2013

Abstracts Travel
Program Organizing committee

Ore pyroxene melilitites from the North Pripyat area of magmatism

Mikhailov, N.D.*, Laptsevich, A.G*., Vladykin, N.V.**

*Republican Unitary Enterprise Belarusian Research Geological Exploration Institute, Minsk, Belarus,

**A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia

mihailov@geology.org.by

 

The Upper Devonian alkaline magmatic formation of Belarus includes petrographically and facially variable rocks. During the last year, one more variety of ultrabasic rocks (ore pyroxene melilitite with specific features of mineral and chemical compositions) was discovered. This suggests a possibility of recognition of rocks with ore specialization within the formation.

Ore pyroxene melilitites were retrieved from a borehole located in the southern part ot the North Pripyat shoulder. They occur at the depth of more than 300 m. In the upper part of the sequence, rocks are represented by volcanoclastic varieties (tuffic sandstones and tuffs). Their petrographic compositions are similar to those of underlying melilitites. Tuffs are strongly changed. In some cases all or most primary minerals are entirely decomposed and substituted by secondary fine dispersed hardly determinable minerals. Melilitites which occur at the depth of 392 m below a unit of melilitite tuffic sandstones are greenish dark-grey rocks with massive structure, hypidiomorphic granular oligophyre texture. They frequently include differently oriented 1-5 mm thick interlayers of carbonate barite zeolite composition.

The main mass consists of several minerals. Pyroxenes (diopside and hedenbergite) comprise about 60%, titanomagnetite and magnetite 15-25%, melilite 10-15%. Phenocrystals are composed of pyroxene, titanomagnetite, rarely of olivine replaced by secondary serpentine and chlorite. Melilitite of the main mass is substituted by montmorillonite.

By their petrographic characteristics, the rocks under consideration are consistent with melilitites, but are less alkaline and contain increased amounts of iron and titan. Also, the rocks are enriched in some trace elements (, Cu,Ti, V, Li, Ta,Th, Nb, Sr, REE).

 

Table. Contents of major and trace elements in pyroxene melilitites

Major elements

Trace elements

SiO2

34.89

34.44

Li

167.9

165.5

Sr

411

414

Tb

2.61

3.73

TiO2

6.254

6.21

Be

2.76

2.30

Y

37.57

45.74

Dy

12.18

16.07

Al2O3

4.29

4.27

Sc

55.9

58.6

Zr

286

280

Ho

1.92

2.46

Fe2O3 .

20.4

19.35

Ti

40665

44389

Nb

127.79

128.48

Er

4.09

4.99

MnO

0.22

0.21

V

507

516

Sn

3.59

3.81

Tm

0.47

0.54

MgO

12.4

13.93

Cr

174

176

Cs

0.21

0.25

Yb

2.47

2.84

CaO

15.36

14.83

Mn

1662

1613

Ba

509

233

Lu

0.37

0.39

Na2O

0.67

0.64

Co

40

72

La

71.40

167.72

Hf

10.30

10.28

K2O

0.17

0.15

Ni

118

125

Ce

207.64

411.48

Ta

14.91

15.58

P2O5

2.12

2.05

Cu

247

509

Pr

30.34

54.84

W

0.93

0.39

Ba+Ce

0.08

0.05

Zn

418

112

Nd

132.35

227.41

Tl

0.01

0.01

Sr

0.05

0.04

Ga

14.01

15.58

Sm

26.24

39.34

Pb

2.38

1.99

Zr

0.04

0.04

Ge

2.50

2.37

Eu

7.31

10.96

Th

26.74

27.75

...

2.86

3.56

Rb

7.33

4.72

Gd

19.37

29.21

U

1.95

2,87

Analyses were performed in the A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, Irkutsk.

 

This research was carried out with financial support from the Belarusian Republican Foundation of  Fundamental Investigations (grant X12P-058) and Russian Foundation of  Fundamental Investigations (grant 12-05-90000).