GEOLOGICAL SURVEY CIRCULAR 842 

The Potential for 

Diamond-Bearing Kimberlite in 

Northern Michigan and Wisconsin 

Prepared in cooperation with the 

Geological Survey Division, 

Michigan Department of Natural Resources 

The Potential for 

Diamond-Bearing Kimberlite in 

Northern Michigan and Wisconsin 

By W. F. Cannon and M. G. Mudrey, Jr. 

GEOLOGICAL SURVEY CIRCULAR 842 

Prepared in cooperation with the 

Geological Survey Division, 

Michigan Department of Natural Resources 

Description of a kimberlite pipe and 

possible cryptovolcanic structures and 

a discussion of the possibility that 

kimberlites in Wisconsin and Michigan 

might be the source for drift diamonds 

in Wisconsin 

Washington 1981 
United States Department of the Interior 

JAMES G. WATT, Secretary 

Geological Survey 

Doyle G. Frederick, Acting Director 

Library of Congress catalog-card No. 81-600130 

Free on application to Distribution Branch, Text Products Section, 

U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 
Abstract --------------------------------------- Introduction ___________________________________ _ 

Diamond discoveries in Wisconsin ------------------

Eagle, Waukesha County----------------------

Plum Creek, Pierce County ___________________ _ 

Saukville, Ozaukee County ____________________ _ 

Kohlsville, Washington County (Theresa diamond) __ 

Oregon, Dane County -------------------------

Burlington, Racine County ---------------------

Collins, Manitowoc County ---------------------

Why no finds since 1913? --------------------------

The Lake Ellen kimberlite -------------------------

CONTENTS 

Page 

1 Possible cryptovolcanic structures _________________ _ 

1 Glover Bluff structure ------------------------- 1 Structures near Pelkie, Michigan _______________ _ 

1 Limestone Mountain-----------------------

3 Sherman Hill ----------------------------- 4 Areas of disturbed Jacobsville Sandstone _____ _ 

4 Brule River outlier ---------------------------

4 Possible relationship between cryptovolcanic struc4 tures and kimberlite -----------~----------------

4 Do Wisconsin drift diamonds have a local source ______ _ 

4 Exploration for kimberlite _______________________ _ 

5 References cited --------------------------------

ILLUSTRATIONS 

Page 

7 

7 

9 

9 

10 

10 

10 

10 

11 

14 

14 

Page 

FIGURE 1. Index and location map of Wisconsin and northern Michigan ------------------------------------------ 2 

2. Photograph of the Saukville and Burlington diamonds----------------------------------------------- 3 

3. Magnetic map of the Lake Ellen kimberlite area---------------------------------------------------- 6 

4. Magnetic and gravity maps of the Glover Bluff disturbed area----------------------------------------- 8 

5. Geologic map of the Pelkie, Michigan, area--------------------------------------------------------- 9 

6. Idealized cross section of a kimberlite pipe--------------------------------------------------------- 11 

7. Map of area and magnetic and gravity profiles across the Lake Ellen kimberlite--------------------------- 13 

III 

The Potential for Diamond-Bearing Kimberlite in 

Northern Michigan and Wisconsin 

By W. F. Cannon and M.G. Mudrey, Jr. 1 

ABSTRACT 

Between 1876 and 1913, diamonds were found in at least 

seven localities in southern and central Wisconsin. All were 

found in Pleistocene glacial deposits or Holocene river gravel. 

The bedrock kimberlite source for the diamonds is unknown but 

has been presumed to be in northern Canada, the only area 

north of Wisconsin previously known to contain kimberlites. 

Recently, a kimberlite pipe, here named the Lake Ellen kimberlite, has been found in Iron County, Michigan. That find suggests the possibility that drift diamonds in Wisconsin have come 

from a more local source--kimberlites in northern Michigan and 

Wisconsin. 

The Lake Ellen kimberlite is very poorly exposed, but a 

strong positive magnetic anomaly indicates that it is roughly circular in plan and about 200m in diameter. Although the kimberlite is entirely surrounded by Precambrian rocks, it contains 

abundant inclusions of fossiliferous dolomite, probably from the 

Ordovician Black River Group that overlay the area when the 

kimberlite was intruded. The post-Ordovician age of the 

kimberlite leads us to suspect that other possible cryptovolcanic 

structures in Paleozoic rocks in the region were formed over 

kimberlite pipes that are not yet exposed by erosion. Such structures include Limestone Mountain and Sherman Hill, in 

Houghton and Baraga Counties, Michigan; Glover Bluff, in Marquette County, Wisconsin; and possibly an area along the Brule 

River south of Iron River, Michigan. 

No diamonds are known in the Lake Ellen kimberlite, but it 

has not been adequately sampled. The cryptovolcanic structures 

could not be the source of the drift diamonds in Wisconsin because even if the structures are caused by kimberlites, those 

kimberlites have not yet been exposed by erosion. 

Elsewhere in the world, kimberlite is seldom found as a single 

isolated body; clusters of bodies are more common, and the 

presence of one kimberlite implies that others may exist nearby. 

The discovery of additional kimberlites may be very difficult 

because of the extensive cover of glacial drift and the typical 

small size of kimberlite bodies. If all are magnetic, they might be 

found by detailed aeromagnetic surveys. However, the magnetism of the Lake Ellen kimberlite appears to be caused by secondary magnetite formed during serpentinization of olivine, so 

an unserpentinized kimberlite may not be strongly magnetic. 

We suggest that one or more diamond-bearing kimberlites 

may exist in northern Michigan or Wisconsin, but the discovery 

of such bodies is unlikely unless a very thorough search is undertaken. 

1 Wisconsin Geological and Natural History Survey. 

1 

INTRODUCTION 

At least seven diamond discoveries were made in 

Wisconsin between 1876 and 1913. All diamonds 

were found in Pleistocene glacial deposits or Holocene river gravel. The diamonds must have been 

eroded from one or more kimberlite bodies because 

kimberlite is the only primary bedrock source of 

diamonds. It has generally been presumed that 

drift diamonds in Wisconsin were carried to their 

discovery sites by glaciers that eroded them from 

the nearest known kimberlites in northern Ontario, 800 km (kilometers) (500 miles) or more 

away. 

In this paper, we describe a newly discovered 

kimberlite in northern Michigan and suggest 

several other areas where kimberlites may exist in 

the subsurface. We discuss the possibility that drift 

diamonds in Wisconsin were eroded from kimberlites in Wisconsin or Michigan. 

DIAMOND DISCOVERIES IN WISCONSIN 

Verified discoveries of diamonds have been made 

at seven localities in Wisconsin (figs. 1, 2). Other 

diamonds have been reported, but they were probably not from Wisconsin and are only briefly 

discussed in the following sections. 

