Geology of the Morningstar mine area, Greaterville mining district, Pima County, Arizona

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Authors Stewart, James Conrad, 1935-

Publisher The University of Arizona.

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Link to Item http://hdl.handle.net/10150/566530 GEOLOGY OF THE MORNINGSTAR MINE AREA,

GREATERVILLE MINING DISTRICT,

PIMA COUNTY, ARIZONA

by James Conrad Stewart

A Thesis Submitted to the Faculty of the

DEPARTMENT OF GEOSCIENCES

In Partial Fulfillment of the Requirements For the Degree of

MASTER OF SCIENCE WITH A MAJOR IN GEOLOGY

In the Graduate College

THE UNIVERSITY OF ARIZONA

1 9 7 1 STATEMENT BY AUTHOR

This thesis has been submitted in partial fulfillment of re­ quirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judg­ ment the proposed use of the material is in the interests of scholar­ ship. In all other instances, however, permission must be obtained from the author.

SIGNED:

APPROVAL BY THESIS DIRECTOR

This thesis has been approved on the date shown below:

2 0 (

of Geology ACKNOWLEDGMENTS

For their contributions which so greatly aided the undertaking, presentation, and completion of this study, I express my appreciation to Dr. John M. Guilbert, my major professor, and to Dr. William C.

Peters, for their guidance and encouragement; to Mr. Eric Braun and

Dr. William Rehrig, fellow students, for their assistance as survey rodmen; to Mr. G. A. Barber of The Anaconda Company for use of Ana­ conda's assay data from the Morning star mine; to Mr. Michael Gross, fellow student, for the benefit of our "geologizing" and discussions of the area; and to M iss Judy Margolis for her drafting work.

To Mr. and Mrs. Fred Harm, lessees of the Morning star mine, go extra special thanks for the generous and enthusiastic donation of their time, efforts, and accommodations. Use of the living quarters at the mine and the splendid board prepared by M rs. Harm greatly facili­ tated the field work and made for a most pleasant and comfortable summer. Mr. Harm's familiarity with the area, acquired from long association and persistently diligent work, was an invaluable aid.

Additionally, the actual physical assistance given by Mr. Harm made possible the study of underground workings otherwise inaccessible.

For their steadfast encouragement and financial support, with­ out which this program would not have been possible, I am especially grateful to my parents, Mr. and Mrs. James A. Stewart.

iii TABLE OF CONTENTS

Page

LIST OF ILLUSTRATIONS...... v i

ABSTRACT...... v iii

INTR O D U C TIO N ...... 1

GEOLOGY...... 8

R o c k s ...... 8 Sedim entary R o c k s ...... 9 • Igneous Rocks ...... 17 Metamorphic Rocks...... 19 . C o r r e la t io n ...... 20 A g e ...... 21 S tru ctu res...... 23 Major Structures of the Sedimentary Rocks...... 23 Minor Structures of the Sedimentary Rocks...... 26 Structures in th e Igneous R o c k s ...... 35

MINERAL D E P O S I T S ...... 36

The Morningstar M in e ...... 36 M in e r a lo g y ...... 40 V e i n s ...... 45 R o c k s ...... 47 S tru ctu res...... 51 Other Mineral D eposits ...... 54 V e in s...... 54 P la c e r s ...... 61

SUMMARY, INTERPRETATION, AND EVALUATION...... 65

Order of E v e n t s ...... 66 R egional Folding of th e Sedim entary R o ck s...... 66 Regional Thrust F au ltin g ...... 67 Quartz M onzonite I n t r u s io n ...... 68 U p lift of G ranite M o u n t a i n ...... 68 Local Minor Faulting ...... 69 C la s sific a tio n o f M ineral D e p o s i t s ...... 70 Economic Evaluation of Mineral Deposits ...... 71 The M orningstar M i n e ...... 71 Other M ineral D e p o s i t s ...... 72

iv V

TABLE OF CONTENTS— Continued

Page

APPENDIX: ASSAY DATA, MORNINGSTAR M IN E ...... 74

REFERENCES 77 LIST OF ILLUSTRATIONS

Figure Page

1. Location Map ...... 2

2. Geologic Interpretation Map Morningstar Mine Area . in pocket'

3 . Geologic Outcrop Map Morningstar Mine Area .... in p ock et

4. Stratigraphic Column Morningstar Mine Area .... in p ock et

— 5 . C ross S ectio n s M orningstar M ine A r e a ...... in p ock et

6 . S h a l e ...... 10

7. Silts tone ...... 12

8 . A rgillite ...... 12

9 . Rock C la s s ific a tio n D ia g r a m ...... •...... 14

10. Q u a rtzite...... 15

11. Arkose R id g e s...... 15

12. Quartz M o n z o n ite ...... 18

13. Folds near the Morningstar Mine ...... 27

14. Folds North of the Morningstar M ine ...... 27

15. Folded L im e s t o n e ...... 29

16. Bedding Plane Fault ...... 33

17. Morningstar Mine ...... 38

18. Block Diagram of the Morningstar Mine ...... in p o ck et

19. Composite Level Plan Map of the Morningstar Mine . in pocket

20. Cross Section of the Morningstar Mine Shaft .... in p o ck et

21. Gold-bearing Quartz Vein in Argillite ...... 44

22. Quartz Vein Cutting A rgillite ...... 56

vi vii

LIST OF ILLUSTRATIONS— C ontinued

Figure Page

23 . A L enticular Quartz V e i n ...... 56

2 4 . Quartz Vein in Quartz M o n z o n i t e ...... 59 •

25. Stream Bench G ravels ...... 62

26. Gold Nuggets ...... 64 ABSTRACT

The Morningstar mine area is located in the Greaterville mining district, Pima County, Arizona. The area constitutes a north-trending, east-dipping, 2,000-foot thick sequence of arkose, quartzite, and shale regionally folded into anticlines and synclines plunging to the southeast.

Later thrusting placed younger rocks in the southeast over older rocks to the northwest. Probably Cretaceous in age, the sedimentary rocks are cut by the small Tertiary quartz monzonite Granite Mountain stock.

The stock produced local hornfelsic alteration of the stratified rocks and emplaced small and presently uneconomic quartz vein deposits of pyrite, galena, sphalerite, chalcopyrite, gold, and silver in both the stock and the sedimentary rocks. The principal deposit, the Morningstar mine, consists of narrow lenticular veins controlled by bedding plane faults in argillite, quartzite, and hornfels occupying the crest and south­ west flank of a regional fold.

Following post-intrusive uplift of the quartz monzonite, rapid early erosion removed the upper, thrust plate south of the fault to reveal the vein deposits and to form gold-bearing placer deposits.

viii INTRODUCTION

The area of study is located in the Greaterville mining district approximately half a mile west of the nearly abandoned community of

Greaterville in the southeast corner of Pima County, Arizona (Fig. 1).

Forty-five miles from Tucson, the site is accessible by automobile and is most easily reached from the east by using the Box Canyon-Thurber

Ranch road from Arizona State Highway 83. The Box Canyon-Thurber

Ranch road is 18 miles south of the junction of State Highway 83 with

Interstate Highway 10. The area is in the eastern foothills of the Santa

Rita Mountains at an elevation approximately 1 mile above sea level. It includes parts of secs . 24 and 25, T. 19 S., R. 15 E ., as shown on the

Sahuarita, Arizona, quadrangle of the U.S. Geological Survey 15-minute topographic series.

The topography of the northern third and eastern half of the area is of rounded, elongate hills and ridges separated by short and very nar­ row, steep-sloped gullies. The average relief between gullies and ridge crests is approximately 100 feet. The western and southwestern part of the area includes a portion of Granite Mountain, whose steep rubble- covered slopes rise nearly 500 feet above the surrounding ridge crests.

The maximum relief of the area, from a low at the eastern end of Ophir

Gulch, or Hughes Gulch as it was called in earlier reports, to the high at the peak of Granite Mountain is 690 feet. Ophir Gulch is the major drainage channel of the area draining seasonal flow from west to east.

1 2 'SONOITA NOGALES TUCSON A A R !Z O N A ■SONOITA AREA THESIS 1 ------1 ------i TUCSON CONTINENTAL Figure 1. Location Map

S 3 1 V 0 0 N 3

Recorded history of the Greaterville mining district is scant, fragmental, and scattered. M iscellaneous bits of original copy concern­ ing the early-day activities of the town and district are contained in the

Greaterville file at the Arizona Historical Society in Tucson. Most not­ able are the papers, correspondence, notations, and personal records of John B. and Mary E. Anderson, two of the more prominent early pio­ neers of the area. The best sources of geological and mining data, which were compiled several decades after the peak of the camp, are the sum­ mary reconnaissance reports by Hill (1909) and Schrader and Hill (1915).

Although lode mineralization is reported to have been found first, it was from the discovery of placer deposits of gold in 1874 that the Smith district was first established and named after the discoverer,

A. Smith. On March 2, 1881, the area was formally organized and re­ named the Greaterville mining district.

Although it contains approximately 50 square m iles, with the western boundary near the crest of the Santa Rita Mountains, the Greater­ ville-district was noted mainly for its few square miles of placer gold deposits. Therefore, the mining history of the district is mainly the his­ tory of the placer operations in the gulches of the lower foothills immed­ iately west of the Greaterville townsite. Hill (1909) reports a statement from P. J. Coyne, an early and long-time resident of Greaterville, that by 1881 the rich gulch gravels had been well worked and that by 1886 the active life of the camp had come to an early demise.

The nature of the placers and the mining conditions of the times must have been determining factors in the short life of the district, for the deposits were certainly not fully exploited. Narrow, short gullies 4

with shallow gravel fill precluded the use of large machinery for exten­

sive mining. Much of the gold is very fine and intimately mixed with

indurated clay. A high recovery was prevented by lack of large volumes

of water necessary to work such material. Furthermore, the heterogen­

eous mixture of fine sands with boulder gravel made necessary the

selective excavation of workable gravels . Consequently, with the

methods and economic conditions of the early days, effective mining

was restricted to recovery of coarse gold from relatively clean coarse

gravels that could be easily obtained and worked with a minimum amount

of water and with such simple equipment as rockers and short sluices.

Burchard (cited by Hill, 1909) estimates that the yearly produc­

tion from 1874 to 1881 was about $12,000. Coyne (cited by Hill, 1909)

estim ates, with the corroboration of several miners, that the total pro­

duction of the camp had a value of $7,000,000 up to 1909. From infor­

mation obtained from local gold buyers, Hill (1909) estimated that the

yearly production from 1902 through 1908 was about $3,000. The sum of

the estimated yearly production up to 1909, even allowing $12,000 per

year for the unreported years of 1882 to 1902, is only about one-twentieth

, the amount of the total production of $7,000,000 estimated by Mr. Coyne

for the same period of time. Lack of accurate records, the usual tenden­

cy to overestimate mineral recovery and value , consideration of the

mining conditions of the late 1800's, and the nature of the placers all

serve to make the $7,000,000 figure seem unreasonably high. I prefer

to accept the lower value of estimated yearly averages giving a total

well below $ 1,000,000. 5

After the decline of the camp in 1886, several attempts were made at hydraulic mining and dredging by the Stetson Company in 1903, the El Oro Mining Company in 1903 (Blake, 1903), the Santa Rita Water and Mining Company in 1905 (Schrader and H ill, 1915), and the Greater- ville Dredge Gold Mining Company in 1914-1915 (Root, 1915). Appar­ ently all were unsuccessful.

Subsequent placer operations were sporadic and meager, and apparently they concentrated on reworking the old dumps and tailings of the gulch gravels with simple one- and two-man methods involving panning, rockers, trommels, and jigs. There was a brief increase of activity in the late 1920's and early 1930's. Total value recovered for the years 1903 through 1926, as reported in Arizona Bureau of Mines

Bulletin 140, was only $50,000. In recent years, a few sm all-scale attempts to exploit new ground have yielded gold, although the opera­ tions have not been profitable.

Lode mining was also of short duration, being limited mainly to the exploitation of near-surface, oxidized, supposedly "high.-grade" ore.

Although the area is marked with numerous shafts, pits, tunnels, cuts,, and trenches, most are very shallow or short, measuring only tens of feet. For the entire district, Schrader and Hill (1915) mention only 12 mines or prospects, and only two of these had shafts as deep as 100 feet. At the time of Hill's visit most of these workings were inactive, as they are today. Many are still accessible, though not easily or

s a fe ly .

Knowledge of the district passed on by recently deceased life­

long residents of Greaterville indicates that most of the underground V

6 work was done in the very early days of the district, at least prior to

1900. Since that time, some new prospects have been opened, and prob­ ably there has been some minor extension and development of older work­ ings but nothing significant or extensive has been accomplished. With the exception of the Morning star mine, the underground workings in the area are probably little changed from the time of their initial development or from the time of Hill's visit in 1909.

The total value of metal production from the Greaterville district for the years 1903 through 1933, as reported in Arizona Bureau of Mines

Bulletin 140, is $93,366. This includes silver, copper, lead, and gold from both placer and lode deposits, with only about $40,000 coming from lode mining. In effect, lode mining for most of the district has not ad­ vanced much beyond the prospect stage, with the result that subsurface geology and mineral potential are virtually unknown. The dearth of know­ ledge and the lack of development probably go hand in hand.

The amount of published geological information on the district is scant and that available, though suitable for its time and purpose, is old and summary in scope or is part of a regional work which incorporates a very generalized interpretation of the district geology. The earliest and best known report on the district, by Schrader and Hill (1915), is a recon­ naissance with attention paid mainly to brief descriptions of the pros­ pects, mines, and placer deposits . Subsequent reports on the district are taken largely from Schrader and H ill. Sm all-scale maps of regional

coverage, such as those of the Arizona Bureau of Mines and the U .S.

Geological Survey, incorporate the district geology necessarily only in

broad categories of rock type, age assignment, and structure. Only 7 within the last few years has the district received renewed attention.

Impetus for this interest was in part prompted by the mineral exploration surge beginning in the early 1960's which has led to mapping, geophys­ ical surveys, and exploration drilling by several mining companies. Also during 1966 and 1967, the U .S. Geological Survey remapped the Sahua- rita and Mount Wrights on quadrangles. Academic focus on the district includes the work by Gross (1969) and this thesis.

