. 100 W. and dips about 650 E. It is about 150 ft long, about 2 ft wide, and of unknown vertical dimensions. It consists of irregular, discontinuous, podlike bodies of dark, fine-grained, uraniferous, sulfide-bearing rock. The original rock is reported to have been replaced by biotite, garnet, epidote, and muscovite. Fluorite is also reported. A 0.5- to 2-ft-wide basalt dike was cut by a shaft at the 50-ft level.
To the east of the Black Dike, there are quartzitic and arkosic beds that strike northerly and dip steeply to the east. The metasedimentary rocks contain zones of sericitic schist. There are radioactive zones in the metasedimentary rocks. The quartz-sericite schists are especially radioactive.
The sulfide minerals are mainly pyrite and chalcopyrite. Some uraninite is reported. The workings were not entered by the authors. No uranium minerals were identified by them. A sample of mineralized rock collected from a dump (MGG 024, App. B1) contained 490 ppm cU308. Green, schistose rock fragments collected from the dump (MGG 025, App. D) are radioactive but were not analyzed for uranium because of time constraints. Gamma-ray spectrometric analyses of quartz-sericite schist samples indicate relatively high equivalent-uranium contents (MGG 367, 370, 374, 375, Table 8). Some samples from brecciated shear zones in the intrusive rock also have anomalously high equivalent-uranium contents (MGG 357, 358, 362, Table 8; Fig. 6).
Chloritization has occurred pervasively throughout the area. Metasomatizing fluids may have invaded the contact zone of the intrusive and metasedimentary rocks. Further work is warranted by the favorable aspects of the area.
Unnamed Intrusive Rocks
Unnamed granodioritic, granitic, dioritic, and quartz monzonitic rocks of Precambrian age crop out west and northwest of the Twin Buttes copper mine (P1. 13). Time did not permit their evaluation during this study.
MESOZOIC AND CENOZOIC ROCKS
Baboquivari Mountains and Papago Indian Reservation
The Mulberry Wash Formation, Chiuli Shaik Formation, and sedimentary, volcanic, and intrusive rocks of Tertiary age are unevaluated. Time did not permit evaluation of these units. Very little is known about their favorability, except that no areas of anomalously high radioactivity were found during reconnaissance studies. The following is a short description of these rocks.
Mulberry Wash Formation. The Mulberry Wash Formation (P1. 8), of Jurassic age, is exposed in the central portion of the Baboquivari Mountains (Haxel and others, 1980). The formation comprises three principal units. The
41 TABLE 8. FIELD RADIOMETRIC DATA FOR THE BLACK DIKE OCCURRENCE
K eU eTh eTh/ Sample No. (%) (ppm) (ppm) eU Comments
MGG 356 5.60 13 48 3.7 alluvium
MGG 357 5.82 15 74 4.9 fractured quartz monzonite
MGG 358 5.07 86 37 0.4 mine dump, sulfides, iron oxides
MGG 359 0.99 2 4 2.0 quartzite
MGG 360 4.23 7 41 5.9 alluvium
MGG 361 4.56 9 16 1.8 quartz monzonite
MGG 362 4.71 16 63 3.9 fractured quartz monzonite
MGG 363 4.55 9 37 4.1 alluvium
MGG 364 3.77 6 30 5.0 alluvium
MGG 365 3.56 10 55 5.5 alluvium
MGG 366 4.40 7 34 4.9 alluvium
MGG 367 3.41 14 67 4.8 quartz-sericite schist
MGG 368 7.13 12 44 3.7 quartzite
MGG 369 , 5.87 13 71 5.5 arkose
MGG 370 4.68 26 76 2.9 quartz-sericite schist
MGG 371 6.28 13 40 3.1 quartzite
MGG 372 5.82 10 54 5.4 metaquartzite
MGG 373 7.37 15 49 3.3 quartzite
MGG 374 7.21 21 91 4.3 quartz-sericite schist
MGG 375 6.12 31 79 2.5 quartz-mica schist
42 lowest unit consists of alternating quartz latite porphyry flows and some fine-grained porphyritic andesite flows. The middle unit is predominantly an agglomerate or conglomerate composed exclusively of quartz latite porphyry cobbles and boulders in a matrix of quartz latite porphyry fragments. The upper unit contains latite porphyry, laminated felsite, and flows of andesite porphyry (Heindl and Fair, 1965). One radiometric measurement, taken on a flow of intermediate composition within the formation (Table 4), indicated no anomalous equivalent-uranium content.
Chiuli Shaik Formation. The Chiuli Shaik Formation, of Late Cretaceous(?) age (P1. 8), is found in the central portion of the Baboquivari Mountains (Haxel and others, 1980). The unit consists of a lower, predominantly sedimentary portion and an upper, almost entirely volcanic portion (Heindl and Fair, 1965). The lower portion is made up of conglomerate, mudflows, pebbly and sandy arkosic and graywacke beds, and a few local lenses of.limestone. Numerous thin flows of laminated felsite and minor lenticular andesitic breccia and flow units are intercalated with the sedimentary rocks (Heindl and Fair, 1965). One radiometric measurement was taken in the lower conglomeratic portion of the Chiuli Shaik (Table 4). No anomalous uranium concentration was noted.
Sedimentary, Volcanic, and Intrusive Rocks of Tertiary Age. Sedimentary, volcanic, and intrusive rocks of Miocene-Oligocene(?) age (P1. 8) are exposed along the west-central and southwest flanks of the Baboquivari Mountains (Haxel and others, 1980). These rocks include the Yellowstone Wash formation and the Kohi Kug volcanics (Fair, 1965). The Yellowstone Wash formation consists of a basal conglomerate overlain by a vesicular porphyritic andesite. The conglomerate is composed of fragments of latite, rhyolite, arkose, and granite. Overlying the basal portion is a sequence of conglomerates with intercalated andesite flows. The Kohi Kug volcanics, which consist of rhyolite, tuff, welded tuff, tuff breccia, andesite, and fluvial clastics, lie conformably(?) on the Yellowstone Wash formation (Fair, 1965). Small pods of monzonite have intruded an andesite flow in the formation.
Two radiometric measurements, one taken in a rhyolite, the other in a tuff, showed no anomalous uranium content (Table 4).
