Moncheite and palladseite of unusual chemical composition from the

Miessi River, Inari, Northern Finland

Kari K. KOJONEN, Geological Survey of Finland

Andrew M. McDONALD , Dept. of Earth Sciences, Laurentian University, Canada

Chris J. STANLEY, Natural History Museum, UK

Bo JOHANSON, Geological Survey of Finland

9/10/2014

21st IMA General Meeting , Johannesburg, RSA, September 1-5, 2014

Janne TRANBERG, Geological Survey of Finland

Outline

• Introduction • General geology of the northern Lapland • Methods of study • Placer PGM in Miessi River • Optical and SEM images + EDS results • EPMA results • VHN and R measurement results • XRD results • Conclusions

9/10/2014 2

9/10/2014

Geological map of northern Finland and the distribution

of PGM bearing layered intrusions and placer deposits

3

9/10/2014

General geology

• The bedrock in Lemmenjoki River tributary is granulite, including felsic granulites and granite gneisses and intrusive mafic enderbite-norites, quartz-, hematite, quartz-feldspar porphyry and pegmatite veins

• The age obtained of zircons is 1.95Ga for the granulite

• Intrusive layered norites and enderbites have an age of 1.905Ga obtained from zircon age determinations

4

9/10/2014

Digital bedrock map of Northernmost Finland in 2014

5

9/10/2014

Low altitude magnetic total intensity airborne map, height 31m

6

9/10/2014

Low altitude magnetic total intensity airborne map, height 31m, Lemmenjoki River area

7

9/10/2014 8

9/10/2014 9

Kaarreoja River, contact between granulite and weathered gabbro MgO 9.9 wt.%

Layered gabbro, lower Miessi River MgO 6.8 wt.%

9/10/2014 10

9/10/2014 11

Layered gabbro, lower Miessi River MgO 8.1 wt.%

9/10/2014 12

Methods of study • Heavy mineral sands were sieved in the laboratory with

a sieve set from 1 mm to 40 microns opening

• Coarser grains were hand picked under stereo-microscope/macroscope

• Grains with size <250 microns were sieved to several fractions and panned iin the laboratory, and finally run with the ”gold hound” spiral separator,

• Optical microscopy; macroscope, polarisation microscope, microphotography

• SEM/EDS

• EMPA at the GTK

• Reflectivity and Vickers hardness measurements at NHM

• XRD at the Laurentian University, Sudbury

9/10/2014

Optical microscopy with a macroscope and polarizing ore

microscope at GTK

13

9/10/2014

Jeol variable vacuum SEM/EDS with an automatic Oxford INCA

Feature analysis program for PGM grain counting

14

Cameca SX100 EMP at GSF

9/10/2014 15

Reflectivity and VHN measurement at NHM in London UK

9/10/2014 16

XRD studies using the Gandolfi camera at the Laurentian University, Sudbury

Canada

9/10/2014 17

Gandolfi XRD method used at the Laurentian University, Sudbury

• XRD analysis flowsheet

Gandolfi XRD camera (two axes of rotation; improved I data).

BaFEu Image Plate (IP, shown in cross-section). Eu2+↔ Eu3+

Advantages over film: Reusable, flexible, no dark room, greater sensitivity (record weak and strong reflections), increased dynamic range, affordable.

Conversion of image to diffractograms in seconds. Can be run under vacuum. Much smaller grains (~ 20 um) can now be run. S/M and Rietveld analyses are now possible. 9/10/2014 18

Optical macroscope studies of the grains monted with double sided tape on a 30 mm diameter

brass plates as monolayer grain mount

9/10/2014 19

Optical macroscope studies of the grains monted with double sided tape on a 30 mm diameter

brass plates as monolayer grain mount

9/10/2014 20

SEM EDS studies of the grains with low vacuum mode and automatic feature analysis of the grains