The purpose of this study is to enlarge upon the knowledge of the ore deposits and mining potential of the Greaterville district. Geo­ logic mapping and laboratory examination of rocks and ore minerals of the Morning star mine and its immediate surroundings are the bases for interpretation.

Laboratory work included the mineragraphic examination of eight polished sections of ore minerals and the petrographic examina­ tion of 25 rock thin sections from the Morningstar mine. Geologic map­ ping, both surface and underground, was done with a Brunton compass and tape and by pacing. Surface mapping was by the isolated outcrop method, the data plotted on a base map of the scale of 1 inch equals

100 feet, with a contour interval of 20 feet. The base map was con­ structed by plane table and alidade topographic surveying. Under­ ground features were mapped on a gridwork mine plan of a scale of 1 inch equals 10 feet. Measurements were made from the center line of the workings at waist height or in some places at half the distance between the floor and the back. Field work time totaled 11 weeks and was done during the spring and summer of 1968, mostly during July and August. GEOLOGY

The study area (Fig. 2, in pocket) is part of a 1- to 2-mile wide strip of generally north- to northwest-trending, folded and faulted,

eastward-dipping sedimentary rocks, bounded on the west by the central

part of the Santa Rita Mountains and to the east by alluvial valley fill.

The sedimentary rocks are cut by the quartz monzonite Granite Mountain,

a small, isolated stock which has locally altered the intruded rocks and

caused emplacement of mineralized quartz veins.

Rocks

Approximately three-fourths of the area, the northern and east­

ern one-half, are underlain by sedimentary rocks (Figs. 2 and 3 , in

pocket) and the southwest quarter is the Granite Mountain quartz mon­

zonite stock. With no evidence to the contrary, the stratigraphic se­

quence is apparently upright. Although interrupted by many local

deflections, the sedimentary rocks have a prevailing gentle eastward

dip, and the oldest units are exposed to the west and the younger units

to the east.

Although construction of the stratigraphic sequence (Figs. 4

and 5, in pocket) is qualified by many uncertainties, the presumed older

and lower part of the column to the west is characterized by thin beds

of fine-grained shale, siltstone, chert, and quartzite. Eastward and

upward in the column the units become thicker, larger in grain size,

with a prevalence of quartzite and a diminution of shale and siltstone.

The youngest and most easterly units are relatively thick, medium- to

8 9 coarse-grained arkose, interspersed with a few thin units of limestone or calcareous silts tone. The youngest rock in the area is the quartz m o n zo n ite.

Sedimentary Rocks

The sedimentary rock sequence is composed preponderantly of numerous thin beds of very fine to coarse-grained siliceous clastic rocks interspersed with a few units of variable carbonate content from minor to that of nearly pure limestone. The contacts of members are commonly gradational, resulting in a sequence of homogeneous units admixed with units of variable composition and texture. The character- • istics of the principal individual units are summarized below.

Bedded Chert. These units are few in number but are readily discerned by their conspicuous outcrop, although no unit thicker than approximately 6 feet was seen. They are white to light-gray micro­ crystalline silica and are very dense, tough rocks which break with a conchoidal, flintlike fracture. Most occurrences of chert are interbedded with and grade into fine-grained quartzite.

Shale. Shale is present throughout the area, although natural exposures are small, inconspicuous, and largely obscured by debris of other rocks. Thickness varies from individual layers of several inches or less separating beds of quartzite to prominent sequences up to ap­ proximately 10 feet thick, such as shown in Figure 6. Exposures in prospect pits suggest that shale probably constitutes a much larger por­ tion of the total sedimentary rock column than outcrops indicate. Colors are yellow, tan, light gray, and brown, with local occurrences of red­ dish-brown iron oxide stain, mostly in thin seams along bedding planes. 10

Figure 6. Shale

Exposure in prospect pit shows very thin individual beds. Blocky bed at upper right is approximately 1 foot thick. 11

Siltstone. Silts tone is common, although distinct homoge­ neous units free from admixture with shale and sandy units probably constitute a very small portion of the total sedimentary rock section.

The maximum thickness is approximately 5 feet. Although the unit in

Ophir Gulch between the two ponds (Fig. 7) possibly exceeds 10 feet, its lower boundary is not visible. Colors are gray, brown, and black, and composition is of quartz and other detritus mixed with clay. Gener­ ally, the siltstones are moderately dense and tough with no apparent bedding laminations. The siltstone of Figure 7 shows an unusual type of weathering as the rock deteriorates by a spalling process to produce a rubble of irregular-shaped, sharp-edged fragments. Some siltstones have a notable amount of very fine grained disseminated pyrite.

Argillite. Argillite is here used to designate those rocks simi­ lar to siltstone and shale in texture and composition, and which show bedding but lack fissility. They are more compact and cohesive than shale but still are readily broken to small blocky fragments (Fig. 8).

Some cuts indicate thicknesses of approximately 15 feet. Color is gen­ erally a mixture of white and dark brown from iron oxide staining, al­ though the units are free from observable pyrite.

Quartzite and Arkose. The fine- to coarse-grained quartz feldspar clastic rocks are represented by a variety of textures and com­ positions, so that a gradational series exists from relatively pure quartz ite to arkose. Precise determination of mineral content and the type and amount of interstitial material would probably establish such intermed­ iate members as feldspathic quartzite, siliceous arkose, subgraywacke, and other modified members .* Only the twofold designation of quartzite 12

Figure 7. Siltstone

Note the flaky rubble produced by a spalling process of weath­ ering .

Figure 8. Argillite

Shattered intraformational folds in road cut north of the Morn­ ing star mine. 13 and arkose are used here, based on the classification system shown in

Figure 9 .

Quartzite units are abundant and conspicuous throughout the area. The maximum thickness is approximately 15 feet, but most units are less than 7 feet. Color is generally tan to dark brown on the surface, with fresh exposures gray to white beneath the iron oxide stain. Com­ position is predominantly of fine-grained, well-rounded to subhedral quartz, tightly cemented with interstitial silica. Feldspar is notable in most units, ranging up to as much as 25 percent of the composition.

With few exceptions, disseminated pyrite is present in amounts varying from negligible to approximately 5 percent. Strongly indurated and very tough, these rocks break with a smooth conchoidal fracture, giving a glassy appearance on the fresh surface. The quartzite units seen in

Figure 10 demonstrate the thin-bedded repetitive nature of the stratig­ raphy in the study area.

Arkose is the most prevalent sedimentary rock in the area. Al­ though no distinct individual unit was measurable, the large areal extent of virtually uninterrupted arkose in the northern half of the area . suggests that individual beds may measure in the tens of feet. Color is from tan to light orange, and a few units are a faint olive drab. Com­ position is predominantly of subrounded to angular quartz grains with abundant feldspar, commonly over 25 percent. Grain size ranges from fine to coarse, with medium size most prevalent. Units vary in con­ tent from relatively pure quartz feldspar to those with notable interstitial clay and silt, giving the rock a dirty appearance. Individual grains and grain boundaries are distinct, although commonly the feldspars, 14

l

QUARTZ 3 CHERT

OR THOQUARTZITE

IMPURE ARKOSE

clay astir FELDSPAR a ACCESSORY UtNERALS a KAOLIN a CEMENT

Figure 9. Rock Classification Diagram.—Modified from Krynine (1948, p. 137)

The dashed line encloses the principal quartzite-arkose rock types found in the Mornings tar mine area. The amount of each type with­ in the line is an approximation of its percentage of the total. 15

Figure 10. Quartzite

Thin beds of quartzite separated by thinner units of shale.

Figure 11. Ark os e Ridges

View to the east shows hill crests formed by steplike ridges of arkose. The rusty-looking spot in the center of the picture is either a cloud shadow or a flaw on the negative. 16 weathered to kaolin, are incohesive and earthy. Iron oxide is present as casts, crusts, and as interstitial fillings, although pyrite is seldom seen. More deeply and evenly weathered and not as strongly cemented, arkose is not as tough as quartzite and breaks to a granular hackly sur­ fa ce .

Arkose and quartzite are the most abundant sedimentary rocks in the area, together making up probably more than two-thirds of the total sequence. These rocks are also the most resistant to erosion and are conspicuous as ridge formers and as the backbone of rounded h ills.

The ridges in Figure 11 are of arkose.

Limestone and Marble. These two rock types are restricted to the southeast quadrant of the map areas (Figs. 2 and 3, in pocket)

in the vicinity of the Old Tucson shaft and to a very thin belt extending west from the shaft. The maximum thickness of limestone is approxi­

mately 10 feet at the shaft, though neither upper nor lower boundaries were seen. The color varies from dark gray to a pale pink, and the

composition is of microcrystalline to very fine grained calcite. The

units are moderately dense and homogeneous with some intraformational

folds and flexures. No fossils were found.

The marble is exposed on the nose of the southeast-trending

hill on which the Old Tucson shaft is located. The plane of the bedding

roughly parallels the slope of the hill so that the actual thickness is

probably very much less than the exposure suggests, probably less than

10 feet. The unit is tan and white and composed of fine- to coarse­

grained recrystallized calcite. It is massive though very severely con­

torted with multiple tight folds and flexures. 17

Silicified Limestone. These units are in the south-central part of the mapped area close to the southern boundary (Figs. 2 and 3, in pocket) and are generally aligned with the limestone. Thickness of in­ dividual beds is approximately 4 feet. The units are white, composed of microcrystalline silica and calcite, and are massive, dense, and homogeneous in structure and texture.

Calcareous Siltstone. The calcareous siltstones are minor in the total stratigraphic column and are most commonly seen interbedded with arkose.and quartzite, primarily in the north half of the mapped area, north of Ophir Gulch. The maximum thickness is approximately 2 feet. The siltstones are dark-gray rocks composed of microcrystalline to very fine grained calcite and silt. Generally, they are moderately compact, consist of very thin, strongly contorted laminations, and con­ tain veinlets and irregular-shaped clumps of white, coarse-grained, recrystallized calcite. In places they are shaly with a platy structure.

Igneous Rocks

Igneous rocks are present as the Granite Mountain porphyritic quartz monzonite stock, which occupies the southwest quadrant of the mapped area. The small mountain mass is strongly broken, the slopes covered largely with boulder rubble with quartz-vein fragments abun­ dantly scattered throughout (Fig. 12).- Outcrops generally consist of massive blocks, nearly in place, but slightly separated and shifted

from their original position. The rock shows light colors of tan to nearly white hues, exhibiting a slight orange cast in places. Iron and man­ ganese oxide stain is pervasive over the rock mass, though not equally distributed or abundant. The rock varies from fine to coarse grained, 18

Figure 12. Quartz Monzonite

Blocky rubble on Granite Mountain. The boulder is approxi­ m ately 4 feet w id e . 19 and is generally, though not consistently, porphyritic with feldspar phenocrysts up to 1 inch long. Hand specimens commonly show medium- grained subrounded quartz "eyes" in a groundmass of sericitized feldspar and chloritized biotite, which is usually present in amounts less than

5 percent. Fine-grained pyrite as both fresh and weathered grains is common. The exact nomenclature of porphyritic quartz monzonite was petrographically determined by Gross (1969) based on an average com­ position of six samples.

A narrow aplite dike, probably less than 10 feet thick, is re­ vealed in two outcrops on the east flank of Granite Mountain. The ex­ posures are in alignment in a northeast direction, with the southerly outcrop dipping 65° SW. Composition is of fine-grained, equigranular quartz and orthoclase.

Metamorphic Rocks

Metamorphic rocks are minor in the area and are located pre­ dominantly in the central part, occurring as both erosional debris on the lower east flank of Granite Mountain and as several thin beds up to 2

feet thick that are within 300 to 500 feet of the approximate.contact with the quartz monzonite. The small patches of erosional rubble found

on the east flank of the mountain just west of the Morning star mine con­

sist of a dark-green and brown banded rock, composed primarily of very

fine grained diopside with metacrysts of garnet. The thin beds are of a

light-green microcrystalline groundmass with thin parallel bands and

clumps of garnet and are referred to on the map (Fig. 3, in pocket) simply

as lim e-silicate rocks. 20

In the western part of the area north of Ophir Gulch and in the central part of the area just east of Granite Mountain are several thin units with a maximum thickness of 4 feet that are designated hornfels.

The rock is black, exhibiting a purplish sheen when broken. It is very dense, homogeneous, and tough and breaks with a conchoidal to flint­ like fracture. All units are microcrystalline to cryptocrystalline. Gross

(1969) determined the composition to include quartz, diopside, sericite, plagioclase, calcite, and the sulfides pyrite, pyrrhotite, and chalcopyrite.

He attributes the formation of the units to preferential metamorphism of shales by the intrusion of the Granite Mountain quartz monzonite.

Correlation

Correlation of sedimentary units and tracing of beds, even in

the small area of this thesis, is tenuous at best and often impossible.

The ground is well covered with a thin blanket of admixed erosional

debris, and outcrop of sedimentary rocks is probably no more than one

percent. Lithologic correlation is often dubious because of the repeti­

tive sequence of nearly identical thin beds. One cannot be sure if an

exposure of several feet of thin shales alternating with thin siltstones

and quartzites is the same sequence as an outcrop of alternating thin-

bedded shales, siltstones, and quartzite seen elsewhere. Additionally,

the short outcrop lengths and the absence of distinct marker beds sug­

gests a rapid lateral change in composition, texture, and appearance of

individual units. Such lensing and interfingering could well be expected

in a sedimentary environment of the type here represented, so that some

units are probably very local with an extent of only tens of feet. The

problem of correlation is further compounded by the compositional and 21 appearance changes caused by metamorphism and by the dislocation and mechanical effects of deformation.

The lack of readily correlative sedimentary sections and the lack of any other substantial evidence permitting correlation with rocks of known age preclude a reliable age assignment. Consequently) the age of the sedimentary rocks was not independently determined.

