GEOLOGICAL SURVEY CIRCULAE 43

November 1949

GEOLOGY OF THE CENTRAL PART

OF THE IRON RIVER DISTRICT

IRON COUNTY, MICHIGAN

By 

Carl E. Button

Prepared with the cooperation of the Geological Survey ]>ivision 

Michigan Department of Conservation
UNITED STATES DEPARTMENT OF THE INTERIOR 

J. A. Krug, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

WASHINGTON, D. C.

Free on application to the Director, Geological Survey. Washington 25. D. C
GEOLOGY OF THE CENTRAL PART OF THE IRON RIVER DISTRICT

IRON COUNTY, MICHIGAN

By 

Carl E. Dutton

CONTENTS

Page

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

General geology........................... 3

Principle features.................... 3

Stratigraphy......................... 3

Footwall strata.................. 3

Iron-formation.................. 4

Hanging-wall strata.............. 4

Stratigraphic relations........... 4

Structure................................. 5

Page

Economic geology........................... 5

Ore deposits........................... 5

Principles of exploration................ 6

Magnetic survey............................. 6

Description of local features.................. 6

Geologic structures..................... 6

Southern part of area.............. 6

Northern part of area.............. 7

Southwestern part of area.......... 8

Western part of area............... 9

Possibilities for exploration.................. 9

ILLUSTRATIONS

Page 

Plate 1. Map of geology at bedrock surface in the south-central

part of Iron River district, Iron County, Michigan...................................... In pocket

2. Map showing geology at two underground levels in the 

south-central part of Iron River district, Iron 

County, Michigan..... *.............................................................. In pocket

3. Structure sections in the south-central part of Iron

River district, Iron County, Michigan................................................. In pocket

4. Map and structure sections showing geology in northcentral part of Iron River district, Iron County, Michigan............................... In pocket

5. Map of magnetic data in central part of Iron River

district, Iron County, Michigan....................................................... In Docket

6. Map and structure sections showing geology in central

part of Iron River district, Iron County, Michigan...................................... In pocket

Figure 1. Index map of Iron County, Michigan, showing areas

covered by preliminary reports............................................................ 2
INTRODUCTION

Iron County la in the western part of 

the northern peninsula of Michigan (fig. 1), 

and in It there are two districts which produce iron ore at the present time. The Iron 

River district is in the western part of the 

county and has 11 active mines. The Crystal 

Palls district is about 15 miles east of the 

town of Iron River and has two mines in operation.

The central part of the Iron River 

district is an area approximately 2^ miles 

from north to south and 3^ miles from east to 

west. It includes most of the town of Iron 

River and also extends southward into the 

western part of the adjoining town of Stambaugh.

The only mines operating at the present time 

in this part of the district are the Hiawatha 

No. 1 and No. 2 mines, but at least ten mines 

formerly produced iron ore. Through 1947, 

the total production of OT?S' from these mines 

was about 17,500,000 tons, and the present 

annual production of the Hiawatha mines is 

about 500,000 tons.I/

I/ Lake Superior iron ores, The Lake Superior 

Iron Ore Association, Cleveland, Ohio, 1938. 

General statistics covering cost and production of 

Michigan iron mines, Michigan Uept. of Cons., 

Geol. Survey Division, 1939-19//7.

R. 35 W. R.3IW.

0 N 0 U N T Y

WISCONSIN

CANADA

Area covered by this report 

Mineral Hills Area 

Crystal Falls-Alpha Area

Ice Lake-Chfcagon Creek Area 

East-central and southeast

Iron River Area 

Stager Area*

Crystal Falls-Paint River Area* 

Work in progress

* Report in preparation

Figure 1. Index map of Iron County, Michigan, showing areas 

covered by preliminary reports.
This report is one of several that have 

resulted from a continuing cooperative investigation of the geology in the iron-ore producing districts of Iron County by the Michigan Department of Conservation, Geological 

Survey Division, and the U. S. Geological 

Survey. Preliminary reports have been issued 

for the Mineral Hills area,2/ the Ice LakeChicagon Creek area,3/ the Crystal Palls-Alpha 

area (two reports),4/ and the eastern and 

southeastern parts of the Iron River District.^/ 

Reports are in preparation for the Stager area, 

the Crystal Palls-Paint River area, and the 

Fortune Lakes area.

The present report is based upon intermittent study and mapping of surface and underground data from June 1943 to October 1947. 

During the investigation the writer received 

wholehearted cooperation from the personnel 

of M. A. Hanna Co., Pickands, Mather and Co., 

Cleveland-Cliffs Iron Co.', Jones and Laughlin 

Iron Co., and Mineral Mining Co. in obtaining 

many data from their files and in having access to drill cores. G. E. Eddy and F. G. 

Pardee of the Michigan Geological Survey 

aided by their advice and continued interest. 

The suggestions and discussions of H. L. 

James of the U. S. Geological Survey were 

especially significant and helpful. Acknowledgment is gratefully made also for the 

contributions of C. P. Park, Jr., J. R. 

Balsley, Jr., and Justin Zinn during planetable mapping; of S. E. Good and L. D. Clark 

during underground mapping; and of R. E. Pagel 

for the final drafting. Special appreciation 

is expressed for the magnetometer su'rvey made 

by K. L. Wier, R. B. Hall, and J. J. Hill.

GENERAL GEOLOGY 

Principal features

Glacial materials form an extensive and 

generally thick cover over the bedrock in 

most parts of Iron County. Outcrops, although 

more numberous in the area covered by this 

report than elsewhere in the district, are 

scarce.

Bedrock in the district is usually called 

"ledge," and the stratified materials are graywackes, slate,s, >/ unoxidized or oxidized ironformation, and locally some iron ore. These 

rocks are believed to be Upper Huronian.

2/ Dutton, C. E., Park, C. F., Jr., and Balsley, 

J. R.,Jr., General character and succession of 

tentative divisions in the stratigraphy of Mineral 

Hills district, Iron River, Iron County, Michigan: 

U. S. Geol. Survey Prelim. Rept., pp. 1-4, 1945.

2/ James, H. L., Clark, L. D., and Smith, L. E., 

Magnetic Survey and geology of the Ice Lake-Chicagon 

Creek area,. Iron County, Michigan* U. S. Qeol. 

Survey Strategic Min. Invest. Prelim. Rept. 3-213. 

pp. 1-11, 1947.

lJ PettiJohn, F. J., Geology of the Crystal 

Falls-Alpha iron-bearing district, Iron County, 

Michigan: U. S. Qeol. Survey Strategic Min. Invest. 

Prelim. Map No. 3-181, 1947. Petti.john, F. J., 

Magnetic and geologic data of parts of the Crystal 

Falls-Alpha iron district, Iron County, Michigan: 

Michigan Dept. of Cons., Qeol. Survey Division, 

pi. 1-9, 1943.

Ji/ James, H. L., and 7,'ier, K. L., Magnetic 

survey and geology of the eastern and southeastern 

parts of the Iron River district, Iron County, 

Michigan: U. S. Geol. Survey Cir. 26, pp. 1-18, 

1948.

As shown on the geologic map of Iron 

County published in 1929,7/ masses of extrusive greenstone and possibly some related 

intrusive material extend along the northern 

and southern sides of the area occupied by 

sediments in southern Iron County. The 

geologic age of these igneous rooks is in 

doubt, but it is believed that they represent 

the underlying material on which the sediments 

of the basin rest.

