Geological Survey Professional Paper

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1/31

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2/31

Computer aidedEstimates

ofConcentrating grade

IronResources

intheNegaunee

Iron formation

Marquette

District,Michigan

9

GEOLOGICALSURVEYPROFESSIONALPAPER1045

1

mi


3/31

COVER PHOTOGRAPHS

1

2

3

4

5

7

6

8

9

1 0

1 1

1 2

1 3

1 4

1 .

A s b e s t o s o r e

2 .

L e a d

o r e .

B a l m a t

m in e . N .

Y .

3 . C h r o m i t e - c h r o m i u m o r e , W a s h i n g t o n

4 .

Z i n c o r e , F r i e d e n s v i t l e ,

P a .

5 . B a n d e d i r o n - f o r ma t i o n . P a l m e r ,

M i c h .

6 . R i b b o n a s b e s t o s o r e . Q u e b e c , C a n a d a

7 . M a n g a n e s e o r e , b a n d e d

r h o d o c h r o s i t e

8 .

Aluminum

o r e , b a u x i t e , G e o r g i a

9 .

N a t i v e

c o p p e r

o r e ,

Keweenawan

P e n i n s u l a , M i c h .

1 0 .

P o r p h y r y

molybdenum o r e ,

C o l o r a d o

1 1 . Z i n c

o r e ,

E d w a r d s ,

N . Y .

1 2 .

M a n g a n e s e

n o d u l e s ,

o c e a n f l o o r

1 3 . B o t r y o i d a l

f l u o r i t e o r e ,

P o n c h a S p r i n g s , C o l o .

1 4 . T u n g s t e n o r e . N o r t h

C a r o l i n a


4/31

Computer aided

Estimates

of

Concentrating gradeIronResources

in

the

Negaunee

Iron formation

Marquette

District,

Michigan

By W. F. CANNON, SANDRA L. POWERS, andNANCYA. WRIGHT

GEOLOGICALSURVEYPROFESSIONALPAPER 1045

An

esti m ati o n of

the

magnitude

quality, and economic potential

o f

subeconomic

resources o f

iron

in

an

important

active

mining

district

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON

:

1978


5/31

UNITED

STATESDEPARTMENT OF THE INTERIOR

CECDL D. ANDRUS,

Secretary

GEOLOGICAL SURVEY

W. A.

Radlinski,

Acting Director

Library o f Congress Cataloging i n P u b l i c a t i o n Data

Canno n,

W F

Computer-aided

estimates o f concentrating-grade

i r o n

resources

i n

t h e

N e g a u n e e

Iron-formation,

Marquette

D i s t r i c t , Michigan.

( G e o l o g i c a l

Survey professional paper

; 1045)

Bibliography: p .

Supt. o f Docs, n o . : I

19.16:1045

1 . Iron

ores

—

ichigan

—

arquette

C o .—a ta p r o c e s s i n g . I . Powers,

Sandra

L . , j o i n t

author.

I I . Wright,

Na ncy A . , j o i n t a u t h o r . I I I . T i t l e .

IV.

S e r i e s : United S t a t e s . Geological Survey.

Professional paper ; 1 0 4 5 .

TN403.M5C36

553'.4'0977496 77- 6 08 12 0

Fo r

s a l e b y

the

Superintendent of

Documents,

U.S.

Government Printing Office

W a sh in g to n , D .C. 2 0 4 0 2

Stock

Number

024-001-03059-4


6/31

CONTENTS

P a g e

Abstract

1

Introduction 1

Acknowledgments 2

N e g a u n e e

Iron-formation

2

Mineralogy a n d texture 2

Structural p o s i t i o n

a n d

thickness 3

Resource

data

b a n k

3

Preparation of the

data b a n k

4

Variables 5

I d e n t i f i c a t i o n a n d l o c a t i o n 5

Taconite

characteristics

P a g e

Resource

data

b a n k

—

ontinued

Variables—ontinued

Deposit

characteristics 7

R e l i a b i l i t y

of

data

8

Iron resources 9

Resource

c l a s s i f i c a t i o n 11

Estimates of t o t a l recoverable iron 13

Future

of taconite

m i n i n g i n

the

Marquette

d i s t r i c t . _ 19

Effect of technol ogi c

advances on

i r o n resources

20

Conclusions

20

References

c i t e d 2 '

ILLUSTRATIONS

P a g e

Figure

1 .

Generalized

geologic

map

of

the

Marquette

d i s t r i c t 2

2 Hypothetical cross s e c t i o n o f data block showing method

b y

which variables are measured a nd assigned

t o

blocks 6

3 . Cumulative

curve showing

relationship

b etween

long

tons

of

Neg a u n e e

Iron-formation

a n d d e pth b e n e ath the surface 9

4

Graph

showing long

tons

of iron-formation i n categories described

i n

the text 10

5 . Hi sto g ra m sho w i ng long tons o f the po ssib ly tre ata bl e i r o n -

formation within 1 ,000 feet of the surface r e l a t i v e t o volume

of consolidated waste rock overly ing i t 1 1

6 . Hi sto g ra m sho w i ng long tons of

the

possi bly tre ata ble i r o n -

formation within 1,000 f e e t o f the surface with various r a t i o s

of volume of iron-formation

t o

volume o f interlayered waste

rock

1 1

7 .

Resource

c l a s s i f i c a t i o n chart 12

8. Histo gra ms sho w i n g r e s u l t s of three types o f metallurgical t e s t s 14

9

Geologic

map

of the

Marquette

d i s t r i c t

showing

the d i s t r i b u t i o n

o f

vario us mineralogical

c l a s s e s

of iron-formatio n within

the

Neg a u n e e

Iron-formation 16

1 0 . Regression

l i n e s showing the negative correlation b etween co n

centrate-iron

percentage a n d concentrate-silica

percentage

fo r

three types of metallurgical t e s t s 18

1 1 .

Curves

showing maximum short tons of i ron pote nti a ll y

available

within

1,000 f e e t

o f

the surface

fo r

tw o metallurgical c l a s s e s

of iron-formation at various c u t o f f grades 18

1 2 .

Graph showing

projected production

trends

fo r

the Marquette

d i s t r i c t

from

operating m in es a nd a nn ou nce d expansion a n d

d evelopment plans 19

TABLES

P a g e

T a b l e 1 . Percentage of variation b etween original calculations a n d r e c a l

culated values of four variables

fo r

\ i -m \ 2 ( 0 .6 5 -km ) v e r t i c a l

columns

through the iron-formation

8

2

Metallurgical d a ta u se d i n simulation

m o d e l

13

i n


7/31


8/31

COMPUTER-AIDED ESTIMATES

OF

CONCENTRATING-GRADE IRON

RESOURCES INTHE

NEGAUNEEIRON-FORMATION,

MARQUETTEDISTRICT, MICHIGAN

By

W.

F. Cannon,

Sandra

L.

Powers, and

Nancy A. Wright

ABSTRACT

The Ne ga u ne e

Iron-formation of

Precambrian

a ge i s

the

principal i ro n -b e ari n g u n it i n the

Marquette

i r o n

range,

Michigan.

Th e Negaunee,

a lo n g w i th other sedimentary a n d

igneous r o c k s , i s folded

i n t o

a complex synclinal structure,

the

Marquette

trough, a n d r e l a t e d

smaller s t r u c t u r e s .

The N e g a u n e e contains a b ou t 2 05 b i l l i o n long tons of rock

a n d

averages 32 percent i r o n . By

u si ng a

computerized

data

bank,

we have

analyzed

the resource

potential

of

the

Negau

n e e ,

a n d

b y

using

a

s t a t i s t i c a l si m ul ati o n m o de l ,

we have

estimated

the

maximum

a m o u n t

o f

iron

recoverable

u n d er

present or

moderately

improved economic

a n d technologic

c o n d i t i o n s .

Within the d i s t r i c t

i s a bout

9 1 . 6 b i l l i o n long tons

of f i n e

grained

hematitic a n d g o e t h i t i c

iron-formation. Ab o ut

2 8 . 4

b i l l i o n long

tons

i s within 1 , 0 0 0 f e e t ( 3 0 4 . 8 m) of the

sur

face; t h i s material could y i e l d a maximum o f a bout 7 b i l

l i o n sho rt to ns o f iron i n concentrates that co ntai n 60-65

weight-percent i r o n . Th e concentrates cou ld be pro d uce d b y

s e l e c t i v e

f l o c c u l a t i o n a n d f l o t a t i o n , or some

modification

o f

that

p r o c e s s , such

that recovery of i r o n i s at

l e a s t 2 0 w e i ght-

percent

of

the crude

o r e .

Magnetic iron-formation constitutes a bout 48 b i l l i o n long

t o n s . Ab o ut

1 0 . 5

b i l l i o n long tons i s within 1,000 f e e t ( 3 0 4 . 8

m) of the

surface a n d

could

y i e l d a maximum

of a bout 3

b i l l i o n

short

tons

of

iron i n concentrates produced

b y

mag

n e t i c

separation.

The

recovery

of iron

i s

at

l e a s t

20 weight-

percent of the crude

o r e .

I n

a d d i t i o n ,

a bout 2 7 . 1 b i l l i o n long tons o f iron-formation

contains coarse-grained hematite. Ab o ut 4 . 8 b i l li o n long tons

i s within

1,000

f e e t

(304.8

m) of

the surface

a n d

could

y i e l d a maximum

of

ab o ut 0 . 7

b i l l i o n

short tons

of iron

i n

concentrates produced

b y froth f l o t a t i o n ; the

iron recovered

i s at

l e a s t 20

weight-percent of the crude o r e .