Age

The earliest age given is Cambrian (Hill, 1909). Although recognizing the uncertainties, he surmised that the igneous rocks were

Precambrian and that the surrounding sedimentary units, on the basis of their position and lithologic similarity to the intrusive rocks, were thus Cambrian. Wilson (1927) states that the sedimentary rocks are probably Cretaceous, although he gives no evidence. Wilson correctly noted that the Granite Mountain intrusion cuts the sediments and is thus probably M esozoic or younger in age. The Granite Mountain quartz mon-

zonite has been dated by the potassium-argon method as 63+1.5 m .y .

(Gross, 1969), thus confirming its Laramide age. The sedimentary rocks are therefore at least pre-Laramide, and they are probably no younger than middle Cretaceous in age.

Use of the Cretaceous for the age of the sedimentary rocks in the Greaterville area is based on their regional proximity and general

lithologic similarity to the Cretaceous sections described elsewhere in

southeastern Arizona. The nearest described stratigraphic sections of

probable Cretaceous age are those of Schafroth (1965) on the south flank

of the Empire Mountains, approximately 8 miles northeast of Greaterville,

and those of Casa Blanca Canyon by Stoyanow (1936) and Adobe Canyon 22 by Moran (1957). Both Casa Blanca and Adobe Canyon are approximately

6 miles south of the thesis area. However, the intervening country be­ tween the Greaterville area and the north and south sections is marked

by faulting and masked by deep alluvial cover, thus precluding direct

visual correlation. Additionally, the correlation handicaps encountered

in the Greaterville area are reported also by the above authors, thus

making their constructed stratigraphic columns of questionable applica­

tion, even locally.

The sedimentary rocks of the Greaterville area seem to compare

most favorably with those of several sections of different locales, all

dated as Early Cretaceous: the Morita Formation described by Ransome

(1904), the lower part of the Lowell formation described by Stoyanow

(1936), and the Turney Ranch Formation described by 8 ch a froth (1965).

In general, these formations are all correlative with one another, and

all are assigned an Early Cretaceous age.

Although no confirmative evidence was found in the field or from

the literature to fix the age of the stratigraphy in the thesis area, several

considerations do suggest an assignment to Early Cretaceous time. The

sedimentary rocks of the thesis area do, in fact, resemble and in some

respects rather closely compare with the described sections mentioned

above. Additionally, I have no knowledge of any similar section of any

other age in the basin area. Also, the relative position of the Greater­

ville rocks as they flank the mountains is similar to the flanking posi­

tion of the Cretaceous sections . In view of the above considerations,

regardless of the spatial and correlative problems discussed, I suggest 23 that, although their actual age remains undetermined, the sedimentary rocks of the Greaterville area are probably Early Cretaceous in age.

Structures

The study area is strongly deformed by folding and faulting, ex­ hibiting adjustments to regional and local stresses which are p re intru­ sive and postintrusive in age. The landforms and configurations of rock units as modified by erosion are primarily the result of an anticline- syncline pattern and an east-west fault that bisects the area (Fig. 2, in pocket), hereafter referred to as the Morningstar fault. For discussion, structures are divided into those of the sedimentary rocks and those of the igneous rocks, with the sedimentary rock structures further divided into major features that are more or less all inclusive of the stratigraphic column, and minor features that are very local.

Major Structures of the Sedimentary Rocks

Folds. The most pronounced structural features of the sedi­ mentary rocks are the regional folds that are displayed as several north­ west-trending anticlines and synclines. Folding is most clearly defined in the south-central part of the area (Fig. 3, in pocket) where the sedi­

mentary rocks make a sharp bend around the synclinal axis from a north­

west strike and northeast dip to an east strike with a south dip. Moving

northward from the southern edge of the area, the beds have an east-

northeast trend dipping to the south to a position in the east-central

part of the area where they begin to turn more sharply to the north. The

turning point or crest of the fold seems to be along a line from the

Morningstar mine to the southeast corner of the area. 24

South of the axial line, the stratigraphy seems to be of one conformable sequence and is generally traceable up to the fold's crest.

North of the crest, the southern rock's are not apparent and a new se­ quence of rocks appears, though their configuration is generally con­ sistent with the established trend. On the north side of the axial line, and most apparent in the vicinity of the Morningstar mine, the north limb of the fold begins to be expressed by a north-northwest strike of the beds. Continuing north of the road, the beds make a gentle curve back to the northeast, and in the northeast corner of the area they again make another bend to the north, thus completing the configuration of a dominant anticline and syncline in the central part of the thesis area, a minor syncline in the southern part, and a portion of an anticline in the northeastern part, all having a northwesterly axial line. Along the eastern edge of the area is a line of outcrops each exhibiting an east to northeast strike, dipping to the south. This attitude does not readily fit into the prevailing pattern discussed above.

A smaller but very distinct fold pattern is exposed in the far northeast corner of the area (Fig. 3, in pocket) by the very tightly folded thin limestone beds which form a northwesterly striking anticline. While the axial line of this small structure is parallel to those already dis­ cussed, the occurrence presents an apparent anomalous situation in that the broadly curving arkose beds which form the ridges topographically

above the limestones are in an oblique, nearly right-angle superposition

overlying the tight fold. The arkoses strike north to northeast, and the

limestones and the fold strike northwest. This anomaly may be due to two different fold patterns . 25

Evidence of folding is not so clear in the northwest quarter of the area where changes of rock attitude are much more gradual. The gen­ eral configuration north of Granite Mountain is one of north-northwest- striking beds gently curving to strike north-northeast, conforming to and probably part of the syncline more sharply developed to the east. In the far northwest corner are a few isolated outcrops of beds with a pronounced northwest strike and northeast dip which suggests another fold pattern.

However, exposures are so few and correlation so tenuous that any inter­ pretation is very speculative.

Faults. Probably the area is cut by many more faults than could be mapped, but at least two prominent faults are present. Begin­ ning in Ophir Gulch at the.west edge of the area (Figs. 2 and 3, in pock­ et), the Morningstar, the dominant of the two faults, strikes east-south­ east, generally following the course of the stream until it reaches the

Morningstar mine. This Ophir Gulch section of the fault separates

Granite Mountain to the south from the north-northwest-striking sedi­ mentary rocks to the north. On the north slope of Granite Mountain is a small exposure of south-dipping sedimentary rocks striking west, which is nearly normal to the beds on the north side of Ophir Gulch. Extension of the Morningstar fault eastward from the mine is not easily corroborated.

Its continuation is postulated on rather indirect and suggestive evidence, such as the apparent truncation of beds described in the section on folding. Several outcrops of sedimentary rocks along a line that is gen­ erally parallel to and coincident with the crest of the fold have very steep dips which are suggestive of drag effects from downward movement 26

Parallel to the west edge of the area (Figs. 2 and 3, in pocket) is a second large fault striking north. This fault traverses both the quartz monzonite of Granite Mountain and the sedimentary rocks to the north, cutting the Morning star fault at a right angle. The fault is traced by a trail of breccia, present as erosional rubble on the slope of the moun­ tain and as an alignment of exposures in prospect pits in the sedimen­ tary rocks. The breccia is of angular fragments of sedimentary rocks and quartz monzonite cemented with vuggy, very coarse grained euhedral quartz. The north stream bank is a section normal to the strike of the fault and shows breccia grading into less broken sedimentary rocks to the west. These beds dip to the northwest, appearing upturned against the fa u lt.

Minor Structures of the Sedimentary Rocks

Folds. Considered here are the small flexures on the scale

of drag and intraformational folds. The limestone units throughout the

area, but particularly the thinly laminated silty variety intercalated with

the arkose in the northern half of the area, are commonly very strongly

distorted with crenulations of folds, faults, and drag effects, all with

no discernible pattern.

The most notable and significant occurrences of minor folding

are in the vicinity of the Morningstar mine, where two distinct patterns

are seen at right angles to each other. In the cut banks on both sides of

the mine shaft, the argillites show small nearly symmetrical folds (Figs.

3, in pocket, 8, and 13), with east-west axial planes inclined 38° E,

conforming to the dip of the beds. These fold zones approach the mine

from the north and south until they reach the small tunnel a few feet 27

Figure 13. Folds near the Morning star Mine

Argillite approximately 30 feet south of the hoisthouse shows intraformational fold plunging 38° E.

Figure 14. Folds North of the Morningstar Mine

Argillite 300 feet north of hoisthouse shows drag fold slightly overturned to the w est. 28

north of the main shaft, where they are obliterated in a zone of crushed, pulverized rock (Fig. 8). Similar folding is exposed in the stream bank

at the base of the mine dump. Confinement of these small flexures re­

flects relative competency of the folded units with respect to that of the

overlying and underlying unfolded beds.

In contrast to the above, another pattern of minor folding is

revealed in the north bank of the stream about 300 feet north of the mine

and in a prospect pit about 200 feet east of the mine. In the north bank

several argillite units show mild, asymmetrical drag folds slightly over­

turned to the west, with a north-south axial plane (Fig. 3, in pocket,

and Fig. 14). Here also, the folding is intraformational, the overlying

and underlying units remaining undisturbed. The prospect pit is on a

thin limestone bed which shows very tight, nearly symmetrical drag

folds (Fig. 3, in pocket, and Fig. 15), and like the argillite in the

stream bank has a north-south axial plane slightly overturned to the

west. However, the limestone has a much steeper eastward dip than

that of the argillite.

Faults. Throughout the area are numerous indications of local

adjustment of the rocks to stress, the effects of which are commonly

seen either for only a few tens of linear feet over a relatively small area

or are restricted to a particular bed or sedimentary unit.. Apparently

depending on both the nature of the stress and the individual rock char­

acteristics, various types of minor faults are present including strike-

slip, normal, and bedding plane. The widespread occurrence and variety

of types suggest that such dislocations are probably much more prevalent

than the few obvious ones discussed below. 29

Figure 15. Folded Limestone

Exposure 200 feet east of Morning star mine shaft, looking south. The point of the pencil in the center of the picture is at the crest of a tight fold slightly overturned to the west. The axial plane of the fold strikes north-south. 30

In the northeast corner of the area is the one notable example of a strike-slip fault, which offsets the nose of the small southeastward- plunging fold. The fault strikes northeast, cutting the strike of the sedi­ mentary rocks at a right angle. The fault appears to be nearly vertical and, as indicated by the relative position of the flanks of the fold on opposite sides of the fault, to have a right-lateral movement of probably no more than 50 feet.

In the south-central part of the area, just west of the Fulton shaft (Fig. 3, in pocket), two parallel strike-slip faults are inferred which strike northeast and are about 300 feet apart. No evidence was seen to suggest the dip. Both appear to have right-lateral movement.

Placement of the northwest fault is based on what seems to be an offset of sedimentary beds. The correlation difficulties and the position of the inferred fault plane subparallel to the strike of the beds does cause un­ certainty as to whether a true break and offset exists or whether the appearance of such is simply due to local flexures of the sedimentary rocks. I conclude that a fault is probable.

The second fault, to the southeast of the first, cuts the sedi­ mentary rocks more obliquely than does the first fault. It is also pos­ tulated to exist mainly on the appearance of bedding offset displayed at its northeast end (Fig. 3). Extension of the fault to the southwest is based on the alignment of two prospect pits showing sheeting and local faulting. Brecciation and the occurrence of m assive, vuggy quartz float mark the southwest end. Although it is still tenuous, the evidence for the existence of this fault seems more positive than that for the fault to the northwest. 31

A small fault is exposed in a draw approximately 400 feet north of the lower dump on the north face of Granite Mountain. A thin bed of arkose striking northeast and dipping approximately 24° SEi, consistent with the prevailing attitude of the adjacent beds, abruptly abuts against a shale bed which strikes northwest and dips 60° NE.

In the southeast quadrant, a fault is inferred along the north- west-southeast gulch to the west of the Old Tucson shaft (Fig. 3, in pocket). The inference is based upon what appears to be truncation of the east-west-striking silicified limestone beds to the west and upon float of brecciated limestone in the draw. The evidence for a fault there is very tenuous as correlation is uncertain. The limestone units to the east near the shaft may or. may not be the same as the units across the draw to the west. I believe that the units are not the same. A fault is thus indicated.

Of yet less significance than the faults just discussed are numerous occurrences of what are probably normal faults with relatively minor displacement. These small dislocations are exposed mainly by prospect pits, most of which are in the south-central part of the area in the vicinity of the synclinal fold (Fig. 3). A few exposures occur along St. Louis Gulch and in some prospects pits on the rubble-covered eastern base of Granite Mountain. Attitudes of the fault planes to bed­ ding of the sedimentary rocks vary from cross-cutting to subparallel.

Thickness of the planes varies from a few inches to about 2 feet. Actual displacement is not usually obvious; movement is indicated by the fault filling of iron-stained, pulverulent, earthy material, commonly contain­ ing fragments of quartz crystals. Most of these small faults in the 32 south-central part show some filling of veinlike quartz or irregular­

shaped masses of quartz. One occurrence does show vein displacement of several feet. At the bottom of the inclined prospect pit east of the

Morningstar mine, a nearly vertical normal fault shows about 2 feet of displacement.

Bedding plane faults present another type of dislocation. The

notable occurrences are seen in the prospect pits, as in Figure 16, on

the hill slope east of the Morningstar mine. Relative movement is not

obvious, the slippage perhaps being due to gravity gliding or to thrust­

ing. Contained within very thin bedded shales and siltstones, the fault

plane is parallel to the bedding and is characterized by a thin seam only

several inches thick of earthy, pulverulent, heavily iron stained material.

Very small crenulations are sometimes seen as well as fragments of broken

quartz. The steplike formation of the arkose outcrops on the hill crests

in the north part of the area (Fig. 11) suggests possible bedding plane

faulting along thin beds of parting shale.

Fractures . Throughout the area are numerous occurrences of

rock breakage in which subsequent movement was negligible or at least

in which the signs of movement are obscure. Included here is breakage

which more specifically might be termed shattering or pulverization.

Many sedimentary units exhibit fracture, but distinct patterns

are virtually absent. The one definite pattern seen appears in the black

siltstone exposed in the cut between the two ponds (Fig. 7). Three direc­

tions of fracture occur in the bed which strikes N. 45° E and dips 43° SE.