Cobre Ridge, Oro Blanco, and Pajarito Mountains
Cobre Ridge Tuff. The Cobre Ridge tuff, of Jurassic(?) age, makes up most of Cobre Ridge (Fig. 3), and it is exposed in several areas just to the east, in the Oro Blanco Mountains. It is unevaluated for magmatic- hydrothermal (Class 330) uranium deposits. It is unfavorable for volcanogenic (Classes 510 through 540) uranium deposits because it is not peralkaline or highly silicic, and it does not contain sodic pyroxenes or amphiboles. It is also unfavorable for sandstone (Class 240) deposits because there are no known reductants. The balancing of favorable and unfavorable characteristics made evaluation of the magmatic-hydrothermal environment inconclusive. Favorable characteristics include the presence of hematitic and silicic alteration, sulfide minerals, and a high degree of fracturing associated with the vein
43 deposits in the unit. But, because of the limited extent of the veins, a deposit of 100 tons of 100 ppm U308 is not probable. Whether a deposit of favorable size is present at depth is not known.
The formation consists of three members. In ascending order, they are the rhyolite member, the welded tuff member, and the arkose member (Knight, 1970). The rhyolite member consists of nonwelded rhyolitic tuff and some welded quartz latitic tuff. The welded tuff member consists of weakly to strongly welded porphyritic quartz latite tuff. The arkose member consists of fine-grained arkosic sandstone and arkose.
Exposures of the formation are extremely fractured and jointed. Some of the faulted and sheared areas have been mineralized. Three types of mineral deposits have been identified in the area. There are quartz sulfide veins present as lensing fracture fillings and partial wall-rock replacements. There are slightly dipping, shallow silicified zones that contain quartz stringers. There are also steeply dipping, tabular zones of kaolinized, bleached, sheared, and brecciated tuff (Knight, 1970; Keith, 1975). The vein deposits of base- and precious-metal minerals in the area are highly irregular and usually of limited strike and dip (Keith, 1975). Quartz, pyrite, sphalerite, chalcopyrite, galena, tetrahedrite, gold, and silver are present (Keith, 1975).
Only one uranium occurrence was found in the Cobre Ridge tuff. The Little Doe occurrence (UOR-46, App. C; P1. 2) consists of a sheared, brecciated, and silicified quartzite lens within a porphyritic rhyolite tuff. The occurrence is probably within the welded tuff member. Minerals tentatively identified as kasolite and zippeite were found within fractures in the quartzite (MGG 109, App. D). Selected samples contained 38 ppm eU and 422 ppm cU3 08 (Table 9).
The relatively high uranium values indicate that the hydrothermal solutions that permeated the shears and fractures in the tuff were uraniferous. But, from what can be seen at the surface, mineral development was very limited. The bottoms of known base- and precious-metal veins in the Cobre Ridge tuff are shallow. Most of the veins in the unit became uneconomic within 350 ft of the surface and many within 200 ft of the surface (Knight, 1970). It is not known whether uranium contents decrease with depth.
Pajarito Lavas. The Pajarito Lavas are unevaluated for magmatic- hydrothermal (Class 330) uranium deposits. They were considered for volcanogenic (Class 510 through 540) uranium deposits, as well, but are unfavorable for such deposits because they are neither highly silicic nor alkalic and do not contain sodic pyroxenes or amphiboles. Uranium occurrences are present at the surface but do not meet the requirement of 100 tons of 100 ppm U308 . Whether the unit is favorable at depth for magmatic- hydrothermal deposits is problematic because available data are insufficient.
The Pajarito Lavas, of Cretaceous(?) age, form the main portion of the Pajarito Mountains (Fig. 3; P1. 7). The base of the formation is not exposed, but a section at least 1,300 ft thick is present (Nelson, 1963). The section thickens to the southwest. The rocks commonly dip to the northeast.
44 TABLE 9. SELECTED URANIUM VALUES, AGPAITIC COEFFICIENTS AND EMISSION SPECTROMETRY RESULTS FOR SAMPLES TAKEN IN THE COBRE RIDGE, ORO BLANCO, AND PAJARITO MOUNTAINS
Occurrence eU cU 0 eTH/eU Aapaitic Associated Sample 1 3 2 3 no. Formation Rock Description no. (ppm) (ppm) ratio coefficient elements
As, B, Cu, Mo, Pb MGG-043 Pajarito Lavas Shear zone in crystal-rich 34 68 279 0.87 rhyolite tuff Sb
MGG-044 Pajarito Lavas Shear zone in crystal-rich 34 0.53 rhyolite tuff
MGG-045 Pajarito Lavas Crystal-rich rhyotite.tuff 0.64 Cu, Pb, Zn MGG-046 Pajarito Lavas Shear zone in crystal-rich 38 511 680 0.08 B, rhyolite tuff
MGG-048 Pajarito Lavas Shear zone in crystal-rich 38 0.44 rhyolite tuff
MGG-164 Pajarito Lavas Crystal-rich rhyolite tuff 4
MGG-165 Pajarito Lavas Crystal-rich rhyolite tuff 0.34
MGG-1 07 Pajarito Lavas Shear zone in crystal-rich 45 0.18 rhyolite tuff Mg MGG-166 Pajarito Lavas Crystal-rich rhyolite tuff 2 0.3
MGG-179 Pajarito Lavas Crystal-rich rhyolite tuff 4 8.5
MGG-416 Pajarito Lavas Crystal-rich rhyolite tuff 6* TABLE 9. SELECTED URANIUM VALUES, AGPAITIC COEFFICIENTS AND EMISSION SPECTROMETRY RESULTS FOR SAMPLES TAKEN IN THE COBRE RIDGE, ORO BLANCO, AND PAJARITO MOUNTAINS (Continued)
Occurrence eU cU0 eTH/eU Agpaitic Associated Sample 1 2 3 no. Formation Rock Description no. (ppm) (ppm) ratio coeffieient elements
MGG-417 Pajarito Lavas Crystal-rich rhyolite tuff 8*
MGG-418 Pajarito Lavas Crystal-rich rhyolite tuff 6*
MGG-108 Cobre Ridge Tuff Shear zone in meta quartzite 46 38 0.18 Ba, Cu, Mn, Pb
MGG-110 Cobre Ridge Tuff Shear zone in meta quartzite 46 422
MGG-172 Cobre Ridge Tuff Crystal-rich rhyolite tuff 3 9.7 MGG-173 Cobre Ridge Tuff Crystal-rich rhyolite tuff 0.64
MGG-170 Oro Blanco Conglomerate Conglomerate 4 4.8
MGG-175 Oro Blanco Conglomerate Conglomerate 3 7.3
MGG-171 Sidewinder Quartz Monzonite Quartz monzonite 4 3.0
'Analyses determined by gamma-ray spectrometry, *Analyses by field gamma-ray spectrometer
2Analyses determined fluorimetrically if value is less than 400 ppm; determined colorimetrically if more than 400 ppm
3Agpaitic coefficient: % Na20 +weightweight % K20 molecular weight Nat j molecular weight K20 ( weight % Al2 03 molecular weight Al2 03
"Analyses determined by emission spectrometry A few minor intrusions cut the formation. They include porphyries of quartz latite, quartz monzonite, and andesite (Nelson, 1963). Veinlets of quartz are found throughout the formation, some contain vugs of quartz crystals lining opaque centers (MGG 147, App. D).
