coppen wumuunou .IN Amwme ssmmsms
05 THE MARQUETTE RANGE mavens COUNTY, meme»:

“acids. {or the Domed of M. S‘
— MICHEGAN STATE UNWERSITY
, Robert C Reed ' ‘

, 1965

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ABSTRACT

COPPER MINERALIZATION IN ANIMIKIE
SEDIMENTS OF THE MARQUETTE RANGE
MARQUETTE COUNTY, MICHIGAN

by Robert C. Reed

Copper mineralization in four areas within Animikie
sediments of the eastern Marquette syncline has been
studied and described in detail. The c0pper mineralization
consists of chalcocite, chalcopyrite, bornite, covellite,
and native copper. Specular hematite, red hematite, pyrite,
and limonite are abundant. Associated silicification is
wideSpread in the Kona dolomite. Other minerals include
sericite and chlorite.

The mineralized areas are practically ”clean” of
most important trace elements. Only copper, titanium,
and manganese were found. Trace c0pper is wideSpread
throughout the Kona dolomite.

The metallic and gangue minerals present in the
eastern Marquette syncline are very simular to those
within and surrounding Mount Bohemia, a syenodiorite intru—
sive in the Keweenaw Peninsula of Michigan, and of Keweenawan

age.

COPPER MINERALIZATION IN ANIMIKIE
SEDIMENTS OF THE MARQUETTE RANGE

MARQUETTE COUNTY, MICHIGAN

By

Robert C. Reed

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Geology

1965

ACKNOWLEDGMENTS

The writer wishes to express his appreciation to

the many persons who aided and supported the present

study:

Dr. Harold Stonehouse for assistance and guidance

in the use of the spectrograph and interpretation of

Spectrographic data.

Dr. Justin Zinn and Dr. James Trow for
guidance.

The North Range Mining Company for use
data and drill core.

Mr. David Bennett for assisting in the
test pits and drill core.

Mr. James Tusa for assisting in taking

graphs and use of equipment.

helpful

of drilling

sampling of

photomicro-

Mr. John Eyerlay for photographing polished Spec—

ii

TABLE OF CONTENTS

ACKNOWLEDGMENTS
LIST OF ILLUSTRATIONS
Chapter

I. INTRODUCTION.

Location

Field and Labratory Procedures

History.
General Geol

II. 'MINERALOGICAL
Description
Description
Description
Description

III. GEOCHEMISTRY.

IV. CONCLUSIONS

REFERENCES.

0 O 0 0 O O 0

0g
AND ROCK DESCRIPTION

of Area
of Area
of Area
of Area

UOUJZ>

iii

9

Page
ii

iv

NO \0 JENNI-J i——'

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.-

UCLA)
\OLJU

AS
50

Figure

\fl-IE'LU

\OCD\10\

IO.

11.

12.

13.

14.

16.

17.

LIST OF ILLUSTRATIONS

 

Geologic and location map

Geologic column

Photograph of polished Specimen

Photomicrograph of

Quartz—chalcocite vein.

Photograph of polished Specimen showing

foliation.
Photomicrograph of
Photomicrograph of
Photomicrograph of

Photomicrograph of
initial stage

Photomicrograph of
advanced stage

Photomicrograph of
chlorite

Photomicrograph of
light .

Photomicrograph of
nicols.

Photomicrograph of
light . . . .

Photomicrograph of
nicols.

Photomicrograph of
ordinary light

Photomicrograph of
nicols. . . .

colloform chalcocite
colloform chalcocite
etched chalcocite 0

chalcocite replacing pyrite,

0

chalcocite replacing pyrite,
chalcocite, pyrite and

chalcocite in vein, ordinary

6 9 O O

chalcocite in vein, crossed

O

vein of chalcocite, ordinary

3 9 O 0 C

vein of chalcocite, crossed
colloform chalcocite,

colloform chalcocite, crossed

iv

Page

17

19

R)
[U

Figure
18.

19.

21.

22.

35.

36.
37.
38.

39.

Photomicrograph

Photomicrograph
light

Photomicrograph
light .

Photomicrograph
light

Photomicrograph
nicols . .

Photomicrograph
Photomicrograph
Photomicrograph
Photomicrograph
Photomicrograph
Photomicrograph
Photomicrograph
Photomicrograph
Photomicrograph
Photomicrograph
Photomicrograph

Photomicrograph

of foliated chalcocite . .

reflected

O O O 0

of native copper,

reflected

of native copper,

of native copper, ordinary

O O O 0 O O O O O

of native copper, crossed

O O 0 Cl 0 O O O

of bornite and chalcopyrite
of chalcopyrite

of chalcopyrite . . . .
of chalcopyrite

of chalcopyrite

of chalcopyrite . . .

of chalcopyrite in vein.
of chalcopyrite in vein.
vein.

of chalcopyrite in

of chalcopyrite in rock.

3

of epidote replacing dolomite.

of bornite, covellite and

Specular hematite . . . . . . . .

Photomicrograph

of bornite, chalcocite and

Specular hematite . . . . . . .

Photomicrograph
Photomicrograph
Photomicrograph

Photomicrograph

of chalcocite and covellite
of chalcopyrite

of bornite

of bornite and chalcopyrite

V

Page
23

LA)
U7

L0
\‘7

Figure
A0.
A1.

42.
A3.
44.

Photomicrograph of chalcopyrite and bornite.

Photomicrograph of Specular hematite, quartz,
bornite and chalcopyrite

Graph of copper content of drill hole 3
Graph of copper content of purple slates.

Generalized geologic map of Keweenawan basin

vi

Page
A2

1:3
1+7

4‘9

CHAPTER I

INTRODUCTION

 

The understanding of the environment and habit of
ore deposition depends largely on the accumulation of
field and labratory data from Known ore. Such descriptive
characteristics as ore and gangue mineralogy, types of
host and source rock, metamorphic grade, and wall rock
alteration serve as aids in the exploration for new
deposits.

