Monazite as an indicator of formation conditions of quartz veins at the Zhelannoe deposit,the Subpolar Urals

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 ThO₂ (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 ThO₂ (0.5–7 wt %) and high contents of CaO and SO₃ (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.