Despite the name Pajarito Lavas, the unit consists predominantly of crystal-rich rhyolitic tuff. The tuff has a seriate porphyritic texture with a hemicrystalline groundmass (Nelson, 1963). Approximately 40 to 50 percent of the rock is fine- to medium-grained, fractured and angular phenocrysts of potassium feldspar, quartz, and plagioclase. The rest of the rock is an extremely fine-grained quartzofeldspathic groundmass with sparse accessory amphibole, muscovite, sphene, and opaques. Flow structures and inclusions of clear glass and scatterings of angular shards are also present (Nelson, 1963).
Numerous closely spaced, steeply dipping fractures, normal faults, and shear zones form the predominant structural features in the area. Three main directions of strike are present: north-northeast, northeast, and northwest. The White Oak and Silver Mine occurrences (UOR-36 and UOR-38, App. C; P1. 2) occupy east-northeast-oriented shear zones. Mineral deposits in the Pajarito Mountains are characterized by irregular and lensing fissure veins, which contain spotty argentiferous galena, pyrite, marcasite, and traces of chalcopyrite, sphalerite, arsenopyrite, cinnabar, wulfenite, vanadinite, and fluorite. Mines in the area, presently inactive, have produced small amounts (less than 1,000 tons) of metal ores (Keith, 1975). The area has been worked principally for silver, gold, lead, copper, and zinc values. Approximately 7 tons of 2-percent and 3.5 tons of 8-percent hand-picked uranium ore was shipped for testing from the White Oak occurrence (unnumbered PRR).
All mineral deposits within the Pajarito Lavas are epigenetic and of probable hydrothermal origin. The temperature-depth zone classification of mineralization includes a range from epithermal through mesothermal. The two uranium occurrences in the area--the White Oak and Happy Day--are vein deposits associated with shear zones. None of the veins in the Pajarito Lavas show any lateral or vertical persistence on outcrop. Alteration halos extend for several feet around the shear zones. Slight to extensive argillic and sericitic alteration and moderate hematitic staining are present (MGG 042, 047, 048; App. D).
Within the shear zones at the Silver Mine occurrence, zippeite and, tentatively, soddeyite and uraninite were identified (MGG 047, App. D; P1. 5). No uranium minerals were identified on surface examination at the White Oak occurrence. Secondary uranium minerals kasolite, uranophane, dumonite, and autunite are reported (Granger and Raup, 1962). Selected samples taken at the White Oak and Silver Mine occurrences contained 279 ppm and 511 ppm cU308, respectively (Table 9). All uranium minerals identified, with the possible exception of uraninite, are hydrated secondary minerals of probable supergene origin. Whether these secondary minerals are the product of the leaching of a vein of primary uranium minerals, which may extend to depth, is not known. Exploration within the Pajarito Mountains has been limited to shallow shafts, adits, and open cuts because of the irregularity and nonpersistence of the mineral deposits both laterally and vertically.
47 The Pajarito Lavas have been considered an extension of the Cobre Ridge tuff (Knight, 1970). Both units are rhyolite porphyries that are highly fractured and contain mineralized shear zones. As in the Cobre Ridge tuff, surficial uranium mineral deposits are limited in extent. How extensive the vein deposits are in the subsurface cannot be determined at this time because of a lack of subsurface data.
No source for the hydrothermal fluids, which permeated the shear zones and fractures in the Pajarito Mountains, has been found. It has been suggested that if an igneous source for the mineralizing fluids existed in the area, it has been concealed below the present level of erosion or hidden beneath the cover of Tertiary volcanic rock (Knight, 1970).
Oro Blanco Conglomerate. The Oro Blanco Conglomerate is unevaluated for magmatic-hydrothermal (Class 330) uranium deposits. It is unfavorable for sandstone (Class 240) deposits because of a lack of any reductants such as carbonaceous material or disseminated sulfide minerals. The unit has several favorable characteristics for the magmatic-hydrothermal environment, but it also has characteristics that detract from these favorable features. Favorable characteristics include the presence of silicic and hematitic alteration associated with the occurrence of base-metal sulfides along faults and fractures within the formation. But, none of the mineral occurrences present in the Oro Blanco are persistent. Within the observed surface environment, the formation is not capable of containing a deposit of 100 tons of 100 ppm U308 . Whether conditions are favorable at depth is not known.
The Oro Blanco Conglomerate, of Cretaceous age, overlies the Pajarito Lavas in portions of the Pajarito Mountains and the Cobre Ridge tuff in parts of the Oro Blanco Mountains (P1. 7). The formation consists of a basal unit of boulder- to sand-sized fragments of underlying rhyolitic tuff. Above this are sandstones and siltstones composed of lithic volcanic fragments and detrital feldspar. Thinly laminated silty limestone and a conglomerate composed of andesite fragments are present at some locations (Nelson, 1963; Knight, 1970).
Mineralized sheared and brecciated zones in the Oro Blanco Conglomerate have produced ores of gold, silver, zinc, lead, and minor copper. One uranium occurrence is reported present within the formation. At this occurrence (UOR-40, App. A3; P1. 2), a shear zone extends from an intrusive granite into the bordering Oro Blanco Conglomerate (Granger and Raup, 1962; Knight, 1970). Strong silicification and sphalerite, galena, chalcopyrite, pyrite, and purple fluorite form webs and stringers in a calcite gangue. Uraninite, disseminated and in hairline fractures in the walls of the vein filling, is reported (Granger and Raup, 1962). The uraninite present in the vein was of a very limited and nonpersistent nature. This does not rule out the possibility that a more extensive uranium mineral deposit may be present at depth.
