UNITED STATES BUREAU OF MINES

UNITED STATES DEPARTMENT OF THE INTERIOR

RI 9582 REPORT OF INVESTIGATIONS/1995

In Situ Stress at the Lucky Friday Mine

(In Four Parts): 

4. Characterization of Mine In Situ Stress Field

By J. K. Whyatt, T. J. Williams, and W. Blake
U.S. Department of the Interior

Mission Statement

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Interior has responsibility for most of our nationally-owned public

lands and natural resources. This includes fostering sound use of our

land and water resources; protecting our fish, wildlife, and biological

diversity; preserving the environmental and cultural values of our

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of life through outdoor recreation. The Department assesses our

energy and mineral resources and works to ensure that their

development is in the best interests of all our people by encouraging

stewardship and citizen participation in their care. The Department

also has a major responsibility for American Indian reservation

communities and for people who live in island territories under U.S.

administration.
Report of Investigations 9582

In Situ Stress at the Lucky Friday Mine

(In Four Parts): 

4. Characterization of Mine In Situ Stress Field

By J. K. Whyatt, T. J. Williams, and W. Blake 

UNITED STATES DEPARTMENT OF THE INTERIOR

Bruce Babbitt, Secretary

BUREAU OF MINES

Rhea Lydia Graham, Director
International Standard Serial Number

ISSN 1066-5552
CONTENTS

Page

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

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

Geology ...................................................................................... 3

Coeur d'Alene Mining District framework ............................................................ 3

Lucky Friday Mine ............................................................................. 3

Analysis of small-scale geologic features ............................................................. 3

Rock mass response to mining ....................................................................... 4

Rock mass behavior ............................................................................ 4

Raise bore breakouts ........................................................................... 4

Alimak raise (3050 to 4250 levels) ............................................................... 5

Silver shaft raise bore ........................................................................ 5

106 and 107 raise bores ....................................................................... 5

97 raise bore ............................................................................... 5

Service raise bore ........................................................................... 5

Grouse vein raise bore, Star Mine ................................................................ 5

Mine stress field characterization ..................................................................... 5

Distribution of horizontal stress direction ............................................................. 6

Distribution of stress component magnitudes .......................................................... 7

Stress estimate ............................................................................... 8

Discussion and conclusions ......................................................................... 8

Acknowledgments ................................................................................ 9

References ..................................................................................... 9

Appendix.—Angle between long axis of ellipse and bedding strike . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

ILLUSTRATIONS

1. Location of Lucky Friday Mine in Coeur d'Alene Mining District of northern Idaho . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2. Major geologic features of Coeur d'Alene Mining District . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3. Major structural features of 5300 level, Lucky Friday Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4. Lithologic subunits in lower Revett Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

5. Alimak raise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6. Silver shaft and system of circular ore passes and service raises developed to support longwall mining of

vein . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

7. Breakouts observed in Silver shaft ore passes on 5100 level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

8. Subunit lithology of Silver shaft ore passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

9. 106 and 107 ore passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

10. 97 ore pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

11. Subunit lithology and breakout indicators of Fh1 orientation in service raise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

12. Raise breakouts, 7300 level, Star Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

13. Rose diagram showing frequency of Fh1 orientation as indicated by overcore measurements and breakouts

plotted in 15E intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

14. Location and subunit lithology of breakout indicators of F orientation in vicinity of LF 5300-level h1

overcore measurement site in soft subunits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

15. Location and subunit lithology of overcore and breakout indicators of Fh1 orientation in vicinity of

LF 5300-level overcore measurement site in hard subunits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

16. Topography over north-south cross section through Lucky Friday and Star Mines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

17. Relationship among stratigraphy, rock elastic modulus, and estimated vertical in situ stress component

at LF 4250 measurement site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

TABLES
ii

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

Metric Units

cm centimeter m meter

GPa gigapascal MPa megapascal

km kilometer pct percent

kPa/m kilopascal per meter

U.S. Customary Units

ft foot psi pound per square inch

in inch psi/ft pound per squatre inch per foot

Page

1. Principal in situ stresses measured at sites in Lucky Friday and Star Mines ................................... 2

2. In situ stress magnitudes in map coordinates and estimated overburden pressures measured at sites in

Lucky Friday and Star Mines ................................................................... 2

3. Fh1 and Fh2 calculated from overcore measurements .................................................... 6

4. General indications of Fh1 orientation .............................................................. 6

5. Specific indicators of Fh1 orientation ............................................................... 6

6. Components of stress measurements with respect to orientation of 38/Offset Fault .............................. 7

7. Stress field estimate, Lucky Friday Mine ........................................................... 8
Mining engineer, Spokane Research Center, U.S. Bureau of Mines, Spokane, WA. 1

Consultant, Hayden Lake, ID. 2

IN SITU STRESS AT THE LUCKY FRIDAY MINE

(In Four Parts):

 4. Characterization of Mine In Situ Stress Field

By J. K. Whyatt, T. J. Williams, and W. Blake 1 1 2

ABSTRACT

Researchers at the U.S. Bureau of Mines collected and analyzed overcore measurements and other indicators of

in situ stress characteristics at the Lucky Friday Mine, Mullan, ID. An analysis of these data revealed that significant

local variations in in situ stress are present in this mine and that these variations existed prior to mining. High stresses

were found to be associated with the most competent strata and a locked section of a fault. An estimate of the

predominant stress field was developed for mine-wide modeling. The estimate shows that the greatest principal stress

was oriented north of northwest. This information should provide a basis for mine-wide structural modeling of the

Lucky Friday Mine and should generate important insights into localized stress conditions, which may significantly

affect both local and mine-to-mine variations in seismicity induced by excavation.
2