S i l i c a t e iron-formation constitutes a bout 3 7 . 6 b i l l i o n long

t o n s , a bout 5 . 6 b i l li o n long tons of which i s within 1,000

feet ( 3 0 4 . 8

m) o f the su rfa ce .

However, the

s i l i c a t e

i r o n -

formation

i s not

a m e n a b l e t o concentration

b y

present tech

nology.

INTRODUCTION

The

Marquette

iron

range

was

the

f i r s t

o f

th e

g r e a t Lake Superior iron- ore districts to be discov

ered. The iron resources o f the district a re in th e Ne

gaunee Iro n -f o rm ati o n, a sedimentary accumulation

o f iron minerals. Shortly after th e d i sco v er y o f the

Negaunee in 1 8 4 4 , iron production began,

and

since

that time,

the district has

been

one

o f the principal

sources o f iro n o re fo r the United States. Most o re

mined b efo re the 1 9 5 0 ' s was from high-grade de

posits that formed a s secondary concentrations

in

the Negaunee Iro n -f o rm ati o n . I n the

19 50's, when

reserves o f

high-grade

o re

were being

depleted rap

idly, the technology fo r

processing

lower grade

o re

was

d e v e l op e d,

and

since

that

time production from

th e Marquette range

has

come increasingly

from

concentrating-grade

ore, commonly ca l l e d t ac on i te .

The technology fo r

producing

a merchantable

iron- ore product from taconite i s complex a n d , in

g e n er a l, i n vo l ve s o p e n -p i t mining, multistage crush

i n g and g ri n di ng , a process fo r separating iron

min

erals from gangue minerals, and an

agglomerating

process (most commonly, pelletizing) fo r the iron-

mineral

concentrate.

The

economic availability

o f

iron

from

a

taconite

deposit i s

determined

by many

factors,

o n l y some o f which

a re geologic.

Hence, by

usi n g o n l y g e o l o g ic d at a a s

i s done in

this study, we

a re n o t

a b l e

to

estimate

reserves'

o f

taconite.

Rather, in

this paper,

we i nt e n d to

present

esti

mates for

the Marquette District

o f

th e maximum

amount

o f iro n

that

i s geologically known a s w e l l

a s the amount that

i s

potentially recoverable. The

e sti m a te s a re d e ri ve d

by usi n g data from a d etailed

data

bank

developed

fo r tha t p u rp o se .

I n

this paper,

iron

r e so u r ce s a r e classified

accord

i n g

to th e

degree to which they approach the g e o l o g

i c

characteristics of presently

economic

deposits and

the degree o f

certainty

with which the

deposit i s

known.

Mathematical

sim u l ati o n models

a re used

to

derive maximum

estimates

o f

recoverable

iron

1 A r e s e r v e i s c o n s i d e r e d t o b e m a t e r i a

f r o m

w h i c h i r o n c a n b e

e c o

n o m i c a l l y a n d

l e g a l l y

e x t r a c t e d

a t

t h e p r e s e n t t i m e . T h i s s t u d y i s c o n

c e r n e d

w i t h

r e s o u r c e s ,

w h i c h a r e

c o n s i d e r e d t o b e m a t e r i a l f r o m w hi ch

e x t r a c t i o n

o f i r o n

i s c ur r en t l y o r p o t e n t i a l l y f e a s i b l e .

R e s o u r c e s t h e r e

f o re i n cl ud e r e s e r v e s , b u t a l s o i n c l u d e much more

m a t e r i a l

w h o s e

r e c o v e r y

may

o r

ma y

n ot b e

e c o n o m i c a l l y f e a s i b l e .

1


9/31

2

IRON-FORMATION, MICHIGAN

STIMATES

OF

NEGAUNEE

from m at eri a l that i s geologically most similar to

presently economic d e po sits. F i n a l ly ,

th e

degree

to

which future

technologic

advances in

several

fields

would

affect the

resource base o f

the

district

i s dis

cussed.

ACKNOWLEDGMENTS

The

d at a

that

have

made

this

report

possible

were

collected during many years o f f i e l d

and

l a b o r atory

work by

U . S. Ge o l o g i ca l Survey personnel.

We wish

to

thank J . E.

Gair,

W.

P.

Puffett, G.

C. Simmons,

L. D.

Clark,

and

J .

S. K l as n er, who, along with the

se n io r a u th or, have participated in studies

of

the

Marquette district,

and

who

have made av a i l a b l e to

u s much

original information

and material.

We

a re

also greatly

i n d e bt e d

to the mining

companies

in

the

area who, fo r many years, have

been very

co

operative in

supplying information from diamond

drilling and mining operations. This information

has i n c l u d e d subsurface data that

have

permitted

an

accurate

thre e - d i m e nsi o n a l

an alysis

o f

the

district.

Lawrence J .

Drew

o f th e

U .S. Ge o l o gi ca l

Survey

designed and wrote

a computer program

used

fo r

Monte

C arl o

si m u l ati o n

o f i ro n

resources.

NEGAUNEE IRON-FORMATION

The Negaunee Iro n -f o rm ati o n, the principal i

resource o f

the Marquette r a n g e ,

i s a stra ti g ra p

u n it in the complexly f o l d e d and faulted Marque

trough and a d j a ce n t sm a l l e r structures

—

he Palm

basin, Republic

trough,

and Mitchigan River tro

(see f i g . 1). Al l the str uct ures a re synclines comp

cated

by

faulting. The

iron-formation

i s

part

o f

Marquette

Range Supergroup,

a

thick

accumulat

o f

sedimentary and vo lc a n ic

m at eri a l about

2

bil

y e a r s

old.

The mineralogy,

texture, and

structura l p osit

o f

the

Negaunee vary greatly

within

the district

have been mapped and d escri b e d by

Simmo

( 1 9 7 4 ) ,

Puffett ( 1 9 7 4 ) , Cannon ( 1 9 7 4 ) ,

G

( 1 9 7 5 ) , Clark, Cannon,

and

Klasner ( 1 9 7 5 ) , C

non ( 1 9 7 5 ) , Cannon and Klasner ( 1 9 7 4 , 1 9 7 5 a ,

and Klasner and Cannon ( 1 9 7 5 a , b ) . The g e n er

ized description that f o l l o w s i s based on

those

mo

d etailed d escriptio ns.

MINERALOGY AND

TEXTURE

The sediments o f the Negaunee Iron-format

were deposited a s very fine grained chemical preci

i -

» »

v

v , ■— —

, s , \

i

* i > -

- I «

R 3 1 W

R 3 0 W

R 2 9

W

C R Y S T A L L I N E ROCK

( P R E C A M B R I A N

W) — M o s t l y g r a n i t i c g n e i s s

0

1 2 3

4

5

M I E S

: :

:

0

1

2 3 4 5 6 7 8 K I L O M E T E R S

Figure 1 .—eneralized geologic map of the Marquette d i s t r i c t showing the

distribution

o f the N e g a u n e e Iron-format

a n d the l o ca t i o n o f metamorphic isograds (modified

from

James,

1955).


10/31

RESOURCE DATA BANK

tates in which siderite, iron-silicate minerals,

and

iron o x i d e s and hydroxides accumulated to form

iron-rich layers, commonly

i n t e r b e d d e d with

s i l i c e

ous

(cherty) layers. The mineralogy differed from

place

to

place, probably a s a result o f varying physi

cal and chemical environments during o r shortly a f

te r deposition

(James,

1 9 5 4 ) . The mineralogy

was

further

affected

by

diagenesis,

regional

metamorph-

ism, and weathering.

Metamorphism has had a very profound effect on

the mineralogy

o f

the Negaunee,

commonly

resulting

in n e a r l y total change in th e

original

m i n er a l o g ica l

makeup. Metamorphic isograds mapped by James

( 1 9 5 5 ) and slightly m o d if i e d by subsequent

work

a re

shown in

figure

1 .

I n the

east

end o f

th e

Marquette

district, the

Negaunee

i s least metamorphosed, and

iro n - b e ari n g

minerals

a re chiefly siderite, minneso-

taite, st i l p n o m e l a n e ,

m a g n e ti te , h em a ti te ,

and

g o e -

thite. Grain size i s

very

small, g e n e r a l l y

less than

0 .0 02 i nch

( 0 . 0 5

mm). As

metamorphic

grade in

creased,

siderite

and

minnesotaite

were

converted

to

other minerals, chiefly grunerite, within the biotite

z o n e, and grain size became progressively larger. At

metamorphic

grades

higher

than

those

in th e biotite

z o n e , no significant mineralogic changes occurred.

Grunerite, m a g n etit e, and hematite remained stable

and are the principal iro n - b e ari n g minerals in

rocks

o f the highest grade attained (sillimanite z o n e ) .

Chert gra i n size

i s

a s

large

a s 0 .0 2 inch

(0.5

mm)

in rocks o f the highest metamorphic grades, and

some iron minerals

a re

several times larger. I n gen

eral,

th e

banded cherty nature o f th e rock i s pre

served to th e highest metamorphic gra d e s. I n the

area shown in figure 1 , west o f the garnet isograd,

the

relatively

c oa r se g ra i n size has

inhibited

second

ary oxidation, and o x i d a t i v e weathering has n o t

been an important mineral-forming

process

; e ast o f

the

garnet

isograd much o f th e iron-formation has

been d e ep l y weathered, and a l l

the

goethite and part

o f

the hematite

were formed by postmetamorphic

weathering o f siderite, minnesotaite, and m a g n etit e.

