Laser Ablation Inductively-coupled Plasma Mass Research Articles

Trace element partitioning between MgAl2O4-spinel and carbonatitic silicate melt from 3 to 6 GPa, with emphasis on the role of cation order-disorder

To better understand the partitioning of trace elements between spinels and silicate melts at high P, a series of experiments have been conducted in the system CaO–MgO–Al2O3–SiO2–K2O–CO2 at the P-T conditions of 3–6 GPa and 1500–1650 °C. These experiments successfully produced large MgAl2O4-spinel crystals coexisting with large carbonatitic silicate melt pools (plus large crystals of olivine and garnet in some cases). The experimental products were analyzed by using an electron microprobe in the wavelength-dispersive mode and an Agilent 7500 Ce laser ablation inductively-coupled plasma mass spectrometry, which led to high-P partition coefficients for 34 elements. The results suggest that pressure may have nominal significant impacts on the partition coefficients of some trace elements such as Nb, Ta, Ti, and nearly all rare earth elements (REEs), with the partition coefficients varying in several orders of magnitudes, but may play negligible roles in the partitioning of U, Mn, Fe, Sr, Ba, Na, K, Rb, and etc. Further analyses have revealed that much of the nominal P effects can be assigned to the Mg–Al cation order-disorder reaction. Cation exchange reactions are common in many geologically important minerals such as olivine, garnet, pyroxene, and plagioclase, and their effects on trace element partitioning should be extensively investigated in the near future before better understanding of the trace element partitioning systematics can be achieved. As one example, our experimental results have clearly demonstrated that due to much larger degrees of the Mg–Al cation order-disorder triggered by high P, spinel can strongly fractionate the REEs (with some heavy REEs compatible in the spinels and thus depleted in the relevant magmas), a phenomenon conventionally attributed to the presence of garnet. Some other important conclusions from our experiments include that Cr (or Ni) in the spinel structure at Cr-poor (or Ni-poor) conditions may be not as compatible as conventionally thought for Cr-rich (or Ni-rich) conditions, and Fe isotopes may be fractionated by spinels at high P.

Distinguishing Ore Deposit Type and Barren Sedimentary Pyrite Using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry Trace Element Data and Statistical Analysis of Large Data Sets

Faced with ongoing depletion of near-surface ore deposits, geologists are increasingly required to explore for deep deposits or those lying beneath surface cover. The result is increased drilling costs and a need to maximize the value of the drill hole samples collected. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis of pyrite is one tool that is showing promise in deep exploration. Since the trace element content of pyrite approximates the composition of the fluid from which it precipitated and the crystallization mechanism, the trace element characteristics can be used to predict the type of deposit with which a pyritic sample is associated. This possibility, however, is complicated by overlapping trace element abundances for many deposit types. The solution lies with simultaneous comparison of multiple trace elements through rigorous statistical analysis. Specifically, we used LA-ICP-MS pyrite trace element data and Random Forests, an ensemble machine learning supervised classifier, to distinguish barren sedimentary pyrite and five ore deposit categories: iron oxide copper-gold (IOCG), orogenic Au, porphyry Cu, sedimentary exhalative (SEDEX), and volcanic-hosted massive sulfide (VHMS) deposits. The preferred classifier utilizes in situ Co, Ni, Cu, Zn, As, Mo, Ag, Sb, Te, Tl, and Pb measurements to train the Random Forests. Testing of the Random Forests classifier using additional data from the same deposits and sedimentary basins (test data set) yielded an overall accuracy of 91.4% (94.9% for IOCG, 78.8% for orogenic Au, 81.1% for porphyry Cu, 93.6% for SEDEX, 97.2% for sedimentary pyrite, 91.8% for VHMS). Similarly, testing of the Random Forests classifier using data from deposits and sedimentary basins that did not have analyses in the training data set yielded an overall accuracy of 88.0% (81.4% for orogenic Au, 95.5% for SEDEX, 90.0% for sedimentary pyrite, 73.9% for VHMS; insufficient data was available to perform a blind test on porphyry Cu and IOCG). The performance of the classifier was further improved by instituting criteria (at least 40% of total votes from the Random Forests needed for a conclusive identification) to remove uncertain or inconclusive classifications, increasing the classifier’s accuracy to 94.5% for the test data (94.6% for IOCG, 85.8% for orogenic Au, 87.8% for porphyry Cu, 95.4% for SEDEX, 98.5% for sedimentary pyrite, 94.6% for VHMS) and 93.9% for the blind test data (85.5% for orogenic Au, 96.9% for SEDEX, 96.7% for sedimentary pyrite, 84.6% for VHMS). The Random Forests classification models for pyrite trace element data can be used as a predictive modeling tool in greenfield terrains by providing an accurate indication of ore deposit type. This advance will assist mineral explorers by allowing early implementation of predictive ore deposit models when prospecting for ore deposits. Furthermore, the ability of the classifier to accurately identify pyrite of sedimentary origin will allow researchers interested in paleoenvironmental conditions of ancient oceans to effectively screen prospective samples that are affected by a hydrothermal overprint.

