The atomic structure and chemical ordering of aluminum ruthenium copper quasicrystal

Understanding the atomic structure of quasicrystals has fundamental importance in studying the formation and properties of this class of materials. In this thesis, the atomic structure and chemical ordering of AlRuCu, one of the stable and phason defect free quasicrystal material, was studied extensively by X-ray diffraction techniques which include regular and anomalous X-ray diffraction measurements at the Ru and Cu K-edges. The diffraction data have been analyzed in both reciprocal and real spaces, yielding the total structure factor and partial structure factors of Ru and Cu in reciprocal space and the atomic pair distribution function (PDF) and the differential partial atomic pair distribution function (DDF) of Ru in real space. An atomic structural model, including chemical ordering, was obtained based on the information of local atomic correlations and short range chemical order provided by the PDF and DDF of Ru. The model of atomic structure can be described by a direct projection of a 6-dimensional hypercubic lattice with vertex decoration using a non-Penrose window. A direct comparison of the structural model with the diffraction pattern in reciprocal space shows that this model can also describe the long range order of the atomic structure. As a comparison, the atomic structures of AlLiCu and MnTiSi, which have moderate and very high concentration of phason defects, were studied based on the PDFs from both X-ray and neutron powder diffraction experiments. Fundamental differences were observed among these quasicrystals in the preferred local atomic environment and nature of the projection window in the perpendicular space. The difference between these three quasicrystals and possible physical meaning were carefully discussed. The conclusion is that the compatibility of the short range order with the long range order is the most plausible reason why the AlRuCu exhibits such a perfect quasicrystalline ordering. Because of the complex nature of the quasicrystal atomic structure, real space analysis of diffraction pattern has been the most important experimental method used in this work. To improve the technique and to study a local atomic structure which has an icosahedral symmetry, the local inter-molecular atomic correlations in C\sb{60} solid at 10 K was studied by real space refinement of PDF. As an example of real space analysis of diffraction data, the result is also presented in this thesis. We found that the orientation of the C\sb{60} molecules is often locally deviated from the long range average structure, and a significant number (30$\sim$40 %) of molecules have a six-fold face oriented toward adjacent molecules

Controls on the formation of porphyry Mo deposits : Insights from porphyry (-skarn) Mo deposits in northeastern China