9/10/2014 21

Results of the automatic SEM EDS feature analysis of the 1019 grains

Class Rank Features % total features Feature area (sq. µm) % total area

Sperrylite 1 380 37.29 29100000.00 49.41

Mertieite 1 10 0.98 908000.00 1.54

Vysotskite 1 1 0.10 82100.00 0.14

Cooperite 1 11 1.08 1050000.00 1.78

Braggite 1 5 0.49 384000.00 0.65

Pt-oxide 1 2 0.20 150000.00 0.25

Pt Te 1 21 2.06 141000.00 0.24

PdSb 1 1 0.10 842.00 0.00

Au 2 14 1.37 325000.00 0.55

Electrum 2 0 0.00 0.00 0.00

Cassiterite 2 66 6.48 4380000.00 7.44

Native Bi 2 44 4.32 2510000.00 4.26

Nb-Ta-minerals 3 14 1.37 1210000.00 2.05

W-minerals 3 1 0.10 382.00 0.00

Fe-sulfides 3 21 2.06 65500.00 0.11

Zircon 4 8 0.79 89800.00 0.15

Monazite 4 27 2.65 1110000.00 1.88

Th-U_oxide 4 199 19.53 12000000.00 20.37

Pb-oxide, galena 4 64 6.28 2210000.00 3.75

Chromite 5 17 1.67 1150000.00 1.95

Titanomagnetite 5 4 0.39 3810.00 0.01

Magnetite, Hematite 5 37 3.63 803000.00 1.36

Ilmenite 5 6 0.59 69200.00 0.12

Rutile 5 8 0.79 69900.00 0.12

Arsenopyrite 5 39 3.83 38200.00 0.06

Phosphates 5 19 1.86 1050000.00 1.78

total 1019 100.00 58900734.00 100 9/10/2014 22

Results of the automatic SEM EDS feature analysis of 431 PGM grains

Class Features

% total

features

Feature area

(sq. µm)

% total

area

Sperrylite 380 88.17 29100000.00 91.46

Mertieite 10 2.32 908000.00 2.85

Vysotskite 1 0.23 82100.00 0.26

Cooperite 11 2.55 1050000.00 3.30

Braggite 5 1.16 384000.00 1.21

Pt-oxide 2 0.46 150000.00 0.47

Pt Te 21 4.87 141000.00 0.44

PdSb 1 0.23 842.00 0.00

total 431 100.00 31815942.00 99.98

9/10/2014 23

Results of the automatic SEM EDS feature analysis of 431 PGM grains

91.46

2.85 0.26

3.30

1.21 0.47 0.44

0.00

Sperrylite

Mertieite

Vysotskite

Cooperite

Braggite

Pt-oxide

Pt Te

PdSb

9/10/2014 24

Manual checkup of unclassified grains with SEM/EDS

Grains in the BSE images: 1) Cu bearing isomertieite, 2) Cu and Te bearing palladseite, 3) tellurian palladseite, 4) UM2004-52 Pd10(As,Te)3 5) Se bearing braggite, 6) Se bearing moncheite. BEI by Kari Kojonen.

5

2 1

4 6

3

9/10/2014 25

Previously discovered new mineral from the same place Miessiite Pd11Te2Se2

Isotropic, color grayish white, 1 polarizer, Miessi River, optical image by K. Kojonen

9/10/2014 26

UD (undefined) minerals in polished section

Reflected light, 1 polarizer. Optical images by K. Kojonen

EDS PtSeTe EDS PdSeTe

EDS PdSeTe

9/10/2014 27

EPMA results of the UD minerals • Calculations for mineral: PdSeTe Run on date: 7-October-2013 • CHEM (Formula Weight) calculations • Total Wt% = 99.06 average of 30 • Formula Weight = 3048.49 • Constit Data Mole Symbol Number • Name Wt % Ratio of Atoms • Cu 1.14 0.0179 Cu 0.55 • Se 35.14 0.4450 Se 13.70 • Pd 57.13 0.5368 Pd 16.52 • Os 0.39 0.0021 Os 0.06 • Pt 0.96 0.0049 Pt 0.15 • Au 0.24 0.0012 Au 0.04 • Sb 0.08 0.0003 Sb 0.02 • Te 4.02 0.0315 Te 0.97 • Total weight % = 99.06 • Total Atom Number = 32.00 • Total Atomic Ratio = 1.0398 • f-Factor = 30.7742 • Formula Weight = 3048.49 • Empirical formulae (Pd15.84Pt0.03Os0.12Cu1.17Au0.02)17.18(Se12.03S0.51Sb0.02Te1.81)14.37

According to Louis Cabri the formulae of palladseite is Pd17Se15.

