PETROLOGY OF THE ALGOMAH MINE AREA

(ENTONAGON COUNTY, MICHIGAN. i‘ ; — 7: l f

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ABSTRACT

PETROLOGY OF THE ALGOMAH MINE AREA
ONTONAGON COUNTY, MICHIGAN

By Chester H. Wilson

The Algomah mine area is located in Ontonagon County,
Michigan. The Keweenaw fault, which traverses the area,
has placed the Portage Lake lava series in contact with
the Jacobsville sandstone.

Copper mineralization of the Algomah flow top consists
of copper chlorides, carbonates, silicates, and oxides
instead of the usual native copper of the Lake Superior
region.

All outcrops in this area were sampled and thin
sections prepared. Polished sections Were prepared of
ore samples. These sections were studied using standard
microscopic techniques.

The results showed that the flow tops had been
albitized during the mineralization. A possible mechanism
involving Precambrian salt deposits for the deposition
of hypogene native copper would account for the sodium
enrichment of the flow top and provide the chloride

involved in the supergene mineralization.

PETROLOGY OF THE ALGOMAH MINE AREA

ONTONAGON COUNTY, MICHIGAN

BY

Chester H. Wilson

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

MASTER OF SCIENCE

Department of Geology

1967

ACKNOWLEDGMENTS

The author wishes to express his sincere appreCiation
to Dr. James Trow for his cooperation and assistance
during the preparation of this paper, to the late Dr.
Justin Zinn for suggesting the project; also to Drs.

C. E. Prouty and H. B. Stonehouse for their helpful
suggestions and criticisms.

He also wishes to thank Mr. Urho Lampi, Mr. Reino
Keranen, and Mr. James O'Meara for furnishing information

about the mining operation.

11

 

 

TABLE

ACKNOWLEDGMENTS . . .
LIST OF FIGURES . . .
LIST OF PHOTOS . . .
LIST OF APPENDICES . .
INTRODUCTION . . .
Geography . . .
History of Algomah Mine
Previous Investigations
GENERAL GEOLOGY . . .
Lithologic Setting .

Structural Setting .

Economic Geology .
PROCEDURE . . . .
PETROLOGY . . . .

Sandstone . . .

Lava Flows . . .
Ore . . . . .
Interpretation . .
BIBLIOGRAPHY . . . .
APPENDICES . . .

OF CONTENTS

0 O I

O O 0

iii

Page
11
iv

vi

\0 \o ¢~ H H H

13
18
23
25
25
28
34
38
43
46

LIST OF FIGURES

Figure Page
1. Location of the Area. . . . . . . 2

2. Generalized Geological Map of a
Part of the Keweenaw Peninsula -. . . . 10

3. General Geology of the Algomah 7
Michigan Area . . . . . . . 15

4. South Lake, Lake, and Algomah
Sections T 50 N, R 38 W and
T51N9R37W- o o o A. o o o 16

5. Cross Section at Lake Mine . . . . . l7

6. Longitudinal Section of Lake Lode
in Plane of Lode. . . . . . . . 21

7. Geology of Algomah Mine Area. . . . . 24

8. Chemical Analyses of Selected
Samples of Melanochalcite.
Columns 1-7 Material From
Southwest United States.
Column 8 was Added by the
Author Using Algomah Material. . . . . 37

1V

LIST OF PHOTOS

Photo Page
1. The Algomah Copper Mine. . . . . . 4

2. Jacobsville Sandstone Showing
Microcline and Quartz . . . . . 27

3. Flow Top. Only Plagioclase Laths
are Visible. I I a O O 0 0 O 30

4. Chlorite Rock Alteration Consisting

Mostly of Penninite with Some

Prochlorite. . . . . . . . . 31
5. Pyroxene Enclosing Plagioclase. . . . 32

6. Gas Hole Filled with Secondary
Minerals 0 o c o o o o o o o 34

LIST OF APPENDICES

Appendix Page
A. Location of Diamond Drill
H0165. o o o o o o o o o o 46

B. Algomah Diamond Drill Core
Information. . . . . . . . . . 48

v1

INTRODUCTION

Much cepper has been mined from the Precambrian Portage

Lake lava series of the western Upper Peninsula of Mich-

igan. Most of this copper has been found as native metal.
The Algomah mine differs from most of these mines in that

it carries a copper ore, black cupric oxide, instead of
the usual native cepper. Various phases of the unique
mineralogy of this area have been previously examined and

.14. ’.. .1.‘,,\ . -.' ,. .0 n-2,, .- .'_ -.~.~ .| .. .4. - r .. ,.
Lb lo the purges: Oi CHLQ b13613 to correlate the facultb

omah mine area is located 1% miles east of
Mass, Michigan in section 3, T 50 N, R 38 W (Figure 1).
This area is easily reached by highway M 35 and county
roads. The area is covered fairly extensively by glacial
deposits, witq rock outcrOpping only in the immediate
vicinity of the mine. Most of the area is swampy and of
little economic use except for dairy farming and pulpwood

production.
History of Algomah Nine

The Algomah mine was originally worked with poor
results by a company of the same name from 1852 to 1854.
On June 4, 1910 the Algomah Mining Company was organized
and exploratory work commenced. During 1910 an assay of

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a sample from sixty tons of selected ore contained 24%
copper. Exploration continued into 1911 with underground
development from the shaft and with diamond drilling. In
1912 S. R. Dow, the company president, went bankrupt,
losing 3 28,725 which should have been in the company
treasury. As a result the company reorganized and called
for a 31 per share assessment to provide $70,000 to
continue development. Shaft sinking continued and in 1914
74,560 pounds of hand picked ore from the developmental
work yielded 12,467 pounds of copper, a yield of 18%.

The mine was idle from 1914 to April 1915 when work
started again after a sale of delinquent stock bid in by
the company for non-payment of the 1912 assessment. After
hand picked ore stoped from the first level proved unprofit-
able, the company devoted itself to sinking the shaft
hoping to strike the rich Lake Lode to the north. By the
end of 1915 the shaft was down to 478 feet. 5,005
pounds of copper were sold at 18¢ per pound from the
hand picked ore.

In 1916 the shaft was sunk 80 feet to a depth of
558 feet. However, in 1916 and 1917 the company was
plagued by high costs and adverse labor problems and
closed with a total of $16,868.54 in the treasury.