Porphyry Mo deposits have traditionally been classified into two major classes, arc-related and Climax-type, based on the tectonic setting and chemistry of associated intrusions. Although there is a consensus that porphyry Mo systems were formed by the optimal coincidence of geological processes operating at different scales, it is unclear what key parameter(s) render systems productive and whether the two classes of porphyry Mo deposits are unique in their mode of formation, or if they share fundamentally similar geological processes. These questions are important as a clearer understanding of the optimum conditions for the formation of porphyry Mo deposits is a prerequisite for more efficient exploration. This contribution presents a detailed assessment of the factors affecting the formation of porphyry Mo deposits through the investigation of barren and mineralized intrusions from the arc-related Songbei-Yangjiazhangzi-Lanjiagou (SYL) ore zone and the Climax-type Hashitu deposit of northeastern China. Our results show that the syn-mineralization intrusions from the SYL ore zone are quite evolved (SiO2 ~ 75 wt%; Na2O+K2O ~ 8.7 wt%) and are characterized by apparent light rare earth element (LREE) enrichments (LaN/YbN = 2.7-33.1) and moderate negative Eu anomalies (Eu/Eu∗ = 0.4-0.7). They show enriched zircon Hf isotopic compositions [ϵHf(t) = -11.9 to -4.8], indicating their parental magmas were likely derived from an ancient crustal source. Melt inclusions from the SYL syn-mineralization intrusions contain negligible F and Cl. In contrast, Hashitu syn-mineralization intrusions are characterized by weak LREE enrichments (LaN/YbN = 2.2-6.9) and strong negative Eu anomalies (Eu/Eu∗ = 0.02-0.10), with SiO2 and Na2O+K2O contents similar to the SYL syn-mineralization intrusions. They show depleted zircon Hf isotopic compositions [ϵHf(t) = 3.1-5.0], indicating their parental magmas were likely derived from a juvenile crustal source. Melt inclusions from the Hashitu syn-mineralization intrusions contain up to 0.4 wt% F and 0.03 to 0.09 wt% Cl. However, in both cases, the syn-mineralization intrusions are Mo-poor (1-7 ppm Mo), oxidized (above the quartz-fayalite-magnetite buffer), water-saturated (4.4-7.8 wt% H2O), and were emplaced at palaeodepths of 3.3 to 8.3 km. These data imply that magma source composition is not a key factor in the formation of porphyry Mo deposits. In contrast, magma oxygen fugacity, water content, and emplacement depth appear to play fundamental roles in the formation of porphyry Mo deposits of both arc-related and Climax-type. Within individual deposits, no systematic differences between pre- and syn-mineralization intrusions are observed in terms of magma source, fractionation degree, oxygen fugacity, emplacement depth, and volatile and Mo contents. Instead, a crucial apparent difference lies in the geometry of the intrusions, i.e., pre-mineralization intrusions generally occur as flat, ponded bodies, whereas syn-mineralization intrusions commonly develop as small stocks or dikes. Our results, in combination with an examination of other porphyry Mo systems, suggest that the sudden depressurization of magma chambers and subsequent venting of voluminous fluids along focusing structures (such as small stocks or dikes) most likely plays a critical role in the formation of porphyry Mo deposits of both arc-related and Climax-type. The findings of this study indicate that fluid processes in the shallow crust are pivotal for the formation of porphyry Mo deposits and that settings with ideal magmatic-hydrothermal architectures are most likely to develop into productive porphyry Mo systems. </p

Concentrations and isotopic variability of mercury in sulfide minerals from the Jinding Zn-Pb deposit, Southwest China

Mercury (Hg) isotopes have been proven as a useful tracer in understanding sources and biogeochemical processes of Hg in the environment. However, the use of this tracer has not yet been explored in economic geology. This paper investigates the concentrations and isotopic compositions of Hg in sulfide minerals from the Jinding deposit, the largest Zn-Pb deposit in China. Total mercury concentration (HgT) is highly variable: with the highest in sphalerite (472-1010 ng.g(-1)), intermediate concentrations in pyrite (195-342 ng.g(-1)) and the lowest in galena (65-310 ng.g-1). The variation was likely due to the fact that Hg2+ can more readily substitute for Zn2+ than for Fe2+ and Pb2+, but an influence of different parental fluids on the isotopic composition of the sulfide minerals cannot be excluded. An overall range of delta Hg-202 from -3.17 to -0.57 parts per thousand is observed in the sulfides. Samples from the early stage feature the enrichments of light Hg isotopes, with delta Hg-202 ranging from -3.17 to -1.59 parts per thousand, suggesting significant mass-dependent fractionation during the transport and/or deposition of Hg. However, the volatilization of aqueous Hg(0) during boiling of hydrothermal fluids was likely the most important process causing the observed fractionation. Relatively higher delta Hg-202 values (-1.84 to -0.57 parts per thousand) of the late stage samples indicate that the Hg was rarely fractionated from its sources. Additionally, small but significant mass-independent fractionations are measured for the deposit with Delta Hg-199 ranging from -0.06 to 0.10 parts per thousand, indicating that the Hg may have been derived from the sedimentary rocks of the Lanping Basin. Finally, we conclude that Hg isotopes have the potential to be a new tracer of sources of ore-forming materials, as well as pathways of fluid evolution in hydrothermal deposits. (C) 2017 Elsevier B.V. All rights reserved

Controls on the metal endowment of porphyry Mo deposits: Insights from the Luming porphyry Mo deposit, northeastern China