Perovskites of the Tazheran Massif (Baikal, Russia)

The paper provides details of local geology and mineralogy of the Tazheran Massif, which was the sampling site of perovskite used as an external standard in perovskite U-Pb dating by sensitive high-resolution ion microprobe (SHRIMP) and laser ablation inductively-coupled plasma (LA–ICP–MS) mass spectrometry. The Tazheran Massif is a complex of igneous (mafic dikes, syenite, nepheline syenite), metamorphic (marble), and metasomatic (skarn, calc–silicate veins) rocks. Metasomatites are thin and restricted to the complex interior being absent from the margins. Perovskite has been studied at four sites of metasomatic rocks of three different types: forsterite–spinel calc–silicate veins in brucite marble (1); skarn at contacts between nepheline syenite and brucite marble (2), and skarn-related forsterite–spinel (Fo-Spl) calc–silicate veins (3). Pervoskite from Fo-Spl calc–silicate veins (type 1) is almost free from impurities (<1 wt.% in total: 0.06%–0.4% REE2O3, 0.10%–0.22% Nb2O5, ≤0.1% ThO2). The U contents are from 0.1 to 1.9 wt.% UO2 and are relatively uniform in perovskites from the same vein but differ from vein to vein of this type. Perovskite from the contact skarn (type 2) contains 1.5 to 4.5 wt.% REE2O3 but is poor in other impurities. Perovskite grains from skarn-related Fo-Spl calc–silicate rocks (type 3) belong to two generations that differ in REE, Nb, Th, Fe, and Na concentrations. Early-generation perovskites occurs as compositionally homogeneous octahedral or cubic-octahedral crystals with contents of impurities higher than in other varieties (3.6 wt.% REE2O3, 1.6 wt.% Fe2O3, 1.3 wt.% Nb2O5, 0.7 wt.% ThO2, 0.6 wt.% UO2, and 0.6 wt.% Na2O) but the lowest is at the respective site. Late-generation varieties show highly variable impurity concentrations of 1.5 to 22.7 wt.% REE2O3, 0.4 to 8.4 wt.% Nb2O5, and 0.8 to 4.5% ThO2, while the perovskite component may be as low as 65%. In addition to the lueshite and loparite, components, they contain REEFeO3 and Th0.5TiO3 endmembers which have no natural analogs.

Geochemistry of middle-late Mesozoic mafic intrusions in the eastern North China Craton: New insights on lithospheric thinning and decratonization

We present detailed geochronological, geochemical and Sr-Nd-Pb isotopic data for late Mesozoic mafic intrusions in the Taili region (western Liaodong Province) of the eastern North China Craton (NCC). We obtained laser-ablation inductively-coupled plasma mass spectrometry U-Pb zircon ages from lamprophyres with ages ranging from 139 to 162 Ma and diorites with clusters of ages at 226 ± 11 Ma, 165 ± 5.8 Ma and 140 ± 4.8 Ma. We interpret the Triassic zircons in diorites to be inherited from the Paleo-Asian Ocean slab. Both the lamprophyres and diorites contain abundant inherited grains (2644–2456 Ma) that were likely derived from the ancient NCC basement, reflecting a contribution from old lower crustal material. Like contemporaneous late Mesozoic mafic rocks in the Jiaodong and Liaodong Peninsula areas of the NCC, the Taili lamprophyres reveal a strong subduction signature in their normalized trace element patterns, including depletion of high field strength elements and enrichment of large ion lithophile elements. The rare-earth element patterns of the Taili intermediate-mafic intrusions are best explained if they were principally derived from partial melting of amphibole-bearing lherzolite in the spinel-garnet transition zone. Slab-derived melts likely contributed to the formation of late Mesozoic mafic rocks along three margins of the craton: due to accretion of the Yangtze Block along the southern margin of the craton, subduction of the Paleo-Asian Ocean along the northern margin, and subduction of the Paleo-Pacific oceanic plate along the eastern margin of NCC. We present a synthesis of the geochemical, spatial, and temporal patterns of magmatic rocks and periods of deformation that contributed to decratonization of the NCC in response to the Mesozoic tectonic evolution of adjacent plates along its northern, southern, and eastern margins.