In 1955 the mine was Opened for the third time,along
with some others in the area, and operated for thirteen

months. At this time selected ore stoped from the first

 

4

level gave 16% to 20% copper but the necessity of shipping

it to the Atlantic Coast made the venture unprofitable.

 

 

 

 

Photo 1. Algomah Copper Mine
Previous Investigations

The Algomah mine and the mines nearby, the Lake and
South Lake, have prOVed interesting to many people be-
cause of the rather unique mineralization and structure
of the area, although little is published on the region.
Lane (1909) incorporates the general results of the
exploratory work in the area in his Keweenaw Series of
1 Michigan but is inclined to simplify the regional structure

by attributing all structural features to faulting as he

states:

"--- I may have been too much influenced in my
feeling that there is no such fold, by the fact that no
similar folds have heretofore been notices." (1)

Other than company reports, early information of the
area is mostly confined to Michigan Geological and Bio-
logical Survey mineral production reports which give
general geological and production facts. R. E. Here in
his article "The COpper Industry of Michigan" in the
1910 report states:

”The Algomah lode is the upper portion of a brown
amygdaloidal bed and differs markedly from all of the
lodes (studied) in carrying black oxide, green silicate
and green carbonate of copper instead of native metal.
Along the strike it shows masses of green colored ore
more or less separated by stretches of brown amygda-
loid." (2)

The unique mineralogy at Algomah is indicated as he
continues:

"The copper minerals in the Algomah lode are chiefly
chrysocolla, melaconite and malachite. The oxide is
usually dull black massive melaconite; but Prof. A. E.
Seamen has found specimens showing black tetragonal crys-
tals of paramelaconite in green malachite. This is the
only known occurrence of paramelaconite other than that
at the COpper Queen Mine, Arizona, where it was first
identified by Dr. Koenig. Prof. Seamen has also found
in the Algomah ore some minute green crystals which are
thought to be dioptase." (2)

Stevens (1911) and Hore (1912, 1914) repeat essentially

1) Lane, Alfred C., The Keweenaw Series 2f_Michi an, Publi-
cation 6, Series 4, Volume 2, Micnigan Geological and
Biological Survey, Lansing, Michigan, 1909, page 947.

2) Hore, R. E., "The Copper Industry of Michigan", Mineral
Resources 3f Michigan, 1910, Publication 8, Geological
Series 6, Michigan Geological and Biological Survey,
Lansing, Michigan, 1912, pages 54-55.

 

the same information as in Hore's 1912 report. However,
it is apparent that the structure of the area was unclear
as shown by this statement from Hore's 1912 article:

"President R. M. Edwards reports of the results of
explorations: 'A Study of the drill cores has yet given
no satisfactory explanation of the conflicting results
obtained. Apparently on the northwestern part of the
property adjoining the Lake and South Lake in the vicinity
to drill holes Nos. 5, 6, and 7, there are copper deposits
at considerable depth, but which way they dip and where
they come to the surface is undetermined.'" (3)

Evidently the structure was becoming clearer in 1914

when Hore stated:

 

"The (Algomah) lode strikes nearly north and dips to
the west at an angle of about 70° at the shaft." (4)

Hopper in 1915 stated that:

"It is believed by General Manager Edwards that at
depth some of the lodes worked in the Lake and South Lake
will be encountered on the Algomah property.” (5)

HOpper (1914, 1915,1916) reports the economic situation
of the company which, as indicated before, was very un-

stable.

3) Hore, R. E., "Michigan Copper Industry in 1912", Mineral
Resources 9; Michigan, 1212, Publication 13, Geological
Series 10, Michigan Geological and Biological Survey,
Lansing, Michigan, 1913, pages 19-20.

4) Hore, R. E., "Michigan Capper Deposits”, Mineral Resources
9; Michigan, 1214, Publication 19, Series 16, Michigan
Geological and Biological Survey, Lansing, Michigan,

1915, page 70.

5) Hopper, W. E., "The Michigan Copper Industry in 1915",
Mineral Resources gf_Michigan, 1915, Publication 21,
Geological Series 17, Michigan Geological and Biological
Survey, Lansing, Michigan, 1916, page 19.

 

Butler and Burbank in The Copper Deposits g; Michigan
mention the area in a number of places. Mention is
made of the unique mineralogy previously studied along
with the note that:

"Atacamite (Cu201(OH)) occurs in well-formed
radiating crystals as an ogidation product at the
Algomah mine." (6)

The structure of the area is summarized by them:

" At the Lake and South Lake mines there is a broad,
gentle syncline (Lake mine syncline or Lake mine basin)
and a narrow, steep antioline between the (Keweenaw)
fault and the point where the rocks have the normal
westerly dip." (7) "The shaft on the Algomah lode is
on the south side of the Lake mine basin, at the
general horizon of the Lake lode and only 60 feet from
the Keweenaw fault. Whether or not this lode is the
same as the Lake lode has not yet been determined." (8)

From their study they also determined that:

"--- the lode is mainly cellular-—-" (8)
and that:

"The rock showed pumpellyite rock alteration char-
acteristic of many of the lodes in this part of the
district." (8)

Zinn (9) mapped this area in 1942 for the Michigan
Geological Survey and this report is listed in An Index

9: Michigan Geology as an open file report. However, it

65mmt1er, B. 8., and Burbank, W. S., The Copper Deposits
of Michi an, United States Geologicalb Survey Profes-
sional Paper 144, United St:ites Geological Survey,
Washington, D. C., 1929, page 58.

7) Butler and Burbank, ibid, pages 48-50.

8) Butler and Burbank, ibid, page 217.

9) Zinn, Dr. Justin, personal communication, 1966.

 

 

 

cannot be located by the Michigan Geological Survey and
seems to have been missing for a number of years.

Spiroff (1942) includes a few outcrops in the Algomah
area on his map of the Firesteel River area.

Williams (1962a, b) made an excellent study of the
ore minerals found at Algomah using samples from the A. E.
Seamen Museum at Michigan Technological University,
Houghton, Michigan. He found the paragenesis of the
copper minerals to be as follows:

”--- (oldest to youngest) native copper - cuprite -

dioptase - paramelaconite - plancheite - atacamite -
paratacamite - nantokite - tenorite - malachite -
chrysocolla." (10)

10) Williams, S. A., "Stability Relations and Paragenesis
of Copper Oxides and Chlorides at the Algomah Mine,
Ontonagon County, Michigan", Economic Geology, Volume
57, 1962a, page 111.