Processes controlling the metal endowment of arc-related porphyry Mo deposits are not well understood. Located in northeastern China, the arc-related Luming porphyry Mo deposit has a proven reserve of 0.75 Mt Mo at an average grade of 0.092 wt % and is characterized by multiple pulses of alteration and mineralization. These features make this deposit an ideal location to investigate the role of multiple pulses of magmatism and fluid release in the evolution and formation of an arc-related porphyry Mo deposit. Molybdenum mineralization at Luming is typically observed as a series of molybdenite-bearing veins hosted within a composite intrusive complex, referred to as the Luming Intrusive Suite. Crosscutting relationships between intrusive units and offset veins indicate that the Luming Intrusive Suite is composed of five major, successive granitic intrusions: the premineralization plutonic biotite monzogranite and monzogranite units, and the synmineralization stock- and dike-like porphyritic monzogranite, granite porphyry, and syenogranite units. Each synmineralization unit is associated with similar vein sequences that comply with the general form of early EB-type biotite veins, through A-type quartz ± biotite and B-type quartz-molybdenite veins, to late D-type quartz-molybdenite ± pyrite ± chalcopyrite, molybdenite, quartz-pyrite ± calcite, and calcite ± clays veins. The intensity and volume of alteration and mineralization within a given synmineralization unit decrease from early- through inter- to late-mineralization units. Although minor Mo mineralization is associated with potassic alteration along B-type veins, the majority of the ore is associated with D-type quartz-molybdenite-pyrite and molybdenite veins rimmed by sericite-chlorite-pyrite alteration, which are primarily hosted in the two premineralization units.A combination of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U-Pb and hydrothermal biotite 40Ar/39Ar studies, together with available isotope dilution-inductively coupled plasma-mass spectrometry (ID-ICP-MS) molybdenite Re-Os data, has resulted in a substantial reappraisal of the timing of magmatism and its association with molybdenite mineralization at Luming. The volumetrically dominant premineralization intrusive units have indistinguishable zircon U-Pb weighted mean 206Pb/238U ages ranging from 187.5 ± 2.8 to 186.5 ± 3.6 Ma (2σ), whereas the synmineralization units yield weighted mean 206Pb/238U ages from 178.6 ± 2.2 to 175.6 ± 3.0 Ma (2σ). The zircon U-Pb weighted mean 206Pb/238U ages of the synmineralization units are indistinguishable from the mean molybdenite Re-Os model (178.1 ± 2.7; 2σ) and hydrothermal biotite 40Ar/39Ar plateau (174.7 ± 1.1 Ma; 2σ) ages within uncertainty, confirming a genetic link with mineralization. Melt inclusion data show that the synmineralization intrusions were Mo poor, with Mo concentrations The data presented here suggest that molybdenite mineralization at Luming was most likely accomplished through three discrete magmatic-hydrothermal events during assembly of the Mo-poor synmineralization intrusive complex. The giant Luming deposit appears to be related to multiple pulses of magmatic-hydrothermal activities, resulting in the superposition of temporally distinct mineralization events. Our results suggest that pulsed release of ore-forming magmas and fluids, which are channeled along focusing structures like small porphyry fingers within a focused area, from a large magma chamber at depth may play a major role in the formation of large to giant porphyry Mo deposits of both the arc-related and Climax types. This conclusion is in line with field observations of a number of large to giant porphyry Mo deposits, which commonly show reversals in magmatic-hydrothermal evolutionary trend and are associated with multiple pulses of small stocks and dikes that are separate in time and space.</p

Fluid and melt inclusion study on mineralized and barren porphyries, Jinshajiang-Red River alkali-rich intrusive belt, and significance to metallogenesis