One sill-like mass of basic rock is known 

in the northern part of the Iron River district 

and another one occurs in the southeastern part 

of the district. Igneous rock of diabasic 

character has been penetrated in diamond drill 

holes in two places in the central part of the 

district.

The general geologic structure of southern 

Iron County is apparently a triangular-shaped 

basin whose apices are at Iron River, at 

Crystal Palls, and at Florence, Wis., about 

15 miles southeast of Crystal Palls. The 

strata of the basin are complexly folded and, 

except at the top or bottom of the folds, are 

characterized by steep or overturned dips. 

The central part of the Iron River district is 

immediately west of the western apex of the 

major basin and contains several faults as 

well as the complex folds that are typical of 

this district. Data are insufficient to 

determine satisfactorily the structure in much 

of the area.

Stratigraphy

The character and sequence of strata in 

the central part of the Iron River district 

are similar to that present in other parts of 

southern Iron County that have been examined 

during this restudy of the area. The concepts 

presented in this report are based on detailed 

mapping of the Hiawatha, Dober, and Isabella 

mines and on examination of all known outcrops 

and available drill cores.

The general designation of the strata and 

their relative stratigraphic sequence are shown 

in the following tabulation. 

Magnetic slate

Graywacke or graywacke- J. Hanging-wall strata 

chert breccia

Iron-formation

Laminated graphitic

slate

Slate breccia 

Sericitic slate

Pootwall strata

Footwall strata. The iron-formation is 

normally underlain by thinly bedded or 

laminated black graphitic slate. Pyrite is 

very abundant as a fine-grained disseminated 

material that is rarely visible megascopically. 

This unit ranges in thickness from 20 to 120 

feet, but the latter figure represents some 

duplication by' folding.

£/ Although most of the "slates" do not exldbit 

cleavage and evidences oi' recrystallization are slight, 

the use of the term for fine-grained rocks is well 

established in the district.

2/ Barrett, L. P., Pardee, F. G., and Osgood, W., 

Geologic map of Iron County, Michigan De^t. of Cons., 

Geol. Survey Division, 1929.
A distinctive slate breccia commonly 

underlies the bedded graphitic slate and 

ranges in thickness from 2 feet to perhaps 

50 feet* This unit of the footwall strata 

is a massive layer in which fine-grained graphitic material constitutes the matrix around 

fragments of graphitic slate, which commonly 

range from minute particles to pieces whose 

maximum dimension is one-half inch. Locally 

fragments of chert are abundant, and some 

fragments of gray slate may be present also. 

The characteristics of this material suggest 

that it is intraformatlonal breccia.

The next stratigraphic unit is the 

lowest one thus far determined in this part 

of the district. It is composed of gray, 

sericitic, nonsideritic slates with some finegrained graywacke or siltstone normally present 

below the uppermost part.

Iron-formation. The unoxldized Ironformation is composed of alternating layers 

in which either chert or siderlte predominate, 

whereas in the oxidized iron-formation the 

slderite has altered to iron oxides (hematite 

and limonite), and ore is composed .of iron 

oxides with little or no chert,. The layers In 

the iron-formation commonly range in thickness 

from slightly less than half an inch to 2 

inches and in a few places any one of them 

may be much thicker. The chert of the unoxidized iron-formation is generally dark gray 

to black but locally the prevailing color of 

the chert la a light grayish green. 

The chert in the oxidized iron-formation is 

almost invariably white, light buff/ or very 

light gray, but In a few places dark-gray to 

black chert is interbedded with soft red 

hematite layers. The chert is rarely discolored by iron compounds and usually has a 

sharp boundary with the adjacent materials.

In some places the upper part of the ironformation Is a breccia composed of conspicuous, 

angular chert fragments and indistinct alderite 

fragments in a matrix of siderlte. The fragments range In size from 12 inches long and 

2 inches thick to chips, so small that a hand 

lens or microscope is necessary to Identify 

the material. Where this fades is oxidized, 

the matrix Is limonite or hematite.

The iron-bearing minerals most commonly 

present in the iron-formation are: hematite 

that is generally soft, red, and earthy but in 

-some places is hard and massive, or an aggregate of small plates; hydrous yellow to 

brown iron oxides forming either soft and 

earthy materials, or very hard and massive 

material that generally has a well-developed . 

conchoidal fracture; granular siderite that 

makes up a rock of light-gray color and finegrained texture.

The'unoxidized iron-formation commonly 

has partings or very thin layers of gray or 

greenish slate that become red where the 

formation is oxidized. Locally the upper part 

of the iron-formation contains interbedded 

graywacke, or graphitic slate somewhat similar 

to the laminated graphitic slate unit below 

the iron-formation but generally sideritic and 

much less pyritlc.

Hanging-wall strata. These materials 

are stratigraphically younger than the ironformation, and in this part of the district 

the most common unit is a graywacke that 

normally contains fragments of chert.

The graywac'ke with chert fragments, if 

present, is immediately above the ironformation. It is an important marker bed and 

occurs in the same stratigraphic position also 

in the Crystal Falls-Alpha area, the Ice LakeChicagon Creek area, the Mineral Hills area, 

and the eastern and southeastern part of the 

Iron River district.

The most conspicuous feature of these 

rocks as compared to other strata in the area 

is the larger grain size and poorly developed 

bedding of the materials. Although rounded 

grains of clear quartz and small rock fragments are characteristic features of these 

rocks, the most abundant material is a matrix 

which is too fine-grained for identification 

of its composition by use of hand lens. The 

fragments of chert are locally rimmed by pyrite, 

and in some places they are completely replaced by this material.

On the 16th to 18th levels at the Hiawatha 

No. 1 shaft, the graywacke with chert fragments 

is overlain by dark-gray, graphitic, coarsegrained graywacke containing small slate fragments and, in turn, Is overlain by blocky, 

bedded graywacke without fragments. The latter 

type of material is, however, immediately above 

the iron-formation in some places.

Coarse graywacke containing abundant pink 

and light-gray feldspar grains was penetrated 

during drill explorations >in the northern part 

of the area, but the relation of this material 

to other fades of graywacke in the hangingwall sequence is not known.

Many of the graywackes are gray, but 

greenish and reddish varieties are present 

and probably the- result of alteration related 

to the formation of ore. Most specimens of 

unoxldized graywacke contain disseminated 

slderite and yield sludge analyses of 15 to 

2Q percent iron. Oxidation produces red 

color and in several places reddish graywackes 

have been designated as "iron-formation" in 

records of drilling. One very peculiar color 

variation of the graywacke is the white or 

buff material that is usually associated with 

ore bodies and is indicative of geologic 

processes, that bleached the rock and made it 

friable.

The next unit of the hanging-wall strata 

Is the magnetic slate, the youngest unit recongnlzed thus far in this area. The rock is 

commonly mauve or purple and Is highly magnetic, 

but it may be greenish gray and only locally 

magnetic, or light gray and essentially nonmagnetic. Although a number of variations in 

its appearance are encountered the material 

is usually sideritic, distinctly bedded, and 

exhibits a subconchoidal fracture. This 

stratigraphic unit is also present in other 

parts of southern Iron County and has been of 

considerable value in the determination of 

structure from magnetic data.