STRUCTURAL

POSITION AND THICKNESS

The

Negaunee

Iron-formation i s f o l d e d into a

doubly plunging synclinorium in the Marquette

trough (see f i g . 1 ). The iro n -f o rm ati o n attains i t s

g re a te st t hi ck n e ss ( 3 , 3 0 0 - 3 , 9 0 0 ft; -1,000-1,200

m)

near

the

west-plunging

keel

o f

th e

synclinorium

a few m i l e s so u th o f

the

towns o f Negaunee and Ish-

peming. Because o f l im ite d erosion o f the

syncline

and the relatively

gentle

plunge (20°-30°) and g r e a t

stratigraphic thickness of the

f o l d e d

unit, a very

large area i s u n d e r l a i n by the iron-formation. The

synclinorium g e n e r a l l y maintains a westward plunge

from i t s e astern end to

the

vicinity o f

Humboldt,

where the d e e p est parts o f the formation

a re

be

lieved

to

be about 8,200

feet

(2,5 0 0 m) below

th e

surface

(Klasner and Cannon,

1 9 7 4 ) .

The

formation

thins abruptly

away from the

exposed

keel,

also thins

along the buried

keel,

and commonly has a thick

ness

o f

250-500

feet

(~80-160

m)

where

exposed

a l o n g th e ste e p ly dipping limbs. I n

much

o f western

Marquette district,

the

Negaunee i s absent a s a re

sult

o f truncation along an ov e r l y i n g unconformity.

The westernmost occurrence o f th e Negaunee i s

along

th e

north limb o f th e synclinorium near

the

community

o f

Three

Lakes.

I n the Palmer b as i n (see

f i g . 1 ) ,

the

Negaunee

i s

about

1 , 1 0 0

feet

(—350

m)

thick

and

i s f o l d e d into

a

ha l f sy n cl i ne co n si sti n g o f a

south

limb and keel ;

the

north

limb

has

been e l i m i n at e d by faulting. The

structure i s a s much a s

2, 5 0 0 f e et

(—750 m) deep.

The

Mitchigan River trough i s likewise a

half

syn

cline

because

th e

west

limb has been

e l i m i n a t e d

by

faulting.

The

Negaunee

there

can be

a s

much

a s

1 , 0 0 0

feet (—300

m)

thick, and the

trough

i s about

6 , 5 0 0 feet (-2,000

m)

deep

The Republic trough i s a

syncline

that plunges

about

4 5 °

NW.

a t

the exposed keel but i s b e l i ev e d to

decrease in plunge toward the northwest. I n this

trough,

the Negaunee i s g e n e r a l l y thin, in several

a r e a s i s absent, and o n l y

near

the exposed keel

re aches a significant thickness o f a s much a s 1 ,0 00

feet (-300 m).

RESOURCE DATA BANK

Between

1957

and

1 97 4, the

U.S. Geological

Sur

vey

mapped the

Marquette district, i n cl u di n g the

Negaunee

Iro n -f o rm ati o n,

in

detail.

During

that

work,

a

vast amount o f

petrologic and

structural

information was accumulated, a n d , with the cooper

a ti on o f

th e mining

companies

active

in the a re a, a

f i l e

o f d i a m o n d - d r i l l i n g

records

was

co mp i l e d .

I n

1 9 7 5 , we

began a pro j ect

to

organize that informa

tion

into

a computerized data f i l e on i ro n re so u rc e s.

The basic element of

the

d at a system co n si sts o f

blocks measuring VnXV-i m i l e (0.8x0.8 km) hori

z ontally and 500 o r 1 , 0 0 0 feet

( 1 5 2 . 4

o r 3 0 4 . 8 m)

vertically. Thus, the area o f the

district

u n d e r l a i n by

iro n -f o rm ati o n was

d i v i d e d into '/i-mi-

( 0 . 6 5 -k m 2 )

a r e a s and d i v i d e d

into horizontal

slabs from the su r

face

to

—500

feet

(—152.4 m) —500 fe et to —1,000

feet (—152.4 m

to

—304.8 m) and then into deeper

1,000-fo ot-

( 3 0 4 . 8 - m - )

thi c k sl a b s to the base o f the

iron-formation. For each thre e - d i m e nsi o n a l b l ock

thus defined, about 45 variables were measured,


11/31

4

ESTIMATES

OF NEGAUNEE IRON-FORMATION,

MICHIGAN

calculated, o r estimated. Al l variables

were e nt ere d

into a

computerized

f i l e ; by means o f th e Ge o l o g ic

Retrieval

and

Synopsis

Program,

GRASP

(Bowen

and

B ot b o l, 1 9 7 5 ) , the

data can

be classified and re

called by

any

o f the

vari a b l es

o r

any

combination o f

variables.

The

data

bank ca n be

us e d

a s

an information

system

that

will answer

any

question that

can

be

phrased in terms o f listed variables, a s l o n g a s the

q u esti o n er c o n si d e r s t he limitations imposed by th e

manner in which va l u es were determined and stored.

PREPARATION OF THE DATA

BANK

For

this

resource ev a l u at i o n,

we

needed

to

pre

pare,

a s quickly

a s

possible,

a computer f i l e

o f

infor

mation

about

the b l ocks within the

Marquette

dis

t r i c t .

I n order to determine what variables would

b e

i n c l u d e d

in th e f i l e and hence, how th e d at a-i np ut

form would be d e s i g n e d, we

needed

to co nsi d er f i r s t

what questions would be asked o f the final data

system.

Once

this

was established,

a

simple

i np ut

form was designed to re co rd the d ata a s efficiently

and easily a s possible.

The next task was

to

make the data machine-

re a d a b l e . The co nv e nti o n a l method i s

to u se

punch

cards, but

because

o f the

large

volume of data

in

vo lv e d

in

this

project,

cassette

tapes were used

to

record the data. The

tapes

a re small, ho ld a

relative

ly large amount o f data, and

a re

re us a b l e once the

data contained on them

have

been transmitted to

the computer.

A problem in making th e data machine-readable

i s th e introduction o f errors. Each time data a re

translated from one

medium

to a n o t he r , e r ro r s may

be introduced.

For

this project, a

programmable

d at a- e ntry station was used,

not o n l y

because i t

g e n er at es cassette tapes,

but

also because i t can do a

l i m it e d amount o f data editing. The d at a- e ntry sta

tion i s much like a keypunch machine in concept. As

d ata a re typed a t a keyboard, they appear on a CRT

(cathode ray

tu b e )

screen. After a certain amount

o f data accumulates on

the screen,

i t can be edited,

corrected

i f necessary,

and then transferred elec

tronically from the scr e en to the cassette tape, thus

clearing

the

screen for more data. For e a s e o f entry

and

editing,

a preprogrammed form appears on

the sc re e n ;

the form nas a format

similar to the

sheet

on

which

d a ta a re

originally

recorded.

Cer

tain errors a r e a u to m a ti ca l l y detected. For instance,

a nonnumeric character cannot be entered in a

numeric-only f i e l d , and vice-versa. I f a mistake i s

made, an alarm sounds, and

the

operator must make

the

correct

e n try b e fo re th e machine will continue.

I n

addition,

the d at a- e ntry station i s

programmab

to the e xt e nt that i t ca n generate new

numbers fo

g i v e n

record on th e b a sis o f numbers already

tered. Using av a i l a b l e

arithmetic

operators,

i t

possible to generate ratios, sums, products, and

on,

in vari o us combinations and to incorporate

t

resultant number a s

part

o f

the

record.

For

t

discussion,

a

record

i s

one

b l ock

in

the

Marquet

district

and

a l l

the

d at a associated with th at b l o

Each record i s written

on

the cassette tape in f i

format, meaning that i n each record, i t e m s alwa

appear in th e same position

and have

th e same

nu

b e r

o f

characters.

After the data a re in machine-readable form, th

a re transmitted to the computer f o r p ro c e ssi n g . T

d at a- e ntry station i s used fo r

this j o b also.

Becau

the d at a- e ntry station i s programmable i t can

made to appear to the ho st computer a s a telet

t erm i n a l . The data can then be transmitted to t

computer through the u se o f a v o i ce - g ra d e t e l e ph

connected to the terminal through an acous

coupler.

Because the final d at a f i l e

needs to

b e

accessi

in an interactive mode, th e host computer has to

a timesharing computer. The computer o f a pri v

company

whose function i s to s e l l computer ti

was deemed

th e most

appropriate, both in cost a

in

speed

o f processing.

The software system chosen

to manage

the d

i s known a s

the

Ge o l o g ic Retrieval and

Synops

Program GRASP) (Bowen and

B ot b o l,

1 9 7

GRASP

i s

a

se t

o f

Fortran

IV su bro uti n es and

main

driver

that provi d es

interactive

access

to

g

logic data. Because GRASP

i s

a machine-indep

dent

interactive

system,

i t

was av a i l a b l e

on

chosen computer.

The Marquette district

GRASP f i l e actually c

sists

o f four

f i l e s

: mask f i l e , definitions f i l e , dict

ary f i l e , and numeric

master

f i l e . The mask

f i l e

c

tains a sho rt

acronym

fo r each o f the 45

variab

abundant iron mineral o r

formation name,

the ma

f i l e t e l l s

the GRASP system whether

a

particu

field

will

co nt a i n

a real

( d e c i m a l )

number, an

i

ger (whole) number,

o r

character-string (alpha

m eric).