Alkali-rich Cu (Au, Mo) deposits are of increasing economic significance and are an attractive exploration target. They include some of the world's highest grade and largest porphyry related gold resources as well as some of the largest gold accumulations in epithermal settings. The Jinshajiang-Red River alkali-rich intrusive belt, with many porphyry Cu (Au, Mo) deposits, is a representative magmatic belt associated with mineralization. The Jinshajiang-Red River alkali-rich intrusive belt contains several Cu (Au, Mo) mineralized alkali-rich porphyry rocks including the Yulong quartz monzonite porphyry, the Machangqing granite porphyry, the Tongchang quartz syenite porphyry, and the Beiya quartz syenite porphyry. Additionally, there are also some barren alkali-rich porphyry rocks in the belt, such as the Yanshuiqing quartz syenite porphyry. Fluid inclusion petrography and microthermometry on those porphyry rocks are carried out in detail. The results show that the fluid inclusion assemblages in ore-bearing and barren porphyries are distinct: inclusions from barren porphyry are dominated by primary melt inclusions, and contain rare or no fluid inclusions, whereas inclusions from ore-bearing porphyries are dominated by fluid inclusions, and contain rare melt inclusions. Furthermore, halite, sylvite, calcite daughter minerals and an opaque phase in fluid inclusions from ore-bearing rocks are common, but rare in fluid inclusions from barren rocks. The results suggests that the evolution of ore forming fluids especially the halite, sylvite, calcite and opaque daughter minerals bearing fluid inclusions of quartz phenocrysts could be used to judge the degree of metasomatism and mineralization of a porphyry system

NanoSIMS element mapping and sulfur isotope analysis of Au-bearing pyrite from Lannigou Carlin-type Au deposit in SW China: New insights into the origin and evolution of Au-bearing fluids

Sulfur isotope signatures of Au-bearing pyrite from Lannigou Au deposit, a typical Carlin-type Au deposit in SW China, provide valuable information about the origin of the ore-forming minerals. Analysis by NanoSIMS was used to determine S isotope compositions of Au-bearing pyrite and to map the grain-scale distributions of Au, Cu, As and S in pyrite from the deposit. Based on different textural pattern of pyrites revealed by back-scattered electron (BSE) images, they are divided into three types: Py-1 diagenetic pyrite without core-rim structure, Py-2 pyrite with an Au-free core and a rhythmically-zoned Au-bearing rim, Py-3 Au-bearing pyrite with rhythmic zoning across the entire grain. The element distributions and S isotope compositions of four paragenetic stages are recognized on the basis of textural observation. Py-1 grains and the Au-free homogeneous cores of zoned crystals were formed in Stage 1 while the Au-bearing rims of the zoned crystals with rhythmic zonation of As and Cu, and to a lesser degree Au, were formed in two superimposed stages: stage 2 formed the inner zone that is enriched in As alone; and stage 3 formed the outer zone that is enriched in both Au and As. Other sulfides such as realgar, cinnabar and stibnite are formed in the last stage. The relationship between Au and As distributions in pyrite rim is complicated, changing from coupled to decoupled at the nanoscale. Such complexity is interpreted to reflect fluctuation of fluid composition and temperature with time, which in turn affect the modes of occurrence of As and Au. It is inferred that As mainly occurs in the crystal lattice replacing S whereas Au is mainly present as nanoparticles that were trapped in pyrite during crystal growth. The Au-bearing rims of the zoned pyrite crystals are characterized by highly variable delta S-34 values from 1.1 to 18.1 parts per thousand, which exceed the values of the Triassic calcareous host rocks (10-14 parts per thousand). In contrast, the delta S-34 values of the Au-free cores of zoned pyrite crystals vary over a narrower interval and are mainly between 6 and 12 parts per thousand, close to the values of pyrite crystals in the sedimentary country rocks. Our new analyses also reveals that the delta(34)5 values of the Au-bearing fluids generally increase during the formation of the deposit. The observed S isotope variations are consistent with mixing between a magmatic-related fluid with mantle-like delta S-34 value (similar to 0 parts per thousand) and a sedimentary or deep basin brine fluid with elevated delta S-34 value (&gt;18 parts per thousand), with an increasing contribution from the latter with time. The notably varied values of delta(34)5 and the disseminations of Au and other trace elements such as As and Cu in pyrite crystals indicate that the process responsible for Au precipitation in this deposit occurred in an open hydro thermal system