El2000

N 8000

El2500

Figure 5. - Index of structural map sheets, 1285 level.

ra


Figure 26. - Structural map sheet, 1415-8.

€€


29

Figure 22. - Structural map sheet, 1415-4.



Figure 31. - Structural map sheet, 1415-13.

se


ROCKS OF MINE AREA

The principal rock units of the San Manuel mine area, from oldest to youngest,
may be generalized as follows :2/

Pre-Cambrian: Quartz monzonite or Oracle granite. Consists essen-
tially of coarse-grained feldspar, quartz, and biotite, The quartz mon-
zonite is one of the principal host rocks of the San Manuel ore body.

Upper Cretaceous (7): Basaltic and andesitic flows, flow breccia,
and agglomerate or conglomerate. Forms a thick series, termed the
"Cloudburst" by San Manuel geologists. Locally shows hypogene sulfide
mineralization, according to Pelletier, Encountered in shaft 3-B between
elevations 1938 and 1384.

Late Cretaceous or early Tertiary: Monzonite porphyry. Consists
essentially of quartz, feldspar, and biotite. Its feldspar phenocrysts
characteristically appear as white spots in grayish groundmass. Intrudes,
with irregular and commonly gradational contacts, the quartz monzonite.
The monzonite porphyry, like the quartz monzonite, is one of the principal
host rocks of the San Manuel ore body.

Late Cretaceous or early Tertiary: Diabase. Typically fine-grained,
dark gray, or reddish gray. Forms dikes and irregular intrusive bodies.
Mineralized in the mine area.

Tertiary: Rhyolite, light gray to pink. Occurs as dikes and irreg-
ular intrusive masses, not known to be mineralized.

Late Tertiary and Early Quaternary: Gila conglomerate, A series of
weakly stratified, moderately to durably consolidated gravels and boulders
in a sandy to silty cement. Locally contains beds of tuff, Absent over a
very small portion of the ore body, but thickens from a feather edge to
more than 1,300 feet in hanging wall of San Manuel fault.

Later Quaternary and Recent: Alluvial slope deposits of locally
stratified, weakly consolidated gravel, sand, and silt, unconformably
overlying the Gila conglomerate northeast of the Cholla fault.

STRUCTURE OF MINE AREA

Many of the main structural elements of the San Manuel mine area are not yet
well enough understood to be illustrated satisfactorily in cross section.

Although Gila conglomerate mantles all features earlier than itself over the
entire area planned for block caving, a considerable array of facts regarding the
fractures and other items that might affect block caving is available from mine
openings, as shown on figures 5 to 50 and from drill-hole records. Much detailed
mapping and correlation are required before these data can be thoroughly appraised.

5/ Schwartz, G. M., work cited in footnote 4.
Steele, H. J., and Pelletier, J. D., unpublished information.


NUMBER OF FRACTURES 45°-90°DIP
- © Ww 2B wo OD Y

°

STATIONS

Sta. Sta.
243 5OSE 100SE ISOSE 200SE 250SE 300SE 267

a DD

ey

o

NO. FRAGS. 0% 44° DIP

°

ORIFT A. O PT. IS STATION 243

Figure 59. - Fracture-density graph, block 7-1, 1475 level, drift A.

99



48

bee |
be 12"
b< @" hes
Zena

bce" 99 Pos

2-3" a9

thin (s s .
myer [et

Yo" - 30" bx, gq thin 92, wie?
wavy thin gq Thin sulga®? yt
( RCo >
Wavy .
@ & Ye yresry.
46, are be ® . “tso9s be
8 a thin suigg
25 ef- ya"
» Wri ae . 99 foutt rune
Sai, * "3°99 thin supa,
Wevy ‘thin
Sulfa, s
as
‘a
Ce bg thin gat thin
‘ ° im Salta
ae, SUT ee o Mos, bce" —]
ots

_—-«

Fee 7

NiSgged sighs? Oe

Peg 4
. G

Jwevy |_ 4600
= 299
as
W 8800
Ce) 50 100

SCALE — FEET

Figure 41. - Structural map sheet, 1415-23.


Figure 39. - Structural map sheet, 1415-21.

94


Figure 45. - Structural map sheet, 1475-2,

es


56

Panel 7 Fringe deifft

A LIV AA LYN

drift

8 _Frong

Fans

Figure 49. - Structural map of part of block 7-1, undercut level.


oY

Figure 37. - Structural map sheet, 1415-19.


16

iN
S| sry snerse py
9
S

b <i

Some fight
Jow-ongle fracs

2"9g

dark porph

4,

1, 1285.

Figure 9. - Structural map sheet,


Figure 27. - Structural map sheet, 1415-9.

bE


so 8 pp BH w

NUMBER OF FRACTURES 45°-90° DIP

(Sta, STATIONS (sta.

HlONW SONW Wr | SOSE ome ISOSE 200SE 250SE.

°

>

ow

NO. FRACS. 0°-44° DIP

°

PANEL 8 FRINGE DRIFT. O PT. IS STATION 137

Figure 58, - Fracture-density graph, block 7-1, 1415 level, panel 8, fringe drift.

$9


GEOLOGIC FACTORS RELATED TO BLOCK CAVING
AT SAN MANUEL COPPER MINE,
PINAL COUNTY, ARIZ.

Progress Report, April 1954—March 1956
by

E, D, Wilsont/

CONTENTS

Location and accessibility
HIStory wecceccsccvcvccvceee
Field work and acknowledgments .
Physical features ...csceccecees
Rocks of mine area ..
Structure of mine area .
Ore body .eccccscccccccccccccesecoe .
Features mapped in San Manuel mine ...
Scope and limitations of study
Fracture systems ..ccesceeee
Density of distribution .
Density graphs ...e...6
Displacement and gouge
Relative age wsscaseoes
Relation to known faults oe
Origin of fractures .eecsececccceccccscevecce
Summary of geologic factors related to block caving
General statement .eececscerececcccecscoeece
FLACtULeS .ecceeccccccvcccccccsevceececeeses
Rock types, alteration, mineralization, and water ..
Suggestions for further work ...csccscccccescccee

1/ Geologist, Bureau of Mines, Tucson, Ariz.

Report of Investigations 5336


FRACTURES 45*-90°DIP

NO. FRACS. 0°-44° DIP

°

STATIONS

St
36a | ose \OOSE 's0se | 2opse | BO0SE 300SE

waew

ote, preety, x,
& “,. a can ; 4

ORIFT CG. O PT. IS STATION 362

Figure 61. - Fracture-density graph, block 7-1, 1475 level, drift C.

89



a x

NUMBER OF FRAGTURES 45°-90°DIP
- n ow > a

°

STATIONS

Sta.
357 SOSE 100SE \SOSE 200SE 250SE 300SE 350SE 425SE

es |

Ed

ow

nn

NO. FRAGS. 0% 44°DIP

°

ORIFT B. O PT. IS STATION 357

Figure 60. - Fracture-density graph, block 7-1, 1475 level, drift B.

19


NUMBER OF FRACTURES 45°90°DIP
ye gf mw et

°

STATIONS
45NE 95NE 145NE I95NE ° 45NE 95 NE 145 NE 195 NE
|
*
5+

>

7

i

NO. FRACS. 0% 44° DIP

°

DRIFT I-N. O PT. IS SW END OF DRIFT ORIFT 5-S. O PT. 1S SW END OF DRIFT

Figure 63. - Fracture-density graph, block 9-1, undercut level, drifts 1-N and 5-S,

OL



27

Figure 20, - Structural map sheet, 1415-2.