 

GENERAL GEOLOGY
Lithologic Setting

The formations of the Keweenaw peninsula are, from
the oldest to youngest, the Portage Lake lava series,
Copper Harbor conglomerate, Nonesuch shale, Freda sand-
stone, and Jacobsville sandstone. The Portage Lake lava
series is locally intruded by a small rhyolite body. A
generalized map of Keweenawan geology is included here
as Figure 2.

The Portage Lake lava series is a thick sequence of
flows ranging in composition from olivine basalt to
andesite with a few interbedded conglomerates with
rhyolitic pebbles. These flows vary in thickness from
a few hundred feet up to about 1300 feet and in extent
along the strike from a few hundred feet up to at least
40 miles. Some of the flows are uniformly fine-grained
but most of them increase in grain size from both the
top and bottom towards the center. The texture of the
coarse-grained lavas may be ophitic, glomeroporphyritic,
or less commonly, porphyritic.

Capping the massive lava that forms the bulk of
each flow is a large layer of amygdaloidal lava usually
5 to 10 feet thick. A few flows have, in addition,
small to large amounts of detrital sand, silt, or clay

in cracks and interstices between fragments in those

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flows with fragmental tops. The minerals filling the
amygdules are mainly calcite, epidote, and quartz,
although other minerals such as prehnite, datolite, red
potash feldspar, analcite, native copper, pumpellyite,
and laumontite are locally abundant.

The conglomerate and sandstone beds within the lava
series are composed primarily of rhyolitic material.

The bulk of the elastic particles range in diameter from

a small fraction of an inch to about 6 inches. The pebbles
and cobbles are generally well rounded. These rocks are
compact and tightly cemented. These sedimentary beds

serve as good stratigraphic markers and a few have

native copper deposited in them.

The Copper Harbor conglomerate that conformably over-
lies the Portage Lake lava series consists mainly of rudely
stratified pebble-to boulder-conglomerate with small sand-
stone lenses and beds. The pebbles and boulders are well-
rounded to sub-angular rhyolite clasts. Basalt fragments
are generally present in small amounts and in some areas
make up as much as one-half the total bulk. There is
little pre-Keweenawan material present. The matrix is sand
and grit of the same character as the coarser material.

Lava flows interstratified with the Copper Harbor
conglomerate are typically fine-grained andesite, with an
amygdaloidal layer 2 to 10 feet thick at the top. The

dominant minerals of the amygdaloidal fillings are

l2

calcite, chlorite, and laumontite.

The Nonesuch shale is predominantly siltstone.
The upper part of the formation is composed of flaggy,
ripplemarked, gray to reddish-gray siltstone, with small
amounts of interbedded gray and greenish-gray silty shale.
The lower part contains dark gray siltstone, mostly
thinly laminated, with several beds of coarse-grained
arkosic sandstone near the base. The lower part contains
chalcocite and native COpper in the White Pine area near
Ontonagon. The total thickness of the formation is about
600 feet.

The typical rock of the overlying Freda sandstone is
a light gray to red, fine to medium-grained sandstone
with prominent white blotches and streaks. The forma-
tion includes minor amounts of red shale and conglomerate.
The total thickness of the Freda is about 500 feet. The
boundary between the Freda and the underlying Nonesuch
shale is transitional.

Jacobsville sandstone is primarily buff or salmon
colored, fine to medium-grained sandstone with small
amounts of reddish-brown pebble conglomerates, red shales,
and silty shales. The sandStone has a large proportion
of well-rounded quartz grains. This formation probably
represents the last phase of the Keweenawan.

Intrusive rhyolite bodies of the Keweenaw are uniform,

fine-grained rocks which are pale reddish- rown on freshly

 

 

13

broken surfaces and white on weathered surfaces. The
main minerals are quartz, orthoclase, and albite-
oligoclase. The rhyolite is closely jointed and the
bodies appear to be stocks. None are older than middle
Keweenawan as they intrude the Portage Lake lava series.
The dominance of rhyolite fragments in the beds of
conglomerate in the lava series indicate that the
rhyolite intrusive rocks, or extrusive rocks, must have
been exposed over large areas during and after middle

Keweenawan.
Structural Setting

The Michigan copper region is on the southern rim
of the Lake Superior syncline or basin of Keweenawan age.
The north limb of this syncline is found on the north
shore of Lake Superior and on Isle Royale. Early
Keweenawan rocks dip steeply (60°) and later ones pro-
gressively less steeply (down to 25°) northwestward
toward the center of the basin.

Transverse to the general strike of the Lake Superior
syncline are folds that pitch down the dip of the larger
fold; among these folds are the northward pitching
Keweenawan anticline with its crest near Keweenaw point,
the Ontonagon sycnline immediately to the southwest, and
the Bessemer anticline. On these broad, open folds
(the distance from the crest of the Keweenaw anticline

to the crest of the Bessemer anticline is about 110

14

miles) are several subordinate folds of similar character
and trend such as Winona anticline, Firesteel River
syncline, and Mass anticline. These are also broad,

Open folds but only 5 to 10 miles across as contrasted with
100 miles for the major cross folds. Some of the smaller
folds show a rather uniform bending of the beds, with

some faulting near the crest. Others, such as the Mass
anticline, have beds bent sharply at the crests and at

the margins of the folds, but the limbs are fairly

straight.

 

At the Lake, South Lake, and Algomah mines there is
a broad, gentle syncline (Lake syncline) and a narrow,
steep anticline (Mass anticline) between the Keweenaw
fault and the point where the rocks have the normal
westerly dip. These folds are shown on the Algomah
area map (Figure 3) and also indicated on the north—
south structural section of the Algomah~South Lake area
(Figure 4) and the east-west section at the Lake mine
(Figure 5).

The greatest fault of the region is the Keweenaw
fault, which bounds the Portage Lake lava series on the
south from the end of Keweenaw point to Lake Gogebic.
This is a reverse fault with a variable dip of 200 to
700 northwest, along which the lava flows have been
thrust over the younger Jacobsville sandstone. The dip

of the fault is nearly parallel to the flows and its

w...

