V-RICH MINERALS IN CONTACT-METAMORPHOSED SILURIAN SEDEX DEPOSITS IN THE POBLET AREA, SOUTHWESTERN CATALONIA, SPAIN
The Lower Llandoverian metasedimentary rocks of the Prades Mountains, southwestern Catalonia, Spain, consist of interstratified anorthite-rich beds, chert beds, phosphate beds, sulfide-rich black shale (with mainly pyrrhotite and minor chalcopyrite), massive sulfide lenses and calc-silicate beds. These metasedimentary rocks are anomalously enriched in V and Cr, and have disseminated minerals of precious metals: mainly sperrylite and palladian lollingite. The V- and Cr-rich associations are the result of an isochemical metamorphism of V- and Cr-rich protoliths. The contact metamorphism of V-rich shale produced metapelitic hornfels with V-rich aluminosilicates and V–Cr oxides. The occurrence of V oxides in apparent equilibrium with V-rich silicates suggests a limit for the V and Cr contents in these aluminosilicates at the conditions of thermal metamorphism. On the other hand, metamorphism of anorthite- and V-,Cr-rich sedimentary rocks produced V- and Cr-rich silicates, such as goldmanite, V-rich amphiboles, V-rich titanite and V-rich allanite.
Barian feldspar and barian-chromian muscovite from the Hemlo area, Ontario
Green mica schists occur in close association with a barite-rich unit in the late Archean Hemlo Heron Bay greenstone belt, approximately 21 km west of the Hemlo gold deposit, Ontario. They are characterized by anomalously high whole-rock Ba, Cr and Ti contents and minerals of unusual compositions. Feldspars include Ba-rich feldspar (celsian), ternary @a-K-Na) and (K-BaNa) feldspar with minor amounts of Sr (up to 0.6 wt. 9o SrO), Ba-poor alkali feldspar and microcline and exhibit three compositional discontinuities at Cnrs-zs, Cn3o-ro and Cn+r<s. The green mica contains high contents of Ba and Cr (up to 10.3 wt. 9o BaO and 6.4 wt. 9o CrzOl) and, occasionally, Ti (up to 5.8 wt. 9o TiOz) as well. Other minerals present are zincian-manganoan chromite (up to 8.9 wt. rlo ZnO and 13 wt. 9o MnO), chromian dravite (up to 9.8 wt. rlo CrzOi, chromian rutile (up to 2.0 $. 9o CrzOr), spessartine-rich almandine, F-rich phlogopite, chlorite, titanite, fluorite, sulfides, and carbonates. Salient mineralogical and geochemical characteristics, along with field relations and textural evidence, indicate that these green mica schists were derived from a mafic-ultramafic precursor(s) by extensive hydrothermal alteration; the barian was derived from an adjacent barite-rich unit. The estimated conditions of crystallization, 530'C and 3-4 kbar, indicate that the main mineral assemblage formed during the waning stage of regional thermal metamorphism. Veins of F-rich phlogopite, calcite, and fluorite, formed during a late alteration at 300-330'C, I kbar by a moderately saline, hieh-X(COz) fluid.
Centrifuge modelling of effects of shield tunnels on existing tunnels in soft clay
With the rapid development of the subway network,the phenomena of shield tunnels going across the adjacent tunnels are becoming more and more common.The interaction between shield tunneling and nearby tunnels is more complicated than the ordinary shield tunneling in intact soil strata.Based on the project of Shanghai Bund Passage crossing Metro Line 2,the method of centrifuge modeling together with the field measurement is employed to study the effects shield tunneling on nearby strata and existing tunnels.In centrifugal model tests,the effects simulation techniques considering the unloading of excavation,ground loss and grouting are developed to analyze the longitudinal settlement of the shield tunnel and the existing tunnel induced by the shield tunneling.Besides,the deformation distribution and settlement curves of the existing tunnels during shield construction are studied by using the monitoring data.