Table 1.—Principal in situ stresses measured at sites

in Lucky Friday and Star Mines

Stress component Magnitude Bearing Plunge

MPa psi 

LF 4250 level:

 F .............. 1 91 13,200 N 40E W 13E

 F .............. 2 55 7,900 S 41E W 33E

 F .............. 3 37 5,400 N 68E E 54E

LF 5300 level:

 F .............. 1 135 19,600 S 80E W 34E

 F .............. 2 73 10,500 N 4E W9E

 F .............. 3 69 10,000 S 81E E 54E

Star 7300 level:

 F .............. 1 54 7,800 N 38E W 10E

 F .............. 2 42 6,000 N 74E E 66E

 F .............. 3 34 4,900 S 48E W 22E

INTRODUCTION

As part of the U.S. Bureau of Mines' (USBM's) ongoing table 1 as principal stresses and in table 2 as stress components in

research to reduce ground control hazards in deep metal mines, map coordinates.

USBM researchers undertook the study described in this Report The most recent of the three measurements, LF 5300, found

of Investigations (RI) to increase basic knowledge of the in situ unusually high stresses and a stress rotation that confused the

stress field in the lower portion of the Lucky Friday Mine, stress picture. The nationwide collection of stress measurements

Mullan, ID. This knowledge was sought to support ongoing compiled by Zoback and Zoback (1980; 1989) failed to provide

applied research projects at the Lucky Friday Mine in the Coeur much clarification because their data set did not include any of the

d'Alene Mining District of northern Idaho (figure 1). In overcore measurements that have been conducted in the Coeur

particular, stress in the lower portion of the mine was of great d'Alene Mining District. In an effort to clarify these results, inforinterest to investigations of intensive rock bursting in this area. mation was sought from other sources, including geologic studies

Sprenke and others (1991) estimated that the Lucky Friday Mine and mining experience, that would provide some insight into the

experiences a rock burst of magnitude 2.5 or greater on the orientation and magnitude of stresses among overcore

average of once every 15 weeks. Knowledge of in situ stress is measurement sites. This fourth and final RI in the series

also important to research on new mining methods for deep synthesizes these overcore stress measurements with geologic and

mines (for example, the Lucky Friday underhand longwall ground control information to form an improved picture of the in

experimental stope) (Whyatt and others, 1992). situ stress state at the Lucky Friday Mine.

Geomechanical engineering practice generally begins with an

estimate of the in situ stress state of the rock before an opening is

excavated. The stress state before and after excavation is one of

the most widely estimated, calculated, and analyzed parameters in

modern rock mechanics. Yet direct measurements of stress are

few and far between because of the expense of current methods.

This series of RI's started with a reexamination of an overcore

stress measurement (hereafter known as LF 4250) from the Lucky

Friday Mine's 4250 level (Whyatt and Beus, 1995). The second

RI covered a stress measurement (LF 5300) conducted by USBM

researchers on the 5300 level of the mine (Whyatt and others,

1995b). The third RI reexamined a stress measurement (Star

7300) from the 7300 level of the nearby Star Mine (Whyatt and

others, 1995a). The results of these measurements are

summarized in

Table 2.—In situ stress magnitudes in map coordinates and estimated overburden

pressures measured at sites in Lucky Friday and Star Mines

LF 4250 level LF 5300 level Star 7300 level 

Stress component,

 MPa (psi):

 F ................... ns 74 (10,700) 74 (10,700) 46 (6,700)

 F ................... ew 64 (9,200) 113 (16,400) 42 (6,100)

 F ................... v 45 (6,600) 90 (13,100) 42 (5,900)

 J ................. ns/ew -19 (-2,700) 7 (1,100) -9 (-1,300)

 J .................. ns/v 3 (400) -5 (-700) 3 (500)

 J .................. ew/v -13 (-1,900) -38 (-4,400) 1 (100)

Elevation, m (ft) .......... -270 (-885) -590 (-1,935) -471 (-1,544)

Depth, m (ft) . . . . . . . . . . . . . 1,295 (4,250) 1,615 (5,300) 2,237 (7,340)

F depth, MPa (psi) ....... v 35 (5,000) 43 (6,300) 60 (8,700)

F model, MPa (psi) ....... v 40 (5,750) 49 (7,130) 55 (7,990)
3

GEOLOGY

The geology of the Coeur d'Alene Mining District, including current depth, which is centered on the 5500 level approximately

the Lucky Friday Mine, is complex. The literature is incomplete 1,675 m (5,500 ft) below the surface and 580 m (1,900 ft) below

and often contradictory on important points. However, there is sea level. The vein ranges from several centimeters to 5 m (15 ft)

sufficient information available to provide a general description thick and is nearly conformal in plan to an anticline plunging 60E

of the geologic structures and stress regime that dominate the to the southeast. Because the vein itself dips steeply (70E to 90E)

district. This section explores the geology of the district with to the south and east, it contacts progressively older rocks with

implications for the predominate stress state on mine and local depth (figure 3). The vein wall rock is the quartzitic Revett

(mine opening) scales. Formation.