Copper mineralization in Animikie sediments in
Michigan has received little attention and has never been
described in detail. It is the purpose of this investiga-
tion to add to the knowledge of copper mineralization, its
environment, and hopefully, information which may lead to

successful exploration.

Location
The four areas described are illustrated on Figure 1.
Area A is in the NEZNWK section 1, T.A7 N., R.25 W. Area B
is in the Nw%8E% section 2, T.A7 N., R.25 w. Area c is
located in the SW%NE%, section 32, T. A8 N., R.25 w. Area
D is in section 10, T.A7 N., R.27 w. at the 10th. level of

1

2

the Cliffs Shaft iron mine. Areas A, B, and C are within
the Kona dolomite series of rocks and Area D mineralization

cuts the Negaunee iron formation.

Field and Laboratorngrocedures

 

Field procedure consisted of collecting Specimens
from test pits and mine, and from drill core in Area A.
Specimens were polished and thin sections were made for
metallographic and petrographic description of minerals.
Samples from test pits and drill core were analyzed
Spectrographically to determine trace elements, and copper

content.

History

The general geology of the area was described by Van
Hise and Bayley (1895, 1897) and Van Rise and Leith (1911),
but copper mineralization was not indicated. The area has
recently been mapped in detail by Gair et_al. (1963).

The location of exploration Shafts of Areas A and
B are illustrated in the Michigan Geological Survey field
notebook 78, in 1888, by A. E. Seaman. He noted that a
Shaft in Area B was being sunk at that time. In old rock
descriptions of the Michigan Geological Survey, M. E.
Wadsworth described "slate impregnated with chalcocite"
in Area A, and "dolomite schist impregnated with sulphurete
of copper" in Area B. The date of these descriptions
was sometime between 1888 and 1892, when Wadsworth was

State Geologist.

The history of copper exploration was compiled by
Mr. Kenneth Boyer of the Marquette County Historical
Society (Boyer 1961). Mr. Boyer reviewed back issues of
the Marquette Mining Journal which described the "big
copper excitement of 1896 to 1898":

The lode has varying widths in this locality of
from two to 65 feet and in some cases seems to
have been split by volcanic action. According to
Mr. Pings, assays on the Case rock have shown a
run of copper as high as 7%}per cent, while the
mill test, which can be depended upon absolutely,
shows 3%Qper cent. The rock is also both gold and
Silver bearing. The former has Shown as high as $16
to the ton and an expert says when the shaft gets
down to 200 feet, the ore will run steadily from
$8 to $12 a ton. It is gray ore, the best in the
world, with no sulphur content and smelting to
separate the copper, gold and silver will be much
easier. Twenty tons of this ore from the Case prop-
erty will be loaded on cars and sent to the furnaces
of the Aurora and Chicago Smelting Company. The
shaft there is now sunk to a depth of 40 feet on a
vein 10 feet wide and though work is now temporarily
suSpended, it will be resumed in the spring when
the shaft will be sunk to at least 100 feet. It
is mineralized from the hanging wall to the foot
wall. The tests so far made Shown it to be con-
siderably richer than the famous Calumet & Hecla.
In Sinking the shaft about 400 tons of rock have been
taken out, none of it waste and all of it fit to
go to the smelter without the intermediate service
of the stamp mill. About a half mile west where the
Wilkinson mine is located, two shafts are being
sunk, one on the Harlow estate property and the
other on lands of the Iron Cliffs Company. The first
has reached about AO feet and the latter about 25,
all of the ore being of the same quality as in the
Case and at a suitable depth Should give the same
generous return. This was much better than the
prospectors had hoped for. George Spencer had taken
over supervision of the work for John W. Ludwig
and associates, of Chicago and 8 to 10 men have
been employed at these two pits. A close study of
the mountain ranges south of MarQuette reveals a
number of veins of copper—bearing rock, but these
Just mentioned are the only ones to receive any

Special attention. However, Mr. Pings says he knows
of other places in areas where indications are just
as good.

The Case property mentioned above is that of Area A
and the Wilkinson, Area B. Evidently there was no further
work on these properties until 1961, when the North Range
Mining Company drilled 5 holes, from late 1961 to early
1963, in Area A.

The history of Area C is obscure. It was located by
J. E. Gair while mapping the bedrock geology of the
Marquette quadrangle. The exploration consist of one large
test pit which possibly was excavated at the same time
that copper was being explored to the southeast. No
written record of this exploration has been found.

Normal development of the Cliffs Shaft iron mine
in the city of Ishpeming exposed iron and copper sulphides
of Area D. The brilliant peacock color of the dominant

mineral, bornite, attracted the miners who have been

removing samples for a number of years.

General Geology

 

AS cited above, the general geology has been des—
cribed by Van Hise and Bayley (1895, 1897), and Van Hise,
and Leith (1911). Currently the area has been mapped in
detail by Gair et_al. (1963). The geologic mapping of
the area is not part of this investigation but the geology

is generally described.

The Marquette range is a tightly folded synclinal
belt of middle Precambrian sediments and basic intrusives
enclosed in a complex of lower Precambrian rocks. The belt
trends approximately east-west for about AO miles. It
plunges gently to the west so that the lower formations
are exposed at the east end.

The surface geology and geologic column of the eastern
part of the Marquette range are illustrated in figures
1 and 2. The copper mineralization of Areas A, B, and C
are found in the Kona dolomite, the second lowest strati—
graphic unit of middle Precambrian rocks. The Kona is ex-
posed at the eastern nose of the syncline south of the
city of Marquette, and trends westward on the north and
south limbs. The north limb is exposed as far as the city
of Negaunee and the south limb to Goose Lake. (Figure l.)
The lithology of the Kona is described by Gair et al.
(1963) as:

Mainly tan, salmon, pinkish—-or pale-mgray fine
and medium grained massive dolomite or thinly lam—
inated chert and dolomite. Dolomite layers commonly
contain scattered detrital quartz. Lower part of
formation contains much maroon, gray, and greenish
sericitic Slate. Thin layers and minor members
consist of reddish quartzite and an orange and
brown laminated Siltite. Locally dolomite and Slate
are Silicified.