The Laqiong Sb-Au deposit: Implications for polymetallic mineral systems in the Tethys-Himalayan zone of southern Tibet, China

The Himalayan mineral field includes over 50 quartz-vein type Sb-Au deposits, and placer Au deposits. The poorly documented Laqiong deposit is a typical example of quartz-vein type Sb-Au mineralisation in Tethys Himalayan sequence. The orebody are controlled by shallow north-dipping normal faults and north–south trending faults. Magmatic zircons extracted from muscovitic leucocratic granite from the southern part of the Laqiong mine area yield a Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry U-Pb age of 14 ± 1 Ma (n = 12, MSWD = 0.9) that is similar to the 40Ar/39Ar age of ca. 14 Ma from hydrothermal sericite in auriferous sulphide-quartz veins. The εHf(t) values for the magmatic zircon rims range from −5.4 to −1.9, corresponding to two-stage Hf model ages of 1403–1214 Ma. Quartz from the mineralised veins has δ18OH2O-SMOW values varying from +4.97 to +9.59‰ and δDH2O-SMOW values ranging from −119.7 to −108.1‰. The δ13CV-PDB values for calcite from the ore Stage III range from −6.9 to −5.3‰, and calcite from Stage IV are −3.5 to −1.7‰. The δ18OV-SMOW values for calcite from Stage III are +20.3 to +20.6‰ and for Stage IV are −6.3 to −4.9‰. The stibnite and pyrite samples have 208Pb/204Pb ratios of 38.158 to 39.02, 207Pb/204Pb ratios of 15.554 to 15.698, and 206Pb/204Pb ratios of 17.819 to 18.681, and bulk and in-situ δ34SV-CDT values for stibnite, arsenopyrite and pyrite range from −1.1 to +2.3‰. The calcite from the orebodies are enriched in MREE and depleted in LREE and HREE. Fieldwork, petrological, and geochemical data collected during our study leads to the following salient findings: the mineralising fluid is a mix of magmatic and meteoric fluids; and the deposit is closely related to the emplacement of Miocene granites originating from a thickened continental crust.

The ion microprobe as a tool for obtaining strontium isotopes in magmatic plagioclase: A case study at Okataina Volcanic Centre, New Zealand

We investigated the potential of multi-collector secondary ion mass spectrometry (MC-SIMS) as a tool for obtaining Sr isotopic compositions in plagioclase, a ubiquitous mineral in igneous rocks that serves as a recorder of crystallization history. MC-SIMS allows for high spatial resolution analysis (~12 μm in this study) of isotopes, and therefore improves the temporal scale at which fluctuations in crystallization conditions can be recognized, ultimately improving our understanding of rates of magmatic processes. Plagioclase crystals from two young rhyolitic deposits from two major eruptive complexes, Tarawera and Haroharo, of the Okataina Volcanic Centre in New Zealand were analysed. Results were corrected for matrix effects using linear modelling of MC-SIMS data versus An contents, as well as 87Sr/86Sr ratios acquired via laser ablation inductively-coupled plasma mass spectrometry (LA-MC-ICP-MS). Corrected MC-SIMS Sr isotopic ratios had an average 2σ uncertainty of ±0.0008 per spot, and were homogeneous in Okataina plagioclase at high spatial resolutions. Average LA-MC-ICP-MS 87Sr/86Sr ratios of plagioclase from both intra-caldera volcanic complexes (Tarawera 87Sr/86Sr = 0.7056 and Haroharo 87Sr/86Sr = 0.7054) suggest similar magma sources and similar assimilation and fractional crystallization processes for the two complexes. Overall homogeneity of plagioclase (excluding relict cores) indicates no significant changes in contributions (i.e., crustal assimilation, mafic influx) to the system during the majority of plagioclase crystal growth. Furthermore, lack of 87Sr/86Sr ratio fluctuations in plagioclase rims suggest interaction between the resident silicic magma and the intruding mafic magma that triggered the eruptions was largely limited to volatile and heat transfer. Using appropriate standards and analysis, this MC-SIMS method can be used to detect short-lived, open-system events in magma reservoirs where differences in 87Sr/86Sr isotopic ratios are significant.