Portions of the Oro Blanco Conglomerate and the uranium occurrence associated with it lie within an airborne radiometric anomaly (larger portion of area D, P1. 3). The cause of such a large anomaly was not discerned. More radioactive shear zones may be present in the area, but they probably do not contain very extensive uranium minerals at the surface. Because all other hydrothermal mineral deposits in the Oro Blanco Conglomerate are limited in
48 extent and depth (Keith, 1974; Knight, 1970), the possibility of finding a favorable uranium deposit within the near-surface environment is low. An assertion about the favorability for uranium deposits at depth is premature.
Cerro Colorado, Las Guijas, San Luis, Tumacacori, and Oro Blanco Mountains
Volcanic and Sedimentary Rocks of Mesozoic age. Volcanic and sedimentary rocks of Jurassic(?) and Cretaceous age are unevaluated for magmatic- hydrothermal (Class 330) deposits. These rocks can be correlated to the Cobre Ridge tuff, Pajarito Lavas, and Oro Blanco Conglomerate discussed previously and are considered unfavorable for volcanogenic (Classes 510 through 540) and sandstone (Class 240) uranium deposits for the reasons given for the named formations. These unnamed rocks exhibit both favorable and unfavorable features, which makes assessment for the possible occurrence of magmatic- hydrothermal uranium deposits indeterminant.
Favorable characteristics include hematitic and sericitic alteration associated with sheared and fractured rock containing sulfide minerals in quartz-filled veins. Detracting from these favorable features is the fact that at the surface the veins are spotty, irregular, and lensing. From what can be seen superficially, the veins could not produce a deposit of 100 tons of 100 ppm U3 08 unless they became more extensive and uranium-enriched at depth.
The Mesozoic volcanics present in the area consist of rhyodacite, andesite, and rhyolite porphyry (Keith and Theodore, 1975; Sheikh, 1966). The rhyolite porphyry is part of the same unit that makes up the Cobre Ridge tuff and Pajarito Lavas. Sedimentary rocks of Cretaceous age consist of shale, conglomerate, and minor limestone (Jones, 1957; Sheikh, 1966; Keith, 1974). These rocks represent the northward extension of the Oro Blanco Conglomerate, and are found extensively in the area (Pl. 7).
In places the Mesozoic sediments and volcanics have been locally metamorphosed by Laramide age intrusives of granitic composition. In the Las Guijas Mountains, sulfide-bearing veins occur in both the intrusive and bordering metamorphosed sediments and volcanics (Keith, 1974).
There are many mineral occurrences in the area within these rocks but they are widely scattered, small, and irregular. They consist mainly of lenticular, structurally controlled, quartz and quartz-calcite veins that contain spotty and commonly small occurrences of pyrite, galena, sphalerite, chalcopyrite, bornite, gold, and silver (Keith, 1974). Tungsten minerals, wolframite, huebnerite, and scheelite, have been mined from a volcanic breccia present along the intrusive contact of the Las Guijas granite.
Uranium deposits of favorable size do not occur within any of the veins exposed at the surface; but, because of unknown concentrations of possibly hydrothermally deposited uranium mineral present at depth, these rocks are unevaluated.
Laramide Intrusives. Laramide intrusive rocks of the Cerro Colorado, Las Guijas, San Luis, Tumacacori, and Oro Blanco Mountains are unevaluated for
49 uranium deposits associated with plutonic igneous rocks because the information now available about them is indeterminate. Stocks, plugs, and dikes intrude Mesozoic volcanic and sedimentary rocks in the area.
The larger intrusives have features that indicate that they may be good uranium source rocks. For example, within the Las Guijas Mountains (Fig. 3) an alaskite portion of the main granite mass is present (Keith and Theodore, 1975), indicating silicic differentiation of the main pluton. Differentiation is also indicated by an agpaitic coefficient for the main granite mass of 0.92 (Sheikh, 1966). One of two samples taken from an argillized shear zone within the granite contained a slightly elevated uranium content of 7 ppm eU (MGG 121, App. B1). The other sample (MGG 122, App. B1) contained only 1 ppm eU. The low values of uranium were not unexpected because of the differences in formation temperatures between tungsten and uranium. Higher uranium contents may be present in the Mesozoic volcanics and sediments peripheral to the intrusion.
Fluorite has been reported within veins in the Las Guijas granite (Keith, 1975) and within a granitic stock in the Oro Blanco Mountains (Granger and Raup, 1962). The presence of fluorite at least suggests the possibility of uranium transport as uranium hexafluorite. This hypothesis is supported by the presence of fluorite in the Oro Blanco Mountains in a reported uranium occurrence (no. 40, App. A3; P1. 2; Granger and Raup, 1963). The uranium minerals present at the occurrence are of limited extent (Granger and Raup, 1963).
Quartz and quartz-calcite veins containing base-metal sulfides and precious metals are not restricted to the intrusives and the rocks peripheral to them. Hydrothermally altered fractures are present in Mesozoic sediments and volcanics several miles from exposed intrusive bodies, which suggests a buried pluton of more extensive size may be present. This buried pluton may be uraniferous, based on the favorable features seen on surface exposures. However, the prospect of finding a uranium deposit near the surface that will satisfy the 100-tons-at-100-ppm-U3 08 requirement does not seem likely since all other mineral deposits in the area are small, irregular, and spotty. The favorable features mentioned make it premature to classify these Laramide intrusives as unfavorable. A more detailed study of the area is needed.
Sierrita Mountains
Sierrita Granite. Although unfavorable for magmatic-hydrothermal uranium deposits (Class 330), the Sierrita Granite remains. largely unevaluated for other uranium occurrences in and associated with plutonic igneous rocks because time constraints precluded adequate evaluation.
The Sierrita Granite, of Jurassic age (Cooper, 1973; P1. 9), is a leucocratic, coarse-grained rock that contains aplite dikes. Outcrops of the intrusive in the area of the Diamond Head uranium occurrence (UOR 7, App. C) are commonly strongly fractured. Limonitic staining of rock surfaces and along joints is accompanied in some areas by hematitic alteration.
The Sierrita Granite shows favorable chemical aspects: its silica content is over 72 percent; the K2 0 and Na2O contents are high (although
50 the agpaitic coefficient is less than one); and both magnesium and calcium oxides are low (MGG 028, 071, App. B1). The composition of the pluton varies from granitic to quartz monzonitic (MGG 064, 072, 085, 090, App. D). Plagioclase feldspars are not sodic, however; they range from oligoclase to andesine. Evidence for internal albitization is lacking, although the rock has been moderately argillized and sericitized. Since there are favorable aspects in this granite, it should be studied in more detail.