Stratigraphic relations. With one possible exception the foregoing stratigraphic 

units constitute a conformable sequence of 

strata insofar as could be determined. The 

chert fragments in the graywacke immediately 

above the iron-formation were evidently derived from chert bands in the iron-formation 

inasmuch as no other source of the chert is 

readily available. The character of the 

graywacke unit therefore apparently records 

an unconformable relation between the graywacke
and underlying iron-formation as has been 

proposed for other parts of the Crystal FallsIron River district. Oraywaoke with chert 

fragments occurs at many places adjacent to 

iron-formation, but in a few places graywaoke 

without chert fragments is interbedded in the 

upper part of the iron-formation, and the 

relations are thus locally conformable. The 

interpretation of these conditions is that 

the iron-formation over most of the area was 

subjected to a slight disturbance perhaps by 

gentle flexing and submarine slump and 

contemporaneous or subsequent submarine 

erosion. The probable sequence and character 

of the processes can be shown by series of 

selected specimens that include (1) normal 

interbedded chert and siderite, (2) siderite 

with interbedded, segmented chert bands, (5) 

breooiated iron-formation, (4) breooiated ironformation 'Containing minor amounts of clastic 

material of .sedimentary origin, (5) graywaoke 

with chert fragments, and (6) graywaoke without chert fragments.

Additional evidence possibly supporting 

an unoonformable relation is present in a few 

places where the interval between the hangingwall graywaokes and the footwall slates is unusually small, suggesting that erosion reduced 

the iron-formation to much less than its normal 

thickness.

Structure

Structurally, the central part of the Iron 

River district is in what may be the western 

apex of a triangular-shaped basin that extends 

eastward to Crystal Falls, Mioh., and southeastward to Florence, Wis. The strata in the 

mapped area are, in general, steeply inclined 

and in many places are in an overturned position. The general structural pattern in the 

area has been only partly determined, but 

many folds and a few faults are .known to be 

present. The principal structural units that 

have been recognized are oriented approximately 

at right angles to each other.

North-trending folds are present in the 

eastern part of the area and include a major 

syncline with several second order anticlinal 

and synclinal folds to the west. Folds of this 

orientation plunge generally southward and most 

of them are overturned toward the east.

East-trending folds are present in the 

southern part of the area where the welldefined units are an anticline between two 

synclines which probably converge toward the 

west into one major synclinal structure. 

These folds have a plunge generally westward 

and are overturned toward the south in a few 

places. Several east-trending anticlines and 

synclines are present also in at least one 

locality in the northern part of the area. 

Some of these folds plunge to the west, but 

others are good examples of doubly plunging 

structures that are very common in the Iron 

River district. The doubly plunging folds are 

undulations along anticlinal and synclinal 

axes, and the pattern of the iron-formation 

on a horizontal surface Is elliptical or is an 

S-shaped curve joined to a reversed S-shaped 

curve.

The strata are sheared and contorted in 

many parts of the area, but only a few specific 

faults are known to be present. The faiilts 

are in two systems that are approximately parallel to the orientation of the folds and undoubtedly are displacements resulting from 

the 'extreme thinning of the limb of an 

adjacent fold. North-trending faults art on 

the eastern side' of the folds in the eastern 

part of the mapped area. Several east-trending 

faults are in or parallel to the prominent 

anticline in the southern part of the area. 

One of the faults in this latter group has an 

apparent vertical displacement of over 8,000 

feet with the result that most of the ironformation and the overlying graywaoke are 

missing and footwall graphitic slate is 

adjacent to hanging-wall magnetic slate.

The description of geologic structures 

in a later part of the report presents additional information that would encumber the 

text at this point and thus detract from the 

emphasis on general features.

BCONOMIC OEOLOOY 

Ore deposits

Hematite and limonite are the principal 

constituents of the iron ore. These minerals 

may be either soft and earthy or hard and 

compact, and consequently the physical character of tiie ore is largely determined by these 

variations. Although locally ore may be dense, 

the ore bodies normally are porous and contain 

a considerable volume of water. \ Much of the 

ore retains the layered structure of the ironformation from which it was derived, but in 

some places this characteristic has been 

destroyed in the transformation.

The ore bodies are essentially tabular in 

form and parallel to the trend of the adjacent 

strata. In many instances, the graphitic slate 

underlies the lower side and the bottom of an 

ore body. A boundary of this type is very 

sharp and its'shape is directly controlled by 

the structural pattern of the stratigraphio 

contact. In a few folds ore in the overturned 

limb rests on younger graywaoke that has 

become a "structural footwall" as a result of 

the overturning. Although some interbedding 

of ore and graywaoke may be present, the zone 

is a stratigraphio feature which can be used 

to map geologic structure. Elsewhere oxidized 

iron-formation is adjacent to. ore. Boundaries 

of this third type are gradational, very irregular, and commonly result in fingerlike 

projections that extend upward from the main 

mass of ore.

The iron ore is the result of alterations 

of the iron-formation. The siderite of the 

unoxidized iron-formation has been changed to 

limonite and hematite. The chert that was 

interbedded with the siderite has been completely or almost entirely removed by either 

solution or replacement or perhaps a combination 

of the two. The oxidation produced some 

concentration of the iron by the formation of 

new minerals. The greater concentration, however, resulted from the removal of the valueless chert which constitutes about half of the 

volume of either oxidized or unoxidized ironformation.

Ore was present at bedrock surfaces in 

several mines of the area, but some of these 

occurrences apparently stopped at depth because 

they rested in synclinal folds of slate .or on 

a structural footwall that steepened. However, 

in one part of the Hiawatha mine, ore continues 

downward for more than 2,000 feet vertically 

below the surface without the lower limit of 

the ore being reached. .
Principles of exploration

The ore-bodies originated by the alteration and enrichment of iron-bearing strata 

Which constitute only a small part of the 

succession of rock layers. It is evident 

therefore that exploration has been, and will 

continue to be guided by two primary considerations. The first factor that guides exploration is the location of the iron-formation 

and, in the absence of other information, this 

matter is usually settled either by test pitting (where the overburden is not too thick) 

or by diamond drilling. The maps indicate 

that considerable exploration Is still necessary to provide sufficient Information for 

the satisfactory determination of the distribution of the iron-formation. The second, 

and much more difficult factor in exploration, 

Is the location of a structure that has been 

favorable for the conversion of the Ironformation to iron ore. The occurrence of 

many ore bodies in the district in synclinal 

structures is the logical basis for examining 

first the localities where the iron-formation 

occurs in these folds. It is well known, 

however, that some ore is not in synclines 

and that not all synclines contain ore; 

consequently, no occurrence of Iron-formation 

should be excluded from consideration as a 

possible site of ore bodies.

Another feature with possibilities as a 

guide to exploration is that the strata in 

the vicinity of most ore bodies are oxidized. 

The members of the hanging-wall sequence may 

be thoroughly and extensively oxidized, but 

the footwall rocks are commonly affected to a 

lesser degree. Inasmuch as the oxidation is 

generally present at the surface of the bedrock above ore bodies, one approach to the 

problem of exploration would be simply to 

examine the bedrock surface to locate areas 

of oxidation and then search within that area 

for ore.

Three types of possibilities for exploration exist in the mapped area:

(1) The extension of iron-formation beyond 

known occurrences.

(2) Unexplored areas between explorations 

in which the rock has been tentatively classed 

as hanging-wall strata and those in which the 

material is believed to be footwall strata.

