Origin of djerfisherite in mantle xenoliths and its relation to kimberlite magmatism

Sharygin I.S., Golovin A.V.

V.S.Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia

isharigin@mail.ru

 

The interest of this study was bred by widespread occurrence of djerfisherite (ideally, K₆Na_0-1(Fe,Ni,Co)₂₄S₂₆Cl) in kimberlite-hosted xenoliths and diamonds (e.g., Bulanova et al., 1990). Usually djerfisherite has been found as overgrowths on primary Fe-Ni-Cu sulfides. Now, it is assumed that metasomatic origin of djerfisherite is due to interaction of primary sulfide with the hypothetical K-Cl-rich fluid or melt (e.g., Bulanova et al., 1990). However, source of metasomatizing agent and P-T-conditions of their interaction is unclear. Recently djerfisherite was found in the groundmass of kimberlites from Siberian craton (Russia) (e.g. Sharygin et al., 2007) and Slave craton (Canada) (e.g. Clarke et al., 1994) as late primary magmatic phase. Thus, at least two basic hypotheses for djerfisherite origin in mantle xenoliths can be supposed: (i) in-situ mantle metasomatism and (ii) infiltration of kimberlitic melt into the xenoliths at different stages of its evolution. Examination of literary data concerning mantle xenoliths from different sources (e.g., alkaline basalts and kimberlites) shows that djerfisherite is observed only in kimberlite-hosted mantle xenoliths. This fact is evident to the close genetic relation of djerfisherite in mantle xenoliths and kimberlite magmatism Here we present the detailed study of djerfisherite in the deepest mantle xenoliths from kimberlites and the comparison of djerfisherite in mantle xenoliths and in groundmass of host kimberlites.

We have studied 22 unaltered sheared lherzolite xenoliths from uniquely fresh kimberlite of the Udachnaya-East pipe (Siberian craton, Russia). Sheared peridotites represent a deepest layer of lithospheric mantle (Boyd et al., 1997) and are the most abundant xenoliths in Udachnaya-East pipe (Boyd et al., 1997). The studied sheared xenoliths show porphyroclastic to fluidal-mosaic-porphyroclastic textures (based on the classification of Harte, 1977). The rock-forming (primary) mineral assemblage of these xenoliths is composed of olivine, orthopyroxene, garnet and  clinopyroxene. The P-T conditions of formation for these paragenesis, based on geothermobarometer of (Brey, Köhler, 1990), can be estimated as P = 60-75 kb and T = 1200-1400 ^оС. Primary sulfides occur as spherical or elongated sulfide blebs enclosed in rock-forming minerals and interstitial large masses. They are represented by pyrrhotite, pentlandite and chalcopyrite. Interstitial spaces between primary minerals are filled with fine-grained aggregate of olivine, monticellite, clinopyroxene, phlogopite, tetraferriphlogopite, humite, sodalite, chromite, magnetite, perovskite, apatite, calcium carbonate, pyrrhotite and djerfisherite. All rock-forming minerals contain secondary melt inclusions located along healed fractures, some of which transect entire grains of host minerals. Melt inclusions consist of finely crystalline aggregate (carbonates, sulfates, chlorides), transparent crystals (silicates, carbonates, sulfates, chlorides) and opaque minerals (oxides and sulfides including djerfisherite).

 

Fig. 1. Djerfisherite in sheared lherzolite xenoliths from Udachnaya-East kimberlite pipe. Symbols: Dj – djerfisherite, Po – pyrrhotite, Pn – pentlandite, Chr – chromite, Mgt – magnetite, Cc – calcium carbonate, Ap – apatite, Phl – phlogopite, Cpx – clinopyroxene, Ol – rock-forming olivine, Opx –rock-forming orthopyroxene.

 

Djerfisherite is the dominant sulfide phase in sheared lherzolite xenoliths from Udachnaya-East pipe. This mineral was observed as rims around early Fe-Ni-Cu sulfides in blebs enclosed in rock-forming minerals (Fig. 1a) and intragranular spaces (Fig. 1b). Individual xenomorphic, subhedral, rarely euhedral grains of djerfisherite occur in find-grained interstitial assemblage (Fig. 4 c) and as daughter phase in secondary melt inclusion (Fig. 4d). The observed textural relationships of the mineral grains clearly indicate that djerfisherite crystallized after rock-forming silicates and Fe-Ni-Cu sulfides.

Our results show that origin of djerfisherite in sheared lherzolite xenoliths from Udachnaya-East pipe is result of infiltration of the host kimberlitic melt. Djerfisherite in melt inclusions and interstitial assemblages, forming individual grains, directly crystallizes from infiltrating kimberlitic melt. Djerfisherite rimming primary sulfides is a product of reaction of infiltrating kimberlitic melt and primary sulfides. Based on comparison our results and literary data concerning djerfisherite in another types of mantle xenoliths from different Siberian kimberlite pipes we can suppose that all djerfisherites in mantle xenoliths are products of infiltration of host kimberlitic melt.