For

character-string

items,

such a s m

abundant iron mineral o r formation name

the

ma

f i l e

also

has a numeric pointer to th e f i r s t e ntry

the d i cti o n a ry

f i l e

associated

with

that

item. T

dictionary f i l e i s a l i s t o f a l l the possible

charact

string

it e ms

that

c ou l d appear

i n

the GRASP

At present i t

has

73 entries. Al l the i te m s

fo r

e

field are grouped together in the d i cti o na ry

which co nt a i ns a count of how many it e ms there


12/31

RESOURCE

DATA BANK 5

for each f i e l d . The definition f i l e ' s main

purpose

i s

to provide a full breakdown o f the 45 vari a b l es into

various

categories

o f

information

in the GRASP f i l e

(such as,

taconite

characteristics,

deposit

character

istics), a s w e l l a s

to

provide a

description

o f each

acronym. The

numeric

master

f i l e i s the

actual data

f i l e , but

i t i s

fa r d ifferent in

appearance from

the

raw

data

a s

they

initially appear

on

the

time-sharing

computer.

Each o f the alphanumeric

entries

has

been replaced

by a

number

indicating

that

entry's

relative position in

the

dictionary f i l e . An important

po i nt i s that

th e

u se o f this method o f storing dic

ti o n ary pointers rather than the l o n g character-

string e n try sa ve s a

co nsi d era b l e

amount o f space

in

the

computer. For

instance,

instead

o f having

the

full county name Marquette appear

in

every re c

ord

in that

county,

th e

word

i s

replaced

by

a

number

indicating

i t s position

in

th e dictionary. Decimal

number and i n t e g e r

d at a fields

a re sto re d a s they

were entered.

For a

given r e co rd , se v e ra l

fields may

have

been

left

blank on

th e

original

input

sheet,

meaning that the data

for a

particular item a re un

av a i l a bl e .

The GRASP software will

compress

the

data

so that the

numeric

master

f i l e i s

a s

sm a l l

a s

possible.

AFortran IV program, BUILD1, changes th e raw

i n pu t re co rd into the compressed unformatted bi

nary

numeric master f i l e . The

BUILD1 program

r e a d s in

each

transmitted record, checks

for

blank

numeric fields to ensure that they do not

g e t sto re d

a s zero, compares each alphanumeric entry in each

raw-data record with the co n te n ts o f th e appropri

a te part o f th e dictionary f i l e in order to determine

that

entry's

numeric

position

in

the

dictionary,

and

finally writ es

th e

transformed record into

the

nu

meric master f i l e . The

program i s

run once fo r each

cassette f i l e that

i s

transmitted to

the

timesharing

computer.

BUILD

has been designed so that re c

ords that are already a

part

o f the

numeric

master

f i l e

may

be updated easily.

The update part o f th e

program

a p pl i e s t o numeric fields

o nly .

The resultant

new numeric

master

f i l e

will then

co nt a i n the

o ld

numeric master

f i l e

and any

updates that have

been

made, a s w el l a s

the

most recently transmitted ca s

sette f i l e . I n a d di ti on to

the

electronic e d it i ng per

formed during th e

initial

data e ntry and the e d it i ng

functions

o f th e programs, th e

entire

data se t was

e d it e d

manually

by

comparing

printouts

o f

th e

data

with

the original

data sheets.

At this po i nt the f i l e can

be

interrogated by th e

GRASP system. Among the

things

GRASP can

be

used fo r i s th e creation o f

subfiles.

Through use

o f

condition,

logic, and

search

commands,

the se su b-

f i l e s

can

be generated

according

to user-specified cri

teria. The f ol l ow i n g a re examples o f subfiles : ( 1 ) a l l

th e blocks whose most

abundant iron

mineral i s

magnetite and which

co nta i n 1 5 m i l l i o n to 30 m i l l i o n

tons

o f i ro n

ore,

and (2) a l l th e b l o cks tha t

have

a

grain size o f less than 0 . 0 2

inch

(0.5

mm)

or a

maximum Pleistocene

thickness o f

no

more than 120

feet

( 3 7

m).

Simple

statistical

o p erati o ns

can be

performed

on

the master f i l e o r

any

subfiles.

By

use

o f th e

function

command, th e

user can

o bt a i n

the

maximum, minimum,

mean, variance,

and standard-

d e v i a t i o n v a l u e s fo r any o f

the

variables. Not

o n l y

are they important numbers in themselves, but the

maximum andminimum v a l u e s a re quite v a l u a b l e a s

secondary e d it i ng numbers. Extremely high o r low

numbers will show up a s e rro rs and can be f l a g g e d

and

changed.

The program will a l so ca l cu la te the

slope, intercept, and correlation coefficient fo r a

least-squares regression line

between

any two nu

meric variables.

The

final

data

f i l e

contains

1,860

records

which

a re a l l

accessible and

updatable by

th e

GRASP soft

ware

system.

On the basis o f

any

given

se t

o f c on d i

tions and associated

logic,

i t takes

about 45

seconds

to search

th e

entire f i l e and to select the

appropriate

records

to be

stored in a

subfile.

The

total

cost

o f

this o p erati o n averages about $2.7 5

fo r each

com

puter run.

VARIABLES

Each o f 1 ,86 0 blocks containing iron-formation i s

characterized by a se t o f va ri ab l es d e scri b e d b e lo w .

A

hypothetical cross

section

and data b l ock

a re

shown in

figure

2

to

illustrate the manner in

which

ce rta i n v ari a b le s were

measured

and assigned to

blocks.

IDENTIFICATION AND LOCATION

These v ar i a b l e s provide information on the identi

fication and geographic and spatial location o f ind i

v i d u a l blocks.

Unique

identification number.—

he district

was

d i v i d e d

on

a half-mile (0.8-km)

grid by

north-south

and

east-west

lines, and

each Vi-mi2 ( 0 . 6 5 -km2) area

was assig n e d a unique i d e n t i f y i n g number, ID1,

that

corresponds to

a

number assigned to that b l ock

on

an index map o f th e district. The district was fur

ther

d i v i d e d

into

horizontal

slabs,

either

500

feet

( 1 5 2 . 4

m)

thick

(for the two

slabs n e ar est

the

sur

face) o r 1 , 0 0 0

feet

( 3 0 4 . 8 m) thick. The depth be

low

the

surface

i s indicated by

I D 3 ,

the

depth

to

th e

bottom o f the slab. These

two

a re separated by ID 2,

an

alpha character coded to indicate the formation


13/31


14/31

RESOURCE DATA BANK

7

TACONITE CHARACTERISTICS

Seventeen variables are

i n c l u d e d

that give infor

mation

on the nature and

magnitude

o f iron-forma

tion

within

a block.

Grade.

—

ive

variables

give

the percentage

o f

iron,

s i l i c a ,

phosphorous,

manganese,

and

alumina

in the

i r o n - f or m at i o n . Values

were obtained mostly

from

assays

o f

drill

core

provided

by mining

com

p a n i e s

but also

from

a n a l y s es by the U.S. Geological

Survey

o f drill core and

samples from

outcrops. Be

ca us e much o f

th e

drilling was done

in e xp l o rati o n

for

high-grade ore, many cores are partly in materi

al that

has

undergone secondary

enrichment,

and

thus, th e

cores a re not r e pr e se n ta t i ve o f

most

o f the

i r o n - f or m at i o n .

To

a v o i d b i a s i n g our v a l u e s

by

these

higher grade cores,

any

a n a l y s e s

o f

gre at er

than 40

percent iron were excluded from our

d ata.

Volume o f iro n -f o rm ati o n .—he volume o f iron-

formation in m i l l i o ns o f cu b ic feet c o n t a i n e d in each

slab i s calculated from cross secti o ns drawn

a t

Va-mi

( 0 . 8-km )

intervals

approximately

perpendicular

to

the strike

o f th e iron-formation. Where the shape

o f the iron-formation

between

cross sections i s to o

irregular to approximate by co n si d e ri n g o n ly

end

areas, the volume i s estimated by approximating the

shape

by means o f combinations

o f po l y he d ra l

forms

whose

volume

can

be calculated from simple

f orm u l as.

Density

of i r o n - f or m at i o n .

—

he

density o f iron-

formation i s

recorded in short tons per cubic foot.

I t

i s

determined i n di vi d ua l ly fo r

each slab from a

graph

relating density to iron

percentage.

M i l l i o ns o f sho rt to ns o f i r o n - f or m at i o n .

—

he

amount o f iron-formation

in

m i l l i o ns o f sho rt tons

i s

determined

by

multiplying

density

by

th e

volume

o f iron-formation

in th e block.

Millions o f

short

tons o f iron.—

he

amount o f

iron in m i ll i on s o f short tons i s

determined

by m u lti

p l y i n g m i ll i on s o f short

tons

o f iron-formation in the

b l ock

by the iron

percentage.

Grain s i z e .

—

he grain-size variable

indicates

th e

size, in m i ll i m ete rs, o f chert grains. The v a l u e i s

determined either by direct measurement in thin

sections o r i s d eriv e d from the

location o f

the

b l ock

with

respect to metamorphic isograds by using ob

served relationships

between

metamorphic grade

and

gra i n

size.

Most

abundant

i ro n m i ne ra l .

—

he

most

abundant

iro n - b e ari n g mineral within th e entire slab

i s

de

term i n e d . It may represent an average determined

from two o r more lithologic types o f i r o n- f o rm a ti o n .

