D. A. Varlamov

New Data on the Gold-Antigorite Association of the Urals

Many placers of the Urals spatially associated withmassifs of serpentinized ultramafic rocks contain gold–magnetite associations [7]. The bedrock analogs of thisassociation are rare, small, and interpreted as deriva-tives of granitoid magmatism. Gold–magnetite occur-rences in the Kagan alpinotype ultramafic massif in theSouth Urals, for example, served as a basis for distin-guishing the Au-productive serpentinite (antigorite)metasomatic association [9]. In addition to the spatialassociation of gold mineralization with antigorite ser-pentinites, the existence of this association is substanti-ated by the fact of significant redistribution and mobili-zation of Au during the development of antigorite,which allowed us to suggest that gold mineralization inthe antigorite serpentinites was formed during crustalregional or local metamorphism of the ultramafic mas-sifs under crustal conditions [6]. The present study ofgold–magnetite ores and altered rocks of the Kaganmassif revealed mineralogical and isotopic–geochemi-cal evidence for the metamorphic origin of mineraliza-tion. In this model, fluid and ore components (Fe, Cu,and Au) were mobilized from ultrabasic rocks.The Kagan Massif is located in the Vishnevogorsk–Il’menogorsk metamorphic complex in the SouthUrals. Lenslike ultrabasic bodies of the complex arecontrolled by deep-seated faults and traditionallyascribed to the Riphean riftogenic ophiolites, whichunderwent Late Cambrian regional zoned metamor-phism and Early Paleozoic siliceous metasomatism [2].According to these concepts, the ultramafic rockstogether with host volcanosedimentary rocks weretransformed with decreasing temperature into olivine–enstatite, talc–olivine, olivine–antigorite, and antigoriteserpentinites during high-grade metamorphism, whilelater metasomatism was responsible for the formationof enstatite, anthophyllite, and talc–carbonate rocks.According to Varlakov, rocks of the Kagan Massifunderwent zoned metamorphism. Its southern part iscomposed of talc–olivine and olivine–antigorite rocks,while the northern part consists of antigorite serpen-tinites with relicts of olivine–antigorite rocks (Fig. 1).The silicic metasomatism is weak and manifested in thedevelopment of anthophyllite in talc–olivine rocks andthe development of talc in olivine–antigorite rocks andantigorite serpentinites. The occurrences of massiveand vein–schlieren magnetite ores containing up to 2–3% sulfides are confined to the tectonic zone extendingover 2 km along the eastern contact of the northern partof the massif. Magnetite lenses up to 5–6 m long and0.2 m thick form chains rapidly pinching out along thetectonic zone. The ores are contained in reticulate ser-pentinite with abundant fine magnetite, which empha-sizes the affiliation of serpentine to chrysotile. In theimmediate contact with ore, the reticulate serpentinitecontains spots and veinlets of antigorite with large mag-netite, talc, chlorite, and amphibole.The gold–magnetite ores were developed by twosmall mines in the mid 20th century. Gold assayaccounts for 0.2–1.2 g/t, sharply increasing in the areaswith visible gold particles. The chemical–spectral anal-ysis of individual samples showed that the magnetiteores contain Au (up to 160 mg/t), Pd (up to 770 mg/t),and Pt (up to 20 mg/t) [5]. The contents of Rh, Ir, Os,and Ru are less than 10–20 mg/t.Magnetite of massive and disseminated ores is char-acterized by a ubiquitous admixture of Mg (1.0–2.4 wt % MgO). Magnetite from the wall rocks, inaddition, contains 0.4–2.0 wt % Cr

A new finding of Cu-Au alloy in association with rodingite minerals in the Kaa-Khem ophiolitic belt, Tuva