COEUR D'ALENE MINING DISTRICT and some of these intersect the vein structure. Two prominent

FRAMEWORK faults are the North and South Control Faults, which delineate the

The Coeur d'Alene Mining District lies within late contains massive argentiferous galena and lesser amounts of

Precambrian sedimentary rocks of the Belt Supergroup. These sphalerite and tetrahedrite. The rock mass surrounding the vein

rocks are exposed primarily in western Montana, northern Idaho, at the current mining depth is the lower member of the Revett

and southern British Columbia, where they define the Belt Formation of the Belt Supergroup. The lower Revett is made up

terrane. The Coeur d'Alene district lies within the west-central of vitreous quartzite and sericitic quartzite beds from 30 to 90 cm

part of the basin, where it is intersected by the Lewis and Clark (12 to 36 in) thick with soft interbeds of argillite generally less

line (figure 1). The Lewis and Clark line is a major tectonic than 2.5 cm (1 in) thick. White has grouped these beds into 15-

lineament that has undergone diverse and intermittent tectonism to 45-m (50- to 150-ft) thick subunits of predominantly hard,

since its inception (Harrison and others, 1986). The northwest brittle, vitreous quartzite and relatively softer argillite and sericitic

orientation of the maximum principal stress in this zone was quartzite (figure 4).

indicated in a recent analysis of a minor earthquake located 15 km

(9 miles) northeast of the Lucky Friday Mine (Sprenke and ANALYSIS OF SMALL-SCALE GEOLOGIC

others, 1991). FEATURES

Major faults in the Coeur d'Alene Mining District include the

Osburn and the Dobson Pass. These two faults define the Small-scale geologic features at a number of sites in the Star

northeast portion of the district, including the Lucky Friday Mine and Lucky Friday Mines have been cited as evidence of current

(figure 2). These faults are generally believed to be some of the and historical principal stress orientations (Gresseth, 1964;

youngest features in the district (Hobbs and others, 1965). Gresseth and Reid, 1968; Allen, 1979).

There is general agreement that the most recent movement on Gresseth (1964) used the orientation of rock fractures and

the Osburn Fault is right lateral, indicating a northwest-trending joints to determine the direction of past and present ground forces

tectonic stress field (Sprenke and others, 1991). There is less on the 5900, 6100, and 6300 levels of the Star Mine. Gresseth

agreement on the direction of movement for the low-angle classified sets of (1) extension joints, (2) release joints, and (3)

Dobson Pass Fault. Hobbs and others (1965) viewed the feature shear joints that indicated at least two periods of rock

as a low-angle normal fault, primarily because younger strata deformation. He identified the first of these as related to folding,

form the hanging wall of the fault. White, however, believes that with a predominantly horizontal, east-southeasterly, 3

the Dobson Pass Fault is a thrust fault, which would indicate west-northwesterly direction of compression. He associated the

significant east-west compression, at least north of the Osburn most recent period of deformation as a north-south compression,

Fault. He cites numerous faults in the region with orientations roughly perpendicular to the vein, and probably caused by

similar to the Dobson Pass, many of which also have younger mining.

strata in their hanging walls (e.g., Harrison and others, 1986).

This study concentrates on understanding the stress state in the

northeast portion of the Coeur d'Alene Mining District as defined

by these features. Any relationship this stress state may have to

the stress state in the remainder of the district is left as an open

question.

Personal communication from B. G. White, geologist, Spokane Research 3 3

Center, USBM, 1994.

LUCKY FRIDAY MINE

Mining has followed the Lucky Friday vein down to the

Numerous faults and secondary folds are found in the mine,

ends of the 460-m (1,500-ft) long Lucky Friday vein. The vein

4

In a paper presented at the Belt Symposium III, August 14-21, 1993, 4 4

Whitefish, MT, entitled "Geology of the Montanore Stratabound Cu-Ag

Deposit, Lincoln and Sanders Counties, Montana," A. R. Adkins reported a

similar identification of subunits in the lower Revett at the Montanore project in

western Montana. Although both sets of subunits are identified by letters, this

similarity is only coincidental. That is, subunit A may not contain the same

strata at the respective mines despite their similar nomenclature.
4

A subsequent report by Gresseth and Reid (1968) looked at a Friday Mine. He concluded that three different stress systems,

wider range of fabrics, from regional and macroscopic faults to with F oriented N 12E W, N 30E to 40E W, and N 30E to 40E

quartz crystals and microfractures, on the 6500 and 6700 levels E, most likely caused the joint and fold patterns. He chose the N

of the Star Mine. They concluded that during epochs of tectonic 30E to 40E W stress system as being the latest on the basis of

deformation, the maximum and minimum principal stresses were corroboration with his accompanying overcore stress

horizontally oriented and acted along northwest and northeast measurement.

axes, respectively. They also concluded that the most recent These early efforts at unravelling the tectonic history of the

tectonic deformation represents a rotation of the direction of Coeur d'Alene Mining District were based on a vastly

minimum principal stress from horizontal to vertical. They oversimplified view of the district's real structural complexity and

observed good interscale correlation and statistical homogeneity tectonic history. Subsequent work on tectonic history by White

o f t h e t e c t o n i c f a b r i c a n d has drawn on a wide variety of geologic evidence to identify

interpreted this as indicating stress field homogeneity in this area several periods of tectonic loading, with the latest evident tectonic

during tectonic deformation. period consistent with a northwest orientation of the maximum

Allen (1979) applied a similar approach to analyses of principal stress (Hobbs and others, 1965).

fractures and joints mapped on the 4250 level of the Lucky

1

5

ROCK MASS RESPONSE TO MINING

ROCK MASS BEHAVIOR into the harder and more-brittle quartzite within the lower

Observations and measurements of rock mass behavior in an increased.

operating mine often provide valuable clues to the stress state and

differences in the stress state in different parts of the mine. Rock Blake and Cuvelier do not speculate whether the changes in

mass behavior in the Coeur d'Alene Mining District, both inside rock bursting resulted primarily from a change in rock properties,

and outside the study region, has been generally, but not entirely, or stress intensity, or a combination of these effects.

consistent with a northwest trend for the maximum horizontal secondary principal stress (Fh1). For example, Board and Beus RAISE BORE BREAKOUTS

(1989) measured rock deformation and loading of the concrete

lining in the Lucky Friday Mine's Silver shaft and concluded that Observations of the deformation of bored raises are especially

these measurements supported a N 45E to 65E W trend of Fh1. In useful for estimating stress direction because of their size and

a more recent project, Pariseau and others (1992) concluded that vertical extent. Rock fracturing (breakouts) in these raises

rock deformation and local ground control problems in an consistently occurs on the sides that parallel the orientation of F

experimental stope on the 5100 level supported a N 40E W trend in a plane perpendicular to the raise. The short axis of the

for Fh1. elliptical cross section created by this fracturing parallels the

Historical experience with rock bursts at the Lucky Friday direction of maximum stress.

