Search

Element imaging aims to provide quantitative data on multi-element distributions from major to trace elements with high lateral resolution. Here, we describe a control system for laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOFMS) imaging with complex integration of translational stage, laser, and mass spectrometer data acquisition which was tested on glass and mineral samples. In particular, besides single pulse imaging at a laser repetition rate of 100 Hz using a 5 μm laser spot size, a hole drilling imaging approach provided higher pixel sensitivity and lower limits of detection (<1 mg kg−1 for most heavy elements) while maintaining the same lateral resolution. An optional surface cleaning pulse can be applied without additional recording of data. Furthermore, the ablation area can be adapted to specific object structures of interest and leads to significant shorter imaging times. Triggering the data acquisition for every ablation position led to binned pixel data in relation to the sample position. This simplifies the data evaluation and allows a more automated image generation. The approach presented in this study enables flexible adjustments of distinct ablation modes to a specific analytical task and provides the basis for fully automated element imaging. To test the applicability of our approach, two complex geological samples containing crystalline solids were imaged to gain insights into the distribution of trace elements that occur typically in the low mg kg−1 range. We show that both single pulse and hole drilling ablation modes allow the determination of a large number of trace elements. However, the hole drilling mode shows a superior sensitivity per pixel, which in turn provides more detailed information about the formation of geological samples. [ABSTRACT FROM AUTHOR]

Laser ablation inductively coupled plasma time‐of‐flight mass spectrometry (LA‐ICP‐ToF‐MS) was used to generate quantitative elemental images of a mineralogically and texturally complex fault rock of the Northern Apennines of Italy (Zuccale Fault, eastern Island of Elba). Using LA‐ICP‐ToF‐MS combined with a low‐dispersion LA cell, we were able to generate large format (4 mm × 2 mm), high‐resolution (5 μm), high dynamic range (1–106 μg g−1) and quantitative multi‐elemental two‐dimensional compositional maps within a data acquisition time of a few hours. To quantify element mass fractions across the heterogeneous sample of the Zuccale Fault, we used a 100% species‐mass normalisation approach that took into account different mineral phases across the specimen. To assign mineral phase directly from LA‐ICP‐ToF‐MS data, we exploited the segregation of sulfur and calcium between distinct phases to threshold element images and develop mineral‐phase‐specific masks. Moreover, we demonstrate agreement between elemental mass fractions determined by LA‐ICP‐ToF‐MS imaging with 100% normalisation quantification and conventional LA‐ICP‐MS analysis with internal standard element‐based quantification. Finally, we discuss how this elemental imaging provides unique insights into the genesis of the Zuccale Fault. Key Points: Low‐dispersion laser ablation combined with ICP‐ToF‐MS provides high‐speed, high‐resolution multi‐elemental imaging.100% normalisation domain‐specific quantification was used to quantify major, minor and trace elements.High‐resolution elemental imaging allows a unique combination of microtextural and elemental analysis to discern the physical and chemical history of the Zuccale Fault cataclasite. [ABSTRACT FROM AUTHOR]