Harris Ranch Monzonite. The Harris Ranch Monzonite, of Triassic/Jurassic age (Cooper, 1973), exposed in the southeastern portions of the Sierrita Mountains, consists of fine- to medium-grained quartz monzonite, granite, and granophyre. Thin-section study (MGG 091, App. D) shows a fine-grained equigranular granite. Ferromagnesian minerals, implying a subaluminous and peralkaline granite, are not present. Part of the Harris Ranch Monzonite is favorable for magmatic-hydrothermal uranium occurrences (Area C, P1. 1), where locally it is a leucogranite-alaskite with a quartz monzonite. It also has favorable chemical aspects: it is silica rich; and its magnesium and lime contents are low (MGG 031, 032, App. B1). Fluorine content is not anomalously high, however. As most of the study was conducted in Area C, time constraints precluded the further evaluation of this intrusive.
Angelica Arkose. The Angelica Arkose, of Early Cretaceous age, is present in the eastern and northeastern parts of the Sierrita Mountains. It consists of a basal conglomerate, a middle member of arkose and siltstone, and an upper member of arkosic grit and conglomerate lenses (Cooper, 1971). Such features as cross-bedding, scour-and-fill structures, and differential permeability indicate that the unit merits field study.
Red Boy Rhyolite. The Red Boy Rhyolite, in the south-central Santa Rita Mountains, is an Upper Cretaceous unit that consists of a basal conglomerate overlain by massive well-indurated rhyolitic tuff and tuff breccias (Cooper, 1971). Favorable mineralogical aspects include crystals and crystal fragments of quartz, albite, sanidine, and devitrified pumice. The unit has been pervasively argillized.
Igneous Complex. An igneous complex of Paleocene age is exposed in and near the Esperanze Mine in the southeastern Sierrita Mountains. It consists of favorable lithologies such as aplitic quartz monzonite, quartz monzonite porphyry, and dikes of quartz latite, biotite rhyolite, and aplite (Cooper, 1972). The quartz monzonite porphyry is spatially associated with copper- molybdenum deposits.
Formation of Tinaja Peak. This unit, of Oligocene and Miocene age (Cooper, 1973), is extensively exposed south of the Esperanze Mine. It comprises andesite and rhyodacites overlain by tuffaceous conglomerates.
51 Santa Rita Mountains
Middle Member of the Mount Wrightson Formation. This unit, of Triassic age, consists of a thick sequence of chiefly rhyolitic and latitic rock. Lava flows are common. The member displays such favorable aspects as the presence of lithophysaelike structures in the lava flows, porphyritic textures, and altered devitrified glass. There are also favorable chemical criteria. The silica contents are in excess of 72 percent; the calcium and magnesium weight percentages are low; the potassium oxide content is high (Drewes, 1971a); and argillization is common.
Lenses of sandstone and quartzite are widely scattered throughout the middle member. Cross-bedding is present in these lenses and some lenses contain considerable amounts of pumiceous shards. Although time constraints precluded study of this member, further studies are warranted because of the its favorable features.
Gardner Canyon Formation. The Gardner Canyon Formation, of Triassic age, is exposed in the eastern Santa Rita Mountains. It is a red-bed sequence at least 1,000 ft thick (Drewes, 1971a). It has a lower member that consists mainly of siltstone, and an upper member that consists mainly of mudstone and interbedded siltstone. Although the unit is generally unfavorable, the presence of fetid shale, carbonaceous limestone, and arkosic sandstone indicates that it warrants some field study.
Temporal Formation. The Temporal Formation, of Cretaceous age (Drewes, 1971a), consists of mixed rhyolitic to andesitic volcanic and sedimentary rocks. It occupies a portion of the east flank of the Santa Rita Mountains. The favorable aspects of the formation include its rhyolitic lithology, its porphyritic textures, and its argillization and sericitization. Unfavorable criteria are its lack of sodic ferromagnesian minerals, alkali feldspars, fluorite, and sulfides.
Bathtub Formation. The Bathtub Formation, of Early Cretaceous age, is exposed southeast of Mt. Wrightson. It consists of a lower member of conglomerate and sandstone, a middle member of rhyolitic pyroclastic rocks and andesite flows, and an upper member of dacitic volcanic breccia. The unit is not very favorable chemically. It has low silica content and high magnesia and lime contents, and it lacks soda-rich pyroxenes and amphiboles (Drewes, 1971a). The evidence is indeterminate enough to justify an unfavorable classification. Favorable features of the Bathtub Formation include the presence of pumiceous and porphyritic rhyolite, some albitized plagioclase in a rhyolitic tuff breccia, small cavities that may be miarolitic, and some sericitization and kaolinization.
Bisbee Group. The Bisbee Group is exposed in widely scattered areas along the flanks of the central and northern Santa Rita Mountains. There it consists, in ascending order, of the Glance Conglomerate, the Willow Canyon Formation, the Apache Canyon Formation, the Shellenburger Formation, and the Turney Ranch Formation.
52 The environments of deposition of the formations range from piedmont to nearshore marine. No uranium occurrences have been found in the Bisbee Group in the Santa Rita Mountains, and no anomalously high radioactivity is known. The group does have such favorable features as channel scours, cross-bedding, arkosic units, and green siltstone beds associated with sandstone beds. The evidence is therefore considered to be indeterminate. The unit should be studied further, especially to determine the presence and distribution of carbonaceous materials.
Fort Crittenden Formation. The Fort Crittenden Formation, of Late Cretaceous age, is exposed mainly along the east flank of the Santa Rita Mountains. A small exposure of these rocks is present along the west flank and on the southwestern side of the Huachuca Mountains. The sequence of the west flank of the Santa Rita Mountains is discussed in "Environments Unfavorable for Uranium Deposits."
Five informal members have been designated within the Fort Crittenden Formation. They consist of shale, red conglomerate, and brown conglomerate beds. In the Huachuca Mountains, there are local conglomerates in the basal part of the formation. These are overlain by a sequence of shale and graywacke. Favorable aspects are found in the brown conglomerates of the Fort Crittenden in the Santa Rita Mountains: arkosic beds and fragments of silicified wood (Drewes, 1971a). These suggest the possible presence of carbonaceous matter in the unit.