(3) Deeper exploration of areas in which 

oxidized iron-formation or oxidized hangingwall graywacke has been found at the bedrock 

surface. Ore in such areas might be confined 

to the bottom of synclinal folds and not be 

encountered in shallow explorations.

Specific examples of the above types 

are discussed under the section, entitled 

Possibilities for exploration, in a later 

part of this report.

MAGNETIC SURVEY

A Wolfson vertical magnetometer was 

used for the determination of magnetic data. 

The instrument was compensated for temperature changes, and corrections for diurnal 

variations were made by check readings at a 

base station several times during each day. 

The base station for the survey was the same as 

that used in compiling magnetic data for the

other parts of the Iron River district. It is 

in the NB^NBi see. 28, T. 43 N,, R. 34 W,8/

In general, traverse lines 300 feet apart 

were run by compass, and determinations along 

these lines were made at paced intervals of 

100 feet. Determinations were not made where 

cultural features such as drill casings, railroad tracks, steel towers, and mine shafts 

would have produced valueless data; readings 

that were questionable have not been used in 

drawing magnetic contours.

The iron-formation Is not magnetic except 

for rare and local areas of small extent. 

However, the iron-formation is overlain in 

normal stratigraphic order by graywacke, which 

may be slightly magnetic, and by the magnetic 

slate. Magnetic surveys reveal the location 

of this material, if present, In areas where 

outcrops are absent and thus aid in geologic 

mapping.

The magnetic survey determined several 

prominent anomalies, and at least three of 

them have been specifically correlated with 

the magnetic slate. A discussion of the 

geology in the area of each major anomaly is 

included in the section, entitled Geologic 

structures.

DESCRIPTION OP LOCAL FEATURES 

Geologic structures

Southern part of the area. The synclinal 

axis of a major structural unit trends approximately north through a prominent hill 

at Stambaugh in the northeastern part of the 

area shown on plate 1. Exposures of magnetic 

slate mark the center of this structure where 

an anomaly determined by the magnetometer 

survey (pi. 5) has the maximum range of values 

found thus far in the Iron River district. 

The graywacke exposed at a number of places 

on the western slope of Stambaugh Hill, and 

the iron-formation of the Chatham mine and 

Riverton mine (also Delta mine, pi. 4), form 

the western limb of this syncline. The 

eastern limb of the structure is east of the 

maps in this report and is represented by the 

iron-formation of properties on the eastern 

side of Stambaugh. Although not shown on 

the maps of this report, the iron-formation of 

the Cyr-Lennox exploration (E^SWi sec. 36, T. 

43 N., R. 35 W.) at the south end of Stambaugh 

Hill possibly marks a partial closure of the 

structure on the south, but there are no data 

to indicate a comparable closure on the north.

Another major structure, in which the 

largest ore bodies of the mapped area occur, 

is the east-trending syncline whose axis lies 

between Hiawatha No. 1 shaft and Hiawatha No. 

2 shaft (pi. 1). Locally, north of Hiawatha 

No. 2 shaft, the axis of this structure is 

probably marked by the outcrops of gray 

sideritic slates that are believed to be 

equivalent to the magnetic slates. Prom the 

surface to the present workings on the 18th 

level, most of the central part of this 

structure is composed of graywacke or graywacke w ith chert fragments (pi. 2), and the

op. cit.

''James, H. L., Clark, L. D., and Smith, L. E.,
two belts of Iron-formation remain approximately 1,500 feet apart. The limbs trend 

slightly north of east, but the southern one 

turns northwest in a series of folds near the 

Dober mine and is then terminated at the 

Isabella mine by a reverse fault that is 

parallel to the orientation of the adjacent 

folds. Although the change to a northwesterly trend in the southern 3,1mb suggests 

the possibility of this structure becoming 

closed at depth, the two belts of ironformation have remained separated down at 

least as far as the 18th level. On and below 

the 13th level, the eastern part of the northern limb turns northeastward and is probably 

terminated by a fault (map of 16th level, 

pl. 2).

The anticlinal fold north of the Dober 

No. 1 shaft is a less prominent structure but 

is of spedial interest because of the volume 

of data substantiating it and because of the 

local effects on the areal map pattern 

(pis. 1 and 2). This fold trends northwest, 

is overturned to the east, and is truncated 

on the eastern side by a reverse fault of 

apparently considerable vertical displacement 

(section A-A 1 , pl. 3).

An anticlinal fold trends east through 

the Hiawatha No. 1 shaft and is one of the 

major structures in this area as shown by maps 

on plates 1 and 2, and by cross-sections 

C-C*, D-D 1 and E-E 1 on plate 3. Detailed 

data are available from the 3d to the 18th 

levels to give the most complete vertical 

section available in the district at the 

present time. The essential features of the 

structure 'include a tightly compressed footwall sequence in the.central part of the fold, 

and a reverse* fault displacement of the north 

limb that brings hanging-wall strata adjacent 

to the footwall strata.

Undoubtedly many more faults occur in 

the area than are shown on the maps and 

sections. Inasmuch as the complex folds are 

normally accompanied by .considerable shear 

and contortion, the positive recognition of 

faults'is difficult. The omission of members 

in the normal succession of strata as shown 

on the maps and sections is the essential 

feature for determining the faults that are 

indicated.

»p synclinal structure'lies between 

;ha No. 1 shaft and the Chatham No.

A deej 

the Hiawatl

1 shaft. The bedrock surface in the area 

between the iron-formation at the two mines 

is apparently graywacke containing chert 

fragments (pl. 1), although a prominent 

magnetic anomaly is present there (pl. 5). 

Drilling has revealed that considerable 

magnetic slate occurs below the surface 

(section C-C', pl. 3) and that the syncline 

is not only overturned to the south but fault 

displacements have isolated a mass of magnetic 

slates among older members of the sequence. 

This synclinal structure appears to occupy a 

large area toward the west as shown by the 

prevalence of graywacke with chert fragments 

in the explorations northwest of the Hiawatha 

No. 1 shaft. The bedrock surface at that 

locality is thus composed of hanging-wall 

strata; but some iron-formation is present, 

probably along the axis of a doubly plunging 

anticline of general northeast trend.

One of the magnetic anomalies in the 

NWfcSWfc sec. 35, T. 43 N., R. 35 W., is in an

area where black slates were reported ..too bet 

present in test pits (pl. l), but the only 

bedrock material observed, during this investigation was graywaoke with chert fragments 

from one pit.

It appears, therefore, that the area is 

underlain by hanging-wall strata, and it is 

possible that these anomalies are related to 

another occurrence of the magnetic slates. 

The form and size of the anomalies suggest 

the presence of small masses of magnetic slates 

along synclinal axes.

The interpretation of the geology near 

the Chatham No. 1 shaft is based largely on 

information from records of the mining 

company although much drill core from adjacent explorations was examined during this. 

investigation. Reported occurrences of 

"graywaoke" and "black slate" in the mine 

workings are apparently hanging-wall and footwall materials and control the pattern of inferred geology at bedrock surface as shown on 

plate 1 and below the surface as shown in 

sections B-B' and C-C 1 on plate 3. In general, the structure in this part of the area 

is believed to consist of folds that trend 

north, are overturned to the east, and plunge 

southward.