Mineralogic co nt e nt i s

determined

from drill

re c

ords, thin sections, and field observations.

Other i ro n m in era ls.

—

hree

variables

indicate

other abundant (more than 1 0

percent) iron miner

als

contained in the slab.

Accessory minerals.

—

he three most common a c

cessory minerals (less than 1 0 pe rce n t) , excluding

quartz, a re

listed

a s s e pa r a te variables.

DEPOSIT

CHARACTERISTICS

The

remaining v ari a b le s d e scri b e mostly

geo

metric

and g e o l o g i c

r e la t io n shi p s o f

the deposit and

can

be used

to judge

i t s m i n a b i l it y .

Formation

name.—he stratigraphic

name o f

the

formation or member i s

i n c l u d e d here

and i s

an

alternative

means

o f

storing

and retrieving th e in

formation

given

by

ID2, but

here i s listed in full in

alpha

characters rather

than

in coded

form.

Formation

thickness.

—

he total

stratigraphic

thickn ess of th e iron-formation o f which

the

materi

al i n c l u d e d

in

th e b l ock i s a part ( I

in

f i g . 2)

i s

ind icated.

Iron-formation

thickness.

—

he

maximum

verti

ca l thickness o f iron-formation within the b lo ck ( j

and k in f i g . 2 ) i s defi n e d.

I nt erl a y er e d waste thickness.—he

thickness o f

waste

rock, determined l arg e l y

from

drill d ata,

i s

listed.

Iron-formation/waste.—ron-formation/waste i s

calculated a s the ratio o f thickn ess of iron-formation

to thickn ess of waste rock.

Dip.

—

he average d i p o f bedding o f the

iron-

formation estimated

to the

n e ar est 5 °

i s

listed here.

Thickness o f

Pleistocene

overburden.

—he thick

ness o f

Pleistocene

cover

i s

measured

in feet and in

clu d es

separate

v ar i a b l e s

fo r

maximum,

minimum,

and average thickness.

Values

a re

determined from

d i a m o n d - d r i l l i n g and

w a t e r - w e l l

records.

Stripping required to

uncover iro n -f o rm ati o n .—

Separate

v a l u e s a re given fo r consolidated (c and d

in

f i g .

2)

and u nco nso l i d at e d ( a and b

in

f i g . 2)

strip

ping. Unconsolidated stripping

i s calculated by using

the average Pleistocene thickness.

Consolidated

stripping

i s

calculated from the same cross

sections

used

to calculate

iron-formation volume.

Only ma

terial

within th e b l ock i s

considered,

so that figures

do not reflect

the

total

amount

o f rock that might

have

to bemoved

to

actually mine th e iron-formation

because

mining might

also

require

moving

rock

in

adjacent blocks.

I nt erl a y er e d

waste-rock

type.—wo

vari a b l es

identify

th e

two most common types

o f rock inter

l a y e r e d with th e

iro n -f o rm ati o n .

They are

deter

mined

l arg e l y

from drill records.


15/31

1 0

IRON-FORMATION,

MICHIGAN

STIMATES

OF

NEGAUNEE

1 0 0 p

9 0

8 0

7 0

W

g o

o

O 5 0

o

m 4 0

3 0

2 0 h

1 0

o

SB

?

°

c c

l u —

z

<

c c

a

z

o

<

2

c c

O

L L

z

o

c c

u

H

Z

C 3

<

C O C O

L ? O

I H

is

H

L U C C

L O

-

C C

<

O

u

L U ( J

b z

C O C O

g

<

C C

O

O

c c

<

U J C 3

b z

C O C O

Figure 4 —raph showing b i l l i o n s of long tons of N e g a u n e e

Iron-formation

i n categories described i n the t e x t . Shaded

part of bars i s

iron-formation

within

1,000 f e e t ( 3 0 4 . 8

m)

o f the

surface.

Smaller bars

indicate

a m o u n t of

each c l a s s

that contains more than 10 percent s i d e r i t e .

m at eri a l i s within 1 , 0 0 0 feet ( 3 0 4 . 8 m) o f the su

face. Next in importance i s iron-formation c ont a i

i n g

magnetite a s

the

most abundant m i n e r a l . Abou

48

billion

l on g to ns

o f this

type

i s present,

of

whi

about 10.5 billion l o n g to n s i s within 1 ,0 00 fe

( 3 0 4 . 8

m) o f the surface. Coarse-grained he m atit

i r o n - f or m at i o n ,

co nce ntrat a b l e by froth flotation,

th e

least

abundant

type, totalling

about

27.1

billi

l o n g

tons, o f which

o n l y about

4.8

billion

l o n g to

i s

within

1 , 0 0 0

feet

( 3 0 4 . 8 m)

o f

th e surface. Silica

iron-formation, not amenable to concentration

means o f present technology, totals about

3 7 . 6

b i

lion l o n g tons, about 5 .6 billion l o n g to ns o f which

within 1,0 0 0 feet ( 3 0 4 . 8 m) o f th e surface. Abou

92.5 billion l o n g to ns o f

th e

iron-formation

i s al

siderite-bearing.

Locally, siderite

i s

the

predomina

iron mineral in the i r o n - f or m at i o n ,

but

we ha

identified no blocks in which i t i s the most abunda

mineral within an entire i/i-mi2 ( 0 . 6 5 -km2) are

Thus, this large tonnage d o es n ot re pre se nt

a d d

tional iron-formation

over tha t o f th e first f o

classes, but

i s

a repetition o f th e

tonnage indicat

f o r h e ma t iti c , magnetic, and silicate

iron-formati

that also co nt a i ns

siderite a s

an

abundant ( >

1 0

pe

cent)

m i n e r a l . The amount

o f each

class that co

tains

siderite in

quantities

gre at er than 1 0

p erce

i s

also shown in

figure 4 .

These figures

indicate t ha t th e Negaunee

co nt a i

a maximum o f about 167

billion

l o n g to n s o f iro

formation that

might

be

treatable

by existing

co

centrating

pro ce sse s o r m o d if ica ti o n s o f

them.

Abou

44 billion

tons o f this

m at eri a l i s

a t depths

o f le

than

1 , 0 0 0

feet ( 3 0 4 . 8

m) beneath

the

surface

a

might

be

accessible

to o p e n -p it

mining. Certainl

some

percentage

o f tha t

amount

will

never be

e c

nomically

av a i l a b l e from open pits. However,

t

error

i ntro d uce d

by

i n c l u d i n g economically u n a v a i

a b l e

iro n -f o rm ati o n

in

this assessment

i s

a t

lea

partly offset

because we excluded

iron-formation

depths gre at er than 1 , 0 0 0

feet

( 3 0 4 . 8

m),

some

which will

probably be

mined a t presently operati

open

pits. Future

pits

might

also be

deeper

th

1 , 0 0 0

feet ( 3 0 4 . 8

m).

We

emphasize

that

these f

ures

can in

no way be

construed

to repres e nt

e c

nomically reco v era b l e ore. They simply i n d i ca te t

maximum amount o f m at eri a l that meets minimu

requirements to be co nsi d ere d a s potential co nce

trating-grade

ore.

Many

other

variables

must

be

d

fined

in order to make a

more certain assessment

the economic potential

o f the m ate ri a l.

Many

the se va ri ab le s are not g e o l o g i c and

cannot

treated by means

o f our

data

b ase. Of

the g eo l og

variables, many require d etailed information

fa r


16/31

IRON RESOURCES

1 1

excess o f our data base and cannot be estimated. A

few a d d it i o n a l

g e ol o gi c v ari a b le s

that we can

esti

mate

are co nsi d ere d

b e l o w .

Two

important v ar i a b l e s

in

determining th e feasi

bility

o f open-pit mining

a re the

amount o f over

l y i n g waste rock that

must

be stripped

and

the

amount o f

interlayered waste rock that

must

b e

moved

along

with

ore.

Figures

5

and

6

show

maxi

mum

tonnages o f possible

treatable

iron-formation

within

1,0 0 0 feet

( 3 0 4 . 8 m)

o f th e su rf a ce that can

be

mined relative to th e

amount

o f waste rock

that

would be moved. No generalizations can be made fo r

the amount o f waste that can

be

moved e c o n o m i c a l l y .

The economics o f i n d i v i d u a l

mining

pl an s a re gov

erned by a complex se t o f factors, and there i s ,

3 5

2

3 0

C O

O

H

P U

< z

D C - 1

O

u .

Z

o

D C

1 1

—

-

- _

J

-

1 0 1 0 0

1 0 0 0 1 0 , 0 0 0

CONSOLIDATED

STRIPPING,

I N M IL L ION

CUBIC

F EET PER '/.-SQUARE-MILE BLOCK

Figure 5 .—i sto g ra m sh ow i n g b i l l i o n s of long tons of the

possibly treatable N e g a u n e e Iron-formatio n within 1,000

f e e t

( 3 0 4 . 8 m) o f the

surface r e l a t i v e t o volume

of co n

s o l i d a t e d

waste rock

overlying i t .

Vo l u m e of waste i s c a l

cu la te d o nl y

within

v e r t i c a l

boundaries

of

each

V i - m i 5

b l o c k , n ot w ithi n

inward

sloping boundaries as w o u l d

probably be

required

for d evelopment

o f

an ope n p i t .