The dominant fracture strikes east-west and dips 80°N. Two lesser Figure 16. Bedding Plane Fault

A bedding plane fault in argillite beds shows the intense iron oxide coloring of the pulverized rock. The fault dips east from upper left to lower right of the photograph. The beams at the top of the picture are 4 x 4's . 34 breaks cross cut> one striking northwest and dipping 68°SW and the other striking northeast and dipping 36°NW.

The most extensive fracturing occurs in argillite, siltstone, and shale, more readily seen in exposures in the central part of the area

on the ridge east of the Morning star mine. The fracture habit is of a

close-spaced network of randomly oriented planes which permit breakage

of the rocks into small blocky fragments. Intense fracturing is well dis­

played in the cut banks and shallow diggings on both sides of the Morn-

ingstar mine (Fig. 8).

A shattering effect producing a jumble of sharp, jagged frag­

ments, which give some semblance of being recemented, is seen in two

outcrops halfway between the mill site and the Fulton shaft in the south-

central part of the area. This breakage is possibly an effect of the in­

ferred adjacent fault.

An additional type of rock breakage seems best termed pulveri­

zation. Though minor in amount, the one prominent occurrence is notable

for its structural implications . Seen in the bank of a road cut a few feet

north of the morning star mine shaft, the pulverized zone, which is ap-.

proximately 30 feet wide, is of very crumbly, earthy, crushed, intensely

weathered rock. The zone seems to be vertical, cutting across the argil­

lite and shale in which it occurs. Approaching from both sides, north

and south, the drag folds and bedding grade into the crushed zone and

are obliterated by it. This pulverized rock coincides with the position

of the apparent axial plane of the large regional fold. 35

Structures in the Igneous Rocks

Little is revealed of the structural relationships of the original intrusion into the sedimentary rocks. In its present position, Granite

Mountain is discordant to the surrounding sedimentary rocks. At the northern contact, marked by the east-w est Ophir Gulch, the mountain cuts the stratified rocks at an angle of nearly 90 degrees to their north- northwest strike. The eastern contact is obscured by erosional debris, but the trend seems to be northeast, generally parallel to St. Louis

Gulch. From the configuration of the sedimentary rocks, Granite Moun­ tain seems to truncate the fold pattern along a line that is approximately normal to the axial lines of the folds. Whether this crosscutting contact is due to initial emplacement of the quartz monzonite or to later faulting is not evident.

Patterns of secondary structures are net distinct a® even the

few massive outcrops are sufficiently broken and dislocated to make

fracture orientation unreliable. A right-angle pattern of northwest and

northeast strike is suggested by a few prominent in-place quartz veins, which will be discussed in a later chapter. The one prominent fracture

independent of the veins is revealed as the east face of the prospect at

the north base of Granite Mountain. This large fracture strikes northeast

and dips 60o-80°NW . MINERAL DEPOSITS

Although mineral deposits in the Morning star mine area includ both lode and placer, the emphasis of this study is on the lode mining potential. Consequently, the examination was concentrated on lode oc­ currences and particularly on the most developed deposit, that of the

Morning star mine.

The Morningstar Mine

The Morningstar mine deposit is a system or lode of thin, dis­ continuous, subparallel veins, predominantly of quartz, occurring as both replacement and open-space filling along bedding planes in a se­ quence of very thin beds of argillite, quartzite, siltstone, and shale which locally have been altered and metamorphosed to hornfels and skarn. The deposit seems to have been localized along the crest and upper flanks of the southwest limb of a northwest-trending anticline.

The northeast extension of the deposit is not well exposed or developed, suggesting that the vein system may not be present, either originally or as a result of post-vein faulting. Generally, minor post-vein faulting did not materially affect the configuration of the deposit. The veins, which were preceded or accompanied by extensive pyrite and sericite alteration of the channel w alls, carry chiefly the ore minerals and metals pyrite, galena, sphalerite, and chalcopyrite, with minor amounts of gold and silver and very minor molybdenum. Erratically distributed throughout, the ore minerals are estimated to make up no more than 15 percent of the vein deposit.

36 37

Surface indications of the deposit are nearly absent and only a few small veins such as that shown in Figure 23 (p. 56) are exposed in cuts near the mine shaft. Probably any outcrop of the veins is now covered by the dump or the hoisthouse.

The Mornings tar mine, originally name the St. Louis mine, is located at the junction of St. Louis Gulch with Ophir Gulch at the base of the northeast corner of Granite Mountain (Fig. 3, in pocket, and Fig.

17). The mine is part of the Morningstar claim group, a group of approx­ imately ten contiguous unpatented claims. There is some question as to the exact boundaries and to the ownership of some of the included and surrounding land.

According to Hill (1909), the mine property, one of the first in the area, was located in 1874; the locator is not mentioned. The earliest owner found recorded was Daniel Johnston, in 1894. In 1911, the mine was recorded to Mr. and Mrs. John B. Anderson. Personal records of the Andersons establish their ownership to 1920. Indirect reference sug­ gests that they held the property at the time of Mr. Anderson's death in

1925, and possibly until Mrs. Anderson's death in 1948.

Current ownership stems from a succession of claimants, begin­ ning in the 1940's. According to Mr. Fred Harm, the property was held in the early 1940's by the late Mr. J. M. Martinez, who apparently ac­ quired the property by relocation. Operations were conducted under the name of the St. Louis Mining and Development Company. About 1953, the property passed to the late Mr. George Kaske, vice-president of the company. In 1965, the property was sold by Mr. Kaske to his nephew. 38

Figure 17. Morningstar Mine

The view is to the east down Ophir Gulch with the Whetstone Mountains in the distant background. The headframe and hoisthouse of the mine, lower center of photograph, are uphill from the junction of Ophir Gulch and St. Louis Gulch. St. Louis Gulch, hidden by the fore­ ground foliage, winds upstream toward the lower right corner of the pic­ ture. The shaft of the mine descends southeast into the hill behind the hoisthouse. 39 the present owner, Mr. Austin Mitchell of Elgin, Illinois. At the time of this writing (May, 1969), the property is under lease to The Anaconda

Com pany.

The amount of early production is unknown, but from the size of what is presumed to be the original workings, production probably measured no more than 50 tons. Schrader and Hill (1915, p . 156) simply state that "some ore" was shipped to El Paso, Texas, in 1886, the ap­ proximate time of the first mine development. Although reportedly the ore was rich, no figures are given for the shipment's value. Tenney (1927-

1929) reports that the St. Louis was operated for a short period in 1929 and that a small tonnage of copper-lead ore was shipped to the Phelps

Dodge smelter at Douglas, along with ore from the Conglomerate mine,

2 miles to the south. Only the combined tonnage and value are given and reportedly most of the ore came from the Conglomerate. About 1945, the St. Louis Mining and Development Company shipped two carloads, presumably about 100 tons, of hand-sorted ore to the smelter at El Paso.

The value of this shipment is not known. In May, 1966, Mr.-Harm shipped 71 tons of mine-run ore to the El Paso smelter. Final evaluation resulted in a net cost to the producer. To date, ore shipments from the

Morningstar mine probably total no more than 250 tons.

The Morningstar is the only one of the old mines in the Greater- ville district that is actively maintained and has been recently further developed. With respect to mining conditions, the mine is workable at present and has been approved by the Arizona State Inspector of M ines.

When inactive, the mine is allowed to fill with water, the level of which 40 varies from 60 to 100 feet down the shaft. The mine is easily dewatered, requiring about 2 weeks of continuous pumping of a 3-inch stream.

The mine is developed by a 241-foot tracked shaft, terminated by a 15-foot sump. The shaft is inclined 38 degrees and trends S. 60°E.

There are approximately 700 feet of underground workings consisting of drifts, a raise, small pocket stopes, and irregularly shaped stopelike drifts (Figs. 18 and 19, in pocket). The lowest level, at the bottom of the shaft, is 140 vertical feet below the shaft collar. The intersection of the shaft and the bottom level is approximately 190 feet below the surface. Hoisting is done with a track-mounted one-ton skip lifted by a

Foos 25 hp engine. Surface fixtures are a headframe and a hoisthouse with attached living quarters .

M ineralogy

The ore minerals and metals, in order of abundance, are pyrite, galena, sphalerite, chalcopyrite, gold, silver, bornite, and molybdenum; the first three listed are far in excess of the others. Chalcopyrite is common, although relatively minor in total; bornite is rare. Silver and molybdenum are revealed by assay, no minerals of these elements having been seen. Gold is relatively common in the upper part of the mine and is revealed by assay at depth. Overall metallic mineral content of the veins is estimated to be 15 percent by volume. The form of occurrence of the predominant sulfide minerals is of fine to coarse disseminated grains and as aggregates of mixed minerals in bands and clumps. Gold occurs as very fine grains and very rarely in the form of wire up to 0.25 inch lo n g . 41

Eight polished sections of ore minerals from various parts of the mine were examined, with composition and sequence of deposition observed to be the same throughout. Minerals present are quartz, pyrite, galena, sphalerite, chalcopyrite, and covellite. The quartz gangue is strongly fractured and fragmented; its boundary with the ore minerals is rough, with irregularly shaped jagged embayments. Pyrite is present in a variety of physical forms, from euhedral crystals to fragmented clus­ ters of "exploded bomb" texture. Sphalerite occurs as massive intersti­ tial filling, infilling the quartz and pyrite and often containing islands of quartz. Chalcopyrite is present predominantly as emulsion texture exsolution blebs in sphalerite. In some occurrences, the chalcopyrite makes up to 30 to 40 percent of the mixture. A few isolated discrete grains of chalcopyrite with very irregular outline are probably the result

of complete unmix:ng from the sphalerite.

Galena occurs as massive interstitial filling. Cleavage traces

are commonly wavy and bent. Galena seems to replace all the other

minerals, particularly sphalerite. A common feature is the presence of

islands of the other minerals in a matrix of surrounding galena. Complete

replacement of the sphalerite leaves the blebs of exsolved chalcopyrite

stranded in the galena. However, the number of such blebs in galena is

small compared to the amount in sphalerite, so that ultimately the galena

must also replace the chalcopyrite. Covellite is very sparse. It occurs

as thin films or as tiny blebs along the borders of galena and is probably

a product of the oxidation of chalcopyrite.

Several examples of quartz veinlets cutting sphalerite indicate

more than one interval of quartz deposition, but generally the paragenetic 42 sequence of gangue and sulfide minerals is established as follows, from earliest to latest: quartz, pyrite, sphalerite and chalcopyrite, galena, and covellite.

Pyrite is widespread throughout the deposit, both in the vein and in the wall rock. The other sulfide minerals are more abundant, both visibly and as reported by assay, in the vein in the central part of the mine from approximately the 55-foot level to the 109-foot level (Figs. 18 and 20, in pocket) where the vein is thickest and more persistent. The assay data (Appendix; positions shown in Fig. 18) provide a more accu­ rate survey of mineral and metal distribution. Lead is contained primarily within the vein and increases in amount with depth until the 140-foot level, where it drops appreciably. Zinc values correspond generally with lead, as would be expected from the common occurrence of mixed aggre­ gates of galena and sphalerite. Copper values generally decline with depth and with distance from the shaft on the 140-foot level. The high copper value of 0.82 percent was obtained from a vein sample; the copper high from wall rock is 0.69 percent. High silver values correlate with high values of lead and zinc and are concentrated approximately midway between the top and bottom of the shaft. Molybdenum, though very minor in amount, is evenly distributed throughout the deposit in both vein and wall rock. The high of 0.008 percent molybdenum was obtained from a vein sample. The monzonite at the end of the crosscut on the 140-foot level assayed 0.006 percent molybdenum.

Gold values underground are very erratically distributed. The underground assays do not adequately reflect the role of gold in the min- eralogical make up of the deposit. In the surface exposures in the 43 vicinity of the shaft, such as the banks of road cuts, the small hole just north of the shaft, and the several other small diggings, gold is the only economic mineral and base-metal and other precious-metal minerals are not present. This singular presence of gold and its form of occurrence misleads one with regard to the nature of the underground deposit. The gold at the surface is free and is present as very fine grains and flakes in an earthy, pulverulent matrix of iron and manganese oxides, resulting from the oxidation and breakdov/n of very thin quartz-rich veinlets (Fig.

21). Fresh pyrite or the mineral which produced the limonite is virtually absent. The seams or veinlets are commonly only a fraction of an inch thick. Generally, the veinlets are along bedding planes and parallel fractures of the argillite and quartzite beds in which they occur. Rarely do they cut the bedding planes. A vertical section of several feet com­ monly discloses a number of these subparallel veinlets, so that the de­ posit as a whole is a stringer lode.

Not all of these veinlets carry gold, nor is the gold evenly dis­ tributed in those that are auriferous. Distribution is very erratic, the only generalization concerning control being that higher values seem to be most common near small flexures in the veinlets. The size of gold particles varies from fine grained, readily seen with the unaided eye, to that of dust or flour so minute that the particles will float. An assay of a rock chip sample of the quartz-bearing argillite taken along an 8- foot vertical section showed only 0.040 ounces of gold, yet I have seen apparently identical material from less than 3 feet away.crushed and panned to give colors so bountiful as to be bonanza ore. 44

Figure 21. Gold-bearing Quartz Vein in Argillite

The vein is just above the pencil eraser and crosses the photo­ graph from upper left to lower right. 45

The oxidation zone of the Morningstar mine is relatively shal­ low, the lower limit making a rather sharp break with the fresh minerals at just below the 20-foot level. Above this line the sulfide minerals are

extensively oxidized to limonite and manganese oxide, with sparse oc­ currences of malachite and cerussite. A peculiar oxidation product,

nearly always associated with galena, is a waxy to resinous, butter-

yellow mineral, commonly in the form of feltlike masses or druses of

prismatic, acicular, needle-sharp crystals up to 0.25 inch long. Dr.

John W. Anthony, Professor of Geology, The University of Arizona, and

Richard Thomssen, graduate student, independently identified this min­

eral in hand specimen as an unusual form of wulfenite.

V eins -

The veins are composed predominantly of milky white quartz,

with subordinate patches of barite intermixed with the quartz in the lower

part of the mine, chiefly on the 140-foot level. Texture varies from mas­

sive and tight to coarsely crystalline, commonly vuggy and exhibiting

comb structure, particularly in the upper mine levels. The maximum vein

thickness of approximately 2 feet is seen on the 55-foot level (Fig. 18,

in pocket). Generally, the thickness of an individual vein is less than

1 foot. Near the bottom of the shaft and on the 140-foot level, individual

veins are noticeably thinner than in the upper reaches .