The Kona has a maximum thickness of 1000 to 1200
feet.

The eastern limit of the Negaunee iron formation is

in the city of Negaunee. Copper mineralization of Area D,

in the Cliffs Shaft iron mine, cuts the hard ore horizon

 

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LEGEND

 

Basic intrusive
FIGURE I

 

Goodrich
PRECAMBRIAN BEDROCK GEOLOGY

Negaunee or THE

 

Siamo

 

EASTERN MARGUETTE RANGE
(FROM GAIRI‘I963 8: BOYUMII964)

ibik n
Scale I to l mile

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PRLCAMLI

 

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at the top of the Negaunee iron formation, immediately
below the Goodrich quartzite. Area D is approximately

13 miles west of area B.

Upper

Precambrian

Keweenawan diabase

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

Middle

Precambrian

Serpentinized peridotite
Syenite

Hornblende lamprophyre
Felsic porphyry
Metapyroxenite
Metadiabase and metagabbro
xxxxxxxxxxxxxxxxxxxxxx
Goodrich quartzite
Negaunee iron formation
Siamo slate

Ajibik quartzite

Wewe Slate

Kona dolomite

Mesnard quartzite
xxxxxxxxxxxxxxxxxxxxxx

Enchantment Lake

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

Lower Granite gneiss
Precambrian Mono schist
Figure 2.——Geologic column of the eastern Marquette range,

Marquette County, Michigan.
(1963).

Modified from Gair et a1.

Chapter II

MINERALOGICAL AND ROCK DESCRIPTIONS

 

Description of Area A

 

Copper mineralization in Area A is found at the
west end of a small enclosed syncline of Kona dolomite.
(Figure l.) The relief is great, almost 300 feet above
Lake Superior, 3500 feet to the east. Several shallow
Shafts and test pits attest the exploratory work done
more than 65 years ago. The most successful shaft was
sunk to a depth of 40 feet in a highly sheared slate
overlain by red quartzite. At the surface the base
of the quartzite, which is exposed, strikes N. 70 degrees
W. and dips 55 degree N.E. The Shaft is in an area in
which malachite, the green carbonate of copper, is clearly
visible and probably guided the exploration. Other Shafts
and pits probed the slate horizon below the quartzite,
but apparently with negligible results.

The rock on the dumps of the main exploration shaft
consists of a tan to reddish—tan, highly sheared and
folliated siliceous slate. Despite the fact the rock is
sheared, most of it is hard, dense, and compact, difficult
to break with the hammer, and cut with the diamond saw.
Mineralization is abundant, chalcocite and pyrite are

9

10

clearly visible, chalcocite being much more prevalent than
pyrite. The green coating of malachite, from alteration
of chalcocite, is noticeable on massive rock and abundant
on the more highly sheared friable slate.

Under the binocular microscope, the rock appears
highly siliceous. It is mostly very fine grained but a
few bands and pods of clastics are observed. Mineralization
occurs in veins, fractures, irregular masses and along
foliation planes. It consists of chalcocite, pyrite and
quartz with chalcocite replacing pyrite. Pyrite, scattered
throughout the rock, where unreplaced, is euhedral to
subhedral in crystal habit. Some Specimens are highly
fractured and Show both granular vein and colloform
chalcocite. Colloform chalcocite appears to occur at the
intersection of two or more fractures.

In polished section, the mineralization is observed
to occur in crosscutting veins (Figures 3 and A) and in ir-
regular layers parallel to bedding and foliation (Figure 5.)
It is also scattered throughout the rock but to a lesser
degree. Many Specimens exhibit a colloform texture.
(Figures 6 and 7.) The chalcocite reacts normally to the
chemical etch determination described by Short (19AO),
and conforms to his description of hypogene origin:

HNO effervesces vigorously; mineral stains
blue; with most varieties brings out parallel
etch structure; with very fine grained super-
gene chalcocite, however, will not show etch

cleavage; with the fine—grained sooty chalcocite
brings out grain boundaries only.

Figure 3.-—Photograph of polished Specimen cut by quartz
chalcocite vein with scattered pyrite and chalcocite in
host rock.

Figure A.-—Photomicrograph of quartz chalcocite vein of
Figure 3. Chalcocite is white and quartz dark gray.
Reflected light, 57 X, 11 micron grid.

11

 

l2

 

Figure 5.-~Photograph of polished Specimen exhibiting
mineralization along foliation planes.

Figure 6.——Photomicrograph of colloform texture of
chalcocite. Reflected light. 57 X, 11 micron
grid.

Figure 7.--Photomicrograph of colloform texture of
chalcocite. Reflected light, 57 X, 11 micron
grid. ‘

13

. (\J'
H

1.7mm):

 

IA

Colloform textured chalcocite etched with HNO3 is
illustrated in Figure 8. This reaction occurred with
every mineral texture. It is similar to that shown by
Butler and Burbank (1929, plate 68, Figure F).

Chalcocite replaces pyrite in all stages from initial
replacement (Figure 9) to advanced (Figure 10), although
most chalcocite does not Show replacement of pyrite.
Chlorite, recognized in thin section, may occassionly
be observed in reflected light. (Figure 11.)

In thin section, the surface rocks of Area A consist
of quartz sericite Slate, foliated quartz sericite slate,
quartz carbonate sericite slate and sericitic quartzite.

It should be noted that though this unit of rock is part

of the Kona dolomite, carbonate is rare. The optical
properties of the carbonates are difficult to differentiate
through the petrographic microscope (Rogers and Kerr,

1942). Specimens of carbonate from the Kona of the Marquette
and Sands quadrangles, submitted for X—ray examination,

Show it to be dolomite (Gair, J. E., personal communication).
Therefore, future references to carbonate minerals in

this paper will be called dolomite.

