Lead Isotope Guides 

For Mississippi Valley 

Lead-Zinc Exploration

By RALPH S. CANNON, JR., and ARTHUR P. PIERCE

CONTRIBUTIONS TO ECONOMIC GEOLOGY

GEOLOGICAL SURVEY BULLETIN 1312-G

A review of correlations of isotopic 

compositions of ore-lead and tonnages 

of known ore in Mississippi Valley 

lead-zinc deposits

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1969
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HIGKEL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 20 cents (paper cover)
CONTENTS

Page

Abstract________________________________________________________ Gl

Introduction._____________________________________________________ 1

Outlook.________________.__.-_--_ .__._.___ 1

Isotopic evolution of lead_-----_--__----------__------__--_-------_- 2

Introduction to ore-lead data_-___-__--___-_-------_-_-----_-_---____ 2

Best-fit curve._-____-__-__--_---------------_ ______________ 4

Ordinary lead.________________________________________________ 4

J-lead.___-__________---_____-------_-__----_-_-_---__-__--._- 5

U-leads______________-___________________ 6

Isotopic varieties of lead in stratiform lead-zinc deposits ________ __ 6

Isotopic composition versus geographic distribution ________________ 6

Isotopic composition versus tonnage of lead.______________________ 7

Lead isotopes in Mississippi Valley districts.__!_______________________ 9

Tri-State district __ __ ____________________. _ _ __ 9

Southeast Missouri.________________ __ _______ _ 11

Illinois-Kentucky_ _ ______._______--_-__-_-_____--___-________ 13

Upper Mississippi Valley district._______________________________ 13

Lead isotope guides for exploration._________________________________ 16

References cited__.________________________________________________ 19

ILLUSTRATIONS

FIGURES 1-7. Diagrams:

1. Isotopic relationships between uranium, thorium,

and lead in the earth's crust-__________________ G3

2. Isotopic composition of lead from 1,280 ore minerals 

plotted in terms of Pb20«+Pb207 +Pb208 =100.____ 4

3. Frequency distribution of lead isotope analyses of

worldwide ore-leads_________________________ 5

4. Ore-leads in Phanerozoic stratiform lead-zinc deposits

of North America.___________________________ 7

5. Ore-leads in Phanerozoic stratiform lead-zinc deposits

of Europe and Africa.________________________ 8

6. Isotopic composition versus tons of lead in worldwide

Phanerozoic stratiform lead-zinc deposits.__-.___ 9

7. Sampling and isotopic variation of growth zones of a 

cross-sectioned galena crystal from the Tri-State 

district____________________________________ 10

8. Map and section showing isotopic variations in Bonne Terre

mine, Southeast Missouri district.____________________ 12

9. Map of Illinois-Kentucky district, with Pb206/Pb207 data and

contours added.____________________________________ 14

m
IV CONTENTS

Page 

FIGURE 10. Map of Upper Mississippi Valley district, with Pb2W/Pb207

data and contours added__-_--__________________.- G15

11. Map of Upper Mississippi Valley district, showing locations 

of major lead-zinc mines in relation to selected pair of 

Pb2o«/pb207 contours._....._.-._.....___.-...-...---. 16

12. Diagram showing generalized lead isotope data for stratiform

lead-zinc deposits..._____. ..____ 17

13. Diagram: A prospector's guide to lead isotope compositions 

of principal tonnages of lead in stratiform deposits shown 

in relation to both trilinear coordinates (206+207+208 

= 100) and Ph^/Ph ratios______.__.......__ 18
CONTRIBUTIONS TO ECONOMIC GEOLOGY

LEAD ISOTOPE GUIDES FOR MISSISSIPPI VALLEY 

LEAD-ZINC EXPLORATION

BY RALPH S. CANNON, JR., and ARTHUR P. PIERCE

ABSTRACT

Lead in statiform lead-zinc deposits in many regions of the world is found to 

vary notably in isotopic composition. These lead isotope variations are potential 

guideposts for the exploration geologist searching for major lead deposits of this 

class. In the Eastern Hemisphere most such deposits in marine sedimentary rocks 

of Phanerozoic age contain ordinary lead of reasonable model age. In the Mississippi Valley, however, stratiform lead-zinc deposits contain so-called J-lead, 

relatively enriched in radiogenic Pb200, Pb207, and Pb208. For each of the four most 

important lead-producing districts of this region we can define a favorable range 

of lead isotope composition within which one may concentrate the search for 

major lead deposits. In two of these districts we can delineate geographic areas 

within which we are most likely to find lead of favorable compositions. Within a 

third district more intensive investigations have detected three-dimensional 

gradients of lead isotope variation in individual mineralized areas. Such gradients 

should prove helpful in finding and exploring tracts of mineralized ground. Lead 

isotope data from these four districts define the compositions of lead most likely 

to guide the prospector to new major lead discoveries in the Mississippi Valley 

region. In current literature we note other localities from which favorable lead 

isotope analyses have been published.

