Mineralogy and Petrology最新文献

The Yidun Terrane hosts huge amounts of Late Triassic granitic plutons. While the southern Yidun Terrane, also referred to as the Zhongdian arc, mainly includes Late Triassic porphyry and related porphyry Cu-Au deposits, rare mineralization was found related to the contemporary granitic batholiths in the northern Yidun terrane (NYT). This paper has explored the chemical compositions of the apatite from these intrusions, which provide insights into the petrogenesis and the mineralization potential. The higher Mg and V concentrations and La/Sm ratios of the Zhongdian apatite than the Cuojiaoma and Daocheng apatite in the NYT suggestes that the Zhongdian porphyries were derived from a mixed source with both mantle and crustal contributions, while the Cuojiaoma and Daocheng granites are dominantly crustal derived. Compared with the Cuojiaoma and Daocheng apatite, the Zhongdian apatite are characterized by higher Sr, Eu/Eu* [Eu_N/(Sm_N×Gd_N)^0.5], S and Cl, and low Mn and Y concentrations with adakitic affinity, indicating an environment with high oxygen fugacity and S and Cl contents for their parental magmas, which is favorable for the formation of porphyry Cu-Au deposits. By comparing the chemical characteristics of apatite from the ore-bearing porphyries and ore-barren granites in the Yidun Terrane, this study proposes that the apatite from the ore-bearing rocks commonly has relatively high Sr, S and Fe concentrations and low Mn, Y and Si/S ratio. These geochemical characteristics can be good indicators for predicting the metallogenic potential of the rocks.

The Hemrin Basalt (HB) is an abnormal occurrence because of its genesis, mineralogy, textures, rare native metals content, and odd geographic-geologic-tectonic setting. It occurs as a caprock for few NW/SE trending hills in a nearly flat-lying area. The HB is a high-K calc-alkaline, collision-related, continental-arc basalt and consists of diopside, labradorite and volcanic glass as the predominant constituents displaying rare firework and feathery textures. The accessory minerals in HB comprise small, discrete grains of native Ni, Fe, Cu, and Sn metals, and scattered grains of sulfides (pyrrhotite, pentlandite, molybdenite), oxides (magnetite, ilmenite, Cr-spinel), and apatite. These minerals occur as disseminated individual or composite grains of variable shapes within the groundmass of HB. Vesicle-filling secondary minerals are zeolite, calcite, anhydrite, and gypsum. The native metals were formed under reducing conditions. The reducing conditions were created as a result of assimilation of C- and S-rich sedimentary rocks by the ascending magma from the continental lithospheric mantle through the thick pile of sedimentary formations. The possible C- and S-rich rocks include the carbonates and evaporites of Fatha Formation and the Hemrin Coal Seam within the upper part of Injana Formation hosting the HB and overlying the Fatha Formation, and possibly the petroleum source, reservoir and caprocks forming the sedimentary column underlying the area. Assimilation of S from these rocks created sulfides, while assimilated C resulted in the formation of native metals.

The Kenticha pegmatite field comprises suites of barren to fertile pegmatite swarms. It shows textural, mineralogical, and geochemical variations. The pegmatites are structurally controlled and emplaced in mafic–ultramafic belts during the Neoproterozoic. This study aims to constrain the genetic and tectonic setting of the Kenticha rare-metal (RM) pegmatite and the associated granite. The presence of minerals such as biotite, muscovite, spodumene, spessartine-almandine garnet, gahnite, beryl, tourmaline, cordierite, and topaz indicate the peraluminous nature of the granite and associated pegmatites. The Kenticha rare-metal granite-pegmatite shows ASI > 1.1, low V, Y, very low Sr, Ba, Th, Zr and REE, very high Be, Li, Rb, Cs, Ga, Nb, and Ta than the upper continental crust. The parental two-mica granite has higher Co, Rb, Ba, and Ce and lower V, Zr, Y, Nb, Ni, La, Pb, Sr, and Th than the upper continental crust. The Ta/Nb value in the two-mica granite is nearly equal to the average upper crustal value. In both parental granite and pegmatites, the normative corundum (C) is greater than 1%. The P₂O₅ content is low in the assumed parental granite. However, in the main ore body, the P₂O₅ content increases towards the more fractionated pegmatite. Due to its peraluminous character and high content of Be, Cs, Li, Ta, and Rb, we can categorise the granite-pegmatite under the LCT subclass of the rare-element pegmatite. It's associated with S-type granite. HFSE and LIL elements show characteristics of bulk continental crust composition and syn-collisional felsic magmatism. Biotite composition suggests partial melting of the metasedimentary protolith as the source of the two-mica granite. The plots of Y vs. SO₂, P₂O₅ vs. SiO₂, % normative C vs. Rb, Y vs. Rb, and Th vs. Rb support the S-type magma source. Geochemical and mineralogical data show a nearly vertical evolutional trend of the granite-pegmatite. It varies from the basal granitic unit to the pegmatite core unit. The mineralization of rare metals in the granite-pegmatite was mainly controlled by genetic (processes).

