Florencite (Sm), a new mineral species of the florencite subgroup, was found in association with xenotime (Y) in quartz veins of the Maldynyrd Range of the Subpolar Urals as thin zones within rhombohe dral crystals of florencite (Ce) with faceting by {01 1} and {10 2}. The thickness of particular florencite (Sm) zones is 0.01-0.1 mm, and the total thickness of a series of such zones is 1-3 mm. Florencite (Sm) is colorless and pale pink or pale yellow with white streaks; its Mohs hardness is 5.5-6.0. Its measured and cal culated densities are 3.70 and 3.743 g/cm 3 , respectively. The mineral is transparent, nonpleochroic, and uniaxial (positive), and ω = 1.704(2) and ε = 1.713(2). The electron beam's fluorescence spectrum was 592 nm (intense green luminescence of Sm 3+ ) and 558 nm (yellow luminescence of Nd 3+ ). The chemical composi tion was as follows (microprobe, average of 2 WDS, wt %):
A detailed study of the florencite and xenotime assemblage from quartz veins of Au-REE occur rences in the Subpolar Urals allowed the REE fractionation and distribution of REE mixtures in the crystal structure to be characterized. In minerals of selective composition, isomorphic mixtures of LREE and HREE are divided into lanthanum La sg (La-Pr) and samarium Sm sg (Nd-Eu) subgroups in florencite and gadolin ium Gd sg (Gd-Dy) and ytterbium Yb sg (Ho-Lu) subgroups in xenotime. Concentrations of elements from these subgroups are inversely proportional to each other. Each florencite or xenotime crystal is characterized by several mineral varieties: xenotime (Y) and Gd bearing xenotime (Y), florencite (Sm), (Nd), and (Ce); they are selectively distributed by growth zones and pyramids of the crystal with formation of direct and inverse zoning. In both cases, cores of the crystals are enriched in HREE. The correlation between REEs, Y, and such trace elements as As, S, Ca, Sr, U, and Sc is established. REE deportment is considered in min erals formed as products of primary crystallization and hydrothermal redeposition. The REE fractionation is interpreted in terms of quantum mechanics.
At the Zhelannoe quartz deposit, the content of monazite attains 0.5 wt % in unaltered sericitolite and 18 wt % in hydrothermally altered sericitolite. Two monazite generations, including four varieties, characterize the sequence of formation and alteration of sericitolite bodies at the Zhelannoe deposit. Monazite of the first generation occurs in unaltered sericitolite as prismatic and tabular crystals characterized by (Nd,Ce) > La and enrichment in HREEs and ThO 2 (5-16 wt %). Its formation is accompanied crystallization of milk white quartz. Monazite of the second generation occurs in altered sericitolite as the product of recrystallization of the first-generation monazite. The large drusy crystals of second-generation monazite were formed similarly with Alpine-type veins. Monazite of the second generation is characterized by Ce > (La,Nd), low contents of HREEs and ThO 2 (0.5-7 wt %) and high contents of CaO and SO 3 (up to 3-5 wt %). Monazite of the second generation appeared as a result of local superimposed processes and is a characteristic feature of the Zhelannoe deposit.
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