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Geology, Geochronology, Geochemistry, and 

Pb-lsotopic Compositions of Proterozoic Rocks, 

Poachie Region, West-Central Arizona— 

A Study of the East Boundary of the 

Proterozoic Mojave Crustal Province

U.S. Geological Survey Professional Paper 1639

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Geology, Geochronology, Geochemistry, and 

Pb-lsotopic Compositions of Proterozoic Rocks, 

Poachie Region, West-Central Arizona— 

A Study of the East Boundary of the 

Proterozoic Mojave Crustal Province

ByBruce Bryant, J.L Wooden, andl. David Nealey

U.S. Geological Survey Professional Paper 1639

U.S. Department of the Interior 

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

Version 1.0 

First printing 2001

For sale by U.S. Geological Survey, Information Services 

Box 25286, Federal Center 

Denver, CO 80225

This publication is also available online at: 

http://geology.cr.usgs.gov/pub/ppapers/p1639/

Any use of trade, product, or firm names in this publication

is for descriptive purposes only and

does not imply endorsement by the U.S. Government

Library of Congress Cataloging-in-Publication Data

Bryant, Bruce, 1930-.

Geology, geochronology, geochemistry, and Pb-isotopic compositions 

of Proterozoic rocks, Poachie region, west-central Arizona : a study of 

the east boundary of the Proterozoic Mojave crustal province / by Bruce Bryant, 

J.L Wooden, and L David Nealey.

p. cm.—(U.S. Geological Survey professional paper ; 1639) 

Includes bibliographical references.

1. Geology, Stratigraphic—Proterozoic. 2. Geology—Arizona— 

Poachie Range Region. I. Wooden, Joseph L. II. Nealey, L. David. 

III. Title IV. Series. 

QE653.5.B792001 

551.7'15'09791—dc21 2001016032

ISBN : 0-607-96229-1
Contents

Abstract................................................................................................................................................. 1

Introduction........................................................................................................................................... 2

Acknowledgments............................................................................................................................... 3

Previous Work ..................................................................................................................................... 3

Geology.................................................................................................................................................. 4

Metamorphic Rocks................................................................................................................... 4

Plutonic Rocks............................................................................................................................. 4

Early Proterozoic Plutonic Rocks ................................................................................... 6

Mafic Gneiss.............................................................................................................. 6

Coarse-Grained Granitic Rocks.............................................................................. 6

Granite at Burro Creek.................................................................................... 7

Fine-Grained Granite................................................................................................ 7

Granite of Thorn Peak.............................................................................................. 8

GneissicTonalite...................................................................................................... 8

Granite, Aplite, Pegmatite, Mica Schist, and Gneiss ......................................... 9

Middle Proterozoic Plutonic Rocks ................................................................................ 9

Signal Granite ........................................................................................................... 9

Mafic Granodiorite ................................................................................................... 10

Porphyritic Biotite Granite ...................................................................................... 10

Granite of Olea Ranch ............................................................................................. 10

Granite of Joshua Tree Parkway ........................................................................... 12

Granite of Grayback Mountain .............................................................................. 13

Diabase ...................................................................................................................... 14

Other Proterozoic Granitic Rocks ................................................................................... 15

Geochronology .................................................................................................................................... 15

Metamorphic Rocks................................................................................................................... 15

Plutonic Rocks............................................................................................................................. 16

Early Proterozoic Plutonic Rocks ................................................................................... 16

Coarse-Grained Granitic Rocks ............................................................................. 16

Granite of Thorn Peak ............................................................................................. 19

GneissicTonalite ...................................................................................................... 20

Middle Proterozoic Plutonic Rocks ................................................................................ 20

Signal Granite and Mafic Granodiorite ................................................................ 20

Granite of Olea Ranch ............................................................................................. 21

Granite of Joshua Tree Parkway and Granite of Grayback Mountain ............ 21

Geochemistry....................................................................................................................................... 22

Analytical Methods .................................................................................................................... 22

Metamorphic Rocks................................................................................................................... 23

Plutonic Rocks ............................................................................................................................ 23

Early Proterozoic Plutonic Rocks.................................................................................... 23

Coarse-Grained Granitic Rocks ............................................................................. 25

Granite of Thorn Peak ............................................................................................. 29

GneissicTonalite...................................................................................................... 29

Middle Proterozoic Plutonic Rocks ................................................................................ 30

Signal Granite and Mafic Granodiorite ................................................................ 32

Granite of Olea Ranch ............................................................................................. 33

Granite of Joshua Tree Parkway ........................................................................... 33

Granite of Grayback Mountain .............................................................................. 33

Diabase ...................................................................................................................... 33
Comparison of Middle Proterozoic Plutonic Rocks with Early Proterozoic

and Other Middle Proterozoic Plutonic Rocks in Region ................................... 34

Other Proterozoic Plutonic Rocks ................................................................................... 42

Whole-Rock and Feldspar Pb-lsotopic Compositions.................................................................... 42

Summary and Interpretation .............................................................................................................. 43

References Cited ................................................................................................................................. 44

Appendix. Location and Description of Chemically and (or)

Isotopically Analyzed Samples...................................................................................................... 47

Figures

1. Map showing location of Proterozoic exposures and the Poachie region ................... 2

2. Geologic map of Proterozoic rocks in the Poachie region............................................... 5

3. Photomicrograph of biotite-quartz-feldspar gneiss.......................................................... 6

4-8. Photographs showing:

4. Porphyritic granodiorite ................................................................................................... 7

5. Granite on Burro Creek..................................................................................................... 8

6. Granite of Thorn Peak....................................................................................................... 9

7. Diorite in gneissic tonalite unit........................................................................................ 9

8. Signal Granite..................................................................................................................... 11

9. Photomicrograph of mafic granodiorite .............................................................................. 12

10. Photograph of fine-grained granite of Olea Ranch............................................................ 13

11. Photographs of diabase......................................................................................................... 14

12-17. U-Pbconcordia diagrams for:

12. Metamorphosed Dick Rhyolite....................................................................................... 16

13. Coarse-grained granite ................................................................................................... 20

14. Granite at Burro Creek and granite of Thorn Peak..................................................... 20

15. Gneissic tonalite............................................................................................................... 21

16. Signal Granite, mafic granodiorite, and granite of Olea Ranch................................ 22

17. Granites of Joshua Tree Parkway and Grayback Mountain..................................... 22

18. Si02 vs. Na20+K20 and Zr/Ti02 vs. Si02 diagrams for Early Proterozoic

metavolcanic rocks................................................................................................................. 23

19. Silica vs. alkalis diagrams for Early Proterozoic plutonic rocks...................................... 30

20. Chemical diagrams for Early Proterozoic rocks................................................................. 31

21. Chondrite-normalized rare-earth element diagrams of Early Proterozoic rocks......... 32

22. Rb vs. Y+Nb discriminant diagram for Early Proterozoic granitic rocks........................ 33

23. Silica vs. alkalis diagrams for Middle Proterozoic granitic rocks and diabase............ 38

24. Chemical diagrams for Middle Proterozoic granitic rocks and diabase........................ 39

25. Chondrite-normalized rare-earth element diagrams of Middle

Proterozoic granitic rocks...................................................................................................... 40

26. Chondrite-normalized rare-earth element diagram of diabase....................................... 41

27. Rb vs. Y+Nb discriminant diagram for Middle Proterozoic granitic rocks..................... 41

28. Chemical diagrams showing comparison of Signal Granite with granite of

Parker Dam and quartz monzodiorite of Bowmans Wash................................................ 41

29. Diagram showing Pb-isotopic whole-rock values for Early Proterozoic rocks

of the Poachie region in regional context........................................................................... 42

IV
Tables

1. U-Pb zircon ages of Proterozoic igneous rocks in the Poachie region................................. 15

2. Analytical data and ages of zircons from the Proterozoic rocks of the

Poachie region................................................................................................................................ 17

3. Major-oxide and trace-element concentrations in some supracrustal rocks 

from the Bagdad metamorphic belt in the Poachie region and of one 

metasedimentfrom cupola in the Signal batholith (sample 1166).......................................... 24

4. Major-oxide and trace-element concentrations in Early Proterozoic gabbro

and coarse-grained granite from the Poachie region.............................................................. 26

5. Major-oxide and trace-element concentrations in Early Proterozoic 

fine-grained granite, granite of Thorn Peak, and gneissic tonalite and other 

Proterozoic granites of the Poachie region................................................................................ 28

6. Major-oxide and trace-element concentrations in Middle Proterozoic

Signal Granite and associated mafic granodiorite.................................................................... 34

7. Major-oxide and trace-element concentrations in the Middle Proterozoic granites 

of Olea Range, of Joshua Tree Parkway, and of Grayback Mountain, 

and diabase...................................................................................................................................... 36

8. Pb-isotopic compositions of whole rocks and feldspars from the Poachie region............. 43
Geology, Geochronology, Geochemistry, and 

Pb-lsotopic Compositions of Proterozoic Rocks, 

Poachie Region, West-Central Arizona— 

A Study of the East Boundary of the 

Proterozoic Mojave Crustal Province

ruce Bryant, J.L. Wooden, and I. David Nealey

Abstract

Plutonic rocks dominate the Proterozoic geology of the 

Poachie region, west-central Arizona, and are about equally 

divided between Early and Middle Proterozoic age. Plutons are 

separated by screens and contain inclusions of amphibolitefacies metamorphosed sedimentary rocks and metamorphosed 

felsic and mafic volcanic rocks. Early Proterozoic plutonic rocks 

range in composition from gabbro to granite; gabbro forms only 

small intrusions, whereas granodiorite and granite form large 

plutons or plutonic suites. Middle Proterozoic plutonic rocks are 

mostly granite but range in composition from granite to mafic 

granodiorite. Textures of plutonic rocks of both ages range from 

coarse grained and porphyritic to fine grained. The Early Proterozoic rocks are variably foliated. The older ones commonly 

but not everywhere have a well-developed foliation; the younger 

ones have an apparently tectonic foliation only in local zones. 

The Middle Proterozoic rocks commonly have a well-developed 

flow foliation.

Ages of the Proterozoic stratified and plutonic rocks are generally well known. A principal belt of metamorphic rocks 

extends south from Bagdad across the area. Two samples of the 

Dick Rhyolite from the belt have a U-Pb zircon age of 1,720 Ma. 

Available data from other studies suggest that at least some of the 

metamorphic rocks in this belt are as old as 1,735 Ma. Ages 

determined for generally foliated plutonic rocks forming the east 

and central parts of the Poachie Range are 1,711±22 Ma for a 

gabbro and 1,706±4 Ma for gneissic diorite, a rock that cuts the 

gabbro. Granite at Burro Creek, possibly correlative with more 

silicic Early Proterozoic rocks in the Poachie Range, is 1,696±13 

Ma. The mostly unfoliated granite of Thorn Peak has a U-Pb zircon age of 1,686±8 Ma. A pluton intruding the east side of the 

Bagdad metamorphic belt has a complex zircon population; the 

youngest grains are about 1,680 Ma and are interpreted to have 

formed during crystallization of the magma. The oldest xenocrystic grains are about 2,500 Ma and indicate the presence of 

Archean crustal material in the source region of the pluton.

Middle Proterozoic granitic rocks form several well-defined 

plutons. The Signal Granite forms a batholith in the Big Sandy 

River area. It and a closely associated mafic granodiorite have a 

U-Pb zircon age of 1,410±4 Ma. The Signal Granite is older than 

the granite of Parker Dam west of the Poachie region near the 

Colorado River, but the mafic granodiorite closely associated

with the Signal Granite has an age similar to the quartz monzodiorite of Bowmans Wash, which is closely associated with the 

granite of Parker Dam. The granite of Olea Ranch is 1,418±2 Ma 

and is older than the well-studied Lawler Peak Granite 20 km to 

the north. The granites of Joshua Tree Parkway and of Grayback 

Mountain are 1,414.3±5 Ma, the same age within analytical 

uncertainty as the granite of Olea Ranch.

Chemically, Early Proterozoic plutonic rocks range from 

calcic to alkalic. No progression with time is noted, except that 

some of the gabbroic rocks, which are early in the sequence, are 

calcic. The rocks range from aluminous to peraluminous. Some 

peraluminous rocks have field relations and Pb-isotopic ratios 

indicating that metasedimentary rock was incorporated in their 

magmas. Middle Proterozoic plutonic rocks are alkali-calcic and 

peraluminous and metaluminous.

Whole-rock samples have high 207Pb/204Pb ratios characteristic of the Mojave crustal province, which both includes and 

extends west of the Poachie region. The highest ratios are from 

mica gneiss, tonalite adjacent to the gneiss, and the peraluminous 

granite of Thorn Peak. Older zircons from the tonalite were probably inherited from a fragmented crust that served as basement to 

the 1,700 Ma events, and the pluton was derived to a large extent 

by melting of that crust. Other Early Proterozoic plutonic rocks 

have Pb-isotopic ratios that in overall aspect are characteristic of 

the Mojave province; some 207Pb/204Pb ratios are lower but not 

as low as those in the Central Arizona crustal province to the east.

The Poachie region is underlain by rocks belonging to the 

Mojave crustal province, which has a complex history and 

includes some crustal material that formed in the Late Archean. 

Volcanic arcs and associated basins formed on this crust during 

west- or northwest-vergent subduction of oceanic crust at 1,730- 

1,710 Ma. This process involved addition of mantle material, 

extensive melting of the crust, magma generation and ascent, 

crustal deformation, and regional metamorphism at 1,710-1,690 

Ma, about coeval with the Ivanpah orogeny in the Mojave crustal 

province. The basement on which the sedimentary and volcanic 

rocks were deposited was removed at the level presently exposed 

by this intense plutonic event. At 1,420-1,410 Ma crustal melting again occurred and large granitic plutons were emplaced. No 

regional deformation accompanied this event, although deformation in restricted zones did. At about 1,150 Ma, mantle-derived 

melts passively intruded along fracture systems to form sheets 

and dikes of diabase.

1
Introduction

Before this study Proterozoic rocks exposed in the Basin and 

Range-Colorado Plateau transition zone west of the PrescottJerome, Arizona, area had not been studied or mapped in detail 

except in a few small areas, such as at Bagdad. In connection 

with a study of the metamorphic and thermal relations between 

the basement rock of the Colorado Plateau and the core complexes of the Basin and Range, the senior author and several junior geologists mapped the Poachie Range at 1:50,000 (Bryant, 

1992). This mapping was extended eastward to the edge of the 

Alamo Lake 1:100,000 quadrangle (Bryant, 1995), one of the 

quadrangles along the Pacific-Arizona Crustal Experiment 

(PACE) transect of the U.S. Geological Survey. The second 

author is conducting a regional study of the Pb-isotopic composition and U-Pb geochronology of the crust in the southwestern 

United States. His geochronologic results have greatly aided the 

geologic mapping, and our joint results have been presented only 

in preliminary and partial summary forms (Bryant and Wooden, 

1986; Bryant and Wooden, 1991a and b). The third author joined 

us to help interpret the chemical data. Some of the whole-rock 

Pb-isotopic data have been summarized as part of a regional 

study (Wooden and DeWitt, 1991). Here we present the data and 

conclusions of our work in the Poachie Range and part of the 

Alamo Lake quadrangle to the east, here referred to as the 

Poachie region. Earlier U-Pb geochronologic investigations in 

this region have never been presented in a form usable by future 

workers; precise locations, analytical data, and isochron diagrams are essential tools to allow our work to be integrated with 

future studies.

The area of this study is in the Colorado Plateau transition 

zone about 150 km northwest of Phoenix (fig. 1). The Proterozoic rocks of the transition zone are divided into a number of 

north-northeast- to northeast-trending tectonic blocks (Karlstrom 

and Bowring, 1993). The Poachie region lies entirely within the 

Hualapai-Bagdad block of Karlstrom and Bowring (1988), or 

Hualapai block of Karlstrom and Bowring (1993) of the Yavapai 

province, or the northwest gneiss belt of P. Anderson (1989a). 

These blocks or belts are based on surface geology. The Yavapai 

geologic province is characterized overall by supracrustal volcanic sequences, whereas the Mojave geologic province to the west 

has supracrustal sequences rich in gray wacke and quartzite and 

relatively poor in volcanic rock. Also, migmatite is common in 

the Mojave province and is lacking in the Yavapai province. The 

Mojave geologic province based on rock types should not be confused with the Mojave crustal province characterized by Pb-isotopic compositions of the rocks.

The Poachie region is in the eastern part of the Mojave 

crustal province (fig. 1), where rocks formed at about 1,700 Ma 

from an average source more radiogenic than the average crust 

model of Stacey and Kramers (1975): they have an average Th/U 

much greater than the crustal average and a depleted mantle 

model age (TDM) signature.of 2,000-2,300 Ma. In contrast, the 

Central Arizona province to the east is characterized by a midocean ridge basalt (MORB)-like mantle Pb-isotopic signature 

and an average Th/U less than the crustal average, crystallization 

ages of 1,760-1,690 Ma, and a TDM <1,800 Ma (Wooden and 

others, 1988; Wooden and Miller, 1990; Wooden and DeWitt,

1991; Bennett and De Paolo, 1987). The boundaries of the Ndisotopic provinces are as yet poorly controlled due to the reconnaissance nature of the studies, but in this region the Pb-isotopic 

data are numerous, and the boundaries of the Mojave and Central 

Arizona Pb-isotopic provinces are quite accurately located. Also, 

the Poachie region spans the boundary between two types of Middle Proterozoic granite: metaluminous to the west and peraluminous to the east (J.L. Anderson, 1989).

EXPLANATION

Quaternary and Tertiary rocks; includes small 

areas of metamorphosed Mesozoic and Paleozoic 

sedimentary and volcanic rocks and of Cretaceous 

igneous rocks in the Basin and Range

£ Paleozoic rocks 

Proterozoic rocks

Belts of Proterozoic metamorphic rocks in 

eastern Mojave Pb-isotope crustal province

Boundary between Central Arizona and 

Mojave Pb-isotope crustal provinces

..- Wooden and others, 1988 

- Chamberlain and Bowring, 1990 

This study

Figure 1. Location of exposures of Proterozoic rocks in west-central 

and northwest Arizona showing boundary between Mojave and Central 

Arizona crustal provinces based on earlier work and this study, and outline of Poachie region (fig. 2). A, Antler-Valentine metamorphic belt; W, 

Whipple Mountains; L, Lost Basin Range; G, Garnet Mountain; CC, Cottonwood Cliffs. Map generalized from Reynolds (1988).

Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province
Acknowledgments

This research was supported by the Geologic Framework, 

National Geologic Mapping, Pacific-Arizona Crustal Experiment 

(PACE), Basin and Range-Colorado Plateau Project (BARCO), 

and COGEOMAP programs of the U.S. Geological Survey. We 

thank Clay Conway, Ed DeWitt, and Phil Blacet for much advice 

on Proterozoic geology of the region. The conventional U-Pb zircon geochronology was accomplished with the assistance of 

Geoff Elliot, Cindy Brown, and Michele Hornberger. Single zircon analyses were determined on the SHRIMP ion probe at Australian National University. JLW thanks Dr. W. Compston for 

making these facilities available and Alien Nutman and colleagues for help with analytical determinations, data reduction, 

and making his visits to Canberra pleasant and productive. We 

appreciate the thoughtful reviews of this manuscript by Ed 

DeWitt and Dan Shawe.

Previous Work

Detailed geologic mapping of about 100 km2 around 

Bagdad (Anderson and others, 1955) has furnished a benchmark 

for the geology of this part of the transition zone (fig. 1). The 

Bagdad area is dominated by a supracrustal sequence of metavolcanic and metasedimentary rocks, and it contains a variety of Proterozoic plutonic rocks. Conway and others (1986) extended that 

mapping 4 km southwest along the Bagdad metamorphic belt 

(fig. 1). Outside the Bagdad area reconnaissance mapping by 

Wilson and others (1969) divided the Proterozoic rocks into 

schist, gneiss, and granite. Immediately to the west detailed mapping by Lucchitta and Suneson (1982, 1994) contributed further 

to knowledge of the Proterozoic geology. The Geologic Map of 

Arizona (Reynolds, 1988) incorporates the published and unpublished mapping through 1986, including that in the Poachie 

Range (Bryant, 1992).

Early geochronologic studies of rocks from the region using 

K-Ar and Rb-Sr methods produced a variety of results (Aldrich 

and others, 1957; Wasserberg and Lanphere, 1965; Shafiqullah 

and others, 1980). These early data were of reconnaissance 

nature and were made before we knew about the complex thermal 

history of the region (Bryant and others, 1991). The U-Pb isotopic system has proven much more useful than the K-Ar and RbSr systems for determining crystallization ages for older plutonic 

or metavolcanic rocks or rocks with complex thermal histories. 

The first such determinations were made for rocks from the 

Bagdad area as part of pioneering regional geochronological 

studies by Silver (1968). Recent references to these data subtract 

1-2 percent, depending on the ratios used (Reynolds and others, 

1986), or 25 m.y. (Conway and others, 1986), in order to make all 

the data consistent with presently accepted decay constants. The 

only zircon date from the Bagdad area for which the exact location and analytical data have been published is 1,411 ±3 Ma from 

the Lawler Peak Granite (Silver and others, 1980).

Ages of Proterozoic rocks elsewhere in central and western 

Arizona northwest and northeast of the Poachie region have been 

published by several workers. In the Prescott-Jerome region, 

about 50 km to the east, metamorphic rocks are about 1,760 to

1,720 Ma, and plutonic rocks that intrude them range from 1,750 

to 1,700 Ma (Anderson and others, 1971; Karlstrom and others, 

1987; Karlstrom and Bowring, 1993). In the northeast-trending 

belt of metamorphic rocks known as the Antler-Valentine belt 

(fig. 1), located 60 km northwest to 100 km north of the Poachie 

region, Chamberlain and Bowring (1990) obtained data that led 

them to revise the boundary between the Mojave and Central Arizona Pb-isotopic provinces of Wooden and others (1988) and to 

place it 50-100 km farther east (fig. 1). East of their boundary, at 

Cotton wood Cliffs at the northeast end of exposures of the AntlerValentine belt, the metamorphic rocks are older than 1,730 Ma 

and are intruded by 1,730- and 1,710-Ma granites. The younger 

granite is interpreted to be late-kinematic in relation to the major 

regional deformation and metamorphism (Chamberlain and 

Bowring, 1990). Rocks west of the boundary, in the Hualapai 

Mountains and in the Lost Basin Range-Garnet Mountain area, 

show complex U-Pb zircon systematics that indicate an inherited

2.3-1.8 Ga zircon component. These rocks also have higher 

207pb/204pb ratios relatiye to 206pb/204pb ratios than r()cks to me

east. The metamorphic rocks are interpreted to be about 1.73 Ga 

and are intruded by plutonic rocks dated as about 1.70 Ga. Chamberlain and Bowring (1990) projected the boundary between the 

two crustal provinces south through the Poachie region southwest 

of U.S. Highway 93 (figs. 1 and 2), and interpreted it to be a 

suture related to the convergence of the two terranes about 1.68- 

1.70 Ga. Wooden and DeWitt (1991) placed the boundary about 

25 km east of Bagdad but did not have the information to extend 

it south of U.S. Highway 93.

Lead-isotopic systematics of Proterozoic rocks in central and 

western Arizona provide a way to reconstruct both the Proterozoic 

tectonic and magmatic evolution of the region. Wooden and 

DeWitt (1991) interpreted the whole-rock Pb-isotopic data of 

these rocks to indicate that volcanic arcs and sedimentary basins 

like those in central Arizona were built on Mojave crust in the area 

between the Central Arizona province and the Mojave province 

proper. Volcanic arcs and sedimentary basins formed on older 

crust in the boundary zone 1,730-1,710 Ma, and plutonism at 

1,730-1,690 Ma tapped both Mojave and central Arizona mantle 

and crust (Wooden and DeWitt, 1991). Although the Poachie 

region is situated within the boundary zone between these provinces, the surface geology more closely resembles that of the 

Yavapai province than that of the Mojave province. Because of 

this resemblance, the area of the boundary zone was included in 

the Yavapai geologic province by Karlstrom and Bowring (1993).

The Antler-Valentine belt is the westernmost volcanic arc 

and sedimentary basin like those of the Central Arizona province, 

and aesthenosphere and (or) subducted Central Arizona mantle as 

well as Mojave crust contributed to the formation of the igneous 

rocks there. Preliminary results of studies in the Cerbat Mountains, north of the Antler-Valentine belt, suggest that the remains 

of a -1.73 Ga metamorphic belt similar to the Antler-Valentine 

belt is preserved among 1.72-1.68 Ga gneissose granitic rock 

(Duebendorfer and Chamberlain, 1994).

In northern Arizona in the Upper Granite Gorge of the 

Grand Canyon, U-Pb geochronologic and isotopic study places 

the east margin of Mojave crust between 154 and 159 km downstream from Lee's Ferry near the Crystal shear zone (Hawkins 

and others, 1996).

Previous Work 3
Geology

Metamorphic and plutonic rocks underlying Paleozoic, 

Mesozoic, and Tertiary supracrustal rocks form the basement in 

west-central Arizona.

Metamorphic Rocks

Our study area is underlain by plutonic rocks separated by 

north- to northeast-trending screens of amphibolite-facies metamorphic rocks (Xm, fig. 2). The principal screen extends south 

from Bagdad about 20 km south-southwest into the Poachie 

region where it separates Early Proterozoic gneissic tonalite 

(Xgt) from Middle Proterozoic granite of Olea Ranch (Yo) and, 

farther south, is within the granite of Olea Ranch, and the Early 

Proterozoic coarse-grained granite (Xcg). Near Bagdad the preservation of some primary textures and structures in the rocks 

reveals a stratigraphic sequence despite amphibolite-facies 

regional metamorphism of the rocks (Anderson and others, 

1955). The stratigraphic sequence from oldest to youngest is (1) 

Bridle Formation (mafic volcanic rocks), (2) Butte Falls Tuff (felsic volcanic rocks), and (3) Hillside Mica Schist (shale and siltstone). According to Anderson and others (1955), Dick Rhyolite 

intrudes the sequence in the Bagdad area. More recent work by 

Conway and others (1986) south of Bagdad indicates that the 

Dick Rhyolite is extrusive and overlies the Bridle Formation 

(Conway and others, 1986).

The Dick Rhyolite, the only formally named formation from 

the Bagdad area shown on the map of the Poachie Range (Bryant, 

1992), is a fine-grained biotite-quartz-feldspar gneiss containing 

scattered quartz and less common feldspar grains and aggregates 

as much as 1 mm in diameter, which probably were phenocrysts 

or crystal fragments (fig. 3). If we project the tops-to-the-east 

relationships from near Bagdad to the south, the unit is overlain 

by interlayered amphibolite and biotite-quartz-feldspar gneiss 

containing a few layers of schist, which is in turn overlain by 

muscovite-biotite schist and gneiss containing sillimanite and 

andalusite in many places. The muscovite-biotite schist and 

gneiss are probably correlative with the Hillside Mica Schist near 

Bagdad. South of U.S. Highway 93 all the metamorphic rocks 

are extensively intruded by granite and pegmatite. Farther south, 

increased intrusion and recrystallization tends to obscure any certain correlations with map units in the Bagdad metamorphic belt 

(fig. 2), although the rocks appear to be a continuation of the unit 

that is correlative with the Hillside Mica Schist. Metamorphic 

rocks in the southern part of the belt are muscovite-biotite schist 

and gneiss, locally containing sillimanite±garnet. They contain 

some layers of amphibolite, biotite-hornblende gneiss, and 

biotite-quartz-plagioclase gneiss. The latter megascopically 

resemble quartzite.

In the western part of the area, a second major screen of 

metamorphic rock (Xm) separates the Middle Proterozoic Signal 

Granite (Ys) on the west from the Early Proterozoic coarsegrained granite (Xcg) on the east (fig. 2). This screen is composed 

of biotite and biotite-hornblende-plagioclase schist and gneiss 

containing a few layers of sillimanite-muscovite schist and gneiss. 

The rocks are migmatized in many places and intruded by gabbro, 

diorite, granodiorite, and granite. The proportions of muscovitebiotite schist and gneiss increase southward within the screen.

Metamorphic rocks within the Signal batholith south of the 

west end of the Poachie Range differ from those elsewhere in the 

area and consist of biotite-quartz-feldspar gneiss locally containing garnet, hornblende-diopside-plagioclase granofels, and 

amphibolite. Their compositions suggest that they were derived 

from siltstones or fine-grained sandstones and (or) felsic tuffs 

containing calcareous or marly layers.

On the Santa Maria River southeast of the Bagdad metamorphic belt is muscovite-biotite schist and gneiss, locally containing 

sillimanite, garnet, or cordierite and layers of muscovite-biotite 

quartzite and intruded by aplite, pegmatite, and the granite of 

Thorn Peak. East of the Bagdad belt, metamorphic rocks are 

sparse in the area, are mostly screens and inclusions in a map unit 

rich in pegmatite, aplite, and granite, and consist of muscovitebiotite and sillimanite-muscovite-biotite schist and gneiss.

Foliation in the metamorphic rocks has a complex pattern. 

Strikes range from north-northwest to east-southeast, and dips are 

predominantly steep to moderate to the east. North-northeast 

strikes and steep east-southeast dips are most common. Mineral 

alignments have a maximum that trends N. 66° E. and plunges 

19° NE. Some lineations have steeper plunges and more easterly 

trends. Axes of minor folds range in plunge from 0° to 80° and 

trend in all directions except northwest. Axial planes of the minor 

folds strike north-northwest to northeast and dip gently to steeply 

northeast and southeast. A few folds have various trends that differ from most folds. The data suggest a complex polyphase history of folding for these rocks. No superposition of folds or 

foliations was observed that would furnish a basis for deciphering 

the history in this area. In the Cerbat and Hualapai Mountains 

(Duebendorfer and others, 1998) and elsewhere in the Proterozoic rocks of Arizona (Karlstrom and Bowring, 1991), complex 

tectonic histories commonly include formation of northweststriking foliation followed by formation of northeast-striking 

foliation. Proterozoic rocks in the Poachie region may have a 

similar history, perhaps obscured by additional deformation 

accompanying the emplacement of numerous Early and Middle 

Proterozoic plutons.

Plutonic Rocks

Plutonic rocks dominate the Proterozoic geology of the 

Poachie region and are about equally divided between Early 

and Middle Proterozoic age (fig. 2). Some of the units mapped 

range from heterogeneous ones composed of gabbro to granite 

to relatively well defined plutons having smaller compositional 

variations.

Figure 2 (facing page). Proterozoic rocks in the Poachie region showing locality of analyzed samples. From Bryant (1995 and unpublished reconnaissance mapping).

Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province
Bagdad

113°

34°22'30"

Porphyritic granite

MOHAVEJYAVAPAI COUNTY iCOUNTY

Quaternary and Tertiary rocks, undifferentiated

Granitesof Olea Ranch

Granites of 

Joshua Tree 

Parkway

Granites of Grayback Mountain

Granite, aplite, pegmatite, and mica schist and gneiss

I Gneissic tonalite 

Granite of Thorn Peak

Fine- to medium-grained granite

Mafic gneiss

Coarse-grained granitic rocks

Metamorphosed sedimentary and volcanic rocks

• 21 Sample of rock analyzed. Number refers to

number in appendix; description and location of analyzed samples

1,410 U-Pb zircon date in Ma. Where enclosed in rectangle 

represents a well-defined pluton

ndex to iV-i topographic quadrangle 

maps
Early Proterozoic Plutonic Rocks

Early Proterozoic plutonic rocks are mafic gneiss, coarsegrained granitic rocks, fine-grained granite, granite of Thorn 

Peak, gneissic tonalite, and a unit of mixed plutonic and metamorphic rocks that includes granite, aplite, pegmatite, schist, and 

gneiss. The granite at Burro Creek, probably part of the coarsegrained granitic rocks but not connected by mapping to them, is 

nonetheless described with those rocks.

Mafic Gneiss

West of the Bagdad metamorphic belt south of U.S. Highway 93 is a discontinuous belt of biotite-hornblende-plagioclase 

schist and gneiss (map unit Xmg, fig. 2). Rocks of this unit are 

abundantly intruded by adjacent Early and Middle Proterozoic 

granitic rocks and are characterized by plagioclase porphyroblasts. These intrusives produce a complex and gradational contact between the mafic gneiss and the bordering granitic rocks. 

The mafic gneiss does not resemble any of the rocks in the 

Bagdad metamorphic belt. The mafic rocks are not layered but 

are partly foliated, and they are tonalite, diorite, and gabbro. In 

one location the mafic gneiss cuts muscovite-biotite schist at the 

east contact of the unit. Where plagioclase porphyroblasts are 

absent, the gneiss has a grain size of 0.5-2 mm in contrast to most 

of the 1,700-Ma mafic plutonic rocks, which have a grain size of 

5-15 mm.

The mafic gneiss consists of green, dark-green, and olive 

synkinematic to postkinematic anhedral hornblende as much as 2 

mm long, anhedral synkinematic to postkinematic biotite as 

much as 1.5 mm long, plagioclase (An25_4o) as anhedral to subhedral grains as much as 2 mm in diameter and porphyroblasts as 

much as 1 cm in diameter. In some rocks 1-2-mm subhedral plagioclase grains are in a plagioclase-rich matrix having an average 

grain size of 0.2-0.4 mm. This texture suggests that the larger 

grains may be relict phenocrysts from an igneous protolith. Some 

rocks of the unit contain anhedral quartz generally 0.02-1 mm, 

but locally as much as 2 mm in diameter. Anhedral to euhedral 

epidote as much as 0.5 mm in diameter is partly contemporaneous with the biotite and partly secondary. Accessory minerals are 

sphene, apatite, opaque minerals, and minor allanite. Secondary 

chlorite replaces biotite and hornblende. Color index ranges 

from 20 to 62. Some of the rocks intruding the unit are hornblende-biotite tonalites, which are similar in composition to some 

of the mafic gneiss rather than the adjacent more felsic granites, 

which also intrude the unit. The composition and texture of the 

mafic gneiss suggest that its protoliths are intermediate to mafic 

hypabyssal or subvolcanic intrusions. Superficially these rocks 

resemble completely metamorphosed volcanic rocks.

Coarse-Grained Granitic Rocks

A heterogeneous group of mostly coarse grained and variably foliated plutonic rocks form the east and central parts of the 

Poachie Range (map unit Xcg, fig. 2). The rocks included in this 

unit form a suite ranging in composition from gabbro to granite. 

Hornblende-biotite and biotite granodiorite and granite are the

Figure 3. Photomicrograph of fine-grained biotite-quartz-feldspar 

gneiss of metamorphosed Dick Rhyolite. Lens of quartz grains probably 

represents recrystallized quartz phenocryst or crystal fragment. Appendix sample No. 8; U-Pb zircon age determination, figure 12; major-oxide 

and trace-element concentrations, table 3; whole-rock Pb-isotope analysis, table 8. Arrastra Mtn NE7>2' quadrangle.

dominant rock types, but rock types in the unit range to syenite 

and tonalite, and also include small bodies of gabbro and diorite. 

The unit generally has a complex and gradational contact with 

migmatitic schist and gneiss along its west contact.

The oldest plutonic rocks in this unit are gabbro and diorite. A few of these bodies are as much as 600 m long and were 

mapped separately (Bryant, 1992), but none are shown in figure 

2. The mafic rocks are most numerous in the northwest part of the 

unit, and they also form small bodies in the metamorphic wallrock of the unit.

Roof pendants or large inclusions of possibly correlative 

gabbro are found in the Middle Proterozoic Signal Granite. Gabbro also intrudes metamorphic rocks of the Bagdad belt and roof 

pendants of metamorphic rock in the Signal Granite. The largest 

mafic intrusion among these is about 1.5 km long and 400 m wide.

The mafic rocks in the unit are generally medium grained, 

although some are coarse grained. Textures range from a thoroughly recrystallized mosaic to hypidiomorphic granular and diabasic, which is partly modified by recrystallization. The rocks are 

composed of plagioclase (An35_45 average; An60 maximum), 

green or olive-green hornblende, and, in many places, biotite. 

Monoclinic pyroxene is present in a few rocks, and orthorhombic 

pyroxene was found in one sample. Quartz is found in a few samples. Common accessory minerals are opaque minerals (locally a 

substantial component), sphene, and apatite. Some rocks have 

secondary chlorite and epidote. Color index is mostly 40-60 and 

is as much as 85. Modal compositions (IUGS classification, 

Streckeisen, 1973) range from melagabbro to quartz diorite.

The granitic part of the unit shows spatial compositional 

variations. These rocks are dominantly granodiorite in the north 

and granite in the south. In the northwest a distinctive porphyritic 

granodiorite and granite containing blocky feldspar phenocrysts 

as much as 3 cm in diameter is common (fig. 4). The various 

granitic rocks grade into each other in many places and were not

Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province
Figure 4. Foliated porphyritic granodiorite near west contact of 

coarse-grained granite. Blocky potassic feldspar phenocrysts are as 

much as 2.5 cm in diameter. Contains mafic inclusions aligned with foliation, and fracture-controlled aplite veinlet. Pen is 13 cm long. Appendi < 

sample No. 20; major-oxide and trace-element concentrations, table 4; 

Arrastra Mtn 7 Yz quadrangle.

mappable as distinct plutons. Locally the granitic rocks contain 

scattered inclusions of metamorphic rock, migmatite, and more 

mafic phases of the plutonic unit, and these inclusions are more 

numerous near the western contact of the unit than elsewhere. 

The coarse-grained granitic rocks are cut by fine- to mediumgrained and porphyritic granitic rocks, many of which could be 

either Early or Middle Proterozoic.

The felsic rocks (CI<40) range in modal composition from 

diorite to granite. In sec. 31, T. 13 N., R. 11 W. and sec. 5, T. 12 

N., R. 11 W., parts of the unit are quartz-poor and are monzonite, 

monzodiorite, or quartz monzonite. No distinct contacts of those 

rock types were detected in fairly good exposures in washes in the 

area, but more detailed work may be needed to make sure that this 

variation cannot be mapped.

The variation in foliation seen megascopically is also apparent under the microscope. About a third of the samples examined 

show some biotite alignment, and between different samples the 

alignment ranges from poor to excellent. Some of the foliation 

measured in the field is on aggregates of mafic minerals, within 

which the individual grains are not aligned. Textures range from

mosaic to hypidiomorphic granular. The latter texture is best 

developed where the rock contains subhedral phenocrysts of 

microcline.

Most of the felsic rocks contain biotite and lesser amounts of 

hornblende, except for the granites, which contain little or no 

hornblende. Opaque minerals, sphene, apatite, and zircon are 

found in almost all the rocks examined, and allanite occurs in 

some of them.

Quartz is as much as 4 mm in diameter and is interstitial to 

the feldspars in some rocks. Microcline is as much as 1.5 cm long 

and is locally perthitic and rarely interstitial to plagioclase. Plagioclase (oligoclase or sodic andesine) is anhedral to subhedral 

and as much as 8 mm long. Biotite as much as 2 mm long generally is in aggregates, many of which contain hornblende. Generally anhedral green hornblende as much as 3 mm long is in 

aggregates with biotite. Many of the larger grains have sieve texture with quartz.

Granite at Burro Creek. Granitic rocks on Burro Creek (unit 

Xcg in fig. 2) are not correlative with the Signal Granite, as suggested previously (Bryant and Wooden, 1986). These rocks are 

probably part of the plutonic complex that forms the east half of 

the Poachie Range, and it is treated as such here. In outcrop the 

differences between the Signal Granite and the granite at Burro 

Creek are as follows: (1) potassic feldspar megacrysts at Burro 

Creek tend to be equant compared to elongate in the Signal Granite, and (2) clots composed of mafic minerals at Burro Creek are 

larger and more irregular than those in the Signal Granite (fig. 5). 

The U-Pb date of a zircon for a sample from Burro Creek was 

erroneously reported as the age of the Signal Granite (Bryant and 

Wooden, 1986). We have not mapped the area between the sample site on Burro Creek and the Poachie Range area (Bryant, 

1992), so we do not know whether it forms a mappable pluton in 

the coarse-grained granite unit or whether it is just another component of that heterogeneous unit.

Fine-Grained Granite

One 2-km-diameter pluton of fine- to medium-grained 

biotite granite (map unit Xg, fig. 2) locally containing muscovite 

forms the high summit at the east end of the Poachie Range. The 

pluton has a moderately sharp contact with the coarse-grained 

granite (unit Xcg) and contains inclusions of the wallrock. Adjacent to the pluton, dikes of fine-grained granite cut the coarsegrained granite. Pb-isotopic composition of a whole-rock sample 

from the pluton (appendix sample No. 28; table 8) shows that the 

granite of that pluton is Early Proterozoic. Other dikes and small 

plutons of fine-grained granite intruding the coarse-grained granite unit (Xcg) are also Early Proterozoic (appendix sample Nos. 

29, 30; table 8), but some may be Middle Proterozoic age. Those 

plutons are mapped as YXg in the Poachie Range (Bryant, 1992).

On the east end of the Poachie Range, the fine-grained granite has an average grain size of about 2 mm, an allotriomorphic 

granular texture, and a color index ranging from 2 to 4. The granite contains <2 percent muscovite that mostly appears to be 

younger than the biotite, but locally some muscovite and some 

biotite crystallized at the same time. Biotite flakes are poorly to 

well aligned, but the foliation is not conspicuous in outcrop 

because of the small amount of biotite in the rock. Accessory minerals are zircon, allanite, sphene, apatite, and opaque minerals. 

Secondary minerals are chlorite, epidote, muscovite, and sericite.

Geology 7
Granite of Thorn Peak

In the central part of the area west of the Santa Maria River, 

moderately coarse grained muscovite-biotite and biotite granite 

(map unit Xt, fig. 2) forms a pluton 4-5 km wide and 15 km long 

and a few small satellitic plutons to the east. Contacts with metamorphic rocks (map unit Xm, fig. 2) along its southern margin 

are generally sharp. Contacts with a unit of mixed granite, aplite, 

pegmatite, and mica schist and gneiss (map unit YXgp, fig. 2) 

along the east part of the pluton and around the satellitic plutons 

range from sharp to gradational. Some of the granite in that 

mixed unit probably is the granite of Thorn Peak.

Potassic feldspar grains in the granite of Thorn Peak are as 

much as 1 cm in diameter, aggregates of biotite and muscovite 

0.5-2 mm long, quartz and plagioclase crystals 2-5 mm in diameter. Accessory garnet is present locally. The granite of Thorn 

Peak has inclusions of mica schist, mica gneiss, and amphibolite, 

is cut by sparse dikes of pegmatite and aplite (fig. 6), and locally 

has a poorly developed to well-developed foliation parallel the 

trend of the pluton and the regional north-northeast structural 

trend. Some of the foliation is formed by aligned potassic feldspar grains and is interpreted to be due to flow, but other foliation 

appears to have formed by subsolidus recrystallization. Mapped 

with this unit is a pluton on Crosby Mountain northeast of the 

main pluton of the granite of Thorn Peak. That pluton consists of 

medium-grained and locally coarse grained granite containing 

accessory garnet. We have little information on the granite on 

Crosby Mountain, but according to Ed DeWitt (oral commun., 

1990), granite of Thorn Peak cuts a granite resembling that on 

Crosby Mountain.

Quartz as interstitial grains as much as 2 mm in diameter and 

mosaic-textured aggregates having a grain size as large as 1 mm 

fill the space between the feldspars, as seen in thin section. Perthitic microcline forms subhedral to euhedral phenocrysts locally 

as much as 1 cm long and smaller anhedral to subhedral crystals. 

Generally subhedral but locally euhedral or anhedral plagioclase 

(An25_35) is as much as 6 mm long, and also is found locally in 

mosaic-textured aggregates with quartz. Biotite is present as 

anhedral grains as much as 2 mm in diameter, and muscovite as 

much as 3 mm in diameter is intergrown and formed contemporaneously with biotite. Secondary muscovite formed by alteration 

of biotite. Common accessory minerals in the granite of Thorn 

Peak are zircon, apatite, and opaque minerals, and less common 

ones are sphene, tourmaline, garnet, and allanite. Epidote, chlorite, and sericite are secondary minerals in this unit. Modally the 

rocks are granite with color indices ranging from 2 to 8.

Gneissic Tonalite

Gneissic tonalite (map unit Xgt, fig. 2) crops out along the 

east flank of the Bagdad metamorphic belt. The northern part of 

this pluton has not been mapped, but reconnaissance indicates 

that parts of it extend only 3 km north of the Poachie map area. 

This unit was called gneissic granodiorite in earlier publications 

(Bryant, 1992,1995 ;Bryant and Wooden, 1 99 Ib), but a review of 

available thin section and chemical data indicates that tonalite is 

a better name for this map unit. The south end of the gneissic 

tonalite is truncated by younger granite. In the Poachie region the

FigureB. Coarse-grained granite at Burro Creek. Hammer is 33 cm 

long. Appendix sample No. 22; U-Pb zircon age determination, figure 14; 

major-oxide and trace-element concentrations, table 4; whole-rock and 

feldspar Pb-isotope analysis, table 8. Greenwood Peak 7 Yz quadrangle.

unit intrudes mica schist and gneiss and contains many xenoliths 

of country rock within 2 km of its western contact. The eastern 

part of the pluton contains scattered inclusions of fine-grained 

diorite, tonalite, or granodiorite. Tourmaline-bearing leucogranite and pegmatite dikes intrude the unit. Much of the west 

contact in our map area is a shear zone, a southwestward extension of the Mountain Springs fault zone mapped by Anderson and 

others (1955) in the Bagdad area, and nearby tonalite has a partly 

healed cataclastic texture. On the east the contact is covered by 

Tertiary gravel. The gneissic tonalite unit contains rocks ranging 

in composition from biotite melagranite to hornblende tonalite 

and quartz diorite (fig. 7). Color index ranges from 25 to 65. In 

the Bagdad area the gneissic granodiorite and gabbro mapped 

south of Sanders Mesa (Anderson and others, 1955) are possibly 

correlative rocks.

Quartz is in anhedral grains as much as 4 mm in diameter 

and as mosaic-textured aggregates having a grain size of 0.1-0.3 

mm. Some of the larger grains are strongly strained and are 

partly broken into subgrains and mosaic-textured aggregates. Plagioclase (An25_35) is in anhedral to subhedral crystals as much as 

8 mm long, which are locally bent and broken, and in mosaic-textured aggregates. Some plagioclase grains are normally zoned. 

Locally perthitic microcline in grains as much as 4 mm long are 

bent, broken, and healed by quartz and epidote. Microcline also 

forms mosaic-textured aggregates with quartz. Biotite forms

8 Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province
Figure 6. Granite of Thorn Peak near its west contact. Contains inclusions of fine-grained mica gneiss and xenocrysts of pegmatitic feldspar. 

Hammer is 33 cm long. Appendix sample No. 31; major-oxide and traceelement concentrations (sample without inclusions), table 5. Arrastra 

Mtn NE 7 Y2 quadrangle.

Figure 7. Biotite-hornblende diorite in gneissic tonalite unit. Cut by irregular pegmatitic segregations. Hand lens is 2 cm in diameter. Appendix sample No. 37; major-oxide and trace-element concentrations, table 

5. Thorn Peak 7 Y^ quadrangle.

flakes as much as 3.5 mm in diameter and aggregates of smaller 

grains. Some of the larger flakes are bent. Green to dark-green 

hornblende in anhedral to subhedral crystals as much as 2 mm 

long forms aggregates with or without biotite between blocky 

subhedral plagioclase. The hornblende is locally altered to lightgreen actinolite. Some rock containing numerous inclusions of 

mica schist and gneiss near the contact contains muscovite intergrown with biotite. Accessory minerals are sphene, apatite, zircon, allanite, and opaque minerals. Secondary minerals are 

chlorite, epidote, sericite, and carbonate group minerals.

Granite, Aplite, Pegmatite, Mica Schist, and Gneiss

In the eastern part of the area, rocks between the granite 

plutons are a mixture of muscovite-biotite schist and gneiss, 

locally containing sillimanite, intruded by pegmatite, alaskite, 

and granite in various proportions (map unit YXap, fig. 2). The 

schist and gneiss content of the unit ranges from as much as 50 

percent to only a few percent. The pegmatite and alaskite contain 

small amounts of biotite, muscovite, and tourmaline, and in many 

places the pegmatite forms indistinct layers with gradational contacts in finer grained granite and aplite. Some of the granite is 

pegmatitic and contains potassic feldspar grains 10 cm in diameter, the grain size of many of the pegmatites. The granite is fineto medium-grained biotite and muscovite-biotite granite like the 

granite of Thorn Peak, but some resembles the undated other Proterozoic rocks in the nearby part of the Poachie region. The granitic rocks are locally foliated.

Middle Proterozoic Plutonic Rocks

Middle Proterozoic rocks are Signal Granite, mafic granodiorite, porphyritic biotite granite, granite of Olea Ranch, granite of Joshua Tree Parkway, granite of Grayback Mountain, and 

diabase.

Signal Granite

The Signal Granite (Lucchitta and Suneson, 1982; map unit 

Ys, fig. 2) forms a batholith about 20 km long and 15 km wide in 

and west of the western part of the area and underlies the west end 

of the Poachie Range. The type locality, the ghost town of Signal, 

is at the west margin of our study area. The Signal Granite generally has well-defined contacts with country rock. However, 

inclusions or septa of metamorphic rock in the western part of the 

area are cut by numerous dikes and irregular intrusions of the 

granite. The granite is metamorphosed to augen gneiss and mylonite along its east contact. This zone of sheared granite is confined to the Signal batholith and might be related to movements 

within the intrusion during a late stage of its emplacement. It dips 

gently to moderately to the south or southeast parallel with the 

contact and has east- to northeast-trending lineation, which 

plunges gently to moderately. In the southern part of this contact 

zone the granite is locally brecciated along the zone of mylonite. 

According to Nyman and others (1994), kinematic indicators in 

this zone show that relative movements in the rock were to the 

northeast in a thrust sense during the formation of this fabric.

The body ranges in composition from granite to granodiorite 

and contains potassic feldspar phenocrysts generally 2-3 cm 

long, but locally as much as 6 cm long, and plagioclase and quartz 

grains as much as 1 cm in diameter (fig. 8A). Biotite and hornblende grains as much as 0.5 cm long form aggregates as much as 

1 cm long. Some of the granodiorite is porphyritic: larger potassic feldspar crystals are scattered in a finer matrix (fig. 85). Oriented lath-shaped, carlsbad-twinned, potassic feldspar crystals 

define flow foliation in most outcrops (fig. 8C). The Signal 

Granite contains widely scattered inclusions of a mafic facies, a 

closely associated mafic granodiorite, hornblende-biotite gneiss, 

and gabbro. A few quartz-microcline pegmatite pods, dikes, and 

lenses 0.1-1 m thick and dikes of medium-grained biotite granite 

cut the coarse-grained granite (fig. 8Z)).

Geology 9
The composition of the Signal Granite ranges considerably, 

as indicated by a range in the color index from 1 to 32. A leucocratic facies consisting of coarse- to fine-grained granite containing sparse biotite intrudes the main mass of the Signal Granite in 

bodies as much as 1.5 km long and 0.5 km wide (Bryant, 1992). 

A mafic facies composed of gray, medium-grained, locally porphyritic, biotite-hornblende tonalite to granite contains potassic 

feldspar phenocrysts as much as 4 cm in diameter. This facies is 

in mappable bodies as much as 3.5 km long and 1 km wide. The 

mafic phase is intruded by and grades to the main phase of the 

Signal Granite.

The Signal Granite contains anhedral quartz grains as much 

as 6 mm in diameter that are interstitial to the feldspar grains. 

Anhedral to subhedral microcline that is commonly perthitic and 

accompanied by myrmekitic intergrowths forms crystals more 

than a centimeter long. Anhedral to subhedral plagioclase (An17_ 

33) forms grains as much as a centimeter long in some samples. 

Anhedral biotite as much as 3 mm in diameter tends to be in 

aggregates between the feldspar grains. Anhedral green hornblende as much as 3 mm long usually occurs in aggregates with 

the biotite but locally is rimmed by biotite. Accessory minerals 

are zircon, apatite, allanite, sphene, and opaque minerals. Secondary minerals are sericite, carbonate minerals, chlorite, and 

epidote. Color index is generally between 10 and 20.

The coarse grain size of the Signal Granite makes modal 

compositions based on a standard thin section somewhat uncertain. Nevertheless it is obvious in the field that compositional 

variations exist. We conclude that composition of the main phase 

of the Signal Granite ranges from granite to granodiorite. Biotite 

is the principal mafic mineral, but many rocks have small 

amounts of hornblende, whereas a few rocks have subequal 

amounts of biotite and hornblende.

The mafic phase of the Signal Granite is commonly granodiorite and tonalite, and in it hornblende generally is as abundant 

as or more abundant than biotite. Grain size of the feldspars is 

smaller, usually in the range of 2-7 mm. Sphene is a more abundant accessory mineral than in the main phase of the Signal Granite. Color index is 20-35.

The leucocratic phase ranges in grain size from 2-3 mm to 

5-10 mm. Finer grained rocks of the phase form dikes that cut 

the main phase of the Signal. Some of the rocks contain late porphyroblasts of quartz as much as 1.5 cm in diameter, and the 

quartz content of the rocks is higher than in the main phase of the 

Signal. Microcline tends to be more perthitic, and the plagioclase 

in some samples is sodic oligoclase. Color index is <1-10.

Mafic Granodiorite

are described in the next paragraph. The body contains hornblende granite pegmatites a few centimeters thick and microcline-quartz pegmatites as much as 10 m thick. Contact relations 

with the Signal Granite are equivocal, for the mafic granodiorite 

contains inclusions of Signal Granite and is cut by dikes of Signal 

Granite, suggesting nearly simultaneous emplacement of the Signal Granite and the mafic granodiorite. However, no dikes of 

mafic granodiorite cut the Signal Granite, suggesting that the Signal Granite is slightly younger at the level of exposure. The color 

index of the mafic granodiorite is 20-30, similar to that of the 

more mafic phases of the Signal Granite.

The granodiorite contains quartz in granophyric intergrowths (fig. 9) 0.02-0.05 mm in diameter with potassic feldspar, 

as anhedral grains 0.1-0.5 mm in diameter and as xenocrysts several millimeters in diameter probably derived from the Signal 

Granite country rock. Plagioclase (An42_23) forms euhedral to 

subhedral normally zoned phenocrysts as much as 2 mm long. 

Anhedral plagioclase grains in the matrix range from 0.04 mm to 

1 mm in length in different rocks and are anhedral to euhedral and 

about 1 mm in equigranular rocks. Potassic feldspar occurs in 

some rocks of the unit as anhedral grains of cryptoperthite and 

microcline as much as 2.6 mm in diameter with or without granophyric intergrowths with quartz (fig. 9). Anhedral augite as much 

as 2 mm in diameter is partly altered to hornblende. Brown, 

greenish-brown, olive-green, and dark-green hornblende in anhedral crystals that are locally skeletal is generally about 0.5 mm 

long but locally as much as 1.5 mm long. Anhedral biotite is 

commonly 1 mm in diameter but locally 2 mm. The proportions 

of biotite, hornblende, and pyroxene range from rocks in which 

all three occur to ones in which either hornblende or biotite is the 

only mafic silicate mineral. Magnetite crystals, locally as much 

as 1.5 mm and commonly 0.2-0.8 mm in diameter, are volumetrically an important constituent in many samples of the unit. 

Accessory minerals are sphene, allanite, zircon, and apatite. Secondary minerals are chlorite, epidote, sericite, and sparse carbonate minerals.

Porphyritic Biotite Granite

A northeast-trending belt of porphyritic biotite granite (map 

unit Ypg, fig. 2) cuts the coarse-grained granite to granodiorite 

gneiss (unit Xcg) east of the Signal Granite. Plutons in that belt 

contain potassic feldspar phenocrysts as much as 1.5 mm in 

diameter in a fine- to medium-grained matrix of quartz, plagioclase, potassic feldspar, and biotite. The unit also has medium- to 

coarse-grained equigranular phases. One sample yielded a Middle Proterozoic whole-rock Pb-isotopic age (appendix sample 

No. 58; table 8).

A distinctive unit of dark-gray fine- to medium-grained 

locally porphyritic hornblende-biotite and augite-hornblendebiotite melagranodiorite, monzogranite, melagranite, and quartz 

monzodiorite closely associated with the Signal Granite on the 

south flank of the west end of the Poachie Range forms a pluton 

about 4 km in diameter (map unit Ygd, fig. 2). The rock is locally 

foliated parallel to dikes of Signal Granite and pegmatite that cut 

it. The foliation is interpreted to be due to flow while the rock 

was still at least partly in the liquid state because plagioclase phenocrysts and aggregates of mafic minerals are aligned, but the 

matrix lacks the distinctive textures typical of this pluton, which

Granite of Olea Ranch

Closely related coarse-grained granite, porphyritic granite, 

and fine-grained granite (map unit Yo, fig. 2) form mappable bodies (Bryant, 1992) and are here included in a unit designated the 

granite of Olea Ranch. Olea Ranch is located in SW/4 sec. 19, T. 

13 N., R. 10 W., Arrastra Mtn lYz quadrangle and is the only feature named on the lYz topographic quadrangle in the area underlain by the unit other than Black Canyon, which was named for 

the basalt along it downstream from granite exposures.

10 Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province
mw^:^^ fcr*g?W".'A'-*%*•!* ' "-

^^*^!¥% i

ET- • " ••¥*•*&•**'* " ' ->W3i»y •tST-'XJK,* ' ' •

B

Figure 8. Outcrops of Signal Granite. A, Coarse-grained granite. Potassic feldspar crystals show some alignment at about 80° to pen. Pen is 

13 cm long. Arrastra Mtn 7 Yz quadrangle. B, Coarse-grained porphyritic granite containing inclusions of hornblende-biotite granodiorite or 

potassic feldspar-bearing quartz diorite. Knife is 6 cm long. Signal 

Mountain 7 Yz quadrangle. C, Flow-aligned potassic feldspar crystals as 

much as 6 cm long and inclusions of fine-grained hornblende-biotite 

granodiorite or potassic feldspar-bearing quartz diorite. Hammer is 33 

cm long. Signal Mountain 7 Yz quadrangle. D, Porphyritic granite containing scattered inclusions of fine-grained hornblende-biotite granodiorite or quartz diorite and cut by a quartz-microcline pegmatite. 

Feldspar phenocrysts and inclusions aligned in plane of flow. Hammer is 

33 cm long. Signal Mountain 7 Yz quadrangle.

D

Geology 11
A 7-km-diameter pluton of coarse-grained biotite granite 

and granodiorite crops out north of Olea Ranch and along U.S. 

Highway 93 for about 3 km either side of the Mohave-Yavapai 

County line (Bryant, 1992). The rock ranges from equigranular 

to porphyritic and contains potassic feldspar crystals generally 

1-2 cm and rarely as much as 3 cm long. Small amounts of primary muscovite are found in some of the coarse-grained granite. Dikes of pegmatite and fine- to medium-grained, locally 

porphyritic granite cut the coarse-grained granite. The coarsegrained granite contains scattered inclusions of biotite-quartzfeldspar gneiss, biotite-hornblende gneiss, biotite schist, 

amphibolite, and migmatite.

To the east, a pluton about 8 km long and 4 km wide (Bryant, 1992) consists of porphyritic biotite granite and granodiorite 

containing well-oriented tabular potassic feldspar phenocrysts 

generally 2-3 cm, but locally as much as 6 cm long that define a 

flow foliation in a medium-grained matrix. This rock is intruded 

by dikes of pegmatite and fine-grained granite and contains 

widely scattered inclusions of biotite-quartz-feldspar gneiss, 

biotite-hornblende-plagioclase gneiss, amphibolite, and finegrained biotite granodiorite. Despite the distinctly different texture of the rock compared to the coarse-grained granite, our 

chemical and isotopic data show that the compositions and ages 

of the granite at Olea Ranch and the porphyritic granite to the east 

are identical.

Although not dated, a fine- to medium-grained, locally porphyritic granite that intrudes the coarse-grained granite appears 

to be closely related to the granites just described. The granite 

contains biotite and, in some places, muscovite. Locally the finegrained granite is crowded with flow-aligned inclusions of 

biotitic rock (fig. 10), and rarely it contains inclusions of coarsegrained granite. In most places the fine-grained granite intrudes 

the coarse-grained granite, but in a few places textural gradations 

between those two rocks are found. The fine-grained granite 

forms plutons as much as 3 km long.

The coarse-grained granite contains anhedral quartz grains 

as much as 3 mm in diameter and mosaic-textured aggregates 

interstitial to the feldspars or in roundish masses. Generally perthitic microcline in anhedral to subhedral grains a centimeter or 

two long commonly includes quartz, plagioclase, biotite, and 

smaller grains of microcline. Plagioclase (An15_30) is variously 

saussuritized and forms anhedral to subhedral grains as much as 

7 mm long. Anhedral to subhedral biotite as much as 3 mm in 

diameter locally forms aggregates and is aligned. Accessory minerals are hornblende, muscovite intergrown with biotite, sphene 

locally as much as 1.5 mm in diameter, apatite, zircon, and allanite. Secondary minerals are muscovite, sericite, and epidote from 

plagioclase. Color index ranges from 2 to 28 and has a mean of 9.

The porphyritic granite contains quartz as anhedral grains as 

much as 3 mm in diameter and mosaic-textured aggregates 

between feldspar grains; anhedral to euhedral microcline and perthitic microcline as phenocrysts several centimeters long and 

matrix grains; subhedral to anhedral plagioclase (An15.30) as 

much as 5 mm long; and anhedral to subhedral biotite as much as 

1.3 mm in diameter usually as aggregates and locally weakly 

aligned parallel to the large microcline phenocrysts. The rock 

contains some myrmekite and accessory apatite, allanite, zircon, 

and opaque minerals. Chlorite from biotite and epidote from plagioclase are the secondary minerals. The matrix of the porphyritic granite generally has a grain size of \-^ mm. Color index 

ranges from 6 to 19.

Figure 9. Photomicrograph of mafic granodiorite. Granophyric intergrowth in groundmass surrounds small euhedral phenocrysts of plagioclase, subhedral grains of augite and hornblende. Plagioclase in center 

is about 1 mm long. Appendix sample No. 47; U-Pb zircon age determination, figure 16; major-oxide and trace-element concentrations, table 6. 

