3.5. Isotope Separation & Analysis

Isotope Distribution, Isoscapes

13C 2H

18O ‰10001

12

13

12

13

13

SMOW

sample

C

C

C

C

C

‰10001

1

2

1

2

2

SMOW

sample

H

H

H

H

H

‰10001

16

18

16

18

18

SMOW

sample

O

O

O

O

O

Isotopic ratios

Isotope ratios for specific elements can change locally

due to geological, climatological, biological, chemical

and physical processes during the history of the earth.

The analysis of isotope ratios is a

unique tool for provenance studies

as seen in previous examples.

Typical isotope ratios used for

provenance studies:

13C/12C 18O/16O 204Pb/208Pb

‰10001

208

204

208

204

204

standard

sample

Pb

Pb

Pb

Pb

Pb

Example: isotope distribution in

different Greek quarries

Determination of the Pb isotope ratio

204Pb(n,)205Pb; 208Pb(n,)209Pb;

Alternative method:

isotope analysis by

mass separation techniques!

Neutron activation technique on 204Pb or 208Pb ?

Not possible since the cross section is

extremely weak and 205Pb and 209Pb

have no characteristic decay radiation!

Separation in magnetic fields

R radiuser spectromet a and B field magnetic fixed afor

m/qby separated are city with veloparticles

;

v

Rv

Bqm

v

RB

q

m

Example: Separation of 204Pb and 208Pb

mmR

mRR

R

R

R

R

R

v

Bq

v

Bq

m

m

Rv

Bqm

v

RBm

q

m

98.0208

204

;1for 208

204

;

1

2

2

1

2

1

2

1

2

1

R1

R2

Separated 204Pb, 208Pb beams

B

Mass spectrum in focal plane detector

Isotope Analyzer

Small sample of material

with mass <g is ionized by

sputter technique, accelerated

and mass separated by sequence

of magnetic and electrical fields

Origin of Hittite Mining Industry

The Hittite empire developed

an extensive metallurgy and

mining industry during the

bronze age, 1500-1300 BC

that initiated the iron age.

Tin bronze statue

Hittite Mining Site determination

by lead (Pb) isotope analysis

Origin of metal in artifact

is determined by their 207Pb/206Pb isotope ratio

Metal contain tin, copper, nickel and lead!

Control over the mining sites was important for Hittite empire trade

A. Yener, Bibl. Archaeologist 58 (1995) 101-107

Volcanic origin (earth quake

prone region); limestone

mountains, lower layers show

lava, basalt, soft tuft pillars

produced by volcanic eruption

and subsequent erosion.

Sizable tin, copper, iron, zinc,

lead composition in deeper

layers; polymetallic composition

with abundance variations..

The Geology of Taurus

A. Yener, J.Archaeol.Sci. 18 (1991) 541-577

40% Fe as hematite, magnetite

10-20% Pb with high Zn content

6-8% Zn (~1/2 Pb)

1-2% Cu in some cases 6-7%

3% Co

1.5% Sn in quartz veins

Layered sediments in caves and

cavities of limestone mass.

1-100 ppm Au

100-1000 ppm Ag

The importance of lead isotopes

Isotope composition of Pb deposits

changes with the environment; this

provides a unique tool for the

analysis of antique mining and

trading patterns!

There are 4 stable lead isotopes: 204Pb, 206Pb, 207Pb, 208Pb

Lead isotope distribution is not necessarily constant but may change if

significant Uranium & Plutonium abundance exist in in the ore material.

Natural decay of these a unstable isotopes feed the Pb isotopes.

Terrestrial Lead and Radiogenic Lead

Natural decay chains & the feeding of

Pb isotopes

206Pb

207Pb

208Pb

Pb isotopic ratio Depending on chemical history and water content of

ore material significant differences exist in abundances

of long-lived “mother” U, Np, Pt elements in the ore

material. This eventually leads to build-up of significant

differences in lead “daughter” isotopic abundances,

which often is characteristic for the mine site.

206

204

206

204

207

204

207

204

208

204

208

204

238 238

235 235

232 232

137 8

Pb

Pbt

Pb

Pbt e e

Pb

Pbt

Pb

Pbt e e

Pb

Pbt

Pb

Pbt W e e

p

t t

p

t t

p

t t

p

p

p

( ) ( ) ( )

( ) ( ).

( )

( ) ( ) ( )

Present day lead = primeval lead + radiogenic lead

Simple evolution model:

tp: time between origin

of earth and last geo-

logical active period

238: decay constant of 238U

235: decay constant of 235U

232: decay constant of 232Th

Evolution model applied for US mines

1.0 1.2 1.4 1.6 1.8

1.6

1.6

1.4

207Pb/204Pb

206Pb/204Pb

=9

=7

Certain lead isotope

ratios help to identify

the original mines, the

analysis of the lead

isotope ratio reveals

ancient trading routes

Pb

ThW

Pb

U

204

232

204

238

Present isotope ratio parameters:

Ancient ship trade ca 1500 BC

Egyptian trading vessel at

Uluburun Kas

C. Pulak, Int. J. of Naut. Arch. 27(1998) 188 - 224 G. F. Bass, Amer. J. Archaeology 90 (1986) 269-296

Difficulty of Underwater Archaeology

The Uluburun Wreck

Copper and tin

ingots

Tin ingot Copper ingots

Origin of metals? Cyprus, Laurion (mainland Greece), and Cappadocia (Taurus Mountains) were antique

mining centers, did the Uluburun transport metals from Laurion eastwards or from

Cyprus or Cappadocia westwards? The Pb isotope composition from Cyprus and

Laurion metals matches most closely the isotope composition of group 4 from the

Taurus mines! But differences show up when comparing different Pb isotope ratios!

Taurus 4

Taurus 4

Cyprus

Cyprus

Taurus 4

Taurus 4

Laurion

Laurion

Origin and destination?

Did the ship sail west or east

Origin of copper and tin can be tested on the

mine specific lead isotope ratio in the ingots.

Typical lead ratio of Taurus mines Typical lead ratio of ship ingots

Lead concentration in copper and tin

Trading Route