Age interpretation in eulachon (Thaleichthys pacificus) as suggested by otolith microchemical signatures

Eulachon (Thaleichthys pacificus) are forage fish that play an important role in the ecosystem as prey for many species. Given their continuing population decline, determining accurate ages is necessary for age-structured stock assessments. This study employed microchemistry analysis to identify group differences and help interpret growth zone patterns on otolith surfaces. Specimens were collected off the coast of Oregon, in the coastal areas of Southeast Alaska, and in the southeastern Bering Sea. Laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) was used to measure elemental ratios in the otoliths along a continuous track from the core to the proximoventral margin. Ba:Ca, Sr:Ca, Zn:Ca, and Mg:Ca signatures suggested that eulachon specimens from three geographic regions are different based on their elemental profiles. For the Oregon specimens, fluctuations in Ba:Ca and Zn:Ca signatures appeared consistent with otolith growth zones and most likely were the result of seasonal coastal upwelling events. Variations in Ba:Ca and Zn:Ca were useful as annual markers for eulachon otoliths from the Bering Sea. For the Southeast Alaska specimens, analysis of the Ba:Ca and Zn:Ca oscillations was not straightforward. Further work is needed to understand the link between otolith microchemistry, fish physiology, and regional environmental factors.

Characterization of Carbonate Crust from a Recently Discovered Methane Seep on the North Atlantic Continental Margin of the USA

This study is focused on mineralogical and chemical characterization of an authigenic carbonate rock (crust) collected at a recently discovered cold seep on the US North Atlantic continental margin. X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicate that the carbonate rock is composed of microcrystalline aragonite cement, white acicular aragonite crystals (AcAr), equant quartz crystals, small microcrystalline aluminosilicates, and trace amounts of iron sulfide microcrystals. Element/calcium ratios were measured with laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) using a calcite standard, which was prepared by annealing USGS certified carbonate powder (MACS-3). The occurrence of microscopic, non-carbonate inclusions precluded evaluation of trace elements in the aragonite cement, but allowed for in situ analysis of AcAr crystals. Carbon and oxygen isotopes were analyzed via isotope ratio mass spectrometry (IRMS) and expressed as δ13C and δ18O. Low δ13C values suggest that aragonite grew as a result of anaerobic oxidation of methane and observed δ18O values indicate that the temperature of aragonite crystallization was 1.7–1.9 °C.

The speciation of thallium in (Tl,Sb,As)-rich pyrite

Three samples of (Tl,Sb,As)-rich pyrite from the ore deposits of the southern Apuan Alps (Tuscany, Italy) were studied through a multi-technique approach in order to constrain the speciation and incorporation mechanism of thallium in pyrite. High concentrations of Tl, Sb, and As were detected in all the studied samples through laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS). Average Tl contents were 1299 ppm, 1967 ppm, and 2623 ppm in samples from Sennari, Canale della Radice, and Fornovolasco, respectively. The LA-ICP-MS time-resolved down-hole ablation profiles were smooth indicating that Tl, Sb, and As are dissolved in the pyrite matrix, or occur in homogeneously distributed nanoparticles (NPs). X-ray absorption spectroscopy (XAS) data revealed that Tl, Sb, and As occurs as Tl+, Sb3+, As3+, and As−. In all the studied samples, bond distances and coordination numbers for Sb3+ and As3+ are constant, whereas Tl displays a range of coordination numbers (∼3 to ∼6), revealing the occurrence of different local environments. Moreover, no hints of features corresponding to coordination shells higher than the first were observed, suggesting an extremely disordered environment around Tl. Transmission electron microscopy (TEM) investigations revealed the presence of dislocations and As-rich “fluid” inclusions, whereas no Tl-rich NPs were observed. The study suggests that Tl+ could occur in structural defects in pyrite, lacking any long-range order. The ‘loose’ nature of Tl in pyrite favours its ready loss during the metamorphic recrystallization of pyrite and its redistribution within ore bodies and country rocks, with important implications from an economic and environmental point of view.

Quantitative Data Extraction from Orthopyroxene Trace Element Maps and Its Potential to Examine the Formation of the UG2 Unit, Bushveld Complex