EAGLE, WAUKESHA COUNTY 

The first documented diamond discovery in 

Wisconsin was made during the digging of a well in 

1876 by Charles Wood, who was a tenant on the 

farm of Tom Devereaux near Eagle in 

southwestern Waukesha County (Hobbs, 1899; 

Vierthaler, 1958; Olson, 1953; Alden, 1918). This 

first important Wisconsin diamond discovery is 

recorded in the files of the Milwaukee County Circuit Court and the Wisconsin Supreme Court. The 

digging passed through 10-15 m (meters) (33-44 
0 

0 

100 MILES 

100 KILOMETERS 

EXPLANATION 

o POSSIBLE CRYPTOVOLCANIC 

STRUCTURES 

1. GLOVER BLUFF 

2. STRUCTURES NEAR PELKIE 

(INCLUDES LIMESTONE MTN 

AND SHERMAN HILL) 

3. BRULE RIVER OUTLIER 

\t DIRECTION OF ICE MOVEMENT 

NEAR DIAMOND LOCALITIES 

+ DRIFT DIAMOND LOCALITIES 

1. EAGLE, WAUKESHA COUNTY 

2. PLUM CREEK, PIERCE COUNTY 

3. SAUKVILLE, OZAUKEE COUNTY 

4. KOHLSVILLE, WASHINGTON COUNTY 

5. OREGON, DANE COUNTY 

6. BURLINGTON, RACINE COUNTY 

7. COLLINS, MANITOWOC COUNTY 

___ EXTENT OF ICE LOBES 

a. GREEN BAY LOBE 

b. LAKE MICHIGAN LOBE 

FIGURE 1.-Map showing the location of diamond discovery sites, marginal moraines of major ice lobes and direction 

of ice movement, possible cryptovolcanic structures, and the Lake Ellen kimberlite. 

2 
~---12mm---~ 

-

FIGURE 2.- The Saukville diamond (left) and Burlington diamond (right). 

ft) of clay and then through loose gravel of approximately 5 m (16ft), when a 2-m (7-ft) layer of a hard 

yellow material was penetrated. A hard stone of 

unknown identity was recovered. Clarissa Wood 

took this peculiar pebble to Col. Samuel B. Boynton, a jeweler in Milwaukee. Boynton identified the 

stone as "topaz" and purchased it for $1.00. Once 

the true identity of the diamond was disclosed, 

Clarissa offered to buy the diamond back, first for 

$1.10 and later for $1.50. Boynton refused, and 

Mrs. Wood sued. The Supreme Court ruled that 

the stone was Boynton's because he had believed it 

was topaz when he bought it. He later sold the 

stone to Tiffany & Company of New York for $850. 

He had offered the stone to the State of Wisconsin 

for $1,000, but his offer was declined. The crystal, 

originally known as the Waukesha diamond and 

later as the Eagle diamond, is a warm yellow color 

and weighs 16.25 carats. 

Boynton formed a diamond-mining company and 

later, in 1883, claimed to have discovered more 

diamonds, along with other precious and 

semiprecious stones, according to Silvers (1978) 

writing in a recent issue of The Milwaukee Journal. 

3 

A mining boom resulted. G. F. Kunz, a noted gemnologist, visited the area and noted that the newly 

found stones differed in size, color, and number of 

crystal faces from the original find. He identified 

the new stones to be of African origin, and the bottom fell out of the great Eagle diamond rush. 

J. P. Morgan, the late 19th century financier, 

purchased the Eagle diamond from Tiffany's and 

ultimately donated the gem to the American 

Museum of Natural History in New York City. The 

stone was on public display at the Museum until the 

evening of October 29, 1964, when the Museum 

was broken into and the Eagle diamond and other 

gems stolen. On February 8, 1965, Jack Roland 

Murphy, a Florida beach boy, also known as 

"Murph the Surf," and two colleagues, admitted 

the theft, but the stone was not recovered. 

PLUM CREEK, PIERCE COUNTY 

In the period 1880-1887, G. H. Nichols and two 

colleagues prospected for gold along Plum Creek 

in Pierce County. While sluicing for gold, one of 

the workmen detected a bright stone, which 
proved to be a diamond. Over several years, this 

group found about 10 small diamonds there (Kunz, 

1892, p. 337). 

In 1906, another discovery of diamonds was 

reportedly made downstream from the earlier find. 

A company was immediately organized and stock 

advertised extensively in Chicago. Samuel W eidman of the Wisconsin Geological and Natural 

History Survey contended that this was a bogus 

find and had been staged (letter to G. F. Kunz on 

December 15, 1907). 

SAUKVILLE, OZAUKEE COUNTY 

Near the Milwaukee River, about 4 km (2.5 mi) 

north of Saukville, a diamond was discovered by 

Conrad Schaefer in 1881. It was not identified as a 

diamond until1896 (Alden, 1904). This diamond is 

6.57 carats and about 12 mm (0.5 in.) in diameter. 

The last known owner is Bunde and Upmeyer Co., 

in Milwaukee (Vierthaler, 1958). 

KOHLSVILLE, WASHINGTON COUNTY 

(THERESA DIAMOND) 

The Theresa diamond created the greatest interest in the possibility of diamonds in Wisconsin. 

It was discovered in 1888 by Louis Endlick of 

Kohlsville on or near the Green Lake moraine. The 

stone weighed 21.5 carats; it is the largest diamond 

on record ever recovered in the State and the fifth 

largest in the United States (Alden, 1918; 

Sinkankas, 1959). 

This diamond was of further interest because of 

its uncommon color. One side of the crystal was 

colorless, whereas the other side was cream 

yellow. These two parts were separated by a flaw 

or distinct cleavage plane. The crystal was almost 

spherical. 

Shortly after the Theresa diamond was 

discovered, the Endlick family moved away from 

Kohlsville, taking the diamond with them. Later 

inquiries regarding the whereabouts of the diamond were fruitless until an article on the subject 

was published in a newspaper and read by a son of 

Mr. Endlick (Olson, 1953). He explained that the 

family had moved to Kewaskum, Wis. In 1918, the 

Theresa diamond had been cut into 10 stones at a 

cost of $400. Total weight of the 10 stones was 9.27 

carats, divided as follows: 1.48 carats, 1.09 carats, 

0.97 carats, 0.96 carats, 0.95 carats, 0.85 carats, 

0.84 carats, 0.83 carats, and two stones weighing 

0.65 carats each. 

4 

OREGON, DANE COUNTY 

In 1893, a 4.0 carat diamond was discovered on 

the Charles Devine farm near Oregon on the 

Johnstown moraine in Dane County (Alden, 1918). 

It was later sold to Tiffany's for $50. Its present 

owner is not known. 