Whole-rock and feldspar Pb-isotopic analysis, table 8. Signal Mountain 

7>2' quadrangle.

The medium- to fine-grained granite is locally porphyritic 

and contains anhedral quartz in grains as much as 2.5 mm in 

diameter and in mosaic-textured aggregates interstitial to plagioclase. Microcline and perthitic microcline are euhedral phenocrysts as much as 1 cm long in some rocks, but in others potassic 

feldspar is 0.3-1 mm in grain size. The larger microcline grains 

contain inclusions of quartz, plagioclase, and biotite. Euhedral to 

anhedral plagioclase (An28_39) is in phenocrysts as much as 4.5 

mm long but is mostly 1-2 mm in length. Anhedral biotite as 

much as 1.3 mm in diameter is locally in aggregates and locally 

aligned, probably due to flow in the crystallizing magma. Accessory minerals are muscovite, apatite, sphene, zircon, allanite, and 

opaque minerals. Secondary minerals are muscovite, sericite, 

carbonate minerals, and epidote from plagioclase and chlorite 

from biotite. Overall grain size of equigranular rocks and matrix 

of porphyritic rocks ranges from 0.1-0.5 mm to 1-1.5 mm. Color 

index ranges from 2 to 18 and has a mean of 10.

Granite of Joshua Tree Parkway

The eastern part of the Poachie region is underlain by two 

distinct but probably closely related rocks. These rocks crop out 

near the rest stop on U.S. Highway 93 about 6 km south of the 

area of figure 2, along a part of the highway designated the Joshua

12 Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province
*

'*

Figure 10. Fine-grained granite of Olea Ranch containing mafic clots 

and inclusions. Hammer head is 19 cm long. Arrastra Mtn NE 7 X>' quadrangle.

Tree Parkway of Arizona, and they form hills to the north. There 

the rocks locally have some inclusions of fine-grained granite that 

appear to be older than the granite here discussed. Megacrystic 

granite and fine-grained granite are the two rock types included in 

this unit (map unit Yj, fig. 2).

The megacrystic granite is characterized by stout prisms of 

potassic feldspar as much as 6 cm long and 4 cm thick. The 

potassic feldspar grains are smaller in many places, and the texture of the granite is coarse-grained porphyritic having potassic 

feldspar phenocrysts 2-3 cm in length. This unit is cut by dikes 

of fine- to medium-grained granite and a few pegmatites. Contacts between megacrystic granite and fine-grained granite are 

difficult to locate precisely, because inclusions of megacrystic 

granite are numerous in the margins of the fine-grained granite 

plutons and dikes of fine-grained granite are numerous in the 

megacrystic granite.

The megacrystic granite consists of quartz in anhedral 

grains as much as 4 mm in diameter and mosaic-textured aggregates with a grain size of 1-3 mm; somewhat perthitic microcline 

containing inclusions of biotite, plagioclase, sphene, smaller 

microcline, and apatite; anhedral to subhedral plagioclase (An20_ 

30) as much as 6 mm long; anhedral to subhedral biotite as much 

as 3.5 mm in diameter, locally in aggregates as much as ] cm long 

and weakly aligned; opaque minerals to 1.6 mm in diameter; and 

myrmekite. Accessory minerals are hornblende, sphene, apatite, 

zircon, and allanite. Muscovite, sericite, and epidote from plagioclase, and chlorite from biotite are secondary minerals. Color 

index is 8-12.

The fine-grained granite is locally foliated. It contains 

biotite and a few pegmatites, and in some places hornblende. In 

one area the rock is more mafic and consists of hornblende-biotite 

quartz monzodiorite, which contains numerous round to ellipsoidal inclusions of diorite, metagabbro, amphibolite, and porphyritic granodiorite as much as 1 m in diameter.

The fine-grained granite consists of anhedral quartz as much 

as 1.5 mm in diameter that is interstitial to plagioclase; anhedral, 

weakly perthitic microcline, locally interstitial to plagioclase; 

anhedra] to subhedral variously saussuritized plagioclase (An32) 

as much as 2 mm long; anhedral biotite as much as 3 mm in diameter; and myrmekite. Accessory minerals are hornblende in the 

more mafic varieties, sphene, allanite, apatite, zircon, and opaque 

minerals. Secondary minerals are chlorite from biotite and epidote and carbonate minerals from plagioclase. Color index ranges 

from 2 to 17.

Granite of Grayback Mountain

In the northeastern part of the area granite forms Grayback 

Mountain (map unit Yb, fig. 2) and extends several kilometers 

beyond the area mapped. This granite has three textural phases. 

Coarse-grained granite is the oldest phase. It contains stubby 

potassic feldspars 1-3 cm in length, quartz 0.5 cm in diameter, 

and biotite as much as 0.5 cm in diameter in clots. A few 0.2-0.3 

m-thick dikes of quartz-feldspar and biotite-quartz-feldspar pegmatite cut the coarse-grained granite. A medium- to fine-grained, 

somewhat porphyritic biotite granite containing scattered 1-2 

cm-diameter potassic feldspars cuts the coarse-grained granite 

and is locally cut by coarse-grained granite. The porphyritic granite is locally cut by quartz-feldspar pegmatites as much as 0.8 m 

thick. The porphyritic granite occupies a somewhat larger outcrop area than the coarse-grained granite. A third phase is found 

as small bodies near the margin and makes up a very small part of 

the pluton. This phase is a porphyry containing phenocrysts of 

quartz and potassic feldspar in a fine-grained matrix. The porphyry superficially resembles dikes of Cretaceous porphyry in 

the region. However, the porphyry locally grades into the 

medium- to fine-grained porphyritic granite.

The coarse-grained granite contains anhedral quartz as 

much as 3 mm in diameter and mosaic-textured aggregates that 

tend to fill in around the feldspar grains. Plagioclase is subhedral and as much as 4 mm long, has a composition of An20_25, 

and is partly saussuritized. Anhedral to subhedral perthitic 

microcline is as much as 6 mm long. Anhedral to subhedral 

biotite as much as 2 mm in diameter locally forms aggregates. 

The rock contains myrmekite and accessory sphene, opaque 

minerals, allanite, apatite, and zircon. Chlorite and sericite are 

secondary. Color index is 10.

In the medium-grained porphyritic granite anhedral phenocrysts of quartz as much as 3 mm in diameter, subhedral to anhedral phenocrysts of perthitic microcline as much as 5 mm long, 

and subhedral to anhedral phenocrysts of plagioclase (An2o) are 

in a matrix of those minerals having a grain size of 0.2-0.8 mm. 

Biotite has the same size and form as in the coarse-grained granite. Myrmekite and muscovite intergrown with biotite are 

present; accessory minerals are opaque minerals, allanite, apatite, 

zircon, and sphene, and secondary minerals are muscovite and 

epidote. Color index is 6-8.

The fine-grained porphyritic phase contains euhedral phenocrysts of quartz as much as 5 mm in diameter, plagioclase 

(An15) as much as 3 mm in diameter, and perthitic microcline as 

much as 6 mm in diameter in a matrix of quartz and feldspar 

with a grain size of 0.01-0.05 mm. Biotite, partly altered to

Geology 13
Figure 11. Outcrops of diabase. A 

Thin sheets of diabase in Signal Granite. 

Sheets have a component of dip in direction of view and dip southwest about 

40°. Thin sheets are locally numerous in 

the Signal Granite west of the Big Sandy 

River and are commonly associated 

with thicker sheets. Hammer is 33 cm 

long. Southwest part of Signal Mountain 7 K' quadrangle. B, Chilled margin 

and layering in diabase sheet in coarsegrained granite in Arrastra Mtn 7 Yz 

quadrangle. Pencil is 13 cm long. Photograph by Karl Wirth.

A A

muscovite, forms xenocrystic-appearing aggregates rimmed by 

opaque minerals. Sphene, opaque minerals, zircon, and apatite 

are accessory minerals, and epidote is a secondary mineral in 

the fine-grained porphyry. Color index is 2.

Diabase

Diabase sheets a few centimeters to a few tens of meters 

thick and 2 km in outcrop length and dikes 10 cm to 100 m thick 

and as much as 1.5 km long (not shown in fig. 2) intrude all the 

other Proterozoic rocks in the Poachie region (fig. 11A). Most of 

the sheets are gently dipping, but a few are nearly vertical (Bryant 

and Wooden, 1991b). These dikes are probably 1,150-900 Ma 

based on petrographic similarity to diabase in eastern and northwestern Arizona dated by various methods (Damon and others, 

1962; Banks and others, 1972; Creasy, 1980; Elston and McKee, 

1982; Silver, 1960,1978). U-Pb dates of sphene from dikes in the 

Hualapai Mountains, Peacock Mountains, and the Cottonwood 

Cliffs area north and northwest of the Poachie region are about 

1,080 Ma and are interpreted to be the crystallization age of the 

dikes (Shastri and others, 1991).

The diabase ranges from fine to coarse grained, and some 

bodies contain veinlets rich in plagioclase several millimeters 

thick. Textural variations are found within individual bodies. 

Locally chilled margins are present, and some sheets have a layered appearance (fig. 1 IB). In some rocks inclusion-like bodies 

of coarse-grained diabase have distinct but gradational contacts 

with surrounding medium-grained diabase. One sheet has veinlets of biotite-quartz diorite cutting it. Some of the dikes were 

emplaced along earlier shear or fracture zones, and those zones 

were reactivated. Many of the sheets are sheared along their contacts, especially in the western part of the area. Locally these 

shear zones contain quartz veins which were prospected for gold.

The bodies range from olivine-pyroxene diabase to pyroxene and hornblende diabase and have a mean color index of 

about 40 (CI=20-62). Some of the diabase bodies are partly to 

completely altered. One of the largest unaltered dikes contains 

euhedral laths of plagioclase (An70) as much as 3 mm long

surrounded by anhedral monoclinic pyroxene as much as 5 mm 

in diameter. Anhedral to subhedral olivine as much as 2 mm in 

diameter is also included in the pyroxene. Opaque minerals as 

much as 2 mm in diameter, accessory biotite, and secondary actinolite derived from the mafic minerals are present. Some rocks 

contain hornblende that has replaced primary pyroxene; in others the principal mafic mineral is acicular brown hornblende as

14 Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province
Table 1. U-Pb zircon ages of Proterozoic igneous rocks in the Poachie region.

Appendix 

sample No.

8 

9

15

16

22

35

38

43 

44

47

50

51

54

57

Unit

JDick metarhyolite 

!Dick metarhyolite

Gabbro

Coarse-grained granite

Granite on Burro Creek

Granite of Thorn Peak

Gneissic tonalite

Signal Granite 

Signal Granite

Mafic granodiorite

Granite of Olea Ranch

Granite of Joshua Parkway

Granite of Grayback Mountain

Field sample 

No.

1161 

P-93-1

JW-84-11

JW-84-12

JW-84-9

1158

JW-85-63

1168 

1164

390

JW-85-13 

JW-85-15

A-151a

A- 153

Age, Ma

1,718±6 

1,721±6

1,711±22

1,706±4

1,696±13

1,686±8

1,677±17

1,410±4

1,418±2

1,414±4

Comment

Data combined for age of 

-1,720 Ma

Younger zircon by ion 

microprobe

Based on discordia 

line from combined 

data of samples

Based on composite 

discordia line

Ages of two plutons 

not statistically 

different; data 

combined

'An informal unit possibly correlative with the Dick Rhyolite.

much as 2 mm long. Some diabase contains small amounts of 

late-stage primary biotite. Opaque mineral and apatite are common accessory minerals.

Many of the diabase bodies are partly to completely altered. 

Plagioclase is saussuritized, and mafic minerals are altered to 

chlorite or actinolite. Secondary epidote, carbonate minerals, 

and, locally, sphene are found in altered diabase.

Other Proterozoic Granitic Rocks

Granites in the Poachie region that could not be correlated 

with dated granites are included in this unit (unit YXg, fig. 2). In 

the central part of the Poachie region, many of the rocks mapped 

in this unit (small bodies in Bryant, 1992; one body in fig. 2) are 

fine- to medium-grained biotite and muscovite-biotite granite. In 

the northeast part of the Poachie region, the granite in this unit is 

medium to coarse grained and equigranular to porphyritic. 

Locally it has a granodioritic composition. In some places the 

rock is weakly gneissose, and in a few other places aligned potassium feldspar crystals form a flow structure. The granite contains 

a few inclusions of gneiss and is cut by sparse pegmatite veins.

In thin section quartz ranges from anhedral to subhedral 

grains as much as 3 cm in diameter to granoblastic textured 

aggregates between the feldspar grains. Plagioclase (An26_32) 

forms subhedral grains as much as 3 mm long. Potassic feldspar 

is perthitic microcline in grains as much as 1 cm long. Anhedral 

to subhedral biotite as much as 2 mm in diameter forms single 

grains or aggregates. Accessory muscovite is partly contemporaneous with the biotite and partly late. Accessory apatite, zircon, 

allanite, and opaque minerals and secondary epidote, chlorite, 

and sphene are present. Color index is 8-10.

Geochronology

The results of U-Pb zircon dating of Proterozoic rocks in the 

Poachie region indicate that Early Proterozoic igneous rocks were 

emplaced between approximately 1.72 Ga and 1.68 Ga (table 1). 

Metamorphic rocks interpreted to be metarhyolite were erupted at 

about 1.72 Ga, and plutonic rocks were emplaced from about 1.71 

Ga to 1.68 Ga. Regional deformation and metamorphism were 

synchronous with the early part of plutonic activity but were completed by 1.69 Ga. A second major plutonic event took place in 

Middle Proterozoic time from about 1.42 to 1.41 Ga.

Metamorphic Rocks

The Bagdad metamorphic belt contains metamorphosed 

volcanic rocks from which zircons were separated. Two samples 

of biotite-quartz-feldspar gneiss or metarhyolite were examined. 

This unit was mapped as Dick Rhyolite (Bryant, 1992) because of 

its apparent continuity with that unit in and south of Bagdad 

(Anderson and others, 1955; Conway and others, 1986). Sample 

1161 (appendix sample No. 8) is nonbedded but foliated metarhyolite, here referred to informally as the Dick metarhyolite. A 

U-Pb zircon age of 1,710±10 Ma was originally reported for this 

sample (Bryant and Wooden, 1991b). An age of 1,718±6 Ma is a 

better interpretation, however, based on further consideration of 

these data. The 1,718 Ma age is based on the regression of data 

for four of the six zircon fractions analyzed for this sample (table 

2). One abraded fraction (NM63-102AB) appears to contain a 

small percentage of older, inherited zircon and was omitted from 

the preferred regression. A repeat analysis of additional material 

from this abraded fraction (NM63-102ABRP) indicated either

Geochronology 15
much less or no significant inheritance, so that its replotted 

position lies along the preferred regression. The second fraction 

omitted from the regression was composed of the larger magnetic 

zircons (M63-102). Omission of the second fraction was based 

primarily on its poor fit with the other four used in the regression.

Sample P-93-1 (appendix sample No. 9) represents a somewhat layered biotite-muscovite schist near the presumed top of 

the Dick metarhyolite (stratigraphic relations extrapolated from 

the work of Anderson and others, 1955, at Bagdad). The rock is 

richer in quartz and mica than typical samples of the metarhyolite, but it contains similar 1-2 mm equidimensional quartz grains 

and aggregates. Zircons from this sample are small well-formed 

crystals with 2:1 to 4:1 length:width ratios; there is no evidence 

of rounded or abraded grains or crystal terminations as would be 

characteristic of a detrital sedimentary rock. Four of the five zircon fractions analyzed from this sample define a discordia line 

with an upper intercept of 1,721+6 Ma. The remaining fraction 

(table 2, NM+100) plots well above this line and has an unusually 

low 206Pb/204Pb ratio indicating a high common lead component 

compared to other analyzed fractions. The ages of the two samples are the same within their 95 percent confidence level errors 

and the age of this unit is interpreted to be about 1,720 Ma.

The 1,720 Ma age of this metamorphosed volcanic rock 

raises the question whether the unit is actually correlative with 

the Dick Rhyolite as mapped at Bagdad. An alaskite porphyry, 

interpreted to intrude the base of the metavolcanic rocks west of 

Bagdad (Anderson and others, 1955), has a U-Pb zircon date of 

1,730±12 Ma (J.L. Wooden and C.M. Conway, unpub. data, 

1994). No zircons were found in a sample of Dick Rhyolite taken 

from its type locality about 2 km east of the aplite sample. An age 

of 1,730 Ma should be a minimum time for the emplacement of 

the lower part of the Bagdad metamorphic belt. Support for older 

ages in the Bagdad metamorphic belt is provided by Silver 

(1968), who gave undocumented dates of 1,715 to 1,735 Ma (corrected for modern decay constants; see Conway and others, 1986) 

for metamorphic rocks near Bagdad. A further complication is 

that Anderson and others (1955) interpreted the Dick Rhyolite to 

be intrusive, whereas Conway and others (1986) interpreted it to 

be extrusive. We interpret sample P-93-1 to be originally an 

extrusive or volcaniclastic rock. The 1,721 Ma date of P-93-1 is 

not statistically different from the 1,718 Ma date of sample 1161, 

a more massive rock. Both dates are significantly younger than 

the minimum age of 1,730 Ma established for the lower part of 

the Bagdad metamorphic belt west of Bagdad. We suggest that 

the age differences are real and reflect a composite section composed of metavolcanic rocks from two separate volcanic events. 

The metamorphic belt has been engulfed by younger intrusive 

complexes and deformed and recrystallized, making original 

stratigraphic relations impossible to determine. This interpretation is consistent with other modern U-Pb dating that has established that metamorphic packages in this region range in age from 

1,750 to 1,710 Ma (Chamberlain and Bowring, 1990; Karlstrom 

and Bowring, 1993; Hawkins and others, 1996) and probably represent two or more discrete events.

0.31

0.30

0.29

0.28

0.27

0.26

1 'I '

1718+/-6& 

358 +/-146 Ma 

(MSWD = 0.41)

1721 +/- 6 & 

247+/-114Ma 

(MSWD=4.3)

P-93-1

3.3 3.7 4.5

Figure 12. U-Pb concordia diagram for two samples from the 

Bagdad metamorphic belt. Samples 1161 (squares) and P-93-1 

(triangles) are massive gneissic and schistose samples, respectively, from a metarhyolite unit possibly correlated with the Dick 

Rhyolite (appendix sample Nos. 8 and 9, respectively). Zircon 

fractions represented by diamonds (1161) and by inverted triangles (P-93-1) were not used in regressions. See text for complete discussion.

Plutonic Rocks

Plutonic rocks described following are Early Proterozoic 

and Middle Proterozoic in age.

Early Proterozoic Plutonic Rocks

Early Proterozoic rocks are coarse-grained granitic rocks and 

associated gabbro, granite of Thorn Peak, and gneissic tonalite.

Coarse-Grained Granitic Rocks

Three samples were taken from this unit for U-Pb zircon 

dating. They include gabbro, diorite, and the granite at Burro 

Creek. Sample 750 (appendix sample No. 15) is a gabbro from an 

area (shown on the map of the Poachie Range; Bryant, 1992) in 

the northwest part of the coarse-grained granite, where gabbro 

and diorite are more widespread than elsewhere in the unit. Gabbro bodies are the oldest components and make up only a minor 

part of the plutonic complex, which forms the east and central 

parts of the Poachie Range. These bodies are commonly metamorphosed to amphibolite at their margins and cut by younger 

members of the plutonic suite. Zircons separated from this sample were well-formed crystals of surprisingly large minimum 

diameters (>100 micrometers). Two zircon fractions from sample 750 indicate an age of 1,711±22 Ma (table 2 and fig. 13). The 

high uncertainty of this age reflects the limited spread of the two 

points and their distance from concordia.

16 Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province
Tab le 2. Analytical data and ages of zircons from the Proterozoic rocks of the Poachie region.

[App. no., appendix number; Field sam. no., field sample number (parentheses indicate J.L.W.'s number for sample from the site]

CD

O 

O3- 

o

3 

O_

O 

CO

App. 

no.

Field Sam.wt. U Pb 

sam.no. Fraction 1 (mg) (ppm) (ppm)

Measured ratios

206p b/ 

204p b

208p b/ 

206p b

Corrected ratios

206p b/

±%

207 Pb/ 

235u ±%

207 Pb/ 

208 Pb 

Early Proterozoic rocks

8

9

15

16

22

35

1161 Dick metarhyolite2 (biotite-quartz-feldspar gneiss)

NM+102 4.0 178 56

NM63-102 5.6 199 61

NM63-102AB 4.2 199 65

NM63-102ABRP 2.6 201 65

M63-102 4.5 264 83

M63 4.2 256 76

P-93-1 Dick metarhyolite2 (biotite-muscovite schist)

NM+100 1.9 164 53

NM80-100 3.3 154 49

NM80 5.6 173 54

M+100 2.4 223 63

M80 4.6 191 60

750 (JW-84-11) Gabbro — coarse-grained granite suite

NM163 5.7 966 336

NM63 3.0 1417 485

1420

6800

7000

6290

5250

8190

680

4367

9524

4184

7175

16680

14416

0.1435

0.1239

0.1492

0.1543

0.1282

0.1216

0.1753

0.1365

0.1309

0.1415

0.1350

0.2499

0.2424

0.29064

0.29100

0.30105

0.29901

0.29620

0.28265

0.28342

0.29622

0.29282

0.26364

0.29200

0.29810

0.29476

0.5

0.5

0.4

0.4

0.4

0.5

0.1

0.2

0.1

0.2

0.1

0.5

0.5

4.1948

4.1942

4.3965

4.3259

4.2651

4.0618

4.0266

4.2970

4.2383

3.7847

4.2246

4.3026

4.2519

0.5

0.5

0.4

0.4

0.4

0.5

0.5

0.2

0.2

0.3

0.1

0.5

0.5

0.10467

0.10453

0.10582

0.10493

0.10443

0.10422

0.10304

0.10521

0.10498

0.10412

0.10493

0.10468

0.10462

751 (JW-84-12) Quartz diorite — coarse-grained granite suite

NM+163 4.4 393 127

NM102-163RP 6.0 363 116

NM102-163AB 4.2 358 119

NM63 7.1 378 122

M+163RP 8.8 373 117

M63-102 4.3 386 121

M63RP 4.8 451 143

749 (JW-84-9) Granite of Burro Creek

NM+163 5.8 449 140

NM+163AB 3.8 441 142

NM 102- 163 9.6 499 157

NM63-102 7.3 512 163

1158 Granite of Thorn Peak

NM63-102 4.3 442 108

M102-163 2.5 433 104

M+102 2.1 434 112

M63 2.4 582 131

4100

8100

4320

11000

4420

5070

5360

15000

11550

15500

15000

2550

1310

2620

1675

0.1703

0.1622

0.1704

0.1703

0.1620

0.1693

0.1737

0.1599

0.1713

0.1713

0.1756

0.0852

0.1153

0.0947

0.0856

0.29315

0.29352

0.30286

0.29334

0.28663

0.28464

0.28786

0.28742

0.29264

0.28565

0.28859

0.23661

0.22420

0.24651

0.21605

0.5

0.5

0.4

0.5

1.4

1.1

0.4

0.5

0.4

0.5

0.5

0.4

0.2

0.2

0.2

4.2052

4.2090

4.3648

4.2231

4.1018

4.0954

4.1395

4.0803

4.1718

4.0544

4.1081

3.3791

3.1929

3.5118

3.0888

0.5

0.5

0.5

0.5

1.8

1.1

0.5

0.5

0.4

0.5

0.5

0.5

0.2

0.2

0.3

0.10404

0.10400

0.10452

0.10442

0.10379

0.10435

0.10430

0.10296

0.10339

0.10294

0.10324

0.10358

0.10328

0.10351

0.10369
Table 2—Continued. Analytical data and ages of zircons from the Proterozoic rocks of the Poachie region.

TJ

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App. Field Sam. wt. U 

no. sam. no. Fraction 1 (mg) (ppm)

Pb 

(ppm)

Measured ratios

206p b/ 208p b/ 

204pb 206p b

Corrected ratios

206p b/

±%

207p b/

235 U ±%

207p b/ 

208p b 

Early Proterozoic rocks — Continued

38 1 163 (JW-85-63) Gneissic tonalite 

NM+163 0.5 1003

NM102-163 3.4 758

M102-163 2.0 500

NM-102 3.6 548

NM63 2.2 537

M-63 2.4 546 

38 1 163 (JW-85-63) Ion probe data 

1 (Grain #) 455

2 199

3 1018

4.1 178

4.2 286

5.1 172 

5.2 567

6 331

7 398 

7.2 440

8 163

9 228

10 199

279

181

159

175

167

168 

151

60

330

86

90

84 

167

105

198

144

49

71

61

4160 0.1215

8770 0.1263

11680 0.1178

10500 0.1344

15860 0.1323

24000 0.1318 

0.1135

0.1078

0.1060

0.1182

0.0885

0.1169 

0.1017

0.1295

0.0809 

0.1419

0.0953

0.0731

0.0825

0.26114

0.22344

0.29980

0.29811

0.29133

0.28983 

0.31510

0.28690

0.31090

0.43600

0.30560

0.44570 

0.28470

0.29890

0.46270 

0.30500

0.29170

0.30820

0.29960

0.4

0.4

0.2

0.4

0.2

0.2 

2.9

3.0

2.9

3.0

1.9

3.0 

2.9

2.9

2.9 

1.8

3.0

1.9

1.9

4.0918

3.4120

4.5536

4.4013

4.2652

4.2252 

4.6807

4.0527

4.4724

9.8136

4.3668

9.8619 

3.9654

4.2545

10.9635

4.4378

4.1356

4.3998

4.4506

0.4

0.4

0.2

0.4

0.2

0.2 

3.1

3.3

3.0

3.2

2.2

3.1

3.1

3.1

3.0 

2.1

3.4

2.4

2.4

0.11364

0.11075

0.11016

0.10708

0.10618

0.10573 

0.1077

0.1024

0.1043

0.1632

0.1037

0.1605 

0.1010

0.1032

0.1719 

0.1055

0.1028

0.1036

0.1077

Middle Proterozoic rocks

43 1168 Signal Granite 

NM+163 3.6 902

M63-102 2.8 914

44 1164 (JW-85-64) Signal Granite

NM+163 3.2 1136

NM102-163 2.1 939

47 390 (JW-84-10) Mafic granodiorite

NM102-163LT 5.6 264

NM102-163DK 3.6 663

NM-63 4.4 293

50 752 (JW-84-13) Porphyritic granite of Olea Ranch

NM63-102 8.0 1229

NM-63 7.7 1336

214

216

250

213

75

180

71

286

309

7375 0.1141

4975 0.1362

4485 0.1203

3750 0.1398

1840 0.2777

5900 0.2355

7550 0.1830

13500 0.1136

14000 0.1232

0.22864

0.22314

0.21051

0.21356

0.23678

0.23751

0.22066

0.22457

0.22140

0.4

0.4

0.4

0.4

0.5

0.5

0.4

0.5

0.5

2.8097

2.7455

2.5867

2.2644

2.9130

2.9220

2.7170

2.7764

2.7392

0.8

1.1

0.5

0.4

0.5

0.5

0.4

0.5

0.5

0.08913

0.08924

0.08912

0.08913

0.08923

0.08923

0.08930

0.08967

0.08971

51 753 (JW-84-15) Coarse-grained granite of Olea Ranch

NM+163 6.6 572

NM102-163 8.5 633

142

155

4735 0.1056

4575 0.1257

0.24109

0.23309

0.5

0.5

2.9781

2.8808

0.5

0.5

0.08959

0.08964
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The second sample (751; appendix sample No. 16) examined from this plutonic complex is a gneissic biotite diorite from 

the northwestern part of the area of generally foliated plutonic 

rocks that form the eastern and central parts of the Poachie 

Range. Seven fractions of zircon were analyzed for this sample 

(table 2 and fig. 13). Six of these fractions fall along two separate 

discordia lines, both of which are anchored by a concordant fraction (NM102-163AB). The 1,706 Ma date of the concordant 

fraction, which was abraded, is the best estimate of the time of 

crystallization of this sample. The two discordia lines are interpreted tentatively to represent periods of Pb-loss that variably 

affected zircon grains. The discordia line with the older period of 

Pb-loss is defined by two of the three magnetic fractions and the 

smallest of the nonmagnetic fractions, a pattern roughly consistent with this interpretation. Uranium concentrations, however, 

show no particular correlation with the two discordia lines. 

Because the quartz diorite is older than the coarse-grained granite (most of unit Xcg), we interpret the peak of the regional metamorphism to be somewhat younger than 1,706 Ma, as the diorite 

has a well-developed superposed solid-state fabric.

Sample 749 (appendix sample No. 22) represents the granite at Burro Creek. This coarse-grained granite with equant feldspar megacrysts was originally thought to be part of the Signal 

Granite. Four zircon size fractions were analyzed and define a 

good discordia line (MSWD=0.6) with an upper intercept of 

1,696±13 Ma, which is taken to be the crystallization age (table 

2 and fig. 14). The relatively large error associated with this age 

in spite of the good fit is a result of the limited spread of the four 

points. The 207Pb/206Pb age of 1,686 Ma from the abraded fraction NM+163AB serves as a minimum estimate of the age of 

crystallization. This plutonic rock is interpreted to have been 

emplaced during the later stages of or after the main regional 

metamorphism because it lacks foliation.

Granite of Thorn Peak

Sample 1158 (appendix sample No. 35) represents muscovite-biotite and biotite granite that forms an elongate pluton west 

of the Santa Maria River. Four zircon fractions (table 2 and fig.

1f\£\ 14) analyzed from this pluton are strongly discordant. Pb/ 

238U ages range from 1,420 to 1,261 Ma despite moderate U concentrations of 430-580 ppm. A regression of the four fractions 

gives concordia intercepts of 1,681±32 and -30 ±206 Ma. This 

regression is rejected because the lower intercept age is negative, 

and the upper intercept date is less than any of the 207Pb/206Pb 

dates. A regression forced through 0 Ma and giving an upper 

intercept of 1,686±8 Ma (fig. 14) is preferred as the best estimate 

of a minimum crystallization age. This regression provides an 

average of the 207Pb/206Pb dates of the four fractions that range 

from 1,684 to 1,691 Ma. Three of the 207Pb/206Pb dates cluster 

between 1,688 and 1,691 Ma, and their average of 1,689±2 Ma 

probably provides a better minimum date. The presence of only 

local zones of foliated rock in this pluton indicates that it was 

emplaced after the main phase of regional deformation but before 

all deformation had ceased. Within statistical uncertainties this 

age is consistent with the 1,696 Ma age of the granite at Burro 

Creek, marking the declining stage of this deformation.