 

Flauaae: 3
. GENERAL GEOLOGY OF THE
ALGOMAH MICHIGAN AREA

 

 

LEGEND

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strike is generally northeast, varying as it follows the
major anticlinal and synclinal structures of the rocks.
In general, the northward-dipping lava flows on the
hanging-wall side of the fault are bent downward so that
in places the dip is reversed, and the flat lying sand-
stones on the foot-wall side are turned up rather
abruptly.

Many branch faults and fissures are associated with
the Keweenaw fault. Relatively small transverse faults
and fissures, which apparently resulted during the
folding of the rocks, are also present around the crests
of the anticlines such as the Mass anticline. Most of
the smaller faults in the peninsula strike northwest
and are vertical or dip steeply northeast. The existence
of these smaller faults is revealed by offsets in key
horizons rather than by actual observations of the

fault planes.

Economic Geology

The Michigan copper deposits are of two basic types,
lode deposits and fissure deposits. The lode deposits
consist of amygdaloid lodes, which are mineralized
amygdaloidal or brecciated tops of lava flows, and
conglomerate lodes, which are mineralized beds of con-
glomerate interbedded with the lava flows. The open

textured material of a flow top is commonly called

 

 

 

l9

amygdaloid. The most common of the several types of

tops is the cellular tOp produced by the simple

freezing of gas bubbles. Coalescing amygdaloid results
when individual bubbles collect into irregular pockets

of gas. Fragmental flow top is due to the breaking up

of a cellular top due to movement during solidification.
Scoriaceous flow top is the result of erosion of any of the
other types of top. Most amygdaloidal lodes are frag-
mental in nature and very few mines have been found in
the cellular amygdaloids. The fissure deposits are veins
found along fractures in the beds. All fissure deposits
are of narrow tabular form.

The mineable copper occurs in ore "shoots" which
are far smaller than the lodes containing them. The ore
in the "shoots" was deposited in the more permeable part
of the lode by chemical solutions, the movement of which
was controlled by relatively impermeable barriers.

In the area north of the Lake mine mining has taken
place in a series of lodes, the base of which is about
400 to 500 feet above the Number 8 conglomerate. From
higher to lower these lodes are the Knowlton, Merchant,
Mass, North Butler, Butler, South Butler, Ogima, and
Evergreen. The correlation of the individual lodes from
development to another is uncertain but at each mine
several lodes carried enough copper to have warranted

development and a considerable amount of copper has

 

 

 

20

been removed from the series as a whole (Figure 3).

The flows of these lodes are intermediate in compo-
sition and texturally they are mainly melaphyres and
glomeroporphyrites. The amygdaloids of this series of
flows are quite commonly thick, coarse fragmental mate-
rial rich in copper with smaller alternating lean areas
which are thin and cellular or trappy and fragmental.

Some of the lodes show a local tendency to pass into the
amygdaloid of the coalescing type. The copper of these
lodes is in small and large masses irregularly distributed
throughout the lode. A large percentage of the copper
found is quite coarse.

This series of beds is involved in the Mass anticline
and the Lake mine syncline, but the correlation of the
individual beds in the Lake mine syncline with the
normally dipping beds to the north is somewhat uncertain.
The Lake lode is a wide amygdaloid involved in the Lake
mine fold. (Figure 6). The copper is irregularly
distributed along the Lake lode with the rich and poor
portions alternating. Structurally this lode continues
onto the Algomah property and this is confirmed by diamond
drilling. However, it is not possible to correlate this
lode with the Algomah lode although mineralization
similar to that in the Algomah lode has been found in the
second level of the Lake mine. Diamond drilling near the

Algomah mine indicated the presence of an amygdaloid with

 

21

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native copper which might also be the Lake lode. This
amygdaloid is about #00 feet above the Algomah lode.
The Algomah lode itself is mostly cellular with some
fragmental areas.

In the area there are faults and fissures that are
associated with the Mass anticline that show a small
amount of movement. Little information is available on
these but most are mineralized and were evidently formed
before the period of mineralization although there has

been some movement on them since mineralization.

PROCEDURE

The field work for the study was accomplished in
the summer of 1966. Since the area of outcrop is rather
small, all outcrops were visited, mapped, and sampled.
Pace and compass mapping_was employed for the study.

As the author was unable to go underground it was neces-
sary to rely on personal interviews with former mine
employees.

Thin sections were made of each outcrop to determine
the mineral compositions and variations. Polished
sections and thin sections were prepared of both high
and low grade ores. These sections were studied using
standard microscopic techniques.

One chemical analysis was made to aid in the study

of the ore mineralization.

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PETROLOGY
Sandstone

The sandstone of the Algomah area is a msaaive,
white, weathered quartz sandstone which easily disinte-
grates in the hand-specimen. It was originally red in
color due to the presence of iron oxide but today retains
only a few streaks and spots of this original color.
Evidently much of the matrix material and color have been
leached from the rock. The main constituent of this
sandstone is rounded quartz grains about % millimeter
in diameter. Also present are a few large grains of
granule size that appear to be metaquartzite or vein
quartz particles.

In the outcrop it is very difficult to determine
the orientation of the bedding of this sandstone because
of its massive nature. However, it appears to weather
along former bedding planes and the attitude of these
apparent bedding planes indicates that this sandstone
has been thrust into a nearly vertical orientation by the
Keweenaw faulting in the area. This situation is very
similar to that at the Natural Wall ravine near Calumet,
Michigan, where the Keweenaw faulting has given the
Jacobsville a similar orientation. The sandstone at

Algomah is probably part of the massive facies of the

25

 

26

Jacobsville sandstone that was defined by Hamblin. (11)

In thin section this is a feldSpathic sandstone
composed mostly of subangular to rounded, unstrained
quartz grains, most of which have strings of gas holes.
A large number of the quartz grains present have been
cracked, especially in the rocks nearest the fault zone,‘
evidently by the faulting. Also present are a few
granules of strained polycrystalline metamorphic quartz-
ite. Orthoclase and plagioclase are present in smaller,
but almost equal, amounts (Photo 2).