A belt of iron-formation extends westward and northward, from the Chatham mine 

passing through the exploration in the 

SWfrNBfr sec. 35, T. 43 N., R. 35 W.; then it 

probably turns to a southwestward trend and 

may continue across the northwestern part of 

sec. 35.

N

orthern part of area. Another belt of 

ormation extends northward from the 

Chatham mine and passes through the Riverton 

mine (pl. 4), the Delta mine, and the 

SWfcNWt sec. 25, T. 43 &., R. 35 W. (Miller 

exploration). Rock exposures around the 

caved areas of the Riverton mine are the most 

extensive in this part of the district and, 

although several members of the sequence are 

present, determination of structural details 

is difficult. In the Riverton mine the ironformation is complexly folded, is overturned 

toward the east (cross-section P-P 1 , pl. 4), 

and is separated from a typical hanging-wall 

strata toward the east by a shear zone that is 

one of the few conspicuous structures in the 

area. The displacement along the fault is 

not clearly defined, but the mass east of the 

fault possibly moved relatively upward. The 

inclination of the fault could hoi be determined exactly, but is known to be steep. The 

graphitic slate in the caved area just south 

of Riverton No. 5 shaft (pl. 4') is represented 

as footwall material, but its true stratigraphic position could possibly be in the 

lower part of the hanging-wall sequence. The 

west side of the remainder of the caved area 

is partly oxidized material that includes 

slaty iron-formation, slate, and some graywacke, but very little typical iron-formation 

is exposed. Most of these rocks belong in 

the lower part of the hanging-wall strata 

and apparently form a long, narrow synclinal 

structure.

The interpretation proposed for the 

geology in the vicinity of the Delta mine is 

generalized and is based entirely on information obtained from records of mining and 

exploration. A map of the third level of the 

Delta mine (pl. 4}shows that a small body of
ore and oxidized Iron-formation at the north 

end of the workings was essentially encircled 

by "black slate". This arrangement probably 

Indicates the bottom of a doubly plunging 

synclinal drag fold similar to one shown 

north of the shaft on the mine map. The 

areal geology at the bedrock surface has been 

drawn in accordance with this concept.

In the SWfcNWi sec. 25, T. 43 N. , R. 35 W, 

(Miller exploration), drill holes are recorded 

as having first penetrated "slate and altered 

graywacke", and then passed into "oxidized 

Iron-formation11 that at least in part was at 

greater depth In the eastern holes than in 

the western ones. It is therefore likely 

that the Iron-formation dips to the east, and 

the inferred geology is represented accordingly. The extension of the belt of ironformation beyond this locality has not been 

determined.

A third belt of iron-formation extends 

northward from the Chatham mine to connect 

with that at the Sheridan shaft In the 

SEiSEfc sec. 26, T. 43 N., R. 35 W. (pi. 4). 

This northern part is probably a synclinal 

structure with associated anticlinal areas of 

footwall slates to the west and to the east 

where, as shown In cross-section P-P f on plate 

4, drilling revealed the slate breccia of the 

footwall strata. Data are lacking concerning 

the continuation of the Iron-formation more 

than a short distance northward from the 

Sheridan shaft.

The Iron-formation at the Inactive 

Wickwlre mine (pi. 4) is probably isolated in 

a synclinal structure but is closely related 

to and at one time was continuous with the 

belt of iron-formation that extends northwestward from the Chatham mine. Breccia in 

which chert fragments are embedded in a 

graphitic matrix is present west of the mine 

and, as previously described, this material 

is a variety of the slate breccia unit of the 

footwall sequence. Drill holes, which were 

vertical or Inclined eastward, passed through 

the breccia and entered the iron-formation; 

they thus establish the overturned position 

of the structure at this locality. Black 

slate reported to be present in test pits to 

the east of the mine are believed to be footwall strata also and, on sections prepared by a 

former mining company, black slate is shown to 

extend westward under the iron-formation. The 

structure at this mine is therefore interpreted 

as a synclinal fold that is overturned to the 

east, and the iron-formation Is the youngest 

stratlgraphlc unit in the fold. The extent of 

the Iron-formation northward and southward 

from the Wickwlre mine is not known at the 

present time.

Exposures and explorations in the vicinity 

of the Beta-Nanalmo mine (pi. 4) show that the 

Iron-formation, footwall strata, and probably 

hanging-wall strata are present in the western 

part of sec. 26, T; 43 N. , R. 35 W. The occurrences of these materials suggest a folded 

structure trending east to northeast, possibly 

a general plunge westward, and one undulatory 

anticlinal axis. Although the true stratigraphic position of the ^black slate" in the 

explorations north of the river is not known, 

It is assumed to .be a part of the footwall 

strata, and an approximate contact with the 

iron-formation has been indicated.

Drilling in the SEfc sec. 27, T. 43 N., R. 

35 W. (pi. 6), penetrated coarse graywacke 

that contains many grains of light-gray and 

pink feldspar, and one hole entered oxidized 

iron-fromation below the graywacke. The graywacke is in the hanging-wall strata, and its 

occurrence at this locality signifies a continued westward plunge of the synclinal structure west of the Nanalmo shaft as shown on the 

map..

Southwestern part of area.- -The trend of 

iron-formation in the S£ sec. 34, T. 43 N., 

R. 35 W. (pi. 6), in the vioinity of,the Cortland and Brule mines, has been drawn* in accordance with information at the bedrock surface 

and with information on maps prepared by the 

mining companies. Maps of the Cortland mine 

show "graywacke" north of southward-dipping 

iron-formation, and "black and gray slate" 

south of it. Several pieces of graywacke containing chert fragments were seen on the Cortland dump, and thus it Is probable that the 

graywaoke in the mine was normal hanging-wall 

material but that at this place the sequence 

of strata is overturned.

Maps of the Brule mine show some Interesting geological data. The formations trend east 

In general, except for a deflection toward the 

north in the vicinity of the shaft, and the 

prevailing dip Is south. Black slate is shown 

north of the iron-formation to the west of the 

shaft, and graywacke south of the iron-formation 

at the west end of the second level workings. 

Qraywacke is also present at the east end of 

the second level (directly below the Cortland 

mine workings), but the structural relations 

at this locality are not clearly represented. 

Qraywacke with chert fragments is present In 

the dump of the Brule mine and presumably came 

from one.1 of these areas or possibly from the 

areas marked "brecclated cherty carbonate 11 and 

"graywacke" In a long exploratory cross-cut 

toward the south at about 1,700 feet west of 

the shaft. The end of this cross-cut to the 

south stopped in "graphitic black slate" that 

apparently belongs to the footwall strata and 

is In a secondary anticlinal fold on the northern flank of a major structure to the south. 

This concept of geologic structure is based 

on the Interpretation that the magnetic anomaly 

in this part of the area (pis. 5 and 6) possibly Indicates the presence of a syncllne 

containing the magnetic slate and the immediately underlying slightly magnetic graywacke. 

If so, it is likely that the footwall slates 

and Iron-formation would not come directly to 

the surface from the end of the long drift but 

would be south of the anomaly.

On the northern side of the Brule mine, 

the material from drill holes along the eastwest center line of sec. 34, T. 43 N., R. 35 W., 

Is similar to normal footwall strata, and the 

map has been drawn to show that interpretation.

