K-bearing sulfides in carbonatites of the Guli massif of the Polar Siberia

N. V. Sorokhtina, A.M. Asavin, V.G .Senin

¹ Vernadsky Institute of Geochemistry and Analytical Chemistry RAS, Moscow, alkaline@geokhi.ru;

 

Fluid regime of alkaline melts is one of the important factors in the evolution of magmatic system. It determines and controls distribution of trace elements and mineral formation. Presence of such specific minerals with the high content H₂O, F and Cl as amphibole, mica, sulfides is an evidence of the big volume of fluid in the crystallization system. Here we present new data for K-bearing sulfides: djerfisherite K₆(Cu,Fe,Ni)₂₄S₂₆Cl, rasvumite KFe₂S₃, chlorbartonite K₆Fe₂₄S₂₆ (Cl,S) of carbonatites of Guli massif. Sulfide minerals were found in some intrusive phases of Guli pluton. Previously djerfisherite was discovered in metasomatic pyroxenite (Zaccarini et al, 2007) and as inclusions in perovskite of first stage calcite carbonatites (Kogarko et al, 1991). We found and studied K-bearing sulfides in calcite and calcite- dolomite carbonatites of Southern Carbonatite Massif. Pyrrhotite, pyrite, chalcopyrite, sphalerite are common for this sulfide mineralization, whereas galena, Ag, lenaite and argentopyrite are less abundant.

The djerfisherite forms as micro inclusions (gas-fluid and melting) or course grains with pyrrhotite (up to 500 mkm) in the earlier generation. The djerfisherite grains substitute pyrite and pyrrhotite grains and intergrow with chalcopyrite (fig.1) at following stages of mineralization. Djerfisherite includes grains of Ag alloy up to 2-5 mkm sometime. Rasvumite was observed as lamellas (5-30 mkm) into big crystals of the pyrrhotite.

 

Fig.1 Back-scattered electron images of minerals of carbonatites from Guli massif. Dj – dgerfisherite, Py – pyrrhotite, P? – Fe-sulfide, cPy – chalcopyrite, Sph – sphalerite, M – magnetite, Fo – olivine, Ap – fluorapatite, Dl – dolomite, Cl - calcite

 

Table 1. Microprobe analyses of djerfisherite (1-16) and rasvumite (17. 18) of carbonatites of Guli massive (wt%)

N	1	2	3	4	5	6	7R	8C	9R	10	11	12	13
sample	85-109		97-47									97-57
K	9.26	9.22	8.47	9.07	8.95	9.13	8.31	8.21	7.91	7.93	8.52	14.39	13.77
Cl	1.41	1.39	1.24	1.39	0.97	0.90	0.91	0.88	0.89	0.89	0.89		0.02
S	34.26	34.26	32.14	33.13	34.95	33.70	32.71	31.43	31.28	32.05	32.81	37.17	36.45
Fe	43.37	40.96	35.83	37.97	45.43	47.33	36.64	34.90	34.05	35.17	37.93	42.64	41.86
Cu	13.06	12.72	16.38	15.29	7.74	6.25	19.23	19.03	19.24	17.62	16.40	0.10
Ni	0.17	0.13	0.17	0.01	1.64	2.07	1.74	1.46	1.41	1.44	0.08	0.13	0.01
Co	0.13	0.16	0.36	0.57	0.09	0.16	0.04	0.11	0.11		0.04	0.08	0.04
Total	101.66	98.84	94.59	97.43	99.77	99.54	99.58	96.02	94.89	95.10	96.67	94.51	92.15
	Formula based on 58 atoms											Formula based on 6 atoms
K	5.89	5.99	5.81	6.02	5.75	5.90	5.49	5.62	5.48	5.45	5.73	0.96	0.96
Cl	0.99	1.00	0.94	1.02	0.69	0.64	0.66	0.66	0.68	0.67	0.66	0.00	0.00
S	26.57	27.16	26.89	26.82	27.36	26.58	26.33	26.25	26.42	26.85	26.91	3.03	3.04
Fe	19.31	18.64	17.21	17.65	20.42	21.43	16.93	16.73	16.51	16.92	17.86	2.00	2.01
Cu	5.11	5.09	6.91	6.24	3.06	2.49	7.81	8.02	8.20	7.45	6.79	0.00	0.00
Ni	0.07	0.06	0.08	0.00	0.70	0.89	0.77	0.67	0.65	0.66	0.04	0.01	0.00
Co	0.05	0.07	0.16	0.25	0.04	0.07	0.02	0.05	0.05	0.00	0.02	0.00	0.00

1,2 – djerfisherite-magnetite inclusions in dolomite crystal from the olivine of calcite-dolomite carbonatite (fig. 1a); 3,4, 10, 11 – individual crystals of djerfisherite 5,6 – pyrrhotite-djerfisherite aggregates in the groundmass of calcite carbonatite; 7-9 – zones in the crystal of djerfisherite from calcite carbonatite (R – rim, C – core); 12,13 – lamellas of rasvumite into pyrrhotite from calcite carbonatite.