Geochronology 19
0.304

0.300 -

0.296

0.292 h

0.288

0.284

0.280

1706+/-4&127+/-175Ma 

(MSWD=0.08)

1702+/-43&284+/-964Ma 

(MSWD = 0.08)

1700

1680

1640

750 

1711 +/-22 

169+/-886Ma

1620

3.8 4.0 4.2 

207pb/235u

4.4

Figure 13. U-Pb concordia diagram for samples from the coarsegrained granite suite. Samples 750 (open squares) and 751 (open 

triangles) represent a gabbro and a quartz diorite, respectively 

(appendix sample Nos. 15 and 16). Age of the quartz diorite is best 

estimated by the one concordant zircon fraction at 1,706 Ma. The 

remaining six fractions appearto define two discordia lines (upright 

vs. inverted open triangles) having upper-intercept ages in agreement with the concordant fraction. The two discordia lines imply 

two distinct times of Pb-loss.

Gneissic Tonalite

Sample 1163 (appendix sample No. 38) represents a variably foliated pluton ranging in composition from melagranite to 

quartz diorite that intruded the mica schist and gneiss in the upper 

part of the Bagdad metamorphic belt, which are interpreted to be 

stratigraphically higher than the metarhyolite (as represented by 

samples 1161 and P-93-1 described previously). The gneissic 

structure in the unit is best developed near the Mountain Springs 

fault and was probably formed during movement along that zone 

during and after emplacement, perhaps as late as =1.4 Ga. The 

rock at the sample locality for sample 1163 has numerous small 

(<2 cm) xenoliths and a few as large as 10 cm in diameter. The six 

fractions analyzed by conventional U-Pb zircon technique (table 

2) do not define a discordia line (fig. 15A). 207Pb/206Pb ages for 

these fractions range from 1,858 to 1,727 Ma and are perfectly 

correlated with the size range of the fractions; the oldest dates are 

from the largest and the youngest from the smallest fractions. 

This is a classic age pattern that results from the overgrowth of 

younger zircon over older cores. The only age information available from these data is that the pluton has a maximum age of 

1,727 Ma and at least some of the inherited zircons are older than 

1,858 Ma.

A limited number of grains from this sample were analyzed 

by the ion microprobe technique (table 2, ion probe data) using 

the SHRIMP I at the Research School of Earth Sciences, Australian National University. Three of ten grains analyzed (analyses 

4.1, 5.1, 7) had cores with 207Pb/206Pb ages of 2,461, 2,489, and 

2,576 Ma clearly identifying a latest Archean to earliest Proterozoic inherited component. The remaining grains analyzed had 

207pb/206pb ages ranging from i j62 to 1^43 Ma. Some of this

age range is probably the result of analyzing areas of zircons that

0.30

0.28

0.26

0.24

0.22

0.20

1696+/-13&555+/-308Ma 

(MSWD = 0.6)

2.4 2.8 3.2 3.6 4.0 4.4

207pb/235u

Figure 14. U-Pb concordia diagram for samples 749, the granite at 

Burro Creek (squares), and 1158, the granite of Thorn Peak (triangles) (appendix sample Nos. 22 and 35). Sample 749 is tentatively 

considered a member of the coarse-grained granite suite.

were part inherited and part younger zircon. Analyses 1, 7.2, and 

10 giving 207Pb/206Pb dates of 1,762, 1,723, and 1,761 Ma, 

respectively, are interpreted to represent this circumstance. 

Alternatively, these three ages, especially the two at 1.76 Ga, 

might represent an additional, younger inherited component. At 

the time this work was done, we had no way to image the grains 

to be analyzed ahead of time to identify cores or zoning patterns 

and guide the positioning of the ion beam. Seven of the ten analyses giving younger dates define a discordia line with intercepts 

of 1,677±17 and 740±392 Ma (fig. 155). These seven analyses 

include both normal and reversely discordant analyses; slightly 

reversely discordant analyses are not unusual with the ion microprobe technique because of the difficulty of determining highly 

accurate U concentrations. Note that errors associated with the 

U-Pb and Pb-Pb dates determined on the ion microprobe are 

much higher than those associated with conventionally determined U-Pb data. One grain (6) gave a concordant date of 1,685

Ma, and five of the seven analyses chosen for regression have 

207pb/206pb dates from { 669 to { 569Q Ma and ayerage i ?68 1 Ma

Although it is obviously difficult to determine a precise crystallization age for sample 1163, an estimated age of 1,680±10 Ma 

seems probable from the ion microprobe analyses.

Middle Proterozoic Plutonic Rocks

Middle Proterozoic rocks discussed herein are Signal Granite, mafic granodiorite, granite of Olea Ranch, granite of Joshua 

Tree Parkway, and granite of Grayback Mountain.

Signal Granite and Mafic Granodiorite

Samples 1168 and 1164 (appendix sample Nos. 43 and 44) 

represent the Signal Granite, which forms a batholith-sized body 

of coarse-grained granite containing very large potassic feldspar

20 Poachie Region, West-Central Arizona—East Boundary. Mojave Crustal Province
0.48 -

0.32

0.30

0.28

0.26

0.24

0.22

1163

1677+/-17&740+/-392Ma 

(MSWD = 0.36)

2.4

B

3.2 4.0 

207pb/235u

4.8

Figure 15. U-Pb concordia diagrams for sample 1163, a gneissic tonalite (appendix sample No. 38). Both conventionally determined (triangles) and ion microprobe (squares and octagons) data are shown 

for this sample. The conventionally determined U-Pb data do not define a discordia line but indicate inheritance of zircons older than 

1,860 Ma by a magma younger than 1,730 Ma. All data are shown in 

figure 15A The ion microprobe data indicate an inherited component 

of earliest Proterozoic to latest Archean age (fig. 15X1). Seven of the 

ion microprobe data points (octagons, fig. 155) can be interpreted to 

define a discordia line with an upper intercept of 1,677 Ma, which may 

provide an estimate of the crystallization age of the gneissic tonalite. 

See text for a more detailed discussion.

megacrysts. Sample 1164 was taken from near the old town site 

of Signal, the type locality for the unit. Sample 390 (appendix 

sample No. 47) is from a pluton 7 km long and 4 km wide of 

mafic granodiorite that is the same age to slightly older than the 

Signal Granite, based on field relations. Three zircon fractions 

from 390 define a discordia line with intercepts of 1,408±4 and 

-36±101. The negative lower intercept is unreasonable, so a discordia line forced through 0 Ma with an intercept of 1,410±3 Ma,

the same as the average 207Pb/206Pb date of the three fractions, is 

preferred (table 2 and fig. 16). Only two fractions each were analyzed for samples 1168 and 1164 of the Signal Granite (table 2). 

U-Pb data are moderately discordant but give a tight grouping of 

207pb/206pb dates (1,407-1,409 Ma). A discordia line defined by 

all four fractions has intercepts of 1,408±15 and 12±169 Ma. 

Data for all three samples indicate that their crystallization ages 

are not resolvable; therefore, a combined discordia with intercepts of 1,410±4 and 26±54 Ma, defined by all seven fractions, is 

considered to provide the best estimate of the age of this batholith 

(fig- 16).

Granite of Olea Ranch

Sample 752 (appendix sample No. 50) represents a pluton of 

porphyritic granite and granodiorite containing oriented phenocrysts of potassic feldspar and located east of the Bagdad metamorphic belt. Sample 753 (appendix sample No. 51) comes from 

a pluton of coarse-grained biotite granite and granodiorite located 

along U.S. Highway 93 west of the Bagdad metamorphic belt. 

These plutons and other granitic bodies are grouped as the granite 

of Olea Ranch. They have no intrusive relations with the Signal 

Granite, which is 7 km to the west, but they are clearly intrusive 

into Early Proterozoic metamorphic and plutonic rocks. Only 

two zircon fractions were analyzed from each of these samples 

(table 2). The data from sample 752 are moderately discordant 

but have little spread in Pb/U ratios; data from sample 753 are less 

discordant but also have limited spread in Pb/U (fig. 16). Pb/ 

206Pb dates for all fractions range only from 1,417 to 1,419 Ma. 

A composite discordia line defines an age of 1,416±5 and 

-51±103 Ma. The negative lower intercept is unacceptable so 

that a regression forced through 0 Ma and giving an upper intercept of 1,418+2 Ma is preferred. The analytical data, particularly 

the 207Pb/206Pb groupings of 1,407-1,411 Ma vs. 1,417-1,419 

Ma, strongly indicate that the granite of Olea Ranch is slightly 

older than that of the Signal batholith.

Granite of Joshua Tree Parkway and Granite of Grayback Mountain

The eastern part of the map area contains two separate Middle Proterozoic granitic complexes. Sample A-15 la (appendix 

sample No. 54) represents the megacrystic phase of the granite of 

Joshua Tree Parkway. The four zircon fractions from this sample 

are moderately discordant and have a very limited spread in Pb/U 

ratios; one fraction (NM-63) plots to the left of the other three 

(fig. 17). No discordia line can be fitted to these data. 207Pb/ 

2 Pb ages of 1,407 and 1,409 Ma for two of the fractions provide 

an estimate of the crystallization age. Sample A-153 (appendix 

sample No. 57) is from the coarse-grained phase of the granite of 

Grayback Mountain. The four zircon fractions from this sample 

are also moderately discordant but have an adequate spread in Pb/ 

U ratios to define a discordia line with intercepts of 1,415±6 and 

110±52 Ma. The oldest 207Pb/206Pb age from these fractions is 

1,413 Ma and is consistent with the upper intercept age of 1,415 

Ma being a reasonable estimate of the crystallization age of this 

sample. The ages of these two granitic complexes are not statistically different; the granite of Joshua Tree Parkway might be 

slightly younger, based on the 207Pb/206Pb ages.

Geochronology 21
The combined U-Pb ages for the Signal batholith, the granite of Olea Ranch, and the granites of Joshua Tree Parkway and 

Grayback Mountain range from only 1,407 to 1,418 Ma. The 

ages of the Signal batholith and the granite of Olea Ranch show 

that the intrusion of these Middle Proterozoic complexes did 

occur at distinct times. Other Middle Proterozoic intrusives in the 

region have similar ages. The Lawler Peak Granite north of 

Bagdad has an age of 1,413±3 Ma (Silver and others, 1980). 

Along the Colorado River east of the Whipple Mountains, about 

60 km west of the Poachie region, the Parker Dam granite of 

Anderson (1983) and Anderson and Bender (1989), which texturally resembles the Signal Granite, has an age of 1,401 ±3 Ma; and 

the Bowmans Wash quartz monzodiorite of Anderson (1983) and 

Anderson and Bender (1989), which resembles the mafic granodiorite, has an age of 1,407±5 Ma (Anderson and Bender, 1989). 

In the Buckskin Mountains 20 km southwest of the Poachie 

region, one intrusive body has an age of about 1,400 Ma, and 

inclusions of coarse-grained granitic rock in the Miocene 

Swansea Plutonic Suite have an age of about 1,410 Ma (Wooden 

and Bryant, unpub. data, 1995; Bryant and others, 1996). About 

30 km southeast of the Poachie region, granodiorite nearYarnell, 

Ariz., has an age of about 1,421 Ma (Wooden and Ed DeWitt, 

unpub. data, 1995). In the Poachie region map area (fig. 1), dated 

Middle Proterozoic intrusives compose about half of the exposed 

area of Proterozoic basement. If the undated granitic rocks are of 

Middle Proterozoic age, about two-thirds of the exposed basement would be that age. In this region, then, the Middle Proterozoic intrusive event is characterized by the episodic emplacement 

of discrete bodies ranging in size from batholiths to smaller plutons over a 20-30 m.y. interval. These intrusive bodies composed 

a large composite batholith comparable in size to the composite 

Mesozoic batholiths of the Western United States.

Geochemistry

Analytical Methods

Ten major elements were determined by wavelength dispersive X-ray fluorescence spectrometry (Taggart and others, 1990). 

In most samples Rb, Sr, Y, Zr, and Nb and, in some samples, Cr, 

Ni, Cu, Zn, Ba, La, and Ce were determined by energy-dispersive 

XRF using a Kevex 700 EDXRF spectrometer with a Kevex 7000 

analyzer (King, 1990). Rare-earth elements were determined by 

inductively coupled plasma-mass spectrometry using an internal 

standard for drift correction, matrix effects, and oxide formation 

calculation (Lichte and others, 1987). Uranium and thorium were 

determined by delayed neutron counting following neutron irradiation of the sample (McKown and Knight, 1990). Fluorine and 

FeO were determined by ion-selective electrode potentiometry 

(Pribble, 1990) and potentiometric titration (Papp and others, 

1990), respectively. In a few samples some rare earths and other 

minor elements were determined by instrumental neutron activation analysis (Baedecker and McKown, 1987). Rare-earth elements shown in diagrams are normalized to chondrite values 

from Hanson (1980).

0.25

0.24

8 0.23

0.22

0.21

0.20

1440

1410 +/- 4&26 +/- 54 Ma 

(MSWD = 0.5)

1320

753

1280

1240

752

1418 +1-2 forced toO Ma 

(MSWD = 0.5)

2.3 2.5 2.7 

207pb/ 235u

2.9 3.1

Figure 16. U-Pb concordia diagram for the Signal Granite (sample 1168, inverted triangles, and sample 1164, rotated triangles; 

appendix sample Nos. 43 and 44), the mafic granodiorite (sample 

390, upright triangles; appendix sample No. 47), and the granite of 

Olea Ranch (sample 752, squares, and sample 753, diamonds; appendix sample Nos. 50 and 51). Ages of the Signal Granite and 

the mafic granodiorite are not resolvable from each other at 1,410 

Ma. Combined data for the granite of Olea Ranch define an age of 

1,418 Ma, which is resolvable from that of the Signal Granite and 

mafic granodiorite.

0.26

0.24

0.22

=?

0.20

0.18

0.16

1415+/-6&110+/-52Ma 

(MSWD = 1.

1100

1.6 2.0 2.4 

207pb/235 u

2.8 3.2

Figure 17. U-Pb concordia diagram for the granites of Joshua 

Tree Parkway (sample A-151 a; appendix sample No. 54; triangles) 

and of Grayback Mountain (sample A-153; appendix sample No. 57; 

squares). The data for sample A-151 a do not define a discordia 

line, and one of the fractions (inverted triangle) plots to the left of 

the others. A minimum age of about 1,408 Ma is indicated by the 

Pb-Pb ages of the zircons. The data for sample A-153 define a discordia line having an upper intercept at 1,415 Ma, which is taken to 

be the crystallization age.

22 Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province
55 65 

SiO2 , IN WEIGHT PERCENT

75 79

Figure 18. Early Proterozoic metavolcanic rocks. Circle, amphibolite; 

cross, rhyolite. A, Si02 vs. Na2 0+K2 0. Fields of interest: PC, picrobasalt; 

B, basalt; AB, alkali basalt; 01, basaltic andesite; 02, andesite; R, rhyolite 

(LeBas and others, 1986). B, Zr/Ti02 vs. Si02 (Floyd and Winchester, 1978).

average upper crust (Taylor and McLennan, 1981), except that it 

falls below the average upper crustal curve. It also resembles the 

pattern of many post-Archean shales. This sample shows a flat 

LREE-HREE pattern compared to sample 1, which shows an 

overall negative slope.

The amphibolites generally have the composition of basalts 

based on both their alkali:silica ratios and the ratio of the less 

mobile elements of zirconium divided by TiO2 plotted against 

SiO2 (fig. ISA, B). Sample 1159a (appendix sample No. 3) from 

an interlayer in the metasedimentary rocks plots in the picrobasalt 

field in fig. ISA and the alkali basalt field in fig. 185. The latter 

name is invalid because the sample has a low alkali content. This 

rock is iron-rich (fig. 205). Sample 633 (appendix sample No. 5), 

a metabasalt from a sliver of the Bagdad metamorphic belt 

included in the granite of Thorn Peak, is also iron-rich. Sample 

M-81 (appendix sample No. 7) from the quartz-bearing amphibolite marker layer at the top of the Dick metarhyolite is derived 

from andesite (fig. 18). The amphibolites are generally calcic but 

range to alkali calcic (fig. 19A) and have average K2O concentrations (fig. 195) and low Rb and moderate Sr contents (fig. 20C). 

Th/U ratios range from 2 to 4 and average 2.5 (fig. 20D). These 

rocks have a small light-rare-earth vs. heavy-rare-earth element 

(LREE/HREE) enrichment [(La/Yb)CN=l.3-4.7]. The sample 

(633; appendix sample No. 5) having the very low enrichment has 

a small negative europium anomaly (fig. 21A).

The metarhyolite sample (appendix sample No. 8) is a calcalkalic rhyolite and is very sodic (fig. 19A, B). It has lower Rb 

and Sr concentrations and a lower Th/U ratio (2.5) than most of 

the plutonic rocks in the Poachie region (figs. 19A, 20C, D). It is 

more zircon-rich than the plutonic rocks of similar high SiO2 

concentrations. These chemical characteristics are similar to 

those of both the Dick Rhyolite and the King Peak Rhyolite in the 

Bagdad area (C.M. Conway, oral commun., 1995). The metarhyolite shows a small light-rare-earth element vs. heavy-rareearth element (LREE/HREE) enrichment [(La/Yb) CN=5.1], and 

a moderate negative Eu anomaly (fig. 21A). The total REE concentration of the rock is high (REE=332 ppm).

Metamorphic Rocks

All but one of the samples of metamorphic rocks analyzed 

are of the Bagdad metamorphic belt. Analyses are from two samples of metasedimentary rock, one of which is from a cupola in 

the Signal batholith, from which we attempted to obtain zircon 

for dating, the massive metarhyolite we dated, and five samples of 

amphibolite (table 3).

The samples of metasedimentary rock are mica gneisses 

derived from shale (appendix sample No. 1) and sandstone 

(appendix sample No. 2), and they have Th/U ratios of 8.3 and 

6.4, respectively. These ratios are characteristic of rocks of or 

derived from the Mojave crustal province (Wooden and DeWitt, 

1991). The metashale shows strong light-rare-earth element vs. 

heavy-rare-earth element (LREE/HREE) enrichment [(La/ 

Yb)CN=35.8], and the metasandstone shows moderate enrichment [(La/Yb)CN=10.0]. Both rock types have small negative 

Eu anomalies. The REE pattern for sample 2 resembles that of

Plutonic Rocks

Early and Middle Proterozoic plutonic rocks from the 

Poachie region have many chemical similarities consistent with 

derivation from the same source regions under similar conditions. 

Early Proterozoic (1,710-1,680 Ma) plutonic rocks were 

emplaced over a period that spanned the main episode of orogeny, 

plutonism, and metamorphism (tables 4 and 5). Middle Proterozoic (1,418-1,410 Ma) rocks from several plutons were emplaced 

in a shorter period during a second episode of widespread plutonism (tables 6 and 7).

Early Proterozoic Plutonic Rocks

Early Proterozoic plutonic rocks described here are coarsegrained granitic rocks and associated diorite and gabbro, granite 

of Thorn Peak, and gneissic tonalite.

Geochemistry 23
Table 3. Major-oxide and trace-element concentrations in some supracrustal rocks from the Bagdad metamorphic belt in 

the Poachie region and of one metasediment from cupola in the Signal batholith (sample 1166).

[App., appendix; nd, not determined; LOI, loss on ignition; FeTO3, total Fe as Fe2O3]

Unit

App. No.

Field No.

Lab No.

Job No.

Metasedimentary rocks

1

1154

D-266709

RV13

2

1166

D-278413

SD65

Metavolcanic rocks

3

1159a

D-568687

WB23

4

W-419

D-568689

WB23

Amphibolites

5

633

D-568688

WB23

6

M-96

D-568690

WB23

7

M-81

D-568687

WB23

Metarhyolite

8

1161

D-266707

RV13

Major-oxide concentration, in weight percent1

SiO2

A12O3

FeTOS

MgO

CaO

Na2O

K2O

TiO2

PiO5

MnO

LOI

Total

2FeO

2F

61.1

17.9

8.89

2.15

.41

1.17

3.50

.79

.11

.46

2.87

96.48

1.24

.08

71.5

13.8

3.43

.98

2.13

2.67

3.58

.41

.07

.06

.59

98.63

2.66

.04

43.6

14.7

18.0

6.63

9.84

1.35

0.49

2.73

0.53

0.97

0.60

98.84

nd

nd

50.0

12.7

12.2

10.1

9.61

2.00

0.17

1.31

0.39

0.24

0.43

99.15

nd

nd

50.3

13.8

15.7

4.09

8.74

4.27

0.29

1.90

0.25

0.23

0.38

99.95

nd

nd

50.6

15.9

9.93

5.98

11.4

2.29

0.60

1.33

0.31

0.16

0.55

99.05

nd

nd

56.8

15.0

8.95

4.06

8.31

4.16

0.57

1.12

0.26

0.16

0.35

99.75

nd

nd

75.2

11.4

3.49

.77

.32

3.53

3.39

.23

.05

.04

.76

98.42

2.28

.08

Trace-element concentration, in parts per million3

Nb

Rb

Sr

Zr

Y

Ba

Ce

La

Cu

Ni

Zn

Cr

12

196

108

200

39

nd

nd

nd

nd

nd

nd

nd

16

152

234

234

38

nd

nd

nd

nd

nd

nd

nd

11

22

93

180

37

108

35

<30

33

118

138

116

10

10

360

120

14

66

<30

<30

54

275

92

690

<10

>10

178

116

34

48

40

<30

10

49

91

60

11

20

340

124

18

116

34

<30

43

62

102

158

16

<10

198

162

28

100

<30

<30

25

26

56

79

31

67

31

579

161

nd

nd

nd

nd

nd

nd

nd

Trace-element concentration, in parts per million4' 5

Ba

Y

La

Co

Sc

Cs

Sb

Ta

Hf

Ce

Pr

Nd

Sm

Eu

Gd

Tb

Dy

Ho

770

9.9

53.7

nd

nd

nd

nd

nd

nd

112

13.6

47.0

8.90

1.67

8.40

1.00

4.60

.72

890

nd

60.4

nd

nd

nd

nd

nd

nd

119

13.4

46.1

9.04

1.40

5.85

.92

5.88

1.21

130

nd

15.9

52.7

35.0

2.8

0.54

0.796

3.72

37.7

nd

24

6.85

2.16

nd

1.14

nd

nd

96

nd

12.7

52.0

23.8

1.1

0.26

0.86

2.6

31.1

nd

16

4.19

1.1

nd

0.65

nd

nd

66

nd

7.3

38.1

36.4

0.41

0.97

0.42

2.92

19.1

nd

14

4.41

1.30

nd

0.961

nd

nd

130

nd

14.6

36.4

32.0

3.13

0.97

0.71

2.64

32.6

nd

17

4.17

1.27

nd

0.59

nd

nd

110

nd

16.7

24.2

22.5

0.43

0.41

0.819

3.59

34.7

nd

18

4.42

1.24

nd

0.68

nd

nd

780

71.5

55.2

nd

nd

nd

nd

nd

nd

115

15.0

67.6

17.4

2.94

19.00

3.00

16.60

3.10

24 Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province
Table 3—Continued. Major-oxide and trace-element concentrations in some supracrustal rocks from the Bagdad metamorphic 

belt in the Poachie region and of one metasedimentfrom cupola in the Signal batholith (sample 1166).

Unit

App. No.

Field No.

Lab No.

Job No.

Metasedimentary rocks

1

1154

D-266709

RV13

2

1166

D-278413

SD65

Metavolcanic rocks

3

1159a

D-568687

WB23

4

W-419

D-568689

WB23

Amphibolites

5

633

D-568688

WB23

6

M-96

D-568690

WB23

7

M-81

D-568687

WB23

Metarhyolite

8

1161

D-266707

RV13

Trace-element concentration, in parts per million4' 5 — Continued

Er

Tm

Yb

As

Lu

6Th

6U

2.30

.23

1.00

nd

.22

21.3

2.58

3.89

.62

4.02

nd

.59

26.2

4.8

nd

nd

3.51

0.92

0.49

1.5

0.5

nd

nd

2.1

1.0

0.29

1.9

0.96

nd

nd

3.82

1.5

0.52

1.6

0.60

nd

nd

2.2

<0.700

0.30

2.2

0.55

nd

nd

2.4

1.3

0.34

4.36

1.3

8.30

1.10

7.20

1.04

12.1

4.76

1 Major oxides determined by wavelength dispersive X-ray fluorescence: A.J. Bartel, K. Stewart, J.E. Taggart, E. Robb, analysts.

2 FeO determined by potentiometric titration and F by ion-selective electrode potentiometry: E. Brandt, S. Roof, G. Mason, J.H. 

Christie, analysts.

3 Trace elements determined by energy dispersive X-ray fluorescence: L. Evans, R.R. Larson, B.W. King, analysts.

Rare earths determined by inductively coupled plasma-mass spectrometry in Nos. 1, 2, 8: A. Meier, D. Fey, P.H. Briggs, J.G. 

Crock, analysts.

Rare earth and trace elements determined by instrumental neutron activation analysis in Nos. 3-7: G.A. Wandless, analyst. 

6 Th and U determined by delayed neutron activation analysis in Nos.l, 2, 8: R.B. Vaughn, D.M. McKown, analysts.

Coarse-Grained Granitic Rocks

Rocks included in the suite mapped as the coarse-grained 

granite unit have silica concentrations ranging from 46 to 70 percent SiO2 (table 4). They range from calcic for the mafic rocks to 

alkalic in some intermediate rocks. Most of the analyzed rocks 

having a SiO2 content >60 percent are mostly alkali-calcic but 

range into the alkalic and calc-alkalic fields (fig. 19A). They have 

normal SiO2 vs. K2O/Na2O+K2O ratios (fig. 195).

The coarse-grained granitic rocks of the Poachie region have 

the same degree of alkalinity as suites 1, 2, and 4 (pretectonic 

biotite granodiorite and granite, pre- to syntectonic hornblendebiotite tonalite and granodiorite, and syn- to posttectonic granodiorite to granite, respectively) in the Prescott region (DeWitt, 

1989). Calcic rocks in the Poachie region are few and have silica 

concentrations <55 weight percent SiO2 , whereas in the Prescott 

region suite 3 (pre- to late tectonic biotite-hornblende granodiorite), particularly, has calcic rocks at higher SiO2 concentrations. 

Many of the plutons in the Prescott region are older than 1.7 Ga 

and older than any dated in the Poachie region. According to 

Anderson and others (1993) 1.7 Ga granitic rocks in the Mojave 

province are alkali-calcic in contrast to the alkalic, alkali-calcic, 

and calc-alkalic nature of those in the Poachie region. In the SiO2 

vs. Na2O+K2O diagram (fig. 19A) the Early Proterozoic rocks of 

the Poachie region form a field that overlaps that of the syn- and 

posttectonic plutons of the Prescott belt and the syntectonic plutons northwest of the Prescott belt of P. Anderson (1989b) but 

extends to more alkalic and potassic compositions than any rocks 

shown in those diagrams.

The coarse-grained silicic granitic rocks have Rb/Sr ratios 

and Rb concentrations (fig. 20C; table 4) similar to syn- and posttectonic plutons of suite 4 in the Prescott region (DeWitt, 1989), 

and they are especially similar to the granite of Iron Springs and 

the Crazy Basin Quartz Monzonite. Some rocks of the coarsegrained granite unit are more mafic than those plutons and have 

higher Sr concentrations.

However, the coarse-grained granitic unit of the Poachie area 

has higher Zr, Ba, and Ce concentrations but similar La concentrations compared to the Crazy Basin, and Iron Springs plutons 

(table 4; DeWitt, 1989). Our data agree with a trend of increasing 

incompatible minor element concentrations, increasing K concentration, and alkalinity of plutonic rocks in a westward direction during the =1,700 Ma episode of plutonic activity (fig. 19; 

DeWitt, 1989). We do not have enough information to allow us to 

divide the Early Proterozoic plutonic rocks of the Poachie region 

into suites, as has been done in the Prescott region (DeWitt, 1989), 

although our geochronological data indicate that the plutonic 

rocks were emplaced over a time ranging from 1,710 to 1,680 Ma, 

a time span that is shorter than the 1,750-1,700 Ma time span of 

pluton emplacement in the Prescott region (DeWitt, 1989; Karlstrom and others, 1987). Our chemical data indicate no simple 

chemical progression with time in the Early Proterozoic rocks of 

the Poachie region; the younger rocks range from alkalic to calcalkalic (fig. 19A).

Chondrite-norrnalized REE patterns for the rocks of the 

coarse-grained granite suite (table 4) suggest that the four analyzed gabbros (appendix samples 10-15) may have been derived 

by a small amount of partial melting of a mantle peridotite. In the 

gabbros LREE/HREE enrichment (La/Yb)CN ranges from 4.5 to 

7.1 (fig. 215), and in the more silicic rocks of the suite that value 

ranges from 9.5 to 24 (fig. 21C). Some of the more silicic rocks 

have small negative europium anomalies (fig. 21C), perhaps due 

to fractionation of plagioclase from a parent magma. Sample W301 (appendix sample No. 19), a feldspar-rich and quartz-poor 

rock, has a prominent positive europium anomaly, probably due to 

accumulation of plagioclase in its magma. These variations probably indicate the range of starting materials and processes of differentiation in the development of this complex suite of rocks. 

Total rare-earth element concentrations range from 61-77 ppm in 

the gabbros to 319^-21 ppm in the granitic rocks of the suite.

Geochemistry 25
30 

(D

ca

Table 4. Major-oxide and trace-element concentrations in Early Proterozoic gabbro and coarse-grained granite from the Poachie region, 

[nd, not determined; LOI, loss on ignition; FeTOS, total Fe as Fe2C>3]

a>

a

a> 

-5

a> 

to 

O

| Small bodies of gabbro in coarse-grained granite, and Signal Granite | Coarse-grained granitic rocks

Appendix

No.

Field No. .

Lab No. .

Job No. .

10

. .. 450

... D3637772

. .. UD76

WB47

11

907

D568685

WB23

12

W-61

D363771

UD76

13

W-307

D363773

UD76

14

1165

D78412

SD65

WB47

15 17 18 19 20

750 192 1137 W-301 1167

D- D- D- D- D259526 259527 363778 363777 278414

SC97 RP40 UD76 UD76 SD65

RP40 SC97

WB47 WB47

21

552a

D363781

UD76

22

749

D259524

RP40

3

Major oxide concentration, in weight percent1

SiO2

A12O3

FeTO3

MgO

CaO

Na2O

K2O

TiO2

P2O5

MnO

LOI

Total

2FeO

2p

45.9

17.5

10.6

7.80

13.50

1.58

0.34

0.66

0.12

0.19

0.88

98.19

nd

nd

46.5

16.4

12.2

7.93

9.49

2.57

0.36

1.65

0.50

0.17

1.39

99.16

nd

nd

49.5

14.9

11.4

7.58

9.00

2.6

1.9

1.11

0.32

0.20

0.97

98.41

nd

nd

49.8

16.2

11.1

6.39

10.0

3.14

0.29

1.7

0.6

0.18

0.85

99.4

nd

nd

51.3

16.0

7.83

7.95

10.8

2.99

1.26

0.51

0.11

0.13

0.93

98.88

6.56

.05

52.0 55.2 56.4 60.8 62.0

16.1 18.3 18.1 18.2 16.0

8.75 7.78 6.85 4.06 6.37

7.83 2.64 2.39 0.85 2.41

10.3 6.18 5.02 2.67 3.52

2.6 4.39 4.15 4.65 2.97

0.64 2.12 3.31 5.36 3.43

0.68 1.45 1.19 0.74 0.93

0.1 0.52 0.39 0.21 0.37

0.15 0.11 0.09 0.11 0.09

0.99 0.81 0.81 0.47 0.77

91.15 98.69 97.7 98.12 98.08

5.84 4.3 nd nd 4.08

.15 .12 nd nd .05

62.3

18.0

3.83

0.70

2.89

4.4

5.48

0.71

0.18

0.09

0.40

98.58

nd

nd

62.4

16.1

5.22

1.89

4.06

3.58

3.73

0.83

0.35

0.07

0.68

98.23

2.7

.12

63

1

4.