INTRODUCTION

On September 19,1968, the senior author presented a paper on lead 

isotope variations (Cannon and Pierce, 1968) at a session on geochemistry applied to Mississippi Valley lead-zinc exploration, sponsored by 

the Society of Mining Engineers, at the Fall Meeting of the American 

Institute of Mining, Metallurgical and Petroleum Engineers at Minneapolis, Minn. The substance of that talk is reproduced herein to make 

the information available to a wider audience.

OUTLOOK

The use of lead isotope data may prove to be helpful in future 

exploration for mineral deposits. The isotopic composition of lead in 

lead minerals of ore deposits varies widely, and studies of these variations have for 30 years been making important contributions to better

Gl
G2 CONTRIBUTIONS TO ECONOMIC GEOLOGY

understanding of the various geologic processes that form ore deposits 

(Cannon and others, 1961; Brown, 1965). Such new scientific knowledge of the genesis of ores will surely help to make mineral exploration more effective in the future. Meanwhile, there are tangible 

opportunities to put lead isotope variations to work in exploration 

now, by using lead isotope data empirically, even though we may not 

understand the geologic causes of the variations. If we are able to 

identify lead isotope variations that show positive correlations with 

quantitative information on known distribution of minable ore, then 

we evidently have a useful guide to help us explore for new ore.

Until now, such possibilities have been generally ignored, for a 

variety of reasons. One reason is that lead isotope analyses are expensive one commercial laboratory quotes $175 per analysis. Second, 

people in exploration have seldom had occasion to review the lead 

isotope story in enough detail to appreciate its potential. And third, 

people engaged in lead isotope measurement have seldom given 

attention to practical applications.

We believe that as soon as a breakthrough is made in cost of lead isotope analyses, this kind of information will be put to use on a broad 

front. In this report we wish to suggest several kinds of applications 

that we anticipate in future exploration for lead and zinc in the 

Mississippi Valley region.

I8OTOPIC EVOLUTION OF LEAD

The isotopic composition of lead (fig. 1) varies in lead ores in 

significant ways. The least abundant isotope, Pb804, is inherited from 

the original or primeval lead of the solar system; whereas the three 

most abundant isotopes, Pb208, Pb207, and Pb2*8, are in part original, in 

part radiogenic. These three continue to increase in abundance because 

they are stable end-products of the radioactive decay of uranium 

and thorium. Figure 1 shows how the average composition of lead in 

earth materials may have changed during earth history by decay of 

IT8 to Pb208, U288 to Pb207 , and Th282 to Pb803. This idealized model implies 

that about two-thirds of earth-lead is original, and about one-third is 

radiogenic. Some such isotopic evolution of lead is the primary 

cause of the variation of isotopic composition that we find in lead of 

ore deposits.

INTRODUCTION TO ORE-LEAD DATA

For simplicity 1 we present data in this report in only two ways. A 

useful index of the radiogenic component in any one sample is the

1 "To extract the utmost information from lead data, simultaneous variations of all 

four isotopes must be compared," (Cannon and others, 1961, p. 6).
ISOTOPE GUIDES FOR MISS. VALLEY LEAD-ZINC EXPLORATION G3

u

238 235

Th

232

NO

PARENT 

KNOWN

204 206 207

Pb

208

FIGURE 1. Isotopic relationships between uranium, thorium, and lead 

in the earth's crust. Black represents primeval lead; gray represents U 

and Th decayed to radiogenic Pb during 4.55 billion years; white represents radioactive parent isotopes that still remain. Reprinted with 

permission from Economic Geology (Cannon and others, 1961, fig. 1).

ratio Pb206/Pb207 , which compares the two isotopes that are formed at 

different rates by decay of U238 and U235. Our second way of representing data involves computing Pb206 + Pb207 -f-Pb208 =100. Differences or 

trends within a group of samples are easily visualized if the three 

major isotopes are thus calculated to 100 percent and plotted on triangular coordinates. Figure 2 shows such a plot of 1,280 analyses, 

mostly of samples of galena. These points represent all analyses of 

lead from lead minerals that were available to us as of 1960 (Cannon 

and others, 1961, p. 11-12). About 95 percent of the analyses plot 

within the smaller triangle that represents less than 1 percent of the 

entire triangular field.
G4 CONTRIBUTIONS TO ECONOMIC GEOLOGY

206

207 208

FIGURE 2. Isotopic composition of lead from 1,280 ore minerals 

plotted in terms of Fb^+Pb^+Pb'^lOO. Reprinted with permission from Economic Geology (Cannon and others, 1901, fig. 5). 

Small triangle added to represent the area enlarged in figure 3.

BEST-FIT CURVE

The heavily populated smaller triangular area is here magnified 10 

times (fig. 3) so that we can contour the distribution of analyses. 