The deposit is formed of several main subparallel veins, pinch­

ing and swelling, splitting, and joining in an anastomosing fashion, as

seen in the shaft (Figs . 18 and 20, in pocket). The deposit is most aptly

described as a vein system, a composite vein, or a lode and is at least

6 to 7 feet thick where exposed to its maximum width in the shaft. 46

Although the system is more or less continuous, individual veins or vein segments commonly appear disconnected from one another, or in some occurrences are connected by only a very thin stringer. Individual veins occur as thin planar bodies, particularly as seen in the shaft, or as stubby lenticular m asses, as seen in the levels. This variation probably is due in part to the view or way in which the vein is cut. The more mas­ sive veins commonly are accompanied by subparallel stringers and seams only a fraction of an inch thick. Internal brecciation of the larger veins is common in places, showing broken fragments of quartz crystals en­ closed by ore minerals.

The attitude of the system is generally conformable to the bed­ ding of the enclosing sedimentary rocks, with a prevailing strike of

N. 50o-60° E. and dip of 280-38°SE. A few veins differ from the above attitude. On the 10-footlevel, on the left side of the shaft, several small veins dip 40 to 50 degrees, and in the crosscut on the 140-foot level the vein strikes nearly north-south. The system as a whole is crudely tabular with a gradual thinning toward the bottom of the mine and to the west, as seen on the 140-foot level. The system seems to widen and become more erratic in attitude toward the surface. The veins in the northeast wall of the shaft are thinner and less developed than on the opposite side, possibly indicating a thinning of the system to the n o rth ea st.

The contact of the larger veins with the wall rock generally is sharp. A vein may be dislodged freely from the wall, indicative of open- space filling. This mode of emplacement is prevalent in the upper levels of the mine and most pronounced above the 24-foot level. Deeper in the 47 mine, where the veins become thinner and more widely spaced, wall and vein are not easily separated, and contacts are not so sharp. The sub­ parallel thin ribbon veins attendant to the larger ones commonly cannot be separated, and vein and wall are one. Replacement deposition is in­ d ic a te d .

Rocks

A residue of mud left from dewatering covered the walls of most of the mine workings at the time of this study, so direct on-site exami­ nation and correlation of the rocks were not possible. However, mega­ scopic and microscopic examination of hand specimens gives sufficient.

evidence on the predominant rock types and nature of the environment.

Correlation of specific units is very tenuous. Probably several thin in­ dividual units are cut by the shaft alone, since the dip of the stratified

rocks and inclination of the shaft vary through several degrees through­

out the shaft length. In general, the two are parallel.

The deposit is contained in an intermixed sequence of very thin

beds of shale, siltstone, argillite, quartzite, and chert, presumably a

part of the sequence seen on the surface around the mine. Underground

and surface rocks are not generally correlatable.

Underground, the stratified rocks can be roughly segregated

into four groups. The first group, into which the mine is opened and

which predominates on the 10-foot, 16-foot, and 21-foot levels, is

composed largely of beds or individual units of argillite, quartzite, and

shale. These units are well fractured and intensely weathered and oxi­

dized, breaking easily to blocky rubble. The rock has an earthy texture 48 and is mottled white and brown from the formation and leaching of iron oxide. This upper group is the same sequence of rocks that contains the gold-bearing stringer lode exposed by cuts on the surface.

Just below the 21-foot level, there occurs a marked change in rock type. Although poor exposure and local variations in composition and appearance make correlation uncertain, it is concluded from general

similarities that this second group is the most abundantly exposed in the mine. It comprises the east end of the 24-foot level, the shaft walls, the

55-foot, 85-foot, 109-foot levels and the main part of the 140-foot level.

Although referred to as a group, individual units could not be conclusive­

ly determined in this section; however, variations in the rock suggest that two, and possibly more, beds may be present. All rock from this

group is very tough and dense but varies from that which is massive

with no structure to that which is composed of thick coarse blocky

p la t e s .

In hand specimen, the blocky rock is microcrystalline and

laminated by alternating gray and green bands, the only discernible min­

erals being pyrite in veinlets or as disseminations. Thin sections show

a homogeneous groundmass of microcrystalline to nearly cryptocrystal­

line material concluded to be sericite. The sericite completely replaces

the original components. Some thin sections show very fine laminations

of.chalcedony and calcite or dolomite.

The massive rock is also microcrystalline, but the color is

uniformly olive drab. M icroscopically, the composition.is an equigranu-

lar groundmass of a mosaiclike pattern of diopside. In some thin sections

poorly defined clumps, best identified as garnet, were noted. Associated 49 minerals in minor amounts include plagioclase, dolomite, idocrase, and quartz. The quartz occurs occasionally as segregated masses of inter­ locking grains suggestive of silicification rather than grains of original components. Strongly prevalent in all specimens of this group is the masking effect of microcrystalline sericite, commonly obliterating the original constituents.

The rocks of this group can properly be called hornfels, with the diopside-garnet portions of the massive variety qualifying as skarn.

The parent rock is interpreted to have been predominantly microcrystal­ line to very fine grained clastic fragments of quartz and orthoclase. The original unit (or units) was probably a calcareous silts tone or shale.

Faint relict laminations of bedding are observed in some specimens.

Underlying the hornfels, and thus stratigraphically the lov/est in the mine, is a third group of beds exposed in the crosscut to the north on the 140-foot level. The beds of this group are cream or white lime­ stone. Hand specimens are of very thinly bedded and platy fine lami­ nations of calcite carrying disseminated pyrite. The beds are intensely shattered and crumpled, especially at the face at the north end of the crosscut where the water flow in the mine issues from fractures and solution cavities. Thin sections show a miniature repetition of the hand specimen appearance, with very thin laminations of calcite or dolomite.

A fourth group is distinguished in the eastern end of the 140- foot level. The rock appears in hand specimen as gray to coal black finely layered shale or silts tone, blocky in structure and homogeneous in texture. It is not as dense nor as siliceous appearing as the hornfels which it overlies. In thin section, the rock appears as a homogeneous 50 groundmass of microcrystalline to cryptocrystalline sericite in very fine laminations. Very fine grained disseminated pyrite is present in amounts up to 30 percent by volume.

This group of siltstone beds seems conformably to overlie the hornfels which comprise the shaft area. However, this distribution pre­ sents a problem in that the argillite, quartzite, and shale at the top of the mine also overlies the hornfels, presumably conformably. In the stratigraphic sequence of occurrence these two groups should be the same. However, the argillite, quartzite, and shale of the first group at the top of the mine are clearly not the same as the siltstone group at the bottom, although both groups appear to occupy the same relative position with respect to the underlying hornfels. I cannot explain this situation with the evidence at hand and can only reconcile it as being an effect of undisclosed structural conditions, as differences between weathered rock at the surface and unweathered rock underground, or to differences in alteration and recrystallization.

Igneous rocks are exposed at three places: in the hole at the end of the 55-foot level, in the southeast wall on the 55-foot level, and in the face in the north end of the crosscut on the 140-foot level. All exposures are less the 1-foot-wide dikelike occurrences cutting across the sedimentary rocks. Although irregular in shape, the exposures in the wall on the 55-foot level and on the 140-foot level have a general trend of nearly east-west and dips, respectively, of 72°N. and 62°N.

White and glassy, the rocks are composed of fine- to coarse-grained

quartz, muscovite, and subhedral orthoclase with phenocrysts up to 0.5

inch in length. Sulfide minerals are present as fine- to medium-grained 51 disseminated pyrite and chalcopyrite, the total sulfide content being less than one percent. Alteration has produced fine-grained epidote throughout the rock and intense sericitization which is present in a- mounts up to approximately 60 percent. These rocks are almost un­ doubtedly related to the nearby quartz monzonite of Granite Mountain, although their composition is more nearly that of alaskite. However, the paucity of plagioclase and mafic minerals is likely explained by their alteration and replacement by epidote and sericite.

The most striking feature of the rocks in the mine is the perva­

sive and extensive alteration to sericite, abundant in most specimens

and dominating in others to the point of masking the original constituents.

Structures -

Much of the structure of the deposit was concealed during map­

ping because the walls of the mine workings were mud coated following

dewatering. Enough was revealed, however, to discern the general

structural environment. Numerous local anomalous features indicated

that underground structure is complex.

The overall attitude of the deposit generally conforms to that

of the enclosing sedimentary rocks, with the major part of the deposit,

southwest of the shaft, having a prevailing strike of N. 50o-60° E.

and dip of 38° SE. An abrupt change occurs in the upper levels on the

northeast side of the shaft and at the eatern end of the 140-foot level

(Figs. 18 and 19, in pocket), where the wall rock and veins have a

strike of nearly north-south and a dip of 36o-40° E. This change of

attitude indicates either a fold or fault, or both. The wall rock on the

10-foot level is shattered and intensely crumpled in places, with 52 intraformational folding very similar to that exposed in the road cut just north of the shaft collar except that underground fold orientation is very confused. The rocks exposed on both sides of the shaft in the upper levels are folded, shattered, and variously broken. Apparently random dislocation and shifting provided abundant open space as shown by the numerous veins of varied orientation. The vein in the crosscut on the

140-foot level appears to diverge from the prevailing pattern to cut across the bedding plane, yet it seems generally to conform to the atti­ tude of the bedding of the sedimentary rocks measured at the end of the crosscut. Because the overall pattern of the veins in the mine is general­ ly conformable to the attitude of the beds, I suspect this vein is also generally parallel to the bedding plane and that its seemingly anomalous position is misleading due to the obscurity of the stratigraphic structure.

Because of the mud-coated w alls, the vein's true relationship to the beds could not be determined.

The dominant structure of the deposit is the bedding plane fault

that localizes the main part of the vein system. Faulting and vein em­

placement may actually have been contemporaneous. The effects of fault

movement are seen throughout most of the mine where the veins are well

developed and well exposed. Movement is less evident on the 140-foot

level where all structures and veins are thinner. The fault is best dis­

played in the shaft walls and in the 55-foot and 85-foot levels where it

pinches and sw ells, the results of movement varying, from place to place

from clay gouge to breccia. Dislocated rock ranges from large horses

enclosed by veins to small fragments of wall rock included in the vein

quartz. The maximum width of a gouge or breccia layer is approximately 53

1 foot, although the total width of the zone of movement may be several f e e t .

The most pronounced of what appear to be crosscutting features of pre-vein age occur on the 140-foot level between the sump and the intersection of the crosscut. In this interval are numerous thin veins filling fractures and shear zones with a northeast strike which transect the bedding of the sedimentary rocks as they change in trend from a strike of northeast to that of north-south. Projection of these shears to the southwest brings them parallel to the bedding so that vein filling of the shears in the southwest end of the 140-foot level is again conform­

able to the attitude of the sedimentary rocks. The very thin shear zone

seen in the back of the southwest half of the 140-foot level, which prob­

ably connects with the vein and shear zone seen at the intersection with the crosscut, is nearly parallel to the bedding but is also nearly vertical

in dip, so that it does cut across the dip of the sedimentary rocks but

does not transect the strike.

Post-depositional movement apparently was minor judging from

the small dislocations and adjustments of the veins. The strongest

movements appear in the lower parts of the mine, on the 80-foot and

140-foot levels, where several reverse faults and shear zones of north­

east strike have caused slight offset and brecciation of the veins. The

most prominent post-vein fault is a reverse fault dipping 720-76°NW ,

seen in the southeast wall of the 85-foot and 109-foot levels . Pinching

and swelling, the fault has a maximum thickness of approximately 3 feet,

with a like amount of vertical movement as indicated by the offset of the

vein in the 109-foot level. A parallel, smaller fault cuts the shaft a few 54 feet above the bottom of the shaft, with both the thickness and displace­ ment of the fault measuring only several inches . On the 140-foot level are several northeast-striking reverse faults and brecciated shear zones,

some of the shear zones measuring 5 to 6 feet across. Relative movement

of these fractures is a maximum of approximately 2 feet as determined

from the drag and offset of the veins. On the 85-foot level is a zone 2 to

3 feet wide, striking northwest and dipping approximately 50°NE, of

brecciated, crushed rock, with no measurable relative movement.

Except for minor local adjustments, the deposit as exposed was

not substantially altered by post-depositional structures. A question of

major dislocation of the deposit is raised by the disappearance of the

vein system on the northeast side of the shaft. Since there is little

development and exposure, the answer becomes one of speculation or

interpretation, which will be discussed in a later chapter.

Other Mineral Deposits

Ore minerals in the Morningstar mine area occur principally in

deposits of two types: quartz veins and placers. Veins occur in both the

sedimentary rocks and the quartz monzonite and were worked for their

metallic sulfide minerals and gold. The placers occur in both the uncon­

solidated recent stream gravels and in older semi-consolidated bench

gravels and were worked for their gold.

Veins

Most of the vein exposures in the sedimentary rocks occur in

the south-central part of the area and in the vicinity of the Morningstar

mine (Figs. 2.and 3, in pocket). In the quartz monzonite most exposures 55 are on the southeast flank of Granite Mountain in the southwest part of the mapped area. Most observed veins are exposed by prospect pits and shallow shafts. The small dumps and excavations indicate that very little development has been done and that most workings qualify only as minor prospects. The more notable workings are the Old Tucson shaft in the southeast corner of.the area, the Fulton shaft, now inaccessible, in the south-central part, and the Zeckendorf shaft on the north face of

Granite Mountain. Records of production are not known, but an estimated total tonnage of vein material extracted from all the workings is probably not more than 200 tons.

Veins in Sedimentary Rocks . Veins in the sedimentary rocks occur primarily in quartzite, arkose, and argillite, with one notable oc­ currence in limestone in the Old Tucson shaft. The attitudes of the veins generally are conformable to the bedding attitude of the enclosing rock, although a few occurrences were noted of low-angle crosscutting (Fig.