We present a mineral chemical stratigraphy across the UG2 Unit, situated in the Upper Critical Zone of the Bushveld Complex. The magmatic evolution of the rocks hosting this world-class ore deposit for chromium and platinum group elements (PGEs) is still under debate. Orthopyroxene is a common phase across the magmatic stratigraphy of the unit. It hosts trace metals, whose relative contents can record information about magmatic processes. This study determined laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) trace element data for orthopyroxene and spot LA multi-collector ICP-MS Sr-isotope data for plagioclase. Mapping of trace element distributions revealed internal zoning in Cr, V, Y, and Th. Unlike in conventional spot analysis, quantitative trace element concentrations were extracted post-analysis from two-dimensional LA-ICP-MS maps. This approach offered advantages over spot analysis. The maps revealed internal complexities (e.g., inclusions, exsolved phases, zonations and diffusion halos) that could be avoided with suitable thresholds for chemical filter elements (i.e., 100 ppm < Cr < 4000 ppm, Y < 6 ppm), permitting fast, automated extraction of pure orthopyroxene data pixels from elemental maps covering noritic, troctolitic, anorthositic and chromititic mineral assemblages. Diffusive equilibration in orthopyroxene was evaluated by comparing zonations in elements with different known diffusivities. Magnesium and Ni are homogenously distributed, indicative of rapid diffusive processes, while Cr and V show zonations, interpreted to largely reflect primary distribution. Thorium and Y apparently diffused along discrete pathways, indicated by concentration anomalies following orthopyroxene lamellae. A systematic study of the trace element inventory of orthopyroxene across the succession of the UG2 Unit, complemented with Sr isotope signatures of plagioclase, revealed clear evidence for open-system processes: compatible elements (Cr, Ni) are decoupled from Mg# variations in orthopyroxene from specific UG2 subunits; distinct Mg# peaks coincide with negative V excursions in orthopyroxene from chromite-bearing subunits; towards the top of the unit, plagioclase shows a distinct 87Sr/86Srinitial peak and orthopyroxene shows Cr-depleted and Th-enriched rims. These chemical features cannot be explained by crystal mixing alone and argue for the involvement of at least two chemically distinct melts in the formation of the studied UG2 section.

Diversity of lithium mica compositions in mineralized granite–greisen system: Cínovec Li-Sn-W deposit, Erzgebirge

The Li-Sn-W deposit Cínovec/Zinnwald in the eastern Erzgebirge (Czech Republic and Germany) represents one of the worldwide best known examples of complex rare-metal plutons with pervasive greisenization. Mica from altogether 38 samples representing all granite and greisen varieties from the present surface to the depth of 1596 m was analysed using electron microprobe (EMPA) and laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) for major (including F, Rb) and trace (Li, Sc, Ga, Ge, Nb, In, Sn, Cs, Ta, Tl, W) elements, respectively. All primary micas at Cínovec are trioctahedral Li-Fe micas close to the annite–zinnwaldite–trilithionite series. Biotite from granites in the deeper part of the pluton (depth of 735–1596 m) contains 33.9–39.6 wt% SiO2, 19.6–23.8 wt% FeO, 0.5–0.7 wt% Rb2O, 0.9–1.8 wt% Li2O, 3.4–4.8 wt% F, 381–937 ppm Nb, 34–134 ppm Ta, 20–46 ppm W, and 93–617 ppm Sn. Zinnwaldite from granites in the upper part of the pluton (depth of 0–735 m) contains 41.2–48.5 wt% SiO2, 8.9–15.2 wt% FeO, 0.9–1.9 wt% MnO, 2.0–4.4 wt% Li2O, 0.8–1.9 wt% Rb2O, 7.0–8.6 wt% F, 43–464 ppm Nb, 101–213 ppm Sn, 6–80 ppm Ta, and 28–52 ppm W. Zinnwaldite from bodies of pervasive greisen and quartz-zinnwaldite veins is, compared to zinnwaldite from granites, relatively slightly enriched in Si, Mn and Ga, and depleted in Fe, F, Rb, Sn, W and Nb; Li and Ta contents are similar. Contents of Li, Rb and F, and the Fe/Mn and Nb/Ta values in mica closely positively correlate with those in the bulk rock, illustrating an upwards fractionation of parental melt. In contrast, the contents of high-field-strength elements in mica do not correspond to their contents in the bulk rock (melt): they were controlled by the order of crystallization of mica vs. accessory oxide minerals. Therefore, biotite generally contains distinctly higher Sn, Nb, Ta, and W than zinnwaldite. Dioctahedral micas of the muscovite–phengite series were found only as a late product of alteration of primary trioctahedral mica. Replacement of greisen-stage zinnwaldite by muscovite is chemically expressed in a strong depletion in Fe, F, and Li, and an enrichment in Sn. The share of trioctahedral mica in the bulk-rock budget of Sn decreases from 40–70% in biotite granite to less than 5% in greisen; in the case of Nb and Ta from 20–50% to less than 10%. The share of mica in the budget of W, mostly in the range of 2–15%, is stable through the whole pluton.