A new Cu-Au alloy occurrence is located at the southeastern flank of the Malye Kopty massif of ultramafic rocks in the Vendian-Early Cambrian Kaa-Khem ophiolitic belt. Lithic clasts with Cu-Au alloy segregations (up to 15 mm in size) intergrown with other minerals were found in alluvium of the Kara-Oss Creek valley, which extends along the fault zone crosscutting ultramafic rocks. Cu-Au alloy occupies the main volume of clasts and fills the network of veinlets in grained aggregates consisting of andradite (2–18% grossular component) and diopside (XFe = 0.01–0.05). Cu-Au alloy contains small ingrowths of andradite (up to 43% grossular component), diopside (XFe = 0.14–0.19), chlorite (penninite), chalcocite that contains up to 1.5 wt % Au, Cu-bearing greenockite (6.07–13.67 wt % Cu, 0.48–1.56 wt % Zn, and 0.76–1.06 wt % Au), and magnetite. The chemical composition of Cu-Au alloy is nonuniform. The central parts of large Cu-Au alloy segregations consist of Ag-bearing tetraauricupride (AuCu) blocks (3.2–6.4 wt % Ag). They contain veinlet-shaped AuCu zones with 13.3–14.5 wt % Ag. The AuCu blocks are cemented by late Cu-Au alloy, whose composition is close to auricupride (AuCu3). Taking into account the limits of component miscibility in the Au-Ag-Cu system, the temperature of the Cu-Au alloy formation was estimated at 350–600°C. This temperature corresponds to the formation conditions of garnet-pyroxene rodingite mineral assemblage (Plyusnina et al., 1993). The studied Cu-Au alloy samples from the Malye Kopty massif are very similar to Cu-Au alloy minerals hosted in the Alpine-type ultramafic rocks of the Karabash massif in the southern Urals. This similarity is confirmed by identical chemical compositions of pyroxene, garnet, and chlorite, and similar PT conditions of their formation. The data show that primary ore mineralization of gold-rodingite type occurs in the Kaa-Khem ophiolitic belt.

Tatarinovite Са3Al(SO4)[В(ОH)4](ОH)6 · 12H2O, a new ettringite-group mineral from the Bazhenovskoe deposit, Middle Urals, Russia, and its crystal structure

A new mineral, tatarinovite, ideally Са3Аl(SO4)[В(ОН)4](ОН)6 · 12Н2O, has been found in cavities of rhodingites at the Bazhenovskoe chrysotile asbestos deposit, Middle Urals, Russia. It occurs (1) colorless, with vitreous luster, bipyramidal crystals up to 1 mm across in cavities within massive diopside, in association with xonotlite, clinochlore, pectolite and calcite, and (2) as white granular aggregates up to 5 mm in size on grossular with pectolite, diopside, calcite, and xonotlite. The Mohs hardness is 3; perfect cleavage on (100) is observed. Dmeas = 1.79(1), Dcalc = 1.777 g/cm3. Tatarinovite is optically uniaxial (+), ω = 1.475(2), ε = 1.496(2). The IR spectrum contains characteristic bands of SO42−, CO32−, B(OH)4−, B(OH)3, Al(OH)63-, Si(OH)62-, OH–, and H2O. The chemical composition of tatarinovite (wt %; ICP-AES; H2O was determined by the Alimarin method; CO2 was determined by selective sorption on askarite) is as follows: 27.40 CaO, 4.06 B2O3, 6.34 A12O3, 0.03 Fe2O3, 2.43 SiO2, 8.48 SO3, 4.2 CO2, 46.1 H2O, total is 99.04. The empirical formula (calculated on the basis of 3Ca apfu) is H31.41Ca3.00(Al0.76Si0.25)Σ1.01 · (B0.72S0.65C0.59)Σ1.96O24.55. Tatarinovite is hexagonal, space gr. P63, a = 11.1110(4) Å, c = 10.6294(6) Å, V = 1136.44(9) A3, Z = 2. Its crystal chemical formula is Са3(Аl0.70Si0.30) · {[SO4]0.34[В(ОН)4]0.33[СO3]0.24}{[SO4]0.30[В(ОН)4]0.34[СО3]0.30[В(ОН)3]0.06}(ОН5·73О0.27) · 12Н2O. The strongest reflections of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are 9.63 (100) (100), 5.556 (30) (110), 4.654 (14) (102), 3.841 (21) (112), 3.441 (12) (211), 2.746 (10) (302), 2.538 (12) (213). Tatarinovite was named in memory of the Russian geologist and petrologist Pavel Mikhailovich Tatarinov (1895–1976), a well-known specialist in chrysotile asbestos deposits. Type specimens have been deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow.