22). Primarily, the veins are of a lenticular shape, pinching and swell­ ing, and are continuous for only short distances. Some are very short and stubby (Fig. 23). No vein was seen on the surface that could be traced for more than approximately 20 feet. The maximum thickness is approximately 1 foot. The boundary between vein and wall rock is usual­ ly sharp, with occurrences of both discontinuous boundaries and very strong adherence. Several veins showed slickensides and broken frag­ ments of quartz crystals indicative of post-depositional movement. A soft, earthy, limonite-stained gouge material between the vein and the wall rock suggests that initial deposition of some veins was along planes of bedding slippage. The veins are of white, massive, coarse crystalline 56

Figure 22. Quartz Vein Cutting Argillite

The vein is approximately 5 inches wide.

Figure 23 . A Lenticular Quartz Vein

Note the size and stubby form of the vein compared to the pencil length. 57 quartz and are commonly pitted with numerous vugs penetrated by sub- hedral to euhedral quartz crystals.

The most extensive working accessible in the sedimentary rocks is the Old Tucson shaft in the southeast corner of the area (Fig. 3, in pocket). The vein was opened by a 12-foot vertical shaft, which then inclines approximately 20°SE. for 60 feet and terminates with a vertical shaft 12 feet deep. The wall rock is a massive, gray, siliceous lime­ stone with minor intraformational folds and fractures. The deposit con­ sists of two subparallel veins 4 to 6 feet apart that strike N. 75° E. and dip 31°SE. Though generally persistent to the bottom of the shaft, the veins pinch and swell forming lenticular segments with a maximum thick­ ness of 10 inches. The vuggy quartz veins generally conform to the bed­ ding of the limestone and occur as both fracture filling and minor replacement of the limestone along planes of bedding slippage. Bound­ aries of the veins are generally sharp.

The predominant ore minerals are galena and pyrite. Minor a- mounts of malachite indicate the presence of copper though no sulfide minerals of such were seen. Oxidation of the vein material to limonite and manganese oxide is thorough to a vertical depth of approximately 30 feet, approximately two thirds of the way down the shaft.

Most other exposures are in very shallow excavations which do not penetrate below the zone of oxidation, so that ore minerals are fre­ quently obliterated by limonite and show only casts of the former sul­ fides . However, remnants of fresh minerals are common enough to indicate that the bulk of the metallic minerals were pyrite and galena, present as disseminations and as segregated masses of intermixed 58 coarse-grained crystals interstitial to the quartz. An overall estimate is that sulfide minerals did not constitute more than about 10 percent of the total volume of the veins. Although no gold or silver minerals were seen, assays show that the metals are present.

Although oxidation of the sulfides in near-surface exposures is extensive, depth of oxidation for the area is judge to be relatively shal­ low as indicated by the Old Tucson workings. Approximately 25 feet be­ low surface is the lower limit of extensive oxidation. The effect of en­ richment within this shallow zone is shown by the contrast of two assays taken at the Old Tucson. One, a dump grab sample of galena with a sub­ stantial coating of cerussite, assayed 3.47 ounces of silver while a second, of a relatively fresh section of the same vein taken approxi­ mately 20 feet below the surface, assayed only 9.7 ounces of silver.

Gold was negligible in both samples.

Veins in the Quartz Monzonite. Veins in the quartz monzonite are shallow dipping and seem to present a pattern of preferred orienta­ tion of two principal strike directions. The larger and longer veins strike northwest and dip to the southwest with dips of 22 to 30 degrees. The ■ shorter, smaller veins trend northeast and dip to the southeast with dips reaching a maximum of 45 degrees. No vein was seen with a northerly dip. In contrast to those in the sedimentary rocks, veins in the quartz monzonite are more tabular in overall dimension, with a long strike length relative to their thickness. Both the maximum thickness of ap­ proximately 2 feet and the longest traceable length of approximately 60 feet are seen in the vein cropping out on the north side of Granite Moun­ tain at the Zeckendorf shaft (Figs. 3, in pocket, and Fig. 24). The 59

Figure 24. Quartz Vein in Quartz Monzonite

The picture is of the vein outcrop at the Zeckendorf shaft. The shaft descends along the dip of the vein to the south toward the lower left corner of the photograph. The head of the pick rests on top of the vein, which is nearly 2 feet thick. 60 prevailing thickness of veins is less than 1 foot, and most are traceable for less than 20 feet. The smaller veins most commonly are in distinct smooth-walled fractures and have a sharp, unfrozen boundary with the wall rock. The larger veins occur within zones of sheeting which exhibit crushing and brecciation of the host rock. Although boundaries are dis­ tinct, commonly thin slivers of vein are separated from but parallel to the main vein. Like the veins in the sedimentary rocks, those in the quartz monzonite are of white, massive, coarse crystalline vuggy quartz.

The most extensive working in the quartz monzonite is the

Zeckendorf shaft on the north face of Granite Mountain. The vein is opened by a shaft approximately 100 feet long, inclined 32°, S. 14° W.

The only lateral work is a short stope drift to the east at approximately

70 feet down the incline, and a large stope extending to the west which terminates the shaft. The vein is generally continuous along the length of the shaft, although the vein pinches and swells with very thin connec­ tions between thick, short lenses. The outcrop (Fig. 24), nearly 2 feet thick, narrows to several inches in less than 20 feet. Recementation of brecciated vein quartz crystals indicates post-depositional movement and probably more than one stage of quartz deposition.

The sulfide minerals seen, in the order of their abundance, are pyrite, galena, chalcopyrite, and bornite, with pyrite and galena far in excess over the others. Ore minerals occur as fine- to coarse-grained disseminations and segregated clusters throughout the vein, with a minor amount of disseminated minerals spreading as far as several feet into the wall rock. Oxidation of sulfide minerals is pervasive throughout the vein, although it does not seem to be as intense as that in the veins in 61 the sedimentary rocks. Fresh sulfide minerals are readily seen very near the surface. The principal secondary minerals are limonite, malachite, and very sparse covellite.

The vein in the large tunnel on the southeast flank of Granite

Mountain (Fig. 3, in pocket) is very similar to that in the Zeckendorf shaft but has a maximum thickness of only 1 foot. Traceable along strike for approximately 90 feet, the vein pinches and swells and was apparent­ ly deposited in undulations of open space along a zone of sheeting and brecciation. Minor offsetting of the vein by several inches indicates post-depositional movement.

P lacers

Both alluvial and eluvial placer gold seem to be widespread throughout the area. Those who work here claim that most of the hillsides and draws will nearly always pan a few colors. The two largest concen­ trations of placer gold known and worked in the map area are in the cut at the Mornings tar mine and in Ophir Gulch in the vicinity of the two ponds (Fig. 3).

The exposure in the cut (Fig. 25) shows sedimentary bedrock overlain by stream bench gravels. The thickness and induration of these gravels indicate that they are relatively old and that water flow in this course was once much more active than it is now. Placer gold obtained at this site is of both alluvial and eluvial deposition, as the cut tran­ sects the boundary of the old channel and the hillside. Additionally, the bedrock contains quartz veins carrying free gold. Understandably, this area is reputed from tales of the oldtimers to have been one of the richest sites in the Greaterville district. Further evidence for the confluence of 62

Figure 25. Stream Bench Gravels

A bulldozer cut 150 feet south of the Morningstar mine shaft reveals bedrock of quartzite, shale, and argillite beds beneath compact bench gravel. The zone of contact contains both worn stream-carried nuggets and free but untransported fresh gold from the weathered quartz veinlets in the bedrock. The hole at the lower right of the photograph is a tunnel entrance of early-day placer operations. 63 lode, alluvial, and eluvial gold is the presence in a single pan of bright, angular, sharp-edged grains together with smooth and rounded nuggets.

In Ophir Gulch, the sedimentary bedrock strikes more or less obliquely to the course of the channel and dips downstream, providing a series of natural riffles for gold collection. In the near-surface gravels of the present stream channel, gold is sparse and scattered and signs of a pay streak or pattern of deposition are absent. Presumably this gold is relatively new to the channel and still is in transport. The greatest concentration and the largest nuggets are observed to come from the more deeply buried stream gravels close to the bedrock and from the older, elevated bench gravels. Although pay streaks most likely did exist, and perhaps still do, the most productive gravels presently worked are so thoroughly mixed and disturbed from repeated handling that courses of pay streaks are obliterated.

Placer gold throughout the area is usually bright yellow and very easy to recognize. Some of the rounded, worn nuggets are subdued to a butter-yellow. Nugget texture varies from well rounded and smooth to flat to angular and sharp-edged. Some of the angular grains are still attached to quartz, indicating a local origin. The largest nuggets ob­ served were slightly larger than a corn kernel (Fig. 26). Most of the gold ranges from pinhead size to a fineness that requires a hand lens for de­ te c tio n . 64

Figure 26. Gold Nuggets

The gold nuggets, at the center of the photograph, were found near bedrock just below the dam on Ophir Gulch. SUMMARY, INTERPRETATION, AND EVALUATION

The study area consists of sedimentary and igneous rocks. The sedimentary rocks, probably of Early Cretaceous age, make up the north­ ern and eastern third of the area and consist of a sequence approximately

2,000 feet thick of thin-bedded quartzite, arkose, shale, and siltstone, with minor amounts of chert and limestone. The sequence has a prevail­ ing eastward dip and is regionally folded into several northwest-trending synclines and anticlines which plunge to the southeast. Occupying the southwest quadrant of the area is Granite Mountain, a quartz monzonite intrusive stock of Laramide age, which has cut the sedimentary rocks, altered them locally, and caused the emplacement of numerous but small quartz veins, both within the quartz monzonite and in the surrounding rocks. The veins are primarily of the fracture-filling type and carry the minerals and metals pyrite, galena, sphalerite, chalcopyrite, gold, and s ilv e r .

The outstanding feature of the area is the dominating influence of structure, as expressed regionally, in the individual rock units, in the control of vein and mineral emplacement, and on the form of the total geologic expression seen today. Possibly many of the individual features were formed contemporaneously, but it is equally possible that a number of periods of stress and major activity are represented. Even though in­ complete knowledge of the sedimentary rock column and the difficulties

of correlation make some suggestions very speculative, several principal

events are postulated to explain the field evidence.

65 66

Order of Events

The following is my interpretation of the nature and order of events in the post-depositional geologic history of the Morning star mine area, from oldest to youngest.

1. Regional folding of the sedimentary rocks .

2. Regional thrust faulting.

3. Quartz monzonite intrusion, vein formation, and mineralization.

4. Uplift of Granite Mountain by faulting.

5 . Local minor faulting .

Regional Folding of the Sedimentary Rocks

The earliest effect of deformation is the folding of the sedimen­ tary rocks. This folding produced several north we s t -trend ing anticlines and synclines (Fig. 2 and 3, in pocket), in response to an apparent re­ gional southwest-northeast compressive stress. Depending partly on the lithology, rock strain at points of maximum stress took several forms, including pulverization and faulting along anticlinal axial planes and tensional pulling apart within syncline troughs. Less competent beds responded to compression by bedding plane slippage and intraformational crumpling, as exposed in the argillite-shale units on both sides of the

Morningstar mine shaft (Figs. 8 and 13). The small folds grade into the zone of crushed, pulverulent rock which coincides in position with that of the fold's axial plane. An alternative consideration is that the crushed rock is a shear zone caused by faulting. The crushed zone is definitely a site of formational weakness and probably represents effects of both faulting and folding. Strain of the rocks in the syncline trough in the south-center part of the area (Figs. 2 and 3) was by fracturing and 67 separation, with the resultant formation of multiple channels and open space, suggested by the random orientation of veins and quartz emplace­ m ent.

Regional Thrust Faulting

Following the period of northeast-southwest compression was a time of stress forces from the east and southeast, producing a westward thrust of younger, thicker, predominantly arkosic beds over the older, thinner quartzites to the w est. The remnant of this thrust sheet makes up the hills to the north of Ophir Gulch, with their steplike arkose outcrops.

Postulation of thrusting is based mainly on occurrences of drag folds striking north-south with overturns to the west, as exposed in the argillite and shale in the stream bank north of the Morning star mine (Fig.

14) and in the strongly contorted limestone (Fig. 15) directly to the east of the mine shaft. This right-angle superposition over the eastwest trend of crumpling in the argillite near the shaft suggests that the limestone may be a thin remnant near the sole of the thrust and that the actual con­ tact of the thrust may be somewhere within the approximately 40-foot vertical spread between the two occurrences. The proximity of the thrust fault plane is further suggested by the unusual erosional embayment on the north side of the hill just north of the mine. The embayment is ap­ proximately where the fault plane, a zone of erosional susceptibility, might be expected to crop out.

Additional evidence for thrusting is offered by the oblique, nearly right-angle superposition of strike of the upper arkose beds over that of the lower tightly folded limestone beds in the northeast corner of the area (Fig. 3, in pocket). It is postulated that the upper arkose 68 was thrust to the. west over the underlying beds, with subsequent erosion removing the thrust sheet to reveal the lower beds which show the effect

of the earlier northeast-southwest compression.

Quartz Monzonite Intrusion

Third in the order of events is the intrusion of the quartz mon­

zonite, with apparently contemporaneous emplacement of veins and

minerals. Although the relationship of intrusion to the time of thrusting

is not clear, the intrusion must be later than the time of initial folding,

as shown by the eastern boundary of Granite Mountain. The stock there

truncates the regional folds (Figs. 2 and 3, in pocket). The presumed

hydrothermal fluids which emplaced the veins made use of the ready open

space of fractures and shears, producing concentrations of veins in the

syncline trough in the south-central part of the area and along the anti­

cline crest in the .central part. The most notable occurrence is the de­

posit of the Morning star mine.

Uplift of Granite Mountain

Following intrusion of the quartz monzonite, or possibly con-.

current with it, there was uplift along the Morning star fault, tilting the

sedimentary rocks to the east and lifting Granite Mountain to its present

position. Nearly right-angle truncation of the sedimentary rocks to the

north was also developed. In effect, the Morningstar fault may be an

actual fault only along its western half until it meets the sedimentary

rocks at the Morningstar mine, where it may continue to the southeast

as a fault or simply grade into the older zone of weakness along the 69 fore limb of the fold, the entrant into the sedimentary rocks marked by the crushed zone just north of the shaft.