Behavior of Tin and Antimony in Secondary Copper Smelting Process

Different types of metal-bearing wastes, such as WEEE (Waste Electrical and Electronic Equipment), are important urban minerals in modern society, and the efficient recycling and reuse of their metal values is of key interest. Pyrometallurgical copper smelting is one of the most prominent ways of treating WEEE, however, more accurate experimental data is needed regarding the behavior of different elements during each process stage. This article investigates the behavior of tin and antimony, both commonly present as trace elements in electrical and electronic waste, in secondary (i.e., sulfur-free) copper smelting conditions. The experiments were conducted in oxygen partial pressure range of 10−10–10−5 atm, covering the different process steps in copper smelting. The basis of the equilibrium system was metallic copper–iron silicate slag, with the addition of alumina and potassium oxide to account for the presence of these compounds in the actual industrial process. The results showed that the distribution coefficients of both trace metals, LCu/slag = [wt % Me]copper/(wt % Me)slag, increased significantly as a function of decreasing oxygen pressure, and the addition of basic potassium oxide also had an increasing effect on the distribution coefficient. A brief comparison between EPMA and LA-ICP-MS (electron probe microanalysis and laser ablation–inductively coupled plasma–mass spectrometry), the two in situ analytical techniques used, was also presented and discussed.

Linking bonefish (Albula vulpes) populations to nearshore estuarine habitats using an otolith microchemistry approach

Identifying the relative importance of various nursery areas is critical for understanding the ecological roles of diverse juvenile habitats, as well as for the sustainable management of fisheries and coastal resources. Recent field collections suggest that a portion of the bonefish (Albula vulpes) population in South Florida may be using nearshore estuarine habitats as nurseries. Nearshore marine habitats are traditionally considered nursery habitat for bonefish. However, the prevalence of their reliance on lower salinity areas is not known. To address this, we used otolith microchemistry using laser ablation inductively-coupled plasma mass spectrometry to examine variation in Strontium (Sr), a marker for salinity, and determine the connectivity between estuarine and marine habitats across the life of bonefish. Sr profiles from otoliths obtained in locations within South Florida (SFL, N = 40) and Southwest Cuba (SCB, N = 10) were compared using a juvenile-migration index (JMI), and change point models to assess the generality of a shift in salinity and thus habitats across life histories. Adult stages of bonefish otoliths collected in SFL and SCB locations showed Sr concentrations connected to marine, high-salinity environments. The JMI showed that a vast majority of individuals (68.4% and 70% in South Florida and Cuba, respectively) moved from low- to high-salinity environments between juvenile and adult stages. The change point models showed that these shifts to high salinity environments occurred suddenly (in 85% of those showing a low to high salinity change), and early in life (after 2 years in South Florida and after 4 years in Cuba) suggesting an ontogenetic habitat change. This study provided evidence that bonefish use low-salinity estuarine environments as juvenile habitats, perhaps more commonly than marine habitats. The reliance on low-salinity environments suggests the potential vulnerability of bonefish nearshore nursery habitats to disturbances associated with coastal freshwater discharges.

Multi-element analysis of size-segregated fine and ultrafine particulate via Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry

In this study a novel and reliable Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) measurement protocol for the elemental characterization of size-segregated particulate was developed. Special efforts were made to improve and optimize sample pre-treatment steps and LA operating conditions to avoid some critical drawbacks encountered during analysis and to make the particulate samples suitable for an accurate and reproducible LA-ICP-MS analysis, regardless of the mass loading on each filter. For example, a new approach for dust-fixation on the sample-carrier was developed using a glycerol coverage, which allowed to overcome problematic sample losses during the ablation process. Under the optimum conditions, dust samples, blank filters and standards for calibration were analyzed by multiple rastering of defined spot areas. Quantitative analysis was accomplished with dried micro-droplets of aqueous standard solutions. Derived method detection limits varied between 0.001 and 0.1 ng m−3 and allowed even for the smallest particle fraction quantitative measurements. The accuracy of LA-ICP-MS results was verified by comparison with conventional ICP-MS analysis of selected PM samples after sample mineralization. The proposed LA treatment procedure benefits from a simple and fast sample preparation, thus overcoming the laborious pre-treatment steps required for wet chemical digestion. Moreover, the better sensitivity of the LA-ICP-MS approach provided more complete information about the mass concentration and size-distribution of the investigated elements, thus allowing to deeper investigate the composition of the most dangerous PM fractions in terms of health concern.