The Sericitic quartzite consist of alternating layers
of medium and fine grained quartz, with layers of fine
grained chlorite as foliated sheaves parallel to the
banding. Fine grained sericite occurs in quartz interstices

and penetrates grain boundaries. Two patches of chlorite

~ ‘A _,
“(it 1.,

'\ -._’

 

Figure 8.—-Photomicrograph of colloform textured chalcocite,
etched with HNO , showing parallel etch structure.
Reflected light, 107 X, 11.5 micron grid.

Figure 9.--Photomicrograph Showing initial replacement of
pyrite by chalcocite. Reflected light, 57 X, 11 micron
grid.

Figure 10.-—Photomicrograph showing adV81C€d replacemei? of
pyrite by chalcocite. Reflected light, 82 X, 11 micron
grid.

16

 

l7

 

Figure ll.—-Photomicrograph showing chalcocite and pyrite
enclosed in lathlike chlorite and quartz. Reflected
light, 153 X, 9 micron grid.

18

were observed, much larger than any other individual grains,
which form an almost rhombic pattern. Sulphide minerali—
zation is found primarily in irregular veins and masses.

It consists of chalcocite and pyrite, with mosaic Quartz,
chlorite, sericite, and lesser dolomite. (Figures 12 and
13.) The chlorite is absolutely colorless. The index of
refraction is greater than Canada Baslam, quartz and
sericite. The birefringence is about .003. It may be
delessite, as this mineral is reported to be sometimes

colorless (Milner 1962) with a refractive index from 1.605
to 1.609 compared to muscovite (sericite) with 1.556 to
1.611. Delessite is the chlorite identified in the upper

Precambrian of the Keweenaw Peninsula (Butler and Burbank,

1929).

Bands of limonite transect the bedding and are found
as clusters and isolated grains within the rock mass. It
is also associated with the mineralization and with chlcri c

layers. It is normally opaque but distinctly yellow to
yellowish brown in oblique reflected and convergent light.
Hematite is also present, and both hematite and limonite
are later minerals. Some dolomite is found in mineralize
veins. It contains dusty hematite, is gray in polorized
light, and anhedral in crystal outline. (Figures 12 and
13.)

The quartz sericite slate consists of large detrital

quartz grains in a matrix of fine grained quartz and

Figure l2.-—Photomicrograph of chalcocite,
and dolomite vein cutting quartz sericitic
light, 25 X, 11.5

5 micron grid.

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r f‘
(”D
if) .
”3
f i
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19

 

sericite. Sericite is found in interstices, penetrating
quartz boundaries, and as inclusions within quartz grains.
Chalcocite occurs in irregular veins (Figures 1A and 15)

and as colloform textures (Figures 16 and 17). Chalcocite
in veins Show textures approaching skeleton crystals,
surrounded by Spherulitic chlorite. The ore normally

occurs with chlorite, large mosiac quartz, and colorful
sericite approaching muscovite in grain size. The

sericite is later than quartz, chlorite, and is found within
the chalcocite.

Foliated quartz sericite slate is illustrated in
Figures 5 and 18. The ground mass is a well layered
foliated rock consisting of fine grained quartz and sericite
with subordinate coarse detrital quartz. Sericite is
equally as abundant as quartz. Some carbonate occurs with
inclusions of dusty hematite. Sulphide mineralization is
parallel to the banding but also cuts across it. Chaluozi‘e
with coarse mosaic quartz and chlorite appear to follow
bedding and foliation planes. In one vein, quartz is
elongate perpendicular to the walls of the vein illustratirg

o -_ a V 0%.. _'.
OCIBLEG 1:11:11 IVE“

(0

comb texture. Limonite is intimately as

J

ore and is a later mineral.

Specimens of drill core from 5 holes drilled by the

North Range Mining Company were taken every 5 feet and all

were examined under the binocular microscope. Copper

r‘

mineralization occurs in buff colored siliceous slate cad

Figure lM.—-Photomicrograph of irregular vein of Chalcocite,
chlorite, and sericite in quartz sericite slate. Ordinary
light, 107 X, 9 micron grid.

Figure 15.--Same as above but with crossed girgols. To
spherulitic “ ' l ” t

21

l’ u.
.51
, 0 '.4

E
\

-)
1' \
'.
-uf.
5!}

 

Figure 16.—-Photomicrograph of colloform chalcocite in

sericite slate. Voids within

hematite and quartz and canada balsam.

11.5 micron grid.

Figure l7.~~Same as above,

7

the chalcocite

‘1 ' , ' . . , , ,
- - ‘ y ,- — ‘V N
[J I. L E Ir"; .1, f; ‘. L \J , , L; l_

contain d1
Ordinary light,

22

\J

: i‘$!‘|‘ !‘ ’ | z
* J, I " ' ‘. '
_ . " } .‘ '4

 

23

 

and
K“.
\J

slate.

11.5 micron grid.

quartz

.9

ograph of chalcocite

Figure 18.-—Photomicr

rossed

cite

Quartz seri

ted

chlorite vein in folia

)

25 X

nicols,

quartzite, The slate is generally fine grained but contains
layers and pods of coarse grained clastics. The quartzite
is fine to coarse grained and colored from almost white to
deep red.

The slate is highly sheared. Chalcocite occurs in

the coarse elastic layers and in shears and fractures in

(D
2.

the fine grained portion. A small amount is scatter.c

)

b‘erved

m

throughout the fine grained slate. No pyrite was t
in the mineralized intersections of drill core, but hematite
is common.

Both chalcocite and native copper occur in quartzite.