The feldspars occur as subangular to rounded grains
with an occasional cleavage fragment present. A few
grains of microcline and orthoclase have secondary over-
growths of orthoclase, while some of the plagioclase
grains have albite overgrowths. These overgrowths tend
to restore the regular crystal form of the mineral and
are most noticeable when they occur on feldSpar particles
coated with iron oxide. Often cracks traverse the core
and the overgrowth. Overgrowths are also seen on a few
quartz grains and are made obvious by a small amount of
opaque dust between the grain and the overgrowth.

Interstitial to the coarser grains in the rock are

fine grained aggregates of quartz and microcline in a

ll; Hamblin, W. K., The Cambrian Sandstones 2: Northern
Michi an, Michigan Geological Survey, Lansing,
Michigan, 1958, pages 42-44.

27

random orientation. The matrix material, most of which
has been removed by weathering, seems to be made up of
quartz and clay minerals. In a few places, such as the
finer segments and where there is residual matrix material,
it is possible to see remnants of the hematite stains,

which had given this rock its original red color.

 

 

 

Photo 2. Jacobsville Sandstone Showing
Microcline and Quartz. Crossed
Nicols, X50.

A few accessories of heavy minerals are visible in
thin section. The most prominent accessory is leucoxene,
some of which shows iron oxide staining. Smaller amounts
of ilmenite or titaniferous magnetite are present and
are accompanied by leucoxene. A Few grains of apatite,

sphene, and zircon with iron oxide staining are present.

28

The mode of this sandstone is:

Unstrained quartz ---- 81.9%

Polycrystalline ------ 6.8%
strained quartz
Microcline --- -------- 5.6%
Plagioclase ---------- 2.6%
Orthoclase --------- -- 2.1%
Leucoxene ------- ----- 1.0%
Zircon
Apatite> ------- ------ Trace
Sphene

‘lO0.0%

It is felt by the author that the sandstone of the
Algomah area is definitely Jacobsville since is has the
usual fault contact with the lave flows that is character-
istic of the Jacobsville in the Keweenaw. Also this
sandstone is very similar to the massive facies of the
Jacobsville as defined by Hamblin (1958) at Victoria
Falls 12 miles away. It is interesting to note that
thin sections of the Algomah area sandstone compared
almost identically with thin sections of Jacobsville from
well known outcrops in Marquette, Michigan. The only
petrographic differences noted were the removal of
hematite stains and the shattering of the quartz grains
in the Algomah sections.

Lava Flows

Parts of two flows outcrop in the Algomah area, the
top part of the Algomah flow and the lower part of the
flow containing the Lake lode(Figure 3). These flows
are shown by petrographic and mining evidence to strike

about N 40 E and dip about 60 NW in accordance with the

29

structure of the Lake syncline (Figure 4). Mining work
shows that much of the Algomah flow has been cut off by
the Keweenaw fault in the Algomah area. Thin sections
were prepared and studied of all outcrops of these flows
in the area.

These flows are essentially ophitic basalts, which
have been extensively altered. The essential minerals
are plagioclase and pyroxene. Compositional variation
as a function of flow position occurs noticeably. The
plagioclase near the flow tops and bottoms is oligo-
clase (Ab72An28) and this changes gradually to andesine
(Ab52An48) near the central part of the lava flows, as
determined by the method of Michel-Levy. This is a
reversal of the normal trend as indicated by the plagio-
clase cooling curve. There is no visible evidence of
replacement in the plagioclases. Augite is the pyroxene
in the flows and this mineral shows some variation with
position although not as striking as that of the plagio-
clase. This variation is noted optically by a slight
increase in color in the augite towards the flow center,
probably resulting from an increase in the amount of iron
in the mineral as a result of slower cooling. The
amount of pyroxene decreases toward the flow top and no
pyroxene is found in the topmost parts of the flows.

The material that would form pyroxene is masked by ferric

oxide (Photo 3).

 

Photo 3.

All of the flow
thermal alteration.
seems to be chlorite
that retain, in some
(Photo 4). There is
present.

What appears to

30

 

Flow Top. Only Plagioclase

Laths are Visible. Crossed

Nicols, X25.

rocks sampled show extensive hydro-
The most widespread secondary mineral
alteration products of all minerals
cases, the original rock texture

also some green-brown pumpellyite

have been early formed olivine grains

have altered to iddingsite, while early pyroxenes have

now completely changed to chlorite, green biotite, and

some clinozoisite.

All of these alteration products are

associated with considerable iron oxide, mostly hematite.

The plagioclase is heavily altered, in some instances it

31

is practically impossible to determine its composition.

 

 

Photo 4. Chlorite Rock Alteration Consisting

Mostly of Penninite with some

Prochlorite. Crossed Nicols, X50.
Alteration products of the plagioclase are paragonite,
iron-rich epidote (pistacite) with high pleochroism, and
probably some clay minerals. The more basic plagioclases
are more extensively altered. The magnetite has altered
to hematite, and some leucoxene.

Texturally, it appears as if this rock had two phases
in its cooling history. The first minerals to form were
ferromagnesians, that have altered to chlorite, epidote-
group minerals, and iron oxide, since the later minerals
crystallized around these original crystals. Following
these first formed ferromagnesians, plagioclase crystal-
lized in a glomeroporphyritic arrangement, followed by
pyroxenes that are fresh in the rock. The resulting rock

has essentially an ophitic texture (Photo 5).

  

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Photo 5. Pyroxene Enclosing Plagioclase.
Crossed Nicols, X50.

A description of a typical rock from the Lake lode
flow is given here.

Sample A-2l (Lake lode flow) - In thin section this
rock has a hypidiomorphic, holocrystalline, ophitic
texture. The essential minenals are pyroxene and plagia—
class.

The plagioclase is andesine (Ab67An ). It varies
from fresh to heavily altered to paragoniée and iron-
rich epidote, with some iron oxide dust present. There
is a tendency for the plagioclase to be glomeroporphyritic.
The pyroxene of the rock is fresh augite. The augite is
poikilitic with plagioclase inclusions and is pale green-
brown in color.

Magnetite is present but most of it has altered to
hematite. Most of this opaque material surrounds what
appears to be an earlier formed pyroxene or olivine but
has now altered completely to clinozoisite, green
biotite, and chlorite.

Chlorite is present as a rock alteration. It is
composes mainly of penninite with some prochlorite and
contains some epidote and a few small patches of dissem-
inated iron oxide. In places the original texture of the
rock is preserved in this alteration. There are veins
of chlorite cutting the entire specimen.