Nearly 85 percent of all analyses plot inside the contour lines shown 

here. A curve has been calculated to best fit the contoured data (Cannon 

and Pierce, 1967, p. 428). The calculation represents the isotopic evolution of lead from the primeval kind of lead that has been found in 

iron meteorites to the most common kind found in geologically young 

ore deposits. It represents evolution during a span of 4,550 million 

years in a closed system containing Pb, U, and Th in proportions 

reasonable for either the earth's crust or mantle. This best-fit curve 

represents the same model as the bar diagram in figure 1.

ORDINARY LEAD

About 75 percent of all analyses fall on this curve, or within limits 

of experimental error. These samples plainly fit a simple history of 

isotopic evolution in the earth, and are called "ordinary lead" (Russell and others, 1954, p. 301). Most samples from major ore deposits 

are exactly such ordinary leads. For most ordinary leads, model ages 

calculated from this model are in accord with geologic evidence of
ISOTOPE GUIDES FOR MISS. VALLEY LEAD-ZINC EXPLORATION G5

NUMBER OF SAMPLES 

PER UNIT AREA

O

Ordinary lead 

evolution

Pb 206=l9 percent \

FIGURE 3. Frequency distribution of lead isotope analyses of worldwide oreleads. Reprinted with permission from Economic Geology Monograph 3 (Cannon and Pierce, 1967, fig. 2, p. 428). This figure is an enlargement of small 

triangle in figure 2.

their age. For the exploration-minded geologist, figuratively anywhere 

inside the contours of this diagram is good hunting ground for big 

ore deposits (Cannon and others, 1962, p. 120-121).

J-LEAD

About 10 percent of all analyses fall beyond the zero end of the bestfit curve, within the contours at the upper apex of figure 3. Most such 

samples represent galenas from the major lead and lead-zinc districts 

of the Mississippi Valley. Such leads have been nicknamed "J-leads" 

because they were first detected in galena samples from Joplin, Mo. 

They evidently represent lead that has somehow become exceptionally 

enriched in radiogenic Pb206, Pb207 , and Pb208 .

350-621 O 69-
G6 CONTRIBUTIONS TO ECONOMIC GEOLOGY

U-LEADS

Another type of exceptional lead with some similarity to J-lead is 

represented by 5 percent of the analyses. We call them "U-leads" 

because they are abnormally enriched in the decay products of uranium, Pb206 and Pb207. Figure 2 shows the gross relationships between 

the field of U-leads, the field of J-leads, and, within the smaller triangle, the field of ordinary leads. The analyses plotted within the 

U-lead field of figure 2 have unique significance for uranium exploration, because they represent analyses of galenas from uranium ore 

deposits. Consequently, any prospector who finds galena containing 

lead of such a composition will know that the odds are very high that 

he is on the trail of a uranium deposit (Cannon and others, 1958).

ISOTOPIC VARIETIES OF LEAD IN STRATIFORM 

LEAD-ZINC DEPOSITS

Several years ago for a symposium sponsored by the Society of 

Economic Geologists on the worldwide class of stratiform lead-zincbarite-fluorite deposits of the "Mississippi Valley type," we plotted 

on triangular coordinates all lead isotope data for such deposits in 

North America, and for such deposits in the rest of the world, principally Europe and North Africa (Cannon and Pierce, 1967, p. 428). 

We found that some deposits so classified contain ordinary lead, almost 

invariable in isotopic composition, whereas other deposits of this class 

contain J-type lead with notable variations in composition.

ISOTOPIC COMPOSITION VERSUS GEOGRAPHIC DISTRIBUTION

Figure 4: shows the result for North America. We see a considerable 

range of values. In general, the values of J-leads from the four principal mining districts of the Mississippi Valley depart farthest from 

ordinary lead of zero model age. At the top of the diagram is the 

Upper Mississippi Valley (Wisconsin) lead-zinc district, then in order 

of decreasing "J-ness," Tri-State lead-zinc, Southeast Missouri lead, 

and the Illinois-Kentucky fluorspar district with subordinate lead and 

zinc. On downward, we find data representing Central Kentucky, East 

Tennessee zinc, a few data from other Eastern States, and finally, 

almost on the ordinary lead curve, the Pine Point lead-zinc district 

of Canada. Figure 12 presents a less cluttered and more up-to-date 

picture for the four major Mississippi Valley districts alone.

In other parts of the world, the range of values is even greater. 

Uppermost in figure 5 are plotted some relatively minor occurrences 

of extreme J-leads from Sweden and the Ukraine, then the important 

Laisvall lead-zinc deposits of Sweden and Norway, and at the bottom
ISOTOPE GUIDES FOR MISS. VALLEY LEAD-ZINC EXPLORATION G7

\ 

\

ARK.

CENT KY

N.Y-ONT 

NJ.-PA.-KY 

PINE POINT, N.

-WIS.

TRI-STATE

SE. MO. 