The position of the crestal line of the fold in its extension to the southeast as seen underground in the Morning star mine is more or less the dividing line between the bulk of the deposit to the southwest and the apparent thinning or truncation to the northeast. Possibly vein and mineral deposition never occurred on the northeast side. No vein outcrops are seen north of this line in the vicinity of the mine. The general termination of the deposit to the northeast may alternatively be due to truncation caused by the Morningstar fault, the uplifted portion to the south constituting the mine, the downthrown side to the north being hidden at depth or displaced to the west where, in fact, the only vein occurrence north of the Morningstar fault is seen (Figs. 2 and 3, in pocket). Whatever the case, uplift probably utilized this zone of weak­ ness, the extent of actual faulting remaining speculative. The north-

south fault near the western edge of the area possibly marks the western height of the uplift.

Local Minor Faulting

Final adjustment of the rocks produced the local faults and gave the environment its present structural form. These adjustments are prob­

ably due to both the uplift of Granite Mountain, which produced a com­

pressive stress to the east and to local gravity settling. Two dominant

trends of faulting are suggested: one northwest, one northeast. The north­

west trend began with the inferred fault in the southeast corner of the map

area near the Old Tucson shaft and extends through the mill site to the

small truncation of the arkose bed in the northwest quadrant of the area. 70

The northeast trend is established by the two parallel strike-slip faults

in the south-central part of the area aligning with the strike-slip fault

that offsets the nose of the plunging fold in the northeast corner of the

area. The uplift and eastward compression by Granite Mountain probably

accounts for the steep westward-dipping reverse faults and shears seen

in the Morningstar mine.

Subsequent erosion of the elevated side south of the Morning-

star fault removed the thick arkose beds of the upper thrust plate and

exposed the older sedimentary rocks now seen south of the fault. Ap­

parently, uplift and early erosion were rapid enough to produce the poor­

ly sorted cobble alluvium that forms the elevated benches that flank the

present stream channels and carry the coarse gold of the older placers.

Continued erosion has cut through these older deposits and in general

modified the landform as it is seen today.

Classification of Mineral Deposits

Judging from the characteristics enumerated below," which were

obtained largely from the study of the Morningstar mine deposit, the

mineralized veins in the study area seem to fit best into the mesothermal

class of Lindgren's (1933) genetic classification of hydrothermal ore

d e p o s it s .

1. Formation at moderate to relatively near-surface depths, local­

ized primarily in open space caused by both regional and local

deformation, folds, faults, and fractures.

2. Vein gangue material primarily quartz with minor barite.

3. Ore mineral suite predominantly of pyrite, sphalerite, galena, 71

chalcopyrite, gold, and silver, a suite considered typical of

medium-temperature deposition.

4. Pyrite and sericite alteration.

5. Absence of other minerals or features strongly characteristic of

other classifications.

Economic Evaluation of Mineral Deposits

The Morningstar Mine

From evaluation of all features, the Morningstar mine deposit,

as presently exposed, is uneconomical to mine, and it is my judgment

that there is no reason to expect any economic improvement by further

development. The deposit is too small, too low grade, and the distribu­

tion of ore minerals is too erratic. Specifically, features against min-

ability are (1) the veins are narrow and discontinuous, (2) the tenor of

ore minerals is too low for base metals, and (3) the tenor of gold and

silver overall is too low, with the minable values too rare and erratic in

distribution.

The prospects for extension of the vein system to more favorable

conditions, both in depth and laterally, are not encouraging. The veins

individually, and the system as a whole, pinches with depth, Although

they both could swell again, there is no reason to believe that they

would be any larger or better mineralized than the veins already exposed.

The same reasoning holds for lateral extension, even to the southwest

which appears to be the most favorable direction. The westernmost ex­

posure of the system, on the 140-foot level, shows thinning veins. As

this position seems to be on the flank of the fold, veining presumably 72 becomes constricted and tighter farther away from the fold crest. Thus the most favorable structural environment of the deposit seems already to be exposed. One consideration for improvement of the deposit lies with depth, with the possibility that the vein system may cut a more re­ active sedimentary unit, such as a thick limestone favorable for replace­

ment like the Mural Limestone in the Bisbee Group. This consideration is simply speculative, there being no evidence to suggest it.

Mineralization that may be an exception to the above discus­

sion is the stringer lode gold occurrence at the surface of the mine. Al­ though it is very difficult to evaluate, gold is present over a distance of approximately 100 feet in one direction and vertically over a span of at

least 30 feet. The gold-bearing argillite is readily accessible to open-

cut mining, and the material is easily crushed and milled. To be ade­

quately appraised, very closely controlled bulk sampling and mill testing

would be necessary. Based on present knowledge, it is my opinion that

mining would not be justified.

Other Mineral Deposits

Veins. The other vein occurrences, in both the sedimentary

and igneous rocks, do not now constitute ore deposits, nor is it reason­

able to expect that they would develop into such at depth. The vein oc­

currences in the sedimentary rocks are essentially in the same environ­

ment, both as to rock type and to structure, as the Morning star mine,

and the same limitations may be applied. Development in the syncline

trough in the south-central part of the area could reasonably be expected

to disclose larger veins and more mineralization at depth, similar to the

outcrop and underground relationship at the Morningstar mine, since the 73 two areas are generally of the same structural type. However, there is no suggestion that any vein system developed in a trough structure would be any better than one developed on an anticlinal crest.

Placers. Although placer deposits were not extensively studied, it is probably safe to say that the same geological restrictions that pre­ cluded full exploitation in the old days, once the easy placer deposits were depleted, still hold today. Narrow, short gulches with shallow gravel fill and erratic distribution of fine gold will not support a modern

mining operation.

Others. Because the emphasis of this study is on vein lodes

and their mining potential, no attention was directed toward the possi­ bility for other types of lode occurrences , such as massive bedded re­

placement deposits, or deposits of disseminated sulfides, such as the

copper- and molybdenum-bearing "porphyry" type. Particularly because

southeast Arizona is noted for porphyry deposits, the local features of

the Morning star mine area that are relevant and commonly associated

with porphyry deposits should not be overlooked, especially the quartz

monzonite Granite Mountain stock. Although the poorly mineralized

stock in itself does not present a favorable target, it is of a favorable

host rock and it is weakly mineralized in places with disseminated

chalcopyrite. The presence of the stock in faulted position in a mineral­

ized, structurally complex area could be significant, with a view toward

hidden disseminated sulfide deposits. Noteworthy is the closeness of

the copper-molybdenum mining districts of Helvetia and Rosemont only

6 miles to the north. APPENDIX

ASSAY DATA, MORNINGSTAR MINE

74 Assay Data, Morning star Mine3

An Ag Pbc Cu Zn Moc Sample*3 Width Rock (oz/t) (o z/t) % % % %

- 20-foot level

1 4.0' w a ll rock trace 0.30 -0.10 - 0.16 0.11 0.003 ' • 10-foot level

la 4.0' w a ll rock trace .3 0 - .10 .1 3 .1 7 .003

55-foot level

2 3.0' w a ll rock trace .86 .14 .10 .4 5 .001 2a 2.5' v e in 0.003 2.36 2.60 .33 2.60 - .0005

85-foot level

3 3.5' w a ll rock .005 1.08 .81 .57 . 56 .004 3a 1.0' v e in .016 3.19 ‘ 2.25 .82 10.60 .001

140-foot level

4 4.5' w a ll rock trace .3 6 - .10 .69 .1 7 .002 4a 3.0' w a ll rock n il trace - .10 .6 9 .1 7 .002 4b .8' v e in .030 5.27 9.90 .15 .24 .0005 4c 4.0' w a ll rock trace .1 2 - .10 .05 .03 - .0005 4d 2.5' v e in trace .06 - .10 .3 2 .03 .008 4e 4.0' w a ll rock nil trace - .10 .0 2 .0 5 .0005 Au Ag Pbc Cu Zn M oc Sam ple^ W idth Rock (o z/t) (o z/t) % % . % %

140-foot level

4 f 4.0' w a ll rock n il trace -0.10 0.09 0.03 0.001 4g 3.0' v e in trace 0.16 - .10 .41 .03 .0005 4h 4.0' w a ll rock n il trace - .10 .0 8 .04 .001 . 41 4.0' w a ll rock trace .36 - .10 .3 5 .26 .001 4j grab w a ll rock n il trace - .10 .1 3 .05 .006 4k 4.0' w a ll rock n il trace - .10 .0 3 .0 8 . .0005

Shaft

SI 2.0' v e in trace .0 8 14.60 .23 .19 .003 82 2.0' v ein 0.02 3.82 10.50 .73 6.40 .003 S3 0.6' v ein 1.44 3.94 12.80 .30 7.20 .0005 S4 1.0' v ein .5 7 . 3.01 .50 .30 11.20 .004 S5 .5' v e in .23 1.01 .75 .14 2.40 .0005

a Assays provided by The Anaconda Company,

b Position of sample shown in Figure 18.

c. Minus sign indicates less than. REFERENCES

B lake, W.. P . , 1903, Geology of Arizona, in Report of Governor of Arizona to Secretary of Interior: Washington, D .C ., p. 126- 135.

Brennan, D. J ., 1962, Tertiary sedimentary rocks and structures of the Cienega Gap area, Pima County, Arizona: Arizona Geol. Soc. Digest, v. 5, p. 45-58.

Brown, W . FI., 1939, Tucson Mountains, an Arizona basin range type: Geol. Soc. America Bull., v. 50, p. 697-760.

Burchard, H. C ., 1884, Production of the precious metals in the United States, cited in Hill, James M., Notes on the placer deposits of Greaterville, Arizona: U.S. Geol. Survey Bull. 430, p. 11- 12.

Cobban, W. A., and Reeside, J. B ., Jr., 1952, Correlation of the Cre­ taceous formations of the western interior of the United States: Geol. Soc. America Bull.., v. 63, p. 1011-1044.

Darton, N. H., 1925, Resume of Arizona geology: Arizona Bur. Mines B ull. 119, 298 p.

Dumble, E. J., 1902, Notes on the geology of southeastern Arizona: AIME Trans., v. 31, p. 696-715.

Elsing, M. J., and Heineman, R. E. S ., 1936, Arizona metal production: Arizona Bur. Mines Bull. 140, 112 p.

Fergus son, W. B ., 1959, The Cretaceous system of southeastern Arizona, in Arizona Geol. Soc. Guidebook II, Southern Arizona, p. 43-48.

Gross, M. P ., 1969, Mineralization and alteration in the Greaterville district, Pima County, Arizona: unpub. M.S. thesis, Univ. of Arizona, 82 p.

Hill, J. M ., 1909, Notes on the placer deposits of Greaterville, Arizona:. U.S. Geol. Survey Bull. 430, p. 11-22.

Krynine, Paul D ., 1948, The megascopic study and field classification of sedimentary rocks: Mineral Industries Experiment Station Tech. Paper 130, College of Mineral Industries, Pennsylvania State University, reprinted from Jour. Geology, v. 56, no. 2, p . 130-165.

77 78

Lindgren, Waldemar, 1933, Mineral deposits , 4th ed.: N ew York, McGraw-Hill Book Company, Inc., 930 p.

Moore, R. A., 1960, Cretaceous (?) stratigraphy of the southeast flank of the Empire Mountains, Pima County, Arizona: unpub. M.S. thesis, Univ. of Arizona, 55 p.

Moran, W. R ., 1957, Cretaceous stratigraphy and oil possibilities of the Sonoita-Elgin area, Pima and Santa Cruz Counties, Arizona: Union Oil Company, unpub. report F-172.

Ransome, F. L ., 1904, The geology and ore deposits of the Bisbee quadrangle, Arizona: U.S. Geol. Survey Prof. Paper 22, 168 p.

Root, W. A ., 1915, Dredge mining operations in Santa Rita Mountains, Arizona: Mining Eng. World, v. 42, p. 377.

Schafroth, D. W ., 1965, Structure and stratigraphy of the Cretaceous rocks south of the Empire Mountains, Pima and Santa Cruz Counties, Arizona: unpub. Ph.D. thesis, Univ. of Arizona, 135 p .

Schrader, F. C ., 1917, The geologic distribution and genesis of metals in the Santa Rita-Patagonia Mountains, Arizona: Econ. Geol., v. 12, p. 237-269.

j______, and Hill, J. M ., 1915, Mineral deposits of the Santa Rita and Patagonia Mountains, Arizona: U.S. Geol. Survey Bull. 582, p. 152-166.

Stoyanow, A. A., 1936, Fossiliferous zones in the Cretaceous and Ter­ tiary deposits of southeastern Arizona (Abst.): Geol. Soc. America, Proceedings, p. 296-297.

______1949, Lower Cretaceous stratigraphy of southeastern Arizona: Geol. Soc. America Mem. 38, 169 p.

Tenney, J. B.,'1927-1929, History of mining in Arizona: unpub. ms., Arizona Bur. M in e s , Univ. of Arizona Open-file Report, 514 p.

Tyrrell, W. W ., Jr., 1957, Geology of the Whetstone Mountain area, Cochise and Pima Counties, Arizona: unpub. Ph.D. t h e s is , Yale University, New Haven, Conn.

Wilson, E. D ., 1927, Arizona gold placers, 2nd rev. ed.: Arizona Bur. Mines Bull. 126, 100 p.