Figure 6. - Structural map sheet, 1285-1.

13


e
Pe py bce *%
te

Fe ox on dork alt te
je #"- 2" zone of py veinlets,|  sadesite, — &
fe foe ox eoreh 3
dork olf
. e
zone 18” wide__J eo _ fault zone
-——_ b< 6°77
Essentiolly olf bes” some dark qmp
fractures. mapped ‘ woter | crushed sone
are minerolized - py, some flot frocs 30 b <3" considerable py
Joc ox bee’ Fa Joc on, loc Cu stain 9500
Tio
tight =} .
, aL |p tight dork porph
dork porp bere"
N bere” 20
ts, ze
é . ‘ yo water from dd holes
43000 h"-6" 9g at o>
P a .
Py, loc ox bc
loc Cu st 22
-LI| &-5"99, py, loc ox,
vol foe Cu st

Figure 12. - Structural map sheet, 1285-7.

61


b <2"
low- ongle fracs | if y
gen 2 ft sp Py
PY r-e"
ls g9
ox, very sparse py
k ih «
much Fe ox & ” <ie"ag

strong chrye SS

tight low-angle fissures
and tight NE verticol fissures

prevail NE of here ————~

S ' "og
Fe ox, focal,

so

chrysocolla & »
b <12
b<6" 2 a 85
oe Re Nght
tight frocs Me 9
a]
A Vee
oly, [YP
ey tight
46
fo tight
Ye b <ie"
4 locally

coarse

some low-angle
2 . Joints

a4 b<eé

loce/ chrys,
much Fe ox

some low-angle

fight fissures tight
= tight] 6
b <l2 &
Jocal chrysecolla,
wren? some Fe ox
tight
b<2"
focal chrysocolla
6<6"

tight

ae

dork porph local chrysocolla
some Fe ox
tight

tis h

e peor? 6

Figure 8. - Structural map sheet, 1285-3.


28

»

ry
a)

rw

“) sv NS
2 20 le, ‘> 40
yy Ae Cy 7.

Nflhe
”\ &
3

Se
ae
we
ys

ey 80 6
of

N
AD
io .)
Pe” AN?
. YR v
5 ON
wv . }
N) v
020 c of oe
sae v ©
ole ‘ eo
ye

Figure 21. - Structural map sheet, 1415-3.


10

Water in the mine workings has not been excessive; for example, in shaft 4, below

the 1475 level, it amounted to 750 gallons per minute during January 1955.
FEATURES MAPPED IN SAN MANUEL MINE

Scope and Limitations of Study

The present study thus far has been devoted largely to structural features
within or near the areas scheduled for early caving, where mapping operations would
be prohibited after subsidence began. Also, incidental observations were made of
other factors that might affect block caving, especially rock types, alteration,
mineralization, oxidation, and presence of water; fortunately, many supplementary
data regarding these items are available from churn-drill and core-drill records.

The observations underground are hampered to a considerable extent by lagging
in the timbered drifts. It effectively conceals all drift backs except in portions
of the undercut level. The grizzly drifts for the most part are tightly lagged.
Wall lagging throughout much of the fringe, panel, ventilation, and haulage drifts
is spaced so closely that comprehensive mapping there is difficult. Satisfactory
exposures of the walls were available in the undercut level and most of the 1285
level.

Fracture Systems

Figure 4 explains the principal symbols used on the map sheets. Mapping for
this study on the 1285, 1415, undercut, and 1475 levels of San Manuel mine (figs.
5 to 51) has demonstrated that the fractures do not as a rule strike at random or
"in every direction"; on the contrary, they trend in definite systems or sets, with
relatively few exceptions. These systems are: N.-S.; E.-W.;N.30°E.-S.30°W; N.45°Er
S.45°W.; N.60°E.-S.60°W.; S.60°E.-N.60°W.; S.45°E.-N.45°W.; and S.30°E.-N.30°W.
For this report, the designations are simplified as N.-S., E.-W., N.30°E., N.45°E.,
N.60°E., N.60°W., N.45°W., and N.30°W.

Density of Distribution

Although the number or density of fractures belonging to each system varies
from place to place, as shown by the graphs (figs. 52 to 66), a rather consistent
order of dominance exists within those areas for which actual counts were made, as
shown by the following table:


STATIONS

390SE 350SE 400SE 450SE sopse | pegse | 600SE

ee ee ee ee |

mg fm

NUMBER OF FRACTURES 45°-90° DIP

°

>

a

nn

NO. FRACS, 0% 44° DIP

°

DRIFT C (CON). O PT. IS STATION 362

Figure 62. - Fracture-density graph, block 7-1, 1475 level, drift C, continued.

69


54

SOP ee 2
Tg og

Figure 47. - Structural map sheet, 1475-4.


|
|
Np
|
|
Copper Creek a." ~!
\
fa
Fal F4
5 >
foJ
2/0
°
Si
a
31g
os Ze
{ Ss - ae
‘ a

33°N. rT

"PINAL COUNTY a4
~ "PIMA, COUNTY\...-°" 7 4
pa? a {1
PONY
F >
i 4 2
¢ Nze
J 83
188
»
ARIZONA

Figure 1. - Index map showing location of San Manuel copper mine.


ap sheets, 1415 level.

ral

18, - Index of structui

Figure


N
o

nN o > a o

NUMBER OF FRACTURES 45°-90° DIP

STATIONS

SONE IOONE ISONE I95NE 9 SONE \OONE ISONE 200NE

DD |

°

+

o

iJ

NO. FRACS. 0°-44° DIP

°

|
3
SS 2
&
MSE _ 1
N
“se oa aN
°
DRIFT 6-S. O PT. IS SW END OF DRIFT DRIFT 9-S. O PT. IS SW END OF DRIFT

Figure 54. - Fracture-density graph, block 7-1, undercut level, drifts 6-S and 9-S.

19


NUMBER OF FRACTURES 45°-90°DIP
- eo w ff wa oO

°

STATIONS

85SE (35SE \85SE 235SE 260SE

Potot oto bot tt

ry

o

Lo

NO, FRACS. 0°-44° DIP

c-}

Piua ew.
< Are
fe

12-W. O PT. 1S NW END OF DRIFT

Figure 56. - Fracture-density graph, block 7-1, undercut level, drift 12-W.

€9


=
f$-4
ae

NUMBER OF FRACTURES 45°-90°DIP
- CJ a > a CJ ~.

°

S5OSE

STATIONS

loose ISOSE 200SE 250SE 300SE l seose rr

ew

>

ow

NO. FRACS. 0% 44° DIP
iJ

°

PANEL 7 FRINGE DRIFT. O PT. IS STATION 104

Figure 57. - Fracture-density graph, block 7-1, 1415 level, panel 7, fringe drift.

09


22

ver

py t

oh
Fe ox

gg9<l"- ®
sulfides a

Jess Fe st

So

s acc” 8
3

e cS)

S

WING bcs”

\\ tight
2"99
tight

tight
?
Steepens to 45° 7 a8
upwerd; 2" 99 »
mullion hors. Bs” SH
~
dork alt. porph; Pr 2
gmp; for S' each sf
Side of dd drift

2 99—.