SO. ILL-KY 

E. TENN.

FIGURE 4. Ore-leads in Phanerozoic stratiform lead-zinc deposits of North 

America. Reprinted with permission from Economic Geology Monograph 3 

(Cannon and Pierce, 1967, fig. 3, p. 428). The area of this diagram corresponds with the upper half of figure 3.

a tight cluster of more than a hundred analyses that fall within a very 

small area around the zero end of the ordinary lead curve.

These two pictures are similar in one sense and opposite in another. 

In North America all three major lead districts of the Mississippi 

Valley produce lead rather similar to Joplin J-lead, whereas Pine 

Point produces ordinary lead. In the Eastern Hemisphere only Laisvall produces lead rather similar to Joplin J-lead, whereas lead 

mined from dozens of stratiform deposits in the rest of Europe and 

North Africa is ordinary lead with model ages close to zero.

ISOTOFIC COMPOSITION VERSUS TONNAGE OF LEAD

Thus, we have a continuous spectrum of isotopic composition, but 

with some suggestion of a bimodal distribution of major lead production. To evaluate this distribution, we have attempted to estimate total 

tons of lead that is, production plus reserves in terms of isotopic 

composition, for worldwide Mississippi Valley type deposits. Figure 6 

is the result, plotted in terms of Pb206/Pb207 ratios. The principal 

tonnages of lead have a bimodal distribution that is quite impressive. 

So here is our first tangible lead-isotope guide for exploration for deposits of the Mississippi Valley type. If you are looking for large 

tonnages of lead in a Mississippi Valley type of geologic environment 

anywhere in the world, your chances of success are 'best if you are on
CONTRIBUTIONS TO ECONOMIC GEOLOGY

SWEDEN 

(SILJAN RING)

UKRAINE

NORWAY-SWEDEN-

(LAISVALL-TYPE)

EGYPT 

ENGLAND-WEST IRELAND

FIOXJBE 5. Ore-leads in Phanerozoic stratiform lead-zinc deposits of Europe 

and Africa. Reprinted with permission from Economic Geology Monograph 3 

(Cannonand Pierce, 1967, fig. 4, p. 428).

the track of ordinary lead with Pb206/Pb207 in the range between 

1.15 and 1.20, or J-lead in the range between 1.29 and 1.42.2

This diagram further illustrates that Pb206/Pb207 ratios in ordinary 

lead range from about 0.89 in the most primitive earth-leads so far 

known from ancient Precambrian ores, to about 1.20 in the evolute 

leads of numerous younger ore deposits of the Phanerozoic. In J-leads 

we note a range from 1.20 for those close to ordinary lead to about 1.95 

for extreme J-leads from Sweden. This ratio will be used in some of 

the following illustrations as an empirical index of "J-ness."

a Scientists in the U.S.S.R. evidently have been aware for some years that the presence 

of Joplin-type J-lead may be a guide to important lead deposits (Tugarniov and others, 

I960, p. 355-356).
ISOTOPE GUIDES FOR MISS. VALLEY LEAD-ZINC EXPLORATION G9

J-LEADS

ORDINARY / * » 

LEADS 10'

Q 

< 

UJ

°io6

CO

z

O

IPINE POINT 

VARIETY

5 _ L

MISSISSIPPI VALLEY 

VARIETY

0.89 1.0 1.5 1.95

pb206/pb207

FIQTJBE 6. Isotopic composition versus tons of lead in worldwide Phanerozoic 

'Stratiform lead-zinc deposits. SE Mo, Southeast Missouri district. Tri-State, 

the Tri-State mining region (Mo.-Kans.-Okla.). UMV, Upper Mississippi Valley 

district (Wis.-Ill.-Iowa).

LEAD ISOTOPES IN MISSISSIPPI VALLEY DISTRICTS

Now, what has been learned so far about lead isotopes in the four 

major districts of the Mississippi Valley ? About 250 lead isotope analyses are available, of which 50-100 are reconnaissance analyses made 

in early years. More recently in the past 2 years several large 

batches of data totaling about 200 analyses have 'been published.

TRI-STATE DISTRICT

First, the Tri-State district. The first suite of galenas ever analyzed 

resulted in the discovery of lead of unusual composition in samples of 

galena labeled "Joplin." This pioneering study was made by Alfred 

Nier, eminent professor of physics at the University of Minnesota. 

Nier's analyses (Nier, 1938; Nier and others, 1941) showed a significant range of composition among his three Joplin samples. For this 

reason we selected a large galena crystal from this district when we 

wanted to make a first test of lead isotope homogeneity within a single 

specimen (Cannon, Buck, and Pierce, 1963). We were amazed when 

we found, within a 3-inch cube of galena, a range of values half as 

great as the known spread of compositions for the entire district 

(Cannon, Pierce, and Delevaux, 1963). Figure 7 shows that we found 

samples from the growth center of the crystal to be least radiogenic,
G10 CONTRIBUTIONS TO ECONOMIC GEOLOGY

and samples from outer growth layers successively more radiogenic. 