“Multi-method-approach” has now been for many years the buzzword in marble provenance analysis. Nevertheless a true combination of the results of different analytical methods is rarely applied in the sense of the combined simultaneous use of a large number of analytically obtained numerical variables. It is demonstrated here that the combination of data from isotope analysis, chemical data, and data from the chemical analysis of inclusion fluids of an artefact and of course in combination with a corresponding database enhances substantially the accuracy of marble provenance analysis. It is explicitly pointed out that the unchallenged collection of data of the chemical composition of marbles from different sources (and different analytical procedures) most probably implies severe differences in their comparability. Exemplarily presented is the nearly perfect discrimination of the most important fine-grained marbles and furthermore the possibility of the intra-site discrimination of the three Carrara districts and the assignment of two portrait heads to the Carrara Torano quarries.

Nickelalumite, ideally NiAl₄(SO₄)(OH)₁₂(H₂O)₃, is a newly approved mineral from the Batken region, Kyrgyzstan, where it occurs in the Kara-Tangi and Kara-Chagyr uranium deposits. It formed in a zone of hydrothermal alteration of U–V-bearing carbonaceous siliceous schists, in association with quartz, calcite, alumohydrocalcite, allophane, crandallite, kyrgyzstanite, ankinovichite and an unknown Al–OH-mineral. It occurs as aggregates of colourless to pistachio-green radiating bladed crystals from 0.05 to 0.50 mm long. It is vitreous to transparent in thin flakes, has a white streak, and shows no fluorescence under long-wave or short-wave ultraviolet light. Cleavage is perfect parallel to {001} and no parting was observed. Mohs hardness is 2, it is brittle and has a splintery fracture. The calculated mass density is 2.231 g cm^–3. In transmitted plane-polarized white light, nickelalumite is non-pleochroic, biaxial, α = 1.542(2), γ = 1.533(2), β could not be measured due to the almost negligible thickness of the flakes. EPMA chemical analysis gave Al₂O₃ 39.94, SiO₂ 0.17, SO₃ 15.20, V₂O₃ 0.29, FeO 0.15, NiO 8.00, ZnO 6.21, (H₂O)_calc. 31.87, total 101.83 wt%, H₂O was determined by crystal-structure analysis, and the empirical formula is as follows: (Ni_0.55Zn_0.39V_0.02Fe_0.01)_Σ0.97(Al_3.99Si_0.01)_Σ4.00 (SO₄)(OH)₁₂(H₂O)₃ based on 4 (Al + Si) cations. There is considerable variation in substitution of Zn, Cu, Fe and V³⁺ for Ni and V⁵⁺ for S⁶⁺. Nickelalumite is monoclinic, P2₁/n, a = 10.2567(5), b = 8.8815(4), c = 17.0989(8) Å, β = 95.548(1)°, V = 1550.3(2) ų, Z = 4. The crystal structure of nickelalumite was refined to an R₁ index of 5.66% and consists of interrupted [NiAl₄(OH)₁₂] sheets intercalated with layers of {(SO₄)₂(H₂O)₃}; nickelalumite is a member of the chalcoalumite group.