1

3.

4.

3.

0.

0.

0.

0.

98

nd

nd

Trace-element concentration, in parts per million3

Nb

Rb

Sr

Zr

Y

Ba

Ce

La

Cu

Ni

Zn

Cr

<10

12

267

43

16

260

33

9

62

52

71

342

<10

15

385

67

13

215

<30

<30

48

164

74

88

<10

88

636

95

23

815

75

25

31

147

101

271

15

10

546

135

33

208

122

50

16

118

90

87

<10

99

232

69

23

250

nd

nd

nd

96

61

355

9 12 12 <10 <10

28 93 146 190 138

317 640 697 377 559

85 450 398 568 245

25 28 26 26 21

320 1830 4090 4650 nd

nd nd 156 77 nd

nd nd 65 9 nd

nd nd 26 3 nd

100 nd 18 <5 nd

60 nd 98 71 nd

237 nd 27 <20 nd

12

147

368

592

32

3220

135

42

10

<5

80

<20

24

149

648

259

41

nd

nd

nd

nd

nd

nd

nd

1

1

30

24

26

84

90

48

17

22

97

27

Trace-element concentration, in parts per million4' 5

Co

Cs

Hf

43.6

0.32

1.3

52.9

0.28

1.7

nd

nd

nd

nd

nd

nd

35.8

3.64

1.71

40.0 17.0 14.8 3.18 nd

1.1 5.07 6.09 6.27 nd

2.0 12.0 9.05 15.5 nd

nd

nd

nd

nd

nd

nd

nd

nd

nd
Table 4—Continued. Major-oxide and trace-element concentrations in Early Proterozoic gabbro and coarse-grained granite from the Poachie 

a

to

o 

o3- 

CD

B

Appendix

NQ

Field No. .

Lab No. .

Job No. .

Small bodies of gabbro in coarse-grained granite, and Signal Granite

10 11

.. 450 907

. . D- D3637772 568685

. . UD76 WB23

WB47

12

W-61

D363771

UD76

13 14

W-307 1165

D- D363773 78412

UD76 SD65

15

750

D259526

SC97

WB47 RP40

WB47

Coarse-grained granitic rocks

17 18 19 20

192 1137 W-301 1167

D- D- D- D259527 363778 363777 278414

RP40 UD76 UD76 SD65

SC97

WB47

21

552a

D363781

UD76

22

749

D259524

RP40

Trace-element concentration, in parts per million4' 5 — Continued

Sb

Ta

Sc

Y

La

Ce

Pr

Nd

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

6Th

6U

<.08 <0.08

0.25 0.50

43.3 24.3

nd nd

11.2 10.7

26 22.2

nd nd

13 14

2.8 3.83

0.89 1.49

nd nd

0.40 0.58

nd nd

nd nd

nd nd

nd nd

1.3 1.6

0.21 0.22

1.1 0.89

0.13 0.19

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

3.1

0.67

nd <0.18

nd 0.60

nd 32.7

nd nd

nd 16.4

nd 30.2

nd 3.7

nd 13.9

nd 2.93

nd 0.76

nd 2.66

nd 0.42

nd 2.75

nd 0.55

nd 1.62

nd 0.24

nd 1.54

nd 0.24

1.8 <2.5

0.52 2.41

0.15

0.32

34.4

19.9

11.7

26.7

2.5

13.5

3.0

1.12

3.8

>0.5

3.4

0.73

2.1

0.3

2.2

0.3

1.8

0.69

0.14 0.16 <0.17 nd

0.90 0.62 0.804 nd

19.0 14.5 11.3 nd

31.8 nd nd nd

67.3 75.0 31.4 99.4

137 134 61.2 191

15.3 nd nd 21.9

61.3 48 28 76.2

10.8 8.83 6.73 12.3

3.09 2.48 4.60 2.19

9.2 nd nd 7.46

1.2 0.90 0.78 1

6.8 nd nd 5.54

1.27 nd nd 0.89

3.0 nd nd 1.97

0.42 nd nd 0.19

2.6 2.1 2.2 0.85

0.33 0.29 0.33 0.1

4.09 4.1 3.7 11.9

1.56 1.13 2.91 2.02

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

6.83

1.14

nd

nd

nd

40.6

58.9

144

17.3

72.3

10.0

2.76

10.7

1.9

8

1.49

3.8

0.53

3.7

0.52

11.9

2.74

n

n

n

n

n

n

n

n

n

n

n

n

n

n

n

n

n

n

5

1

Major oxides determined by wavelength dispersive X-ray fluorescence spectroscopy: D.F. Siems, I.E. Taggart, A.J. Bartel, K. Stewart, E. Robb, J.S. Mee, a

FeO determined by potentiometric titration and F determined by ion-selective electrode potentiometry: E. Brandt, J. Sharkey, G. Mason, J.H. Christie, anal

3Trace elements determined by energy-dispersive X-ray fluorescence: J.R. Evans, B.W. King, R. Johnson, S. Fleming, analysts. Ba, Ni, Zn, and Cr in sample

neutron activation analysis: C.A. Palmer, G.A. Wandless, analysts.

4Rare earths determined by inductively coupled plasma-mass spectrometry: J.G. Crock, K. Kennedy, A. Meir, analysts.

5Rare earths and trace elements in samples 10, 15, and 19 by instrumental neutron activation analysis: C.A. Palmer, G.A Wandless, analysts.

6Th and U determined by delayed neutron counting: E.J. Knight, R.B. Vaughn, D. McKown, analysts.
Table 5. Major-oxide and trace-element concentrations in Early Proterozoic fine-grained granite, granite of Thorn Peak, and gneissic tonalite 

and other Proterozoic granites of the Poachie region.

[nd, not determined; LOI, loss on ignition; FeTO3, total Fe as FeoC^]

Appendix No.

Field No.

Lab No.

Job No.

Fine-grained

granite

27

172b

D-363764

UD76

Granite of Thorn Peak

31

636a

D-363770

UD76

32

175b

33

A-10

D-363766 D-363767

UD76 UD76

34

A-21

D-363769

UD76

WB47

Major-oxide concentration.

SiO2

A1203

FeTO3

MgO

CaO

Na2O

K2O

TiO2

P205

MnO

LOI

Total

2FeO

2F

74.7

13.5

1.06

0.19

0.93

3.39

5.09

0.08

<.05

0.03

0.55

99.02

nd

nd

68.7

14.1

4.64

1.1

2.00

2.32

4.26

0.73

0.27

0.13

1.05

98.25

nd

nd

68.7

14.1

4.7

1.08

1.85

2.14

4.63

0.74

0.3

0.12

1.00

98.36

nd

nd

69.7

14.0

4.08

0.96

1.81

2.45

4.63

0.62

0.23

0.1

0.89

98.58

nd

nd

71.6

14.0

2.09

0.45

1.32

2.96

5.33

0.27

0.13

0.06

0.72

98.41

nd

nd

35

1158

D-266705

RV13

Gneissic tonalite

36

A-108

D-366774

UD76

WB47

37

A-111

D-363775

UD76

38

1163

D-27841 1

SD65

Other Proterozoic

granitic rocks

39

A-85

D-363768

UD76

40

A-152

D-327701

TG29

in weight percent1

73.8

13.5

1.51

0.48

1.20

2.67

4.72

0.22

0.14

0.07

0.89

98.31

0.67

0.05

52.6

16.7

8.66

4.61

5.68

4.3

2.82

1.22

0.91

0.12

1.55

97.62

nd

nd

53.4

15.1

10.3

5.81

7.55

3.0

1.73

1.03

0.32

0.14

1.39

98.38

nd

nd

61.0

16.0

6.22

2.93

3.52

2.72

3.67

0.98

0.59

0.09

1.80

97.72

3.65

0.09

65.9

13.6

6.47

1.4

3.27

2.44

3.86

1.13

0.54

0.14

0.66

98.75

nd

nd

66.5

14.9

4.83

1.12

2.66

3.09

3.67

0.83

0.53

0.08

0.92

97.93

2.05

0.08

Trace-element concentration, in parts per million3

Nb

Rb

Sr

Zr

Y

Ba

Ce

La

Cu

Ni

Zn

Cr

21

386

64

74

51

324

74

39

4

<5

33

<20

30

207

242

296

59

1020

175

77

33

7

85

<20

25

311

244

286

58

1090

172

63

16

<5

106

<20

21

241

204

241

52

915

157

69

21

9

95

<20

20

325

132

171

39

753

122

52

7

<5

52

<20

Trace-element concentration

Co

Cs

Hf

Sb

Ta

Sc

La

Ce

Pr

Nd

Sm

Eu

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

2.70

18.9

5.06

0.12

2.75

5.93

49.3

94.7

nd

37.0

4.87

1.05

15

286

151

93

37

nd

nd

nd

nd

nd

nd

nd

>10

110

1380

294

23

1100

193

106

81

91

108

140

12

71

694

102

24

561

87

31

83

106

81

155

13

193

635

261

26

nd

nd

nd

nd

nd

nd

nd

20

155

286

282

55

1100

172

82

18

6

108

<20

29

181

312

354

52

nd

nd

nd

nd

nd

nd

nd

in parts per million4

nd

nd

nd

nd

nd

nd

26.9

55.2

7.2

24.6

4.8

1.21

49.6

9.06

7.05

0.31

0.83

18.0

94.6

183

nd

82.3

15.3

3.60

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

41.1

86.4

10.8

42.0

8.21

2.26

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

99

200

22

88

15

2.6

28 Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province
Tables—Continued. Major-oxide and trace element concentrations in Early Proterozoic fine-grained granite, granite of Thorn Peak, and 

gneissic tonalite and other Proterozoic granites of the Poachie region.

Fine-g

gra

rained Granite of Thorn Peak

nite

Appendix No. 27 31 32

Field No. 172b 636a 175b

Lab No. D-363764 D-363770 D-363766

Job No. UD76 UD76 UD76

33 34 35

A-10 A-21 1158

D- D-363769 D-266705

363767

UD76 UD76 RV13

WB47

Gneissic tonalite

36 37 38

A-108 A-111 1163

D-366774 D-363775 D-278411

UD76 UD76 SD65

WB47

Other Proterozoic

granitic rocks

39 40

A-85 A-152

D-363768 D-327701

UD76 TG29

Trace-element concentration, in parts per million4 — Continued

Gd nd

Tb nd

Dy nd

Ho nd

Er nd

Tm nd

Yb nd

Lu nd

5Th 30.2

5U 5.03

Maior oxides deter

nd nd

nd nd

nd nd

nd nd

nd nd

nd nd

nd nd

nd nd

16.1 17.5

3.04 3.93

mined by energy dispersive X-ra^

nd nd 4.6

nd 0.978 0.6

nd nd 4.3

nd nd 0.81

nd nd 2.3

nd nd 0.34

nd 3.71 2.4

nd 0.519 0.35

20.8 23.9 9.34

3.63 3.78 1.81

/ fluorescence: D.F. Siems, I.E. Tassart

nd nd 6.18

1.4 nd 0.88

nd nd 4.98

nd nd 0.90

nd nd 2.36

nd nd 0.28

2.6 nd 1.04

0.37 nd 0.12

11.9 3.2 2.5

2.90 1.13 2.78

A.J. Bartel, K. Stewart, analysts.

nd 11

nd 1.7

nd 10.0

nd 1.8

nd 5.2

nd 0.69

nd 4.2

nd nd

<2.5 17.9

3.94 3.3

2FeO determined by potentiometric titration and F by ion-selective electrode potentiometry: E. Brandt, S. Roof, C. Papp, J. Sharkey, analysts. 

3Minor elements determined by energy dispersive X-ray fluorescence: J.R. Evans, R.R. Larson, analysts.

4Rare earth determined by inductively coupled plasma-mass spectrometry: J.G. Crock, K. Kennedy, G. Riddle, analysts. Rare earths and minor elements 

determined by instrumental neuron activation analysis in Nos. 34 and 36: C.A. Palmer, analyst.

5Th and U determined by delayed neutron counting: E.J. Knight, R.B. Vaughn, D.M. McKown, analysts.

Granite of Thorn Peak

The granite of Thorn Peak has a distinctive chemical character, and analytical data for it form a cluster of points on the various chemical diagrams (table 5; figs. 19, 20). It has 70-75 

weight percent SiO2 , is slightly Mg rich, and is generally calcalkalic, somewhat more calcic than rocks of the coarse-grained 

granite unit having a similar SiO2 concentration. The granite of 

Thorn Peak is more strongly peraluminous than rocks of the 

coarse-grained granite having a similar silica concentration and 

has high Rb and low Sr concentrations and high U concentration 

compared to most samples of the coarse-grained granite unit. 

Thorium concentrations are similar to those of the more Th-rich 

samples of the coarse-grained granite and range from 4.5 to 6.3. 

The granite of Thorn Peak shows a gently sloping chondrite-normalized REE pattern and a small negative europium anomaly 

(fig. 2ID). Light-rare-earth element enrichment is less than that 

of the coarse-grained granite [(La/Yb)CN=7.5-8.9]. Total rareearth element concentration in sample 1158 (appendix sample 

No. 35, fig. 21D) is 136 ppm. The fine-grained granite (Xg) that 

intrudes the coarse-grained granite at the east end of the Poachie 

Range is chemically similar to the granite of Thorn Peak in 

major-element concentration but is richer in Rb, Th, and U.

Gneissic Tonalite

The gneissic tonalite has SiO2 concentrations of 52-62 percent and is slightly more alkalic and more potassic (fig. 19A, B) 

than rocks of the coarse-grained granite unit. It is magnesium-rich 

and metaluminous to peraluminous and has a low Th concentration (fig. 20A, B, and D). Th/U ratios range from 0.9 to 4. The

most silicic, peraluminous gneissic tonalite sample is from a part 

of the pluton that contains numerous mica schist and gneiss inclusions. The gneissic tonalite is moderately enriched in LREE [(La/ 

Yb)CN=24.4-26.6] (fig. 2ID), and sample 1163 (appendix sample No. 38) has a rare-earth element concentration of 208 ppm.

The Early Proterozoic rocks of the Poachie region have normal K2O concentrations for their SiO2 concentrations (fig. 195), 

similar to rocks in the Mojave province in California (Anderson 

and others, 1993). They differ from those in the Central Arizona 

province in north-central Arizona where many of the Early Proterozoic plutonic rocks are sodic and very sodic rocks (DeWitt, 

1989; written commun., 1999).

Th/U ratios based on delayed neutron counting (tables 4 and 

5; fig. 20D) in the Early Proterozoic plutonic rocks are similar to 

the ratios calculated on the basis of Pb-isotope data (table 8). 

They average about 4.6 if we ignore the two samples in which the 

Th concentration was below the limits of detection. If we include 

them and assume that they have Th concentrations not far below 

that limit, the average Th/U ratio of the Early Proterozoic plutonic rocks is 4.3; that figure would be lower if their Th content is 

lower. The Th/U ratios calculated from the whole-rock isotopic 

data for some of these rocks average about 2.8 (table 8; Wooden 

and DeWitt, 1991). This value is intermediate between that of the 

Central Arizona and Mojave crustal provinces (Wooden and 

DeWitt, 1991).

Zirconium concentrations (fig. 20£) form a trend with low 

values in rocks having silica concentrations of ==75 weight percent SiO2 to high values at 65 weight percent SiO2 and lower 

values at lower SiO2 contents. Some rocks with 62-67 percent 

SiO2 have low Zr contents. The trend of Zr contents increasing 

with decreasing SiO2 is best defined by analyses from the granite 

of Thorn Peak.

Geochemistry 29
10

n XV

n

B

.ftV*

Qo

^ O

o ^ +

'+ o

40 45 50 55 60 65 

SiO2, IN WEIGHT PERCENT

70 75 80

80

70

60

B

50

45

n

very

sodic ^ ^\

sodic

average

/

+HO +0 9

••

potassic /

/ , . / verV potassic

0.2 0.4 0.6 

K2O/Na2O + K2O

0.8

Figure 19. Silica vs. alkalis diagrams for 

Early Proterozoic rocks of the Poachie region. 

Cross, metavolcanic rocks; open circle, gabbro of the coarse-grained granite suite; solid 

circle, coarse-grained granite (Xcg); x, fineto medium-grained granite (Xg); open square, 

granite of Thorn Peak (Xt); solid square, 

gneissic tonalite (Xgt); diamond, granitic rock 

of uncertain correlation (YXg). Fields of analytical data from Prescott region (DeWitt, 

1989; written commun., 1999) shown but not 

closed at less siliceous end because no analyses of diorite or gabbro were included in his 

diagrams. ASi02 vs. Na 2 0+K2 0. Fields of alkalinity from Anderson (1983) and DeWitt 

(1989). 5,Si02 vs. K2 0/Na2 0+K2 0. Fields from 

Fridrich and others (1998).

In an Rb versus Nb+Y diagram, which has been suggested 

as a tectonic discrimination diagram (Pearce and others, 1984), 

the Early Proterozoic granitic rocks straddle the boundary 

between volcanic arc and within-plate granites (fig. 22). The 

younger, more evolved granite of Thorn Peak plots in the withinplate field, as does the fine-grained granite. Yet the youngest unit, 

the gneissic tonalite, plots in the volcanic arc field. The overall 

pattern of data points may reflect either magmatic processes, different source involvement, or an evolving tectonic setting.

30 Poachie Region, West-Central Arizona—East Boundary,

Middle Proterozoic Plutonic Rocks

Middle Proterozoic rocks discussed herein are Signal Granite and mafic granodiorite, granite of Olea Ranch, granite of 

Joshua Tree Parkway, and granite of Grayback Mountain. The 

Middle Proterozoic plutonic rocks (tables 6 and 7) have some 

similarities to and some differences from the Early Proterozoic 

rocks. Other than the ~ 1,150 Ma diabase, the Middle Proterozoic 

plutonic rocks are intermediate to silicic (60-76 percent SiO2),

Mojave Crustal Province
1.2-

1.0-

0.8-

0.6-

0.4-

4

A

• BD °+ ^ "r

* • D X

• • •

•

0 • 

0 o

o

-p" O

+

o 50 e'o 70

SiO2/ IN WEIGHT PERCENT

4UU

350

z 300

o

| 250

cc

| 200

cc

^ 150

02 100

50

n

xl 1 1 1 1 1 1 1 1 1 1 1 1 1

- -

• D

D

D

~~ D ~

D 

* • • •

O

" ° • • • V*"

0 •

^

+ •

+ 0 +

1 U+°l S 1 o | | | | | | | | |

Sr, IN PARTS PER MILLION

-

70-

i—

LU 

O

cc

LU 

Q_

LU

^

CNI

O 

c/5

50

-

/

•

•/

• 1^

m t ' •

/ •

,£ +

/ *

Mg-rich •

0° //'^

+ O O '

*^

^ O

o

Fe-rich +

10

o

i

cc

LU

°- c

GO 3

CC

^

D

li I /I I I

/ /

— / ~

^. /

^ / %

x—— • / <^/ /'

- / ^ —

"/ + / '

/ I *\ /

-' AS * ^

^ ^ ""

VT' II I I I I

0 10 20 30 40 50 60 70 80

£) Th, IN PARTS PER MILLION

700

602

z 502

o

2 402

cc

LU 40 -• —————— i - ———— ' ——————— i ——————— i ——————— . ———— n

0.4 0.6 0.8 £ 302 

(FeT03.8998)/FeT03 . 8998 + MgO £

" ~~ 202

N

Figure 20. Chemical diagrams for Early Proterozoic 102

rocks of the Poachie region. Cross, metavolcanic rock; 

open circle, gabbro of the coarse-grained granite suite; 2

cnlirl rirrlo rnarca-nrainarl nranita l\rn\- N/ firm- tn ma.

I I I I I I I

• +

-

•

•

/ V-

/ ° . \

/ o H X -

• /'• -• v

+ _^ • ^

0 + + /

+ 1 o 0 • D r*-

o + OB ^^ X ,

i i T i r-- ^^ r ^^ r^'

0 45 50 55 60 65 70 75 8

dium-grained granite (Xg); open square, granite of Thorn 

Peak (Xt); solid square, gneissic tonalite (Xgt); diamond, 

granitic rocks of uncertain correlation (Yxg). A, Si02 vs. 

A/CNK. 5,Si02 vs. Fe/Fe+Mg. Mg-rich-Fe-rich field 

boundary from Anderson (1983). C, Srvs. Rb. Line separates group 4 rocks of DeWitt (1989) above from his 

groups 1-3 below. D, Th/U. Dashed line is field of Early 

Proterozoic granitic rocks from the Prescott area in the 

Arizona crustal province (Ed DeWitt, written commun., 

1999). E, Si02 vs. Zr. Dashed line outlines field of Early 

Proterozoic granitic rocks from the Prescott area (Ed DeWitt, written commun., 1999).

p SiO2, IN WEIGHT PERCENT

generally alkali calcic, and similar to the Early Proterozoic granitic rocks having similar silica concentrations, except for some 

alkalic rocks in the Early Proterozoic assemblage (fig. 23). The 

Middle Proterozoic granitic rocks range from average to potassic 

on the SiO2 vs. K^O/TS^O+K^O diagram and are more potassic 

than the Early Proterozoic granitic rocks. The Signal Granite in 

the western part of the area shows a full range of silica content, 

whereas the plutons to the east have silica >61 weight percent 

SiC>2. The Signal Granite and associate mafic granodiorite are

Geochemistry 31
1000p

MOO

10

1000

u

EXPLANATION

o3 • 6

• 4 07

n 5 x 8

EXPLANATION

o 17 * 20 

n 18 O 22 

D 19

1000 1000p

100

B

u

EXPLANATION

o 10 "14 

n 11 O 15

D

3 TO £> >• uj O t—i f) 

EXPLANATION

o 34 

n 35 

• 36

T 38 

O 40

Figure 21. Chondrite-normalized rare-earth element contents of Early Proterozoic rocks. Numbers on symbols refer to appendix sample 

number. A, metavolcanic rocks; B, gabbros of the coarse-grained granitic suite; C, monzodiorite to granite of the coarse-grained granite suite; 

D, granite of Thorn Peak, gneissic tonalite, and other Proterozoic granite of undetermined age.

potassic, except for the felsic phase of the Signal, which is average. The Middle Proterozoic rocks range from metaluminous to 

peraluminous (fig. 24A). The Signal Granite is metaluminous 

except for its most silicic variant, whereas the plutons in the central and eastern part of the area are weakly metaluminous to peraluminous (fig. 24A). The Signal Granite is Fe-rich, whereas the 

granite of Joshua Tree Parkway is partly Fe-rich and partly Mg 

rich. The granites of Olea Ranch and of Grayback Mountain are 

Mg-rich. The Middle Proterozoic rocks have less Sr and more Rb 

than the Early Proterozoic rocks (fig. 24C).

Signal Granite and Mafic Granodiorite

The Signal Granite has the full range of SiC>2 concentration 

(61-76 percent) of the Middle Proterozoic granitic rocks. It is 

alkali-calcic and potassic and is metaluminous except for the

32 Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province

most silicic variant (fig. 23A, B; fig. 24A). The Signal is Fe-rich 

except for its most silicic varieties, which have average Fe/ 

FeO+MgO ratios (fig. 245). Average Th/U ratio is 7.3, and it 

ranges from 4.3 for the mafic phase to 12.3 for the main phase. 

The main and mafic phases of the Signal Granite have high REE 

concentrations ranging from 559-682 ppm for the mafic phase to 

479-530 ppm for the main phase (fig. 25A). The main phase 

shows moderate LREE/HREE enrichment patterns [(La/Yb) 

CN=10-18], and the mafic phase an LREE/HREE ratio of about 

10. Both phases have small to moderate negative europium anomalies. Although the patterns for the main and mafic phases are 

parallel to that of the felsic phase of the Signal Granite, the felsic 

phase (sample 467B; appendix sample No. 46) has a much lower 

REE content (120 ppm) and a significantly less light REE enrichment [(La/Yb)CN=6] (fig. 25A). That rock has few minerals that 

contain those elements.
2000

1000 -

^ 100 =-

^ 10 -

syn-COLG WPG

VAG ORG

10 100 1000 2000

Y + Nb, IN PARTS PER MILLION

Figure 22. Rb vs. Y+Nb discriminant diagram (Pearce and others, 

1984) for Early Proterozoic granitic rocks of the Poachie region. ORG, 

ocean ridge granites; VAG, volcanic arc granites; WPG, within plate 

granites; COLG, syn-collision granites. Solid circle, coarse-grained 

granite (Xcg); open square, granite of Thorn Peak (Xt); solid square, 

gneissic tonalite (Xgt); diamond, granitic rock of uncertain corrrelation (YXg).

The mafic granodiorite (60-62 percent SiO2 ) chemically 

overlaps the mafic phase of the Signal. The mafic granodiorite is 

more Fe-rich and slightly more metaluminous than the mafic 

phase of the Signal and has a slightly lower Th/U ratio of 3.5. The 

mafic granodiorite has a somewhat smaller europium anomaly 

compared to the mafic and main phases of the Signal Granite, and 

it has rare-earth element concentrations of 504-550 ppm.

Granite of Olea Ranch

The granite of Olea Ranch has a range in SiO2 concentration of 66-73 percent, is alkali-calcic, and is normally potassic 

for its SiO2 concentrations (fig. 23A, B). It is weakly peraluminous and has somewhat Fe-rich to average FeO/FeO+MgO 

ratios (fig. 24A, B). Th/U ratios average 6.7. The granite of 

Olea Ranch shows moderate LREE/HREE enrichment patterns 

[(La/Yb)CN=10-13] and small to moderate negative europium 

anomalies (fig. 255). The largest negative europium anomaly is 

from the fine-grained granite, which is the youngest phase of the 

granite of Olea Ranch. The porphyritic phase is somewhat 

richer in FeTO3 and MgO and poorer in SiO2 than the coarsegrained granite phase.

Granite of Joshua Tree Parkway

The granite of Joshua Tree Parkway has SiO2 concentrations of 67-72 percent, is alkali-calcic, and has average K2O 

concentrations (fig. 23A, B}. It is mildly peraluminous (fig. 24A) 

and ranges from Mg-rich to Fe-rich (fig. 245) and has Th/U 

ratios of 7.4 (fig. 24D). It shows moderate to strong LREE/ 

HREE enrichment patterns [(La/Yb)CN=12] in the megacrystic 

phase and [(La/Yb)CN=52] in the fine-grained phase (fig. 25C). 

A positive europium anomaly in the megacrystic phase of the 

unit is consistent with feldspar accumulation in the magma that 

formed that phase, and a negative europium anomaly is

consistent with feldspar depletion in the fine-grained phase. 

Total rare-earth element concentration is 258 ppm in the megacrystic phase and 355 ppm in the fine-grained granite phase.

Granite of Grayback Mountain

The granite of Grayback Mountain is alkali-calcic and has 

average K2O concentrations for rock of its SiO2 content (71-73 

percent) (fig. 23A, B). It falls on the line between the metaluminous and peraluminous fields (fig. 24A) and is somewhat Mg-rich 

(fig. 245). Th/U ratios average 5.2 (fig. 24D). The granite of 

Grayback Mountain is depleted in Ba, Zr, and Sr compared to the 

Signal Granite, the granite of Olea Ranch, and the granite of 

Joshua Tree Parkway. The one sample of this unit for which REE 

analyses are available is moderately LREE enriched [(La/Yb) 

CN= 13], has a total rare-earth element concentration of 280 ppm, 

and shows a moderate negative europium anomaly (fig. 25C). 

The chondrite-normalized pattern for that sample resembles that 

of the megacrystic granite of Joshua Tree Parkway but has a 

greater negative europium anomaly.

Diabase

The diabases in the Poachie region are calc-alkalic to 

alkali-calcic and have normal K2O concentrations for mafic 

rock (fig. 23A, B), and are metaluminous (fig. 24A), Fe-rich (fig. 

245J, and Rb-poor (fig. 24Q. Th/U ratios are 3.9 for the samples for which we have data. They show almost no LREE 

enrichment [(La/Yb)CN=2.8^.8]. One has a small positive Eu 

anomaly that is consistent with plagioclase accumulation (fig. 

26). Total rare-earth element concentrations are 60-79 ppm. 

These diabase samples are only slightly more enriched in LREE 

compared to the most primitive tholeiitic basalt from northeastern Minnesota (Arth and Hanson, 1975). The relatively flat 

REE patterns suggest that garnet was not involved in the generation of the diabase. The difference in LREE abundances 

between the two samples can be accounted for by olivine±clinopyroxene±plagioclase fractionation or by different degrees of 

partial melting of mantle peridotite. Other potentially important 

interpretations cannot be made with the limited amount of data.

In a regional study of the chemistry of diabase in the southwestern United States, Hammond (1990) found differences in 

the composition of samples of diabase from Death Valley, the 

Colorado River trough, and central Arizona. On a P/Zr vs. Ba/ 

Zr diagram, the diabases fall into two groups, but the samples in 

each group come from more than one of the three areas just 

mentioned. One sample from the Poachie region falls into each 

of the two groups. The two groups were attributed to two separate but similar parental magmas forming the source for the diabase bodies. Sample suites from the Colorado River trough are 

generally tholeiitic, whereas those from Death Valley and central Arizona are generally alkalic. The Poachie region diabases 

are tholeiitic as indicated by their Fe-rich composition (fig. 

245), and they plot in the field of Colorado River trough diabases, which are tholeiitic (Hammond, 1990, fig. 2). They also 

fall within the field of Colorado River trough samples on several 

geochemical diagrams, including total alkali versus silica, TiO2 

vs. MgO/(MgO+FeO), SiO2 vs. MgO/(MgO+FeO), and TiO2 

vs. P2O5 , perhaps due to similarities in source regions in the 

upper mantle.

Geochemistry 33
Table 6. Major-oxide and trace-element concentrations in Middle Proterozoic Signal Granite and associated mafic granodiorite. 

[nd, not determined; LOT, loss on ignition; FeTO3, total Fe as FeoC^]

Sample No.

Field No.

Lab No.

Job No.

Mafic phase

41

NAP154

42

876

D-266702 D-266701

RV13 RV13

Main phase granite

43 44

1168 1164

D-278416 D-278415

SD65,WB47 SD65

45

49a

D-259525

RP40

Felsic phase

46

467b

D-266703

RV13

Mafic granodiorite

47

390

D-259523

RP40,WB47

48

1144

D-266704

RV13

Major-oxide composition, in weight percent1

SiO2

A12O3

FeTO3

MgO

CaO

Na2O

K2 6

TiO2

P2 05

MnO

LOI

Total

2FeO

2F

Nb

Rb

Sr

Zr

Y

Ba

Co

Cr

Cs

Hf

Sb

Ta

Zn

Sc

La

Ce

Pr

Nd

Sm

Eu

61.3

13.3

9.09

1.76

4.19

2.71

3.89

1.47

0.58

0.13

0.55

98.42

3.66

0.24

28

124

426

495

82

nd

nd

nd

nd

nd

nd

nd

nd

nd

107

228

28.9

111

20.8

3.68

64

13.7

7.18

1.29

3.64

2.91

4.08

1.21

0.5

0.1

0.52

98.61

3.76

0.25

31

183

287

444

86

nd

nd

nd

nd

nd

nd

nd

nd

nd

123

209

30.7

114

21.5

3.21

64.3 65.4

13.9 13.4

6.79 5.95

1.14 1.01

3.04 2.76

2.83 2.75

5.06 4.91

1.06 0.93

0.4 0.37

0.1 0.09

0.4 0.49

98.62 97.57

3.2 3.15

0.11 0.11

Trace-element concentration.