 

33

The mode of this rock is:

Andesine ------ 45.8%
Augite -------- 24.3%
Magnetite ----- 3.3%
Hematite ------ 5.3%
Biotite ------ - .5%
Clinozoisite -- Trace
Penninite ----- 9.0%
Paragonite ---- 5.2%
Epidote ------- 1.3%
Prochlorite --- .
100.0

The flow top exhibits a number of noticeable differ-
ences from the body of the flows, such as finer texture,
more sodic plagioclase, gas holes, greater alteration,
little or no pyroxene, and a larger percentage of ferric
oxide. These differences are best shown by describing a
typical sample from the Algomah flow top.

Sample A—9b (Algomah flow top) - In thin section
this rock has a hypidiomorphic, holocrystalline, ophitic
texture. The main minerals visible are plagioclase and
chlorite.

The plagioclase is oligoclase (Ab72An ) which shows
heavy alteration to paragonite and iron-ric epidote.
Chlorite (penninite) present as rock alteration retains
the ephitic texture of the rock. No pyroxene is visible,
although it may by masked by iron oxide as commonly occurs
in the flow tops. Some magnetite is present but most of
it has changed to hematite and leucoxene. Chlorite and
clinozoisite with iron oxides may represent an original
ferromagnesian mineral.

Gas holes in the rock have been filled with a number
of minerals in a layered arrangement. (Photo 6). The
outermost mineral is prochlorite, while the center is
filled with radiating fibers of penninite and pistacite.
Between the inner minerals and the prochlorite some of the
vesicles have a thin layer of a colorless mineral that the
author feels is a zeolite, probably chabazite.

The mode of this rock is:

34

Oligoclase ---- 60
Paragonite ---- 5
Epidote -------

Chlorite ------ l8
Magnetite ----- 4
Hematite ------ 9
Leucoxene ----- l

Clinozoisite --
99.3;

 

 

 

Photo 6. Gas Hole Filled with Secondary
Minerals. Crossed Nicole, X50.

Ore

The ore at Algomah consists of essentially concentric
bands of cupric oxide, and chrysocolla occurring in the
vesicles of the cellular top of the Algomah flow. The
flow top in the vicinity of this copper mineralization
is heavily oxidized so that in thin section all of the
rock-forming minerals except the plagioclase laths are
masked by ferric oxide.

The ore mineralization at Algomah has been studied

35

by Williams (1962a, b) in some detail using museum quality
specimens. From a study of a number of polished sections
the author concurs for the most part with the findings

of Williams and will attempt to add to his work. Williams
describes the ore mineralogy as follows:

"If all of the copper minerals found at the Algomah
mine are listed in sequence the paragenesis is as
follows: (oldest to youngest) native cepper - cuprite -
diaptase - paramelaconite - plancheite - atacamite -
paratacamite - nantokite - tenorite - malachite -
chrysocolla. Native copper and cuprite are both rare
and both are commonly enclosed by later paramelaconite
which may pseudomorphose cuprite. Tenorite, which di-
rectly replaces paramelaconite is in places cut by
veinlets of later paramelaconite, which, in turn, shows
incipient alteration to a second generation of tenorite.
The atacamite, which occurs as large bladed crystals,
commonly is replaced by twinned aggregates of paratacamite
crystals. Nantokite occurs as microcrystalline material
that embays the paratacamite; nontokite was not observed
as a direct replacement product of atacamite." (12)

In his second article describing the Algomah minerals
he states that:

"The matrix of the specimen contains small blebs
of cuprite which are ringed by tenorite and then
chrysocolla." (13)

This description is very similar to that of Koenig
(1902) when he named the copper oxide ”mineral"
melanochalcite:

"The nodules' nucleus is formed by granular cuprite,

with occasional druses, the later lined with octahedral
crystals. This kernel is surrounded by a zone of pitchy-

12) Williams, S. A., op. cit., 1962a, page 111.

13) Williams, S. A., "Paramelaconite and Associated Minerals
from the Algomah Mine, Ontonagon County, Michigan",
American Mineralogist, Volume 47, 1962b, page 778.

 

 

 

36

black mineral, a few millimeters in thickness. Upon
this follows a banded green zone of chrysocolla and
malachite." (l4)

Melanochalcite was later shown by Hunt and Krauss
(1916) to be essentially a mixture of tenorite, chryso-
colla, and malachite.

The concentric arrangement of minerals noted by
Williams at Algomah was studied by the author in polished
section. A pitchy—black material was noted in some in-
stances between the tenorite and chrysocolla. This
material appears to have the properties of melanochalcite
or "copper pitch ore" as described by previous workers.
Therefore, a chemical analysis was performed on a sample
of this pitchy material that was separated from the other
ore minerals under the microsc0pe. The results of this
analysis are included in Figure 8 as column 8. This
analysis indicates that the ore mineral mixture
melanochalcite is present at Algomah as would be eXpected,
and microscopic examination indicated that it forms an
appreciable amount of the ore minerals. Perhaps, since
he makes no mention of such a mixture being present,
Williams has assigned melanochalcite to what he calls
"massive paramelaconite”.

The chemical analysis of the melanochalcite from

14) Koenig, G. A., "On the New Species Melanochalcite and
Keweenawite", American Journal g: Science, Series 4,
Volume 14, 1902, page 40 .

 

37

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SAMPLE 4 I

OXIDE l 2 3 4 5 6 7 8
8102 29.51 17.95 7.80 4.31 24.64 5.75 14.65
A120} 3.10 6.07
Fe203 .64 50.85 .07 .22 4.00 1.73 4.40
FeO .27
GuO 84.22 12.12 76.88 88.94 28.60 33.68 62.30 67.22
CaO .36 .84 Trace
ZnO .25 I,41 .12 8.40 Trace Trace
MnO .28 21.20 19.19 .04.
MgO Trace
Na20 1.05
K20 .21
H20 6.99 20.55 7.71 4.48 8.40
002 5.17 7.17 1.94
Insol. 22.80
Ignit. 13.70 17.76
TOTAL 100.78101.47 100.04 99.85 100.94 99.85

 

 

 

 

 

 

 

 

 

 

 

Figure 8. Chemical Analyses of Selected Samples of Melanochal-
cite. Columns 1-7 Material From Southwest United
States. Column 8 was Added by the Author Using
Algomah Material. (15)

15) Guild, F. N., "Copper Pitch Ore”, American Mineralogist,
Volume 14, 1929, page 315.