Mine indicates that lithology exerts significant control on rock Breakouts and their relationship to principal stresses have been

bursting. Blake and Cuvelier (1992) describe the evolution of studied extensively. A recent report by the National Research

rock-burst problems as different major lithologic units were Council (1993) provides a good review of the breakout

encountered. phenomenon. The variety of orientations of these breakouts to

During the 1960's, pillar bursts accompanying mining primarily by stress, as opposed to being determined by

. . . within the upper Revett quartzite were the major preexisting geologic structures. Several observations of borehole

ground control problem encountered at the Lucky Friday breakouts from active areas of the Lucky Friday Mine are

Mine . . . Bursting problems decreased during the 1970's discussed in the remainder of this section.

as overhand cut and fill mining progressed through the

softer and more argillaceous middle Revett . . . During the

early 1980's, mining activity progressed 

Revett formation. The bursting frequency dramatically

h1

local structure suggests that the breakouts are determined

Personal communication from B. G. White, geologist, Spokane Research 5 5

Center, USBM, 1994.
5

Alimak Raise (3050 to 4250 Levels)

The 2.1-m (7-ft) diam "Alimak raise" was bored in the late

1970's from the 3050 to the 4250 levels. It passed from the

upper levels in the shadow of mining to the deeper, unmined

levels of the mine. The final shape of the cross section and bed

orientation was measured at seven elevations by one of the

authors (Blake). The lower three cross sections were least affected

by mining-induced stress. These cross sections and a schematic

showing contemporary mining progress are shown in figure 5.

The authors have estimated the locations of these sections with

respect to locally defined lithologic subunits of the lower Revett

Formation. Section 1 is believed to be in the middle Revett,

section 3 is in a hard subunit (A) of the lower Revett, and section

2 is somewhere near the boundary between the middle and lower

Revett.

The long axis of the ellipse created by the breakouts is roughly

parallel to the strike of bedding in these cases. This observation

is significant because it contradicts most experience in the district.

That is, ground control problems are generally concentrated

where bedding is parallel to the opening (Whyatt, 1986; Whyatt

and Beus, 1987). Thus, the shape of the borehole breakout

appears to be controlled primarily by stress, not structure.

However, the breakouts do rotate with rotation of bedding strike.

The appendix lists the orientation of bedding with respect to all

borehole breakouts.

Silver Shaft Raise Bore

Surveys were also made of raise bores developed for use as ore

passes and service raises in conjunction with underhand cut-andfill stopes developed below the 5100 level (figure 6). Raises were

developed as part of the Silver shaft loading pocket system in

1983 at the 5100 level, and breakouts provide evidence of stress

orientation at some distance from the vein (figure 7). On the

5100 level, both raise bores broke out into ellipses during excavation, showing a northwest-trending Fh1. Later observations

on the 4900 and 5500 levels found elliptical cross sections of

similar orientation. Thus, the orientation of Fh1 appears to be

consistently northwest in subunits E through H at this location

(figure 8).

106 and 107 Raise Bores

The 107 raise was drilled during 1985 in the northeast portion

of the mine from the 5300 to the 5100 level. On the 5100 level,

the 107 raise broke out from an initial 1.5-m (5-ft) diam circle to

a 4.6- by 9.1-m (15- by 30-ft) ellipse with the long axis oriented

to the northeast, indicating a N 45E W trend for F (figure 9). h1

Breakouts on the 5160-access, 5210-sublevel, and 5300-level

horizons of the raise indicated Fh1 orientations of N 40E W, N 35E

W, and N 55E W, respectively. Subsequent development of the

106 raise between the 4900 and 5100 levels during late 1988 was

accomplished without breakouts. Underhand mining during

1988 (see figure 9) was concentrated below the 5100 level.

97 Raise Bore

The 97 raise bore was developed about 64 m (200 ft) west of

the 5300-level overcore measurement site. The observed

breakout suggested a trend of N 55E W for F on the 5300 level h1

(figure 10). In this case, the ellipse was oriented parallel to

bedding.

Service Raise Bore

The service raise was developed from the 5400 level to the

5480 sublevel using the Swedish blasthole method. The ring of

14-cm (5.5-in) blastholes showed a consistent N 74E W

orientation of Fh1 on the 5400 level. Further development of the

raise to the 5560 sublevel was accomplished with a 1.2-m (4-ft)

diam raise bore. This section of the raise was observed to break

out to a northeast-southwest elongated ellipse showing a N 35E

to 45E W trend of Fh1 on the 5480 sublevel. This raise was then

slabbed out to a diameter of 2.4 m (8 ft). A section through the

raise showed a transition from the hard G subunit on the 5400

level to the soft H unit on the 5480 sublevel (figure 11).

Grouse Vein Raise Bore, Star Mine

A raise bored on the 7300 level of the Star Mine at a stress

measurement site broke out to indicate Fh1 oriented N 30E to 40E

W. The raise and the stress measurement site are located in

vitreous quartzite strata of the Revett Formation. This breakout

(figure 12) was minor compared to many observed in the Lucky

Friday Mine.