Constraints on the behavior of trace elements in the actively-forming TAG deposit, Mid-Atlantic Ridge, based on LA-ICP-MS analyses of pyrite

The distribution of trace ore elements in different paragenetic stages of pyrite has been documented for the first time in the sub-seafloor of the actively-forming TAG massive sulfide deposit. Trace element distributions have been determined by in-situ laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) of pyrite formed at different stages of mineralization, and at different temperatures constrained by previously published fluid inclusion analyses. The data reveal a strong dependence on paragenetic stage, with distinct low- and high-temperature enrichments. Porous pyrite (and marcasite) formed at low temperatures (<300 °C) in the outer margins of the deposit is enriched in As, Ag, Tl, Pb, Sb, Mo, W, Zn, Ga, Ge, Cd, In, Te, Au, Mn, V, and U. Coarse-grained pyrite formed at higher temperatures (>350 °C) at the base of the hydrothermal mound and in the stockwork zone is enriched in Co, Se, Bi, Cu, Ni, and Sn. A number of different sub-types of pyrite also have characteristic trace element signatures; e.g., the earliest pyrite formed at the highest temperatures is always enriched in Co and Se compared to later stages. Ablation profiles for Co, Se, and Ni are smooth and indicate that these elements are present mainly in lattice substitutions rather than as inclusions of other sulfides. Profiles for As, Sb, Tl, and Cu can be either irregular or smooth, indicating both lattice substitutions and inclusions. Lead and Ag have mostly smooth profiles, but because Pb cannot substitute directly into the pyrite lattice, it is interpreted to be present as homogeneously distributed micro- or nano-scale particles. The behavior of the different trace elements mainly reflects their aqueous speciation in the hydrothermal fluids at different temperatures, and for some elements like Co and Se, strong partitioning into the pyrite lattice at elevated temperatures. Adsorption onto pyrite surfaces controls the distribution of a number of redox-sensitive elements (i.e., Mo, V, Ni, U), particularly in the upper part of the mound which is infiltrated by cold seawater. Where micro- or nano-scale inclusions of chalcopyrite, sphalerite, galena, or sulfosalts are present, there is still a strong temperature dependence on the inclusion population (e.g., more abundant chalcopyrite in the highest-temperature pyrite), suggesting that the inclusions were co-precipitated with pyrite rather than overgrown. However, at the deposit scale, the trace element distributions are also strongly controlled by remobilization and chemical zone refining, as previously documented in bulk geochemical profiles.The results show that pyrite chemistry is a remarkably good model of the chemistry of the entire hydrothermal system. For many trace elements, the concentrations in pyrite are highly predictive in terms of the conditions of mineral formation over a wide range of temperatures, from the stockwork zone to the cooler outer margins of the deposit. Calculated minimum concentrations of the trace elements in the fluids needed to account for the observed concentrations in pyrite show good agreement with measured vent fluid concentrations, particularly Pb, As, Mo, Ag, and Tl. However, significantly higher concentrations are indicated for Co (and Se) than have been measured in sampled fluids, confirming the strong partitioning of these elements into high-temperature pyrite.

Characteristics of hydrothermal chlorite from the Niujuan Ag-Au-Pb-Zn deposit in the north margin of NCC and implications for exploration tools for ore deposits

The Niujuan Ag-Au-Pb-Zn deposit is located in the northern Hebei Province of North China, which is hosted by Permian coarse-grained granite. The orebodies are controlled by a NE striking fault. Chloritization is the most extensive alteration with increasing alteration intensity from the distal to proximal end of the orebody. Chlorite and biotite from twenty-one altered samples from different depths of four drill holes were analyzed using electron microprobe (EMPA) and laser ablation inductively-coupled plasma mass spectrometry (LA-ICPMS). Empirical geothermometry shows that chlorite formed at 206–340 °C. Through comparing with compositions of unaltered biotite, two biotite converted to one chlorite (2Bt → 1Chl) is the main chloritization mechanism in weakly and moderately altered granites during the hydrothermal alteration in the Niujuan deposit. During the alteration, hydrothermal fluid mainly brought in Fe, Sr, Th, Pb and CO2 and took out Mg, Ti, Si, F, K, Li, Zn, Sc, Ga, Co from the biotite, which was accompanied by the formation of quartz, rutile, calcite and fluorite during the chloritization. Chlorite in quartz-chlorite veins was precipitated directly from the hydrothermal fluids. Veined chlorite in intensely altered granites formed by the dissolution-transport-precipitation mechanism. Under the high fluid/rock conditions, veined chlorite has nearly the same compositions as chlorite in quartz-chlorite veins. According to the compositions of chlorite from intensely altered granites and quartz-chlorite veins, we infer that the hydrothermal fluid had low HFSEs and transition elements, such as Ti, Ga, Sc and V, and low fO2. From weak to intense chloritization granites, FeO, Sr, Th and Pb contents of chlorite increase, while MgO, TiO2, Li, Zn, Sc, Ga, V, Co and Nb contents decrease. The composition variations of chlorite are controlled by the composition of biotite, the compositions of fluids and the intensity of fluid-rock interaction during alteration. This indicates that the chemical variations of chlorite could be as a tool for mineral exploration in the moderate-low temperature Ag-Au-Pb-Zn deposit. Comparison with chlorite of different genesis shows that compositions of chlorite mainly differ in Mg, Fe and AlIV, which are mainly controlled by the composition of host rocks and the formation temperature.