21 24

203 175

252 243

378 382

71 69

Trece-element concentration.

1280 nd

10.1 nd

7.4 nd

2 nd

12.3 nd

<0.100 nd

1.77 nd

96 nd

14.9 nd

94.9 111

199 232

25.5 27.4

87.5 95.9

18.8 13.3

2.48 2.62

69.1

14

3.17

0.62

2.26

2.91

5.24

0.54

0.19

0.05

1.33

98.08

1.74

0.17

74.6

13.1

1.14

0.18

1.05

2.54

6.07

0.16

0.05

0.02

0.46

98.91

0.37

0.04

59.6

12.7

10.7

1.69

4.76

2.52

3.76

1.76

1.07

0.16

0.63

98.72

6.08

0.18

61.7

12.7

9.73

1.42

3.93

2.5

3.88

1.61

0.96

0.13

1.04

98.56

4.52

0.16

in parts per million3

24

221

240

300

61

11

248

52

126

28

17

100

339

595

85

22

107

338

567

77

in parts per million4

nd

nd

nd

nd

nd

nd

nd

nd

nd

126

241

25.1

89.3

10

2.39

nd

nd

nd

nd

nd

nd

nd

nd

nd

23.7

45.6

5.6

21.1

5

1.06

1500

17.4

<12.20

1.9

15.5

0.15

1.41

150

21.6

96.8

201

26.1

98.3

21.4

4.25

nd

nd

nd

nd

nd

nd

nd

nd

nd

105

219

29.7

115

22.2

4.92

Comparison of Middle Proterozoic Plutonic Rocks 

with Early Proterozoic and Other Middle Proterozoic 

Plutonic Rocks in Region

As mentioned previously, the Middle Proterozoic plutonic 

rocks are more potassic than the Early Proterozoic rocks, 

although their alkalinity is similar to that of the Early Proterozoic 

rocks at similar SiO2 contents. However, the concentrations of 

some minor elements differ.

Zirconium concentrations increase with decreasing SiO2 

within the 60-75 percent range of SiO2 concentrations of the 

Middle Proterozoic granitic rocks, as they do in the Early

34 Poachie Region, West-Central Arizona—East Boundary,

Proterozoic granite of Thorn Peak. The Middle Proterozoic rocks 

have less Sr and more Rb than the Early Proterozoic rocks (fig. 

24C).

Overall the Middle Proterozoic rocks have higher total REE 

concentrations but lower LREE/HREE ratios than do the Early 

Proterozoic rocks (figs. 25 and 21). The Middle Proterozoic rocks 

give patterns with well-developed negative europium anomalies, 

indicating that differentiation of plagioclase played a greater role 

in their genesis than it did in the Early Proterozoic rocks.

The Middle Proterozoic rocks have higher Th and U concentrations and Th/U ratios than the Early Proterozoic rocks (figs. 

24D and 20D). U/Th ratios average 6.4. Our data show a

Mojave Crustal Province
Table 6—Continued. Major-oxide and trace-element concentrations in Middle Proterozoic Signal Granite and associated mafic granodiorite.

Sample No.

Field No.

Lab No.

Job No.

Mafic phase

41

NAP154

42

876

D-266702 D-266701

RV13 RV13

Main phase granite

43

1168

D-278416

SD65,WB47

44

1164

D-278415

SD65

45

49a

D-259525

RP40

Felsic phase

46

467b

D-266703

RV13

Mafic granodiorite

47

390

D-259523

RP40,WB47

48

1144

D-266704

RV13

Trace-element concentration, in parts per million4 — Continued

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

As

5Th

5U

17.4

2.30

14.4

2.74

7.3

1.00

7.00

0.94

nd

12

3.26

18.2

2.40

15.6

3.00

8.1

1.2

8.30

1.11

nd

32.2

6.53

13.5

2.22

13.3

2.50

6.93

1.03

6.5

0.91

4.2

22

3.3

13.7

2.23

13.6

2.62

6.96

1.04

6.24

.82

nd

37

3.38

12.0

2.10

10

1.90

4.8

0.68

4.52

.64

nd

43

4.23

5.0

.80

4.9

.99

2.8

.41

2.7

.35

nd

52.1

7.05

20.2

2.48

16.0

3.00

7.6

.99

6.5

0.926

<1.60

7.05

1.25

20.2

3.00

16.1

3.05

8.6

1.1

6.8

1.01

nd

3.8

2.49

Major oxides determined by wavelength dispersive X-ray fluorescence: I.E. Taggart, A.J. Bartel, K. Stewart, E. Robb, analysts. 

"FeO determined by potentiometric titration and F by ion-selective electrode potentiometry: E.L. Brandt, J. Starkey, S. Roof, G. Mason, J.H. Christie, 

analysts.

- Trace elements determined by energy dispersive X-ray fluorescence: R.R. Larson, R. Johnson, S. Fleming, J. Evans, analysts.

4Rare earths determined by inductively coupled plasma-mass spectrometry: J.G. Crock, P.H. Briggs, D. Frey, A. Meier, analysts. Rare earths and other trace 

elements in samples 1168 and 390 determined by instrumental neutron activation analysis: G.A. Wandless, analyst. 

5Th and U determined by delayed neutron counting: R.B. Vaughn, D.M. McKown, analysts.

westward increase from an average of 5.2 for the granites of 

Grayback Mountain and Joshua Tree Parkway to 7.3 for the Signal Granite (tables 6 and 7). Th/U ratios of 1.4 Ga granitic rocks 

averaged by plutons are 12.6 in the Mojave province in southeastern California and 6.7 in the Central Arizona province, east of the 

Poachie region (Anderson and Bender, 1989). Thus the average 

Th/U ratio of 1.4 Ga rocks in the Poachie region closely resembles that of 1.4 Ga rocks in the Central Arizona province.

The high Th and U concentrations in the 1,400 Ma rocks in 

the Poachie region are well shown by the distribution of anomalies on aerorad maps produced during the NURE (National Uranium Resource Evaluation) program. Uranium deposits in the 

Date Creek basin south of the Poachie Range are in carbonaceous tuffaceous siltstone and mudstone and were deposited in 

early Miocene inter-fan lakes (Otton, 1985). Streams draining 

into the basin before the formation of the Poachie Range 13 Ma 

or later probably were carrying detritus from the Signal Granite 

and the granite of Olea Ranch. Altered and silicified ash in the 

lacustrine rocks is also enriched in uranium, but whether the 

volcanic rocks originally contained anomalous concentrations 

of uranium or whether uranium was added from another source 

during alteration is not known (Otton, 1985). Lower Miocene 

silicic volcanic rocks from the Poachie region have low U (1-3 

ppm) and Th (4-10 ppm) concentrations (Bryant, unpub. data, 

1985-87). Certainly the Middle Proterozoic plutonic rocks 

could have contributed to the uranium deposits in the Date 

Creek basin through leaching of uranium from those rocks by 

ground water and by leaching of uranium from detritus derived 

from them by surface water and, after deposition of that detritus 

in the basin, by ground water.

In a regional overview of the chemistry of the Middle Proterozoic rocks in the southwestern United States, Anderson (1989)

defined a boundary between metaluminous rocks to the west and 

peraluminous rocks to the east bisecting the Poachie Range. The 

Signal Granite, except for the leucocratic phase, and the mafic 

granodiorite are definitely metaluminous. The granite of Olea 

Ranch, on the other hand, is slightly peraluminous, the finegrained phase of the granite of Joshua Tree Parkway is weakly 

peraluminous, and the coarse-grained granite and the porphyritic 

granite of Grayback Mountain are on the boundary between the 

metaluminous and peraluminous fields (table 7; fig. 24A). The 

change in chemistry of these Middle Proterozoic plutonic rocks 

from metaluminous on the west to weakly peraluminous to neutral 

on the east may be related to a change in composition of the underlying crust from which they probably were at least partly derived, 

or a change in the level in the crust which was melted or partly 

melted to produce the granitic magmas (Anderson, 1989). Many 

of the Early Proterozoic plutonic rocks are peraluminous, and 

overall for a given SiO2 concentration the Early Proterozoic plutonic rocks are more peraluminous or less metaluminous than the 

Middle Proterozoic rocks (figs. 20A, 24A). The Early Proterozoic 

peraluminous rocks generally have pelitic schist and gneiss country rock or (and) inclusions. They also have 207Pb/204Pb to 206Pb/ 

204Pb ratios like those of the pelitic schist (table 8, appendix sample Nos. 1 and 2 compared to Nos. 35 and 38). Those ratios resemble those to the west in the main area of the Mojave crustal 

province (Wooden and Miller, 1990; Wooden and DeWitt, 1991).

Middle Proterozoic granites show more of a within-plate 

tectonic signature than the Early Proterozoic granites (figs. 27, 

22). All samples of the Signal Granite and associated mafic granodiorite and of the granite of Olea Ranch plot in the within-plate 

granite field. The granites of Joshua Tree Parkway and Grayback 

Mountain show more of a volcanic arc geochemical signature.

Geochemistry 35
Table 7. Major-oxide and trace-element concentrations in the Middle Proterozoic granites of Olea Ranch, of Joshua Tree Parkway, and of 

Grayback Mountain, and diabase.

[nd, not determined; LOI, loss on ignition; FeT(>3, total Fe as Fe2C>3]

Granite of Olea Ranch

Porphyritic granite

Appendix

No.

Field No.

Lab No.

Job No.

49

666

D363783

UD76

50

752

D259528

RP40

Coarse-grained

granite

51 52

753 M72

D- D259529 363782

RP40 UD76

WB47

Finegrained

granite

53

1160

D266705

RV13

SC97

Granite of Joshua

Tree Parkway

Mega- Finecrystic grained

granite granite

54 55

A-151a A-151b

D- D327699 327700

TG29 TG29

Granite of Grayback

Mountain

Porphyritic granite

56

A-107b

D367765

UD76

Coarsegrained

granite

57

A-153

D327702

TG29

WB47

Diabase

60

1052

D266700

RV13

SC97

61

A-91

D568683

WB23

62

G-38

D568684

WB23

63

852

D266699

RV13

SC97

Major-oxide composition, in weight percent1

SiO2

A1203

FeTO3

MgO

CaO

Na2O

K2O

TiO2

P2O5

MnO

LOI

Total

TeO

¥

66.1

14.6

5.35

1.36

2.27

2.65

5.01

.76

.35

.09

.94

98.54

nd

nd

68.2

14.3

4.44

1.18

2.49

2.74

4.06

.66

.25

.07

.71

98.39

2.45

.16

69.2 69.6

13.7 13.7

3.75 3.82

.78 .81

2.46 2.13

2.91 2.87

4.55 4.68

.64 57

.29 .24

.07 .07

.88 .41

73.0

13.5

1.79

.28

1.2

2.98

5.55

.22

.05

.04

.75

98.35 98.49 98.61

1.77 nd

.15 nd

.77

.05

67.3 72.1

15.7 13.9

3.05 1.98

.53 .43

2.68 1.31

3.19 2.73

5.4 6.04

.50 .23

.19 .08

.06 .03

.54 .52

98.6 98.83

1.46 1.01

.03 .01

71.4

135

2.68

.85

1.77

2.88

619

.28

.08

.05

.56

98.68

nd

nd

73.3

13.2

1.78

.38

1.65

2.91

5.03

.25

.10

.03

.56

98.63

.94

.08

46.3

17.1

12.5

6.97

9.73

2.67

.67

1.83

.58

.19

1.51

98.54

nd

nd

48.6

16.8

13.7

6.83

9.54

2.73

.66

1.29

.24

.19

<.01

100.54

nd

nd

49.1

16.5

12.5

6.75

9.48

2.82

.85

1.19

.26

.18

.11

99.74

nd

nd

49.1

15.6

13.0

7.13

10.9

2.26

.51

1.22

.17

.19

.39

100.08

nd

nd

Trace-element concentration, in parts per million3

Nb

Rb

Sr

Zr

Y

Ba

Ce

La

Cu

Ni

Zn

24

286

239

311

49

1270

209

112

16

<5

75

25

259

229

364

62

nd

nd

nd

nd

nd

nd

30 20

270 218

294 243

265 330

73 212

nd 1110

nd 207

nd 96

nd 4

nd <5

nd 62

34

412

95

166

59

nd

nd

nd

nd

nd

nd

16 15

111 162

332 231

363 213

34 17

nd nd

nd nd

nd nd

nd nd

nd nd

nd nd

16

207

133

176

30

636

131

64

10

6

52

16

170

166

156

38

nd

nd

nd

nd

nd

nd

10

30

437

75

21

nd

nd

nd

nd

nd

nd

<10

<10

355

98

18

255

<30

<30

120

128

76

<10

10

320

112

16

320

<30

<30

86

142

58

<10

15

178

90

22

nd

nd

nd

nd

nd

nd

Trace-element concentration, in parts per million4

Ba

Co

Ni

Cr

Cs

Hf

Sb

Ta

Zn

Sc

La

Ce

Pr

Nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

102

204

23.3

85.4

776 nd

5.25 nd

<17 nd

2.1 nd

11.4 nd

9.06 nd

<0.220 nd

3.80 nd

64 nd

9.12 nd

102 nd

204 nd

22.6 nd

83.7 nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

88.2

181

19.0

64.2

nd nd

nd nd

nd nd

nd nd

nd nd

nd nd

nd nd

nd nd

nd nd

nd nd

61 92

110 170

12.0 16.0

45 56

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

642

2.66

>12

2.9

7.74

4.66

0.13

1.60

32

2.83

63

120

13

48

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

11.7

27.7

3.2

17.2

260

56.1

160

105

0.20

2.46

0.11

0.34

93

24.8

10.7

24.3

nd

14

330

51.9

180

62.7

1.4

2.68

<.09

0.38

88

25.2

13.3

28.8

nd

17

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

7.5

20.2

2.3

12.7

36 Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province
Table 7—Continued. Major-oxide and trace-element concentrations in the Middle Proterozoic granites of Olea Ranch, of Joshua Tree Parkway, 

and of Grayback Mountain and diabase.

Granite of Olea Ranch

Porphyritic granite

Appendix

No.

Field No.

Lab No.

Job No.

49

666

D363783

UD76

50

752

D259528

RP40

Coarse-grained

granite

51 52

753 M72

D- D259529 363782

RP40 UD76

WB47

Finegrained

granite

53

1160

D266705

RV13

SC97

Granite of Joshua

Tree Parkway

Megacrystic

granite

54

A-151a

D327699

TG29

Finegrained

granite

55

A-151b

D327700

TG29

Granite of Grayback

Mountain

Porphyrit- Coarseic granite grained

granite

56 57

A-107b A-153

D- D367765 327702

UD76 TG29

WB47

Diabase

60

1052

D266700

RV13

SC97

61

A-91

D568683

WB23

62

G-38

D568684

WB23

63

852

D266699

RV13

SC97

Trace-element concentration, in parts per million4 — Continued

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

5Th

5U

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

31.60

4.13

1.7

2.31

12.3

2.20

11.0

1.99

5.4

.76

5.38

.76

30.4

3.61

10.6 nd

2.34 nd

12.4 nd

2.3 nd

11.0 nd

2.18 nd

6.0 nd

0.86 nd

6.04 nd

0.82 nd

36.00 25.20

6.02 6.38

11.3

.96

9.1

1.40

8.1

1.61

4.5

.76

5.40

.79

75.80

11.30

7.4

2.90

5.9

.96

5.2

1.0

3.1

.44

3.30

nd

9.94

1.84

7.3

1.20

4.7

.76

3.3

.60

1.7

.24

1.16

nd

29.50

3.07

nd 9.2

nd 1.2

nd 7.9

nd 1.4

nd 7.6

nd 1.4

nd 4.0

nd 0.47

nd 3.3

nd 0.41

25.40 18.90

4.35 4.04

4.1

1.79

4.3

.5

3.6

.67

1.8

.27

1.6

.21

<1.9

<.22

4.09

1.26

nd

.64

nd

nd

nd

nd

2.06

.29

.67

.25

4.34

1.40

nd

.66

nd

nd

nd

nd

2.2

.29

.86

.21

3.3

1.26

4.1

.5

3.6

.68

1.9

.26

1.8

.24

<2.0

.32

Major oxides determined by wavelength dispersive X-ray fluorescence: D.F Siems, I.E. Taggart, A.J. Bartel, K. Stewart, analysts. 

FeO determined by potentiometric titration and F by ion-selective potentiometry: C. Papp, J. Sharkey, E. Brandt, S. Roof, J.H. Christie, analysts. 

Trace elements determined by energy dispersive X-ray fluorescence: J.R. Evans, R.R. Larson, R. Johnson, S. Fleming, analysts.

Rare earths determined by inductively coupled plasma-mass spectrometry: J.G. Crock, K. Kennedy, G. Riddle, analysts; sample Nos. 51, 57, 61, and 62 rare 

earths and other minor elements by instrumental neutron activation analysis: G.A. Wandless, analyst.

5Th and U determined by delayed neutron activation except for sample Nos. 61 and 62: R.J. Knight, R.B. Vaughn, D.M. McKown, analysts.

The general similarity in the chemical characteristics of the 

1.7 Ga and 1.4 Ga plutonic suites in the Mojave crustal province 

has been discussed by Anderson and Bender (1989) and Anderson and others (1993), and comparison of figures 19 and 23, 20 

and 24, 21 and 25 shows that those similarities exist in the 

Poachie region. In both suites, melting of similar crustal material 

was probably an important process in magma production. For 

instance, the 1.4 Ga granite of Olea Ranch and the 1.7 Ga granite 

of Thorn Peak are adjacent to each other, and they have many 

chemical similarities: high Rb, within-plate classification on the 

discriminant diagram, normal K, and both peraluminous and 

somewhat enriched in Mg. One difference is that the granite of 

Olea Ranch is more U- and Th-rich than the granite of Thorn 

Peak, and the granite of Thorn Peak is calc-alkalic, whereas the 

granite of Olea Ranch is alkali-calcic.

The Parker Dam granite and the Bowmans Wash quartz 

monzodiorite in the upper plate rocks above the Whipple Mountains detachment fault east of the Whipple Mountains (fig. 1) near 

the Colorado River, about 60 km west of the Signal Granite in the 

Poachie region, resemble the Signal Granite and the mafic granodiorite, respectively. However, the Parker Dam is, and the Bowmans Wash may be, slightly younger than the Signal Granite; and 

the Parker Dam granite is a few million years younger than the

Bowmans Wash quartz monzodiorite (Anderson and Bender, 

1989). The Parker Dam does not have as wide a range of silica 

content as the Signal Granite. Silica for the Parker Dam (Anderson and Bender, 1989) ranges from 64.6 to 69.9 weight percent 

SiO2, and the rocks have a color index ranging from 2 to 18. Silica for the Signal Granite ranges from 61.3 to 74.6 percent, and 

the color index ranges from 1 to 28. Taken together, the Signal 

and mafic granodiorite compared to the Parker Dam and Bowmans Wash are remarkably similar in chemical composition, 

except that the Parker Dam granite has a higher potassium concentration at high silica concentrations (fig. 28A) and the Th/U 

ratios of the Parker Dam and Bowmans Wash are greater than 

those of the Signal because they contain much less uranium (fig. 

285). The average Th/U is about 16 for the Parker Dam and 28 

for Bowmans Wash (Anderson and Bender, 1989) compared to 

9.2 for the main phase of the Signal Granite, which has the same 

range of silica content as the Parker Dam granite, and 3.5 for the 

mafic granodiorite. The Th/U ratio in the Parker Dam and Bowmans Wash is higher than the average for 1.4 Ga granitic rocks in 

the Mojave crustal province west of the Poachie region, whereas 

the Th/U ratio in the Signal Granite and other 1.4 Ga plutons in 

the Poachie region is similar to that of 1.4 Ga plutons in the Central Arizona province (Anderson and Bender, 1989).

Geochemistry 37
10

0

n x \

o

n \

40

A

45 50 55 60 65 

S\O2,\N WEIGHT PERCENT

70 75 80

70 -

60

50

/ ' ' '

/'//oc/V '

/ / n ( _/ /

very sodic

sodic

average

-

( x

> ®

o

X y

potassic / very potassic

/

/\_____________

B

0.2 0.4 0.6 

K2O / Na2O + K2O

0.8

Figure 23. Silica vs. alkalis diagrams for Middle Proterozoic granitic rocks and diabase. Fields of Early Proterozoic igneous rocks from 

figure 19 outlined. ASi02 vs. Na20+K2 0. Fields of alkalinity from Anderson (1983) and DeWitt (1989). B, Si02 vs. K20/Na20+K20. Fields 

from Fridrich and others (1998). Open circle, Signal Granite (Ys), mafic phase; half-filled circle, main phase; x, felsic phase; solid circle, 

mafic granodiorite (Ygd); open square, granite of Olea Ranch (Yo); solid square, granite of Joshua Tree Parkway (Yj); open diamond, granite of Grayback Mountain (Yb); solid diamond, diabase.

38 Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province
^

§0.8-

<

0.6-

0.4

4

70

i—

LU

DC 

LU 

Q_

£ 60

Ui

z

(N 

O

c/5

50

40

^/

n

_ _ _ _ _ _ _ — /__ _ — _ »_ P_

^*x^ ***^

/" X^ 0» °

»n / •

* y

ii i i i i

0 50 60 70

^ SiO2 , IN WEIGHT PERCENT

—

"

U-" /D

) '-yc

/ y •

( 1 **•

J

\ /

/ '

./ / '

Mg-rich *^

' si

^< >

^- ^

Fe-rich

~l i i i i 

0.4 0.6 0.8

B (FeTOg .8998)/(FeTO3 .8998 + MgO)

•jx.

O

tju

400

^ 350

o 

^ 300 ^

cc 

£ 250

CO

!£ 200

Q.

^ 150

,0

100

1 50

1 1 1 1 1 1 1 1 1 1 1 1 1 1

n

r^ N

_\ ,

\ n \

\ n n

V «, ^- ———— _^

O ®. \

~ f \

_ . • 1 _

^ y

i *i V i i i 'i i i i i i i i

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 150

(

/

f

12 r

10

— 8

QC

a! 6

COi—QC

^ 4

D

2

p br, IN PAKTS PbK MILLIUN

l 1 1 ' / ' ' !/

/

/ / ^ /

' -""o /£ 

^

/n ^

/• // ^^

0 <v ————————————————————————————————————— i i i i i i — 1 -- — — 

0 10 20 30 40 50 60 70 8

D Th, IN PARTS PER MILLION

700

600

rTM» cnn | ±± 3UU

DC 400

LU 

Q_

CO

fe 300

-200

N

100

n

i I I I i I i

~~ X4"^ / ~

/ 66X^ X

D 6 _

/ " \

— / / ~^" —— - ^" N. —

/ / \ ?> \

- /__/ V) -

1 1 1 1 1 1 1 40 45 50 55 60 65 70 

E SiO2, IN WEIGHT PERCENT

75 80

Figure 24. Chemical diagrams for Middle Proterozoic granitic rocks and diabase. Fields of Early Proterozoic rocks from figure 20 outlined. A, 

Si02 vs. A/CNK. B, Si02 vs. Fe/Fe+Mg. Mg-rich-Fe-rich field boundary from Anderson (1983). C,Srvs.Rb. 0,Th vs. U (diabase not shown). E, 

Si02 vs. Zr (diabase not shown). Open circle, Signal Granite (Ys), mafic phase; half-filled circle, main phase; x, felsic phase; solid circle, mafic 

granodiorite (Ygd); open square, granite of Olea Ranch (Yo); solid square, granite of Joshua Tree Parkway (Yj); open diamond, granite of Grayback Mountain (Yb); solid diamond, diabase.

Geochemistry 39
1000

100

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

1000

100

10

EXPLANATION 

O 41 A 45 

• 42 

D 43

44

• 46 

X 47 

+ 48

B

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

EXPLANATION 

O 50 

• 51 

x 52

1000p

100

10

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

EXPLANATION 

O 54

• 55

• 57

Figure 25. Chondrite-normalized rare-earth contents of Middle Proterozoic granitic rocks. A, Signal Granite and related mafic granodiorite; B, granite of Olea Ranch; C, granite of Joshua Tree Parkway and granite of Grayback Mountain. Numbers by symbols referto appendix sample numbers.

40 Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province
1000c

£2100

10

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

EXPLANATION 

O 60 

D 61 

• 62 

O 63

Figure 26. Chondrite-normalized rare-earth contents of diabase.

A

AA 

A

40

A

50 60 70 

SiO2, IN WEIGHT PERCENT

80

10 100

Y + Nb, IN PARTS PER MILLION

1000 2000

Figure 27. Rb vs. Y+Nb discriminant diagram (Pearce and others, 

1984) for Middle Proterozoic granitic rocks of the Poachie region. 

ORG, ocean ridge granites; VAG, volcanic arc granites; WPG, withinplate granites; synCOLG, syn-collision granites. Distribution of Early 

Proterozoic plutonic rocks (fig. 22) shown by dashed outline. Open 

circle, Signal Granite, mafic phase; half-filled circle, main phase; x, 

felsic phase; solid circle, mafic granodiorite; open square, granite of 

Olea Ranch; solid square, granite of Joshua Tree Parkway; open diamond, granite of Grayback Mountain.

100

80

60

•40

20

A

A

•A

0

B

4 6 8 

U, IN PARTS PER MILLION

10

EXPLANATION

A Parker Dam granite and Bowmans Wash quartz monzodiorite

0 Signal Granite and mafic granodiorite

Figure 28. Chemical diagrams comparing the Signal Granite, including the mafic granodiorite, with the granite of Parker Dam and 

the quartz monzodiorite of Bowmans Wash. Data forthe Parker Dam 

granite and the Bowmans Wash quartz monzodiorite from Anderson 

and Bender (1989). /4,Si02 vs. K2 0. 5,Thvs. U.

Geochemistry 41
Other Proterozoic Plutonic Rocks

Granitic rocks of uncertain correlation are alkali-calcic to 

calc-akalic, have average K and Fe concentrations, are peraluminous to weakly metaluminous, and have Th/U ratios averaging 

5.4 (table 5; figs. 19A, B, 20A, B, D). One sample (A-152; appendix sample No. 40) has moderate LREE enrichment [(La/Yb) 

CN=15.8] and has total rare-earth element concentration of 452 

ppm and a small negative europium anomaly. We interpret these 

rocks to be of Middle Proterozoic age because of the high rareearth element concentration and negative europium anomaly (fig. 

2 ID) in the sample for which we have those data. In many 

respects they resemble the Early Proterozoic granite of Thorn 

Peak, but the Thorn Peak rocks have less LREE enrichment and 

lower total rare-earth element concentrations.

Whole-Rock and Feldspar Pb-lsotopic 

Compositions

Whole-rock and feldspar Pb-isotopic analyses of rocks from 

the Poachie region were made as part of a regional study of Proterozoic Pb-isotopic crustal provinces (Wooden and Miller, 1990; 

Wooden and DeWitt, 1991, table 2; unpublished data by J.L. 

Wooden; table 8, fig. 29).

On a 207Pb/204Pb vs. 206Pb/204Pb diagram, whole-rock samples from rocks of the Mojave and Central Arizona crustal provinces fall on two distinct lines (Wooden and Miller, 1990; 

Wooden and DeWitt, 1991). In order to better illustrate the differences between 207Pb/204Pb ratios of different rocks, we normalize the data in reference to the analytical results from an ore 

lead from the United Verde mine at Jerome in the Central Arizona 

province (Wooden and DeWitt, 1991). A model 1.7 Ga 207Pb/

12

NORTHWEST SOUTHEAST

204T 206Du/204 Pb vs. zu°Pb/ wPb isochron passing through the data from that 

sample was calculated. For any 206Pb/204Pb ratio measured for a 

sample, a 207Pb/204Pb ratio can be calculated that falls on the 

model isochron. The 206Pb/204Pb measured for the sample is 

compared to the calculated value by subtracting the model value 

from the sample value and multiplying by 100. This value is 

expressed as A 207Pb/204Pb. Analytical error in this derived value 

is ±1.5 units, so small differences between samples are not 

significant.

The high 207Pb/204Pb relative to 206Pb/204Pb and high but 

variable Th/U ratios obtained from Early Proterozoic plutonic 

rocks of the Poachie region are much more similar to those from 

the Mojave crustal province than those from the Central Arizona 

crustal province. However, both those parameters are also more 

variable than those from the Mojave province (fig. 29A). The 

Poachie region apparently lies in the Mojave crustal province but 

near its eastern margin where magmas had some variable, but 

usually minor, input from central Arizona mantle and (or) aesthenosphere. Single crystal zircon studies of samples from the 

gneissic tonalite and similar studies of the Butte Falls Tuff, a unit 

in the Bagdad metamorphic belt north of the Poachie region, indicate that the source region for the magmas which crystallized to 

form those units was Mojave crust containing some Archean

10 - 

8-

3

< 6

J

- 4 -

] 2-

0

-2 H

-4

,o o *> ^ 

o „ o o ,

-

A 

A A

A

A X**^ i^iA^T

. AA A A 

A \

28 NORTHWEST

24-

20

16-

12-

4-

SOUTHEAST

00 i 

> O «

00 <b • 

o o° •

B

EXPLANATION

d Cerbat Mountains (Mojave province)

O Boundary zone

• Poachie region

-$T Galenas, Bagdad area 

A Central Arizona province

Figure 29. A 207Pb/204Pb values and calculated Th/U ratios of Early Proterozoic rocks of the Poachie region in a data array across the 

Mojave-Central Arizona Pb-isotopic crustal boundary plotted 

against a curved transect from the Cerbat Mountains in the Mojave 

province in the northwest to the Bradshaw Mountains in the Central Arizona province in the southeast. No distance scale. Data 

from the Poachie region in table 8. AA 207Pb/204Pb. See text for 

explanation. B, Th/U calculated from Pb-isotopic analysis.

zircon (Wooden and others, 1994). Differences in the lithospheric mantle beneath the Mojave and Central Arizona crustal 

provinces are suggested by a regional Pb, Sr, and Nd study of 

1.15 Ga diabase bodies (Hammond and Wooden, 1990). However, none of the samples in their study come from in or near the 

Poachie region so that we might relate their data to our Pb-isotopic data on the granitic rocks.

42 Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province
TableS. Pb-isotopic compositions of whole rocks and feldspars from the Poachie region.

[U/Pb, Th/Pb, and Th/U calculated using 206/204, 207/204, 208/204 values of 15.8, 15.31, 35.4, and 16.5, 15.42, 36.0 for 1.7 and 1.4 Ga samples respectively. 