S URLINGTON, RACINE COUNTY 

In 1903, G. Pufahl recovered a diamond 

weighing 2.11 carats near Burlington, in Racine 

County (Alden, 1918). The last known owner is the 

Bunde and Upmeyer Co., in Milwaukee (Vierthaler, 1958). 

COLLINS, MANITOWOC COUNTY 

The Milwaukee Sentinel carried a short article 

on January 19, 1913, about Peter Zagloba of Collins, in Manitowoc County. Zagloba had passed 

away several days earlier. While examining his 

property, local farmers found several uncut 

diamonds in an old coffee pot. Zagloba was a hermit and spent his time digging into hillsides. This 

suggested that the diamonds might have come 

from gra.vel deposits in the Collins area. 

WHY NO FINDS SINCE 1913? 

The seven localities in Wisconsin yielded a total 

of 16 diamonds. All diamonds were found in 

Pleistocene. glacial deposits or Holocene river 

gravel. Although none of the discoveries was made 

by geologists and no further documented 

discoveries have been made since 1913, the 

Wisconsin diamond discoveries, in conjunction 

with discoveries in other Midwest States, argue 

that the diamonds did in fact come from the 

Midwest and do in fact provide evidence for 

kimberlite in the Midwest. 

A possibility exists that the finds may have been 

bogus. The diamonds could have been found 

elsewhere and subsequently brought to Wisconsin. 

Examples of such fraudulent discoveries include 

the second Eagle discovery and the second Plum 

Creek discovery just discussed. In both cases, 

almost immediately after discovery of the 

diamonds, shares of stock were offered for sale. 

Kunz and Weidman were able to demonstrate that 

these two finds were not in situ but rather were 

salted. 

Similarly, the lack of strong field control at the 

seven discovery localities in Wisconsin leaves open 

the possibility that factors other than geologic 

processes were agents in their discovery. Gunn 
(1968) summarized the known diamond discoveries 

in the Midwest. In order of number of diamonds 

found, Indiana lists 34; Illinois, 25; Wisconsin, 16; 

Michigan, 3; and Ohio, 3. This tends to suggest 

that diamonds are geologically distributed 

throughout the Midwest. The paucity of discoveries in Ohio and Michigan suggests sources west of 

Lake Michigan. 

In Wisconsin at least, none of the diamond 

discoveries was adequately documented at the time 

of discovery. The geologic details of the occurrences are not known and can only be inferred 

from the geology in the area of the discoveries. 

Most were found at shallow depths and presumably 

in the youngest glacial material. Similar relations 

are known for the discovery of drift copper nuggets in southeastern Wisconsin (Clayton, oral commun.,· 1980). The drift copper has a source in the 

upper peninsula of Michigan and is spatially close 

to the Lake Ellen locality discussed later. 

No effort was made at the time of the original 

diamond discoveries to exploit them, suggesting 

accidental finds offering little possible financial 

return. The Kohlsville diamond may be a typical 

example, in that the stone was cut and mounted for 

members of a family, rather than sold. 

Why then have so few diamonds been found in 

the last 80 years? Brummer (1978) reported that 

most of the diamonds found in the upper midwest 

were located by prospectors panning or sluicing 

river gravels for gold, especially in Indiana. The 

Wisconsin diamonds were found by a prospector 

sluicing at Plum Creek and by enterprising 

farmers at the other localities. 

Since the last Wisconsin discovery in 1913, excavations in Pleistocene materials have continued. 

In recent years, nearly 30 million tons of 

Pleistocene sand and gravel have been produced 

annually for industrial use, and numerous excavations for buildings, utilities, and roadways have 

been constructed. Although machinery is commonly used, a significant percentage of hand labor is 

also used, and thus the chance of finding additional 

diamonds should be quite high compared with the 

era of the diamond discoveries. 

Why then, have no additional discoveries been 

made? 

The diamonds were found during the era of 

"gold" rushes. Although modern society 

remembers the rushes, few rushes have attracted 

the excitement of those in the 19th century. Since 

that time, rock hounds and mineral collectors have 

prowled pits, quarries, and streams for colorful 

stones, but no diamonds have been reported. Part 

5 

of the answer may lie in the story of the Eagle diamond, which sat unreported on a shelf for some 20 

years. Stones may well have been found in the past 

80 years, but their significance is poorly 

understood by the finder, and the stone rests on a 

shelf or in a box awaiting rediscovery. 

THE LAKE ELLEN KIMBERLITE 

A kimberlite pipe, here named the Lake Ellen 

kimberlite, has recently been discovered about 15 

km (10 mi) northeast of Crystal Falls, Mich., and 

about 1.5 km (1 mi) west of Lake Ellen, from which 

it derives its name. The kimberlite was apparently 

first recognized by William H. Spence and Klaus J. 

Schulz about 10 years ago during a mining company exploration project, but its existence and 

location have not been widely known, and it has 

not been described previously. 

The only two known exposures of the kimberlite 

are in the SW1/4 sec. 27, T. 44 N., R. 31 W. (fig. 3). 

They consist of low exposures of rubbly reddishbrown, highly weathered kimberlite along the 

roadbed of an abandoned logging road. The two exposures are about 120 m (390 ft) apart and provide 

a limit for the minimum dimension of the body. The 

exposed kimberlite is strongly magnetic. A 

magnetic survey of the area (Gair and Wier, 1956) 

defined an elliptically shaped positive magnetic 

anomaly about 180m (590ft) long in an east-west 

direction and 120 m (390 ft) wide (fig. 2). Gair and 

Wier did not know of the existence of the kimberlite (the logging road had not yet been constructed) 

and believed the magnetic readings were spurious, 

caused by magnetic boulders in glacial drift. 

However, the close spatial correspondence of the 

anomaly to exposures of magnetic kimberlite lead 

us to conclude that the anomaly is caused by the 

kimberlite and roughly defines the size and shape 

of the body. 

The kimberlite is intruded into volcanic rocks of 

the Hemlock Formation, a part of the Proterozoic 

X Marquette Range Supergroup. The weathered 

exposures of the kimberlite are heavily ironstained rubble consisting of fragments about 1 em 

(0.4 in.) in diameter. The material is soft enough to 

be dug with a shovel to a depth of about 0.5 m (1.5 

ft) below the surface, at which depth it becomes 

harder, although still largely rubbly and disaggregated, and in places somewhat gray, in contrast 

to the browner colors nearer the surface. The rubble fragments are a mixture of fine- to mediumgrained kimberlite and inclusions of a variety of 

other rocks. The kimberlite is composed of olivine 
SECTION 

CORNER 

0 

0 

R 31 W 

r.a\~'3 v~.,. 

o"~' ...... ,'/f 

It 

II 

\\ 

,, 

II 

I/ 

.~:~q OUTCROPS OF 

KIMBERLITE 

T 44 N 

2000 FEET 

500 METERS 

FIGURE 3.-Map showing the location of the Lake Ellen kimberlite and its magnetic expression. The magnetic data are from Gair 

and Wier (1956). Magnetic contours in the immediate area of the Lake Ellen kimberlite were drawn by W. F. Cannon in 1979 

from the original data. Contours in gammas. 

