Geochemistry of the rhyolitic magmas from the Streltsovka caldera (Transbaikalia, Russia): a melt inclusion study

Geochemistry of Carboniferous peralkaline felsic volcanic rocks, central New Brunswick, Canada: examination of uranium potential

“…Silica-oversaturated peralkaline felsic volcanic rocks, particularly rhyolite, are commonly enriched in U and represent a potential source of uranium for volcanic-related hydrothermal U deposits, such as the Streltsovka caldera (Transbaikalia, Russia: Ischukova 1997;Chabiron et al 2001Chabiron et al , 2003Cuney and Kyser 2009;Nash 2010), sediment-hosted U deposits in siliciclastic sedimentary basins, such as the U deposits in the Tim Mersoi basin in Niger (Forbes et al 1984;Forbes 1989;Plant et al 1999;Pagel et al 2005 The crystallization of U-bearing accessory minerals in highly depolymerized peralkaline melts is typically suppressed (Cuney 2009;Cuney and Kyser 2009) leading to progressive enrichment of U in residual melts during fractional crystallization and entrapment of U in the glassy groundmass. Subsequently U can be leached during the alteration or devitrification of the glass (Nash 2010).…”

Interaction of model F-bearing silicic melt with chloride fluid, uraninite, and columbite at 750°C and 1000–2000 bar and its implications for estimation of the ore-forming capability of the upper crustal magma chamber beneath the Strel’tsovka caldera, eastern Transbaikalia

“…Although buffer charges were verified after the runs with XRD, the work of oxygen buffers in runs 2-4 weeks long with a charge 100 mg in weight (Peiffert et al, 1996) is doubtful (Gramenitsky and Kotelnikov, 1984). In rhyolitic melt inclusions, the U content was 15-23 ppm (Chabiron et al, 2001(Chabiron et al, , 2003, or (1.5-2.3) × 10 -3 wt %, i.e., two orders of magnitude lower than in experiments with UO 2 . The U concentration in the fluid containing 1.0m Cl + 0.018m F in equilibrium with such melt should be very low (m U < 10 -6 ).…”

“…As follows from the melt inclusion study, the average water content in the erupted silicic magma was 2.4 wt % (Chabiron et al, 2001). A part of water was inevitably lost during the magma ascent and eruption.…”

“…It is assumed that the silicic magma chamber deduced beneath the Strel'tsovka caldera from geophysical data was enriched in U and F and could have been a source of uranium. As was shown by Chabiron et al (2001), rhyolite derived from this chamber contained 15-25 ppm U and 1.5-3.0 wt % F. The chemical composition of the model silicic melt was accepted on the basis of melt inclusions in quartz phenocrysts from rhyolite of the Strel'tsovka caldera. The chemical composition of this rhyolite, its geochemical specialization, and its isotopic age are close to the corresponding parameters inherent to rare-metal Li-F granites and subvolcanic ongonites, which are widespread in the eastern Transbaikalia (Kuznetsov et al, 2004;Badanina et al, 2004Badanina et al, , 2006.…”

“…The partial oxygen (hydrogen) pressure was set by the corresponding metal-oxide mixtures (Ni-NiO, Co-CoO, Chabiron et al (2001Chabiron et al ( , 2003, this melt could have been a possible source of uranium at deposits of the Strel'tsovka ore field. The transparent and homogeneous (according to EDS data) glass was ground and used in experiments.…”