The "Snowball Earths" were cataclysmic events during the late Neoproterozoic's Cryogenian period (720-635 Ma) in which most, if not all, of Earth’s surface was covered in ice. Paleoenvironmental reconstructions of these events utilize isotopic systems, such as Δ¹⁷O and barium isotopes of barites. Other isotopic systems, such as zinc (Zn), can reflect seawater composition or environmental conditions (e.g., temperature changes) and biological productivity. We report here a multi-isotopic C, O, and Zn data set for carbonates deposited immediately after the Marinoan glaciation (635 Ma) from the Otavi Group in northern Namibia. In this study, we chemically separated calcite and non-calcitic carbonate phases, finding isotopically distinct carbon and oxygen isotopes. These could reflect changes in the source seawater composition and conditions during carbonate formation. Our key finding is largescale Zn isotopic variations over the oldest parts of the distal foreslope cap carbonate sections. The magnitude of variation is larger than any found throughout post-snowball cap carbonates to date, and in a far shorter sequence. This shows a heretofore undiscovered difficulty for Zn isotopic interpretations. The primary Zn sources are likely to be aeolian or alluvial, associated with the massive deglaciation related run-off from the thawing continent and a greater exposed surface for atmospheric aerosol entrainment. The samples with the lightest Zn isotopic compositions (δ⁶⁶Zn < 0.3 ‰) potentially reflect hydrothermally sourced Zn dominating the carbonates’ Zn budget. This finding is likely unique to the oldest carbonates, when the meltwater lid was thinnest and surface waters most prone to upwelling of hydrothermally dominated Snowball Earth brine. On the other hand, local variations could be related to bioproductivity affecting the Zn isotopic composition of the seawater. Similarly, fluctuations in sea-level could bring the depositional site below and above a redoxcline, causing isotopic variations. These variations in Zn isotope ratios preclude the estimation of a global Zn isotopic signature, potentially indicating localized resumption of export production.

Three new copper-lead selenite bromides were synthesized by chemical vapor transport reactions. Pb₅Cu⁺₄(SeO₃)₄Br₆ is monoclinic, space group C2/m, a = 17.7248(14), b = 5.5484(5), c = 12.7010(10) Å, β = 103.398(2)º, V = 1215.08(17) ų, R₁ = 0.024; Pb₈Cu²⁺(SeO₃)₄Br₁₀ is orthorhombic, space group I222, a = 9.5893(5), b = 12.4484(9), c = 12.7927(6) Å, V = 1527.08(15) ų, R₁ = 0.027; Pb₅Cu²⁺(SeO₃)₄(Br,Cl)₄ is monoclinic, C2/c, a = 24.590(6) Å, b = 5.5786(14) Å, c = 14.248(4) Å, β = 102.883(7)º, V = 1905.3(9) ų, R₁ = 0.026. The crystal structure of Pb₅Cu⁺₄(SeO₃)₄Br₆ consists of two distinct parts: corner- and edge-sharing Cu⁺Br₄ tetrahedra form infinite [Cu⁺₄Br₆]^2- layers which alternate with [Pb₅(SeO₃)₄]²⁺ layers. Pb₈Cu²⁺(SeO₃)₄Br₁₀ contains positively charged unique [Pb₈Cu²⁺(SeO₃)₄]¹⁰⁺ rod-like chains with Cu²⁺ cations in the core. These chains are held together by Br^- anions. Pb₅Cu⁺₄(SeO₃)₄Br₆ and Pb₈Cu²⁺(SeO₃)₄Br₁₀ belong to new structure types. Pb₅Cu²⁺(SeO₃)₄(Br,Cl)₄ is a synthetic analogue of the mineral sarrabusite, Pb₅Cu(SeO₃)₄Cl₄, previously known from an electron diffraction study. The investigation of this synthetic equivalent of sarrabusite by conventional single-crystal X-ray diffraction provides a distinctly improved insight in this crystal structure. Cu atom has well-defined [2O+(2O+2X)] (X = halogen) distorted octahedral coordination. PbO_n and SeO₃ polyhedra interconnect via common oxygen atoms into [Pb₅(SeO₃)₄]²⁺ layers parallel to (001). Cu²⁺ cations interconnect the layers into the framework with the large cavities filled by halide X anions. In all three new compounds described, a common feature is the formation of the selenophile substructure which is terminated by a ‘lone-pair’ shell that faces bromide complexes thus forming the surface of a halophile substructure.