______, and Moore, R. T ., 1963, Cretaceous and Tertiary ore deposi­ tion in Arizona: Arizona Geol. Soc. Digest, v. 6, p. 1-6.

f - 79

Wood, P. A., 1959, Tertiary deposits in southern Arizona, in Arizona Geol. Soc. Guidebook II, Southern Arizona: Arizona Geological Society, p. 58-61. 157

6 2 0 8 7 N \ E XP LANA T/ON

SEE OUTCROP M THE SEDIMENTARY ROCKS ARE GROUPED INTO AREAS OF MAP $ THE PREDOMINATING TYPE OR TYPES, AND ARE LISTED IN EACH AREA, FROM LEFT TO RIGHT, IN THE OZT, SH, ARC, a HELS * / ORDER OF DECREASING PREVALENCE ARK i S, SR, a ARK / THE FOLLOWING EXPLANATION IS ARRANGED FROM / TOP TO BOTTOM IN THE ORDER OF YOUNGEST IN ARK ' AGE TO THE OLDEST. FOR THE MORE COMPLETE 'ft a Lt EXPLANATION, REFER TO FIGURE 4 fPOCKETJ

STREAM GRA VEL, UNCONSOL IDA TED

STREAM (BENCH) GRAVEL, WEAK TO MODERATELY CONSOLIDATED. s# ^40 APLITE

QUART2 MONZON!TE GULCH OPHIR ARK ARKOSE

POND LIMESTONE, SHALE, AND ARKOSE

'3# QUARTZITE, SHALE, ARGILLITE, AND HORNFEL SECTION 24 GULCH SEC 25 QUARTZITE, ARKOSE, SHALE, AND LIMESTONE [SECTION 25 ^MORNINGS TAR META-LIMESTONES

QUARTZITE. ARGILLITE, SHALE, ARKOSE, OZT.SH, Qm, ARK, META - SED. Lm-Sil V HORNFEL,CHERT, AND LIMEST6NE ARG, HELS SHst SILTS TONE

HFLS HORNFELS

OZT, ARG, SH, ARK, HELS,CHERT, IS Lm-Sil LI ME- SILICA TE ROCK

ROAD

a;:i SHAFT, INCLINED, DASHED UNDERGROUND

* SHAFT, INACCESSIBLE

TUNNEL, CLOSED, DASHED UNDERGROUND

DUMP, OR PLACER TAILING. HACHURES ON UPPER LEVEL.

QUARTZ VEIN, IN PLACE

EULTON QUARTZ, FLOAT

SHEAR

s^ 20° STRIKE AND DIP

ARK GRANITE CONTACT, APPROXIMATE MOUNTAIN >1 25 ? INFERRED OR UNCERTAIN

THRUST FAULT, SAWTEETH IN UPPER PLATE TUCSON FAULT, SHOWING DIRECTION OF RELATIVE 0 ^ 0 MOVEMENT - LATERAL, UP AND DOWN

SYNCLINE

ANTICLINE

TREND OF SEDIMENTARY ROCKS

FIGURE 2 GEOLOGIC INTERPRETATION MAP

MORN/NGSTAR MINE AREA GREATERVILLE MINING DISTRICT JAMES C STEWART, 1971, GEOLOGY THESIS PIMA COUNTY, ARIZONA T 19S, R I S E

O 200 400 FEET SCALE

,00 6 4 0 4 t (Q 1 f (Q O

^n%£D ^4.0 AT COV£A

Qjssffirrz: / T£_. T * A U g AFt<.iJ.L)7>£, *- //0/1/VTSl.S /V

' \ \ V

'/^i. o a t vov’je/i eooMwnMTLr a a k o s s . A ^ /VX TION

ROAD

a z j INCLINED SHAFT, DASHED UNDERGROUND

SHAFT, INACCESSIBLE

)=ZD TUNNEL, CLOSED, DASHED UNDERGROUND

6> ZHD PROSPECT PIT AND TRENCH, OR OPEN CUT.

"=9 DUMP OR PLACER TAILINGS, HACHURES FROM UPPER LEVEL D U

OUTCROP SHOWING TREND

STRIKE AND DIP

PONO FLOAT CONTACT, APPROXIMATE

APPROXIMATE CONTACT t

SHATTERED

A INTRAFORM ATI ONA L OR DRAG FOLDS

Ozr.sH'+s ir s r ////// SHEARING

0UART2 VEIN, IN PLACE

QUARTZ VEIN FLOAT

FAULT SHOWING UP AND DOWN SIDES, OR DIRECTION OF RELATIVE MOVEMENT, SEC 2 4 QUESTION MARK WHERE UNCERTAIN. Se c t i o n 2 4 1/4 COR. SEC. 25 SECTh SYNCLINE SHOWING DIRECTION OF PLUNGE

ANTICLINE SHOWING DIRECTION OF PLUNGE

STREAMSBENCH) GRAVEL, WEAK TO MODERATELY CONSOLIDATED

AP APL/TE

Om QUARTZ MONZON/TE

ARK ARKOSE

i s L IMESTONE

S/—Ls SILICEOUS LIMESTONE 'X£D FI. OAT

A-’£TA - S£0//TjtrASTS L m -SH LIME-SILICATE ROCK

S/i Ff/XFO FA PA T CO\sMF F ^L O A T COVJER SHALE AFcUaa/TE-, s/ al.£. F A E OtHM/VA A/TLY A RK O SE //*£ST£>ASJS •0 /9 /VF£i. 3 , C4i'FFTy ^ strsr SILTS TONE

ARC ARGILLITE

02 r QUARTZITE SLTST CH CHERT

Hfls HORNFELS LA - S/i

FIGURE 3 GEOLOGIC OUTCROP MAP MORNINGSTAR MINE AREA GREATERV/LLE MINING DISTRICT PIMA COUNTY, ARIZONA p z r T 19 S , R 15 E

OLD TUCSO O______too 200 FT. c : s c a l e : / " c io o ' S/l -LS ’/FED FLOAT Ci CONTOUR INTERVAL^20' 'A c e 9- LIME %TOAS4. •

-ZfQy

C o v f - ^

JAMES C STEWART, 1971, GEOLOGY THESIS ^ 9 7 ^ / 1911 ! o o z q n 0! I /

r AGE RECENT ALLUVIUM AND RECENT ELUVIUM TO QUATERNARY -STREAM BENCH GRAVEL THE ROCK UNITS ARE ARRANGED FROM TOP TO BOTTOM IN THE ORDER OF YOUNGEST TO OLDEST. THE SEDIMENTARY ROCKS WERE CONVERTED TO VERTICAL THICKNESS FROM OUTCROP. THE LOWER PART OF THE TERTIARY QUARTZ TO SEQUENCE BEGINS AT THE MORN/NGSTAR MINE AND CONTINUES UPWARD CRETACEOUS MONZONITE IN COLUMN TO THE SOUTHEAST, APPROXIMATELY ALONG THE SAME TREND AS SECTION B - B \ FIGURE 3 . THE UPPER PART OF THE COLUMN BEGINS AT THE NORTH-SOUTH FAULT AT THE WEST EDGE OF THE MAP, UPPER PART OF SEDIMENTARY FIGURE 3 AND CONTINUES UP COLUMN TO THE EAST ALONG APPROX­ ROCK COLUMN NORTH OF IMATELY THE SAME TREND AS SECTION A-A.' THE TIGHTLY FOLDED UNITS MORN/NGSTAR FAULT IN THE NORTHEAST CORNER, FIGURE 3 WERE NOT INCORPORATED INTO THE STRATIGRAPHIC SEQUENCE

THE NOTATION (F) SHOWN ON COLUMN INDICATES THE THICKNESS AND a r k o se ROCK TYPE IS BASED ON THE DOM INANT TYPE OF ROCK DEBRIS AND (FJ COVER, AND NOT ON OUTCROP THICKNESSES IN EXCESS OF 20 FEET PROBABLY CONSIST OF A LOCAL SEQUENCE OF THINNER UNTTS, AS NO SINGLE UNIT OF ONE TYPE WAS OBSERVED GREATER THAN 15 FEET IN THICKNESS ~ ^■LIMESTONE DESCRIPTIONS OF THE PRINCIPAL ROCK UNITS ARE IN THE TEXT.

ARKOSE (FJ

LIMESTONE ARKOSE (F)

ARKOSE

ARKOSE (FJ VERTICAL SCALE

SHALE LOWER PART OF SEDIMENTARY ROCK COLUMN SOUTH OF ■CHERT MORNHGSTAR FAULT.

SEDIMENTARY ARKOSE /i/t/i/V'V'LyL/i/v ROCKS PROBABLY (F J LOWER CRETACEOUS MIXED FLOAT ■LIMESTONE IMES TONE ARGILLITE SILICEOUS LIMESTONE ARKOSE (FJ 200 FEET limestone

LIMESTONE (F) ______SILTS TONE CHERT ARKOSE QUARTZITE AND CHERT ARKOSE (FJ S/LTSTONE

ARKOSE (FJ

— LIME- SILICATE ROCK

QUARTZITE (FJ

CHERT SHALE

QUARTZITE

QUARTZITE (FJ \-HORNFELS CHERT ARKOSE ( FJ ______-■CHERT

MIXED CHERT, S!L TSTONE. AND ARGILLITE

QUARTZITE

MIXED SHALE, QUARTZITE, AND ARGILLITE

FIG U R E 4 STRATIGRAPHIC COLUMN

MORNINGS TAR MINE A REA GREATERV/LLE MINING DISTRICT PIMA CO., ARIZONA

JAMES C. STEWART, I9ZI, GEOLOGY THESIS

1 1 0 9 ARGILLITE, QUARTZITE, AND SHALE FAULT

CEMENT

t t § SHAFT FLOOR 'o kk.

k CEMENT

VEIN

BACK

FAULT ■r

FIGURE 2 0 CROSS SECTION OF THE MORNINGSTAR MINE SHAFT

FIGURE 5 CROSS SECTIONS

------n o r th w e st 5530 ROAD MORNINGSTAR MINE AREA GREATERVILLE MINING D IST R IC T PIMA COUNTY, ARIZ.

POSITION OF SECTIONS SHOWN BY LETTERS ON THE OUTCROP MAP ------5460 LIM-SIL 5480

5440 5440

PREDOMINANTLY LIMESTONE ARK

X i FAULT- PREDOMINANTLY ARKOSE 80 FEET 5400 ST. LOUIS 5400 GULCH

OPH/R GULCH TC wmirwMrw tut wis** r% i 4. i i i ~ t- l. HORNFELS, CHERT AND SPARSE LIMESTONE

5350 5350 ■MORNINGSTAR FAULT

ZOO FEET HORIZONTAL SC ALE A' A WEST 5490 5490

\ \ \ \

450 MORNINGS TAR PAUL T (NEARL Y PARALLEL TO SEC NON) 5450

-NORTH-SOUTH ARK FAULT QUARTZITE, SHALE, ARGILLITE AND HORNFELS

----- 5400 CHERT POSS/BL E 5400 THRUS T PAUL T PREDOMINANTLY ARKOSE

SH PREDOMINANTLY ARKOSE ARK

5360 ----- 5360

POSSIBLE THRUST FAULT FAULT

LIMESTONE, SHALE, AND ARKOSE FAULT I 5320

I

JAMES C STEWART, 1971, GEOLOGY THESIS fA 9 <2? I 1 9 7 J tO O

f

CROSS SECTION OF THE MORNINGSTAR MINE SHAFT

FIGURE 5 CROSS SECTIONS B B' SOUTHEAST^•5^ MORNINGSTAR MINE AREA GREATERVILLE MINING D IST R IC T PIMA COUNTY, ARIZ.

POSITION OF SECTIONS SHOWN BY LETTERS ON THE OUTCROP MAP

'80 FEET

A' A

5490 5490

450 \ \ MORNINGSTAR FAULT (NEARLY PARALLEL TO SECTION) 5450

^SHats ■ 'ORTH-SOUTH \ QUARTZITE, SHALE, ARGILLITE AND HORNPELS CHERT POSS/BL E 5400 THRUST PAUL! PREDOMINANTLY ARKOSE

I VM PREDOMINANTLY ARKOSE

5360

POSSIBLE THRUST FAULT

LIMESTONE, SHALE, AND ARKOSE FAULT

I

JAMES C STEWART, 1971, GEOLOGY THESIS * (

SURFACE 5430'

E X PL A N A T I 0 N

HORIZONTAL AND VERTICAL SCALE ARE EQUAL. MEASUREMENTS MADE ALONG OR PARALLEL TO ANY OF THE COORDINATES ARE TRUE THE WEST OR RIGHT WALL OF THE SHAFT IS VIEWED AS THOUGH LOOKING THROUGH THE ROCK INTO THE SHAFT

FIGURE 18 BLOCK DIAGRAM VEIN, RED-QUARTZ; YELLOW- CALC/TE AND BARITE INTERMIXED VERY THIN UNITS OF ARGILLITE, QUARTZITE, AND SHALE INTENSELY WEATHERED AND FRACTURED O F THE MORNINGSTAR MINE %%%%% FAUL T OR SHEETED ZONE \ MASSIVE TO PLATY HORNFELS AND SKARN, VERY DENSE GREATERVILLE MINING DISTRICT

STRIKE AND DIP OF BEDS »r i THIN LAYERED SHALE AND SILTS TONE PIMA COUNTY,ARIZONA

ASSAY SITE (SEE APPENDIX FOR VALUES) VERY FINELY LAMINATED LIMESTONE AND CALCAREOUS SHALE 30 FEET

------APPROXIMATE CONTACT SCALE JAMES C STEWART, 1971, GEOLOGY THESIS

, ' /. I..,: C474I ,49/ /oo

1000E 1050 E UOOE H 50E 1200 E 1250E 130 OE 1210 N 1210 N

EX PL AN A T/ON

DATUM OF ZERO ELEVATION AT SHAFT COLLAR; LEVEL ELEVATIONS ARE VERTICAL FEET BELOW DATUM.

IO, 16, 21, AND 24 FOOT LEVELS

55 FOOT LEVEL

65 AND 109 FOOT LEVELS

140 FOOT LEVEL

VEIN, QUARTZ-RED; CALCITE - BARITE -YELLOW

FAULT OR SHEETED ZONE

STRIKE AND DIP OF BEDS

SEN ERA L TREND OF BEDS

APPROXIMATE CONTACT

MASSIVE TO PLATY HORNFELS AND SHARN, VERY DENSE

THIN LAYERED SHALE AND S/LTSTONE U50 N II SON VERY FINELY LAMINATED L I ME STON E AND CALCAREOUS SHALE

HOO N hoon

1050 N 1050 N

IOOON IOOON IOOOE 1050 E HOO E HSOE I200E 1250 E 1300 E

JAMES C STEWART, 197f, GEOLOGY THESIS

FIGURE !9 COMPOSITE LEVEL PLAN MAP OF THE MORN/NGSTAR MINE GREATERV/LLE MINING DISTRICT PIMA COUNTY, ARIZONA

20 FEET SCALE