Partitioning of Nb, Ta, Ti, Ce, and La between Granitoid Magmatic Melts and Minerals
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Partitioning of Nb, Ta, Ti, Ce, and La between Granitoid Magmatic Melts and Minerals V. Yu. Chevychelova,*, A. A. Viryusa, and Corresponding Member of the RAS Yu. B. Shapovalova Received August 17, 2020; revised September 4, 2020; accepted September 8, 2020
Abstract—Experimental data on the Nb, Ta, Ti, Ce, and La concentrations in felsic magmatic melts of various alkalinity and alumina content upon dissolving ilmenorutile, ferrotapiolite, and loparite in them and the partitioning of these metals between the melt and the mineral at 650–850°C and 100 MPa, which allow one to obtain quantitative characteristics for creating physicochemical models of the genesis of rare metal and rare earth deposits, are presented. It is shown that ilmenorutile and ferrotapiolite are stable in the peraluminous melt. Ilmenorutile is also stable in the subaluminous melt and at 650°C in the alkalized melt, and loparite is unstable in all melts participating in the experiments. The dependences of the content and partitioning of Nb on dissolving ilmenorutile and loparite are similar to each other and to those on dissolving columbite and tantalite. At the same time, the dependence obtained by dissolving ferrotapiolite is similar to that obtained by dissolving microlite and pyrochlore. Keywords: solubility, partitioning, ilmenorutile, ferrotapiolite, loparite, experiment, granitoid melts, niobium, tantalum, Nb/Ta ratio DOI: 10.1134/S1028334X20110045
The partitioning of Ta and Nb in the Earth’s crust is in many respects determined by the processes of fluid-magmatic interaction and differentiation in granitoid magmatic melts. Study of the physicochemical conditions of such interactions was conducted primarily with the minerals from a columbite–tantalite group [6, 8, 11–13], to a lesser degree, from a pyrochlore–microlite group [7, 12] and, as a rule, at a Nb/Ta ratio >1 in the melt [9–11]. This work presents for the first time experimental data on the contents of Nb, Ta, Ti, Ce, and La in felsic magmatic melts of various composition on dissolving other accessory minerals of granites, pegmatites, and nepheline syenites (ilmenorutile (Ti, Nb, Fe3+)O2, ferrotapiolite Fe2+(Ta, Nb)2O6, and loparite (Na, Ce, La, Ca, Nd)(Ti, Nb)O3) at T = 650–850°C and P = 100 MPa, as well as such data on partitioning of these metals between a melt and a mineral in felsic magmatic systems. The results obtained make it possible to evaluate the stability and deposition capability of these Nb- and Ta–Nb-minerals under high-temperature conditions directly from the magmatic melts enriched in volatile components. aD.S.
Korzhinskii Institute of Experimental Mineralogy, Russian Academy of Sciences, Chernogolovka, Moscow Region, 142432 Russia *e-mail: [email protected]
The initial water-saturated model glasses of SiO2– Al2O3–Na2O–K2O composition with added 0.5 wt % of CaO and 1 wt % of LiF were melted from the gel mixtures. In the experiments, we used glasses of three compositions with different aluminium saturation indexes (molAl2O3/mol(Na2O + K2O + CaO) = (A/NKC)): ≈
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