Genesis of the volcanic-related Be-U-Mo Baiyanghe deposit, West Junggar (NW China), constrained by mineralogical, trace element and U-Pb isotope signatures of the primary U mineralisation

The Volcanic-related Be-U-Mo Baiyanghe deposit is located in the Paleozoic Xuemisitan Volcanic Belt West Junggar (NW China). It largest Be Asia which dominantly hosted late Devonian rhyolitic tuff and Carboniferous Yangzhuang granite (313 ± 2 Ma) that were emplaced after closure of oceanic domain. a strongly fractionated peralkaline A1-type volcanic rock with major magmatic enrichment Nb, Y, Th, Be, Ta U. Highly REE patterns significant concentrations Pb, Zr, Th primary U mineralisation identified these tuffs as dominant probably source for Be-U ore genesis Junggar. high (6.5 < Umean 15.0 ppm) released through glass devitrification mobilised by oxidising fluids formation hydrothermal mineralisation. to contrary moderately moderate- high-K calc-alkaline A2-type characterised low (Umean = 2.9 ppm; Bemean 4.7 ppm), thus constituted minor demonstrated release remobilisation from metamict U-bearing accessory minerals. In deposit, structurally-controlled was temporally constrained an situ U-Pb isotopic minimum crystallisation age 240 7 Ma on pitchblende. This event represents stage occurred during early Permian–middle Triassic post-accretion paragenetically postdates (ca. 303–265 Ma). mainly Pb-Nb-Ti-Zr-Mo-rich pitchblende veins associated calcite quartz, crosscut Be-stage fluorite veins. During this episode crustal extension, therefore formed two-stage model within same mineralising event: (i) meteoric possibly basinal waters percolated downward into basement structures mixed CO2-bearing derived generations mafic dykes intruded host rocks area. circulation thermal solutions along faults fractured zones, leached alteration transported fluoride complexes fluids. These low-temperature (130–150 °C) then reacted Ca-rich minerals rocks, resulted pH increase triggered precipitation turn promoting deposition bertrandite; (ii) second stage, additional surface-derived including brines infiltrated basement. also likely chlorine and/or uranyl carbonate precipitated due fO2 decrease when (120–125 encountered favourable reducing environments represented dolerite diabase crosscutting carbonaceous shales at contact tuff. Pitchblende locally experienced dyke-emplacement related post-ore potassic abundant illite crystallisation, Si gain relative Ti, strong Pb depletion. largely oxidised uranophane supergene further water infiltration Mesozoic–Cenozoic extension characteristics volcanic-related show key similarities Streltsovka (U-Mo-F) Spor Mountain (Be-U) world-class districts, although has much smaller resources than ones Streltsovka.