We inferred that the samples may represent a family of mixtures: 

ordinary lead mixed with increments of radiogenic lead. In this interpretation, the relative abundance of radiogenic component increased 

from about 9 percent of the lead present in the ore-forming solution 

when the crystal first started to grow, to about 11 percent when the 

outer growth layers were deposited. Another early study of samples 

from the Tri-iState district, made by Farquhar and Gumming (1954)

MiMltllppi 

Vallty

Ordinary lead 

evolution \j-|.0 d

207 208

FIGURE 1. Sampling and isotopic variation of growth zones of a cross-sectioned 

galena crystal from the Tri-State district. A, Sample sites. B, J-leads and 

ordinary lead evolution on three-component diagram. C, Detail of B (X35), 

showing trend (dashed line) of crystal data (dots) in relation to Tri-State 

(white area) and Mississippi Valley (stippled area) J-leads, and evolution of 

ordinary lead (curve). Reprinted with permission from Science (Cannon, 

Pierce, and Delevaux, 1963, fig. 1).
ISOTOPE GUIDES FOR MISS. VALLEY LEAD-ZINC EXPLORATION Gil

of the University of Toronto, showed what appeared to be stratigraphic variations an orderly progression from lower mineralized 

beds to higher mineralized beds. But our single crystal from M bed, 

near the center of the stratigraphic sequence they tested, showed just 

about as much variation as they reported in a suite of 11 samples from 

different beds. On the basis of these meager data we are not yet prepared to say how lead isotopes should be used in exploration within 

the Tri-State district.

SOUTHEAST MISSOURI

The old Lead Belt of the Southeast Missouri district, on the other 

hand, has had the most thorough reconnaissance of all Mississippi 

Valley districts. Some 10 years ago J. S. Brown and his staff of St. 

Joseph Lead Co. collaborated with J. L. Kulp and associates of Lament 

Geological Observatory in a lead isotope study of a suite of nearly 

175 galenas from the Southeast Missouri district. These results were 

made 'available to the public recently in Monograph 3 of Economic 

Geology, printed in 1967 but distributed in 1968. Brown reported 

(1967, p. 414-416) from the Southeast Missouri district systematic 

variations with depth which he illustrated for the Bonne Terre mine 

area 'by projecting his data onto a vertical longitudinal section. We 

have plotted our Pb206/Pb207 ratios on Brown's section (1967, fig. 3, 

p. 415) and contoured them (our fig. 8). The contours fit his generalization that lead is progressively less radiogenic upward away from 

the Precambrian basement, and outward toward the fringes of 

mineralization.

If Brown's generalization is valid, then lead isotopes should give us 

a useful guide for exploration in Southeast Missouri. For the Bonne 

Terre mine we see a convex pattern of variation with progressively 

smaller Pb^/Pb207 ratios upward and outward. A difference in isotopic composition for two galenas from the same horizon in a pair of 

adjacent drill holes, as shown, for example, diagrammatically in 

figure 8, might thus be expected to point toward the center of the area 

of mineralization.

Brown also reported (1967, p. 416-417) evidence that early galena in 

Southeast Missouri is less radiogenic, and late galena more radiogenic, 

as we had found in the Tri-State crystal. He believes, then, that the 

fringe ore of the Bonne Terre mine area was deposited early, and ore 

near the basement in the center of the mine area was deposited later.

We have also plotted (fig. 8) and contoured Pb206/Pb207 values on 

the map of the Bonne Terre mine (his fig. 2, p. 414) without paying any attention to stratigraphic position of the samples. On this 

plan, likewise, the contours suggest a concentric pattern of isotopic
G12

DAVIS

UJ

w o

? ° 2 *

O

LAMOTTE

CONTRIBUTIONS TO ECONOMIC GEOLOGY

OH DH

I'XiV^'^N/ PRECAMBRIAN^ x - x ',^>?5v

»'-<?^t * S \ \ " s ^ J \^/-^ I -^ I X v>^*»

SWH- 2 MILESVERTICAL SECTION

-HNE

I MILE

PLAN

FIGURE 8. Isotopic variations in plan and section. Bonne Terre mine, Southeast 

Missouri district, after Brown (1967, figs. 2, 3), with Pb^/Pb207 data and contours (heavy lines) added. Gray pattern represents mine area; dots, sampling 

sites; DH, hypothetical drill holes.
ISOTOPE GUIDES FOR MISS. VALLEY LEAD-ZINC EXPLORATION G13

variation. Here again, the same pair of samples points toward the 

center of the mineralized area. From this example alone, lead isotopes 

would appear to provide an excellent tool for prospecting in Southeast 

Missouri. Brown's data (1967, p. 423-424) from other mines in the 

old Lead Belt the Leadwood-Desloge and Federal-Flat River mine 

areas appear to show variations somewhat similar, but clearly less 

systematic, than his picture for the Bonne Terre mine.