6 
(in part serpentinized), pyroxene, mica, garnet, 

and ilmenite, and fine-grained serpentine (?) 

matrix. 

Preliminary petrographic and analytical studies 

have been done by B. Carter Hearn, Jr., and Elaine 

S. McGee of the U.S. Geological Survey (written 

commun., 1980), and the following is their description of the kimberlite: 

Electron microprobe analysis of grains picked from a panned 

concentrate and from fragments of weathered kimberlite show 

the presence of typical kimberlite indicator minerals: chromian 

pyrope garnet, magnesian ilmenite, chromian diopside, and 

forsteritic olivine. 

Garnets of 1-5 mm size were sorted into 6 color groups (purple, pink, red, red-orange, orange, light orange) from which 3 to 

6 grains of each color group were analysed. Sixteen garnets 

classified as purple, red, and pink are pyrope-rich and 

chromium-rich. These 16 garnets form a tight cluster on a CaMg-Fe plot with a range of 67 to 75 percent Mg molecule and 12 

to 20 percent Ca molecule and have the following ranges of 

weight percent Cr20 3: 4.64-9.29 for purple garnets, 3.18-6.17 

for red garnets, and 1.72-3.43 for pink garnets. The ranges of 

MgO and Cr20 3 content are similar to those of garnet in garnet 

peridotite zenoliths and garnet xenocrysts, which occur in 

kimberlites in North America (Mitchell, 1979; Hearn and Boyd, 

1975; McCallum and others, 1975) and in Africa (Dawson and 

Stephens, 1975; Reid and Hanor, 1970). Ten red-orange, orange 

and light orange garnets are more iron-rich and more widely 

scattered on a Ca-Mg-Fe plot, and contain less than 0.79 weight 

percent Cr20 3• One red-orange and one orange garnet plot in 

the Mg-rich cluster of purple, red and pink garnets, but contain 

only 1.80 and 0.82 weight percent Cr20 3• The compositions of 

most red-orange, orange and light orange garnets fall into a 

compositional field which includes garnets from eclogites and 

granulites. 

Ilmenite grains are either single crystals or granular 

multicrystal aggregates up to 6 mm in size. Five single crystals 

and two aggregates form a tight cluster near 50 percent 

geikielite molecule (MgTi03) on a geikielite-ilmenite-hematite 

plot (MgTi03-FeTi03-Fe20 3). Weight percent of MgO ranges 

from 12.85 to 14.96 and is typical of ilmenites in North 

American and African kimberlites (Mitchell, 1973, 1977; Haggerty, 1975). 

Six analysed diopside grains 1 to 3 mm size are green to bright 

green, and contain 0.11 to 0.95 weight percent Cr20 3 and 0.87 

to 1.31 weight percent NazO. These ranges are typical of diopside xenocrysts, diopside in garnet lherzolite xenoliths 

(Stephens and Dawson, 1977), and diopside from spinel lherzolite xenoliths in kimberlite (McCallum and others, 1975). 

Al20 3 and Na20 are too low for typical eclogitic pyroxenes. CaO 

content of pyroxenes indicates relatively low temperatures of 

equilibration, 900 to 1,000°C according to the Davis and Boyd 

(1966) solvus. 

Olivine grains of 1-3 mm size contain 91 to 92 percent 

forsterite molecule, typical of kimberlitic olivines. 

A common type of inclusion in the kimberlite is 

buff, gray, and black dolomite. Fragments are as 

much as about 10 em ( 4 in.) in diameter and 

generally angular to subrounded. The dolomite is 

fossiliferous and may be derived from the Ordovician Black River Group that apparently overlay the 

area when the kimberlite was intruded, although 

7 

other stratigraphically higher Paleozoic carbonate 

units could also have provided the fragments. At 

present, we do not have an adequate fossil collection to determine the precise age of the fragments, 

but their Paleozoic age seems certain. Paleozoic 

strata have since been eroded away, except for 

scattered outliers of basal Paleozoic sandstone 

(Gair and Wier, 1956). The nearest exposures of 

the Black River Group are now about 60 km (36 mi) 

to the east, but the Black River Group could have 

been as little as 200 m (660 ft) stratigraphically 

above the present surface when the kimberlite was 

intruded. 

POSSIBLE CRYPTOVOLCANIC STRUCTURES 

Several small areas of disturbed Paleozoic rocks 

have been known in Wisconsin and northern 

Michigan for many years (fig. 1), but the cause of 

the disturbance is not known. Until the recognition 

of the Ordovician or younger age for the Lake 

Ellen kimberlite, no intrusive or major structural 

events of Ordovician or younger age were known 

in the region. We now suspect that these disturbed 

areas may be collapse features formed over buried 

kimberlite bodies. No intrusive rocks have been 

found at the surface in any of the disturbed areas. 

We know of no drill holes in the disturbed areas. 

GLOVER BLUFF STRUCTURE 

The Glover Bluff structure is an area of disturbed Cambrian and Ordovician strata in Marquette County, Wis. (fig. 1). The structure was 

mapped and described by Ekern and Thwaites 

(1930). The authors stated that the disturbed 

strata are exposed on three adjacent hills in the 

SW1

/4 sec. 3, T. 17 W., R. 8 E. (fig. 4). The area of 

the disturbance appears to be roughly circular and 

about 500 m (1,600 ft) in diameter. Because exposures are discontinuous, the complete structural 

pattern has not been determined, but Ekern and 

Thwaites showed the structure to be folded and 

complicated by several faults. The exposed disturbed strata range in age from the Cambrian 

Galesville Sandstone to the Ordovician Oneota 

Dolomite. The structure is complex but generally 

synclinal. Beds dipping as steeply as 30° are common, and locally bedding is vertical. The strata 

within the structure have been dropped at least 60 

m (200 ft) relative to their altitude in the surrounding undisturbed area, where they dip less than 1 o 

to the southeast. Outside of the structure Proterozoic rocks are at a depth of about 200m (650ft) 

below the surface. 
R7E R8E 89"30' 

.-------,~-.-,,---,---~----~----~--~7>--------~ «000' 

25 

13 

24 19 20 

~~ .g.~~ I I I I I 

• POINTS AT WHICH GRAVITY OBSERVATIONS WERE MADE 

BOUGUER GRAVITY MAP 

A 

R7E R8E 89"30' .--------,------,~--~-,--~--~r---~~-,--------~ «000' 

• POINTS WHERE MAGNETIC READINGS WERE TAKEN 

VERTICAL INTENSITY MAGNETIC MAP 

8 

0 3 MILES 

0 3 KILOMETERS 

FIGURE 4.-A, Bouguer gravity map showing the location of the Glover Bluff disturbed area (gravity data from Koenen, 1956). Contours in milligals. B, Ground magnetic map showing the location of the Glover Bluff disturbed area (magnetic data from Koenen, 

1956~ Contours in gammas. 