The iron-formatIon at the Brule mine 

probably continues northeastward to join the 

belt of iron-formation that extends northwestward from the Chatham mine. The magnetic 

anomalies in the NWfcSWfc sec. 35, T. 43 N., 

R. 35 W., tend to confirm this probability.

The indirect extension of the ironformation westward from the Brule mine is 

based on the magnetic values in this vicinity, 

and the core from two of the drill holes in
the SE£ sec. 33, T. 43 N., R. 35 W. (QreigJackson exploration), supplied valuable information concerning the geology of that part 

of the area (pi. 6, map and section !-!') 

Drill hole no. 15, which was inclined to the 

northwest, penetrated iron-formation and 

then passed into a normal footwall sequence of 

graphitic slate and slate breccia. Drill 

hole no. 14, which also was inclined to the 

northwest and was 300 feet southeast of hole 

no. 15, penetrated graywacke at the bedrock 

surface and at greater* depth went into the 

magnetic slate. The magnetic anomaly in the 

SEi sec. 33 and the SW£ sec. 34, T. 43 N., 

R. 35 W., is related therefore to magnetic 

slate that is in a synclinal structure. 

Furthermore, the character and sequence of 

strata in this part of the area establish 

the correlation of these strata with those 

elsewhere in.the district. In some places 

.the inferred- contacts of the iron-formation 

have been drawn to conform as closely as 

possible to the magnetic data rather than 

accepting the reported description of drill 

cores that were not available for examination. 

This choice was made because in many other 

cases the reported descriptions of pores that 

were examined were not adequate for determining the stra'tigraphic position of the strata.

The extension of the iron-formation from 

the Greig-Jackson exploration to ironformation present in a small area of outcrops 

and in explorations in the SW^ sec. 33, T. 

43 N., R. 35 W.. and the NWfc sec. 4, T. 42 N., 

R. 35 W. (pi. 6), is hypothetical but is approximately parallel to the trend of- small 

magnetic anomalies in that part of the area. 

The drill core that was available for examination was predominantly unoxidized ironformation or iron-formation breccia. Very 

minor amounts of graywacke and graphitic 

slate were present also, and these associated 

materials probably indicate axes of a series 

of small folds. There is very little 'information however, concerning the probable 

limits of the iron-formation, its approximate 

trend, or the general structure at this 

locality. The stratigraphic position of the 

materials from drill holes north of the creek 

is uncertain, but the inference shown is that 

they are a part of the footwall strata.

The reported occurrence of iron-formation 

in a drill hole near the southwest corner of 

sec. 34, T. 43 N., R. 35 W., is the basis 

for the map pattern in that vicinity. Similarly, data on maps of the Edlund exploration 

in the northeast corner of sec. 3, T. 42 N., 

R. 35 W., and adjacent part of sec. 34, indicate the possibility of iron-formation as 

inferred.

Although the magnetometer survey covered 

the adjacent portions of the area and drill 

records of some explorations are available, 

the geologic structure remains indeterminate.

Western part of the area. Magnetic 

values in the western part of the area in 

general higher than those in other parts of 

the Iron River district. The reason for these 

higher values is not known, but the magnetic 

attraction outside the mapped area continues 

to increase toward the south where there are 

exposures of greenstone that bound the southern side of Iron County. Therefore it is inferred that greenstone may be relatively near 

the surface in the western part of the mapped 

area.

POSSIBILITIES FOR EXPLORATION

The following brief descriptions are of 

several localities in which some exploration 

might be warranted.

The iron-formation in the southern limb 

of the major west-trending syncline between 

the Hiawatha shafts has not been located or 

explored west of the NEi-NEj' sec. 2, T. 42 N., 

R. 35 W.

The well oxidized condition of the graywacke and the few occurrences of iron-formation 

in the NEiSWfc sec. 35, T. 43 N., R. 35 W., 

favor further examination of this general 

°rea.

The stratigraphic position of material in 

the drill holes in the SWj-NWi sec. 35, T. 43 

N., R. 35 W., is undetermined thus far, but 

if it belongs to the footwall strata, a belt 

of iron-formation would normally pass between 

the drill holes and the magnetic anomaly in 

the NWfcSWi sec. 35, T. 43 N., R. 35 W.

Inasmuch as the large ore bodies of the 

Hiawatha No. 1 mine occur more than 1,000 feet 

below the surface, some deep exploration of 

the belt of iron-formation in the southern 

part of sees. 33 and 34, T. 43 N., R. 35 W., 

might be considered.

The probable presence of the ironformation in several other localities between 

the Brule mine and the Beta-Nanalmo mine may 

warrant further investigation, but it is 

stressed that recent explorations in the 

NWfcSWi sec. 26 and SE£ sec. 27, T. 43 N., R. 

35 W., have revealed the prevalence of unoxidized material in that vicinity, and a 

similar condition may extend widely into adjacent areas. (1) If the footwall strata are 

present along the east-west center line of sec. 

34, T. 43 N., R. 35 W., as suggested previously, 

then one or more belts of iron-formation would 

normally be present between this locality and 

that of the graywacke with feldspar grains 

west of the Nanaimo explorations. So far as 

is known, explorations based on this possibility have not been made. (2) However, if the 

material in sec. 34 is a part of the hangingwall strata, then the northern limb of an 

anticlinal st-ructure near the Brule mine has 

not been located, and information concerning 

its possibilities for ore is lacking. (3) 

As stated previously and shown on the_map, 

it has been assumed that the materials in the 

SW^NWi sec. 35, T. 43 N., R. 35 W., and along 

the east-west center line of sec. 34, are 

part of the footwall strata. However, if they 

are hanging-wall strata, favorable exploratory 

conditions may exist over a large part of the 

area to the north and west of these localities.

The ore body at the Nanaimo shaft is 

located in a synclinal structure, and further 

exploration along the axis of the fold has 

been in progress. The westward-pitching 

syncline continues on the west side of the 

road and thus has warranted investigation in 

that direction especially. Except for the 

water hazard, another possibility for exploration could be the westward continuation 

of the iron-formation on the north side of the 

Iron River.

The foregoing examples do not exhaust the 

possibilities for exploration but will be sufficient perhaps to .indicate some of the 

potentialities in the central part of the Iron 

River district.
UNITED STATES DEPARTMENT OF THE INTERIOR 

GEOLOGICAL SURVEY

PREPARED WITH THE COOPERATION OF THE 

GEOLOGICAL SURVEY DIVISION. MICHIGAN DEPARTMENT OF CONSERVATION Circular 43 PLATE I

w-ch bands, lew Iragt

 gw-eh frag*

gw-ch fragtPt

magnetic anomaly

x l°" .. * gw-ch frag* Ia-»l

Crtst line of 

B CHATHAM NO. 2

ll-eh fragi Paftl»

EXPLANATION

Hanging-wall strata Fold axis, showing direction of plunge

(Mostly groywocke)

Section 35 T43N R35W Section 36 T43N R35W

Section I T42N R35V)

Area of outcrop

Other small outcrops represented 

by isolated structural symbols

unox lf-»J xu"°» 

gw-ch frag. " x»«-ch fra«»l Iron-formation

fw 

Faatwoll strata

gw-ch fragtx xfl* (Slate and groywocke) Strike and dip of bede ff?«

60

Fault

Dashed where location Is approximate 

and dotted where inferred

Fold showing direction 

and amount of plunge

ai If O" "O- (I

Drill holes, vertical and inclined,

showing type of bedrock

Number is mining company

designation of hole

Line of geologic crass section 

shown on Plate 3

Geologic boundary

Dashed where location is approximate 

and dotted where Inferred

ax: oxidized 

qtz: quartz 

ser: sericitic

sid: slderite or 

sideritic 

si: slate 

unax: unoxidized

bl: block 

brc: breccia

gr: gray 

graph: graphitic 

gw: graywacke 

if: iron-formation 

Jo:jasper 

loc: locally 

mag: magnetic

corb: carbonate 

(slderite) x 

Test pit

B DOBER NO. 

