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Genesis of rare-metal pegmatites and alkaline apatite-fluorite rocks ofBurpala massif, Northern Baikal folded zone
Sotnikova I.A., Vladykin N.V.A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences,
Irkutsk [email protected]
Fig. 1. Schematic geological map Burpala massif..1 – Q-deposits, 2 - carbonatites, 3 - alaskite and alkaline granites, 4 - apatite
fluorite rocks, 5 - rare-metal pegmatites, 6 - quartz syenites, 7 - pulaskites , 8 - nepheline syenites, 9 - shonkinites, sodalite syenites , 10 - hornfels, 11 -
sandstones and siltstones holodninskoe formation (U. Vendian), 12 - space sampling for U-Pb geochronological studies (1 - sample B-305-10, 2 - sample
B-313-10).
The scheme of the massif’s magmatism is the following:Rocks of the main facies: dykes of shonkinites nepheline
syenites alkaline pulaskites quartz syenites Rocks of veined facies: nepheline and alkaline syenites rare metal pegmatites nepheline-sodalite mariupolites alaskites and alkaline granites dyke of apatite-fluorite rocks veins of carbonates.
1 – Zr-silicates (1 - eudialyte, 2 - lovenite and seidozerite, 3 - katapleite), 2 - astrophyllite, 3 - Mn-ilmenite, 4 loparite, 5 - albitite, 6 – loparite and ilmenite.
1 - syenites of the main phase, granites-alaskite,2 - mariupolites, nepheline syenites, 3 - pegmatites,4 - fenites,5 – apatite-fluorite rocks(green.), carbonatites.
The samples of apatite-fluorite rocksMulti-phase fluid he inclusion of chloride brines in fluorite deposits of Burpala massif:a, b, в, г - Nicole parallel, е, ж - Nicole crossed. The scale of 50 μm.
NaCa
K Sr
B
MnRb
Mo
Co
Cr
Cd
U Au
Cl-
CO2
Th
Cu
BrCs
Mg
HCO3-
Li
FeBa
SO42-
CH4
0,00001
0,0001
0,001
0,01
0,1
1
10
100
1000
С, г
/кг
Н2О
The concentration of the various components of fluid inclusions in fluorite deposits of Burpala massif. Among the trace elements is dominated by Sr, Ba, B, Fe, Mn, Li, Rb, Cs, components that are characteristic of magmatic fluids.
The Burpala massif belongs to unique rare-metal alkaline occurrences. The massif includes the intrusion of the central type (250 sq. km., 287 Ma).
Isotopic studies (Sr-Nd) indicate the mantle source of primary magma Burpala massif close to EM-2, which is characteristic of alkaline intrusions in the folded belts.
As a whole REE spectra in the studied early rocks of the massif and pegmatites are characterized by the a great similarity that indicates their genetic relationship. The distribution of rare elements on the spider-diagrams also verifies the genetic association of all rocks of the Burpala massif.
The pegmatites of the massif are associated with Zr, Nb, REE and Y deposits. Average REE contents in alkaline silicate rocks of the main intrusive phases and dyke alkaline rocks of the Burpala massif are two times higher as compared with the Clarke level in syenites (500-4000 ppm). All spectra lines demonstrate a slight inclination that indicates the primary high contents of heavy REE rather than a slight differentiation of rocks.
The rare-metal pegmatites from the Burpala massif are marked by a great dispersion of REE total, which varies from 500 ppm up to 36000 ppm that can be accounted for high alkalinity of pegmatites.
Apatite-fluorite rocks are found in the central part of massif. Previously, these rocks were regarded as hydrothermal low-temperature phase. New geological and thermobarometric evidence suggests that apatite-fluorite rocks were formed from the residual fluid-melt, separated after crystallization of rare-metal pegmatites.
The work was supported by the Russian Foundation for Basic Research (project no. 114-45-04057)