A few preliminary analyses from other ore deposits in Bonneterre 

Formation (Brown, 1967, p. 425) in extensions of the Southeast Missouri district suggest that such deposits can be expected to have much 

the same kinds of lead isotope variation as have been observed in the 

old Lead Belt. However, the traces of galena in the barite deposits in 

higher Cambrian and Ordovician formations are somewhat different; 

they are measurably richer in radiogenic lead (Brown, 1967, p. 420).

ILLINOIS-KENTUCKY

For the Illinois-Kentucky fluorspar district we have 10 analyses, 

eight of them published by Heyl and his colleagues in 1966. Heyl, Delevaux, Zartman, and Brock (1966, p. 947-951) noted districtwide 

variations in isotope ratios and contoured their data on a map of the 

district (their fig. 5). We have modified their illustrations slightly to 

show our contours of Pb206/Tb207 values for their eight analyses. 

The Pb206/Pb207 contours (our fig. 9) imply a simple gradient across 

the district, with increasing abundance of radiogenic isotopes toward the southeast. We note, however, that samples from major 

mines represent only a limited portion of this gradient. On the basis 

of this scant evidence we suggest that a major deposit in this district 

is likely to contain lead with Pb20fl/Pb207 ratios in the range between, 

say, 1.265 and 1.285. If a pair of contours were drawn across the map 

for these values, they would define a belt that includes most of the 

larger mines of the district.

UPPER MISSISSIPPI VALLEY DISTRICT

Heyl, Delevaux, Zartman, and Brock (1966, p. 938) also published 

lead isotope analyses from 16 mines and prospects in the Upper Mississippi Valley district, 'together with similar lead isotope contour 

maps of the district (their fig. 2, p. 940-941). In our figure 10 we have 

likewise drawn Pb206/Pb207 contours on Heyl's district map. Here 

again, a gradient of lead isotope values appears to sweep across 

the district rather systematically from west to east, with the least 

radiogenic samples near the northwest corner and the most radiogenic 

toward the northeast. Two lines of independent evidence tend to suggest that some such gradient is real. First, most lead isotope analyses
G14 CONTRIBUTIONS TO ECONOMIC GEOLOGY

ILLINOIS ^KENTUCKY

HICKS

E-IN-ROCK

PRINCETON

10 MILES

j

FIGUBB 9. Map of Illinois-Kentucky district (gray pattern), after Heyl, Delevaux, Zartman, and Brock (1966, fig. 5), with Pb^/Pb207 data and contours 

(heavy lines) added. Dots indicate sample localities.

from other investigators (Bate and Kulp, 1955; Russell and Farquhar, 1960) fit quite well the contours based on Heyl's data. Second, 

we have made two different attempts to look for lead isotope variations at a single locality in this district, and the maximum variations 

found are equal to approximately one contour interval on this map 

only one-tenth of the total range that Heyl found across the district. 

Many years ago we obtained analyses of seven samples from a vertical 

range of stratigraphic positions in the large Bautsch ore body near the 

town of Galena, 111. As compared with Heyl's Pb206/Pb207 value for 

a sample from the Bautsch mine (near the bottom of the map) of 

1.381, our seven Bautsch analyses ranged from 1.369 to 1.385. Then, in 

1968 we sampled a large galena cube from the Bautsch mine and 

obtained a value of 1.363 from the exterior of the crystal and a value 

of 1.383 from the interior. This recent pair of analyses would seem to 

imply that early lead is more radiogenic, and later lead is less radiogenic just the opposite of evidence from Tri-State and Southeast 

Missouri districts.

The 13 small mines or prospects that Heyl and his colleagues sampled yielded a broad range of values, ranging from 1.30 to 1.50. The 

three large mines that they tested yielded values ranging only from 

1.38 to 1.41. As before, these data suggest that lead in most large lead-
ISOTOPE GUIDES FOR MISS. VALLEY LEAD-ZINC EXPLORATION G15

WISCONSIN 

JLUNOIS"

FOREST 

CITY 

BASIN

ILLINOIS 

BASIN

FIGURE 10. Map of Upper Mississippi Valley district (gray pattern), after Heyl, 

Delevaux, Zartman, and Brock (1966, flg. 2), with Pb^/Pb807 data and contours 

(heavy lines) added. Dots indicate data from Heyl and colleagues; crosses, 

other sources.