Intrusive Igneous Rocks. Intrusive igneous rocks of Paleocene age (Drewes, 1971a) crop out as small, elliptical stocks along the flanks of the northern Santa Rita Mountains. They are mainly of granodioritic and quartz monzonitic composition and intrude a wide range of Precambrian and Paleozoic rocks. Intrusive contacts are mostly sharp, and chilled zones are lacking.
The units are coarse grained, massive, and only slightly altered. Narrow aplitic dikes occur locally. The dominant minerals in the rocks comprise quartz, plagioclase, potassium feldspar, biotite, and some hornblende. Accessory minerals are magnetite, apatite, sphene, and zircon. Some of the stocks carry tourmaline and traces of radioactive allanite (Drewes, 1976b).
The quartz monzonite and granodiorite stocks show favorable chemical aspects: high silica contents; low magnesium oxide contents; and low ferrous and ferric iron oxide contents. An unfavorable feature is that the agpaitic coefficients are less than one.
Whetstone Mountains
Bisbee(?) Formation. Certain clastic sedimentary rocks exposed along the northern and western flanks of the Whetstone Mountains have been assigned to the Bisbee(?) Formation (Creasey, 1967). They consist mainly of sandstone, arkosic sandstone, and siltstone. There is some shale and conglomerate. There are black to brown thin-bedded, fetid limestone beds near the base of the formation (Hayes and Drewes, 1978). The fetidness suggests the presence of H2S, a good reductant.
53 A sample (MGG 060, App. B1) from a copper prospect in the Bisbee(?) Formation beds on the southwestern flank of the Whetstone Mountains contained 55 ppm cU3 08 and 220 ppm vanadium. The prospect is found in a clean, white sandstone. Leaf imprints found locally suggest the possibility that carbonaceous material is present in the area. Because the evidence is presently indeterminate, the unit is unevaluated.
Extrusive Igneous and Sedimentary Rocks. Scattered outcrops of extrusive igneous and sedimentary rocks of Oligocene and Miocene age are exposed northwest of the Whetstone Mountains. The units consist mainly of andesitic and rhyolitic flows. There is some sedimentary breccia. They were not evaluated because of insufficient data.
Patagonia Mountains
Siliceous Volcanic Rocks. Unnamed siliceous volcanic rocks, of Triassic or Jurassic age, exposed in the southern half of the Patagonia Mountains, were not investigated in the field because of time constraints.
The units comprise rhyolitic lava, welded tuff, tuff interlayered with minor sandstone and conglomerate, and less silicic volcanic rocks (Simons, 1974). The volcanic sequences show favorable textures and also have favorable mineralogical and chemical aspects. These are: porphyritic and spherulitic devitrification textures are common in some of the rhyolite and welded tuff members; sodic plagioclase phenocrysts are prevalent in the tuffaceous and rhyolitic rocks; and, chemically, the rhyolite and rhyolitic tuff have high silica (greater than 72 percent) and high alkali (about 8 to 10 percent) contents and low to very low magnesium and calcium oxide percentages. Silicification, ericitization, and argillization are common to all units.
Unfavorable aspects are: the agpaitic coefficients for all volcanic rocks are less than one; there is no mention in the literature (Simons, 1974) of the presence of fluorite or sodic ferromagnesium minerals; and there are no reported uranium occurrences in, or airborne radiometric anomalies attributable to, the siliceous volcanic rocks.
Quartz Monzonite of Mount Benedict. The Quartz Monzonite of Mount Benedict, of Jurassic age (Simons, 1974), just north of Nogales, Arizona (P1. 7), remains unevaluated despite the fact that the unit was studied in some detail. It has some favorable characteristics: it is porphyritic (MGG 101, 102, App. D); it has aplitic phases; and it has minute anhedral yellow grains that are radioactive. It also has high silica content, low magnesia and lime contents, and low ferrous and ferric iron contents (MGG 103, App. B1). Microcline is abundant, and some of the microcline has a perthitic texture (MGG 102, App. D).
Unfavorable aspects of the intrusive are the absence of sodic ferromagnesian minerals, metamict fluorite, extensive albitization, and hematitic alteration along fracture zones. Furthermore, there are no airborne radiometric anomalies over, or uranium occurrences within, the unit. Ground
54 scintillometer traverses recorded normal background values. As the evidence for favorability is inconclusive, the unit merits further evaluation.
Granite of Comoro Canyon. This unit, of Jurassic age, is exposed along the west flank of the Patagonia Mountains. It is an equigranular to porphyritic granite. More than half of the rock consists of potassium feldspar, which is commonly perthitic (MGG 128, App. D). The rock also contains abundant sodic plagioclase. The unit includes an alkalic syenite (Simons, 1974) that is peraluminous (MGG 127, App. B1).
The granite has other favorable aspects besides its high contents of sodic and potassic minerals and its porphyritic phases. Its silica content is high; its magnesia and lime contents are low (MGG 104, App. Ba); and argillic and sericitic alteration are common.
Unfavorable aspects include the lack of sodic pyroxenes and amphiboles, fluorite, and miarolitic cavities. Also, the granite has low to average equivalent-uranium contents (MGG 106, 126, 129, App. B1). No airborne radiometric anomalies were discerned over the unit. The unit has no known uranium occurrences.
The Granite of Comoro Canyon resembles the Squaw Gulch Granite, which contains favorable Area B in the Santa Rita Mountains. In view of the favorable aspects of the unit, and because of its similarity to the Squaw Gulch Granite, the evidence is considered indeterminate. The unit is therefore classified unevaluated.
Bisbee Formation. The Bisbee Formation of the central Patagonia Mountains consists of siltstone, mudstone and intercalations of limestone, sandstone, and epiclastic volcanic sandstone and siltstone. The sediments appear to contain considerably more epiclastic volcanic material in the Patagonia Mountains than they do elsewhere. The fine-grained matrix resembles devitrified volcanic glass. Limestone beds are marine and are very limited in extent. The Bisbee has been metamorphosed in part to hornfels and is commonly pyritic (Simons, 1972).
