PGM in chromite ores

Placer and host PGE-mineralization of the Nizhniy Tagil massif
(the Urals, Russia)

N.S. Rudashevsky, A.A. Yefimov


Crystals and grains of Pt-Fe alloys from EP-product of disseminated chromite ores in dunites of Nizhniy Tagil massif, (1-15); SEM images (BIE);

1-6 and 8-14 — crystals and grains, 7 and 15 — polished sections.

IFP — isoferroplatinum, TFP — tetraferroplatinum; Os, (Os,Ir) — Os-Ir alloys, CHR — chromite, OL — olivine.


Investigated sample of disseminated chromite ore (sum of PGE ~ 100 ppm):

Main PGMs — isoferroplatinun and tetraferroplatinum;

Secondary PGMs — Os-Ir alloy;

Rare minerals — Ir-Os alloy, Fe-Pt alloy, Nu-Pt alloy of Cu3Pt composition, laurite, irarsite.

 

Pt-Fe alloys with exsolution texture; the placer from the Nizhniy Tagil massif region. The method of aching of the polished section surface by HNO3+HCl (concentrated). SEM-image (BIE).

1 — sample U-1/9, 2 — sample U-4/3; IFP — isoferroplatinum, TFP — tetraferroplatinum, TUL — tulameenite, CHR — cromite.


PGMs of the placer:

Main PGMs — isoferroplatinum and tetraferroplatinum;

Secondary PGMs — tulameenite, Os-Ir alloys;

Rare minerals — Ir-Os alloys, laurite, irarsite etc.



X-ray data:

Samlple U-1/9

Isoferroplatinum: a = 3.849 (4) Å;

Tetraferroplatinum: a = 3.845 (6) Å, c = 3.740 Å



Samlple U-4/3

Isoferroplatinum: a = 3.843 (5) Å;

Tulameenite: a = 3.889 (3) Å, c = 3.596 (3) Å

 

Chemical compositions of Pt-Fe-Cu-Ni alloys of the
host dunite and the placer from Nizhniy Tagil massif


 

Separation of accesory minerals from rocks by hydroseparation (HS) technology: method and application to CHR-2 chromitite, Niquelandia intrusion, Brazil.

Trans, Instn Min. Metal. (Sect. B: Appl. earth sci.), 111/Proc. Australas. Inst. Min. Metal., 307, January-April 2002. P.B87-B94

N.S. Rudashevsky, G. Garuti, F. Zaccarini, Yu. L. Kretser, and V.N. Rudashevsky



Minerals and characteristic mineral associations of chromitite CHR 2
(sample NQ660); polished sections of chromitite, SEM images (BIE)

CHR I and CHR II — two generations of chromite, GKL — geikielite, RUT — rutile, HRD — Fe,Ni,Cr hydroxides, KLN — kaolinite


CRT I (wt. %) — TiO2 0.35 Al2O3 22.9 Cr2O3 44.4 V2O3* 0.33 MgO 12.1 FeO 18.8 MnO 0.26 NiO* 0.18 ZnO* 0.09 Total 99.4;

(Mg0.56Fe2+0.44Mn0.01)1.01(Cr1.08Al0.84Fe3+0.05V0.01Ti0.01)1.99O4;

CRT II (wt. %) — TiO2 0.14 Al2O3 9.0 Cr2O3 59.3 V2O3* 0.30 MgO 7.3 FeO 21.2 MnO 0.62 NiO* 0.09 ZnO* 0.09 Total 98.04;

(Fe2+0.61Mg0.38Mn0.02)1.01(Cr1.62Al0.36V0.01)1.99O4;

GEIKIELITE (wt. %) — TiO2 62.7 Cr2O3 0.25 MgO 18.3 FeO 20.0 Total 101.25;

(Mg0.59Fe0.36)0.95(Ti1.02Cr0.01)1.03O3.

*wave dispersion analysis

 

PGMs found in polished sections of the sample NQ660, SEM image (BIE)

LR — laurite, ERL — erlichmanite, TFP — mineral of tetraferroplatinum composition, CHR — chromite, GKL — geikielite, HRD — Fe,Ni,Cr hydroxides, KLN — kaolinite


 

PGM grains found in heavy HS concentrate of the sample
NQ660 (1-13), SEM image (BIE)

LR — laurite; ERL — erlichmanite; KSH — kashinite; (Pt,Fe) — Pt-Fe alloys; IFP — isoferroplatinum composition Pt-Fe alloy; TFP — tetraferroplatinum composition Pt-Fe alloy; (Ru,Fe) — Ru, Fe, Ni, Cr, Os, Ir alloys (oxides?); CHR — chromite; HRD — Fe, Ni, Cr-hydroxide


 

Chemical compositions of PGM of the sample NQ660
(in polished sections and in heavy mineral concentrates)

a — laurite and erlichmanite; b — Pt-Fe alloys


 

Grain sizes of PGM (n=38), extracted in the heavy concentrate of the sample
NQ660 of chromitite (a) and (c) and intersections of PGM grains
in polished sections (n=62) of the chromitite (b);


a, b — histograms; c — lognormal probability plot


 

Native metals and other accessories from the heavy concentrate of the sample NQ660, SEM image (BIE)

Sulphides: Chalcopyrite, Pyrrhotite, Pentlandite, Millerite, Heazlewoodite, Sphalerite, Molibdenite, Acanthite, Breithauptite
Other minerals: Barite, Bastnasite-(La)

a, b — histograms; c — lognormal probability plot

Ag — native silver, (Au,Ag) — gold, Ni — nickel, Cu — copper, Pb — lead,
Sb — antimony, BRTH — breithauptite, (Cu,Zn,Sn) — brass, CRT — chromite.


 

Isotopic data for native lead:

Pb206/204207/204208/204
Grain 118.14715.58638.057
Grain 217.70715.50337.700
Several grains17.90615.57537.849

Mass-spectrometer - Finnigan MAT-261,
isotopic standard - NBS-982, error of definition on unit of mass differences - 0.03%

Isotopic analysis of Pb in native lead correspond to ABSOLUTE AGE ~700 m.a. in Pb-Pb isotopic systematization; indicating the source to be a mixture of the depleted mantle and lower crust.

Measured by Dr. Yu. Pushkarjev

CNT MC Inc.