8 
A gravity and magnetic survey of the area was 

made by Koenen (1956). Part of his maps are 

reproduced in figure 4. The Glover Bluff structure 

is near the east end of a prominent west-trending 

positive magnetic anomaly and also is within the 

area of a positive Bouguer gravity anomaly. 

Koenen has calculated that both anomalies could 

be caused by a mafic plug at a depth of about 2 km 

(1.2 mi) below the surface. He proposed that the 

Glover Bluff structure could be caused by faulting 

and collapse during intrusion of the plug. 

STRUCTURES NEAR PELKIE, MICHIGAN 

Several anomalous disturbances of Proterozoic 

and Paleozoic strata are in Houghton and Baraga 

Counties near the town of Pelkie, Mich. (fig. 5). 

These may be cryptovolcanic features. 

I f- I 

LIMESTONE MOUNTAIN 

Limestone Mountain, in sees. 13, 14, 23, 24, T. 51 

N., R. 35 W., is an outlier of Paleozoic strata 

overlying the Proterozoic Jacobsville Sandstone. 

The Paleozoic rocks at Limestone Mountain, mostly dolomite and dolomitic limestone, form a prominent bluff that rises about 100m (330ft) above the 

surrounding gently rolling topography. The outlier 

is about 1.5 km (1 mi) long in a north-south direction and about 1 km (0.6 mi) wide. The Paleozoic 

strata generally dip gently to steeply centripetally 

inward; therefore, the gross structure is a doubly 

plunging syncline. 

The earliest detailed description of the area was 

by Case and Robinson (1914), who mapped the 

mountain and studied the paleontology to determine the age of the strata. They identified formaI 

SHERMAN -

Yj 

11 12 I ~HILL 8 9 

I ; 

I Pzu 

T 51 N 

I 8 

I 45~ 

14 13 I 18 17 16 

I 0 r- --, ' I I 

Yj 0 I _}'Pelkie ~ LIMESTONE -- I 70)_ 11 6DY 5~ 0 f7 =>>::..\ MOUNTAIN 0 I 0 0 ,..., 