Primarily they occupy the interstices between the quartz

R}

\fl/

often penetrating into the grains, (Figures lg to 2 .
Native copper and hematite are also found cutting the
quartzite in elongated fractures. Sericite also occupies
the interstices between and penetrates their boundaries

and is found as inclusions in quartz grains and :nalua lie,
There appears to be no mineral zoning. For example, in

"\

drill hole hoe :, chalcocite occurs in Quartz slc"

l1
F I
(D
D)

f
r a

_,

feet, and in red quartzite at 73 and r;

\ W
W
r‘T“.
.V
IT
("f'
I‘
I

native copper is found in red quartzite with limonite in
fractures. Again at 100 feet, chalcocite is in red

quartzite with some limohite. Native copr,
in red quartzite at loi, 11c, and 130 feet.

Specular hematite was not found associated with the

mineralization of Area A. But it was found in drill core

Figure 19.——Photomicrograph of native copper (white) in red
quartzite. Reflected light, 82 X, ll micron grid.

Figure 20.--Photomicrograph of native copper (white) in red
quartzite. Reflected light, 82 X, 11 micron grid.

25

1..

l‘.

 

at .Q.L4A.hunrmv I

5..

 

in I! .

 

 

 

 

Figure 2l.-—Photomicrograph of native copper (black) in red
sericitic quartzite. Ordinary light, 37 X, 11.5 micron
grid.

Figure 22.--Same as above, but with crossed nicols.

26

 

 

27

in fractures in gray slate, and in one place forming the

border of red feldspar veins cutting the slate.

Description of Area B

 

The copper mineralization of Area B is located
approximately 4500 feet west-southwest of Area A southeast
of Buschell Lake. It occurs at the eastern end of a
broad syncline of Kona dolomite. (Figure 1.) Between
Area A and Area B, the Kona has been eroded and the
underlying Mesnard quartzite has been exposed. Several
shallow shafts and test pits occur in Area B only one of
which contains interesting mineralization. It is located
in a valley trending northwest to Buschell Lake (formerly
Copper Lake), and, observing the amount of rock on the
dump and the cribbing of the shaft, it must have been
one of the 25 or 40 foot shafts previously described.

The rock from the shaft is of two distinct colors,
a grey banded argillaceous slate and a reddish—tan well
banded siliceous slate. The slate is massive, not sheared
as in Area A, but is highly fractured. It exhibits parallel
bedding and crosscutting fractures and veins. Most
fractures and veins are normal to the bedding but a few
cross it at an angle of about A5 degrees. A small amount
of malachite is found on fractured surfaces.

Under the binocular microscope, the gray slate is

mostly fine grained with alternating coarse grained layers.

28

The coarse grained clastics also occur as irregular con-
torted pods at a high angle to normal banding. Mineraliza-
tion occurs in hairline fractures and in small veins up

to % inch. It is also found in the coarse Clastic bands
and a small amount in the fine grained sediment. Clastic
bands also contain some limonite and hematite.

The reddish tan slate appears very much the same as
the gray slate except for color. It is fine grained with
alternating coarse grained clastic layers. Mineralized
veins and pods cut across the banding at a high angle.

Most mineralization occurs in fractures, veins, and coarse
elastic bands with a small amount in the fine grained
portion. Some hematite is present.

In reflected light, the metallic mineralization is
more than 99 per cent chalcopyrite. Only a few small
grains show chalcopyrite and bornite, with bornite apparently
replacing chalcopyrite. (Figure 23.) Chalc0pyrite in veins
and in the coarse elastic portions in the gray slate is
commonly intimately associated with chlorite. (Figures 2A
and 25.) In the reddish—tan slate, chalcopyrite is primarily
restricted to coarse clastic bands within the sediment
(Figures 26 and 27) but does occur in the fine grained
portion. (Figure 28.) In the larger quartz—dolomite veins,
chalcopyrite surrounds and penetrates grain boundaries.

(Figure 29.)

29

     
 

i

 

Illrli‘P

llllTil

  

 

    

   

 

' IFHHHH‘{(

 

.AIII [[1111 Iii]

  

.‘1

 

Figure 23.--Photomicrograph of bornite (light gray) appar-
ently replacing chalcopyrite (white) enclosed in reddish-
tan slate. Reflected light, 130 X, 11 micron grid.

Figure 2&.——Photomicrograph of chalcopyrite (white) in vein
in gray slate with chlorite (gray lathlike inclusions).
Reflected light, 82 X, 11 micron grid.

Figure 25.-—Same as above, a different vein.

30

 

 

Figure 26.-—Photomicrograph of contact between coarse and
fine grained sediment displaying concentration in coarse
layer. Reflected light, 82 X, 11 micron grid.

Figure 2 .--Fhotomicrograph of chalcogyrite in coarse

grained reddish-tan slate. Reflected lignt, d; I, ll
micron grid.

3].

 

Figure 28.—~Photomicrograph of chalcopyrite in fine grained
matrix of reddish tan slate. Reflected light, 82 X, ll
micron grid.

Figure 29.—-Photomicrograph of chalcopyrite in one of the
larger quartz-dolomite veins. Reflected light, 52 X, ll
micron grid.

 

fl Tu“ ‘_ \.,

 

32

 

 

 

33

In thin section, the fine grained rock shows scattered
large clastic quartz with some dolomite and chalcopyrite
in a matrix of sericite, or, fine dolomite and Quartz with
interstitial sericite. The coarser layers are predominantly
quartz and dolomite, with chalcopyrite, coarse sericite and
a few grains of feldSpar.

The mineralization occurs as described above. It is
found in veins with Quartz, dolomite and chlorite inclusions.
(Figures 30 and 31.) It is common in clastic bands with
:Lesser amount in the fine grained rock. (Figure 32.)

