Colin M. MacRae

Luminescence Database I—Minerals and Materials

A luminescence database for minerals and materials has been complied from the literature, the aim being to create a resource that will aid in the analysis of luminescence spectral of ionic species in minerals and materials. The database is based on a range of excitation techniques and records both major and minor lines, and their activators. The luminescence techniques included in the database are cathodoluminescence, ion luminescence, and photoluminescence. When combined with other traditional X-ray measurements collected on the same region, use of the luminescence database will give additional insight into the chemistry of minerals and materials.

A design for monolithic all-solid-state dye-sensitized solar cells with a platinized carbon counterelectrode

The high cost of electricity produced by solar cells compared to electricity from other energy sources is an inhibitor to a more widespread adoption of solar energy. Here a low-cost monolithic all-solid-state dye-sensitized solar cell (DSSC) was developed with a platinized carbon counterelectrode. The vacuum pore-filling technique proved to be effective for uniform infiltration of polymer nanocomposite electrolytes into the multilayer thick films. This monolithic design will be used for other solid-state or quasisolid electrolyte material-based DSSC, which allows for the development of stable and low-cost solar cells.

A study of cathodoluminescence and trace element compositional zoning in natural quartz from volcanic rocks: Mapping titanium content in quartz

This article concerns application of cathodoluminescence (CL) spectroscopy to volcanic quartz and its utility in assessing variation in trace quantities of Ti within individual crystals. CL spectroscopy provides useful details of intragrain compositional variability and structure but generally limited quantitative information on element abundances. Microbeam analysis can provide such information but is time-consuming and costly, particularly if large numbers of analyses are required. To maximize advantages of both approaches, natural and synthetic quartz crystals were studied using high-resolution hyperspectral CL imaging (1.2-5.0 eV range) combined with analysis via laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Spectral intensities can be deconvolved into three principal contributions (1.93, 2.19, and 2.72 eV), for which intensity of the latter peak was found to correlate directly with Ti concentration. Quantitative maps of Ti variation can be produced by calibration of the CL spectral data against relatively few analytical points. Such maps provide useful information concerning intragrain zoning or heterogeneity of Ti contents with the sensitivity of LA-ICPMS analysis and spatial resolution of electron microprobe analysis.

Complex mineral zoning patterns caused by ultra-local equilibrium at reaction interfaces

Chemically zoned minerals are useful records of temporal variations in ambient conditions and bulk chemical composition of the fl uid from which the minerals precipitate. In fl buffered systems, zoning of mineral compositions is expected to refl ect directly the evolution of fl composition. Here we show that during rapid fl uid-rock reactions, ultra-local equilibrium can form complex mineral zoning patterns, even when the overall system is highly fl uid buffered. We reacted cleaved calcite single crystals with aqueous arsenate-phosphate solutions with molar ratios of As/(As + P) between 0.01 and 0.15 at 250 °C and water-saturated pressure. We fithat complex zoning patterns and solid solution between hydroxylapatiteand arsenate-bearing hydroxylapatite that pseudomorphically replaced calcite formed within hours, and these zoning patterns were destroyed within days during secondary reactions. We propose a two-stage reaction process in the formation of the fi nal reaction product. (1) On an hour time scale, calcite is dissolved and replaced by compositionally heterogeneous apatite. The thin reaction-interface fllayer becomes extremely enriched in arsenic at an ultra-local scale as the reaction removes phosphate faster than the interface fl uid can re-equilibrate with the bulk fl uid. (2) The heterogeneous apatite is replaced by homogeneous apatite that refl ects the bulk fl uid composition over a longer (days) time scale through interface-coupled dissolution-precipitation. This paper highlights the complexity that can arise from ultra-local fl uid composition variations due to rapid fl uid-rock interaction in a short-lived fl uid fl ow event, for example during a seismic cycle. Subsequent interpretation of complex zoning patterns as refl ecting the evolution of bulk fl uid would be erroneous.