oo~ooo~o· I 0 0 .. 0 uo ro::;~( 0>0 .... 0 I 

<\~ I ~ 23, 24 I 21 

~~~ 19 20 :E 

~~oh sl~ ulo 

zlu 0< '\ !I: I<.:) Yj 

26 25 (!)I;:; 30 29 28 ~< Oal 

:I: I 

I I 

R 35 W R 34 W 

0 1 MILE 

0 05 1 KILOMETER 

EXPLANATION 

~ Paleozoic rocks, undivided-Mostly 

Ordovician dolomite Contact-Approximately located 

~ Fault Jacobsville Sandstone-Reddish 

sandstone, conglomerate, shale c:;) Area containing outcrops 

6!l_ Strike and dip of bedding 

FIGURE 5.--Map showing the general geology of an area near Pelkie, Mich., including Limestone Mountain, 

Sherman Hill, and areas of disturbed Jacobsville Sandstone. Geologic data modified from Case and Robinson (1914) and Roberts (1940). 
tions ranging in age from Proterozoic to Late Ordovician in outcrops and also found talus 

fragments of rocks as young as Early Devonian 

that could not be found in outcrops. The area was 

remapped by Roberts (1940), whose detailed work 

confirmed the structures identified earlier by Case 

and Robinson. 

SHERMAN HILL 

Sherman Hill is in sec. 7, T. 51 N., R. 34 W., 

about 2 km (1.2 mi) northeast of Limestone Mountain (fig. 5). The area was included in the studies of 

Limestone Mountain by Case and Robinson (1914) 

and Roberts (1940). Like Limestone Mountain, it is 

an outlier of deformed Paleozoic rocks surrounded 

by Jacobsville Sandstone. Strata dip from about 5o 

to as much as 30° inward along a semicircular 

ridge, suggesting that a roughly conical depression 

about 0.5 km (0.3 mi) in diameter exists in the area, 

although its topographic expression is not as complete. The area was included in the studies of Case 

and Robinson (1914) and Roberts (1940). 

AREAS OF DISTURBED JACOBSVILLE SANDSTONE 

Several areas where the Jacobsville Sandstone 

has been disturbed and dips steeply were identified 

by Roberts (1940). Along the north, west, and 

south sides of sec. 17, T. 51 N., R. 34 W. (fig. 4), 

scattered small exposures of Jacobsville, consisting of reddish-brown sandstone and conglomerate, have dips ranging from 45° to 70°. In 

the rest of the region, the Jacobsville is generally 

nearly horizontal or locally has dips as steep as 

20°, apparently as initial dips on large-scale 

crossbedding. 

Exposures of the Jacobsville are widely 

separated, and there is no obvious topographic expression of structure, so the size and shape of the 

disturbed area is not known. 

BRULE RIVER OUTLIER 

An outlier of limestone about 10 m (33 ft) in 

diameter is exposed in the bed and banks of the 

Brule River on the Michigan-Wisconsin border, in 

sec. 27, T. 42 N., R. 35 W., about 8 km south of 

Iron River, Mich. (fig. 1). The limestone was first 

described by Allen (1910), who dated it paleontologically as Ordovician. It apparently lies on and 

is surrounded by Proterozoic X metavolcanic 

rocks. James and others (1968) described the 

limestone as "* * * light gray to tan, flaggy and irregularly bedded. The general attitude of bedding 

is probably horizontal, although, in the stream 

10 

bank, possibly because of slumping, some strata 

dip as much as 15° E." In July 1979, the outcrop 

could not be located, perhaps because of high water 

in the Brule River or slumping of the river bank. 

About 2 km (1.2 mi) northwest of the limestone exposure, basal sandstone (Cambrian?) of the 

Paleozoic section is exposed on hills about 50 m 

(160ft) higher than the limestone, suggesting that 

the limestone has been dropped down on the order 

of 100m (330ft) relative to surrounding Paleozoic 

outliers. 

We suggest that this could be a cryptovolcanic 

structure. Although the downdropping of the 

limestone could have been caused by faulting, 

faults having post-Ordovician throws of 100m (330 

ft) are not known in this region. The 15 o dip 

reported by James and others (1968) might be a 

true dip into a cryptovolcanic depression rather 

than a slump feature. 

POSSIBLE RELATIONSHIP BETWEEN 

CRYPTOVOLCANIC STRUCTURES AND 

KIMBERLITE 

The four areas of deformed Paleozoic rocks 

described have several features in common: 

1. All disturbances occurred in Ordovician or 

later time. At Limestone Mountain, the 

disturbance was apparently of Devonian or 

younger age. 

2. All disturbed areas are relatively small, at 

most about 1.5 km (1 mi) in diameter and are 

surrounded by apparently undisturbed rocks. 

At least three of the areas are roughly circular. The fourth, the Brule River outlier, is 

not adequately exposed to determine the 

shape or size of the disturbed zone. 

3. The three well-exposed areas are synclinal or 

basinal structures characterized in general 

by moderate to steep inward dips and local 

complications caused by faulting and smallscale folding. 

4. Strata in all structures have dropped at least 

50 m (160ft) below their normal altitudes in 

surrounding undisturbed areas. 

The area of disturbed Jacobsville Sandstone near 

Pelkie is also similar in that generally flat-lying 

sedimentary rocks are locally highly deformed. 

Lack of outcrops, topographic expression of structure, and marker beds do not permit the determination of the size and shape of the disturbed 

area or the amount of downdropping that might 

have occurred. The close proximity to Limestone 

Mountain and Sherman Hill, however, suggest a 

common origin for all three structures in Devonian 

or later time. 
We suggest that all five disturbed areas could be 

cryptovolcanic structures formed over kimberlite 

pipes. Although this is certainly not proved with 

available data, we offer the suggestion as a starting point in the search for kimberlites. 

Alternatively, the disturbed areas might be explained as (1) solution collapse features or (2) 

grabens related to faults in the Proterozoic basement. Alternative 1 seems unlikely because, for 

most features, no soluble rock is known 

stratigraphically beneath the disturbed strata. 

Alternative 2 is possible, but we know of no faults 

in the region having well-documented postOrdovician throws of 100m (330ft) or more. Also, 

the circular, rather than linear, nature of the 

downthrown areas make this alternative seem 

unlikely. 

We feel that a more likely explanation is that the 

disturbed areas are collapse features formed over 

kimberlite pipes. Figure 6 shows an idealized cross 

section of a kimberlite pipe in which massive 

kimberlite at depth grades upward into a breccia 

with kimberlite matrix and, still higher, grades into a zone of downfaulted and downfolded sedimentary rocks. Various levels of erosion of such structure could account for the Lake Ellen kimberlite 

and all the other areas of disturbed strata described. The Lake Ellen kimberlite would represent the deepest level of erosion, at which the 

kimberlite containing downdropped xenoliths of 

Paleozoic rocks is exposed. Limestone Mountain, 

Sherman Hill, and the Brule River outlier would 

represent higher levels of erosion, which have exposed subsided Paleozoic strata above the main 

kimberlite intrusion. Glover Bluff would be a still 

higher level of erosion, at which Paleozoic strata 

are downdropped and deformed but erosion was 

not deep enough to expose Proterozoic rocks or an 

underlying intrusion. 

DO WISCONSIN DRIFT DIAMONDS HAVE A 

LOCAL SOURCE? 

In the early 1900's, shortly after the discovery of 

diamonds in glacial deposits of Wisconsin, it was 

generally assumed that the bedrock source for the 

diamonds was far from Wisconsin, probably in 

northern Ontario. Six of the seven diamond occurrences in Wisconsin are in the marginal moraines 

of the Green Bay and Lake Michigan ice lobes (fig. 