CEhlorite inclusions are common in the chalcopyrite and
'knost rock of the gray slate. In the reddish—tan slate,
<::halcopyrite contains inclusions of sericite. A small

EEamount of epidote replacing dolomite is in the reddish—

‘1:an slate. (Figure 33-)

Description of Area C

Copper mineralization of Area C is in the Kona
(dolomite on the north limb of the Marguette syncline
Eabout 1400 feet southeast of Enchantment Lake. The
eexploration is limited to one large test pit just above
a narrow valley, on the south limb of a 160 foot hill of
'Kona, and is about 600 feet above Lake Superior. Green
malachite and red iron oxide are plentiful and obviously
the reason for the test pit. There is no known record of

this exploration, which was encountered by J. E. Gair

Figure 30.——Photomicrograph of chalcopyrite in Quartz

dolomite vein cutting Quartz sericitic slate. Lathlike

inclusions of chlorite are colorless in ordinary light

and dark gray under crossed nicols. Ordinary light,
107 X, 11.5 micron grid.

Figure 31.——Photomicrograph of chalcopyrite in Quartz

dolomite vein cutting coarse and fine grained Quartz

dolomite sericitic slate. Crossed nicols, 25 X, 11.5
micron grid.

 

Figure 32.--Photomicrograph of scattered chalcopyrite in

banded Quartz sericitic slate, showing preference to the

coarse grained member. Note cross cutting large segment

of chalcopyrite with Quartz in upper right of photo.
Ordinary light, 37 X, 11.5 micron grid.

Figure 33.—-Photomicrograph of epidote replacing dolo ite
adjoining Quartz dolomite vein. Ordinary light, 107 X,
11.5 micron grid.

. 0 N ‘O: -
-w 23‘s“ ~" ‘ 3* ' " {‘1

r "
mm” film 1*

(SAG! 8e;..."‘3_¥

 

36

while mapping the Marquette Quadrangle, and subsequently
brought to the attention of the writer.

The rock from the pit is of two types, a buff—
colored siliceous dolomite, and white vein Quartz. Most
specimens exhibit sulphide mineralization which is clearly
visible. The structure appears to be a north-south shear
zone although the mineralization may be associated with
wideSpread regional silicification of the Kona dolomite
described by Gair (1961).

The mineralization is more varied than in Areas A
and B. Chalcopyrite, bornite, covellite, chalcocite, and
Specular hematite are found associated with considerable
red hematite and malachite. Chalcopyrite is sometimes found
alone but may be replaced by bornite, covellite, and
Specular hematite in that order. Bornite is replaced by
covellite and Specular hematite. (Figure 34.) Bornite
and chalcocite are replaced by covellite (Figure 35) and
by Specular hematite. No relationship of chalcopyrite and
chalcocite were observed. A few scattered grains of
anhedral pyrite occur as islands surrounded by other
minerals, but were not internally replaced by them, The
Specular hematite is made up of very fine blades which form
dendritic patterns penetrating all minerals except pyrite.
Covellite also replaces chalcocite. (Figure 36.)

In thin section, the dolomitic rock consists of

small to large grain mosiac Quartz with MO to EO per cent

Figure 3M.-—Photomicrograph of bornite replaced by covellite
and Specular hematite. Reflected light, 153 X, 9 micron
grid.

Figure 35.-—Photomicrograph of bornite and chalcocite
replaced by Specular hematite. Reflected light, 153 X,
9 micron grid.

37

'

 

38

 

 

Figure 36.--Photomicrograph of covellite replacing
chalcocite. Reflected light, 190 X, 9 micron grid.

39

dolomite scattered equally throughout the rock. Both Quartz
and dolomite exhibit frequent euhedral and subhedral grain
boundaries. Most dolomite is clouded with hematite which is
normal in many areas of the Kona. Mineralization is Scat—
tered and occurs primarily in association with the larger
grains of quartz and dolomite. (Figure 37.) A small
amount of mineralization appears to follow fractures but
most are found surrounding grains of Quartz and dolomite.
The vein Quartz is wholly fine to coarse grained
mosiac Quartz with metallic mineralization primarily asso—
ciated with the coarse grained Quartz. dalachite is found
in fractures and surrounding boundaries of ore minerals.
The mineralization is Scattered and appears to be fracture
controlled. It may have been introduced following

silicification. (Figure 38.)

Description of Area D

 

The copper mineralization of Area D is found in the
Cliffs Shaft iron mine located within the City of Ishpeming.
The mineralization described is on the tenth level at an
elevation of +735 feet or approximately 725 feet below the
surface. The mineralization is in a two foot vein cutting
the iron formation and is exposed for about NO to 5O feet.
The vein trends approximately east—west. Copper mineraliza—
tion has been intersected in other parts of this mine but

the veins are smaller and more erratic in trend.

Figure 37.--Photomicrograph of chalcopyrite in quartz-
carbonate vein. Crossed nicols, 37 X, 11.5 micron grid.

Figure 38.——Eornite in mosiac Quart: vein. Crossed hisols,
37 X, ll.r micron grid.

1
./

4O

 

41

The dominant mineral is bornite, followed by
chalcopyrite, pyrite, hematite and Quartz. The chalcopyrite-
bornite relationship appears to be that bornite replaces
chalcopyrite (Figure 39), but some textures suggest
exsolution. (Figure #0.) The predominance of surfaces
suggesting the replacement of chalcopyrite by bornite
entices the writer to believe this is the true relationship.
Specular hematite is clearly later than bornite and
chalcopyrite. It penetrates the bornite in long thin
stringer in an elongated and dendritic pattern and also
irregular larger masses with erratic borders. It is almost
always found within the bornite, rarely intersecting
chalcopyrite. The hematite is of three types; a gray
relatively large bladed type which takes a high polish
(Figure 41), pods with fine grained borders and extending
in elongated groups of small crystals, and red hematite
adjoining borders of the gray variety as isolated red
clusters.