 

 

38

Algomah has a rather high percentage of aluminum and
sodium when compared with the analyses from other areas.
This may be the result of copper mineralization replacing
a sodium-aluminum zeolite vesicle filling.

The only other addition that can be made to the work
of Williams concerns the mineralogy of the flow top. In
a number of instances chrysocolla has replaced plagioclase
lathe in the rock. Schwartz (1934) states that this is a
common occurrence in oxidized copper deposits of this

type.
Interpretation

There are a number of factors which must be con-
sidered in interpreting the results of the present study
of the Algomah mine. These factors are: (1) reversal of
the normal plagioclase composition trend in a lava flow,
(2) the unique mineralogy present, (3) the extreme
leaching of the Jacobsville sandstone, and (4) the
proximity of the Keweenaw fault and the isolation of a
segment of the Algomah flow by the fault.

Since the Keweenaw lava flows are not oceanic, the
spilitization of the plagioclase in the flow tops is
indicative of post consolidation effects, probably
closely associated with the copper mineralization.
Studies by the writer of the Greenstone flow at Phoenix,

Michigan, which is noted for its lack of copper mineral-

 

39

ization, indicates that here the plagioclase is calcic

at the base and that it shows the normal tendency to
become more sodic towards the central portion of the

flow. Therefore, the spilitization of the plagioclase

in the flow tops tends to indicate that copper mineral-
ization was associated with fluids containing considerable
sodium, since the copper mineralization is essentially
localized in the flow tops where spilitization occurs.

The presence of chlorides in the suite of supergene
copper minerals at Algomah indicates that there must have
been appreciable amounts of chlorides in the water. Mine
waters of the Keweenaw are noted for their high concentra-
tions of chlorides. However, the chloride concentration
at Algomah did not have to be excessive since higher
partial pressures of oxygen present during the supergene
alteration greatly expanded the copper chloride stability
field as shown by Williams (1962a). These facts indicate
that the supergene copper deposition was from sodium
chloride rich waters.

A possible, yet little considered mechanism involving
Precambrian salt deposits in the vicinity of the magma
chamber for the deposition of Keweenawan native copper
Would easily account for the presence of appreciable
concentrations of sodium and chloride ions in the vicinity
of the copper deposits. Trow (1966) indicates that

reactions of the following nature may possibly explain

 

40

what would take place if silica rich hydrothermal solu-
tions, containing sodium chloride from a Precambrian
salt bed were to interact with basic rocks containing
a mineral or minerals such as cupiferous olivine.
(l) Halite-+ Silicfln + Cupiferous Olivine + Labradorite——+
lONaCl llSi Fe-Cu-8104 lONaAlsi 08
. lOCaAlQSEBOa

Ferric Chloride + Cuprous Chloride Complex + Quartz
FeCl; Ou012 23102

Albite + Calci + Aluminum +’ Chloride
2ONaAlSi308 100a+ 10Al+ 501-

(2) F3013+ 3H20 ————> F6203 + 3H01

The albite and hematite would be left in the under-
ground magma chamber and solutions containing NaCl, CuCle:
Ca 2, Al 3, Cl', and 3102 then moved up the fault channel-
way to react and deposit the copper in the flow tops by
cooling, decrease in pressure, and dilution by ground
water. The various ions present would aid in the forma-
tion of quartz, chlorite, epidote, pumpellyite, and
clinozoisite in the wall rock, along with spilitization
of the plagioclase present. The calcium ions eliminated
during spilitization could very possibly account for the
calcite which is so common in the copper mineralized flow
tops. In addition, such a mechanism would account for
the presence of chloride rich mine waters. A variation
of this mechanism suggested by Davidson (1965) would call

for sodium chloride to be carried down to the magma

 

41

chamber from above by deep circulating brines.

Supergene mineralization at Algomah also bears
consideration. A wedge of the Algomah flow is isolated,
since the permeability of the flow top is much greater
than that of the basalt, and thrust to the surface by
the Keweenaw fault in the area studied. Therefore,
considerable surface water charged with carbon dioxide
was available to mingle with the chloride rich waters
which were held in the isolated flow t0p. Under such
conditions cupric oxides can form native copper via cuprite
if the log of the partial pressure of oxygen is greater
than -37.9. This partial pressure is within that of normal
surface water. If cuprite were to persist metastably
under such oxygen pressures the field of the copper
chlorides would be expanded so that they would form under
the Algomah conditions. Under surface conditions of high
partial pressure of oxygen and a high partial pressure
of carbon dioxide of 10"3‘5 malachite would form. The
copper silicates here could have resulted by silica
precipitation because of the presence of the electrolytes.

To interpret fully the supergene mineralization at
Algomah it is necessary to study the inter-relations in
the copper systems such as C02 - Cl2 - 02, 002 - 012 -

02 - $102, which is beyond the scope of this paper. The
hypothesis of copper being carried as a cuperous chloride

complex also needs laboratory and thermodynamic study

 

 

42

which also exceeds the breadth of this thesis.

 

 

BIBLIOGRAPHY

Algomah Mining Company, Algomah Mining Company Report,
1910.

Butler, B. S., and Burbank, W. S., The Co er Deposits
of Michi an, Professional Paper 14 , United States
Geological Survey, Washington D. 0., 1929.

Coombs, D. S., "The Pumpellyite Mineral Series",
Mineralogical Magazine, Volume 30, 1953, pages 113-
135.

Davidson, 0. F., "A Possible Mode of Origin of Strata-
Bound COpper Ores" , Economic Geology, Volume 60,
1965, pages 942-954.

Deer W. A., Howie, R. A., and Zussman, J., Ag Intro-
duction to the Rock- Forming Minerals, John Wiley
and Sons, New York, 1966.

Frondel, Clifford, "Paramelaconite: A Tetragonal Oxide of
Copper" , American Mineralogist, Volume 26, 1941,
pages 657-672.

Carrels, Robert, Mineral Eguilibria, Harper and Brothers,
New York, 1960.

Guild, F. N., "Copper Pitch Ore" , American Mineralogist,
Volume 4, 1929, pages 313- 318.