zinc ore bodies of this district will fall within a limited range of values, 

such as the 1.38 and 1.42 contours. One simple test of this suggestion 

is to see from what parts of the district most of the production has 

come. In figure 11 we have plotted the positions of the 30 largest mines 

(Heyl and others, 1959; Mullens, 1964) in the district. Of these 30 

mines, 26 fall between the same two contours. These 26 mines represent 

about 50 percent of the district production of lead-zinc ore. When 

adjacent smaller mines are taken into account, something like 80 percent of the lead-zinc production of the district has come from the area 

between these contours. Lead in the composition range 1.38 to 1.42, 

therefore, seems to have the best chance of guiding the prospector to 

the discovery of a major ore body in the Upper Mississippi Valley 

district. Furthermore, the likeliest place to look for lead of this composition, so far as we can judge from this limited sampling, should be 

the area between the 1.38 and 1.42 contours. The exploration geologist
G,16 CONTRIBUTIONS TO ECONOMIC GEOLOGY

will be quick to note that the area so defined appears to point eastward 

beyond the southeast edge of the district toward uplands where the 

favorable ore horizons are mostly concealed by younger strata.

LEAD ISOTOPE GUIDES FOR EXPLORATION

Finally, we have generalized the data for each of the four districts 

on triangular coordinates (fig. 12) to present the overall picture for 

the Mississippi Valley. The upper dashed line encloses data for the

* 

LANSING

N

10 MILES i

ILLINOIS 

BASIN

MAJOR MINES 

TONS OF ORE PRODUCED

 2,500,000 

+ 1,500,000

 ±750,000

FIGURE 11. Map of Upper Mississippi Valley district, showing locations of 

major lead-zinc mines in relation to a selected pair of Pb^/Pb207 contours.
ISOTOPE GUIDES FOR MISS. VALLEY LEAD-ZINC EXPLORATION G17

Upper Mississippi Valley district, and the gray patch near the center 

of this polygonal area represents our guess about "big ore" in the 

Upper Mississippi Valley district. This gray patch encloses all samples 

between the 1.38 and 1.42 contours. The long dashes at lower left 

enclose all Southeast Missouri samples, and the gray patch below the 

center of this area represents the major tonnage of lead that has been 

produced from the old Lead Belt. The solid line at upper center enTRI-STATE

\

\

\

SE. MISSOURI \ 

LEAD BELT *

ILLINOIS-KENTUCKY

PINE POINT VARIETY

y.

FIGURE 12. Generalized lead isotope data for stratiform lead-zinc deposits. This 

is a trilinear plot that corresponds to figure 4. Polygonal lines enclose data 

from individual districts; gray patches are restricted to data representing 

"big ore."
G18 CONTRIBUTIONS TO ECONOMIC GEOLOGY

closes all Tri-State samples, and the gray patch from top to center 

represents samples from M bed, the most important ore horizon. The 

lower solid line encloses samples from the Illinois-Kentucky fluorspar 

district, and the small gray patch represents samples from larger 

mines in that district. For added perspective, a fifth polygon has been 

plotted in order to represent the ordinary kind of lead, at the zero 

end of the best-fit lead isotope evolution curve, such as has been found 

in stratiform lead-zinc deposits in Europe and North Africa and at 

Pine Point, Canada.

We should like to show you more specifically how the major tonnages of Mississippi Valley J-lead are related to the trilinear coordinates and to Pb 206/Pb 207 ratios as well. Figure 13 is a chart to guide 

the exploration geologist who wishes to use lead isotope analyses in 

prospecting for lead in the Mississippi Valley region. If you hope to 

make a new discovery of a major tonnage of lead in the Mississippi

N^

FIGURE 13. A prospector's guide to lead isotope compositions of principal tonnages of lead in stratiform deposits (gray patches from figure 12) shown in 

relation to both (trilinear coordinates (206+207+208=100) and Pb^/Pb8"7 

ratios (heavier lines). Added clues for exploration: line pattern represents 

data from Southeast Missouri barite district; open circles, the northern Arkansas lead-zinc region.
ISOTOPE GUIDES FOR MISS. VALLEY LEAD-ZINC EXPLORATION G19

Valley a new mine, or a new district it seems wise to search for 

J-lead of isotopic composition much like that outlined here for the 

Tri-State district, or as shown by the gray patches representing major 

tonnages of lead so far produced from the principal Mississippi Valley 

districts.

To illustrate this approach to prospecting, we have also plotted on 

figure 13 several potential lead isotope guides for the prospector, based 

on published lead isotope analyses. The barite deposits of Southeast 

Missouri, in Ordovician and underlying Cambrian formations stratigraphically above the lead-bearing Bonneterre Dolomite, are so far 

known to contain relatively small amounts of galena. But this lead 

(Brown, 1967, p. 418) is of favorable isotopic composition, as is shown 

by the line pattern on this diagram, and thus offers to guide the prospector to "big ore." The other examples concern northern Arkansas. 

Only two galenas have been analyzed from the northern Arkansas lead 

and zinc region (Bate and Kulp, 1955, p. 44). These analyses, represented by the two circles (fig. 13), suggest that the northern counties 

of Arkansas (McKnight, 1935), like the Tri-State district, may be a 

favorable place to look for "big ore." We suggest that these several 

J-lead clues deserve thoughful consideration and further investigation.