A 207/204 calculated for a 1.71 Ga Pb-Pb isochron through the Jerome, Ariz., galena (See text; Wooden and DeWitt, 1991)]

| Measured

Appendix 

sample No. Field sample No.

206pb/ 

204pb

207 Pb/

204pb

208 pb/

204pb

Calculated

238U/ 

204pb

235u/

204pb

232Th/

204p b

Th/ 

U

A

207Pb/

204pb

Galena

Bagdad 

Bruce mine 1

15.818 

15.805

15.336 

15.318

35.461 

35.422

0.1 

0.0

0.8 

0.2

0.7 

0.2

11.7 

15.2

5.6 

4.0

1.7-Ga rock and feldspar (F) samples

1

2

8

8

15

15

16

16

22

22

28

28

29

29

30

30

35

35

38

38

1154

1166

1161

1161(F)

750(JW-84-ll)

750(F)

751(JW-84-12)

751(F)

749(JW-84-9)

749(F)

B-95

B-95(F)

W-325

325(F)

317

317(F)

1158

1158(F)

1163(JW-85-63)

1163(F)

17.797

16.884

25.402

20.214

17.968

16.737

17.126

16.342

18.040

16.292

23.219

21.006

24.899

20.469

19.372

17.868

19.105

17.153

19.231

16.974

15.568

15.496

16.330

15.817

15.51

15.437

15.468

15.386

15.553

15.403

16.094

15.93

16.280

15.903

15.715

15.595

15.689

15.502

15.710

15.494

35.658

36.787

43.300

37.719

36.854

35.891

36.785

35.808

39.392

35.912

39.597

36.997

38.381

36.643

40.563

37.737

36.855

35.895

36.306

35.621

6.5

3.5

31.2

14.3

7.0

3.0

4.3

1.8

7.3

1.6

24.1

16.9

29.6

15.2

11.6

6.7

10.7

4.4

11.1

3.8

7.9

5.7

31.3

15.6

7.4

3.9

4.8

2.3

7.5

2.9

24.0

19.0

29.8

18.2

12.4

8.7

11.6

5.9

12.3

5.6

36.5

15.5

88.4

25.9

16.3

5.5

15.5

4.6

44.7

5.7

47.0

17.9

33.4

13.9

57.8

26.2

16.3

5.5

10.1

2.5

5.6

4.4

2.8

1.8

2.3

1.8

3.6

2.6

6.1

3.6

1.9

1.1

1.1

0.9

5.0

3.9

1.5

1.3

0.9

0.6

8.2

10.5

4.9

7.8

4.7

6.1

5.2

5.2

4.1

7.4

4.1

10.8

5.1

13.7

6.4

10.1

6.6

8.3

7.4

9.4

1.4-Ga rock and feldspar (F) samples

43

43

44

47

47

50

50

51

51

54

57

58

58

59

59

1168

1168(F)

1164F(JW-85-64)

390(JW-84-10)

390(F)

752(JW-84-13)

752(F)

753(JW-84-15)

753(F)

A-151a(F)

A-153(F)

W-295

W-295(F)

W-322

W-322(F)

18.413

16.606

16.527

17.146

16.642

19.117

16.841

21.079

16.907

17.079

16.677

23.200

18.290

19.628

17.588

15.613

15.450

15.428

15.467

15.449

15.678

15.475

15.845

15.481

15.472

15.417

16.015

15.597

15.696

15.524

40.771

37.392

36.962

37.358

36.517

39.427

36.105

41.041

36.260

36.586

36.032

42.490

37.227

42.329

37.841

7.8

0.4

0.1

2.6

0.6

10.6

1.4

18.6

1.7

2.4

0.7

27.2

7.3

12.7

4.4

8.7

1.4

0.4

2.1

1.3

11.7

2.5

19.2

2.8

2.3

0.1

26.9

8.0

12.5

4.7

65.6

19.1

13.2

18.7

7.1

47.1

1.4

69.3

3.6

8.1

0.4

89.2

16.9

87.0

25.3

8.4

44.5

120.6

7.1

12.3

4.4

1.0

3.7

2.2

3.4

0.6

3.3

2.3

6.9

5.7

6.2

8.8

7.4

4.9

8.3

5.4

8.8

1.6

8.8

6.0

4.7

3.6

5.9

1.8

5.9

J Stacey and others (1976). Massive sulfide deposit in the Bagdad metamorphic belt 5 km north of the Poachie region.

Summary and Interpretation

The Poachie region consists of Early and Middle Proterozoic plutonic rocks in about equal amounts. Plutons are separated 

by screens of, and contain inclusions of, amphibolite-facies metamorphosed sedimentary and volcanic rock. No basement to the 

metamorphic sequence has been identified, but inherited zircons 

in some of the metamorphic and plutonic rocks indicate that earliest Late Archean and Proterozoic crustal material forms some 

part of the lower crust.

Metamorphic rocks are not well dated but are probably 1.74 

to 1.72 Ga. The oldest plutonic rocks may be of similar age, but 

most of them are 1.71-1.68 Ga. Deformation and metamorphism 

probably reached a peak about 1.71-1.70 Ga but continued at 

least locally to <1.69 Ga. Local faulting and formation of mylonite zones occurred at least as late as 1.68 Ga and at least locally 

as late as -1.4 Ga. The main deformation, metamorphism, and 

plutonism occurred at about the same time as the Ivanpah orogeny in the Mojave province in southeastern California (Wooden 

and Miller, 1990) and destroyed evidence of older crustal rocks at

Summary and Interpretation 43
levels now exposed in the region. Similar metamorphism and 

plutonism were associated with the Ivanpah orogeny in southeastern California.

Early Proterozoic mafic metavolcanic rocks are more primitive than the gabbros emplaced during the regional metamorphism. They are more Fe-rich and contain less Sr. The gabbros 

show more LREE/HREE enrichment and have higher Th/U ratios 

than the metavolcanic rocks. These metavolcanic rocks may represent contributions from the aesthenosphere and (or) Central 

Arizona province mantle to volcanic arcs built on Mojave province lithosphere.

Early Proterozoic plutonic rocks range from gabbro to granite and from calcic to alkalic and show metaluminous to peraluminous signatures. No evidence of changing composition with 

time has been detected, except our data do indicate that the gabbros are older than all the other granitic rocks. The peraluminous 

rocks have higher whole-rock 207Pb/204Pb relative to 206Pb/204Pb 

ratios than the metaluminous plutonic rocks, and those ratios are 

similar to ones from the metasedimentary rocks. Pb-isotopic 

ratios indicate that the metasedimentary rocks were derived from 

crust having the Mojave Pb-isotopic signature. The peraluminous chemistry of some of the Early Proterozoic plutonic rocks 

appears to be related, at least in part, to contamination by aluminous metasedimentary rocks. For both metaluminous and peraluminous rock the Pb-isotopic compositions range from 

transitional to about equal to those in the Mojave crustal province. Variable Pb-isotopic ratios in Early Proterozoic whole-rock 

samples and feldspars indicate that these rocks were derived in 

various degrees from a combination of Mojave crust and a 

younger, central Arizona, mantle component.

Large volumes of alkali-calcic magma invaded the crust in 

Middle Proterozoic time, about 1.42-1.41 Ga. The mostly metaluminous Signal Granite was emplaced 1,410 Ma. Farther east 

the granites of Olea Ranch crystallized at 1,418 Ma and were followed about 1,415 Ma by the granites of Joshua Tree Parkway 

and Grayback Mountain. Middle Proterozoic granites east of the 

Signal Granite are weakly peraluminous to weakly metaluminous. These rocks may have originated in part by crustal anatexis 

involving Early Proterozoic peraluminous material, which crops 

out extensively in the region. Emplacement and cooling of these 

rocks were locally accompanied by movement along shear zones.

Whole-rock Pb-isotopic studies indicate that the Poachie 

region lies at the east edge of the Mojave crustal province where 

some magmas may have had input from subducted Central Arizona mantle or from the aesthenosphere (Wooden and DeWitt, 

1991; Bryant and others, 1994). Moreover, chemical similarities 

between the Early and Middle Proterozoic granitic rocks in the 

Mojave crustal province suggest that magmas of both ages may 

have shared sources in preexisting crust at the edge of the Mojave 

crustal block, and differences may reflect the addition of some 

juvenile components into melts that formed the 1.7 Ga rock suite.

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46 Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province
Appendix. Location and Description of 

Chemically and (or) Isotopically Analyzed 

Samples

1. Andalusite-bearing garnet-plagioclase-quartz-muscovite

gneiss from large angular block slumped into wash from 

3 m above. Sec. 14, T. 13 N., R. 10 W. 760 m N. 84° W. 

from BM 2906, lat 34°28'02" N., long 113°16'40" W., 

Arrastra Mtn NE lYz quadrangle, Yavapai County. Unit 

of mica gneiss in the Bagdad metamorphic belt probably 

equivalent to the Hillside Mica Schist of the Bagdad 

area. Anhedral quartz 0.1-0.3 mm in diameter. Muscovite in synkinematic to postkinematic flakes 0.1-0.3 mm 

long and in postkinematic porphyroblasts as much as 1.1 

mm long. Euhedral to subhedral garnet as much as 0.3 m 

in diameter. Andalusite mostly altered to muscovite. 

Secondary chlorite, probably from biotite. Accessory 

zircon, tourmaline, and opaque minerals. Major-oxide 

and trace-element concentrations, table 3. Whole-rock 

Pb-isotopic analysis, table 8. Field No. 1154.

2. Garnet-biotite-microcline-plagioclase-quartz gneiss from layered schist and gneiss containing lenses and stringers of 

pegmatite as much as 1 cm thick. From outcrop on north 

side of wash and about 2 m above its floor in E. part sec. 

7, T. 13 N., R. 12 W. 800 m N. 46° W. from spot elevation 2730 and 150 m west of east line of sec. 7, lat 34°28 T 

N., longll3°32'51"W., Signal Mountain 7/2'quadrangle, Mohave County. Granoblastic to mosaic texture. 

Anhedral quartz as much as 1 mm in diameter, except 4 

mm in a segregation; plagioclase (An32) as much as 0.7 

mm in diameter; microcline as much as 7 mm in diameter; synkinematic and postkinematic biotite as much as 

0.3 mm long; garnet in skeletal crystals as much as 3 mm 

in diameter and as smaller anhedral to euhedral grains as 

much as 0.3 mm in diameter. Accessory zircon. Majoroxide and trace-element concentrations, table 3. Feldspar Pb-isotope analysis, table 8. Field Nos. 1166 and 

JW-85-66.

3. Garnet-bearing amphibolite layer 7 m thick from Bagdad

metamorphic belt in mica gneiss and schist unit (Xmg of 

Bryant, 1992). In wash 300 m S. 67° W. from summit hill 

3283. NW corner sec. 23, T. 13 N., R. 10 W., lat 

34°27'31" N., long 113° 15'H"W, Arrastra Mtn NE7^' 

quadrangle, Yavapai County. Synkinematic to postkinematic green hornblende as much as 2 mm long, anhedral 

plagioclase 0.3 mm in diameter, subhedral garnet 2 mm 

in diameter, and accessory opaque minerals and apatite. 

Major-oxide and trace-element concentrations, table 3. 

Field No. 1159a.

4. Quartz-bearing amphibolite from Bagdad metamorphic belt 

in mica schist and gneiss unit (Xsg of Bryant, 1992). 

SW^SEK sec. 6, T. 12 N., R. 10 W., lat 34°24'27" N., 

long 113°20'14" W., Arrastra Mtn NE lY2 ' quadrangle, 

Yavapai County. Anhedral to subhedral synkinematic to 

postkinematic green hornblende as much as 1.2 mm 

long, locally grades to colorless amphibole having the 

same extinction. Anhedral plagioclase (An35_2g) as much 

as 1 mm in diameter and quartz as much as 3 mm in

diameter in segregation lens. Accessory opaque minerals, apatite, and sphene. Major-oxide and trace-element 

concentrations, table 3. Field No. W-419.

5. Fine-grained amphibolite from outlier of Bagdad metamorphic belt (Xa in Bryant, 1992) included in the granite of 

Thorn Peak and cut by numerous bodies of pegmatite 

and leucogranite as much as 20 m thick. In wash 200 m 

N. 9.5° W. from Negro Ben Spring NE1XSW% sec. 12, T. 

12 N., R. 10W., lat 34°23'11"N., long 113°15'11" W, 

Arrastra Mtn NE lYs quadrangle, Yavapai County. 

Untwinned plagioclase 0.1 mm in diameter interstitial to 

euhedral to anhedral synkinematic to postkinematic 

green hornblende 0.3-0.6 mm long. Accessory opaque 

minerals and sphene. Cut by epidote veinlet 0.1 mm 

thick. Major-oxide and trace-element concentrations, 

table 3. Field No. 633.

6. Amphibolite from unit 20-40 m thick used as a marker for the 

west boundary of the interlayered gneiss unit (XI) of 

Bryant (1992) in the Bagdad metamorphic belt. In wash 

250 m S. 21°E. from 3324 spot elevation. N. 30° E. from 

center sec. 11, T. 13 N., R. 10 W, lat 34°28'52" N., long 

113°16'29" W. Arrastra Mountain NE 7^' quadrangle, 

Yavapai County. Anhedral to subhedral synkinematic to 

postkinematic green hornblende as much as 0.6 mm 

long, anhedral to subhedral plagioclase (An 25.45) 0.05- 

0.2 mm in diameter. Sparse biotite and accessory sphene. 

Major-oxide and trace-element concentrations, table 3. 

Field No. M-96.

7. Quartz-bearing amphibolite from Bagdad metamorphic belt 

from interlayered gneiss unit (XI) of Bryant (1992). 

South line of sec. 1, T. 13 N., R. 10 W. 320 m east of SE 

corner of sec. and triangulation point 3390, lat 34°29'18" 

N., long 113°29'17" W, Arrastra Mtn NE 7^' quadrangle, Yavapai County. Green hornblende as much as 0.7 

mm long in aggregates, quartz and untwinned plagioclase 0.05-0.3 mm in diameter, and accessory sphene 

and opaque mineral. Major-oxide and trace-element 

concentrations, table 3. Field No. M-81.

8. Biotite-quartz-feldspar gneiss from outcrop in wash in NW1/ 

sec. 11, T. 13 N., R. 10 W, 660 m S. 75° E. from BM 

3104; lat 34°28'59" N., long 113°16'51" W, Arrastra 

Mtn NE 71/2 quadrangle, Yavapai County. Southward 

extension of unit mapped as Dick Rhyolite by Anderson 

and others (1955) and Conway and others (1986). Scattered quartz phenocrysts to 1 mm in diameter in nonlayered biotite-quartz-feldspar gneiss. Some streaky biotite 

concentrations, quartz segregations, and quartz-potassic 

feldspar-tourmaline pegmatites. Quartz in poly crystalline aggregates to 1 mm and in mosaic-textured groundmass with plagioclase (An32) and microcline with a grain 

size of 0.1 mm, synkinematic and postkinematic biotite 

0.1-0.3 mm long, sparse muscovite, accessory sphene 

and zircon, and secondary chlorite (fig. 3). U-Pb zircon 

age determination, figure 12. Major-oxide and trace-element concentrations, table 3. Whole-rock and feldspar 

Pb-isotopic analyses, table 8. Field No. 1161.

9. Biotite-muscovite-quartz schist from outcrop in wash at sharp 

bend 160 m N. 11° E. from center of sec. 11, T. 13 N., R. 

10W, lat 34°28'57" N., long 113°16'31"W, Arrastra Mtn

Appendix. Location and Description of Chemically and (or) Isotopically Analyzed Samples 47
NE lYz quadrangle, Yavapai County. Quartz in sparsely 

scattered roundish grains and aggregates as much as 0.8 

mm in diameter and in a mosaic-textured matrix with a 

grain size of 0.1-0.2 mm. Synkinematic muscovite and 

biotite as much as 0.5 mm long, accessory opaque minerals and zircon, and secondary chlorite from biotite. U-Pb 

zircon age determination, figure 12. Field No. P-93-1.

10. Metagabbro from small body foliated and cut by pegmatite 

in Signal Granite (Bryant, 1992). Interpreted to be a roof 

pendant or inclusion in the granite. Sec. 28, T. 13 N., R. 

12 W. 550 m S. 45° W. from Arrowhead Spring. Lat 

34°26'27" N., long 113°30'45" W., Signal Mountain 7/21 

quadrangle, Mohave County. Anhedral to subhedral 

greenish-brown hornblende as much as 2 mm long, anhedral plagioclase (An55_65) as much as 1 mm in diameter, 

accessory apatite and opaque minerals, and secondary 

chlorite and epidote. Major-oxide and trace-element 

concentrations, table 4. Field No. 450.

11. Diabase cut by sparse quartz-feldspar pegmatites. 125 m N. 

85° W. from spot elevation 1854. South-central sec. 19, 

T. 13 N., R. 12 W., lat 34026'55" N., long 113°33'20" W., 

Signal Mountain 7J4T quadrangle, Mohave County. Plagioclase laths (An58_65) as much as 2 mm long; monoclinic pyroxene as much as 3 mm in diameter encloses 

the plagioclase laths. Accessory opaque minerals and 

apatite; secondary amphibole, chlorite, and epidote. 

Major-oxide and trace-element concentrations, table 4. 

Field No. 907.

12. Biotite-hornblende gabbro from outcrop in wash 680 m N. 

22° E. of center sec. 19, T. 13 N., R. 11 W., lat 24°27'25" 

N., long 113°26'50" W., Arrastra Mtn T/z quadrangle, 

Mohave County. In unit of mixed plutonic and metamorphic rocks rich in gabbro and diorite shown on Poachie 

Range map (Bryant, 1992). Included in coarse-grained 

granite unit (Xcg) in figure 2. Intrudes hornblende and 

biotite schist and gneiss. Locally saussuritized, anhedral 

to subhedral, normally zoned plagioclase (An3Q_3g); 

anhedral to subhedral green hornblende as much as 1.5 

mm long in aggregates locally accompanied by biotite; 

anhedral biotite as much as 1.5 mm long in aggregates 

with or without hornblende; accessory opaque minerals 

and sphene, and secondary epidote and carbonate minerals. Major-oxide and trace-element concentrations, table 

4. Field No. W-61.

13. Hornblende gabbro from outcrop on top of hill 170 m S. 20° 

E. from NW corner of sec. 5, T. 12 N., R. 11 W., lat 

34°24'52"N., long 113°25'57" W., Arrastra Mtn 7/2 ' 

quadrangle, Mohave County. Forms a 150x400 m body 

shown on the Poachie Range map (Bryant, 1992) in 

coarse-grained granite unit (Xcg) and is cut by leucocratic granite. Anhedral to subhedral green hornblende 

as much as 3 mm long having sieve texture with plagioclase and opaque mineral; subhedral normally zoned, 

weakly saussuritized plagioclase (An4Q.47) as much as 4 

mm long; opaque minerals, minor quartz, accessory apatite and allanite, and secondary epidote and chlorite. 

Major-oxide and trace-element concentrations, table 4. 

Field No W-307.

14. Metagabbro from small body on north side of wash up

drainage from crossing on county road, E center sec. 7,

T. 13 N., R. 12 W.; 1,580 m N. 41/2 ° W. of spot elevation 

2730; lat 34°28'54" N., long 113°32'48" W., Signal 

Mountain lYz quadrangle, Mohave County. Biotitehornblende-plagioclase granofels with a grain size of 

0.3-0.5 mm and a few hornblende grains as long as 1 

mm. Plagioclase (An45), green hornblende, biotite, and 

sparse monoclinic pyroxene and accessory apatite. 

Pyroxene is partly altered to hornblende in places. Cut 

by a sheared and altered zone rich in epidote. Majoroxide and trace-element concentrations, table 4. Field 

No. 1165.

15. Biotite-hornblende gabbro from outcrop on northwest side 

of wash, 220 m S. 32° W. of center sec. 17, T. 13 N., R. 

11 W.; 420 m S. 20° E. from spot elevation 2952; lat 

34°27'52" N., long 113°26'04" W., Arrastra Mtn 7/2 ' 

quadrangle, Mohave County. Typical of the small bodies 

that form the oldest rock type in the complex of generally 

foliated plutonic rocks underlying much of the Poachie 

Range. In area of mixed plutonic and metamorphic 

rocks shown on the Poachie Range map (Bryant, 1992) 

but included in coarse-grained granite unit (Xcg) in figure 2. Anhedral to subhedral grains of plagioclase 

(An47) to 3 mm in diameter with weak normal zoning 

and locally partly saussuritized, anhedral green hornblende to 1 mm but mostly 0.2-0.4 mm in diameter as 

aggregates between the plagioclase grains, anhedral 

brown biotite to 1.5 mm long, and accessory sphene and 

opaque minerals. U-Pb zircon age determination, figure 

13. Major-oxide and trace-element concentrations, table 

4. Whole-rock and feldspar Pb-isotopic analysis, table 8. 

Field Nos. 750 and JW-84-11.

16. Gneissic biotite diorite from 1.5 m long boulder in wash 

where this rock type forms numerous outcrops. Northwest corner of outcrop area of Early Proterozoic plutonic 

rocks forming the central and eastern parts of the Poachie 

Range. 580 m S. 33° E. from center sec. 17, T. 13 N., R. 

11 W., 1,350 m S. 83° W. from Colorado Spring; lat 

34°27'43" N., long 113°25'47" W., Arrastra Mtn 7/2 ' 

quadrangle, Mohave County. Rock fairly typical texturally but somewhat more mafic than foliated plutonic rock 

typical of this part of large heterogeneous unit underlying much of the Poachie Range. Anhedral to subhedral 

variously saussuritized grains of plagioclase (An30) as 

much as 4 mm in diameter, dark-brown synkinematic to 

postkinematic biotite as much as 2 mm long, accessory 

sphene, apatite, zircon, and secondary epidote, chlorite, 

and carbonate minerals. Chemical analysis was made of 

quartz monzodiorite 130 m up wash (appendix sample 

No. 17; field No. 192, following) containing much less 

secondary epidote than this sample. U-Pb zircon age 

determination, figure 13. Whole-rock and feldspar Pbisotopic analysis, table 8. Field Nos. JW-84-12 and 751.

17. Gneissose hornblende-biotite quartz monzodiorite from

northwest corner of area underlain by Early Proterozoic 

rocks in the Poachie Range. Outcrop in wash. 540 m N. 

69/2 ° W. from SE corner sec. 17, T. 13 N., R. 11 W, lat 

34°27'40" N., long 113025'48" W., Arrastra Mtn 7/2 ' 

quadrangle, Mohave County. Anhedral to subhedral plagioclase (An2g) to 4 mm long; anhedral quartz to 2 mm 

diameter; anhedral locally strained and bent potassic

48 Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province
feldspar to 4 mm diameter; sieve-textured green hornblende to 3 mm long; weakly aligned biotite as much as 

1.5 mm long; sparse myrmekite, accessory sphene, apatite, opaque minerals, and epidote. Major-oxide and 

trace-element concentrations, table 4. Field No. 192.

18. Hornblende-bearing biotite quartz monzodiorite from outcrop in wash 330 m S. 10° W. from center sec. 27, T. 13 

N., R. 11 W., lat 34°26'03" N., long 113°23'56" W., 

Arrastra Mtn lYz quadrangle, Mohave County. Anhedral 

to subhedral plagioclase (An2g) as much as 4 mm in 

diameter; biotite as much as 2 mm long in aggregates 

with sphene and opaque minerals; anhedral quartz as 

much as 3 mm in diameter; and anhedral microcline as 

much as 1.2 cm long, sparse myrmekite and hornblende, 

accessory sphene, hornblende, apatite, zircon, opaque 

minerals, epidote containing cores of allanite, and secondary chlorite. One glob of sphene grains has inclusions of opaque mineral and interstitial allanite and 

epidote. Major-oxide and trace-element concentrations, 

table 4. Field No. 1137.

19. Coarse-grained leucomonzonite from outcrop in wash 100 

m N. 32° W. from center sec. 33, T. 13 N., R. 11 W., lat 

34°25'29" N., long 113°24'58" W., Arrastra Mtn 7/2 

quadrangle, Mohave County. At contact with granodiorite. Biotite in clots. Anhedral microcline as much as 8 

mm in diameter; anhedral to subhedral plagioclase 

(An38) as much as 1 mm in diameter; anhedral to subhedral biotite as much as 2 mm long in single grains and in 

clots; interstitial quartz as much as 1 mm in diameter; 

sparse myrmekite, accessory opaque minerals, sphene, 

and zircon, and secondary epidote. Major-oxide and 

trace-element concentrations, table 4. Field No. W-301.

20. Porphyritic microcline-bearing biotite tonalite gneiss typical 

of the porphyritic granodiorite containing large equant 

feldspar phenocryst phase of the coarse-grained granite 

unit shown on the Poachie Range map (Bryant, 1992), 

but not shown in figure 2. This sample is from a sill(?) 

about 15m thick in metamorphic rocks east of the Signal 

batholith. Outcrop in wash in north part sec. 18, T. 13 

N., R. 11 W.; 1,320 m S. 55° W. from NE corner sec. 18; 

lat 34°28'11" N., long 113°26'51" W., Arrastra Mtn T/2 

quadrangle, Mohave County. Anhedral, strongly 

strained quartz as much as 3 mm in diameter between 

plagioclase grains; anhedral to subhedral plagioclase 

(An34) as much as 6 mm long; synkinematic and postkinematic biotite as much as 1.3 mm long in aggregates 

between larger plagioclase grains; microcline as much as 

4 mm in diameter; sparse myrmekite, accessory opaque 

minerals, apatite, and zircon, and secondary epidote and 

chlorite. Major-oxide and trace-element concentrations, 

table 4. Field No. 1167.

21. Hornblende-biotite granite from outcrop on ridge 690 m S. 

21° W. from center sec. 15, T. 12 N., R. 12 W., lat 

34°22'37" N., long 113°29'50" W., Arrastra Mtn 7/2' 

quadrangle, Mohave County. Well-foliated, migmatitic 

granite containing potassic feldspars as much as 3 cm in 

diameter in coarser grained layers. Biotite concentrated 

in clots 1-2 cm long. Locally clots outline swirly structure. Anhedral to subhedral plagioclase (An24) as much

as 8 mm long; anhedral microcline as much as 2 mm in 

diameter; anhedral quartz; anhedral to subhedral biotite 

as much as 0.5 mm long; dark-green anhedral hornblende as much as 2 mm long; sparse myrmekite and 

accessory opaque minerals and sphene. Major-oxide and 

trace-element concentrations, table 4. Field No. 552a.

22. Biotite granite from boulder associated with large outcrops 

in channel of Burro Creek. Possibly part of the Early 

Proterozoic plutonic suite of the Poachie Range. Middle 

of S>2 sec. 9, T. 14 N., R. 12 W.; 230 m downstream 

from NNW.-trending tributary of Burro Creek fed by 

warm spring; 1,450 m S. 33° W. from triangulation point 

2272. Lat 34°33'51" N., long 113°3riO" W., Greenwood Peak T/2 quadrangle, Mohave County. Porphyritic 

biotite granite containing equant potassic feldspar phenocrysts as much as 2 cm in diameter; subhedral normally zoned plagioclase (A^y-iy) as much as 4 mm 

long; perthitic microcline; greenish-brown anhedral 

biotite as much as 2 mm long in aggregates; anhedral to 

euhedral epidote as much as 1 mm long; sparse myrmekite, accessory sphene, apatite, and zircon, and secondary chlorite from biotite. Compared to the Signal 

Granite the potassic feldspars in this rock are equant as 

opposed to elongate and the mafic clots are longer and 

more irregular. U-Pb zircon age determination, figure 

14. Major-oxide and trace-element concentrations, table 

4. Whole-rock and feldspar Pb-isotopic analysis, table 8. 

Field Nos. JW-84-9 and 749.

23. Hornblende-bearing biotite granodiorite from outcrop in 

wash 460 m S. 25° W from center sec. 16, T. 13 N., R. 

11 W, lat 34°27'50" N., long 113°25'05" W, Arrastra 

Mtn T/z quadrangle, Mohave County. Intruded by 

coarse-grained granite nearby. Anhedral quartz as much 

as 3.5 mm in diameter; plagioclase (An23) as much as 4 

mm in diameter; anhedral to subhedral perthitic microcline as much as 6 mm in diameter; biotite as much as 1 

mm long in aggregates; epidote in mafic clots with 

biotite and hornblende; accessory opaque minerals, zircon, apatite, and green hornblende in mafic clots with 

biotite and epidote. Major-oxide and trace-element concentrations, table 4. Field No. 1132a.

24. Biotite granite from outcrop in wash on line between sees. 

30 and 31, 450 m E. of township line T. 13 N., R. 11 W, 

lat 34°25'50" N., long 113°27'13" W., Arrastra Mtn T/z' 

quadrangle, Mohave County. Foliated porphyritic biotite 

granite cut by dike of leucogranite containing faint foliation parallel to that in granite. Anhedral to subhedral 

microcline phenocrysts as much as 2.5 cm long; anhedral 

to subhedral plagioclase (An33> as much as 3 mm long; 

anhedral quartz as much as 2 mm in diameter partly in 

mosaic-textured aggregates as much as 5 mm in diameter; anhedral biotite as much as 2 mm long; sparse hornblende and accessory sphene, opaque minerals, and 

apatite. Major-oxide and trace-element concentrations, 

table 4. Field No. 212.

25. Biotite granite from outcrop in wash 100 m N. 85° W. from 

SE corner sec. 16, T. 11 N., R. 10 W, lat 34°22'33" N., 

long 113°17'44" W, Arrastra Mtn NE T/2 quadrangle, 

Yavapai County. In outcrop porphyritic granite contains

Appendix. Location and Description of Chemically and (or) Isotopically Analyzed Samples 49
a few xenoliths of biotite schist and gneiss. Anhedral to 

subhedral microcline as much as 3.5 mm in diameter; 

anhedral partly saussuritized and normally zoned plagioclase (An30) as much as 6 mm long; anhedral to subhedral biotite as much as 2 mm long; and accessory opaque 

minerals, zircon, and apatite. Major-oxide and trace-element concentrations, table 4. Field No. 713.

26. Biotite granite gneiss from outcrop in wash 600 m east of 

center sec. 18, T. 12 N., R. 10 W, lat 34°22'59" N., long 

113°19'52" W, Arrastra Mtn NE 7>£' quadrangle, Yavapai County. Rock typical of unit Xcg in vicinity. Anhedral quartz as much as 6 mm in diameter; partly 

saussuritized anhedral plagioclase (An12) as much as 1.5 

mm in diameter; anhedral microcline as much as 4 mm in 

diameter; synkinematic to postkinematic biotite as much 

as 0.5 mm long; accessory allanite, apatite, zircon, and 

opaque minerals; secondary chlorite and epidote. Majoroxide and trace-element concentrations, table 4. Field 

No. 680.

27. Biotite granite gneiss from pluton of finer grained granite at 

the east end of the high crest of the Poachie Range (Xg 

of Bryant, 1992). Outcrop about 15m above and east of 

wash at east margin of Arrastra Mtn 7/4' quadrangle, 650 

m S. 49° E. from center sec. 26, T. 13 N., R. 11 W, lat 

34°26'00" N., long 113°22'31" W, Mohave County. 