The elongated stringers of hematite are fine grained
Specular and often form a dendritic pattern. The stringers
are primarily in the center of the bornite along
fractures suggesting that bornite replaced chalcopyrite
(Figure 39) and hematite replaced bornite from the same
fractures. Hematite is predominatly within the bornite,
but in a few places, chalcopyrite forms a border between

hematite and bornite. Hematite also occurs as rims

Figure 39.--Bornite (dark) replacing chalcopyrite (white).
Reflected light, 130 X, 11 micron grid.

Figure AO.—-Bornite (dark) and chalcopyrite (white) exhib—
iting exsolution textures. Reflected light, 153 X, 9 micron
grid.

42

 

 

 

 

M3

 

Figure 41.--Specular hematite in Quartz adjacent to

bornite (light gray) replacing chalcopyrite (white) and

replacement by specular hematite (high relief mineral).
116 X, 9 micron grid.

AA

between the chalcopyrite—bornite and pyrite-quartz,
penetrating the chalcopyrite-bornite but not the pyrite.

Pyrite is found within the chalcopyrite—bcrnite
primarily as enhedral to subhedral crystals but occasionally
has corroded borders suggesting replacement. Pods of
Quartz, sometimes with pyrite, are within the chalcopyrite—
bornite. They are often rimmed with Specular hematite.

Most pyrite occurs as massive groups of crystals, in
rcunded form some almost perfect Spheres. They are
sometimes vugular, but more often the interstices between
the crystals are filled with Quartz. The pyrite masses
are commonly highly fractured and in one instance the
fractures are Quartz filled. Isolated chalcopyrite—bornite
is also found within the pyrite masses.

The quartz is coarse grained crystalline suggesting
slow cocling. The faces are clearly visible under the
binocular microscope. The Quartz contains pyrite, both fine
and coarse crystalline; hematite and bornite; along
crystal faces and within Quartz grains. Eladed Specular

hematite is also found within the Quartz. (Figure A1.)

Chapter III

GEOCHEMISTRY

 

Nintey Specimens were prepared for Spectrographic
examination to determine trace elements and the dissemina—
tion of copper adjacent to the ore zone. The samples
were aroed in a Baush & Lomb grating Spectrograph with
diSpersion of A A per millimeter in the first order. The
source unit was an A. R. L° multisource. Arc conditions
were as follows: a resistance of MO ohms, an inductance
of 360 microhenries, a capatance of 12 microfarads for 12
seconds, and a tabulate wave length of 3100 — 4100 were
used. Prior to arcing, samples were heated to 900 degrees
C., Quenched in distilled water to facilate grinding,
ground in mortar and pestle and mixed with carbon and an
internal standard of strontium carbonate.

The ore samples of Areas A, B, and C were examined
for Ag, Au, As, Ba, Be, Cd, Cr, Co, Cu, Hg, Li, Mn, Mo,
Ni, Pb, Sb, Th, Ti, U, V, and Zn. Only Cu, Ti, and Mn of
the examined elements were represented in the samples,
and Ti and Mn only in minor amounts. As clastic pods and
layers are present, titanium probably exists as ilmenite
granules. Manganese may be a minor constituent of the

fine grained portion of the sediment. There are no good

45

46

elemental guides to ore. Copper may be a guide, but it
is wideSpread in trace amounts.

In the Spectrographic determination of copper, a
sample from Area A with colloform texture chalcocite
shows an estimated copper content of 6 to 7 per cent. In
Area B, the green slate contained 1.8 per cent while the
buff Slate showed 1.2 per cent copper. In Area C. bornite
mineralization was 2.6 per cent copper. Two samples of
chalcocite Showed .85 and 1.1 per cent and chalcopyrite
.15 per cent. The above determinations Should not be
representative of the mineralization, although those of
Areas B and C are more representative than that of Area A.

A Keweenawan diabase dike, located about 1300 feet
south-east of Area B has a copper content of approximately
.04 per cent.

The copper content of drill hole 3 of Area A is
illustrated in Figure 42. Small samples of core are
represented for each 5 feet of the drill hole. Figure
42 shows 2 ore zones with trace copper surrounding each
zone. All samples contain copper although some was less
than .01 per cent. As the samples examined are small,
they are not meant to represent the average analysis of
copper in the ore zone.

The Slates and Quartzites along the road cut south

of the City of MarQuette, generally known as the ”purple

 

 

 

 

 

 

 

 

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9 ) I .‘ 1 . LI .I I O O
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7...... ~ F. .1 ...11» r .1!3..11 n....... 1-

 

 

F E E T

 

M8

" have been mapped as part of the Kona dolomite

slates,
(Gair, et_al,, 1963). These rocks were sampled every
25 feet, normal to the bedding, for a length of 500 feet.
The results of the copper content are illustrated in

Figure H3. Admittedly, the copper content is low, but

it does illustrate copper penetration 3500 feet east of

Area A.

IIIILIIIIA . III) 7.1 . .

I
NORTH

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I N

 

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FIGURE
COPPER CONTENT or

 

KONA
SOUTH OF

 

 

co

 

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A A . III I I II II III! I VIII I Ila I III I I I .A .. A A
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7 5. AA . a. 1'.

«uanu ...Zwuamn—

.O'I

  

a... . ....‘I‘I\

 

DJ

Chapter IV

CONCLUSIONS

 

In summarizing the four described areas, we have:

In Area A, chalcocite obviously replaces pyrite and
is associated with Quartz, chlorite and sericite.
Also, native copper in clastic quartz with sericite
occurs at depth. Specular hematite is found in
fractures in drill core as well as in the Mesnard
Quartzite stratigraphically below the Kona.
In Area B, the metallization is primarily chalcopyrite
with a small amount of bornite. It is asociated with
quartz, chlorite and sericite and also occurs in
Quartz—dolomite veins. Specular hematite is found

in abundance in a test pit in the Kona about BUOO
feet to the west of Area B (Holway 1952).
In Area C, metallic mineralization consists of chal-
copyrite, bornite, covellite chalcocite and Specular
hematite, with red hematite and malachite. Chalco—
pyrite is replaced by bornite, covellite, and Specular
hematite. Chalcocite may be replaced by bornite, and
is replaced by covellite and Specular hematite.
In Area D, chalcopyrite is replaced by bornite and
Specular hematite. The relationship of quartz and

SO

51

pyrite to the other minerals is not clear, but quartz
contains inclusions of pyrite, bornite, and hematite
along quartz crystal boundaries and within crystal
grains. Pods of quartz are found within the chalco—
pyrite bornite and also chalcopyrite bornite, quartz,
and red hematite are found within the pyrite.

