Sample No.

Weight (mg)

Concentration (ppm)

Pb isotope composition*

Isotope ratios and age, Ma**

Rho

Pb

U

²⁰⁶Pb/

²⁰⁴Pb

²⁰⁶Pb/

²⁰⁷Pb

²⁰⁶Pb/

²⁰⁸Pb

²⁰⁷Pb/

²³⁵U

²⁰⁶Pb/

²³⁸U

²⁰⁷Pb/

²⁰⁶Pb

Foscorite ores, Kovdor (1)

1 (bd)

16.80

18.3

318.8

7660

17.88

23.61

0.4541

0.06086

376

2 (bd)

18.90

9.8

170.3

4790

17.53

44.67

0.4612

0.06194

371

3 (bd)

29.40

9.2

161.9

4520

17.71

44.11

0.4483

0.06111

338

4 (bd)

25.00

7.9

139.7

4020

17.66

44.47

0.4457

0.06099

329

5 (bd)

29.90

9.6

160.9

2920

17.54

50.78

0.4391

0.06123

286

6 (bd)

30.40

7.6

133.9

3170

17.69

50.75

0.4364

0.06127

281

7 (bd)

19.90

4.4

73.9

1680

15.89

18.33

0.4584

0.06131

381

Carbonatites and pyroxenites, Vuorijarvi (2)

2 (bd)

14.50

4.3

71.9

1220

15.120

12.027

0.442

0.0593

376

0.35

3 (bd)

11.00

6.5

113.3

2840

16.866

19.240

0.447

0.0599

377

0.37

1 (zr)**

8.62

6.7

10.7

670

8.717

0.118

0.951

0.0735

1513

0.48