A b<s"
y.

>

Ye
Sa

I" Fe st %

bes"

2" Fe st gg

2"-6"9g

KN tight acs
“e dork-grey porph
[se 2G
b<e"
o tight
:
Pay
oD)

ot 699, loc py

atphd — 8 99., fee g

(Z; Qe Lo
Fe st 2%.4 99

dork pPorph

le 42" gg

foc Fe st —_#fy
el J

Ke py &< 6"
eo

<£/3750

100

Et)

Feet

Seale

Jerk porps

iy, tight

ot tgg bee”
yy foe ox
some st
flat Fis
eS 99
y
° many flat
° fracs
i b<3"
Py, loc ox
The tight
i b<e Py, loc ox
%6 tight

many float
frocs

rong
sures

Figure 15. - Structural map sheet, 1285-10.


Feet

Frac-

Percent
of |tures | Percent! Percent} Percent] Percent|Percent|Percent|Percent| Percent| with low-
Level Interval drift|mapped| E.-W. | N.-S. |N.45°W.|N.45°E.|N.60°W. |N.60°E.|N.30°W.|N.30°E.| angle dip
Uncaved
before .
1285 May 1954 2,400} 612 41.0 15.7 14.7 13.9 5.7 4.1 2.6 2.3 23.5
1285 Block 7-1 400} 113 31.8 23.0 | 15.0 9.8 6.2 6.2 3.5 4.4 17.7
Undercut do. 1,340} 233 37.3 13.7 3.0 4.7 9.9 16.3 7.7 7.3 21.0
Block 7-1,
panel 7
1415 fringe drift 375} 185 37.3 14.0 5.4 6.0 13.5 10.8 7.0 6.0 17.3
Block 7-1,
panel 8
1415 fringe drift 360) 148 36.5 20.9 4.0 2.0 13.5 8.8 12.8 1.3 17.6
Block 7-1,
1475 drift A 350 91 38.5 17.6 4.4 5.5 13.2 10.9 5.5 4.4 16.5
Block 7-1,
1475 drift B 425 93 30.1 26.9 11 to) 18.3 7.5 7.5 8.6 18.3
Block 7-1,
1475 drift C 600} 147 40.1 17.7 7 7 12.9 7.5 18.4 2.0 21.8
Undercut | Block 9-1 1,340] 269 41.6 25.3 3 0 9.7 9.7 4.1 9.3 29.0
Block 9-1,
panel 9
1415 fringe drift 200) 62 38.7 8.1 1.6 i) 17.7 9.7 14.5 9.7 29.0
Block 9-1,
panel 10 I
1415 fringe drift 2/400} 106 37.7 34.0 oO oO 7.5 2.8 11.3 6.6 33.0

1/ Includes connecting 25-ft. segments of grizzly drifts 9-1-1 to 9-1-7, inclusive.

oh


Fig.
48.
49.
50.
sl.
52.
53.
54.
55.
56.
57.
58,

59.
60.

62,
63.
64,
65.

66.

ILLUSTRATIONS (Con.)

Structural map sheet, 1475-5 ..ccccccccccccccccscecccccece
Structural map of part of block 7-1, undercut level ......
Cross section through southeastern portion of block 7-1,

looking northwest (refers to fig. 49) wecccccscceeee
Structural map of part of block 9-1, undercut level
Fracture-density graph, block 7-1, 1285 level ....seeseoee
Fracture-density graph, block 7-1, undercut level,

Axifts L-N and 3-S ..cccccscccccccccccvccsccvcccceecvees
Fracture-density graph, block 7-1, undercut level,

drifts 6-S and 9-S ....... dene ceessccoseccceseeee
Fracture-density graph, block 7-1, undercut level,

ALLEt LW cccecccccccccccccccccnccccccnsesscesesscceeees
Fracture-density graph, block 7-1, undercut level,

ALLLt 1L2-W ccccccccscccccccccccvcccscvrcesscesaccccesees
Fracture-density graph, block 7-1, 1415 level, panel 7,

fringe drift .ccccccccccccccccccccccerceccescceccvcccees
Fracture-density graph, block 7-1, 1415 level, panel 8,

Fringe drift ..cccccccccecccccccccccsceescsscscccccesece
Fracture-density graph, block 7-1, 1475 level, drift A...
Fracture-density graph, block 7-1, 1475 level, drift B ...
Fracture-density graph, block 7-1, 1475 level, drift C ...
Fracture-density graph, block 7-1, 1475 level, drift C,

Continued ..sescccecccccsccscccvecccecrscssescssssescees
Fracture-density graph, block 9-1, undercut level,

drifts 1-N and 5-S ...eeeeee eee cece eeseceee
Fracture-density graph, block » undercut level,

drifts L-W and 4-W ccsccccccccccccccocccscscesccevcesces
Fracture-density graph, block 9-1, undercut level,

drifts 8-W, 9-W, lLO-W, 11-W, and 12-W.cceccecccccccccces
Fracture-density graph, block 9-1, 1415 level, panels

9 and 10, fringe drifts ..cccccecccccecccccccecccceceece

iii

67


ii

34.

43.

47.

ILLUSTRATIONS

Ditect-reading azimuth protractor ......
Composite map of San Manuel mine workings ....

Explanation of symbols used on structural map sheets .
Index of structural map sheets, 1285 level ........0..

Structural map sheet, 1285-1 .
Structural map sheet, 1285-2
Structural map sheet, 1285-3
Structural map sheet, 1285-4
Structural map sheet, 1285-5
Structural map sheet, 1285-6
Structural map sheet, 1285-7
Structural map sheet, 1285-8
Structural map sheet, 1285-9
Structural map sheet, 1285-10
Structural map sheet, 1285-11
Structural map sheet, 1285-12 ..
Index of structural map sheets, 1415 leve
Structural map sheet, 1415-1 .
Structural map sheet, 1415-2 .
Structural map sheet, 1415-3 .
Structural map sheet, 1415-4 .
Structural map sheet, 1415-5 .
Structural map sheet, 1415-6 .
Structural map sheet, 1415-7 .
Structural map sheet, 1415-8 .
Structural map sheet, 1415-9 .
Structural map sheet, 1415-10
Structural map sheet, 1415-11
Structural map sheet, 1415-12
Structural map sheet, 1415-13
Structural map sheet, 1415-14
Structural map sheet, 1415-15
Structural map sheet, 1415-16
Structural map sheet, 1415-17
Structural map sheet, 1415-18
Structural map sheet, 1415-19
Structural map sheet, 1415-20
Structural map sheet, 1415-21
Structural map sheet, 1415-22
Structural map sheet, 1415-23
Structural map sheet, 1415-24 .....eeeeee
Index of structural map sheets, 1475 level
Structural map sheet, 1475-1 .....ccceeee
Structural map sheet, 1475-2 .
Structural map sheet, 1475-3 .