3 0

1 0 0 0

VOLUME IRON-FORMATION/VOLUME WASTE

Figure

6—

i sto g ra m sho w i n g b i l l i o n s

o f

long tons of

the

possibly treatable N e g a u n e e

Iron-formation

within 1,000

f e e t ( 3 0 4 . 8

m) o f the

surface with various r a t i o s

o f

volume

o f

iron-formation t o volume

of

interlayered waste

r o c k .

therefore,

a wide

range in

tolerance

fo r waste rock.

No attempt i s made in this report to estimate

amounts o f iron-formation that

c ou l d

be mined

e co

nomically relative to amounts o f a sso ci a te d waste

rock that would need to b e moved.

Figure 5

shows,

however, that development

o f

a

major

part o f

the resource may not be hindered

seriously

by

large

amounts

o f

o v e rl y i n g w a s te .

Near

ly three-quarters o f the m at eri a l within 1,0 0 0 feet

( 3 0 4 . 8 m) o f th e su rf a ce

requires

stripping o f less

than

1 m i l l i o n

f t 3

( 2 8 , 3 2 1 m3) o f consolidated ma

terial

fo r

each

Vi-mi- ( 0 . 6 5 -k m 2 ) area

to

uncover th e

i r o n - f or m at i o n . These figures

fo r o v erl y i n g consoli

d a t e d

waste must be co nsi d ere d

approximate mini

ma for two reasons.

First, we

have

d ef i n e d o v erl y i n g

stripping a s

being

restricted mostly to

quartzite and

conglomerate stratigraphically above th e Negaunee,

whereas an i n d iv i d u a l

mine

may

be in

a

stratigraph

ically medial position in th e

Negaunee

and

have

a

metadiabase

s i l l , i n c l u d e d

in

our figures a s inter

l a y e r e d

waste,

a s

o v erl y i n g

rock.

When

i n d i v i d u a l

mines are

considered,

therefore,

there may

in fact

be m at eri a l to b e

stripped,

such a s metadiabase, that

in our figures i s

i n c l u d e d

a s i n te rl a y e re d waste rath

e r

than

a s o ve rl yi ng w a ste . Se co nd , in

calculating

volumes o f stri pp in g , we have calculated o n l y ma

terial directly above the iro n -f o rm ati o n o f interest,

which, in effect, assumes

vertical

pi t w a l l s i f our

figures are applied

to

an

i n d iv i d u a l

mine.

Because

vertical

pits a re

g e n e r a l l y

n o t feasible in actual

min

i n g

practice, o v e r l y i n g

and adjoining waste volumes

fo r an i n d iv i d u a l

mine would often be somewhat

gre at er

than our figures indicate.

Figure 6 indicates that more than 90 p erce nt o f

th e 44 billion to ns o f

possibly

treatable iron-forma

tion within 1 , 0 0 0 feet

( 3 0 4 . 8

m) o f the

surface has

iro n -f o rm ati o n : waste ratios gre at er than 1 : 1 and

that

nearly

16 billion tons has a

ratio

o f better than

1 0 : 1 .

Thus,

excessive volumes o f interlayered waste

rock do not

seem

a major hindrance

to

development

o f a large percentage o f th e

resources.

Much o f the

waste i s interlayered

metadiabase

s i l l s ,

which a re

g e n e ra l l y l a rg e discrete b o d i e s

(see

f i g . 1 ). I n min

ing,

much

o f

the

s i l l s c ou l d be left i n pl a ce , e ff e cti ve

ly improving th e iron-formation : waste ratios o f th e

m at eri a l actually mined. However, in places, th e

presence o f the

metadiabase

s i l l s

would

cause min

i n g

o f

some

underlying iron-formation

to

be

e co

nomically unattractive.

RESOURCE CLASSIFICATION

A

classification system f o r r e so u r ce s based on de

gree o f economic feasibility o f mining and process


17/31

12

IRON-FORMATION, MICHIGAN

STIMATES OF NEGAUNEE

i ng the

o re and on degree o f

g e o l o g i c

assurance with

which

th e deposit i s

known was proposed by McKel-

vey 1973 and has been adopted

by

the U .S. Geo

logical Survey

and

the

U.S.

Bureau

o f

M i n es. A

m o d i f i e d ve rsi on o f tha t classification i s used here.

Our classif ication d if fers from McKelvey's in two

ways. First, we do n o t i n c l u d e

c ate g o ri e s f or

u n d i s

covered

resources.

We

co nsi d er

that

the

Marquette

district i s so thoroughly e xp l o re d that a l l the ma

terial indicated by our figures i s known with ade

quate degree o f assurance to be co nsi d ere d an identi

fied resource.

The possibility

that

substantial a d d i

tional

deposits

o f


exist in the

district

i s negligible in light o f the

g r e a t

amount o f g e o l o g ic

and geophysical data on th e area. Seco n d , we do not

subdivide re se rve s a s

suggested

by

McKelvey.

We

co n si d e r tha t the

definition

o f economic availability

o f iro n

o re i s dependent

on

many

factors

that can

not be estimated

without

very d e ta i le d stu d ie s and

that reserves

a re

restricted

to thoroughly tested

ma

terial

a t existing

mines

o r

in

a r e a s

where

d e v e l o p

ment i s known

to

be feasib le in the immediate

future.

I n figure 7 , th e tonnage that we assign to each o f

seven resource

categories

i s shown. Under

economic

deposits,

we

include

estimates o f e co n om i ca l ly re

c ov e ra b l e m a te r i a l a t

three existing

taconite mines

plus

one deposit a t which development in th e near

E C O N O M I C

MEASURED, I N D I C A T E D , AND INFERRED

2-3

P A R A M A R G I N A L

MEASURED

INDICATED

INFERRED

S U E C O N O M I C

2 6 . 1

7.9

7 . 3

S U M R G I N L

7.6

20.9

133.1

—DECREASING

GEOLOGIC ASSURANCE

-*

[ A l l f i g u r e s i n b i l l i o n long t o n s ]

Figure 7 .—

esource

c l a s s i f i c a t i o n chart showing b i l l i o n s o f

long tons of Neg a u n e e Iron-f ormatio n assig ned

t o

cate

gories based

o n

varying degrees

t o

which material a p

proaches the characteristics

of presently

economic

deposits

a n d the

degree of

a ssu ra n ce w i th which the d epo si t

i s

known.

future has been announced.

These

estimates a

based

on annual production

capacity

of co nce ntra

i n g plants and

presumed

minimum l i f e span of th

mi n es, a s w el l a s on pu b l ishe d reserve figures.

Under subeconomic resources, we

have

d i v i d

m at eri a l into two

categories—

aramarginal r

sources and submarginal resources—n th e

basis

mineralogy

and

depth

below

the

surface. Parama

g i n a l

resources include

m at eri a l that has m a g n etit

hematite, o r

goethite

a s the

most

abundant

iron

mi

eral

and that i s within

1 , 0 0 0 feet

( 3 0 4 . 8 m) o f th

surface.

Thus, paramarginal

resources include ma

terial

that

i s potentially

accessible

to

open-pit

min

ing, and

that

has

m i n er a l o g ica l similarities to ma

terial presently

being

processed commercially. A

though

large

amounts o f this m at eri a l may not b

processible by techn iq u es currently used, we consi

e r i t likely that new processes o r m o d i f i c at i o n s o

current ones c ou l d successfully beneficiate much o

i t . Al l the m a te ri a l has one feature in common—

a l a rge

percentage

o f

the

contained

iron

i s

presen

in a mineralogic form ( ox id e o r hydrous o x i d e min

erals), fo r which

b eneficiatio n requires

o n l y

th

physical separation o f iron

minerals

from gangu

minerals.

Submarginal resources include m at eri a l

a t depth

gre at er than

1 , 0 0 0

feet

( 3 0 4 . 8

m) and

a l l m at eri a l

r e ga r d l e ss o f d e pth ,

that

co nt a i ns iron-silicate a s th

most abundant m i n e r a l . Submarginal resources

therefore, include (1 ) m at eri a l that to

become

e co

nomically reco v era b l e would require a

substantia

improvement in mining o r p ro c e ssi n g technology o

a substantial increase in price o f i ro n co n ce n tra te s

o r b o th; and (2) m at eri a l fo r which the concentra

tion

o f

much

o f

th e

contained

iron

requires

a

chemi

ca l a s w el l a s a phy si ca l process.

We have rather a r bi tr a ri l y d e f in e d limits

on

de

gree o f g e o l o g i c assurance a s five o r more data point

(outcrops plus drillholes) per mi2 ( 0.65 km2) fo

measured resources, and one to four data points pe

Vi m i 2 ( 0 . 6 5

km2)

f o r i n d ica te d resources. Materia

not known directly but whose presence

i s predicte

by projection o f data for relatively

short

distance

i s co nsi d ere d an inferred resource.

Figure 7 shows that fo r paramarginal

resource

about 34 billion l o n g tons, o r more than 80 percen

o f the ca te g ory , i s known

from

a t

least one

dat

p oi nt

per

Vi

m i 2

( 0 . 6 5

km2) and

more

than 60

per

cent i s known from five o r

more data

points. Thi

high

degree

o f g e o l o g ic assurance reflects the de

tailed surface mapping o f th e district a s w e l l a s th

gre at number o f

drillholes

that pe n e tra te the firs

1 , 0 0 0

feet

beneath

the

surface.


18/31

IRON RESOURCES

1 3

For submarginal

r e so u rce s th e situation i s

re

versed.