P–T Conditions, Mechanism and Timing of the Localized Melting of Metapelites from the Petronella Shear Zone and Relationships with Granite Intrusions in the Southern Marginal Zone of the Limpopo Belt, South Africa

Evidence is presented for the localized melting of cordierite–orthopyroxene–biotite metapelites within the Petronella shear zone in the Southern Marginal Zone of the Limpopo Belt of Southern Africa. This process is expressed by the formation of centimetre-scale, K-feldspar-rich, garnet– orthopyroxene-bearing leucosome patches. Structural data indicate that the leucosomes formed after regional peak metamorphic and deformational events, but were synto late tectonic with respect to the shear fabric of the host metapelites. Phase equilibria modelling using the PERPLE_X software shows that the leucosomes were produced via fluid-deficient partial melting of the metapelites at temperatures above 900 C and pressures of 6 0–6 5 kbar. Melting reactions involving mainly biotite, plagioclase, quartz and accessory phases (including sulfides) produced peritectic Cr-enriched orthopyroxene, as well as Sc, Y, Cr, P-enriched garnet along with the potassium-rich melt. The melt was segregated around the peritectic minerals into the leucosomes. During nearisobaric cooling, the segregated melts crystallized to produce abundant K-feldspar and Sc, Y, Cr and P-poorer garnet inside the leucosome patches. Partial melt loss from the patches on cooling assisted with the preservation of anhydrous assemblages inside the patches and with re-hydration of the surrounding melanosome, with extensive formation of biotiteþquartz6sillimanite assemblages after orthopyroxene and cordierite, as well as late Sc, Y, Cr, and P-free garnet (þsillimaniteþquartz) at temperatures down to<600 C. Field and P–T data suggest a link between the localized melting of metapelites and trondhjemite intrusions that were synto late-tectonically injected into the Petronella shear-zone at about 2 67 Ga after the peak metamorphic and deformational event in the Southern Marginal Zone. This link is proven by U–Pb ages for monazites (a weighted average Pb/U age of 2666 6 4 Ma) from the leucosome patches. The trondhjemites provided additional heat and, probably, also a small amount of fluids, for the leucosome formation.

Nickeltsumcorite, Pb(Ni,Fe3+)2(AsO4)2(H2O,OH)2, a new tsumcorite-group mineral from Lavrion, Greece

Abstract A new tsumcorite-group mineral, nickeltsumcorite, Pb(Ni,Fe3+)2(AsO4)2(H2O,OH)2, the Ni-dominant analogue of tsumcorite and cobalttsumcorite, was found in the oxidation zone of a hydrothermal orebody containing gersdorffite and galena at the Km-3 mine, Lavrion, Attikí Prefecture, Greece. It is associated with annabergite, nickellotharmeyerite, nickelaustinite, gaspéite, calcite, dolomite, aragonite, quartz, goethite, cerussite, arseniosiderite, mimetite, oxyplumboroméite and Mn oxides/hydroxides. Nickeltsumcorite occurs as open-work aggregates and interrupted crusts up to 3 mm × 5 mm in area and up to 0.2 mm thick. They typically consist of coarse radial spherulites or dense concentric nodules up to 0.15 mm in diameter. Bunches or hemispherical clusters of crude individuals and separate imperfect, elongated crystals (up to 0.02 mm long) are also observed. Nickeltsumcorite is yellow, brownish-yellow, light brown or brown, with a yellow streak and a vitreous lustre. The Mohs hardness is ~4. The mineral is brittle; one direction of distinct cleavage is observed under the microscope. D(calc.) = 5.02 g cm-3. Nickeltsumcorite is optically biaxial (-), α = 1.82(2), β = 1.87(1), γ = 1.90(1), 2V(obs.) is large. The chemical composition (wt.%, electron-microprobe data, H2O by difference) is CaO 2.79, PbO 28.12, MgO 0.30, CoO 0.15, NiO 17.39, ZnO 0.76, Mn2O3 0.57, Fe2O3 6.83, As2O5 38.17, H2O 4.92, total 100.00. The empirical formula, calculated based on 10 O apfu, is (Pb0.76Ca0.30)Σ1.06(Ni1.39Fe3+0.51Zn0.06Mn3+0.04 Mg0.04Co0.01)Σ2.05As1.99O7.97[(H2O)1.25(OH)0.78]. The strongest reflections in the powder X-ray diffraction pattern [d,Å(I )(hkl)] are 4.64(100)(1̅11), 4.47(41)(2̅01), 3.238(82)(1̅12), 3.008(60)(201), 2.859(41)(021), 2.545(79)(3̅12, 112), 2.545(79)(3̅12, 112) and 2.505(61)(220, 2̅03). The cation composition, powder Xray diffraction data and IR spectrum show that nickeltsumcorite belongs to the tsumcorite structure type. The newmineral ismonoclinic, space group C2/m, a = 9.124(8), b = 6.339(3), c = 7.567(7) Å, β = 115.19(6)°, V = 396.0(7) Å3 and Z = 2. Nickeltsumcorite forms a solid-solution series with nickellotharmeyerite.