Structural map sheet, 1475-4 ..ccccecccccsccccsnccsceeseo


EXPLANATION FOR STRUCTURAL
MAP SHEETS

Cp - chalcopyrite

Fe - fron

Cu - copper

py - pyrite

porph - porphyry

st - stoin

Ox - oxidized

wk - weok

Sp - spaced

gen - generally

Joe - locally

b - blocks

< - (less than

> - more than

fracs — froctures

99 - gouge

its - joints

ad - dork

hw - hanging woll

fw - footwoll

v - vein

N

Ss

E&

w - directions

NE

Nw

GE

Sw

“3 ~ fracture, dip in degrees
x - fracture, vertical
Q 25 50 100 FEET

SCALE

BASE MAP OF MINE WORKINGS FURNISHED BY
SAN MANUEL COPPER CORR

Figure 4. - Explanation of symbols used on structural map sheets.
Geology by E. D. Wilson.

1


SUMMARY AND INTRODUCTION

A study of factors related to subsidence was specified in a project proposal
entitled "Structural Analysis of Block-Caving Operation, San Manuel Copper Mine,
Pinal County, Ariz.," approved by the Bureau of Mines early in 1953. This proposal
was designed by Charles H. Johnson, then chief of the Base Metals Branch of the
Minerals Division, Washington, D. C., assisted by Dr. Leonard Obert, chief of the
Applied Physics Branch, Region VIII (now Region V), College Park, Md., and E. D.
Gardner, chief mining engineer, Bureau of Mines, Washington, D. C. It read as
follows:

This project is a study of the mechanics of undercut block caving in
a deep ore deposit. The San Manuel is a low-grade disseminated copper
deposit containing nearly a half billion tons of ore lying at depths of
500 to 2,000 feet. Development is just starting. Production is to begin
in 3 to 4 years (in 1956) at a rate of 30,000 tons of ore a day, or 60,000
tons of copper a year. A Government loan of $90,000,000 /subsequently
increased to $94,000,000/ and a long-term Government purchase contract
support the capital investment, which will total about $110,000,000.

Justification for the proposed investigation is partly in the belief
that a better understanding of the laws that govern caving, subsidence,
and the transmission of ground pressures will have application in future
mining ventures of this type, and partly in the expectation that the San
Manuel operation itself will benefit from such knowledge as is gained.

The work will consist first of a structural analysis of the problem
based on a thorough study of the geology, the physical properties of the
rock types, and the proposed system of mining; secondly, the use of various
test techniques and types of equipment to measure ground movement and rock
stresses from the time of initial development until a substantial segment
of the ore body has been extracted, so that the complete pattern of behav-
ior can be determined,

Although devoted mainly to such structural features as faults, fractures, and
joints, the geologic study also concerns miscellaneous factors that might affect
rock strength.

LOCATION AND ACCESSIBILITY

The San Manuel copper mine, owned by the San Manuel Copper Corp., is situated
in the Old Hat district of southeastern Pinal County, Ariz., 45 miles by highway
northeast of Tucson, 5 miles southwest of Mammoth, and 8 miles north of the new
town of San Manuel (fig. 1). The San Manuel ore body is less than 1 mile south of


76

Relative Age

The present fracture pattern at San Manuel was initiated before sulfide miner-
alization, as proved by primary sulfide veinlets in the fractures of all eight sys-
tems, As pointed out by Schwartzl3/ on the basis of drill records, the premineral
fracturing occurred during at least three intervals - before and after intrusion by
the monzonite porphyry and after intrusion by the diabase. He also noted the
existence of many preconglomerate shear zones,

So far as determined by the present study, the N.-S. and E.-W. fractures are
mutual in age and as a rule cut all other steeply dipping fractures in the mine
workings, except possibly those of the Cholla, East (Mammoth?), and West type, which
vary from approximately N. 30° W. to N. 60° W. in strike. The relative ages of the
steeply dipping fractures of the other systems have not yet been determined. So far
as observed underground, some low-angle fractures are earlier than the sulfide min-
eralization, but in many places low-angle fractures of a late generation, presumably
akin to the San Manuel fault, cut or displace all others.

Detailed mapping of 950 feet of surface drainage ditch, less than one-half mile
south of shaft 3-A, shows N.-S., N. 45° W., and N. 30° W. fractures to be the most
common in the Gila conglomerate at that locality. A few fractures of the N. 30° E.
and E.-W. systems were noted, but the other three systems appear to be rare or lack-
ing. The N. 45° W. fractures seem to cut all others there.

It is believed that the influence of a fracture upon subsidence will depend
somewhat upon its age relation to the other fractures present. For example, the
youngest fractures, cutting all others, would tend to form relatively persistent and
predictable zones of weakness,

Relation to Known Faults

The steeply dipping faults that are prominent at the surface may be projected
only with difficulty or considerable uncertainty underground. So far as known, the
fracture pattern in the rocks beneath the San Manuel fault bears no tangible rela-
tion to them. On the other hand, the faults mapped underground generally constitute
zones of breccia, gouge, or intense shearing which are reflected by the fracture
pattern within adjacent ground; in many instances the strike and dip of a major zone
of weakness may be deduced in advance from the predominant system of fracturing
within its walls.

Numerous low-angle breaks occur throughout the mine workings, For the most
part, these fractures roughly parallel the San Manuel fault, although wavy in both
strike and dip, as shown in figure 50. Cutting essentially all the other fractures,
they form sheets of variable thickness that are of primary importance from the
standpoint of block caving.

To a certain extent, at least, the E.-W. fractures of 60°-80° N. dip occurring
in the footwall of the San Manuel fault possibly are complementary to it.

Is/ Schwartz, G. M., work cited in footnote 4, pp. 59-60.




. es
rt)
iM e<cs”
0 logged
cy © little woter
° from dd hole
0
0
(7)
Ol
lagged
Zp py
logged
Joe Cu st

aa . bP a3
much PY

much py

much
Fe ox

Na

of

legged
—
bes”
bce" logged
Some Flot frocs
> logged

17

Figure 10. - Structural mop sheet, 1285-5.


—L.29.23: 5336

Bureau of Mines
Report of Investigations 5336

GEOLOGIC FACTORS RELATED TO BLOCK CAVING
AT SAN MANUEL COPPER MINE, PINAL COUNTY, ARIZ.
PROGRESS REPORT, APRIL 1954-MARCH 1956

By E. D. WILSON

S. Govy of oA oy,
Doct MENTS ery oS
. JUN 11°59 wor rt
COLORADG 4eRARY
SY GOLD EC COL OL ah ates

United States Department of the Interior — May 1957

| metadc38661




40

igure 33, - Structural map sheet, 1415-15.

F


1955: By latter part of year, the fifth shaft had been sunk, and under-
ground development was sufficient for block-caving operations to be begun.
The new town of San Manuel, including concentrator and smelter, in addition
to 29-1/2 miles of railway to Hayden, had been built.

1956: Production of copper was begun early in the year. San Manuel is
rated as probably the world's largest underground copper mine from the
standpoint of ore tonnage.

FIELD WORK AND ACKNOWLEDGMENTS

The geologic field work for this project was begun in April 1954. To March 15,
1956, approximately 100 days had been spent in underground mapping and 21 days in
surface studies.

Mapping of the faults, fractures, and joints underground was done by means of a
15-inch plane table, Brunton compass, and tape on a scale of 1 inch equals 50 feet.
In many places, however, the compass was unsatisfactory because of strong local mag-
netic variation caused by electric trolley systems, iron pipe, steel sets, or equip-
ment. For measuring directions in such areas, a special direct-reading azimuth
protractor (fig. 2) was designed. It has been found to be adequate for this purpose
as well as more rapid and accurate than the compass for mapping structural features,
wherever good base maps are available.