Foliated medium-grained, rather leucocratic granite. 

Anhedral to subhedral plagioclase (An28) as much as 2 

mm in diameter; anhedral microcline as much as 2 mm in 

diameter; anhedral quartz as much as 3 mm long; synkinematic and postkinematic biotite as much as 1 mm long; 

accessory opaque minerals and zircon; secondary muscovite and epidote. Major-oxide and trace-element concentrations, table 5. Field No. 172b.

28. Leucocratic medium-grained granite (Xg) from pluton at 

the east end of the Poachie Range. From triangulation 

station Poachie at spot elevation 4807 in south-central 

sec. 35, T. 13 N., R. 11 W, lat 34°25'16" N., long 

113°22'53 M W, Arrastra Mtn 7>2 quadrangle, Mohave 

County. Anhedral quartz and plagioclase (An23) as much 

as 2 mm in diameter; microcline and biotite as much as 

1.5 mm in diameter; accessory muscovite at least partly 

contemporaneous with biotite, zircon, allanite, apatite, 

and opaque minerals. Whole-rock and feldspar Pb-isotopic analysis, table 8. Field No. B-95.

29. Subhorizontal sheet of weakly foliated leucocratic granite 

intruding coarse-grained granite in SW1/iSW1/4 sec. 7, T. 

12 N., R. 11 W, on south side of wash 330 m N. 82° W 

from spot hilltop 3199; lat 34°23'43" N., long 

113°26'47" W, Arrastra Mtn lYz quadrangle, Mohave 

County. Anhedral quartz as much as 2.3 mm in diameter; 

anhedral saussuritized plagioclase and microcline as 

much as 1.5 mm long; sparse aligned biotite, accessory 

allanite, zircon, and opaque minerals, and secondary 

sericite from feldspar. Whole-rock and feldspar Pb-isotopic analyses, table 8. Field No. W-325.

30. Leucocratic biotite granite from small pluton mapped as 

YXg (Bryant, 1992). In wash in SW1/4 sec. 2, T. 12 N., 

R. 11 W, 480 m N. 40° W. from spot elevation 3580, lat 

34°24'21" N., long 113°22'10" W, Arrastra Mtn NE 7/2' 

quadrangle, Mohave County. Anhedral quartz 0.1-0.6

mm but locally as much as 1.3 mm in diameter; anhedral, 

partly saussuritized plagioclase (about An2o) as much as 

1 mm in diameter; anhedral microcline mainly 1 mm, but 

locally as much as 2 mm in diameter; well-aligned biotite 

as much as 0.7 mm in diameter; sparse myrmekite and 

muscovite partly contemporaneous and partly later than 

the biotite; accessory zircon, apatite, sphene, and opaque 

minerals; secondary epidote and chlorite. Whole-rock 

and feldspar Pb-isotopic analysis, table 8. Field No. 317.

31. Biotite-muscovite granite from outcrop in wash 570 m S. 5° 

W. from Negro Ben Spring in sec. 13, T. 12 N., R. 10 W, 

lat 34°23'14" N., long 113°15'12" W., Arrastra Mtn NE 

7/4 quadrangle, Yavapai County. Weakly developed foliation shown best in outcrop by aligned inclusions of 

mica gneiss. Plagioclase (An30) as much as 2 mm in 

diameter. Potassic feldspar as much as 3 mm in diameter; muscovite as much as 1.3 mm long, some in aggregates; biotite as much as 1.3 mm long; accessory opaque 

minerals, apatite, and zircon. Major-oxide and traceelement concentrations, table 5. Field No. 636a.

32. Muscovite-biotite granite from outcrop south side of wash 

in sec. 9, T. 13 N., R. 9 W, 350 m N. 23° E. of Quail 

Spring; lat 34°28'47" N., long 113°11'55" W, Thorn 

Peak T/2 quadrangle, Yavapai County. Intrudes and 

includes xenoliths of hornblende-biotite-plagioclase 

gneiss and contains some zones of pegmatite dikes. 

Anhedral quartz as much as 1.5 mm in diameter mostly 

in granoblastic textured aggregates between feldspar 

grains; subhedral saussuritized plagioclase (An32); anhedral to subhedral strained microcline as much as 4 mm in 

diameter; anhedral, locally bent, biotite and muscovite as 

much as 1 mm long—muscovite partly contemporaneous 

with biotite and partly younger; accessory opaque minerals, apatite, and zircon, and secondary sphene and epidote. A few zones of mortar structure cut the rock. 

Major-oxide and trace-element concentrations, table 5. 

Field No. 175b.

33. Biotite-muscovite granite gneiss from outcrop in wash 700 

m N. 78° W. from center sec. 20, T. 12 N., R. 9 W, lat 

34°22'H" N., long 113°13'24" W, Ives Peak 7/2 ' quadrangle, Yavapai County. Granite in outcrop has numerous inclusions of fine-grained muscovite gneiss. 

Subhedral sericitized plagioclase as much as 6 mm long; 

subhedral microcline as much as 6 mm long; anhedral 

quartz as much as 0.6 mm in diameter in aggregates with 

mosaic texture; anhedral to subhedral, synkinematic to 

postkinematic biotite and muscovite as much as 1 mm 

long; accessory opaque minerals, apatite, allanite, zircon, 

and sphene; and secondary chlorite. Major-oxide and 

trace-element concentrations, table 4. Field No. A-10.

34. Biotite-muscovite granite from outcrop in wash 250 m S. 

23° W. from center sec. 28, T. 13 N., R. 9 W, lat 

34°26'07" N., long 113°12'25" W, Thorn Peak 7/2' quadrangle, Yavapai County. Anhedral quartz as much as 0.5 

mm in diameter in mosaic-textured areas interstitial to 

the feldspars; sericitized subhedral plagioclase as much 

as 5 mm in diameter; subhedral microcline as much as 9 

mm long; anhedral muscovite as much as 1 mm long and 

anhedral biotite as much as 1.5 mm long in aggregates; 

accessory zircon, allanite rimmed by epidote, and

50 Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province
secondary epidote. Major-oxide and trace-element concentrations, table 5. Field No. A-21.

35. Muscovite-biotite granite from large roadcut in granite of 

Thorn Peak on U.S. Highway 93 in SWK sec. 5, T. 12 N., 

R. 9 W.; 690 m S. 19° E. from Bridge triangulation 

point. Sample from first bench in cut about 8 m above 

highway; lat 34°24'24" N., long 113°13'19" W., Thorn 

Peak iVz quadrangle, Yavapai County. Rock in roadcut 

somewhat sheared and fractured, and unweathered rock 39. 

is scarce. A few pegmatite dikes and one gently dipping 

diabase sheet cut the granite. Quartz in mosaic-textured 

aggregates with a grain size as much as 1 mm; anhedral 

to subhedral plagioclase to 2.3 mm in diameter; euhedral 

phenocrysts of microcline to 5 mm in diameter; anhedral 

muscovite and biotite to 1 mm long intergrown; accessory garnet, apatite, zircon, and opaque minerals and secondary epidote and chlorite. U-Pb zircon age 

determination, figure 14. Whole-rock and feldspar Pbisotopic analysis, table 8. Major-oxide and trace-element 

concentrations, table 5. Field No. 1158.

36. Biotite monzodiorite from outcrop on east side of wash in 

Skunk Canyon 200 m north of section line, sec. 8, T. 13 

N., R. 9 W., lat 34°28'32" N., long 113°14'52M W., Thorn 40. 

Peak lYz quadrangle, Yavapai County. Medium-grained 

granodiorite to diorite containing inclusions of finegrained diorite or granodiorite and cut by some pegmatite. Locally foliated. Anhedral to subhedral saussuritized, locally antiperthitic plagioclase; anhedral to 

subhedral biotite as much as 2 mm long; anhedral microcline; anhedral sphene as much as 1.5 mm in diameter; 

accessory quartz, green hornblende, apatite, allanite, and 

secondary epidote. Major-oxide and trace-element concentrations, table 5. Field No. A-108.

37. Biotite-hornblende diorite from outcrop on east side of wash 

in Skunk Canyon 50 m north of section line, sec. 5, T. 13 

N., R. 9 W., lat 34°29'19" N., long 113°14'51 M W., Thorn 

Peak 7X>' quadrangle, Yavapai County. Saussuritized 

anhedral to subhedral plagioclase (An32) partly having 41. 

normal zoning; anhedral to subhedral dark-green hornblende as much as 2 mm long; anhedral to subhedral 

biotite as much as 2 mm long; accessory opaque minerals 

and apatite; secondary sphene, epidote, and chlorite. 

Major-oxide and trace-element concentrations, table 5. 

Field No. A-l 11.

38. Gneissic biotite tonalite from pluton on east side of Bagdad 

metamorphic belt. Numerous inclusions of amphibolite 

and muscovite-biotite gneiss and some of biotite-quartzfeldspar gneiss 1 cm to 10 cm long in outcrop but not in 

sample. Outcrop in bottom of wash near west edge of 

the center of sec. 13, T. 13 N., R. 10 W., 530 m N. 74° E. 

from BM 2906; lat 34°28'06" N., long 113°15'05" W., 42. 

Arrastra Mtn NE lYz quadrangle, Yavapai County. Plagioclase (An32) in locally bent and broken grains as 

much as 4 mm in diameter and in mosaic-textured areas 

with quartz; quartz as much as 1.5 mm in diameter but 

mostly in mosaic-textured aggregates; microcline as 

much as 2 mm in diameter and in mosaic-textured aggregates with quartz and plagioclase; synkinematic and 

postkinematic biotite as much as 2 mm long in

Appendix. Location and Description

aggregates—a few of the larger biotite grains are bent, 

and a minor amount of muscovite is intergrown with the 

biotite and is locally bent. Accessory opaque minerals, 

sphene, apatite, and zircon, and secondary chlorite from 

biotite. U-Pb zircon age determination, figure 15. Majoroxide and trace-element concentrations, table 5. Wholerock and feldspar Pb-isotopic analysis, table 8. Field 

Nos. JW-85-63 and 1163.

Somewhat gneissose biotite granodiorite from outcrop in 

wash on section line 130 m west of SE corner sec. 23, T. 

13 N., R. 8 W, lat 34°26'41" N., long 113°03'31" W, 

Malpais Mesa NE 7X>' quadrangle, Yavapai County. 

Locally saussuritized plagioclase (An32) as much as 2.7 

mm in diameter; quartz 0.2-0.5 mm in diameter in 

mosaic-textured aggregates; anhedral microcline as 

much as 1 mm in diameter; synkinematic to postkinematic biotite as much as 2 mm long in aggregates; sparse 

muscovite, accessory allanite, opaque minerals, apatite, 

zircon, and sphene, and secondary epidote. Muscovite is 

partly contemporaneous with biotite and partly younger. 

Major-oxide and trace-element concentrations, table 5. 

Field No. A-85.

Muscovite-biotite granite from east-facing outcrop on Black 

Canyon Wash in SW1/ sec. 35, T. 12 N., R. 8 W, 760 m S. 

2lY2° W. from spot elevation 2903; lat 34°20'08" N., long 

113°04'20" W, Malpais Mesa 7X>' quadrangle, Yavapai 

County. Coarser grained porphyritic granite phase in 

mixed unit containing fine-grained granite and migmatite. Potassic feldspars as much as 2 cm long in outcrop. 

Strained and locally broken grains of perthitic microcline 

as much as 1 cm long; anhedral to subhedral, slightly 

altered plagioclase (An27) as much as 3.5 mm long; anhedral quartz as much as 2 mm in diameter; muscovite and 

biotite as much as 1.5 mm long; sparse myrmekite, accessory apatite, zircon, and opaque minerals, and secondary 

carbonate and chlorite. Major-oxide and trace-element 

concentrations, table 5. Field No. A-152.

Biotite-hornblende granodiorite from mafic phase of the 

Signal Granite. From outcrop in gully 700 m N. 24° W. 

from Signal triangulation point on Signal Mountain. 

SE1/ sec. 15, T. 13 N., R. 13 W, lat 34°27'58" N., long 

113°36'11" W, Signal Mountain T/2 quadrangle, 

Mohave County. Anhedral quartz as much as 1.2 mm in 

diameter; anhedral to subhedral plagioclase (An32) as 

much as 2.5 mm in diameter; anhedral microcline as 

much as 1.6 mm in diameter; anhedral green hornblende 

as much as 2.2 mm long; opaque minerals as much as 1 

mm in diameter; anhedral biotite as much as 2.2 mm 

long; accessory sphene. Major-oxide and trace-element 

concentrations, table 6. Field No. NAP 154.

Porphyritic hornblende-biotite granite from mafic phase of 

the Signal Granite on south side of Government Wash, 30 

m east of fault contact with Tertiary arkosic sandstone 

and conglomerate. 520 m S. 33° E. of spot elevation 

1792; NW1/NW^ sec. 1, T. 12 N., R. 13 W, lat 

34°24'51" N., long 113°34'19" W, Signal Mountain T/2' 

quadrangle, Mohave County. Anhedral quartz as much 

as 6 mm in diameter; anhedral to subhedral plagioclase 

(An29) as much as 1 cm in diameter; anhedral to

of Chemically and (or) Isotopically Analyzed Samples 51
subhedral microcline as much as 2 cm in diameter; anhedral biotite as much as 3 mm long in aggregates; anhedral green hornblende intergrown with biotite; accessory 

allanite, sphene, apatite, zircon, and opaque minerals. 

Major-oxide and trace-element concentrations, table 6. 

Field No. 876.

43. Hornblende-biotite granite from near the type locality of the 

Signal Granite. Outcrop on south side of wash, 200 m 

west of Big Sandy River; lat 34°27'17" N., long 

113°37'38" W., Signal T/2 quadrangle, Mohave County. 

Anhedral quartz as much as 1 cm in diameter; anhedral 

to subhedral plagioclase (An38) as much as 4 mm long; 

well-aligned subhedral to euhedral perthitic microcline 

as much as 6 cm long and 2 cm wide; biotite as much as 

3 mm long as aggregates with hornblende; anhedral 

green hornblende as much as 3 mm long, sphene rimming opaque minerals and in anhedral to subhedral 

grains as much as 1.3 mm in diameter; accessory opaque 

minerals, apatite, and zircon. U-Pb zircon age determination, figure 16. Major-oxide and trace-element concentrations, table 6. Whole-rock and feldspar Pbisotopic analysis, table 8. Field No. 1168.

44. Biotite granite from block on slope below outcrop. At contact of Signal Granite in NWK sec. 9, T. 13 N., R. 12 W.; 

220 m N. 25° E. from Big Sandy Spring; lat 34°29'03" 

N., long 113°31'20" W., Signal Mountain 7/21 quadrangle, Mohave County. Anhedral quartz as much as 3 mm 

diameter in aggregates that tend to surround feldspars; 

anhedral to subhedral plagioclase (An2g); perthitic 

potassic feldspar in grains as much as 2 cm in diameter; 

biotite as much as 1 mm long in aggregates as much as 4 

mm long with or without hornblende; anhedral to subhedral dark-green hornblende as much as 2.5 mm long 

locally surrounded by biotite; sparse myrmekite and 

accessory allanite, zircon, sphene, apatite, and opaque 

minerals. U-Pb zircon age determination, figure 16. 

Major-oxide and trace-element concentrations, table 6. 

Feldspar Pb-isotopic analysis, table 8. Field Nos. JW85-64 and 1164.

45. Coarse-grained porphyritic biotite granite containing phenocrysts of potassic feldspar 1-4 cm long from Signal 

Granite from 1,950' altitude in gully in SW^> sec. 10, T. 

12 N., R. 13 W.; 750 m S. 82° W. of spot elevation 2278; 

lat 34°23'32" N., long 113°36'26" W., Signal Mountain 

7)4' quadrangle, Mohave County. Anhedral quartz as 

much as 5 mm long; anhedral plagioclase (An17) as 

much as 6 mm long; subhedral microcline, anhedral 

brown biotite as much as 2 mm long, partly in aggregates; sparse dark olive-green hornblende and myrniekite, accessory sphene rimming opaque minerals, 

sphene, apatite, and zircon, and secondary sericite, carbonate minerals, and chlorite. Major-oxide and trace-element concentrations, table 6. Field No. 49a.

46. Coarse-grained leucocratic granite cutting the main phase of 

the Signal Granite. Outcrop at junction of two washes. 

SW/4 sec. 18, T. 13 N., R. 12 W.; 330 m S. 14° E. from 

spot elevation 2530, lat 34°27'50" N., long 113°33'30" 

W., Signal Mountain 7)4' quadrangle, Mohave County. 

Anhedral quartz as much as 3 mm in diameter; anhedral

52 Poachie Region, West-Central Arizona—East Boundary,

to subhedral plagioclase (An33) as much as 4 mm in 

diameter; anhedral perthitic microcline as much as 1 cm 

in diameter; anhedral biotite as much as 2 mm long in 

aggregates; accessory apatite, zircon, and opaque minerals. Major-oxide and trace-element concentrations, table 

6. Field No. 467b.

47. Pyroxene-hornblende-biotite granodiorite (Ygd). From

dump of adit NW1/4 sec. 9, T. 13 N., R. 12 W. at adit symbol on Signal Mountain 7)4' quadrangle. 470 m N, 35° 

W. from Big Sandy Spring; lat 34°29'08" N., long 

113°31'33" W., Mohave County. Quartz in granophyric 

intergrowths with potassic feldspar; anhedral to euhedral, 

normally zoned plagioclase (An27_42) as much as 2 mm 

long; very finely perthitic potassic feldspar; anhedral 

brown hornblende as much as 1.5 mm long; opaque mineral as much as 0.2 mm in diameter; monoclinic pyroxene mantled by hornblende; accessory zircon and apatite 

and secondary carbonate minerals. U-Pb zircon age 

determination, figure 16. Major-oxide and trace-element 

concentrations, table 6. Whole-rock and feldspar Pb-isotopic analysis, table 8. Field Nos. JW-84-10 and 390.

48. Hornblende-biotite granodiorite (Ygd). In wash 390 m S. 

19/2° W from Big Sandy Spring. SWJ4 sec. 9, T. 13 N., 

R. 12 W., lat 34°28'52" N., long 113°31'30" W, Signal 

Mountain 7)4' quadrangle, Mohave County. Quartz as a 

6.6-mm-diameter xenocryst and as round grains 0.02- 

0.05 mm in diameter in a matrix of alkali feldspar; euhedral to subhedral phenocrysts of normally zoned plagioclase (An23_32) as much as 1 mm in diameter; anhedral 

biotite to 0.3 mm long; anhedral to subhedral green hornblende as much as 0.3 mm long; accessory epidote, allanite, apatite, sphene, and opaque minerals, and secondary 

carbonate minerals. Epidote apparently contemporaneous with biotite and hornblende. Major-oxide and traceelement concentrations, table 6. Field No. 1144.

49. Porphyritic biotite granite from the porphyritic granite phase 

of the granite of Olea Ranch. Outcrop by wash in Cottonwood Canyon, 320 m S. 43° W of center sec. 35, T. 13 

N., R. 10 W, lat 34°25'15" N., long 113°16'40" W, 

Arrastra Mtn NE 7)4' quadrangle, Yavapai County. In 

outcrop granite contains a few lenses of pegmatite a few 

centimeters thick. Microcline as phenocrysts as much as 

2 cm long; subhedral to anhedral, locally saussuritized 

and sericitized plagioclase (An30) as much as 1.5 mm in 

diameter; anhedral quartz as much as 4 mm in diameter; 

anhedral to subhedral biotite as much as 1.2 mm long in 

aggregates; accessory apatite, allanite, opaque minerals, 

and zircon, and secondary epidote. Major-oxide and 

trace-element concentrations, table 7. Field No. 666.

50. Porphyritic biotite granite from the porphyritic granite phase 

of the granite of Olea Ranch containing potassic feldspar 

phenocrysts as much as 4 cm long in a medium-grained 

matrix. From large boulder in Cottonwood Wash, 720 m 

from E edge of Arrastra Mountain NE 7)4' quadrangle, 

Yavapai County. 620 m S. 7° E. from spot elevation 

3078; NW^ sec. 1, T. 12 N., R. 10 W, lat 34°24'46" N., 

long 113°15'12" W. Anhedral quartz generally 0.3 mm 

in diameter but a few larger ones as much as 3 mm; anhedral to euhedral locally saussuritized plagioclase (An30)

Mojave Crustal Province
as much as 2 mm in diameter; anhedral to euhedral perthitic microcline as much as 2 cm long; anhedral to subhedral biotite as much as 1.3 mm long aligned parallel to 

the potassic feldspar; sparse myrmekite, accessory allanite, zircon, apatite, and opaque minerals, and secondary 

epidote and chlorite. U-Pb zircon age determination, figure 16. Major-oxide and trace-element concentrations, 

table 7. Whole-rock and feldspar Pb-isotopic analysis, 

table 8. Field Nos. JW-84-13 and 752.

51. Coarse-grained biotite granite of the granite of Olea Ranch. 

Sample from unweathered remnant in roadcut on U.S. 

Highway 93, S edge sec. 8, T. 13 N., R. 10 W. 270 m W. 

of triangulation point 3376; lat 34°28'24" N., long 55 - 

113°19'22" W., ArrastraMtnNE T/2 quadrangle, Yavapai 

County. Mosaic-textured quartz with a grain size as 

much as 1 mm interstitial to feldspars; subhedral, partly 

saussuritized plagioclase (An 17) as much as 3 mm long; 

anhedral, somewhat perthitic microcline as much as 1 cm 

in diameter; green to brownish-green anhedral to subhedral biotite as much as 2 mm long; accessory sphene, 

apatite, and zircon, and secondary epidote, muscovite, 

and sericite. U-Pb zircon age determination, figure 16. 

Major-oxide and trace-element concentrations, table 7. 

Whole-rock and feldspar Pb-isotopic analysis, table 8. 

Field Nos. JW-84-15 and 753.

52. Porphyritic biotite granite from coarse-grained granite phase 56. 

of the granite of Olea Ranch. Sample of spoil from excavation for power line tower site on crest of shoulder in 

west part of sec. 15, T. 13 N., R. 10 W; 270 m N. 89° E. 

of spot elevation 3258, lat 34°27'57" N., long 

113° 17'59" W., Arrastra Mtn NE T/2 quadrangle, Yavapai 

County. Subhedral perthitic microcline as much as 2 cm 

long; anhedral to subhedral partly saussuritized and 

sericitized plagioclase (An27> as much as 2 mm in diameter; anhedral quartz as much as 2 mm in diameter in 

mosaic-textured aggregates between feldspar grains; 

anhedral greenish-brown biotite in aggregates; sparse 

muscovite, accessory sphene, zircon, allanite, apatite, 

and opaque minerals, and secondary epidote. Major- ?-, 

oxide and trace-element concentrations, table 7. Field 

No. M72.

53. Porphyritic medium-grained biotite granite in the finegrained phase of the granite of Olea Ranch from outcrop 

in wash in NEK sec. 16, T. 13 N., R. 11 W; 170 m N. 

31° W. of spot elevation 3183; lat 34°28'21" N., long 

113°2r32" W, Arrastra Mtn NE TA' quadrangle, 

Mohave County. From pluton of finer grained granite 

intruding coarse-grained granite. Anhedral quartz as 

much as 3 mm in diameter; subhedral to anhedral saussuritized plagioclase as much as 2 mm long; euhedral to 

anhedral microcline as much as 1 cm long; anhedral, 

partly chloritized biotite as much as 1.3 mm long; accessory opaque minerals, primary and secondary muscovite, 

and secondary epidote. Major-oxide and trace-element 

concentrations, table 7. Field No. 1160.

54. Megacrystic phase of the granite of Joshua Tree Parkway

from a 2-m-diameter block in wash near windmill about 

30 m down wash from location 55. SWK sec. 19, T. 11 58. 

N.,R. 7W, 300 m S. 53° E. of hill 3267; Iat34°16'45" 

N., long 113°02'13" W, Malpais Mesa T/2 quadrangle,

Yavapai County. Quartz in mosaic-textured aggregates 

with a grain size of 1-3 mm between feldspar grains; 

anhedral to subhedral plagioclase (An25) as much as 5 

mm long; somewhat perthitic microcline as much as 4 

cm long; anhedral dark-green hornblende as much as 2 

mm long; anhedral biotite as much as 3.5 mm long; 

accessory sphene, apatite, allanite, zircon, and opaque 

minerals, and secondary chlorite from biotite. Mafic 

minerals are concentrated in clots as much as 1 cm long. 

U-Pb zircon age determination, figure 17. Major-oxide 

and trace-element concentrations, table 7. Feldspar Pbisotopic analysis, table 8. Field No. A-15la.

Fine-grained biotite granite from the granite of Joshua Tree 

Parkway from outcrop containing a 0.2-m-long inclusion 

of megacrystic granite. SWK sec. 19, T. 11 N., R. 7 W; 

300 m S. 53° E. of hill 3267; lat 34°16'45" N., long 

113°02'13" W, Malpais Mesa T/2 quadrangle, Yavapai 

County. Anhedral quartz as much as 1.5 mm in diameter; 

anhedral, locally saussuritized plagioclase as much as 1 

mm in diameter; anhedral, weakly perthitic microcline as 

much as 2 mm in diameter; anhedral biotite as much as 1 

mm long; accessory sphene, allanite, zircon, and opaque 

minerals and secondary chlorite from biotite. Majoroxide and trace-element concentrations, table 7. Field 

No.A-151b.

Medium-grained porphyritic biotite granite from float in 

wash 480 m N. 25° E. from center sec. 32, T. 13 N., R. 7 

W, lat 34°25'40" N., long 113°00'45" W, Malpais Mesa 

NE T/2 quadrangle, Yavapai County. Typical of finer 

grained, porphyritic phase of the granite of Grayback 

Mountain. Anhedral microcline as much as 1 cm in 

diameter, anhedral quartz as much as 1.3 mm in diameter; anhedral to subhedral, locally saussuritized plagioclase (An15_ 2()) as much as 6 mm in diameter; anhedral 

biotite as much as 1.3 mm long; accessory sphene, 

opaque minerals, and allanite, and secondary epidote. 

Major-oxide and trace-element concentrations, table 7. 

FieldNo.A-107b.

Coarse-grained biotite granite from the granite of Grayback 

Mountain from roadcut on south side of where Arizona 

Highway 96 crosses Tank Wash. N. 9° E. of center sec. 

22, T. 13 N., R. 7 W, lat 34°27'15" N., long 112°58'44" 

W, Hillside T/2 quadrangle, Yavapai County. Cut by 

sparse quartz-feldspar and biotite-quartz-feldspar pegmatites. Anhedral quartz as much as 2 mm but mostly 

about 1 mm in diameter in mosaic-textured masses interstitial to feldspars; subhedral, partly saussuritized plagioclase as much as 3.5 mm in diameter; perthitic 

microcline as much as 3 mm in diameter; anhedral biotite 

as much as 2 mm long in aggregates; accessory opaque 

minerals, allanite, apatite, and zircon, and secondary epidote and sericite from plagioclase and chlorite from 

biotite. Cut by a few thin shear zones containing sericite 

and epidote. U-Pb zircon age determination, figure 17. 

Major-oxide and trace-element concentrations, table 7. 

Feldspar Pb-isotopic analysis, table 8. Field No. A-153.

Medium-grained porphyritic granite intruding the coarsegrained granite unit east of the Signal batholith, in gully 

in NEK sec. 5, T. 12 N., R. 11 W, 1,070 m N. 4° E. from

Appendix. Location and Description of Chemically and (or) Isotopically Analyzed Samples 53
spot elevation 3555; lat 34°24'53" N., long 113°25'21" 

W., Arrastra Mtn 7/4' quadrangle, Mohave County. In 

outcrop contains microcline phenocrysts as much as 2 

cm in diameter. In thin section anhedral quartz as much 

as 5 mm in diameter; anhedral to subhedral plagioclase 

(about An2s) as much as 2 mm in diameter; anhedral to 

subhedral microcline as much as 3 mm in diameter; 

anhedral biotite as much as 1 mm in diameter; sparse 

myrmekite and accessory sphene, zircon, and apatite. 

Whole-rock and feldspar Pb-isotopic analyses, table 8. 

Field No. W-295.

59. Coarse-grained porphyritic granite containing phenocrysts of 

potassic feldspar as much as 2 cm long in an elongate 

pluton in the coarse-grained granite east of the Signal 

batholith. From wash in NE1/ sec. 7, T. 12 N., R. 11 W., 

1,020 m S. 67° W. from spot elevation 3555, lat 

34°24'06" N., long 113°26'01 W., Arrastra Mtn 7# 

quadrangle, Mohave County. No thin section available. 

Whole-rock and feldspar Pb-isotopic analyses, table 8. 

Field No. W-322.

60. Diabase in flat-lying sheet 2-3 m thick from wash NW1/4 sec. 

22, T. 13 N., R. 10 W, 210 m N. 37° W. from spot elevation 3168, lat 34°27'25" N., long 113°17'42" W, Arrastra 

Mtn NE 7/4' quadrangle, Yavapai County. Plagioclase 

(An55 .60) with some normal zoning as nonoriented laths 

as much as 4 mm long; anhedral monoclinic pyroxene as 

much as 3.5 mm in diameter between the plagioclase 

laths; light-green actinolite and green chlorite from 

pyroxene; biotite to 0.6 mm long; opaque minerals as

much as 1 mm in diameter. Major-oxide and trace-element concentrations, table 7. Field No. 1052.

61. Coarse-grained diabase from small plug not shown on published map (Bryant, 1995). From 70 m S. 81° W. from 

top of hill 3124, SWY^W% sec. 14, T. 12 N., R. 8 W, lat 

34°23'19" N., long 113°04'13" W, Malpais Mesa NE TA' 

quadrangle, Yavapai County. Euhedral laths of plagioclase (An55 .75) as much as 3 mm long, anhedral to subhedral olivine as much as 2 mm in diameter, monoclinic 

pyroxene as much as 5 mm in diameter includes plagioclase laths. Accessory opaque minerals and secondary 

actinolite and biotite. Major-oxide and trace-element 

concentrations, table 7. Field No. A-91.

62. Diabase forming sill 2-3 m thick in coarse-grained granite. 

In wash east part sec. 1, T. 13 N., R. 13 W, 760 m S. 84° 

W. from spot elevation 3124; lat 34°29'31" N., long 

113°34'08" W, Signal Mountain TA' quadrangle, Mohave 

County. Thin section not available. Major-oxide and 

trace-element concentrations, table 7. Field No. G-38.

63. Diabase sheet 3-4 m thick dipping 10° SW. in wash southwest side of the Big Sandy River in Signal Canyon, 

NW1/4 sec. 27, T. 13 N., R. 13 W, lat 34°26'22" N., long 

113°36'32" W, Signal Mountain T/2 quadrangle, 

Mohave County. Plagioclase (An60) in laths as much as 

3 mm long; anhedral monoclinic pyroxene as much as 1 

mm in diameter between the laths; amphibole and biotite 

from pyroxene, and opaque minerals. Major-oxide and 

trace-element concentrations, table 7. Field No. 852.

54 Poachie Region, West-Central Arizona—East Boundary, Mojave Crustal Province

* U.S. GOVERNMENT PRINTING OFFICE: 2001 — 673-049 / 30049 Region No. 8
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