3D representation of geochemical data, the corresponding alteration and associated REE mobility at the Ranger uranium deposit, Northern Territory, Australia

Interrogation and 3D visualisation of multiple multi-element data sets collected at the Ranger 1 No. 3 uranium mine, in the Northern Territory of Australia, show a distinct and large-scale chemical zonation around the ore body. A central zone of Mg alteration, dominated by extensive clinochlore alteration, overprints a biotite–muscovite–K-feldspar assemblage which shows increasing loss of Na, Ba and Ca moving towards the ore body. Manipulation of pre-existing geochemical data and integration of new data collected from targeted ‘niche’ samples make it possible to recognise chemical architecture within the system and identify potential fluid conduits. New trace element and rare earth element (REE) data show strong fractionation associated with the zoned alteration around the deposit and with fault planes that intersect and bound the deposit. Within the most altered portion of the system, isocon analysis indicates addition of elements including Mg, S, Cu, Au and Ni and removal of elements including Ca, K, Ba and Na within a zone of damage associated with ore precipitation. In the more distal parts of the system, processes of alteration and replacement associated with the mineralising system can be recognised. REE element data show enrichment in HREE centred about a characteristic peak in Dy in the high-grade ore zone while LREEs are enriched in the outermost portions of the system. The patterns recognised in 3D in zoning of geochemical groups and contoured S, K and Mg abundance and the observed REE patterns suggest a fluid flow regime in which fluids were predominately migrating upwards during ore deposition within the core of the ore system.

Quantitative Cathodoluminescence Mapping with Application to a Kalgoorlie Scheelite

A method for the analysis of cathodoluminescence spectra is described that enables quantitative trace-element-level distributions to be mapped within minerals and materials. Cathodoluminescence intensities for a number of rare earth elements are determined by Gaussian peak fitting, and these intensities show positive correlation with independently measured concentrations down to parts per million levels. The ability to quantify cathodoluminescence spectra provides a powerful tool to determine both trace element abundances and charge state, while major elemental levels can be determined using more traditional X-ray spectrometry. To illustrate the approach, a scheelite from Kalgoorlie, Western Australia, is hyperspectrally mapped and the cathodoluminescence is calibrated against microanalyses collected using a laser ablation inductively coupled plasma mass spectrometer. Trace element maps show micron scale zoning for the rare earth elements Sm 3+, Dy 3+, Er 3+, and Eu 3+/Eu 2+. The distribution of Eu 2+/Eu 3+ suggests that both valences of Eu have been preserved in the scheelite since its crystallization 1.63 billion years ago.

Cathodoluminescence properties of quartz eyes from porphyry-type deposits: Implications for the origin of quartz

Abstract Hyperspectral cathodoluminescence (CL) mapping, combined with electron probe microanalysis (EPMA) and Fourier transform infrared spectroscopy, was used for the reconstruction of crystallization conditions of quartz from porphyry environments. Quartz eyes from the two porphyry deposits Rio Blanco (Chile) and Climax (U.S.A.) were studied. Three peaks are found to be responsible for the total CL emission: 1.93, 2.05, and 2.72 eV. The first two peaks are assigned to O-M (with M being an alkali ion) and oxygen vacancies, respectively. The 2.72 eV peak shows a linear correlation with the Ti concentration determined by EPMA point measurements. In addition, a negative correlation between the 1.93 eV emission and the Al concentration was observed. Quartz grains often form clusters in which adjacent grains show identical CL patterns, indicating that they crystallized attached to each other and were not disturbed later. Quartz cores display sector zoning and enrichment in Li, OH, and sometimes Al, which points to rapid crystallization from an extremely evolved melt. Quartz rims show high Ti, and low Li and OH contents, indicating crystallization from a less evolved melt either at higher temperatures or at higher titanium activities. The Al and Ti distribution patterns are frequently not correlated and both show uneven distribution indicating fast growth from inhomogeneous melts. Only Ti displays sharp transitions and fine oscillatory zoning, which can be explained by the higher mobility of Al in the quartz lattice. The quartz eyes crystallized after magma emplacement under non-equilibrium conditions. It is likely that the crystallization occurred from the melt enriched in Al, Li, and OH and probably other metals and/or volatiles on the brink of fluid exsolution. Subsequent fluid exsolution brought about disequilibrium to the system, resulting in dissolution of quartz and redistribution of elements between the melt and the fluid. The OH, Li, and other alkali metals and volatiles partitioned into the fluid, whereas Ti and Al remained in the melt. Resorption of quartz caused by the fluid exsolution continued until equilibrium was reached again, after which crystallization of quartz rims began from the water-, alkali-, and volatile-poor melt with higher Ti activity. Further accumulation of Al and Ti in the residual melt led to crystallization of extremely Al- and Ti-rich quartz.