A transit was used for control in mapping surface features.

Officials of San Manuel Copper Corp. generously made available maps, informa-
tion, and facilities for the work. Special acknowledgments are due H. J. Steele and
J. D. Pelletier, geologists, and H. W. Seaney and M. A. Zappia, stope engineers, for
their efficient cooperation. Richard T. Moore of the Arizona Bureau of Mines,
University of Arizona, contributed valuable assistance, Much fundamental informa-
tion was obtained from B, S. Butler of the University of Arizona, and P. C. Benedict,
geologist for Newmont Exploration Limited, §. C. Creasey and Robert Davis of the
Federal Geological Survey mapped the Mammoth 7-1/2-minute quadrangle during 1954,
and Creasey continued underground studies in 1955 for a forthcoming report.

PHYSICAL FEATURES

The San Manuel mine area is within secs, 34 and 35, T. 8 S., R. 16 E., ona
sharply dissected slope that rises southwestward from the San Pedro River, Thus the
topography is characterized by steep-sided, northeastward-flowing gulches between
moderately hilly ridges. Locally the relief ranges from 3,450 feet above sea level
on Red Hill to 3,000 feet in Tucson Wash west of shaft 1, and 2,400 feet at the San
Pedro River, 3-1/2 miles east of Red Hill.

Rainfall there probably amounts to about 13 inches per year. Most of it occurs
during July-August and December-February.

During the summer rainy seasons, the washes and the San Pedro River may carry
torrential floods, although throughout most of the year they tend to be dry.

The relations of water levels to oxidation and block caving will be discussed
in a subsequent section of this report,


the Mammoth-St, Anthony or Tiger mine area, which has been described by Peterson2/
and by Creasy .3

HISTORY
Detailed accounts of the discovery and development of San Manuel have been
published .4/ From these sources and subsequent information, the history may be

outlined as follows:

1870-80, approximate: Small-scale prospecting of copper-stained outcrop
area at southern base of Red Hill.

1906: Location of some claims in Red Hill area.

1915-17: Two exploratory churn-drill holes put down on or near the out-
crop, with discouraging results.

1925: Location of San Manuel claims 1-5.
1942: The owners of the San Manuel group of claims applied to the Recon-

struction Finance Corporation for a development loan. Henry W. Nichols,
one of the owners, submitted a supporting report.

1943: B. S. Butler and N. P. Peterson, Federal Geological Survey, ex-
amined the San Manuel area in March and recommended exploration. Federal
Bureau of Mines started churn drilling in November,

1944: Federal Bureau of Mines drilling gave important results. Magma
Copper Co. arranged to purchase property and began drilling in December.
Shortly afterward Anaconda Copper Mining Co. began drilling on adjacent
ground, the Houghton group.

1945: Federal Bureau of Mines drilling terminated in February after at-
taining a total of 15,839 feet in 17 holes. San Manuel Copper Corp., a
subsidiary of Magma Copper Co., organized in September,

1948: San Manuel Copper Corp. completed churn-drilling program and
started shaft sinking and underground development.

27 Peterson, N. P., Geology and Ore Deposits of the Mammoth Mining Camp Area, Pinal
County, Ariz.: Univ. of Arizona, Arizona Bureau of Mines Bull. 144, 1938, 63
pp.; (summary), Bull. 145, 1938, pp. 124-127.
3/ Creasey, S. C., Geology of the St. Anthony (Mammoth) Area, Pinal County, Ariz.:
Univ. of Arizona, Arizona Bureau of Mines Bull. 156, 1950, pp. 63-84.
4/ Steele, H. J., and Rubly, G. R., San Manuel Prospect: AIME, Tech. Pub. 2255,
1947, 12 pp.
Chapman, T. L., San Manuel Copper Deposit, Pinal County, Ariz.: Bureau of Mines
Rept. of Investigations 4108, 1947, 93 pp.
Goss, Wesley P., Exploration and Development of the San Manuel Ore Body: Min.
Cong. Jour., vol. 34, No. 12, 1948, pp. 22-26.
Schwartz, G. M., Geology of the San Manuel Copper Deposit, Arizona: Geol.
Survey Prof, Paper 256, 1953, 65 pp.


>
oe
at
se
A

wean tone
.
ons zs
oo
Aer eg

9°
by £ i ssh DN * sy
X

”
LN ve $y tne L

TET al a5 oo
Kage TT PNET

_

lb an 12 av. about oO”

PO HS SLES BNE NI 2 78 LoS Xe Sed Rs Parry g my
- e on om 8 eZ” a F ‘ i \ of
ioe, J ole oo PIO SPP P me we? ° Ad » Oa *
Ie HN ot
J
=
o
{o} 50
SCALE —- FEET

Figure 46. - Structural map sheet, 1475-3.

ia


Figure 29. - Structural map sheet, 1415-11.


77

Origin of Fractures
As aptly stated by Schwartz,16/

The conditions at San Manuel seem effectively to dispose of the
suggestion that shattering of the rock in the "porphyry-copper" deposits
was a result of cooling of the intruded porphyry. The grade of the ore
is remarkably uniform in pre-Cambrian quartz monzonite, in much younger
(Mesozoic or Tertiary) monzonite porphyry, and diabase. A tectonic
origin seems necessary to account for equal shattering of three distinct
rocks of different age.

The present study has demonstrated that the fracture pattern in the mine work-
ings is tectonic. The fracturing is systematic and can be explained best as the
results of compressional forces that were of regional scope and reacted in a system-
atic manner intermittently through long geologic time, The San Manuel fault fits
well into the compressional pattern as a low-angle reverse fault wavy in both strike
and dip.

SUMMARY OF GEOLOGIC FACTORS RELATED TO BLOCK CAVING
General Statement

The geologic factors that affect block caving are essentially those which per-
tain to rock strength. As far as determined by the present study, the principal
ones in the San Manuel mine are structure, rock types, alteration, mineralization,
oxidation, and presence of water,

Fractures

Here the main structural feature is fracturing. The caving rock breaks or
spalls along definite fracture surfaces. Folding is of potential importance insofar
as it has affected the conglomerate in the hanging wall of the San Manuel fault.

The density of fracturing in the several different systems, discussed on pre-
vious pages and shown by the graphs (figs. 52 to 65), constitutes an index of the
zones of weakness trending in those directions. Large fault zones or shear zones
appear to be reflected by the relative density of fractures in adjoining ground,

The density of low-angle fracturing is particularly significant, as exemplified
by comparing block 7-1 with block 9-1 (figs. 49 to 66). Characterized by a strong
predominance of steeply dipping fractures of the E.-W. system, these two blocks show
somewhat similar structural patterns except that block 9-1 displays a relatively
greater abundance of low-angle fractures. Partly for this reason, as indicated by
the caving operations before March 1956, the rock of block 9-1 tends to break into
boulders small enough for ready passage through chutes and grizzlies; on the other
hand, the rock of block 7-1, less thinly laminated by low-angle fractures, tends to
break into boulders often thick enough to clog chutes and grizzlies.