Mine shaft //'

ch: chert or cherty 

dk: dark 

fe: ferruginous 

frogs: fragments

Hyphen in rock description means either "with" or "and", as in 

gw-ch frogs: groywocke with chert fragments 

gw-sl: groywocke and slate

Axis of anticline

Axis of syncline

-fVAxis of overturned anticline

-AAxis of overturned syncline

Plan of underground workings on

one major level, and underground

drill hole Quotation marks indicate that description is from mining company

records

MAP OF GEOLOGY AT BEDROCK SURFACE IN SOUTH-CENTRAL PART OF IRON RIVER DISTRICT,

IRON COUNTf, MICHIGAN

Geology by C. E. Dutton, 1948

ZOO 2::j 400 600 800 Feet

H H

SGALt
UNITED STATES DEPARTMENT OF THE INTERIOR 

GEOLOGICAL SURVEY

PREPARED WITH THE COOPERATION OF THE 

GEOLOGICAL SURVEY DIVISION, MICHIGAN DEPARTMENT OF CONSERVATION Circular 43 PLATE 2

EXPLANATION

Hanging-wall strata 

(Mostly graywackc)

Iron-formation

Foot wall strata 

(Slate and graywacke)

Fault

Dashed where location is approximate 

and dotted where .inferred

Geologic boundary

Dashed where location is approximate 

and dotted where inferred

Axis of anticline

Axis of syncline

-Fh

Axis of overturned anticline

Axis of overturned syncline

Strike and dip of beds

so

Fold showing direction 

and amount of plunge

MOI Q \DDH 304

\ \grepli (I

If-gwO" ' ^

 loty gat) \r

Drill holes-vertical, inclined, and horizontalshowing rock type penetrated 

Number is mining company 

designation of hole

E DOBER NO. I 

Mine shaft

Line of geologic cross section 

ABBREVIATIONS USED

hem: hematite

if: iron-formation

ja: jasper

loc: locally

mog: magnetic

ms: massive

ox: oxidized

qtz: quortzite

ser: sericitic

sid: siderite or siderltic

si: slate

graph: graphitic unox: unoxidized 

gw: graywacke

Hyphen in rock description means either "with" or "and", as in 

gw-ch frogs: graywocke with chert fragments 

gw-sl: groywocke ond slote 

Quotation marks indicate that description is from mining company records

bdd: bedded

bl: black

brc: breccia

corb: carbonate (siderite)

ch: chert or cherty

cs: coarse

dk: dark

fe: ferruginous

f: fine-grained

frags: fragments

.R35» Coordinate BOM Lln* f

. graph (I

' .contorUd 

_|A|X> Bih*or*d

GEOLOGIC MAP OF 3W LEVEL OF HIAWATHA MINE

6I2--736-1-IOC mogn.tlc 

767'-990'J

m» to (( bdd f gwdk gr »l lot ox-eh frog*- 

vcln qtz

HIAWATHA NO. I (

 l«v.-255'? "' IF"

CoordtnoU BOM Lln« 4Section 36 T43N R35W

jSection I T42N R35W

I GEOLOGIC MAP OF 16 LEVEL OF HIAWATHA MINE

MAP SHOWING GEOLOGY AT TWO UNDERGROUND LEVELS IN SOUTH-CENTRAL PART OF THE IRON RIVER DISTRICT,

IRON COUNTY, MICHIGAN

eoo eoo 400 600 eoo

SCALt
UNITED STATES DEPARTMENT OF THE INTERIOR 

GEOLOGICAL SURVEY

PREPARED WITH THE COOPERATION OF THE 

GEOLOGICAL SURVEY DIVISION, MICHIGAN DEPARTMENT OF CONSERVATION Circular 43 PLATE 3

 1000

HIAWATHA NO. 2

ISOO DOBER NO. I ISOO 

 IOOO 

5OO

S«o

Uv«l

 500

^mlnorg^^s. ^

Hanging-wall strata 

(Mostly graywacke)

Iron -formation

fw 

Foatwall strata

(Slate and graywacke)

Section C-C'

SECTION ALONG LINE A-A'

, . : :

M j\ e«*tH%« ttiflE NO. I /

1 ! : i' * / "S

hw

 gw'P

SECTION ALONG LINE B-B'

 1500 

-IOOO 

 500 

S«a

EXPLANATION

______ gw-ch frags

~ ~ lODHSOf

ABBREVIATIONS USED

Drill holes, showing type of rock

penetrated

Dashed where projected to 

plane af cross section

Fault

Dashed where location Is approximate 

and dotted where inferred

Geologic boundary

Dashed where location is approximate 

and dotted where inferred

Section af mine workings

Dashed where projected ta

plane of crass section

bdd: bedded 

bi: black 

brc: breccia

carb: carbonate 

Csiderite)

ch: chert or cherty

cs: coarse

dk: dark

fe: ferruginous

frags: fragments 

gr: gray

graph: graphitic 

gw: graywacke 

if: iron-formation 

Ja: jasper 

lac: locally 

mag: magnetic

ox: oxidized 

qtz: quartz 

ser: sericitic

sid: siderite ar 

sideritic 

si: slate 

unax: unoxidized

Hyphen in rack description means either "with" a r "and", as in 

gw-ch frags: graywacke with chert fragments 

gw-sl: graywacke and slate

Quotation marks indicate that description is from mining 

company records

I500

"gw gT «» 9" [80 ft E)

Section B-B'

IOOO

soo

S«a 

UV«I

15'

I hw

groph

I6»"

HIAWATHA MINE NO. 2 

ope

xlf IT 1 "

-500

hw i

HIAWATHA MINE NO. I

 Igw-rors eh frags / gw-sl-

- \ . ^ :--V.; .>/:I ----.-I.^ I:: A:II,...^- I-. -

:ms sl"A i/gr««Blsh-gr sld si- 'gwtS^-. ' ' if "«' \|

.(29T.F«liJ' loe ox V : .: >^A« »: :. -:::- . -

' dk gr es gw- 

\ loe graphitic 

' si frags

 1500 

 IOOO 

 SOO 

S«a

17

 500 

SECTION ALONG LINE C-C'

gw-eh frags

: i I . .- \ sneorea gw-vim qii £;£ Kj*

i.i\ M a T / / f& '*^*}b» ' v - - * - /gw-ch frogs-si frags ./ 

/ -SSSH. f

hw

sheared gw-v*ln qtz

'^:|h frags and / 

bond. y

hw /

./ / fw

..

bl

500 

S«a 

Uv«l

-SOO 

SECTION ALONG LINE D-D'

DON VH-4-4S

ox lf?-g*-c

gw-ch

10 K> » M

tow

/jji:

f /

\ on R * '1 sheared gV

i

ox sl-gw-ch 

unox-ox sl-gw

'"

