Cathodoluminescence of Rare Earth Doped Zircons. I. Their Possible Use as Reference Materials

Synthetic zircon crystals (ZrSiO4), undoped and doped with Y3+, La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+, Lu3+, were grown from a flux consisting of a mixture of Li2MoO4 and MoO3 heated to 1125°C and then cooled to 750°C. The cathodoluminescence (CL) spectra of these zircons were analyzed at room-temperature and near liquid nitrogen temperature with a CL spectrometer attached to a scanning electron microscope (SEM). This study highlights the complexity of the intrinsic emission band extending from 200 to 500 nm. The relative intensities of the major emission band centered at 230 nm (5.4 eV) and peaks of less energy were found to depend upon the crystallographic orientation of the crystals. Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+ and Tm3+-doped zircons display sharp emission peaks being characteristic of the doping rare-earth element (REE). These lines are frequently multiplets but only the average position of the peaks are reported because of the instrumental conditions used in this study. The CL intensities of the intrinsic and extrinsic features were found to depend on the crystal orientation, and numerous experimental factors such as the electron beam energy and the beam current density

Cathodoluminescence of Rare Earth Doped Zircons. II. Relationship Between the Distribution of the Doping Elements and the Contrasts of Images

Cathodoluminescence (CL) color photographs using an optical CL microscope with a cold cathode electron gun are compared with non-spectrally resolved (polychromatic) and selected wavelength CL images obtained by means of a scanning electron microscope equipped with a CL spectrometer. It is the aim of this paper to show how the interpretation of the contrasts of CL images depends on the knowledge of the CL photon energy distributions participating to the observed contrasts as well as the matrix effects modifying the number of emitted photons compared to that of generated photons. It is shown that the impurities different from the rare earth elements (REE) activators are responsible for charge trapping mechanisms leading to the development of internal electric fields modifying the energy and spatial distribution of the electrons within the insulators and consequently modifying the relative intensities of the intrinsic (host lattice) emission and characteristic emission of a REE activator. In addition, the mechanisms of production of photons must be better understood before trying to express the CL intensity of a monochromatic line as a function of the corresponding REE activator

Cathodoluminescence Applied to the Microcharacterization of Mineral Materials: A Present Status in Experimentation and Interpretation

Experimentation and interpretation of cathodoluminescence (CL) microscopy and spectroscopy applied to the microcharacterization of material minerals are reviewed. The origins of the intrinsic (host lattice) and extrinsic (impurities) luminescence emissions in crystals are briefly discussed. Merits and limitations of the available techniques are illustrated. CL emission changes as a function of the incident electron dose are illustrated for the case of natural quartz and sphalerite (ZnS) crystals. These effects are discussed in terms of the development of bulk charging, production of heat, diffusion of impurities, and creation of lattice defects induced by the incident ionizing particles. Although CL emission is mostly extrinsic in origin there is no general rule for identifying the nature of impurities from the CL emission spectra of minerals. However there is potential for using CL spectroscopy for trace element analysis as presented for the case of minerals containing rare-earth luminescent ions. The CL emission is a signature of the crystal-chemistry properties of minerals and hence contains potential genetic information. Some of the applications of CL emissions in the geosciences are summarized

Gem corundum deposits in Vietnam

Since 1983, gem-quality rubies have been recovered from the Luc Yen and Quy Chau mining areas in northern Vietnam. Since 1991, 'basaltic'-type blue-green-yellow ('BGY') sapphires have been mined in southern Vietnam. This article briefly reviews the history and geology of these different areas and shows the importance of marble and basalt-type deposits. Other types of corundum occurrences are found in amphibolite, pegmatite, gneiss and metasomatite. The gemmological, chemical and isotopic characteristics of these different types of corundum are described.<br /> The most notable features of rubies contained in marbles are that many crystals have blue colour zones, and inclusions of rutile, anhydrite and salts. The primary fluid inclusions are composed of carbon dioxide and hydrogen sulphide with native sulphur and diaspore daughter minerals. Sapphires from placers in basalts are characterized by inclusions of columbite, pyrochlore and baddeleyite. The trace element contents of corundums allow distinction of rubies in marbles from sapphires in basalts and metamorphic rocks. Rubies have high chromium (0.54<Cr<sub>2</sub>O<sub>3</sub><O.66 wt.%)and low iron (0.01<FeO<0.07 wt.%) contents. The geological origin of Vietnam corundums can be clearly determined from the isotopic composition of their structural oxygen, i.e. δ 18O = 21.0 ± 0.9% for rubies in marbles and δ 18O = 6.6 ± 0.4% for sapphires in basalts

Extreme enrichment of Se, Te, PGE and Au in Cu sulfide microdroplets: evidence from LA-ICP-MS analysis of sulfides in the Skaergaard Intrusion, east Greenland

The Platinova Reef, in the Skaergaard Intrusion, east Greenland, is an example of a magmatic Cu–PGE–Au sulfide deposit formed in the latter stages of magmatic differentiation. As is characteristic with such deposits, it contains a low volume of sulfide, displays peak metal offsets and is Cu rich but Ni poor. However, even for such deposits, the Platinova Reef contains extremely low volumes of sulfide and the highest Pd and Au tenor sulfides of any magmatic ore deposit. Here, we present the first LA-ICP-MS analyses of sulfide microdroplets from the Platinova Reef, which show that they have the highest Se concentrations (up to 1200 ppm) and lowest S/Se ratios (190–700) of any known magmatic sulfide deposit and have significant Te enrichment. In addition, where sulfide volume increases, there is a change from high Pd-tenor microdroplets trapped in situ to larger, low tenor sulfides. The transition between these two sulfide regimes is marked by sharp peaks in Au, and then Te concentration, followed by a wider peak in Se, which gradually decreases with height. Mineralogical evidence implies that there is no significant post-magmatic hydrothermal S loss and that the metal profiles are essentially a function of magmatic processes. We propose that to generate these extreme precious and semimetal contents, the sulfides must have formed from an anomalously metal-rich package of magma, possibly formed via the dissolution of a previously PGE-enriched sulfide. Other processes such as kinetic diffusion may have also occurred alongside this to produce the ultra-high tenors. The characteristic metal offset pattern observed is largely controlled by partitioning effects, producing offset peaks in the order Pt+Pd>Au>Te>Se>Cu that are entirely consistent with published D values. This study confirms that extreme enrichment in sulfide droplets can occur in closed-system layered intrusions in situ, but this will characteristically form ore deposits that are so low in sulfide that they do not conform to conventional deposit models for Cu–Ni–PGE sulfides which require very high R factors, and settling of sulfide liquids

The geology and genesis of gem corundum deposits

The aim of this review is to present the state of the art on the geology and genesis of gem corundum deposits, including the main characteristics and classifications, to an audience of non-specialists, academic students, professional geologists and gemologists. The careful detailed descriptions and studies on the geology, mineralogy and structures of the deposits carried out over the last century provides a foundation to unravel their genesis through new field and laboratory research including petrography, mineralogy, gemology, fluid inclusions, and stable and radiogenic isotopes. Descriptive geology coupled with recent advances in geology of gems permits decoding of how some of these historical and fabulous deposits formed as well as to estimate exploration potential in the future. New oxygen isotope data are presented here for the first time