Gougy fractures, as well as zones of gouge and breccia, are recognized as zones
of weakness, especially where wet,

16/7 Schwartz, G. M., work cited in footnote 4, p. 60.


24

sulfides

oo %
2-699 —.

4

—_——

nests

W-2"9q
many tight W fracs ~

bce
b<s”

>
+
tight"
-

wh,

locally oxidized

tight

8s

Bb < ie"

Yumerous fight fracs
[T | dipping 20° SW
is? dark porph
20 1%" gq loc Fe ox

fro fight b gen < 12"

Yo sulfides foc ox
a

30 I~ 4°99

many tight — ~
2-aa9 > If
*

tigh
b gen <6" hg
ox 2

2
zone 12°—P|
I

tight 22

85)

b< 12” tight

sulfides

b<e6" thin gg

aN tight

b<e"
so tight

dark porph
eo

K~

20

2o9

py, loc Fe ox

b gen <6"

$ omeny taht, sp 2 -H

Keen

Figure 17. - Structural map

sheet, 1285-12.


Figure 34. - Structural map sheet, 1415-16.

Tv


Figure 16. - Structural map sheet, 1285-11.

23


~~
ro)

o ww & a @

NUMBER OF FRACTURES 45%-90°DIP

°

SONE | \OONE \SONE.

sone | roone | ISONE | roane

>

w

Ld

NO. FRACS. 0°-44°DIP

°

DRIFT I-N. O PT. 1S SW END OF DRIFT

ORIFT 3-S. O PT. IS SW END OF DRIFT

Figure 53, - Fracture-density graph, block 7-1, undercut level, drifts 1-N and 3-5,

09





puo
uo

2 j229t

2)9o49P!

avez

42144, OF

41224 2/bu0-moy

Figure 7. - Structural map sheet, 1285-2.

1


78

During the mapping efforts were made to estimate the average diameter of boul-
ders or blocks into which the rock would break when caved, and these estimates are
indicated on the maps (figs. 5 to 43) as less than 3 inches, less than 6 inches, or
less than 12 inches. Areas where the broken fragments average less than 3 inches
tend to include considerable gouge and are notably weak.

The youngest fractures within an area as a rule exert the most influence upon
subsidence,

As premineral and postmineral fractures alike tend to be gougy, there appears
to be little difference in their effects upon rock strength.

Rock Types, Alteration, Mineralization, and Water

Thus far, little distinction has been noted between the relative strengths of
the quartz monzonite and monzonite porphyry. It is believed that the strongest rock
here is indurated Gila conglomerate, and the weakest is kaolinized porphyry. Compre~
hensive data regarding the influence of various types of alteration and stages of
oxidation have not yet been obtained,

As the presence of water tends to result in heavy ground, wet spots were in-
dicated on the maps. Commonly they are associated with rhyolite dikes and persist-
ent fracture zones,

In general, the ore tends to be less blocky than the barren rock.
SUGGESTIONS FOR FURTHER WORK

The progress already made during the current study, as set forth on preceding
pages, seems clearly to indicate that the geologic factors related to block caving
at San Manuel are tangible in character. Much additional effort will be required,
however, before they can be thoroughly appraised.

Many fundamental data may be obtained by continuing the detailed mapping of the
fracture pattern throughout the mining area, including the haulage level, grizzly
level, and undercuts, As this mapping proceeds, adequate cross sections may be
drawn to show further correlation among the caving operations, fracturing, rock
types, alteration, mineralization, and presence of water, Progress to date suggests
that such correlations would lead to better understanding of block caving.

INT. BULOF MINES. POH. PAL 2338


Figure 44. - Structural map sheet, 1475-1.

TS


75

Density Graphs

Variations in density for each fracture system within the areas of blocks 7-1
and 9-1 are shown graphically in figures 52 to 66.

On these graphs a relatively high point denotes for its particular fracture
system a fault or a zone of weakness generally less than 25 feet wide. A plateau
or high average of points denotes for its system a correspondingly wider fault zone
or zone of weakness.

For example, on figure 58, block 7-1, 1415 level, panel 8, fringe drift, a
N.-S. high, at sta. 136 + 50 ft. SE., indicates a narrow fault zone which the map
(fig. 36) confirms as narrow.

On figure 58, panel 8, fringe drift, a notably strong E.-W. high, at sta.
137 + 175 ft, SE., indicates a fault zone that projects on the map in alinement with
a similarly strong E.-W. high indicated on figure 66, panel 9, fringe drift, at sta.
154 + 80 ft. NW. On the map (figs. 18, 36, and 49) it projects from the southeast
portion of block 7-1 undercut, drift 12-W, westward past the intersection of coor-
dinates E. 12600 and N. 9800, a total distance of more than 600 feet.

Figure 57, block 7-1, 1415 level, panel 7, fringe drift, provides examples of
wide zones of fracturing. From sta. 104 to 104 + 140 ft. SE. to 104 + 300 ft. SE.
it builds up a high average and indicates an important zone. On the same graph,
E.-W. fracturing is seen to be important throughout; also it forms a high average
from sta, 104 to 104 + 50 ft., and a higher plateau from sta, 104 + 25 ft. to
104 + 350 ft.

The graphs serve also to show at a glance the abundance and persistence of low-
angle fractures. For example, figures 52 to 66 indicate that low-angle fractures
are more abundant in block 9-1 than in block 7-1,

Displacement _and Gouge

As shown on the maps (figures 4 to 51), many of the fractures are marked by
gouge, which commonly ranges from less than 0.1 inch to a few inches in thickness.
At many places it occurs associated with breccia to form zones as much as 10 or
more feet across.

As a rule, gouge is most abundant along fractures of wavy, rather than planar
surface, Wavy fractures of steep dip are relatively abundant among the N.=S and
E.-W. systems, much less common on the N. 60° W. and N. 60° E., and rare but not
lacking among the other systems, Wavy surfaces and gouge are characteristically
common on the low-angle fractures.

Although numerous gougy fractures or fracture zones may be traced for consid-
erable distances horizontally and vertically, a large proportion may not be pro=
jected with certainty from one level to another or even across a drift. This lack
of continuity may represent local pinching together of the fracture walls, but more
commonly it is found to result from displacement.

Aside from the interesting question as to the amount of displacement implied,
the presence and quantity of gouge are important from the standpoint of block
caving; a weak material, gouge is noted for acting as a lubricant, especially when
wet,


58

Panel 9 / Fringe deigt

S.
oO

“S Gone 10 Fringe drift

Figure 51. - Structural map of part of block 9-1, undercut level,



Os deo My

oye
oO e
en zt 4\ Q ? * a
fy é ve
ot . vo» 0
° 4 e eS Y
of v \| ) o et
a aN KH 9 a
° :
or oe] ots
4, efor brace”
2 oe War
© fe
We Pa) K 6 PA e see
ieee oh
rad
> alan 3
of 104 f “ats a
0% r) i
«

"

Figure 24. - Structural map sheet, 1415-6,

Te


STATIONS

230SE.

65SE, 100SE ISOSE 200SE 235SE 0 30SE 1OOSE. 1S0SE. 200SE.
eyo} i | io tof 7 | | | | | |
pet 6+

;

Ost 5+ NO RECORD

n

#4, at

2

337 3+

&

% 2+ 2

&

Z| | "7 as |
20 °

st | | | oioiol, | | ht o|
7, 34 NO RECORD

é

°

ge at “°

<

eit it £3"

Z |
20 0

ORIFT I-W. O PT.1IS NW. END OF DRIFT

ORIFT 4-W. O PT. IS NW END OF DRIFT

Figure 64, - Fracture-density graph, block 9-1, undercut level, drifts 1-W and 4-W.