MINE STRESS FIELD CHARACTERIZATION

The objective of this work, characterization of the in situ stress stress evidence gathered in this study, most notably the overcore

field at the Lucky Friday Mine, has been addressed before (Beus measurement from the 5300 level, is at odds with this

and Chan, 1980; Whyatt, 1986). These studies assumed that the assumption. Thus, characterization of the mine in situ stress field

stress field was homogeneous, varied linearly with depth, and did must start with examination of stress field variability.

not vary laterally. Some of the in situ
6

DISTRIBUTION OF HORIZONTAL The locations of F measurements from the 5100 through the

STRESS DIRECTION 5700 levels are plotted on a map of the 5300 level by soft and

The most common stress field characteristic obtained in this Breakouts in softer subunits are uniformly oriented and show a

study was the orientation of Fh1. The best information on northwest orientation of F . Breakouts and stress measure- ments

maximum and minimum horizontal principal stress (F and F , in the harder subunits also indicate a northwest orienta- tion of h1 h2

respectively) magnitudes and orientation was provided by F , except for breakouts at the 5400 level of the service raise and

overcore measurements (table 3). These results, however, do not the LF 5300 measurement. Both sites are adjacent to the

provide a consistent picture. While the orientations of the LF 38/Offset Fault. These stress rotations must be local as they are

4250 and Star 7300 measurements are similar, a major rotation in not reflected by most of the stress evidence. They imply that

orientation of F was measured at the LF 5300 site. The spatial localized left-lateral shear stresses exist on the adjacent 38/Offset h1

extent of this rotation can be examined using stress directions Fault, which has an apparent left-lateral offset. The Alimak raise

indicated by borehole breakouts, summarized in tables 4 and 5. breakouts in sections 2 and 3 suggest a similar mechanism.

The frequency of these various orientations were plotted in Localized locking up of the fault would create the observed

15E segments on a rose diagram (figure 13). Orientations of Fh1 concentrations of shear stress. Locking up could occur where

are clearly distributed around a northwest-centered arc. Two of hard subunits come into contact across the fault, which is the case

the overcore measurements lie in this central arc as well, with the at both sites of rotated stress. The degree of rotation is greatest at

LF 5300 measurement showing the only orientation outside the the LF 5300 site, where the area of contact is smallest and the

northwest quadrant. shear stress would be expected to be most

h1

hard lithologic subunits in figures 14 and 15, respectively.

h1

h1

Table 3.—Fh1 and 

 Fh2 calculated from overcore measurements

Site Fh1 Fh2

MPa psi Bearing MPa psi Bearing

LF 4250 level . . . . . . . . . . . . . . 89 12,900 N 38E W 49 7,100 N 52E E 

LF 5300 level . . . . . . . . . . . . . . 114 16,500 S 80E W 73 10,600 N 10E W

Star 7300 level . . . . . . . . . . . . . 53 7,700 N 39E W 35 5,100 N 51E E 

Table 4.—General indications of Fh1 orientation

Location Source Orientation of Fh1 Reference

Coeur d'Alene Mining District ....... Recent tectonic activity ....... Northwest ............ Hobbs and others (1965).

Star 5900 to 6300 levels ........... Rock fractures, joints ........ West-northwest ....... Gresseth (1964).

Star 6500 and 6700 levels .......... Geologic fabrics ............. Northwest ............ Gresseth and Reid (1968).

LF 4250 level .................... Rock fractures, joints . . . . . . . . N 30E-40E W ......... Allen (1979).

Table 5.—Specific indicators of Fh1 orientation

Location and level Bearing Notes

Alimak raise:

 3980 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N 40E W

 4020 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N 65E W

 4100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N 75E W

Silver shaft loading pocket:

 4900 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N 45E W Subunit E, hard.

 5100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N 45E W Subunit G, hard.

 5500 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N 45E W Subunit G, hard.

Ore passes:

 5100-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . N 55E W

 5100-107 . . . . . . . . . . . . . . . . . . . . . . . . . . N 45E W

 5160-107 . . . . . . . . . . . . . . . . . . . . . . . . . . N 40E W

 5210-107 . . . . . . . . . . . . . . . . . . . . . . . . . . N 35E W

 5300-107 . . . . . . . . . . . . . . . . . . . . . . . . . . N 55E W

Service raise, 5480 . . . . . . . . . . . . . . . . . . . . N 35E-45E W

Blastholes, service raise, 5400 . . . . . . . . . . . N 74E W Diameter = 14 cm (5.5 in).

Grouse vein raise, Star Mine . . . . . . . . . . . . N 30E-40E W
7

concentrated. Physically, the strong, clay-poor, hard subunits sites. The F at LF 5300, on the other hand, cannot be

could be expected to produce a higher resistance to slip along the reconciled by topographic influence. The high F at this location

fault than areas with relatively clay-rich wall rocks. Geologic evidently reflects some local perturbation in the distribution of

information in the vicinity of the Alimak raise is insufficient to stress. Thus, overburden loading can account for the F measured

investigate whether this mechanism might explain the rotations of at two of the three sites.