Hamblin, W. K., The Cambrian Sandstones of Northern
Michigan, Michigan Geological Survey, Lansing,
Michigan, 1958.

Hopper, W. E., "Michigan Copper Industry, 1914", Mineral
Resources of Michi an, 1214, Publication 19, Series
16, Michigan Geological and Biological Survey,
Lansing, Michigan, 1915.

Hopper, W. E., "Michigan Copper Industry in 1915", Mineral
Resources of Michigan, 12 5, Publication 21, Series
17, Michigan Geological and Biological Survey,
Lansing, Michigan, 1916.

HOpper, W. E., "Michigan Copper6 Industry in 1916", Mineral
Resources of Michigan, m2 Publication 24, Series
20, Michigan Geological and Biological Survey,
Lansing, Michigan, 1917.

43

 

44

HOpper, W. E., "Michigan Copper Industry in 1917", Mineral
Resources 2; Michigan, 1917, Publication 27, Series
22, Michigan Geological and Biological Survey,
Lansing, Michigan, 1918.

Hore, R. E., "The Copper Industry of Michigan", Mineral
Resources g£_Michi an, 1210, Publication 8, Series
, Michigan Geological and Biological Survey,
Lansing, Michigan, 1912. '

Hore, R. E., "Michigan Copper Industry in 1912", Mineral
Resources Lf Michigan, 1212, Publication 13, Series
10, Michigan Geological and Biological Survey,
Lansing, Michigan, 1913.

Hore, R. E., "Michigan Copper Deposits, Mineral Resources
Lf Michigan, L214, Publication 19, Series 16,
Michigan Geological and Biological Survey, Lansing,
Michigan, 1915.

Hunt, W. F., and Krause, E. H., "Note on the Variable
Composition of Melanochalcite“ , American Journal
Lf4Science, Series 4, Volume 41,1916,pages 211-
21

Kennedy, George 0., "Some Aspects of the Role of Water
in Rock Melts', Crust Lf the Earth, Special Paper
62, Geological Society offi America, 1955, pages
489‘ 501 o

Keranen, Mr. Reino, Personal Communication, 1966.

Koenig, G. A., "On the New Species of Melanochalcite and
Keweenawite", American Journal of Science, Series 4,
Volume 14,1902, pages 4543416."

Lampi, Mr. Urho, Personal Communication, 1966.

Lane, Alfred C., The Keweenaw Series Lf Michigan, Publi-
cation 6, Series 4, Michigan Geological and Bio-
logical Survey, Lansing, Michigan, 1909.

Martin, Helen, The Centennial Geological __p_ of the
’Northern Peninsula Lf Michigan, Publication“ 39.
Series 33, Michigan” Geological Survey, Lansing,
Michigan, 1936.

 

Martin, Helen, and Straight, Muriel, An Index Lf Michigan
Geology, Michigan Geological Survey, Lansing,
Michigan, 1955

 

 

45

O'Meara, James, Personal Communication, 1966.

Palache, C., Barman, H., and Fronde1,C., Lhe System
p§_Mineralo , Volume I, John Wiley and —Sons,
New York, Seventh Edition, 1944, pages 507-511.

Schwartz, G. M., "Paragenesis of the Oxidized Ores of
Copper", Economic Geology, Volume 29, 1934,
pages 55- 7 .

Spiroff, K., Geology 2; the Firesteel River Area, Open
file report, Michigan Geological Survey, Lansing,
Michigan, 1942.

Stevens, Horace J., The Copper Handbook, Published by
the author, Houghton, Michigan, Volume 10, 1911.

Trow, Dr. James, Personal Communication, 1966.

Van Rise, 0. R., and Leith, C. K., The Geology Lf the
Lake Superior Re ion, Monograph 52, United States
Geological Survey, Washington, D. 0., 1911.

Williams, S. A., "Stability Relations and Paragenesis of
Copper Oxides and Chlorides at Algomah Mine,
Ontonagon County, Michigan," Economic Geology,
Volume 57, 1962a, pages 111-113.

Williams, S. A., "Paramelaconite and Associated Minerals
from the Algomah Mine, Ontonagon County, Michigan",
American Mineralogist, Volume 47, 1962b, pages 778-
779.

Zinn, Dr. Justin, Petrography Lf the Keweenawan Lava
Flows Lf Michigan, M.S. Thesis at Michigan College
of Mining and Technology, Houghton, Michigan, 1930.

Zinn, Dr. Justin, Personal Communication, 1966.

 

APPENDIX A

Location of Diamond Drill Holes

46

 

 

 

 

 

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is

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:74 on 1': C

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APPENDIX B

Algomah Diamond Drill Core Information

48

 

49

"Two diamond drill holes: viz: No.1 and No.2 were
put down on the line of the shaft, one of these cutting
the lode at a depth of 500 feet and the other at 800
feet. Both showed the lode from thirty to forty feet
thick, but no native copper was seen in the cores from
this lode. No. 2 hole cut an amygdaloidal bed about 400
feet above the main lode from which very little solid core
was taken, but the cuttings showed considerable fine
copper, and several nuggets of native COpper were obtained.
Two more diamond drill holes: viz: No. 3 and No. 4, were
put down immediately adjoining the Lake Mine boundary.
They both out the Lake lode but no native copper was found
in the cores. No. 3 showed some copper ore similar to
that found at the Algomah shaft indicating a connection
between the lodes. No. 5 drill hole is now being put
down at a point shown on the accompanying maps, which
also show the location of other drill holes and the
shaft." (16)

"In addition to the work at the shaft, exploration
has been carried on during 1911 on other parts of the
property by diamond drilling. Two vertical holes were
put down as far as possible, No. 5 to 2,241 feet and

No. 6 to 2,538 feet. There are several lodes cut in

155 Algomah Mining Company Annual Report, 1910, page 2.

 

50

No. 6 hole, one at 2,090 feet, 2,090 to 2,119 feet being

particularly promising." (l7)

17, More, R. E., "The Copper Industry of Michigan", Mineral
Resources 2; Michigan, 1210, Publication 8, Series
6: Michigan Geological and Biological Survey, Lansing,
Michigan, 1912, pages 67-68.

 

 

MICH GQN S‘MTEUIV LIBRQ

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