In the last decade the role and source of chlorine in kimberlitic melts have been widly discussing (e.g., Kamenetsky et al., 2009). The Udachnaya-East pipe presents a only example of exceptionally fresh kimberlitic rocks with very low water (less then 0.5 wt.%) and high chlorine (up to 6 wt.%) contents. This enrichment of chlorine is defined by presence abundant chlorine-bearing minerals such as halite, sylvite, sodalite and djerfisherite. It is suggested (Sharygin et al., 2007) that the presence of djerfisherite in other djerfisherite-bearing kimberlites indicate high activity of chlorine in the magma, even if is depleted in the rocks and other chlorine-bearing minerals are absent in groundmass. However, finds of djerfisherite in kimberlite groundmass are more rare then those in mantle xenoliths. According to our results concerning genesis of djerfisherite in mantle xenoliths we can suppose that the presence of this sulfide in xenoliths also indicate enrichment of kimberlitic magma in chlorine, even if now djerfisherite is absent in groundmass of host kimberlite. At present djerfisherite were recognized in 13 kimberlite pipes in East Siberia (Russia), Northwest Territories (Canada) and Northern Cape Province (South Africa) (Dobrovol’skaya et al., 1975; Clarke et al., 1977, 1994; Bulanova et al., 1990; Distler et al., 1997; Sharygin et al., 2007, 2008). Thus, widespread occurrence of djerfisherite in kimberlites and kimberlite-hosted mantle xenoliths argues that chlorine is significant component in protokimberlitic melts.

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This study was financially supported by RFBR grant 07-05-00575-a) and IGM SB RAS (grant No. VMTK-13).

 

References:

Brey G. P., Köhler T. Geothermobarometry in four phase lherzolites II. New thermobarometers, and practical assessment of using thermobarometers // Journal of Petrology. 1990. Vol. 31. Part 6. P. 1353-1378.

Boyd F.R., Pokhilenko N.P., Pearson D.G., Mertzman S.A., Sobolev N.V., Finger L.W. Composition of the Siberian cratonic mantle: evidence from Udachnaya peridotite xenoliths // Contribution to Mineralogy and Petrology. 1997. Vol. 128. P. 228-246.

Bulanova G.P., Spetsius Z.V., Leskova N.V. (1990): Sulfides in diamonds and xenoliths from kimberlitic pipes of Yakutia. Novosibirsk: Nauka, 120 p. (in Russian).

Clarke D.B., Mitchell R.H., Chapman C.A.T., MacKay R.M. Occurrence and origin of djerfisherite from the Elwin Bay kimberlite, Somerset Island, Northwest Territories.// Canadian Mineralogist. 1994. Vol. 32. No 4. P. 815-823.

Clarke D.B., Pe G.G., MacKay R.M., Gill K.R., O’Hara M.J. Gard, J.A. A new potassium-iron-nickel sulfide from a nodule in kimberlite // Earth and Planetary Science Letter. 1977. Vol. 35. P. 421–428.

Distler V.V., Ilupin I.P., Laputina I.P. Sulfides of deep-seated origin in kimberlites and some aspects of copper-nickel mineralization // International Geology Review. 1987. Vol. 29. P. 456–464.

Harte B. Rock nomenclature with particular relation to deformation and recrystallisation textures in olivine-bearing xenoliths // Journal of Geology. 1977. Vol. 85. P. 279-288.

Kamenetsky V.S., Maas R., Kamenetsky M.B., Paton C., Phillips D., Golovin A.V., Gornova M.A. Chlorine from the mantle: Magmatic halides in the Udachnaya-East kimberlite, Siberia // Earth and Planetary Science Letter. 2009. Vol. 285. P. 96–104.

Dobrovol’skaya M.G., Tsepin A.I., Ilupin I.P., Ponomarenko A.I. Djerfisherite fromYakutia kimberlites // in “Mineraly i Paragenezisy Mineralov Endogennykh Mestorozhdenii”. ed. P.M. Tatarinov. Leningrad: Nauka. P. 3–11 (in Russian).

Sharygin V.V., Golovin A.V., Pokhilenko N.P., Kamenetsky V.S. Djerfisherite in the Udachnaya-East pipe kimberlites (Sakha-Yakutia, Russia): paragenesis, composition and origin // European Journal of Mineralogist. 2007. Vol. 19. P. 51-63.

Sharygin V.V., Kamenetsky V.S., Kamenetsky M.B. Potassium sulfides in kimberlite-hosted chloride-“nyerereite” and chloride clasts of Udachnaya-East pipe, Yakutia, Russia // Canadian Mineralogist. Vol. 46. P. 1079–1095.