Only

about

7 .6 billion

l o n g tons,

o r

about 5

percent o f the category

i s

known from more than

five data

points per V4 m*2 (0.65 km-),

whereas

gre at er than 80 percent o r 1 3 3 . 1 billion l o n g tons

i s

inferred

by

projection o f d ata. Because i n f e rr e d su b -

marginal resources account fo r about 65 p erce nt of

th e

total

resource,

we

would like

to

co nsi d er

briefly

th e

degree

o f assurance with which the m a te ri a l i s

inferred. We a re d e a l i n g with a stratigraphic unit,

th e Negaunee Iro n -f o rm ati o n, that i s known from

surface and n e ar-surf ace data to vary g r a d u a l l y

along

stri ke i n a manner in which th e most impor

tant

variables such a s

thickness and

mineralogy

can

g e n er a l l y be

predicted

rather w e l l between

data

points 1 mile (1.6 km) apart. Our data bank i s n o t

co nstructe d so a s to i d en ti fy re a d i ly the n e a re st d a ta

point to a block, but we believe, from

our

e xp eri e nce

in

analyzing

the data, that seldom i s a b l ock more

than 1

m i l e from

a data point.

Therefore,

although

by

projecting

data

we

i ntro d uce

some

u ncerta i nt y

into our figures f o r i n f e rr e d resources,

wefeel,

from

the

degree and scale o f

variation se e n

a t

the surface,

that

in projecting

our data

relatively

short distances,

we have notintroduced

any

gross errors.

ESTIMATES OF TOTAL RECOVERABLE

IRON

Ultimately the most important va l u es

for

iron re

sources

are estimates o f the amount o f m e ta l l ic iron

that can b e produced from av a i l a b l e

i r o n - f or m at i o n .

As wehave indicated previously, we do not

attempt

to d ef in e

amounts o f

economically

reco v era b l e iron.

We have,

however,

estimated the maximum amount

o f iro n that

might

be produced from known iron-

f orm ati o n,

given

economic

c o nd i ti o n s th a t

a l l o w

i t s

profitable mining

and

processing.

These

f i gu re s i n di

cate

the maximum g e o l o g i c availability

o f i ro n

under

existing o r somewhat improved technologic and e co

nomic conditions

and

can

be

co nsi d ere d an

upper

limit

for

iro n r eserves.

To d efine

the

amount o f

recoverable iron,

we

must

answer

two b a s i c

questions.

First, what percentage

o f th e

iron-formation i s

amenable to processing

to

make a concentrate that meets quality

standards

fo r

co nt a i n e d iron and silica? Seco n d , o f

the

amount o f


that

meets

minimum

quality stand

ards, what

percentage o f

th e

iron can be recovered

?

To answer these questions requires data on the

metallurgical response o f iro n -f o rm ati o n to vari o us

concentrating processes. Comprehensive tests fo r

th e

Negaunee

a s a whole

have

never been made;

rather,

a few areas, which for a variety o f reasons

have received concentrated study,

have

been rather

thoroughly tested, and we are l arg e l y without

data

fo r

the

remainder o f

th e

district. Precise

estimates

based

directly on

e mp irica l measurements

cannot

be

made, but

the

av a i l a b l e metallurgical data can be

us e d

to predict

the maximum amount o f i ro n recov

e r a b l e from untested m at eri a l . To do this, a Monte

Carlo sim u l ati o n model was d e s i g n e d, based on

the

assumption

that

th e

m at eri a l

fo r

which

test

results

are

known

i s

th e

same

a s

m at eri a l

to

which

the

data

a re

being projected.

The

results provided

by

the

model a re no more o r less valid than that assump

tion. P oss i b l e e rrors o f o v e r e st i m a ti o n i n t ro d u c e d by

this assumption a re discussed in more detail

b e l o w .

The e mp irica l base fo r th e

model

was d e r i v e d from

metallurgical tests by

the

U.S. Bureau o f Mines

(Heising and Frommer, 1 9 6 7 ) and

from

data pro

v i d e d by

mining

companies. I n

a l l ,

more than 3 6 , 0 0 0

feet

( 1 0 , 9 7 3 m) o f

drill core

i s i n c l u d e d

in

th e tests;

an i n d iv i d u a l test i s g e n e r a l l y

on 5-20

f ee t ( 1 .5 -6 .1

m) o f core.

Metallurgical data a re

av a i l a b l e

fo r

4 1

sample

blocks.

They

a re

d i v i d e d

into

three

types

o f

tests

and a re

shown in

figure

8 and

table

2 . Ten sample

Table 2 —

etallurgical

d a ta u se d

i n

simulation m o d e

[ E a c h l i n e

r e p r e s e n t s a v e r a g e

r e s u l t s

f o r o n e

d a t a b l o c k I

I r o n -

C on ce n t r a t e C on ce n t r at e R e c o v e r a b l e

f o r m a t i o n

Fe

S i O = F e i n b l o c k L e n g t h o f

( i n w t . ( i n w t . ( i n w t .

( m i l l i o n

d r i l l c o r e

p e r c e n t )

p e r c e n t ) p e r c e n t )

l o n g t o n s )

t e s t e d ( f e e t )

Magnetic s e p a r a t i o n

6 0 . 8

1 2 8

3 8 . 2

2 9 6 . 9

3 , 3 2 0

6 7 . 2

5 . 9

2 5 . 2 1 7 9 . 9 1 5 3

6 3 . 4

1 0 . 7

2 4 . 7 2 4 9 . 3

4 , 8 4 2

6 3 . 6

9 . 4

2 1 . 0

1 4 2 . 9 1 , 2 4 1

6 6 . 0

9 . 8 2 8 . 6

3 3 2 . 9 1 , 6 2 1

6 4 . 7

8 . 8

2 5 . 8

3 0 9 . 3 1 , 7 0 6

6 7 . 2

1 7 . 6

3 4 . 2

6 9 . 2 6 9 7

5 5 . 6

1 9 . 1 3 1 . 1 8 4 . 7

2 , 3 8 8

6 4 . 1

9 . 1

1 7 . 3 2 4 . 9

2 3 4

6 3 . 6

9 . 3

2 5 . 7

5 2 . 3

9 1 1

6 0 . 6

a . s

2 7 . 0

5 2 . 4

6

6 5 . 7 6 . 4 2 7 . 2

3 9 . 2

5

6 2 . 7

8 . 0

4 9 . 5

1 3 . 3 1 5

6 6 . 6 7 . 2

1 9 . 0 2 8 . 8

1 0

6 7 . 1

7 . 2

4 3 . 8

8 . 9

1 0

6 5 . 7 2 0 . 3

2 9 . 4

4 7 . 0

5

5 8 . 0

1 5 . 7

5 0 . 2

3 9 . 2

6 0

5 5 . 9 2 2 . 4

4 4 . 2 2 7 . 4

4 6 7

5 7 . 6

1 6 . 3

4 8 . 2 9 . 6

1 8 7

S e l e ct i v e f l o c cu l at i o n

6 0 . 2

1 8 . 4 3 6 0

1 2 7 . 4

7 1 5

6 6 . 3

4 . 0

2 0 . 6 3 4 5 . 8

T r e n c h

s a m p l e s

6 4 . 1 5 . 8

2 9 . 6 1 4 5 . 8 D o .

6 6 . 4

5 . 3

2 8 . 7

1 5 3 . 8

D o .

6 6 . 7 4 . 4

2 5 . 5

2 0 5 . 9

D o .

5 1 . 1 1 9 . 0

I S .

7

1 4 2 . 2

D o .

6 1 . 6

1 1 . 8

3 3 . 9 2 0 4 . 5

3 , 9 7 4

5 7 . 5

1 6 . 0

3 0 . 1 1 8 2 . 8

6 5 4

6 0 . 5

1 3 . 1

3 3 . 7

2 8 7 . 3 3 , 9 2 9

6 2 . 3

1 0 . 6 3 4 . 8 7 6 9

7 , 9 4 8

Froth

f l o t a t i o n

6 4 . 9 4 . 0

2 4 . 7 1 2 . 4

1 7 2

6 3 .

8 . 1

2 7 . 8 2 0 . 6

1 0

6 4 . 1

4 . 3

3 8 . 7

1 9 . 3

5

5 9 . 5

6 . 8 3 0 . 2

1 5 . 5

5

6 7 . 9

8 . 1

3 9 . 3

2 8 . 8 1 0

6 7 . 0

2 . 1

3 5 . 5

3 3 . 1 3 0

6 6 . S 4 . 0

3 6 . 4 2 7 . 4

6

6 5 . S

5 . 8

4 1 . 7

8 . 4

1 0

5 8 . 8 1 3 . 4 3 7 . 0

3 9 . 2

2 0 7

5 2 . 2

9 . 8

2 3 . 9

2 7 . 4

T

6 5 . 5

8 . 2 1 9 . 8

1 3 5 . 7

2 94

6 1 . 7

8 . 8 2 5 . 2

7 9 . 0

3 3 5


19/31

1 4

ESTIMATES OF NEGAUNEE IRON-FORMATION, MICHIGAN

L U

t c

<

— I

1 1

C O

O

t r d

u j 5

c o

D

5

4

-

3 -

2

1 -

0

r r T T I

5 0 5 5 6 0 6 5 7 0

PERCENT

CONCENTRATE

F e

DAVIS MAGNETIC TUBE TESTS

[Average r e s ul t s f o r each %- s q u a r e - m i l e b l o c k ]

u

1

2

1

0

n _i _

n

4 - i i 1 1 1 1 1 1 1 1 1 1

1 1 i 1 1 1 1 1 1

m

0 5 1 0 1 5 2 0

PERCENT CONCENTRATE

S i 0 2

2 5 3 0 3 5 4 0 4 5

PERCENT RECOVERABLE

F e

T 1

5 5

C C

<

_ l

u _ C D

O m

c c =

u j

5

C O

5

z >

z

5 -

4

3

2 -

1 —

0

L

I I I Mill 1 i 1 '