Huachuca and Mustang Mountains
Volcanic and Sedimentary Rocks of the Mustang Mountains. There are volcanic and sedimentary rocks of Triassic and Jurassic age in the Mustang Mountains that were not evaluated. Available published data are sparse. The units comprise siliceous volcanic flows and minor welded tuff. They are locally porphyritic and have flow banding (Hayes and Raup, 1968). The welded tuffs are commonly coarse grained and quartzose. The sedimentary rocks are conglomeratic in part and include sandstone, siltstone, mudstone with local rhyolitic and latitic flows(?), and tuff. There are also some exotic blocks of Paleozoic sedimentary rocks contained in them.
Canelo Hills Volcanics. The Canelo Hills Volcanics, of Triassic and Jurassic age, occur in the Santa Rita, Patagonia, and Huachuca Mountains. The
55 type locality is in the Canelo Hills between the Patagonia and Huachuca Mountains. The unit comprises volcanic sedimentary rocks, rhyolitic tuffs, and welded tuffs. At the northern end of the Santa Rita Mountains, slightly metamorphosed Canelo Hills(?) Volcanics comprises arkose, tuffaceous sandstone, crystal lithic tuff, and conglomerate. The units occupy only a small area there, however. The Canelo Hills has such favorable features as rocks with high silica content, lithophysae, sodic minerals, and devitrified groundmass. The lack of adequate information about the Canelo Hills Volcanics precludes evaluation at this time.
Siliceous Volcanic Rocks. Volcaniclastic units of Early and Middle Jurassic age are present in three structural blocks in the southern Huachuca Mountains (Hayes, 1970). The rocks are tuffs that range in composition from quartz latitic to rhyodacitic. Favorability is suggested in that they contain some flow-banded lavas that have spherulitic textures and devitrified groundmasses. The unit was not evaluated because its limited areal extent gave it low priority.
Intrusive Crystalline Rocks. Intrusive igneous rocks of Tertiary age, consisting of quartz monzonite, granodiorite porphyry, and rocks of dioritic composition (Hayes and Raup, 1968), were not evaluated in the Huachuca Mountains because of their limited areal extent and very poor accessibility. These units occur mainly as dikes and sills.
Morita Formation. The Morita Formation, a unit in the Bisbee Group, is present along the crest of the Huachuca Mountains. It consists mainly of feldspathic sandstone, siltstone, and mudstones. Pebble conglomerate, greenish-gray claystone, and impure limestone are minor constituents (Hayes, 1970). Such favorable characteristics of the Morita as abundant silicified wood and scour-and-fill structures in some coarse sandstone beds make evaluation indeterminate pending more field studies of the unit.
Dragoon Mountains: Stronghold Granite
The Stronghold Granite, of Oligocene age (Marvin and others, 1978), intrudes Precambrian and Cretaceous rocks and thrust sheets in the northern Dragoon Mountains. The granite is, in turn, intruded by aplitic dikes. The intrusive contains quartz, sodic plagioclase, orthoclase, and biotite. The main body of the Stronghold is coarse grained and has hypidiomorphic texture (Gilluly, 1956). Near the contact with country rock, the granite is porphyritic.
The aplitic dikes contain less biotite than does the main body. Favorable aspects are their high alkali contents; agpaitic coefficients of 0.07 for the main body and 0.82 for the aplite; and a high fluorine content for the main body (Gilluly, 1956). Skarn deposits along intrusive contacts with limestone contain pockets of clear to purple fluorite as well as calc- silicate minerals (Rushing, 1978).
56 Average uranium content of the granite is about 11 ppm eU--somewhat higher than the average uranium contents of granites. The average eTh/eU ratio is 4.7 (MGG 419 through 422, App. B2). However, no anomalous radioactivity was detected at the surface, in prospect pits, or on mine dumps. Although showing favorable aspects, the intrusive could not be fully evaluated because of time constraints.
TERTIARY BASINS
Rocks and sediments in the Tertiary basins that underlie the San Pedro, Sanoita, San Rafael, Santa Cruz, Altar, and Baboquivari valleys (Fig. 3) were not evaluated because of insufficient subsurface information. Considering the abundance of silicic volcanic and granitic source rocks, within mountains that provided the detritus to the basins, it is probable that uraniferous solutions have flowed through permeable sediments and rocks in the Tertiary basins. No subsurface data are available at this time to determine if appropriate reduction sites, such as carbonaceous beds, are present in the basins.
QUATERNARY DEPOSITS
Alluvial deposits and local lacustrine beds cover older rocks in the valley and pediment areas of the Nogales Quadrangle. Lacustrine deposits, Late Pliocene to middle Pleistocene in age (Gray, 1965), consisting of fine sand, silt, clay, limestone, and waterlaid pyroclastics and are found near Benson and St. David, in the San Pedro Valley (P1. 13).
No airborne radiometric anomalies or uranium occurrences are associated with any of the deposits. A ground radiometric survey of the lacustrine sediments in the St. David area showed no areas of anomalous radioactivity. Because of low priority, time did not permit sufficient evaluation of the Quaternary units.
INTERPRETATION OF AERIAL RADIOMETRIC DATA
During 1974-75 and 1977-78, fixed-wing aerial gamma-ray spectrometer and magnetometer surveys were flown over the Nogales Quadrangle by Texas Instruments, Incorporated (1978). Data were collected along parallel north- south flight lines 3 mi apart. During the 1977-78 survey, the extreme western portion of the quadrangle was flown along parallel east-west flight lines 3 mi apart and along north-south flight lines 12 mi apart. Mean terrane clearance was 400 ft. Aircraft speed averaged 150 mph.
Texas Instruments identified 83 first-priority anomalies and, of these, 47 were recommended for field checking. Interpretation of the Texas Instruments results by BFEC personnel in Grand Junction, Colorado resulted in the delineation of four areas of radiometric anomalies (P1. 3). The areas were selected on the basis of the degree of statistical significance and geologic location on the geologic map (P1. 7). These four areas, designated as A, B, C, and D, are in the Santa Rita Mountains, in the Patagonia Mountains, and southwest of the Tumacacori Mountains (P1. 3; P1. 13).
57 Anomaly A, in the Santa Rita Mountains, is over the Upper Cretaceous Elephant Head Quartz Monzonite. The Elephant Head is not favorable for uranium deposits, but it is chemically similar to the Squaw Gulch Granite (Drewes, 1976). It could have been the source of the uranium in the Duranium
occurrence.
Anomaly B, in the southern Santa Rita Mountains, lies partly over the Josephine Canyon Diorite and the southern part of the Squaw Gulch Granite. Chemical and petrographic data (Drewes, 1976) do not indicate any favorable characteristics. The Squaw Gulch Granite, near the Blue Jay uranium occurrence in the southern half of the intrusive, is anomalously radioactive. The anomaly may be attributable to this radioactivity.