Chiral edge-shared octahedral chains in liskeardite, [(Al,Fe)32(AsO4)18(OH)42(H2O)22]·52H2O, an open framework mineral with a pharmacoalumite-related structure

Abstract The type specimen of liskeardite, (Al,Fe)3AsO4(OH)6·5H2O, from the Marke Valley Mine, Liskeard District, Cornwall, has been reinvestigated. The revised composition from electron microprobe analyses and structure refinement is [Al29.2Fe2.8(AsO4)18(OH)42(H2O)22]·52H2O. The crystal structure was determined using synchrotron data collected on a 2 μm diameter fibre at 100 K. Liskeardite has monoclinic symmetry, space group I2, with the unit-cell parameters a = 24.576(5), b = 7.754(2) Å, c = 24.641(5) Å, and β = 90.19(1)°. The structure was refined to R = 0.059 for 9769 reflections with I > 3σ(I). It is of an open framework type in which intersecting polyhedral slabs parallel to (101) and (101̅) form 17.4 Å × 17.4 Å channels along [010], with water molecules occupying the channels. Small amounts (<1 wt.%) of Na, K and Cu are probably adsorbed at the channel walls The framework comprises columns of pharmacoalumite-type, intergrown with chiral chains of six cis edge-shared octahedra. It can be described in terms of cubic close packing, with vacancies at both the anion and cation sites. The compositional and structural relationships between liskeardite and pharmacoalumite are discussed and a possible mechanism for liskeardite formation is presented

Release of uranium from highly radiogenic zircon through metamictization: The source of orogenic uranium ores

Although circumstantial evidence from ore deposit mineralogy and geochemistry can imply potential sources for fluids and metals, rarely is direct evidence for metal leaching from source rocks seen in the vicinity of deposits. Here, we investigate the source of metals for a series of fault zone– and shear zone–hosted uranium occurrences in the Mount Isa inlier, Australia. As well as containing uranium, these deposits are enriched in Zr and rare earth elements (REEs), requiring that unusual fluids were responsible for addition of these typically immobile elements. During the Isan orogeny, highly saline metamorphic fluids infiltrated the sheared margin of a highly evolved granite intrusion, which contains elevated U, Th, F, Zr, and REEs. Synchrotron X-ray fluorescence spectroscopy and high-resolution electron microprobe mineral mapping show that this radioactive element–rich characteristic caused zircon crystals to become highly metamict, allowing the elements therein to become mobile. Thus, when orogenic fluids pervasively infiltrated along shear zones ?100 m.y. after granite intrusion, their unusually saline character allowed enhanced dissolution of regional carbonates and fluorite from the granite, providing the ligands needed for transport of uranium and the normally immobile elements from the metamict zircons.

Aluminium-bearing strunzite derived from jahnsite at the Hagendorf-Süd pegmatite, Germany

Abstract Aluminium-bearing strunzite, [Mn0.65Fe0.26Zn0.08Mg0.01]2+[Fe1.50Al0.50]3+(PO4)2(OH)2·6H2O, occurs as fibrous aggregates in a crystallographically oriented association with jahnsite on altered zwieselite samples from the phosphate pegmatite at Hagendorf Süd, Bavaria, Germany. Synchrotron X-ray data were collected from a 3 μm diameter fibre and refined in space group P1̄ to R1 = 0.054 for 1484 observed reflections. The refinement confirmed the results of chemical analyses which showed that one quarter of the trivalent iron in the strunzite crystals is replaced by aluminium. The paragenesis revealed by scanning electron microscopy, in combination with chemical analyses and a crystal-chemical comparison of the strunzite and jahnsite structures, are consistent with strunzite being formed from jahnsite by selective leaching of (100) metal-phosphate layers containing large divalent Ca and Mn atoms.