5 0

5 5

6 0 6 5 7 0

PERCENT

CONCENTRATE

F e

SELECTIVE

FLOCCULATION TESTS

(Average

r e su lt s f o r

each %-square-mile b l o c k ]

u

3

2

i i i

0

5

1 0 1 5

2 0

2 5

PERCENT CONCENTRATE

S i 0 2

| i t M | 1 i i i i i | i i i |

2 5

3 0

3 5

4 0 4 5

5 0

PERCENT

RECOVERABLE

F e

U J

D C

<

eg

- J

L L 0 3

c o

D

6

4

3 -

2 -

1

0

1

I 1 1 | 1 1 i i |

i i

i

5 0 5 5 6 0 6 5 7 0

PERCENT

CONCENTRATE

F e

FROTH FLOTATION TESTS

[Average r e s ul t s f o r each V i - s q u a r e - m i l e b l o c k ]

5

4

3

-

2 -

1

0

- rnrn

[ i I I | I I | i i i n ]

0 5 1 0 1 5 2 0 2 5

PERCENT

CONCENTRATE

S i 0 2

5

4 -

3 -

2 -

1

0

1 M 1 1

I I

i i 1 i i 1

1 5 2 0 2 5 3 0 3 5 4 0

PERCENT

RECOVERABLE

F e

5 0

U J

c c

<

_ i

u _ C D

o

m

a : =

u j 5

m

Z

6

5

4 -

3 -

p.

I 1

COMBINED

FROTH FLOTATION,

DAVIS

TUBE,

AND

SELECTIVE

FLOCCULATION TESTS

[Average r e s ul t s f o r each V 4 - s q u a r e - m i l e b l o c k ]

n

5 0

5 5 6 0

6 5

7 0

PERCENT CONCENTRATE

F e

1

I I I

1 i 1

0

5

1 0

1 5

2 0

PERCENT

CONCENTRATE

S i 0 2

2 5

3 0 3 5

4 0 4 5

PERCENT RECOVERABLE

F e

5 0

5 5

Figure

8—

istograms

showing r e s u l t s of

three types

of metallurgical t e s t s . Se e t a b l e 2

for tabulated r e s u l t s . Perce

concentrate

Fe i s

percentage

b y

weight

of

F e i n

f i n a l concentrate; percent

concentrate

Si O

i s

percentage

b y w e ig

of Si02 i n f i n a l concentrate; percent recoverable Fe i s

percentage

of crude ore

recovered

as

F e

i n

f i n a l concentra

(weight Fe i n concentrate/weight crude o r e ) .


20/31

IRON

RESOURCES 1 5

blocks represent f i n e - g ra i n e d hematitic iron-forma

tion, 1 9 b lo cks represent magnetic i r o n - f or m at i o n ,

and 1 2 blocks re pre se n t co a rse - gra i n ed he m a ti ti c

iro n -f o rm ati o n .

Each v a l u e on

th e

histograms and

in th e table represents an average for one o f our

blocks.

Each

average i s d eriv e d from one to more

than 100

i n d i v i d u a l tests.

The model i s designed to test

o n l y

paramarginal

resources, because metallurgical d ata a re av a i l a b l e

o n l y fo r m at eri a l in

which

o x i d e s and hydroxides

a re the most abundant iron minerals and that

can

b e concentrated by means o f current technology.

Thus, large

qu an ti ti es o f i ro n c o n t a i n e d

in

silicate

and carbonate minerals

are a ut o m atica l l y excluded

because

no technology exists

to concentrate iron

con

tai n e d

in th ese m i n era l s. Also,

iron

co nt a i n e d

in

iron-formation

a t

gre at er

than 1,0 0 0-foot ( 3 0 4 . 8 - m )

depths

i s excluded

because we have l i m it e d our esti

mates to m at eri a l within 1,0 0 0

feet ( 3 0 4 . 8 m) of

the

surface.

Paramarginal resources were

d i v i d e d

into

three

categories

according

to

mineralogy and

gra i n

size

fo r

testing a g a in st the

most

appropriate

metallurgical data. Fine-grained hematitic and g o e -

thitic iro n -f o rm ati o n was

tested a g a i n st

d at a

fo r

selective

flocculation

tests. Coarse-grained

hematitic


was

tested a g a i n s t

froth-flotation

d ata,

and magnetitic


was tested

a g a i nst

Davis magnetic tube d ata.

The distribution

o f these

th re e ty pe s o f iron-formation in the Mar

quette

district

i s shown in figure 9 .

When

the si m u l a ti o n experiment

was

performed,

the

quality

criteria used

fo r

an

acceptable concen

trate were iron in excess o f 60 percent and silica less

than

1 0

percent.

These

v a l u e s

a re

a

few

percentage

points short o f currently a c ce p ta b l e s ta n d a r d s, but

were

chosen for

two

reasons. First,

metallurgical

tests are likely to y ie ld re su lts a few percentage

points

poorer than

results that

can

be achieved

through a

concentrating process

appropriately ad

justed and

fine-tuned to

a

particular

o re b o dy .

Seco n d ,

i f

a cutoff

closer to present

standards

were

used

—

o r instance,

65 percent iron

and 6-8

percent

silica

—he

calculated

va l u es

would exclude much

m at eri a l that we feel should be i ncl ud ed a s a para

marginal

resource. The data

in

tab le

2 ,

for

example,

indicate that o n l y about one quarter o f

the

m at eri a l

tested meets current

standards. Yet

m a te ri a l tha t

fails to

meet those

standards

by o n l y 5 p erce nt o r

less

requires o n l y a slight improvement in

process

ing. Even

though

those improvements

may

be tech

nically difficult to make, we b e l i ev e tha t a high po

tential

for

such improvements exists

and

that

m at eri a l

meeting

our cutoff

criteria

i s clearly

a

paramarginal resource.

We used

the

Monte Carlo sim u l at i o n, a

computer

ized statistical

sampling

procedure, to

test each

b l o ck

r ep e at e d l y a g a i nst known l a b o r atory

tests. I n

our

m o d e l ,

the sampling

began

by

selecting

an

i n d iv i d u a l

b l ock

from the

array

o f b lo cks containing paramar

g i n a l resources.

A

v a l u e

f o r c o n ce n tr a te - i ro n

per

centage was chosen a t random from an

empirical

cumulative distribution curve

d eriv e d from

the

con

centrate-iron

data in table

2 . The

random

selections

were performed in a manner whereby the results o f

a large number

of selections,

i f plotted a s a

cumula

tive frequency

diagram,

would approximate th e

shape

o f the

empirical

cumulative distribution. If

the

concentrate-iron percentage

va l u e

chosen fo r th e

f i r s t

b l ock

was

less

than 6 0 percent ( n ot

acceptable

quality), 0.0 tons

o f

reco v era b l e

iron was

assig n e d

to that block.

The

sampling procedure continued by

again se l ecti n g a t random a v a l u e

fo r

concentrate

iro n fo r

a

second

b lo ck. I f

the

selected

v a l u e

this

time

was

greater

than

60

p erce nt

concentrate iron

(acceptable

quality), the

percentage

o f

concentrate

silica was

tested.

Figure

1 0

shows that

concentrate

iron and concentrate silica a re n ot independent vari

a b l es

;

rather,

a s e x pe cte d , a strong n e g ativ e correla

ti o n e x ists

between

the

two

because

iron and

silica

a re the o nl y important co n sti tu e n ts o f

th e rock.

Thus, concentrate-silica

percentage cannot

be

sam

pled

from the

empirical distribution

a s

an

independ

e n t

variab le. It

was

d eriv e d instead

from th e

regres

sion relationship: SiO, =A0+A (co ne. Fe)±


21/31

ESTIMATES OF NEGAUNEE IRON-FORMATION, MICHIGAN

R 3 1 W 8 8 ° 1 0

R

3 0

W

WOO'

R 2 9 W

4 6 ° 3 5

T .

4 8

N .

T 4 7 N

T . 4 6

N

4 6 ° 2 0

T .

4 5

N

v

-

r

2 3

M

~ 1

I

3 4

K I L O M

B a s e m o d i f i e d

f r o m

t h e C l e v e l a n d -

C l i f f s I r o n C o m p a n y , 1 9 5 0


22/31

IRON

RESOURCES

1 7

R . 2 8 W

4 6 ° 3 5

T . 4 8

N .

4 6 ° 3 0

T 4 7 N .

DESCRIPTION

OF MAP UNITS

DIABASE AND METAMORPHOSED DIABASE

MARQUETTE RANGE SUPERGROUP—I n

c l u d i n g

Negaunee

I r o n - f o r m a t i o n ( X n )

CRYSTALLINE

ROCKS

(PRECAMBRIAN

W)

—

M o s t l y

g r a n i t i c

g n e i s s

Contact—Approximately l o c a t e d ; dashed under

w a t e r

Fault—

Approximately l o c a t e d ;

dashed

under

w a t e r

MINERALOGICAL CLASSES OF

NEGAUNEE

IRON-FORMATION ( X n )

Magnetic i r o n - f o r m a t i o n—o m m o n l y i n c l u d e s

i r o n - c a r b o n a t e

a nd

i r o n - s i l i c a t e

m i