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.
Vanadio-pargasite NaCa2(Mg4V)(Si6Al2)O22(OH)2: a New Mineral of the Amphibole Supergroup
A new mineral was discovered in Cr–V-bearing marbles of the Sludyanka Complex from the Pereval marble quarry, Sludyanka district, southern Baikal region, Russia. It was named vanadio-pargasite as vanadium-bearing analog of pargasite according to the amphibole supergroup classification and CNMNC recommendations. Black Cr–V-spinel (magnesiocoulsonite–magnesiochromite), red Cr–V-bearing spinel, calcite, dolomite, Cr–V-bearing diopside and chlorite, phlogopite, and forsterite are associated minerals. Vanadio-pargasite occurs as subhedral long- and short-prismatic crystals 0.10–0.8 × 0.05–0.10 mm in size, with (110) and (010) faces and perfect cleavage by (110). Macroscopically, the new mineral is bright green to emerald green with vitreous luster; in thin sections and powder, it is pale green, without pleochroism. The new mineral is biaxial, positive, 2V = 86° ± 2°, γ = 1.659(2), β = 1.651(2), α = 1.643(2). The Mohs hardness is ~ 6, average VHN50;100 is 795; range 752–824 kg/mm2. The measured and calculated density is 3.05(5) and 3.112 g/cm3, respectively. In a thermogram over the range 654–1081°С, H2O is released with a endothermic effect. Over the range 900–1183°C, the main endothermic effect is caused by water and, possibly, F release, as well as melting of the mineral (1020°C). The absorption bands in the IR spectrum are, cm–1: 3445, 1633, 980, and 469. Vanadio-pargasite is monoclinic, space group 2C/m; the unit cell parameters are: a = 9.914(3), b = 18.003(2), c = 5.300(2) Å, β = 105.69(3)°, V = 910.7(5) Å3, Z = 2. The strongest reflections in the X-ray diffraction pattern are [d, Å (I) (hkl)]: 8.98 (15) (020), 8.43 (40) (110), 3.27 (30) (240), 3.14 (100) (310), 2.82 (35) (330), 2.70 (18) (151), 2.34 (15) ($$4.10\bar 1$$4.101¯), 1.898 (15) (510), 1.445 (25) (4.101). The average chemical composition (528 point analyses) is, wt %: 42.75 SiO2, 0.14 TiO2, 12.75 A12O3, 0.44 Cr2O3, 5.92 V2O3, 19.15 MgO, 0.03 FeO, 0.01 MnO, 12.52 CaO, 3.45 Na2O, 0.41 K2O, 0.74 F (wet chem.) 1.75 H2O (calc.); the total is 99.91. The simplified formula is K0.1Na0.9Ca2.0Mg4.0V0.7Al0.3(Si6.1Al1.9)8.0O22(OH1.7F0.3)2.0. Holotype material has been deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia (registration nos. 5035/1, 5035/2, and 5035/3).
Primary geochemical and mineralogical dispersion in the vicinity of the Lady Loretta Zn-Pb-Ag deposit, Northwest Queensland
Abstract Lady Loretta is a stratiform Zn-Pb-Ag deposit occurring within carbonate- and pyrite-rich argillaceous rocks of the southern part of the Lawn Hill Platform, northwestern Queensland. The deposit consists of a single massive sulphide lens within a steep-sided basinal structure and contains reserves of 8 690 000 tonnes of ore at 18.1% Zn, 6.7% Pb and 110 g t −1 Ag. The proportion of pyrite-rich layers in the host rocks increases progressively from about 2% at 150 m stratigraphically below the ore to > 90% in the top 10 m of the footwall rocks. Hanging-wall rocks contain up to 20% pyrite-rich layers for at least 100 m above the ores. Siderite is the carbonate phase present within the ore and within the host rocks in an aureole that extends from 75 m beneath to 50 m above the ore. Both older and younger rocks are dolomitic. The two carbonate phases do not occur together within unmineralized host rocks although they may coexist within veins. Siderite contains up to 13 mol% ZnCO 3 and 32 mol% MgCO 3 . There is an antipathetic relationship between Zn and Mg, the latter increasing with distance from the ore. Zinc and, to a lesser extent, Hg, Pb, Ag and Ba show extensive primary dispersion within the host rocks. Within the plane of sedimentation, haloes vary in width from 50 m to 1.5 km and these dispersions are thought to be dependent on the shape of the sedimentary basin floor at the time of exhalative activity. Perpendicular to the sedimentary layering, Zn and Hg show the most extensive primary dispersion with anomalous values extending up to 100 m into the footwall and at least 50 m into the hanging wall.