Trace copper in the Kona shows a wide distribution.
Examination of other important trace elements shows that
most are not present and mineralized areas of the eastern
Marquette range are practically "clean” of trace elements.

Wall rock alteration of the mineralized zones is
primarily silicification followed by sericitization and
chloritization. The area is within the chlorite or
equivalent metamorphic zone (James 1955).

The nearest local approximation to the mineralization
existing in the eastern Marquette range is that adjacent
to, and within, the syenodiorite intrusive of Mount Bohemia
in the Keweenaw Peninsula. Exploration in the vicinity of
Mount Bohemia has disclosed copper sulphides in amygdaloidal
flows, intrusive basic dikes and the syenodiorite intrusive.
Sulphides in the amygdaloid and basic dikes consist of
predominant chalcocite with bornite, chalcopyrite, pyrite,
and covellite. Subordinate native copper also occurs, and
Specularite. In the syenodiorite, the predominant sulphide
is bornite followed by chalcopyrite, chalcocite, and a

little pyrite. Associated minerals include calcite,

52

chlorite, and epidote with minor silification (Weege, R. J.,
personal communication).

Calcite, chlorite and epidote are the most important
gangue minerals surrounding Mount Bohemia. Quartz, chlorite,
sericite, and dolomite are predominant in the eastern
Marquette syncline. While the simularity in mineralogy
is striking, it is not direct proof of a genetic relation—
ship. But it may be inferred as indicative of a Similar
source of rock type and age. Figure AA illustrates the
geographical relationship of the copper area described
with the Keweenawan basin and Keweenawan dikes.

One dissenting objection to a Keweenawan age of this
mineralization is that the Mount Bohemia intrusive shows
a positive aeromagnetic anomaly of llBO gammas (Balsley
et al., 1963). In the eastern Marquette range, over the
copper mineralization, there is no aeromagnetic expression.
An intrusive source of mineralization may be at some
depth.

An interesting note, Wright (1909), discussing
area of Mount Bohemia stated:

Jear Marquette, diabase dikes outcrop whose
jointing cracks are often filled with diklets of
red feldspathic material not unlike certain felsites
in aSpect, thus indicating that there also the sialic

portion of the diabase magma finally solidified to
produce such a rock.

 

 

 

 

 

 

00
I
é?lfl   / ///—~ c0PPER
jag-42:, ‘
FLT/7,: 7/
//

’\.,

FIGURE 44

GENERALIZED GEOLOGIC MAP
snownqc KEWEENAWAN 3A5|N_
AND ASSOCIATED DIKES

O 5 0
g I

 

 

REFERENCES

 

Balsley, J. R., Meuschke, J. L., and Blanchelt, Jean.
Aeromagnetic map of the Delaware quadrangle, Michigan:
U. S. Geological Survey Map GP 315, 1963.

Boyer, Kenneth. Copper proSpects south of Marquette near
Chocolay: Radio program delivered February 12, 1961
over WDMJ, Marquette, Michigan, 1961.

Boyum, Burton H. The Marquette mineral district, Michigan:
Conference on Lake Superior Geology, 1964, 37 pp.

Butler, B. S., and Burbank, W. S. The Copper Deposits of
Michigan: U. S. Geological Survey Professional
Paper 144, 1929, 237 pp.

Gair, J. E., Thaden, R. E., and Jones, B. F. Silification
of the Kona dolomite in the eastern part of the
Marquette iron range, Michigan: U. S. Geological
Survey Professional Paper 424-C, 1961, p C78~C8©.

Gair, J. E., Thaden, R. E., and Jones, B. F. Geologic
maps of the Marquette and Sands quadrangles, Michigan:
U. S. Geological Survey open file maps, 1963.

Holway, W. The origin and occurrence of Specular hematite
(Specularite) in the Lower Huronian of the
Marquette district, Michigan, Unpublished M. S.
Thesis, Michigan State College, 1952, 46 pp.

James, H. L. Zones of regional metamorphism of the
Precambrian of northern Michigan: Geological Society
of America, vol. 66 (1955), pp. l455~1488.

Milner, Henry B. Sedimentary Petrography (The Macmillan
Company, New York, New York, 1962), 715 pp.

 

Rogers, A. F., and Kerr, P. F. Optical Mineralogy (McGraw-
Hill Book Co., Inc., New York, 1942), 390 pp.

 

Short, M. N. Microscopic determination of the ore
minerals: U. S. Geological Survey Bulletin 914,
1940, 314 pp.

R4

/

\D
\N

Van Hise, C. R., and Bayley, W. S. Preliminary Report of
the Marquette Iron—Bearing District of Michigan:
Fifteenth Annual Report of the U. S. Geological Survey,
1895: pp~ A77‘6500

Van Hise, C. R., and Bayley, W. S. The Marquette Iron—

Bearing District of Michigan: U. 0. Geological
Survey Monograph 28, 1897, 608 pp.

Van Hise, C. R., and Leith, C. K., The Geology of the Lake
Superior Region: U. S. Geological Survey Monograph
52, 1911, 641 pp.

Wright, F. E. The Intrusive Rocks of Mount Bohemia,
Michigan: Geological Survey of Michigan Annual Report,

1909.

ROOM USE ONLY

“LY

HICHIGQN STQTE UNIV. LIB

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