9/10/2014 28

EPMA results of the UD minerals • Calculations for mineral: PtSeTe

• CHEM (Formula Weight) calculations

• Total Wt% = 100.05

• Formula Weight = 420.02

• Constit Data Mole Symbol Number

• Name Wt % Ratio of Atoms

• Se 10.05 0.1273 Se 0.53

• Pd 0.66 0.0062 Pd 0.03

• Pt 43.92 0.2251 Pt 0.95

• Ag 0.02 0.0002 Ag 0.00

• Sb 0.02 0.0002 Sb 0.00

• Te 45.38 0.3556 Te 1.49

•

• Total weight % = 100.05

• Total Atom Number = 3.00

• Total Atomic Ratio = 0.7146

• f-Factor = 4.1981

• Formula Weight = 420.02

• empirical formulae (Pt0.95Pd0.03)0.98(Se0.53Te1.49)2.02, that corresponds the formulae of moncheite

9/10/2014 29

VHN values of the UD minerals

For 25g load: PtSeTe mean (3) 101 range 83-116 sf-cv. Equivalent to Mohs ~ 3 (moncheite QDF 381 VHN 128-153) PdTeSe 1 mean (5) 472 range 459-484 p-sf. Equivalent to Mohs ~ 5. PdTeSe 2 mean (3) 478 range 462-489 p-sf. Equivalent to Mohs ~ 5. (palladseite QDF 409 VHN 390-437)

9/10/2014 30

Reflectance curves of the UD minerals

40

45

50

55

60

65

70

400 420 440 460 480 500 520 540 560 580 600 620 640 660 680 700

R%

lambda nm

Selenian moncheite and moncheite Ro data

selenian moncheite

QDF3.379

QDF3.380

QDF3.381

CIE color values (illuminant C) x 0.312, y 0.318, Y% 59.4, λd 585, Pe% 1.5. 9/10/2014 31

Reflectance curves of the PdTeSe mineral

30

35

40

45

50

55

60

400 420 440 460 480 500 520 540 560 580 600 620 640 660 680 700

R%

lambda nm

R data for tellurian palladseite and palladseite

pal.Nm1

pal.Nm2

QDF3.409

CIE color values (illuminant C) x 0.314, y 0.323, Y% 48.1, λd 572, Pe% 2.8

9/10/2014 32

XRD of the PtSeTe mineral

• The PtSeTe phase gave a moncheite pattern.

• Moncheite crystallizes in the space group P3̄̄ m1 and unit-cell refinement based on 18 reflections (20-125º2Θ) gives a 3.994(2) Å, c 5.233(3) Å, V 70.49 Å3, Z = 1, class 3̄̄ m, c:a=1.310, density 9.590 g/cm3(calc). The chemistry shows Te>Se, so the mineral is a Se-bearing moncheite.

9/10/2014 33

XRD of the PdTeSe phase

• The PdTeSe has an XRD pattern of palladseite.

• Palladseite crystallizes in the space group Pm3m. The refined unit-cell edge for the calculated Te-bearing palladseite (based on 28 reflections for 32-123º2Θ) is: a 10.653(2) Å, V 1208.97 Å3, Z 2, space group Pm3m, class m3m, density 7.958 g/cm3(calc.).

• Te replacing Se in the lattice of palladseite increases the cell size, VHN and the reflectance values compared to the normal palladseite .

9/10/2014 34

Summary and conclusions

• The PtSeTe phase gave a moncheite pattern. The decrease in the unit cell of selenian moncheite can be explained by the increased substitution of Se for Te: the radius Te2-=2.21 and Se2- = 1.98 Å, so the more Se there is, the smaller unit cell will be.

• Se replacing Te in the moncheite lattice decreases the lattice size and the VHN values.

• The PdTeSe has an XRD pattern of palladseite . Te replacing Se in the lattice of palladseite increases the cell size, VHN and the reflectance values compared to the normal palladseite.

9/10/2014 35

Summary and conclusions • The PGM paragenesis is poor on sulphur containing only a few

grains of cooperite – braggite – vysotskite, which have crystallized with the early magmatic minerals ca. 1000-1200 o C

• Thus, it is evident that Se and Te are replacing each other in the

lattice of natural moncheite and palladseite in the Miessi River area. Both elements belong to the group 16 of the periodic system of the elements and have a similar charge and less than 15 % differing ionic radius ( Se2- 1.98Å and Te2- 2.21Å, Vaughan and Graig, 1978)

• Almost similar replacement of Te and Se have been recently reported (Kojonen et al. 2007) in the description of miessiite discovered nearby. Miessiite is isostructural with isomertieite that is quite common in the area. The PGM paragenesis contains both Te and Se and miessiite is an example of a Te-Se member of the isomertieite group minerals.

9/10/2014 36