Anomaly C is over intrusive rocks of granodioritic composition in the Patagonia Mountains. Surface investigations indicate that the anomaly has no geologic validity, although the anomaly might reflect the presence of radioactive shear zones associated with base-metal sulf ides. The southern half of the intrusive was not investigated during this study.
Anomaly D, southwest of the Tumacacori Mountains, lies over exposures of the Cobre Ridge tuff, Oro Blanco Conglomerate, and Atascosa Formation. Plugs and dikes of quartz monzonite intrude most of the area of Anomaly D. The Annie Laurie occurrence (no. 40, App. A3) is within the anomaly. The occurrence is associated with a shear zone in the quartz monzonite, but ground checks of the quartz monzonite and surrounding units failed to reveal additional evidence of radioactivity.
RECOMMENDATIONS TO IMPROVE EVALUATION
PRECAMBRIAN INTRUSIVE ROCKS
Whetstone Mountains
The quartz monzonite intrusive has chemical and petrographic characteristics favorable for authigenic uranium deposits in shear zones. The intersections of the shear zones may be especially favorable for uranium deposits. The extent and number of such shear zones is not known at present. It is suggested that the exposures be mapped for the purpose of determining the locations of shear-zone intersections. Should it be indicated, on the basis of mapping, that the quartz monzonite merits drilling, a drilling program should be considered.
Huachuca Mountains
The granite in the southeastern Huachuca Mountains merits further study because there is lack of data about uranium favorability for that pluton. Surface studies should include rock sampling for mineralogical studies to determine if sodic mineral assemblages are present, indicative of uraniferous plutons. Shear zones should also be sought, mapped, and their radioactivity measured. The granite lies partly within the Fort Huachuca Military Reservation. Permission to enter must be obtained.
58 Sierrita Mountains: Continental Granodiorite
The unit needs further investigation because the surface study results were inconclusive. Contact metasomatic uranium deposits may occur here. Zones of anomalous radioactivity along the contact between the granodiorite and the metasedimentary sequence should be delineated by geologic mapping and by radiometric measuring.
MESOZOIC AND CENOZOIC ROCKS
Sierrita Mountains: Sierrita Granite and Harris Ranch Monzonite
Although these units were partially investigated and found to contain favorable aspects for magmatic-hydrothermal uranium deposits, field studies should be extended. Radioactive and nonradioactive sheared or brecciated zones should be mapped and their radiometric response measured.
Santa Rita Mountains
Middle Member of the Mount Wrightson Formation. The middle member of the Mount Wrightson Formation has lithophysaelike structures and altered devitrified glass. Analyses should be made to determine if the glass is uraniferous. Fluorine determinations should also be made, as a high fluorine content is common for volcanogenic uranium occurrences.
Squaw Gulch Granite. The Squaw Gulch Granite should be further investigated by surface studies. These studies should consist of scintillometer surveys to delineate other possible radioactive areas in the intrusive. Gamma-ray spectrometric measurements of anomalously radioactive areas should be part of a followup study.
Huachuca Mountains: Morita Formation
The Morita Formation, of the Bisbee Group, contains silicified wood. It may have reductants. Scour-and-fill sedimentary structures are present. Field investigations are warranted to examine these structures and to determine if carbonaceous material or other reductants are present. The unit is exposed for a combined length of 21 km along the crest of the Huachuca Mountains.
Patagonia Mountains: Intrusives of Jurassic Age
The Granite of Comoro Canyon and the Quartz Monzonite of Mount Benedict need further study because they are products of late-stage magmatic evolution. Also, traces of uranium were found in the Quartz Monzonite of Mount Benedict. Moreover, the granites of the Patagonia Mountains resemble the Squaw Gulch Granite in lithology and geologic relationships. Mapping and sampling are warranted, and they should focus on sheared and brecciated zones because such zones are most likely to contain uranium occurrences.
59
SELECTED BIBLIOGRAPHY
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----- 1973, Map showing distribution and estimated thickness of alluvial deposits in the Tucson area, Arizona: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-884-C, scale 1:250,000.
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62 Devere, G. J., Jr., 1978, The Tombstone Mining District--history, geology and ore deposits: in Callender, J. F., Wilt, J. C., and Clemons, R. C., eds., Land of Cochise, Southeastern Arizona, New Mexico Geological Society in cooperation with the Arizona Geological Society, 29th Field Conference, p. 315-320.
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63 ----- 1976b, Plutonic rocks of the Santa Rita Mountains, southeast of Tucson, Arizona: U.S. Geological Survey Professional Paper 915, 75 p.
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64 Hayes, P. T., and Drewes, Harold, 1968, Mesozoic sedimentary and volcanic rocks of southeastern Arizona: in Titley, S. R., ed , Southern Arizona Guidebook III, Arizona Geological Society, p. 49-58.
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65 ----- 1974, Index of mining properties in Pima County, Arizona: Arizona Bureau of Mines Bulletin 189, 156 p.
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66 Manger, R. L., and Damon, P. E., 1965, K-Ar ages of Laramide magmatism and copper mineralization in the southwest: in Damon, P. E., compiler, Correlation and chronology of ore deposits and volcanic rocks, U.S. Atomic Energy Commission, Annual progress report no. COO-689-SO, Tucson, Arizona, University of Arizona Geochronology Laboratory, p. AIT-1-8.
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67 Nelson, F. J., 1963, The geology of the Pena Blanca and Walker Canyon Areas, Santa Cruz County, Arizona: Tucson, University of Arizona, M.S. thesis, 82 p.
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68 Scarborough, R. B., and Wilt, J. C., 1979, A study of uranium favorability of Cenozoic sedimentary rocks Basin and Range Province, Arizona; Part I, General geology and chronology of pre-late Miocene Cenozoic sedimentary rocks: State of Arizona Bureau of Geology and Mineral Technology, Geological Survey Branch, Tucson, University of Arizona, 101 p.
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69 Stewart, J. H., 1978, Basin-Range structure in western North America: A review: Geological Society of America, Memoir 152, p. 1-31.
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----- 1976, Evidence for a Mesozoic linear tectonic pattern in southeastern Arizona: Arizona Geological Society Digest, v. 10, p. 71-102.
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70 i Sr