1). Hobbs (1899) concluded on the basis of the 

shape and character of the diamonds, and known 

glacial transport directions, that the ultimate 

source of the diamonds was probably in the James 

FIGURE 6.-Idealized cross section of a kimberlite pipe and overlying disturbed strata. 

Dashed lines suggest the stages of erosion of various features mentioned in the text. 

11 
Bay lowland of northern Ontario, at least 800 km 

(500 mi) distant. The existence of kimberlite in the 

James Bay lowland lends support to this idea. 

Hobbs' conclusions seem to have persisted over the 

years (see, for instance, Gunn, 1968), and the 

possibility of a kimberlite source in Wisconsin or 

northern Michigan has been given little consideration. However, we feel now, that in view of the occurrence of one kimberlite in Michigan and the 

suspicion that several other disturbed areas may be 

related to kimberlites, diamond-bearing 

kimberlites could exist in Wisconsin and Michigan. 

The fact that diamonds have been found at seven 

or more localities in Wisconsin, all by accidental 

discoveries, suggests that diamonds may be a 

widespread, although certainly very rare, constituent of drift in Wisconsin. To our knowledge, no 

concerted effort to find diamonds in drift has been 

made, and we suspect that such a search could 

yield substantially more diamonds. That is, the 

diamonds already found are almost surely only a 

very small sampling of a much larger number that 

may be scattered widely through the drift. 

Although glacial ice is known to transport 

material for hundreds of kilometers and could have 

carried the drift diamonds in Wisconsin from 

Canada, several factors suggest that a more local 

source is likely. 

Glacial drift commonly is composed largely of 

material eroded from nearby bedrock that has been 

transported only a few kilometers or less and 

material from very distant sources forms a minor 

part of the drift. This is clearly demonstrated in 

many areas of Wisconsin 'and Michigan. Although 

it has recently been shown (Gwyn and Dreimanis, 

1979) that heavy mineral assemblages may reflect 

bedrock sources 50-150 km (30-100 mi) away, we 

question whether a kimberlite source at least 800 

km (500 mi) from Wisconsin is adequate to explain 

the number of diamonds that probably exist in drift 

in Wisconsin. 

As glaciers transport material from its source, 

the material tends to become progressively diluted 

as it becomes mixed with rocks from other areas. 

Diamonds, which would be a very small fraction of 

the drift, even at their bedrock source, may 

become so diluted through 800 km (500 mi) or more 

of transport that we question whether a source as 

remote as northern Ontario is adequate to account 

for the large number of diamonds that probably exist in the drift in Wisconsin. 

In the James Bay lowland, the predominant rock 

type is Paleozoic carbonate rock. Paleozoic rock 

fragments are very rare in the drift on Proterozoic 

terranes in northern Michigan and Wisconsin. It 

seems, therefore, that the principal bedrock type 

from the James Bay lowland makes very little contribution to drift in the study area. We feel that the 

rare kimberlites in the lowland are very unlikely to 

contribute diamonds to the study area. 

We feel that the discovery of the Lake Ellen 

kimberlite places a new perspective on a possible 

source for drift diamonds in Wisconsin. 

Throughout the world, kimberlites are found in 

clusters rather than as a single body. Wellexplored kimberlite fields, as in southern Africa 

and Siberia, contain tens or even hundreds of individual bodies in regions that commonly have 

dimensions of a few tens to a few hundreds of 

kilometers. The discovery of one kimberlite is a 

strong, but not necessarily conclusive, indication 

that others exist nearby. On the basis of the existence of the Lake ElleD-kimberlite and five possible kimberlite-related structures, we suggest that 

one or more kimberlite fields exist in Wisconsin or 

northern Michigan. The fact that many of the diamond finds are in the area of the Green Bay lobe 

further suggests that sources are concentrated in 

northeastern Wisconsin or northern Michigan. 

Brummer (1978) stated that, on a world-wide 

basis, about 1 kimberlite in 10 contains diamonds 

and about 1 in 100 contains diamonds in commercially recoverable quantities. 

If we are correct in our suggestion that the five 

areas of disturbed strata described are underlain 

by kimberlite, then at least six kimberlites are in 

the region. However, those proposed to exist 

beneath the disturbed areas are not exposed at the 

surface and could not be the source of drift 

diamonds in Wisconsin. No diamonds have been 

found in the Lake Ellen kimberlite, but it has not 

been adequately sampled to our knowledge. Diamond is a very minor constituent in kimberlite, 

even at economic grades, and many tons of rock 

might have to be processed to determine if 

diamonds are present. 

Because most of Wisconsin and northern 

Michigan is covered by glacial drift, much less than 

1 percent of the bedrock is exposed at the surface. 

Kimberlite pipes, which typically are nonresistant 

to erosion and at best would be small bodies, probably no more than 500 m (1,600 ft) in diameter, 

are unlikely to be exposed. 

The discovery of one kimberlite, the tendency for 

kimberlites to occur in clusters, the very limited 

amount of exposed bedrock, and the presence of 

diamonds in the glacial drift suggest that more 

kimberlite bodies, some of which are diamond bearing, may exist in the area. 

12 
~ 

C/.:) 

A 

R 31 W 

RQ~~­ e,\;,-:::-\- ~G--------.:::::-.:::::-

o

(jl; 3500ft 

/f 

....., II- 3000ft 

\\ 

\\ 

,, 

1\ 

)!..__ 2500ft 

~ ~ -'/ 

,.;,o'////// /7Jk- 2000 ft 

/f 1500ft 

II 

II 

IL_ 1000ft II 

II 

ll 

\\ 

\~~500ft 

~ ~ ~ ~ 

SEC. 27 

SEC. 34 

0 2000 FEET 

0 500 METERS 

<n 

i1000 

< (.!) 

T 44 N z 

>-.. ...... 

~ 500 OUTCROPS OF 

0 

z 

< 

u 

~ 

w s 1..4- z 

CORNER (.!) 0 

SEC. 27 ~ 0 500 1000 1500 2000 2500 3000 3500 

B DISTANCE ALONG LOGGING ROAD, IN FEET <n 

...... 

~ 2.0 

:::::i 

...... 

~ 1.6 

z 

.. 1.2 

>-

...... 

~ 0.8 

z 

< 0.4 0::: 

w 

:::::> 

.. --\_ - -~-~OBSERVED VALUES 

\ 

OUTCROPS OF ""'' 

KIMBERLITE~ """ , '----, / - - ''-....,., '-..... 

(.!) 0 :::::> 0 500 1000 1500 2000 2500 3000 3500 

0 

ICC c DISTANCE ALONG LOGGING ROAD, IN FEET 

FIGURE 7.-A, Map of area around Lake Ellen kimberlite. B, Total intensity magnetic profile across the Lake Ellen kimberlite. C, Bouguer gravity profile across the Lake Ellen 

kimberlite. 
EXPLORATION FOR KIMBERLITE 

The general scarcity of bedrock exposures in 

northern Michigan and Wisconsin and the relatively complete geologic mapping in northern 

Michigan during which most exposures have been 

examined suggest that few, if any, kimberlite 

bodies remain to be found in outcrop. If additional 

~imb~~lites. are discovered they will probably be 

Identified first by geophysical techniques that will 

recognize a diagnostic signature of kimberlite 

beneath glacial deposits. 

Macnae (1979) has reviewed the state-of-the-art 

of geophysical exploration for kimberlite. Electrical and magnetic surveys, and in some cases 

gravity surveys, have been successful in finding 

buried kimberlite. 

Electrical methods depend on the existence of 

conductive residual clay overlying the kimberlite. 

Such clay cappings are common on kimberlite in 

unglaciated regions but are unlikely to be pres~rved in Wisconsin or Michigan because glaciation has probably eroded them. No residual clay is 