Fig.2 Composition (in at. %) of K-sulfides from different rocks alkaline and alkaline-ultrabasic complexes

Fig.3 Composition (in at.%) of K-sulfides from different alkaline and alkaline-ultrabasic complexes

 

The chemical composition of sulfide minerals is presented in table 1. Calculated formulas of K-bearing sulfides helped us to determinate 3 groups of specimens - djerfisherite, chlorbartonite (?) and rasvumite. S content of djerfisherite varies significantly. We determinated fields for different K-bearing sulfides of Guli carbonatites: djerfisherite, chlorbartonite (?) and rasvumite (Fig.2). The diagram (Fig 2) displays composition of djerfisherite from different alkaline intrusions and rocks - pyroxenites of Guli, phoscorites of Kovdor and alkaline rocks of Khibiny. Compositions of the djerfisherite from different alkaline and carbonatitic rocks are located in the same field (Fig. 2). It is an evidence, that conditions of djerfisherite crystallization were similar for different carbonatite and alkaline massives.

There is strong negative correlation between Fe and Cu in the composition of K-bearing sulfides (Fig.3). Especially it is obvious for Guli samples. Djerfisherite of early generations was formed at high temperature and has high Fe and low Cu contents, whereas concentration of Cu in djerfisherite of following generations is higher. We can assume that concentrations of chalcophile elements (Cu, Ag, Pb, Zn et all) increase with decreasing of mineral equilibrium temperature during evolution of the alkaline systems.

According to Henderson et al. (1999) the temperature of the formation djerfisherite melt inclusions is about 1000°С, however the lowest temperature of djerfisherite with Ag phases formation was estimated as 150°С (Sorokhtina et al., 2010).

Appearance of K-bearing sulfides in carbonatites is an evidence of rich- K, Cl and S fluid in the magmatic camera. It indicates the high migration potential of volatile elements and sulfur in crystallization system. High content of alkalis in the fluid leads to the shift of sulfide-sulfate equilibrium to the side of sulfate sulfur. As a result sulfur and chalcophile elements accumulate in silicate fluid or primary spinel oxides instead of sulfides. At the late stages, due to metasomatic fluid activity chalcophile elements are released as sulfides from the last portions of carbonatite fluids.

 

Research was sponsored by RFBR grant 09-05-12026-ofi_m, NSH-3848.2010.5, contract 0762.

 

 

References:

Balabonin N.L., Voloshin A.V., Pakhomovsky Ya.A, Poljakov K.I. The composition of djerfisherite in alkali complexes of the Kola Peninsula // Miner. J. 1980. V.2. P. 90-99. (in Russian)

Henderson C.M.B., Kogarko L.N., Plant D.A. Extreme closed system fractionation of volatile-rich, ultrabasic peralkaline melt inclusions and the occurrence of djerfisherite in the Kugda alkaline complex, Siberia // Min. Mag. 1999. V. 63. P. 433-438.

Kogarko L.N., Plant D.A., Henderson C.M.B., B.A. Kjarsgaard Na-rich carbonate inclusions in perovskite and calzirtite from the Guli intrusive Ca-carbonatite, Polar Siberia// Contrib Mineral Petrol. 1991. V. 109. P. 124-129.

Sorokhtina Y.D., Zaitsev V.A., Senin V.G. Ag ore mineralization of Guli massif // Moscow. 2010. Abstract of XXI Intern. S. conf. “Fundamental problems of geology of the ore deposits and metalogenesis”. P. 63.

Subbotina G.F., Subbotine V.V., Pakhomovsky Ya.A Same features of sulfide mineralization of apatite-magnetite ore and carbonatites of the Kovdor deposite / Apatity. KFAS USSR. 1981. In the book: Composition of alkaline intrusive complexes of the Kola Peninsula. С.88-95.

Zaccarini F., Thalhammer A.R., Princivalle F., Lenaz D., Stanley C.J., Garuti G. Djerfisherite in the Guli dunite complex, Polar Siberia: a primary or metasomatic phase? // Can. Min., 2007. V. 45. P. 1201-1211.