". //

)* »aj)'r-green si

7 sheared graphitic si

hw

blcochsd 

and ox sl-gw

fw

.* WEST HIAWATHA MINE

hw'i

 > fw

ij^l si*

if

« / 6* If-tl .jidfti;*^ ^sheared? blk, red si -ax If 

W :" :*'..' ; 

. .' >*

SECTION ALONG LINE E-E'

12 « 

13

1500 

IOOO 

500 

S«a

-500 

STRUCTURE SECTIONS SHOWING GEOLOGY IN SOUTH-CENTRAL PART OF IRON RIVER DISTRICT,

IRON COUNTY, MICHIGAN

Gealagy by C. E.Dutton, 1948

200_____O

H H hT

200 4OO 600 SOO F««t

SCALE
UNITED STATES DEPARTMENT OF THE INTERIOR 

GEOLOGICAL SURVEY

PREPARED WITH THE COOPERATION OF THE 

GEOLOGICAL SURVEY DIVISION, MICHIGAN DEPARTMENT OF CONSERVATION Circular 43 PLATE 4

-SECTION ALONG LINE G-G'

g»-ch fragi 

bit g«

J /; : 1 hw

26 T43N R35W

Section 35 T.43N R35W 2^^^^fl&purpi«,r«d,«h,buff il Section 36

SECTION ALONG LINE F-F'

: RIVER TON NO. 5

rn-tf

"iloty If-lpCjOrii _/

«£ch-giT-lf" '

 if-il4lh l«v«l 

 Uv. 1207' EXPLANATION "Cograph il-eh fragi

Hanging-wall strata 

(Mostly graywacke)

Drill holes, showing type of rock penetrated 

Dashed where projected to plane of cross section Fold axis, showing direction of plunge

Area of outcrop

Other small outcrops represented 

by isolated structural symbols

eo 

Strike and dip of beds

Section of mine workings

Dashed where projected to plane of crass section 

A'

»o0flroph ^a Cflroph

Footwall strata 

(Slate ond graywacke) Line of geologic cross section 

ABBREVIATIONS USED

bl: block gw: graywacke sll: siliceous 

brc: breccia if: iron-formation si: slate 

ch: chert or cherty jo: jasper unox: unoxldlzed 

dk: dark loc: locally wh: white 

frogs: fragments mag: magnetic 

ox: oxidized

Fold showing direction 

and amount of plunge

bl si o3 I£ O- gr sl-bl il

Drill holes, vertical and inclined,

showing type of bedrock

Number is mining company

designation of hole

x 

Test pit

RIVERTON NO I Hyphen in rock description meons either with or and

gw-ch frogs: grcywocke with chert fragments

gw-sl: groywocke and slote

v

DDK S i £ 

Plan of underground workings on

one major level, and underground

drill hole

Fault

Dashed where location is approximote 

and dotted where inferred

Geologic boundary

Dashed where location is approximate 

and dotted where Inferred graph: graphitic sid: siderite or sideritic ild il-graph il-eh fragi STAMEAUGH

Axis of anticline

Axis of syncline

-aAxis of overturned anticline

Quotation marks indicate that description is from 

mining company records

4j

Axis of overturned syncline

MAP AND STRUCTURE SECTIONS SHOWING GEOLOGY IN NORTH-CENTRAL PART OF IRON RIVER DISTRICT,

IRON COUNTY, MICHIGAN

Geology by C. E. Dutton, 1948

2OO 200 400 6OO 800 F»»t

H H H

SCALE
UNITED STATES DEPARTMENT OF THE INTERIOR 

GEOLOGICAL SURVEY

PREPARED WITH THE COOPERATION OF THE 

 EOLOGICAL SURVEY DIVISION, MICHIGAN DEPARTMENT OF CONSERVATION Circular 43 PLATE 5

EXPLANATION

Magnetic determination. Value In gammas of

vertical intensity above or below value of

bast station In section 28, T.43N., R.34W.

Reliability of the magnetic determinations 

near southeastern corner of map anti of 

Isolated abnormal values Is questionable 

because of possible cultural interferences

60

Magnetic contours at 50 gamma Intervals

from -50 to+200 gammas

Contour of -100 and +500 gamma value shown locally 

Determinations in western part of section 36, T.43N., R.35W. 

and isolated single values not contoured

Closed contour around magnetic depression

Crest line of major magnetic anomaly

Drill hole, description on geologic map

 ISO ls- O 

1* 

^94 |«0' l

MAP OF MAGNETIC DATA IN CENTRAL PART OF IRON RIVER DISTRICT,

IRON COUNTY, MICHIGAN

Surveyed by K.L.Wier, R. B. Hall.and J.J. Hill, 1947-1948

500_____0

M M HI

500 1000 1500 2000 F««t

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UNITED STATES DEPARTMENT OF THE INTERIOR 

GEOLOGICAL SURVEY

PREPARED WITH THE COOPERATION OF THE 

GEOLOGICAL SURVEY DIVISION, MICHIGAN DEPARTMENT OF CONSERVATION Circular 43 PLATE 6

EXPLANATION

-.500-1 - 

Hanging-wall Drill holes, vertical and Inclined, showing type of bedrock strata

Number is mining company designation of hole (Mostly graywacke)

Iran-for motion

L* 

Footwall strata

B BRULE 

Mine shaft

SECTION ALONG LINE J-J' (Slate and graywacke)

Plan of underground workings on one major level

DON 4 00" 

Fault SECTION ALONG LINE 1-1'

Dashed where location is approximate 

and dotted where inferred

Drill holes, showing type of rock penetrated 

Dashed -where projected to plane of cross section ALONG LINE H-H'

Section of mine workings 

Geologic boundary Dashed where projected to plane of cross section

Dashed where location is approximate 

and dotted where inferred ABBREVIATIONS USED

bl: black or. gray *r. quartz

brc: breccia flroph: graphitic ser: sericitic

carb: carbonate gw: graywocke sld: siderite or

(siderite) |f. Iron_f0rmotion

Axis of anticline

 Merltic 

*l: slate 

unox: unoxidized

eh' Ch«»* nr rhartv

3k: dork loc: locally 

fe: ferruginous mog. mognet|C

frags: fragments Ox: oxidized 

at: quartzite

Axis of overturned anticline

__y 

Axis of overturned syncline

var: variegated 

(red, green

Geologic data

of this area

shown on Plate 4

Axls of overturned fold showing direction of plunge Hyphen ln rock ^9Crlpnon means either 'with' or 'and', as In

gw-ch frags: groywacke with chert fragments 

**-* «r°y««ke and slate Crtst line of major magnetic anomaly

Quotation marks indicate that description is from mining 

company records

pIVERTON NO. 8

gr Mr il-gw ^ 4 (>d *' ? fl*~0r *' 8*-Or 

8 gw-gr f«r flp *

ox-uiiox gw l! «-«"

'/ 'gr-bl & tl" I<5 T42N R35W

If) obltl EDLUND 1 

Uv.,

Geologic data

of this area

shown on Plate I

MAP AND STRUCTURE SECTIONS SHOWING GEOLOGY IN CENTRAL PART OF IRON Rk/ER DISTRICT,

IRON COUNTY, MICHIGAN

Geology by C. E. Dutton, 1948

5OO 5OO IOOO I5OO 2OOO F««t

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