Fh1 in sections 2 and 3. This possibility requires further study, but The high F measured at the LF 5300 measurement site may

for the purposes of this report, it is sufficient to recognize that be related to the stress rotations near the 38/Offset Fault discussed

observed horizontal stress rotations are a small-scale phenomenon earlier. On the other hand, a striking contrast in F was apparent

relative to the scale of the mine and should be disregarded in between hard and soft subunits at the LF 4250 measurement site

developing estimates of average mine-wide stress conditions. (figure 17), although the overall measurement was dominated by

DISTRIBUTION OF STRESS COMPONENT subunit. The absence of elevated F in the hard quartzite at the

MAGNITUDES Star 7300 measurement site departs from this pattern, but may

Evaluation of the variability of stress magnitudes must, by measurements indicate that steeply dipping hard subunits in the

economic necessity, rely on relatively few overcore lower Revett carry at least 50 pct more F than neighboring soft

measurements. Resolving overcore stress estimates into vertical subunits. This effect appears to be widespread and is likely to be

and map direction coordinates (table 2) provides a way to significant on a mine-wide scale.

compare measurements with average overburden stress. While Variations in other stress components, particularly the

the estimates of vertical stress (Fv) from the LF 4250 and Star magnitude of horizontal stress parallel to bedding, are more

7300 measurements approximate the pressure expected from problematic. The LF 4250-level measurement, for instance,

overburden loading [approximately 35 and 60 MPa (5,000 and while obtained using many redundant vertical overcore strain

8,600 psi), respectively] (Beus and Chan, 1980), the vertical measurements, does not include a measurement of horizontal

stress measured at the LF 5300 measurement site is clearly greater overcore strain in the hard subunit parallel to bedding.

than expected [approximately 43 MPa (6,300 psi)]. Also, while Furthermore, the concentration of shear stress required to generate

this is the deepest site in terms of absolute elevation, the location the principal stress direction rotation noted at the LF 5300 site

of the Star Mine within mountains northwest of the Lucky Friday clouds examination of larger scale variations.

Mine (figure 16) makes the Star Mine deepest in terms of However, normal stress components oriented parallel and

overburden. perpendicular to the 38/Offset Fault should not be greatly affected

At these depths, the effects of local topography are spread over by this stress concentration and should provide some indication

a large area. Thus, the average elevation of the surface in the of whether other horizontal stress variations are present.

vicinity of the mine, not just depth below the immediate surface, Comparison of these stress components from the three overcore

becomes important. For this reason, the overburden loading sites (table 6) shows remarkable agreement among the Lucky

calculation overestimates Fv for the Star Mine and underestimates Friday measurements of the horizontal stress component that lies

Fv for the Lucky Friday Mine. A numerical model of overburden parallel to the 38/Offset Fault. Normal and traction stresses on the

loading for a north-south vertical section was constructed to fault are dramatically different, however, and show a different

account for this influence. The results (table 2) closed about half sense of shear traction. Moreover, there is a definite concentration

the gap between measured and calculated Fv for the Star 7300 and of horizontal stress oriented normal to the fault, suggesting

L F 4250 measurement concentrated horizontal stress at least across hard subunit contacts.

v

v

v

v

v

readings from doorstopper cells installed in the relatively softer

v

reflect any number of other factors. The Lucky Friday overcore

v

Shear 

Table 6.—Components of stress measurements with respect to orientation of 38/Offset Fault 1

Measurement Subunit Parallel Perpendicular Shear2

site MPa psi MPa psi MPa psi 

LF 5300 level ........... Vitreous quartzite (hard) ................. 91.2 13,230 95.6 13,870 -21.0 -3,040

LF 4250 level ........... Mainly sericitic quartzite (soft) ............ 85.5 12,400 52.0 7,540 9.7 1,400

Star 7300 level .......... Vitreous quartzite (hard) ................. 52.3 7,580 36.0 5,220 4.3 630

t is approximately N 53E W. Orientation of 38/Offset Faul 1

Shear component is positive right-lateral. 2
8

Table 7.—Stress field estimate, Lucky Friday Mine

Stress Magnitude1 Bearing Plunge

component kPa/m psi/ft

F ................ ns 57 2.5

F ................ ew 49 2.2

F ................ v 35 1.6

J .............. ns/ew -15 -0.6

J ............... ns/v 2 0.1

J ............... ew/v -10 -0.4

F ................ 1 70 3.1 N 40E W 13E

F ................ 2 42 1.8 S 41E W 33E

F ................ 3 29 1.3 N 68E E 54E

Magnitude is a functio n of overburden depth. 1

NOTE.—Empty cells in columns intentionally left blank.

traction at the 5300 level is at a maximum at this orientation. orientation of F provided by raise bore breakouts. The localized

Shear traction components at the 4250 level in the Lucky Friday nature of the stress field at the LF 5300 measurement site and the

Mine and the 7300 level in the Star Mine peak for a plane generally reduced magnitudes at the Star 7300 measurement site

oriented N 80E W. The peak shear stress for the LF 4250 suggest that the best overall estimate will rely heavily on the LF

measurement is comparable to the LF 5300 measurement, but the 4250 measurement as representative of the mine stress field.

peak stress for the Star 7300 measurement is less than half the Linear variation of stress with depth, with an unstressed surface

Lucky Friday values. The Star measurement follows the pattern and no lateral variations in stress, will be assumed in line with

set by the LF 4250 measurement, but at a greatly reduced previous studies. The stress gradients and principal stress

magnitude all around. orientations that result from this procedure are presented in table

Thus, widespread variations can be expected in F magnitudes, 7. v

depending on lithology. Large, but spatially more limited,

variations in normal and shear stress components relative to the

38/Offset Fault can be expected in the immediate vicinity of the

faults. However, the magnitude of the horizontal stress

component parallel to the 38/Offset Fault is remarkably stable,

although all stress magnitudes are larger than those measured at

the adjacent Star Mine.

STRESS ESTIMATE

After eliminating stress measurements and indicators that

reflect localized stress variations, estimates of the overall stress

field at the Lucky Friday Mine must be accomplished primarily

with the same information available to previous studies, although

overcore stress estimates have been refined. The exception is the

widespread confirmation of the northwest

h1

DISCUSSION AND CONCLUSIONS

The availability of a new overcore stress measurement and state because they had already been influenced by miningsuccessful reexamination of two earlier measurements from the

same area promise to refine understanding of the in situ stress

field in the vicinity of the Lucky Friday Mine. Although a

northwest-trending Fh1 and overburden Fv were generally

indicated, and an average stress field proposed, there were

significant local deviations as well. There seems to be a limited

set of possibilities that would explain these deviations.