known on the Lake Ellen kimberlite. 

Magnetic surveys have also been successful. 

~ost fresh (unweathered) kimberlite is magnetic. 

FI~re 7A shows the location of a ground magnetic 

profile over the Lake Ellen kimberlite. A prominent positive anomaly of about 1,000 gamma 

amplitude, shown in figure 7B, clearly marks the 

~imberli.te. The magnetism is apparently caused by 

fine-gramed magnetite produced during serpentinization of olivine. Ilmenite, a somewhat abundant primary mineral, is apparently not magnetic. 

The amplitude of the magnetic anomaly may depend, therefore, on the degree of serpentinization 

of the olivine and could vary substantially from one 

body to another. 

The use of magnetic surveys to find kimberlite in 

Wisconsin and Michigan is hindered by two factors: · 

1. The relatively small size of kimberlite bodies 

requires close flight-line spacing of 

aeromagnetic surveys to locate bodies. 

Aeromagnetic surveys have been done for 

much of the region of interest at a line spacing of one-half mile, but at that spacing, even 

a. relatively large body (500 m (1,600 ft) in 

dmmeter for instance) might not be intersected by a flight line. Hence, to be effective, magnetic surveys that have a closer 

flight-line spacing would be needed. 

2. Many of the Proterozoic rocks in the region 

have strong magnetic expression and commonly cause anomalies as strong as or 

stronger than would be expected from 

kimberlite. An anomaly caused ·by a 

kimberlite would be difficult to recognize in 

such magnetically "noisy'' regions. 

Gravity surveys have had limited success in finding kimberlite (Macnae, 1979) but will probably not 

be very useful in Wisconsin and Michigan .. Figure 

7C shows a gravity profile across the Lake Ellen 

kimberlite. Even in this rather precise survey in 

which station elevations were surveyed to a precision of less than 0.1 ft, no anomaly was detected 

over the kimberlite. The density of the kimberlite is 

apparently very nearly the same as that of surrounding rocks. 

Apparently, then, magnetic surveys offer the 

best hope for finding buried kimberlite, but new 

surveys that have closely spaced flight lines will be 

needed. Problems of recognition of kimberliterelated anomalies from abundant anomalies from 

other sources must be solved. Magnetic surveys 

could be done more efficiently if relatively small 

areas of high potential could be identified. 

Regional studies of heavy minerals in drift using 

kimberlite-indicator minerals, such as pyrope 

garnet, magnesian ilmenite and chrome diopside, 

, might be used to define zones likely to contain 

buried kimberlite. Such studies have been· used 

'with some success in Canada (Brummer, 1978). 

We conclude that the discovery of kimberlite 

bodies will be difficult but that detailed magnetic 

surveys of areas where kimberlite indicator 

minerals are in glacial drift holds some promise of 

success. For each kimberlite found, however, there 

may be only about one chance in 100 that it will 

contain economically exploitable concentrations of 

diamonds. 

REFERENCES CITED 

Alden, W. C., 1904, The Delavan lobe of the Lake Michigan 

glacier of the Wisconsin stage of glaciation and associated 

phenomena: U.S. Geological Survey Professional Paper 34, 

106 p. 

--1918, The Quaternary geology of southeastern Wisconsin 

with a chapter on the older rock formations: U.S. Geological 

Professional Paper 106, 356 p. 

Allen, R. C., 1910, The Iron River iron-bearing district of 

Michigan: Michigan Geological and Biological Survey 

Publication 3, 151 p. . 

Brummer, J. J., 1978, Diamonds in Canada: Canadian Mining 

and Metallurgical Bulletin, v. 71, no. 798, p. 64-79. 

Case, E. C., and Robinson, W. I., 1914, The geology of 

Limestone Mountain and Sherman Hill in Houghton County, Michigan: Michigan Geological and Biological Survey 

Publication 18, p. 165-181. 

Davis, B. T. C., and Boyd, F. R., 1966, The join 

MgzSiz06-CaMgSiz06 at 30 kilobars pressure and its applica14 
tion to pyroxenes from kimberlites: Journal of Geophysical 

Research, v. 71, no. 14, p. 3567-3576. 

Dawson, J. B., and Stephens, W. E., 1975, Statistical classification of garnets from kimberlite and associated xenoliths: 

Journal of Geology, v. 83, no. 5, p. 589-607. 

Ekern, G. L., and Thwaites, F. T., 1930, The Glover Bluff structure, a disturbed area in the Paleozoics of Wisconsin: 

Wisconsin Academy of Science, Arts, and Letters Transactions, v. 25, p. 89-97. 

Gair, J. E., and Wier, K~L~ 1956, Geology of the Kiernan 

Quadrangle, Iron County, Michigan: U.S. Geological Survey 

Bulletin 1044, 88 p. 

Gunn, C. B., 1968, Relevance of the Great Lakes discoveries to 

Canadian diamond prospecting: Canadian Mining Journal, 

v. 89, no. 7,p. 39-42. 

Gwyn, Q. H. J., and Dreimanis, A., 1979, Heavy mineral 

assemblages in tills and their use in distinguishing glacial 

lobes in the Great Lakes region: Canadian Journal of Earth 

Sciences, v. 16, no. 12, p. 2219-2235. 

Haggerty, S. E., 1975, The chemistry and genesis of opaque 

minerals in kimberlites: Physics and Chemistry of the 

Earth, v. 9, p. 295-307. 

Hearn, B. C., Jr., and Boyd, F. R., 1975, Garnet peridotite 

xenoliths in a Montana, U.S.A., kimberlite: Physics and 

Chemistry of the Earth, v. 9, p. 247-255. 

Hobbs, W. H., 1899, The diamond fields of the Great Lakes: 

Journal of Geology, v. 7, no. 4, p. 375-388. 

James, H. L., Dutton, C. E., Pettijohn, F. J., and Wier, K. L., 

1968, Geology and ore deposits of the Iron River-Crystal 

Falls district, Iron County, Michigan: U.S. Geological 

Survey Professional Paper 570, 134 p. 

Koenen, K. H., 1956, Geophysical studies in south central 

Wisconsin: Madison, University of Wisconsin, unpub. MS 

thesis, 44 p. 

Kunz, G. F., 1892, Gems and precious stones of North America: 

New York, The Scientific Publishing Co. (reprinted by 

Dover Publications, New York, 1968), 336 p. 

McCallum, M. E., Eggler, D. H., and Burns, L. K., 1975, 

Kimberlitic diatremes in northern Colorado and southern 

Wyoming: Physics and Chemistry of the Earth, v. 9, p. 

149-161. 

Macnae, J. C., 1979, Kimberlites and exploration geophysics: 

Geophysics, v. 44, no. 8, p. 1395-1416. 

Mitchell, R. H., 1973, Magnesian ilmenite and its role in 

kimberlite petrogenesis: Journal of Geology, v. 81, no. 3, p. 

301- 311. 

--1977, Geochemistry of magnesian ilmenites from 

kimberlites in South Africa and Lesotho: Lithos, v. 10, no. 

1, p. 29-37. 

--1979, Mineralogy of the Tunraq kimberlite, Somerset 

Island, N.W.T., Canada, in International Conference on 

Kimberlites, 2d, Santa Fe, New Mexico, 1977, Proceedings, 

v. 1: Washington, D.C., American Geophysical Union, p. 

161-171. 

Olson, E. E., 1953, Historyof diamonds in Wisconsin: Gems 

and Gemology, v. 7, no. 9, p. 284-285. 

Reid, A. M., and Hanor, J. S., 1970, Pyrope in kimberlite: 

American Mineralogist, v. 55, nos. 7, 8, p. 1375-1379. 

Roberts, E., 1940, Geology of the Alston district, Houghton and 

Baraga Counties, Michigan: Pasadena, California Institute 

of Technology, unpub. MS thesis, 48 p. 

Silvers, Amy, 1978, When Eagle pinned hope on diamonds: The 

Milwaukee Journal, November 9, 1978, Accent section, p. 1 

and 10. 

Sinkankas, John, 1959, Gemstones of North America: 

Princeton, N.J., Van Nostrand, 675 p. 

Stephens, W. E., and Dawson, J. B., 1977, Statistical comparison between pyroxenes from kimberlites and their 

associated xenoliths: Journal of Geology, v. 85, no. 4, p. 

433-449. 

Vierthaler, A. A., 1958, Wisconsin diamonds: Wisconsin 

Academy Review, v. 5, no. 2, p. 53-55. 

1:r U.S. GOVERNMENT PRINTING OFFICE: 1981-341-614/228 

15