TL


ce

Figure 25. - Structural map sheet, 1415-7.


47

"2,

Figure 40. - Structural map sheet, 1415-22.


Ww V—-VwUn Tank

b<6*
lor ox ;
b< 6" N45"
‘4-2 99 Cy Py, loc ox
PY, loc ox AZ
beet
° 50 o _
P-3" Gg
t
Scale - Fae

dork porph

899 By, Joc ox
thi v7 bere
saga eu op tight some flat frocs
@ little woter » ;
from ad hole ooo bcu

~-
very tight} ss)

OI oF py loc ot

en

b <r”
thin py loc ox

See Biase snes EE from reek
eloy (2) off marked preted
%"-I" By loc om

30 ~/"-2" gg

6b <3"
b< 3"
SO Dght
*
‘>
b< 6"
‘ ”
Spe guise eth ber {
pork Pereh ~ song spaced ae N20, Pont
UR 2° py j % fight
thin py
loc ox
loc ox

water from dd hole
35 <2"

thin py loc ox

b<e

thir py, loc ox
T20

some filet Frace

+99

Figure 13. - Structural map sheet, 1285-8,


WI

‘
Nae

\
SAN
‘

9000

EW =

Figure 43. - Index of structural map sheets, 1475 level.

os


STATIONS
Sta. SONE 1OONE Sto. ISONE 200NE Sta. 250NE 3OONE Sta 350NE 400NE

a

ns
°

NUMBER OF FRACTURES 45°-90° DIP
- 7» Ww & w @

°

ry

ow

ew

KS
S

NO. FRACS. 0% 44°DIP
»

5 WN WZ
wy > N w
° :
1285 DRIFT. © PT. IS STATION 40

Figure 52. - Frocture-density graph, block 7-1, 1285 level.

6S




2,

Figure 32. - Structural map sheet, 1415-14,

6€


Figure 30. - Structural map sheet, 1415-12.

LE


NUMBER OF FRACTURES 45°-90° DIP
- » 8 pp Oa ow 4

°o

STATIONS

) S5OSE loose ISOSE 200SE 260SE

ee ee ee

>

ow

NO. FRAGS. 0% 44°DIP

°

DRIFT I-W. O PT. 1S NW END OF DRIFT

Figure 55. - Fracture-density graph, block 7-1, undercut level, drift 1-W.

2



%
(hf “00,
Ni No. SHAFT! / 0
C09 ‘pi
\
va)
\ Y-
\y

EXPLANATION

1265 LEVEL
— 4s LeveL
(475 LEVEL,

Figure 3. - Composite map of San Manuel mine workings.


49

Figure 42. - Structural map sheet, 1415-24.


Figure 48. - Structural map sheet, 1475-5.

cS


3. Long period of erosion accompanied by oxidation and secondary
(supergene) enrichment.

4, Deposition of Gila conglomerate.

5. Renewal of regional compression; development of San Manuel fault
asa low-angle thrust, accompanied by folding and tilting of rocks in its
hanging wall.

6. Relaxation of regional compression, followed by normal faulting
of N. 20° to 30° W. strike,

ORE BODY

For descriptions of the San Manug} ore body, the reader is referred to the
works of Steele and Rubly ,& Chapman ,2/ Goss ,10/ and Schwartz.1l/ A brief outline,
based largely upon their descriptions, is given for orientation.

With a copper content of 0.5 percent or more, the ore body is 6,800 feet in
known length, trending N. 60° E., by 3,000 feet in maximum known width. The great-
est thickness of ore drilled was 1,700 feet. The depth to ore averages several
hundred feet. According to Schwartz,12/ the western part of the ore body is a
tabular mass dipping southeast, with a lower boundary of hydromica-pyrite rock and
an upper boundary of marginal biotite rock.

To the east, however, the deposit expands in width, particularly at
depth; and the copper-bearing zone swings around to the south, making it
hook-shaped, 13/

The copper ore consists of mineralized quartz monzonite, monzonite
porphyry, and a minor amount of diabase, with little distinction in grade
between different kinds of rock that have undergone similar hydrothermal
alteration. 14

The ore mineralization is associated with hydrothermal rock alteration to seri-
cite, pyrite, quartz, chlorite, kaolinite, and minor amounts of other minerals.

Oxidation, in general, ranges from 285 to more than 1,600 feet below the sur-
face. Supergene or secondary enrichment here is relatively unimportant from the
standpoint of ore. Neither the oxidation nor the enrichment is related to the pres-
ent erosion surface or the present water table, Their structural history appears to
be somewhat complex.

The water table before the beginning of mine development ranged from 2,450 to
2,992 feet above sea level, or approximately 300 to 800 feet below the surface.

‘8/ “Steele, H. J., and Rubly, G. R., work cited in footnote 4.

9/ Chapman, T. L., work cited in footnote 4.

10/ Goss, Wesley P., work cited in footnote 4, San Manuel Copper Corporation:
Eng. and Min, Jour., vol. 150, No. 7, 1949, pp. 92-95.

11/ Schwartz, G. M., work cited in footnote 4.

12/ Schwartz, G. M., work cited in footnote 4, pp. 46-55.

13/ Work cited in footnote 12.

14/ Work cited in footnote 12,


GEOLOGIC FACTORS RELATED TO BLOCK CAVING
AT SAN MANUEL COPPER MINE, PINAL COUNTY, ARIZ.
PROGRESS REPORT, APRIL 1954-MARCH 1956

By E. D. WILSON

+ «© «© «# «+ «+ « « « Report of Investigations 5336

UNITED STATES DEPARTMENT OF THE INTERIOR
Fred A. Seaton, Secretary
BUREAU OF MINES
Marling J. Ankeny, Director

Work on manuscript completed March 1956, The Bureau of Mines will welcome reprinting of this paper, provided
the following footnote acknowledgment is made: ‘Reprinted from Bureau of Mines Report of Investigations 5336,"

May 1957


30

Figure 23. - Structural map sheet, 1415-5,


STATIONS
0 50SE O 75SEO 75SE 0 T5SE 0 T5SE
“tT | | f to | lp od } tt tobotpode bd
a
os } 4
CJ
el
354 7
a,
|] ¢
23 7
E
Ss? 7
&
7X
—}
Zo
sl | ol | |
&
mM
aet
°o
<
f! ote
: ‘
go) 2”
DRIFT 8-W DRIFT 9-w DRIFT 10-w ORIFT li-w DRIFT 12-w

O PT. OF EAGH DRIFT IS NW END

Figure 65. - Fracture-density graph, block 9-1, undercut level, drifts 8-W, 9-W, 10-W, 11-W, and 12-W.

aL


18

at 4
some flot fracs at Wee py, loc ox, foc Cu st
~ b<e Sy £0 b<6
zs, %
tight le en
‘3 tight S277 99
tight De
378g le » &¢6
py, loco }—~s zo| <6
Joe Cu st rr
ez b<e
Joc ox many tight joints
1-2" py .
‘N b<eé
s+ $0
I"-2°gg, slight Cu st

Too Cu st 22
| |45 7"-5" gg, py, loc ox,
col A Yoc Cu st
“~ b< 12" dork porph
Fhe b<6"
rvs } ¥e"-3"gq py, loc ox
zone 12” %"- 2" 99
py, loc ox hee
b< 12” ; b cle" dork porph
50 st ctzone py, foc ox,
Seaie 100 21 \go loc Cu st
Feet+ g

leo, —%"-3" 99, py, loc ox

Figure 11. - Structural map sheet, 1285-6.