First, one or two estimates may be of poor quality or simply

wrong. Errors in measurement, data screening, or data reduction

could result in erratic estimates. However, the data screening and

reduction procedures described in earlier parts of this series

identified and removed a number of errors. The thorough review

of field notes and reported procedures, as well as the careful

screening of strain readings and an update of stress calculations,

suggest that the stress estimates developed in this series of RI's are

accurate. Also the general consistency of breakout results from a

number of raise bore breakouts across the Lucky Friday Mine

provides confirmation of the orientation of F . h1

Second, it is possible that the stress field estimates were

correct, but that they did not represent the premining stress

induced stresses at the sites. Such effects at the two sites in the

Lucky Friday Mine were calculated, assuming an elastic rock

mass, and found to be negligible. There is a possibility that some

inelastic mechanism may be able to increase the influence of

mining on these sites to considerable levels. While impossible to

disprove, it seems unlikely that the strong, localized variations in

stress observed could be generated by mining.

Third, it is possible that all measurements are correct and that

the premining in situ stress field in the vicinity of the Lucky

Friday Mine includes significant local variations. This idea is not

entirely new; for example, stress variations throughout the Coeur

d'Alene Mining District have been suggested on the basis of

differences observed in mining-induced seismicity throughout the

district (Sprenke and others, 1991). Furthermore, this complexity

would seem to exist at a number of scales, from individual beds

to subunits to entire mines, prior to excavation. Finally, this

complexity appears to be dependent on geologic structure and

lithology.

This conclusion has important implications for research on

rock-burst activity at mines throughout the Coeur d'Alene Mining

District. This is especially true west of the axis of the 
9

Hook anticline in the Lucky Friday Mine, where concentrated units, in particular, should be evident in records of miningrock-burst activity was noted in development openings, including induced seismicity. Furthermore, numerical models need to be

the crosscut used for the LF 5300 measurement. If the extent and developed to explore how stress variations may be expected to

severity of this and other natural concentrations of stress can be evolve with further mining in the Lucky Friday Mine and

estimated, the relative severity of rock-burst hazards may be provide a guide to variations in stresses likely to be encountered

anticipated, especially in development openings unaffected by by mining anywhere in the Revett Formation. Work on these

mining-induced stress. topics is continuing as part of ongoing USBM investigations of

Additional research is needed to develop this capability. methods to identify and reduce rock-burst hazards. Completion

While hypotheses for concentration of Fv and rotation of of this research will provide mine engineers with a tool to

horizontal principal stresses have been advanced, further research anticipate and reduce rock-burst hazards.

is needed to confirm and further define these mechanisms. The

widespread variations in Fv between sub

ACKNOWLEDGMENTS

Charles Fairhurst, professor, Department of Civil Engineering, WA, provided invaluable support and guidance during this study.

University of Minnesota, Minneapolis, MN; Mark Board, The assistance provided by Brian White, geologist, Spokane

manager of mining engineering, Itasca Consulting Group, Research Center, with geologic mapping and development of

Minneapolis, MN; and Mel Poad, group supervisor, Spokane subunit classifications for the Lucky Friday Mine is gratefully

R e s e a r c h Center, USBM, Spokane, acknowledged.

REFERENCES

Allen, M. A. Determining the In-Situ Stress Field on the 4250 Level in the Validation of a Stope-Scale Finite-Element Model. USBM RI 9434, 1992,

Lucky Friday Mine: Using the CSIR Biaxial Strain Gage and Structural 16 pp.

Geologic Mapping. M.S. Thesis, Univ. ID, Moscow, ID, 1979, 73 pp. Sprenke, K. F., M. C. Stickney, D. A. Dodge, and W. R. Hammond.

Beus, M. J., and S. S. M. Chan. Shaft Design in the Coeur d'Alene Mining Seismicity and Tectonic Stress in the Coeur d'Alene Mining District. Bull.

District, Idaho—Results of In Situ Stress and Physical Property Measurements. Seismol. Soc. Am., v. 81, No. 4, Aug. 1991, pp. 1145-1156.

USBM RI 8435, 1980, 39 pp. Whyatt, J. K. Geomechanics of the Caladay Shaft. M.S. Thesis, Univ. ID,

Blake, W., and D. J. Cuvelier. Rock Support Requirements in a Rockburst Moscow, ID, 1986, 195 pp.

Prone Environment: Hecla Mining Company's Lucky Friday Mine. Paper in Whyatt, J. K., and M. J. Beus. Field Measurement of Rock Displacement

Rock Support in Mining and Underground Construction: Proceedings of the During Sinking of a Deep Rectangular Shaft. USBM RI 9108, 1987, 12 pp.

International Symposium on Rock Support, ed. by P. K. Kaiser and D. R. . In Situ Stress at the Lucky Friday Mine (In Four Parts): 1. Reanalysis

McCreath (Sudbury, ON, June 16-19, 1992). Balkema, 1992, pp. 665-674. of Overcore Measurements From 4250 Level. USBM RI 9532, 1995, 26 pp.

Board, M. P., and M. J. Beus. In Situ Measurements and Preliminary Whyatt, J. K., M. J. Beus, and M. K. Larson. In Situ Stress at the Lucky

Design Analysis for Deep Mine Shafts in Highly Stressed Rock. USBM RI Friday Mine (In Four Parts): 3. Reanalysis of Overcore Measurements From the

9231, 1989, 46 pp. Star Mine. USBM RI 9567, 1995a, 30 pp.