Finally, it is conceivable that some future prospecting in the Mississippi Valley region may discover, instead of Mississippi Valley-type 

J-lead, ordinary lead like the Pine Point variety illustrated in figure 

13. Any such discovery of ordinary lead likewise would deserve careful 

evaluation, inasmuch as some millions of tons of such ordinary-type 

lead have been found in recent years, in a distant part of the Interior 

Lowlands province, at Pine Point in Canada.

REFERENCES CITED

Bate, G. L., and Kulp, J. L., 1955, Variations in the isotopic composition of common lead and the history of the crust of the earth: Columbia Univ. Lamont 

Geol. Observatory Ph. D. dissert., 124 p.

Brown, J. S., 1965, Oceanic lead isotopes and ore genesis: Econ. Geology, v. 60, 

no. 1, p. 47-68.

 1967, Isotopic zoning of lead and sulfur in Southeast Missouri, in Genesis 

of stratiform lead-zinc-barite-fluorite deposits (Mississippi Valley type deposits) A symposium, New York, 1966: Econ. Geology Mon. 3, p. 410-426 

[1968].

Cannon, R. S., Jr., Buck, K. L., and Pierce, A. P., 1963, Sampling a zoned galena 

crystal for lead isotope study, in Short papers in geology, hydrology, and 

topography: U.S. Geol. Survey Prof, Paper 450-E, p. E73-E77.

Cannon, R. S., Jr., and Pierce, A. P., 1967, Isotopic varieties of lead in stratiform 

deposits, in Genesis of stratiform lead-zinc-'barite-fluorite deposits (Mississippi Valley type deposits) A symposium, New York, 1966: Econ. Geology 

Mon. 3, p. 427-433 [1968].
G20 CONTRIBUTIONS TO ECONOMIC GEOLOGY

 1968, Lead isotope variations in the Mississippi Valley lead-zinc districts

[abs.] : Mining Eng., v. 20, no. 8, p. 25. 

Cannon, R. S., Jr., Pierce, A. P., Antweiler, J. C., and Buck, K. L., 1961, The data

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v. 56, no. 1, p. 1-38.

 1962, Lead-isotope studies in the northern Rockies, U.S.A., in Petrologic 

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Cannon, R. S., Jr., Pierce, A. P., and Delevaux, M. H., 1963, Lead isotope variation with growth zoning in a galena crystal: Science, v. 142, no. 3592, p. 

574-576.

Cannon, R. S., Jr., Stieff, L. R., and Stern, T. W., 1958, Radiogenic lead in 

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Farquhar, R. M., and Gumming, G. L., 1954, Isotopic analyses of anomalous 

lead ores: Royal Soc. Canada Trans., 3d ser., v. 48, sec. 4, p. 9-16.

Heyl, A. V., Agnew, A. F., Lyons, E. J., and Behre, C. H., Jr., 1959, The geology 

of the Upper Mississippi Valley zinc-lead district [Ill.-Iowa-Wis.]: U.S. 

Geol. Survey Prof. Paper 309, 310 p.; with special sections by A. E. Flint.

Heyl, A. V., Delevaux, M. H., Zartman, R. E., and Brock, M. R., 1966, Isotopic 

study of galenas from the Upper Mississippi Valley, the Illinois-Kentucky, 

and some Appalachian Valley mineral districts: 'Econ. Geology, v. 61, no. 5, 

p. 933-961.

McKnight, E. T., 1935, Zinc and lead deposits of northern Arkansas: U.S. Geol. 

Survey Bull. 853, 311 p.

Mullens, T. E., 1964, Geology of the Cuba City, New Diggings, and Shullsburg 

quadrangles, Wisconsin and Illinois: U.S. Geol. Survey Bull. 1123-H, p. 

437-531.

Nier, A. O., 1938, Variations in the relative abundances of the isotopes of common lead from various sources: Jour. Am. Chem. Soc., v. 60, p. 1571-1576.

Nier, A. O., Thompson, R. W., and Murphey, B. F., 1941, The isotopic constitution 

of lead and the measurement of geological time. Ill: Phys. Rev., v. 60, p. 

112-116.

Russell, R. D., and Farquhar, R. M., 1960, Lead isotopes in geology: New York, 

Intersci, Pubs., 243 p.

Russell, R. D., Farquhar, R. M., Gumming, G. L., and Wilson, J. T., 1954, Dating 

galenas by means of their isotopic constitutions [Pt. 1]: Am. Geophys. 

Union Trans., v. 35, no. 2, p. 301-309.

Tugarinov, A. I., Shcherbakova, A. N., and Bedrinov, V. P., 1960, Isotopic composition of lead in the Dnestr region: Geochemistry, no. 4, p. 352-360.

U.S. GOVERNMENT PRINTING OFFICE: 1969 O 359-621