Darasun, Teremkyn, and Talatui are neighboring deposits in the Darasun gold district of Transbaikalia (Russia) that are hosted by Middle-Late Jurassic subduction-related porphyry intrusions and dikes. Darason consists of vertically extensive, steeply dipping Au mineralized veins and zones, spatially related to a K-rich granodiorite-porphyry intrusion, within the deposit are also pipelike bodies of tourmaline sulfide hydrothermal breccias. Teremkyn consists of gently and steeply dipping veins and zones, always associated with felsic dikes comagmatic with the Darasun intrusion. Talatui consists of variably shaped mineralized zones systematically associated with dikes of different compositions and with the host Middle-Late Jurassic granite porphyry. A large proportion of both veins and mineralized zones in these deposits consists of sulfide and oxide minerals, with pyrite and arsenopyrite mostly present at Darasun and Teremkyn and pyrite, magnetite, and hematite present at Talaui. The three deposits host also a large number of sulfosalt, bismuth, oxide, and telluride minerals. Gold of variable purity occurs as free nuggets or hosted by opaque phases. The gangue mineralogy, is similar in the three deposits and includes commonly quartz, tourmaline, and calcite. Microthermometry and microchemical analyses of fluid inclusions with petrographic and compositional data on ore minerals constrain the stages of ore deposition in the district. At room temperature, the entrapped fluids are of four compositional types: (1) multiphase, with a vapor bubble, liquid, and one or more solids; (2) liquid-vapor aqueous; (3a) vapor-rich with a small proportion of liquid and rare solids, and also (3b) vapor-rich with a small proportion of aqueous liquid and carbonic liquid. Types (1) and (3) or (2) and (3) coexist within the same assemblages and are present mostly in paragenetically early quartz, whereas the type (2) fluid within later quartz, sphalerite, and calcite shows consistent phase proportions. At Darasun and Teremkyn, type (2) fluid is the main ore fluid, but all fluid types are associated with gold deposition at Talatui. Microthermometric measurements from all fluid types show a range of phase transitions that vary systematically at the deposit scale. At Darasun and Teremkyn, coexisting types (1) and (3) and types (2) and (3) homogenize into the vapor and liquid states, respectively, within the same 290° to 460°C range. The corresponding bulk salinities vary between 0.7 and 44.8 wt percent NaCl equiv. In contrast, at Talatui coexisting types (1) and (3) and types (2) and (3) homogenize into the vapor and liquid phases and show a distribution of Th(total) and bulk salinities between about 300° and 610°C and 0.9 and 48 wt % NaCl equiv, respectively, Mass spectrometric and chromatographic data from bulk samples show that the main-stage orefluid in the three deposits varies compositionally according to location within the district. In detail, Cl, Na, K, Cs, Br, Sr, Rb, Mn, and Tl are relatively enriched in the Talatui fluid, whereas CO2, CH4, HCO, Cu, Pb, Sb, Fe, Hg, and REE are enriched at Darasun and Teremkyn or show no systematic variations. Au concentrations vary within the 0.01-to 3-g/t range at Darasun and Teremkyn, whereas at Talatui values do not exceed 0.4 g/t. The salinities and homogenization temperatures of the main-stage ore fluids types (1), (2), and (3) are typical of the intrusion-related class of gold deposits. This suggests a dominant magmatic component of the ore fluid during the first stages of mineral precipitation and a magmatic derivation of gold itself in the district. Phase separation was active during the early stages of ore deposition and took place between about 600° to 400°C at Talatui and 450° to 300°C at Teremkyn and Darasun at pressures of 10 to 160 MPa (i.e., 1- to 2.5-km depth).… [ABSTRACT FROM AUTHOR]

Abstract: Three hypogenic caves within the Naica mine of Mexico (Cueva de los Cristales — CLC, Ojo de la Reina — OR, and Cueva de las Velas — CLV) host spectacular gypsum crystals up to 11m in length. These caves are close to another shallow cave of the area (Cueva de las Espadas — CLE), with which they cover a 160m-deep vertical section of the local drainage basin. Similar to other hypogenic caves, all these caves lack a direct connection with the land surface and should be unrelated with climate. A record of multi-technique fluid inclusion data and pollen spectra from cave and mine gypsum indicates surprisingly that climatic changes occurring at Naica could have controlled fluid composition in these caves, and hence crystal growth. Microthermometry and LA-ICP-Mass Spectrometry of fluid inclusions indicate that the shallow, chemically peculiar, saline fluid (up to 7.7eq. wt.%NaCl) of CLE could have formed from evaporation, during a dry and hot climatic period. The fluid of the deep caves was instead of low salinity (∼3.5eq. wt.% NaCl) and chemically homogeneous, and was poorly affected by evaporation. We propose that mixing of these two fluids, generated at different depths of the Naica drainage basin, determined the stable supersaturation conditions for the gigantic gypsum crystals to grow. Fluid mixing was controlled by the hydraulic communication between CLE and the other deep caves, and must have taken place during cycles of warm-dry and fresh-wet climatic periods, which are known to have occurred in the region. Pollen grains from a 35ka-old gypsum crystal of CLC corresponds to a fairly homogenous catchment basin made of a mixed broadleaf wet forest, which suggests precipitation during a fresh-wet climatic period and confirms our interpretation of the fluid inclusion data. The unusual combination of geological and geochemical factors of Naica suggests that other hypogenic caves found elsewhere may not host similar crystals. However, this work shows that fluid inclusions and pollen spectra represent a useful tool for cave studies in general, and if used in future studies might be essential to unravel the mechanisms of hypogenic deposition. [Copyright &y& Elsevier]

The article presents the views of author on the research conducted by Krüger et al. regarding the determination of temperature of gypsum speleothems in two caves of Naica, Mexico including Cueva de las Espadas and Cueva de los Cristales. It further mentions that femtosecond-laser system and fluid inclusions were used to determine the temperature growth of gypsum in the caves. The fluid inclusions data, cave geochemistry and mineralogy reveal that the Naica caves are hypogenic.