Gresseth, E. W. Determination of Principal Stress Directions Through an Whyatt, J. K., F. M. Jenkins, and M. K. Larson. In Situ Stress at the Lucky

Analysis of Rock Joint and Fracture Orientations, Star Mine, Burke, Idaho. Friday Mine (In Four Parts): 2. Analysis of Overcore Measurement From 5300

USBM RI 6413, 1964, 43 pp. Level. USBM RI 9560, 1995b, 34 pp.

Gresseth, E. W., and R. R. Reid. A Petrofabric Study of Tectonic and Whyatt, J. K., T. J. Williams, and W. G. Pariseau. Trial Underhand

Mining-Induced Deformations in a Deep Mine. USBM RI 7173, 1968, 64 pp. Longwall Stope Instrumentation and Model Calibration at the Lucky Friday

Harrison, J. E., A. B. Griggs, and J. D. Wells. Geologic Structure Maps of Mine, Mullan, Idaho, USA. Paper in Rock Mechanics: Proceedings of the 33rd

the Wallace 1E × 2E Quadrangle, Montana and Idaho. U.S. Geol. Surv. Misc. Symposium, ed. by J. R. Tillerson and W. R. Wawersik (Santa Fe, NM, June 3-

Invest. Ser. Map I-1509-A, 1986. 5, 1992). Balkema, 1992, pp. 511-519.

Hobbs, S. W., A. B. Griggs, R. E. Wallace, and A. B. Campbell. Geology Zoback, M. L., and M. D. Zoback. State of Stress in the Coterminous

of the Coeur d'Alene District, Shoshone County, Idaho. U.S. Geol. Surv. Prof. United States. J. Geophys. Res., v. 85, 1980, pp. 6113-6156.

Pap. 478, 1965, 139 pp. . Tectonic Stress Field in the Continental U.S. Paper in Geophysical

National Research Council. Stability, Failure, and Measurement of Framework of the Continental United States, ed. by L. Pahiser and W. Mooney.

Boreholes and Other Circular Openings. Natl. Acad. Press, Washington, DC, Geol. Soc. Am. Mem. 172, 1989, pp. 523-539.

1993, 92 pp.

Pariseau, W. G., J. K. Whyatt, and T. J. McMahon. Rock Mechanics

Investigations at Lucky Friday Mine (In Three Parts): 3. Calibration and
10

APPENDIX.—ANGLE BETWEEN LONG AXIS OF ELLIPSE AND BEDDING STRIKE

Location and level Angle

Alimak raise:

 3980 ......................................................... 0E 

 4020 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40E 

 4100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20E 

Silver shaft loading pocket: 

 4900 ......................................................... 0E 

 5100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45E 

 5500 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45E 

Ore passes:

 5100-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45E 

 5100-107 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45E 

 5160-107 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45E 

 5210-107 .................................................... 0E 

 5300-107 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55E 

Service raise, 5480 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35E-45E 

Blastholes, service raise, 5400 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74E 

Grouse vein raise, Star Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80E-90E 
11

Figure 1

Location of Lucky Friday Mine in Coeur d’Alene Mining District of northern Idaho.
12

Figure 2

Figure 3

 Major geologic features of Coeur d’Alene Mining District.

 Major structural features of 5300 level, Lucky Friday Mine.
13

Figure 4
14

Lithologic subunits in lower Revett Formation. A, Simplified geologic column; B, 5300 level, plan view. Dotted line indicates axial

plane of Hook anticline.
15

Figure 5

 

Alimak raise. A, Location of Alimak raise on 4250 level; B, vertical section showing mapped

breakouts on sections 1,2 and 3. Breakouts were interpreted to indicate orientation of F . h1
16

Figure 6

Silver shaft and system of circular ore passes and service raises developed to support longwall mining of vein.
17

Figure 7

Breakouts observed in Silver shaft ore passes on 5100 level. A,

Plan view. Circle (dotted line) indicates original shape of ore

pass, while ellipse (solid line) indicates final shape after

breakouts occurred. B, Breakout as observed looking down

north ore pass.
18

Figure 8

 Subunit lithology of Silver shaft ore passes (4900 to 5300 levels).
19

Figure 9

106 and 107 ore passes. A, Subunit lithology, breakout indicators of F orientation in 107 ore pass, and mining progress on nearby h1

vein; B, geology and breakout in plan view, 5100 level; C, 5100-107 ore pass looking up 5160 access. Vein was unmined during

development of 107, but some mining had been conducted before completion of 106.
20

Figure 10

97 ore pass. A, Subunit lithology and breakout indicators of F orientation in h1

97 ore pass; B, geology and breakout in plan view, 5300 level.
21

Figure 11

Subunit lithology and breakout indicators of F orientation in service raise. h1
22

Figure 12

Raise bore breakouts, 7300 level, Star Mine.
23

Figure 13

Rose diagram showing frequency of F orientation as indicated by overcore measurements and breakouts plotted in 15E intervals. h1
24

Figure 14

Location and subunit lithology of breakout indicators of F orientation in vicinity of LF 5300-level overcore measurements site h1

in soft subunits.
25

Figure 15

Location and subunit lithology of overcore and breakout indicators of F orientation in vicinity of LF 5300-level overcore h1

measurement site in hard subunits.
26

Figure 16

Topography over north-south cross section through Lucky Froday and Star Mines.
27

Figure 17

Relationship among stratigraphy, rock elastic modulus, and estimated vertical in situ stress component at LF 4250 measurement site.

Numbers indicate doorstopper cells. Both doorstopper cells and elastic modulus (heavy crosses) are plotted as to relative stratigraphic

position. Note that elastic modulus is read as gigapascals, while F is read as megapascals. A, Variations in vertical in situ stress v

component by stratigraphic location; B, plan view of measurement site.