‘ x
we ct
e 0
» :
Vv
u
oO
A
c a) cs >
oe
ol ot:
@ 7 0 3 s
q 2 Fa <
Pata DS boo >
Tee 9° | 183he lage
ee ae y) Up hick $9: heavy grbund
ie COME ae ° A——_—~

£ oat Odo | ye |
oN 7 aN
SAY as a 6 1 Mya fh
a s~ a e o
iS >” foe -
nt a » of
G Ne

wo
as
i
v BY

—7t =
tA Ale %
< a of
r >

\

Figure 35. - Structural map sheet, 1415-17.

C7


Figure 19. - Structural map sheet, 1415-1.

92


Figure 28. - Structural map sheet, 1415-10.

S¢e


PY,

Py,

Joc ox

loc ox

Sparse

derh porph

Py ehundant

blocky, not
Much min eralized

py, loc ox

many flet

fracs
tome flat fracs
b<6”

tight

B< 8 some Hol frocs

dork porph
bie"
Ngbt; slight Cu sp
tight

b<s2e"

21


Figure 2. - Direct-reading azimuth protractor. Compass card (A) is adjusted so that bearing
of drift being mapped is indicated at (B); it is then locked to strike board (E)
with friction lock operated by thumb screw also located at (B). If edge of strike
board is held parallel to strike of a fracture, and handle (D) is held perpendicular

to bearing of drift, the strike of the fracture is shown by pointer (C). Designed
with collaboration of Richard T. Moore.


57

Sta.42 Sta.44 Sta.46
tig | at eny | Pores 2°83
aX \ > L 7a t
AE AAS RENT —al
\Nig thin A
[ue fe 9.5"
Ie Z Dz
99.54
PX 1072499 ‘ 4 |
Farrel 8 Panel 7
Fringe drift rringe adrift
Ys
| I>
Wass
Lritt Drit? Orr tf
Cc 8B A
£13200 £/3400
7800 NV/0000

(285
urder-
cur 2
N
[4/5 SS
/475

Figure 50. - Cross section through southeastern portion of block 7-1, looking northwest (refers to fig. 49).


STATIONS
1OONW SONW Sia S5OSE loose Bauer ISOSE 200SE 250SE 300SE

ryt ToT Por dp py yp pp dp

Roe Ff a

NUMBER OF FRACTURES 45°%-90°DIP

°

>

0°-44° DIP
ew

Nn
h

NO. FRACS.

°

PANEL 9 FRINGE DRIFT. O PT.1S STA.154 PANEL 10 FRINGE DRIFT. O PT. IS STA. 110

Figure 66. - Fracture-density graph, block 9-1, 1415 level, panels 9 and 10, fringe drifts.

€L


Yo e “
t
ra <0
’
é of ar
o « r)
rs oe a
“Se > a oS >
x o oo? <O ”
Caan ne é eo
eo? 49.5% - et, omg ae we
° Cas moeXse io oe 9 4) bd @ xd
oe . ¢ yk cy % 9 B
See ote oy, wee RS sae OC Oe ght a) N
ay , . SON, oe PM Mo ut, oa $ A866) 4 OG Fa foe ey. opp 6
Ke” | ee 8 LE NY Oy. ENS IO i. y tK
* 3 rs eo z g
ws 8 oe £Q 61% 9 S  &, ee Oe Sey Merb ae t 8 Zz WY
wb ae Ie tH 6G ran mo vp tf aN V7 LTA Noe Ke ‘ 4AF t os 7
bad A pan ete os eye” SY) fe bey Key LN ge a
° SLR ON oo epet Ay] 2) ela Ue oo
= a) © be ‘ POE oat) <7 we
RS rt Dey Q

Ce

Figure 36. - Structural map sheet, 1415-18,

ev


ie 4 vies
outs ok Oe °
Y
9
of
e& 9 4
% ob?
¢ .
4
4
4

eee > Oh 6
ai EA
L oy
s ‘ev eal gy rE) Klee

Figure 38. - Structural map sheet, 1415-20.

7]


One of the earliest structures deduced in the mine area is indicated by the
configuration of the monzonite porphyry, This rock intrudes the quartz monzonite
in a complex manner that probably was controlled largely by a preexisting low-angle
fault zone; as stated by Schwartz,6/ the principal mass of monzonite porphyry in the
explored area lies above quartz monzonite and becomes thicker eastward.

Numerous fractures of both high- and low-angle types cut the quartz monzonite
and monzonite porphyry in the mine, as described in subsequent paragraphs. Some of
these breaks are pre-mineral, and others are later than mineralization.

Most of the latest fractures observed in the mine are of low-angle type, ex-
emplified by the San Manuel fault, which separates the Gila conglomerate and the
Cloudburst formation from the older rocks. The outcrop of this great fault, how-
ever, is displaced by steeply dipping faults of N. 20°-30° W. strike.

The San Manuel fault, so far as known, strikes between northwest and westward
and is traceable for several miles, Within the mine area it dips approximately 30°
southwestward at the surface but flattens to 15° or less at depth, In its hanging
wall the Gila conglomerate beds prevailingly strike northwestward and dip northeast~-
ward 20°-45°; at least one reversal of dip in the conglomerate beds occurs south and
east of the outcrop known as the Purcell window, The San Manuel fault characteris-
tically forms a gouge zone several feet thick, immediately above which the conglom-
erate shows relatively little disturbance other than the aforementioned tilting.

In strong contrast, the porphyry below the gouge zone is markedly sheared (fig. 6);
this shearing is common at many places throughout the mine workings and in surface
exposures.

In previous descriptions2/ the San Manuel fault has been interpreted as a
normal fault, formed before the conglomerate beds were tilted to their present at-
titude. On the contrary, evidence obtained during the present study indicates it to
be a thrust fault of rather wavy strike and dip that rolls northeastward over the
porphyry outcrop 2,000 feet northeast of shaft 2.

The type or relative direction of displacement on the San Manuel fault is an
important item from the standpoint of fracture-pattern interpretation; it generally
is recognized that the compressive stresses causing a thrust fault would result in a
fracture pattern quite different from the pattern associated with a normal tensional
or gravity fault.

In summary, the main events since deposition of the Cloudburst series are
interpreted by the writer as follows:

1. Regional compression and development of fracturing.
The deformation culminated with low-angle faulting and emplacement of
the monzonite porphyry. Continuance of the compressional forces caused
the fracturing to extend throughout the monzonite porphyry.

2. Primary (hypogene) sulfide mineralization,

6/ Schwartz, G. M., work cited in footnote 4.

7/ Steele, H. J., and Rubly, G. R., work cited in footnote 4.
Chapman, T. L., work cited in footnote 4,
Schwartz, G. M., work cited in footnote 4.