Statistical approaches to the discrimination of mantle- and crust-derived low-Cr garnets using major and trace element data

Diamond exploration focuses on geochemical analysis of indicator minerals that are more abundant than diamond itself. Among such indicators, low-Cr (Cr2O3 < 1 wt%) garnets from mantle eclogites are problematic since they overlap compositionally with many lower-crust-derived garnets also transported by kimberlite. Misclassification of these garnets may create “false positive” mantle signatures and possible misdirection of exploration efforts. Statistical solutions using major elements in low-Cr garnet (Hardman et al. in J Geochem Explor 186:24–35, 2018) provide improved error rates for the discrimination of low-Cr crustal and mantle garnets recovered from kimberlite. In this study we analysed a large suite of garnets (n = 571) from both crustal and mantle settings, already characterised for major elements, for a wide range of trace elements by laser ablation inductively-coupled plasma mass spectrometry and use these new data along with literature data (n = 169) to evaluate the effectiveness of adding trace elements to garnet-based diamond exploration programs. A new garnet classification scheme, initially using a major-element based filter, uses garnet Sr contents and Eu anomalies to help identify low-Cr garnets that are misclassified using major element methods. Combined with existing methods, our new trace element classifiers offer improvement in classification error rates for low-Cr, crustal and mantle garnets to as low as 4.7% for calibration data.

Rapid determination of initial 87Sr/86Sr and estimation of the Rb-Sr age of plutonic rocks by LA-ICPMS of variably altered feldspars: An example from the 1.14 Ga Great Abitibi Dyke, Ontario, Canada

Sr isotope analysis of plutonic rocks is an important method for deriving the provenance and age of ancient magmatic episodes, and the petrogenetic processes operating during intrusive activity. We determined the 87Sr/86Sr isotopic compositions of fresh and variably altered feldspars from the 1.14 Ga gabbroic Great Abitibi Dyke, Ontario, Canada, through the use of Laser Ablation Inductively-Coupled Plasma Mass Spectrometry (LA-ICPMS). The data show an alteration trend between fresh, low-Rb plagioclase with 87Sr/86Sr ratios of 0.7045 and high-Rb alkali feldspar with 87Sr/86Sr ratios of 0.7059, which may be used to constrain the 87Sr/86Sr ratio of the mantle source. This trend is incompatible with simple mixing and instead has age significance. As post-intrusive alteration through hydrothermal circulation starts immediately following emplacement, LA-ICPMS analysis allows rapid estimation of initial 87Sr/86Sr ratios and intrusive age, suitable for sample screening and selection for more precise dating. For the Great Abitibi Dyke, the Rb-Sr age estimate of emplacement of 1.10 ± 0.23 Ga (2σ) is concordant with the precise U-Pb emplacement age of the dyke (1140.6 ± 2.0 Ma). The most altered high-Rb alkali feldspars return younger ages, suggesting that post-intrusive alteration lasted several hundred million years. This study highlights the need for microanalysis to differentiate between alteration and magmatic processes on basis of Sr isotopic signatures, and outlines a rapid method to determine initial 87Sr/86Sr ratios and to estimate Rb-Sr ages of plutonic rocks in terranes with long histories of multiple intrusive magmatic episodes.

Columbite-Group Minerals from New York Pegmatites: Insights from Isotopic and Geochemical Analyses

Columbite crystals from niobium-yttrium-fluorine (NYF) pegmatites lacking zircon or containing metamict cyrtolite were analyzed for major and minor elements (Electron Microprobe (EMP)), trace elements (Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)), and U-Pb geochronology (Laser AblationMulti-Collector-Inductively Coupled Plasma-Mass Spectrometry (LA-MC-ICP-MS)). All four pegmatite localities sampled are hosted by the Proterozoic Fordham gneiss and/or Paleozoic Bedford gneiss (Columbite-(Fe); Kinkel and Baylis localities) and the Manhattan Schist of Lower Paleozoic age (Columbite-(Mn); Fort George and Harlem River Drive localities) and yield Neoacadian ages. The weighted average U-Pb ages are 372.2 ± 8.2 Ma (Baylis Quarry), 371.3 ± 7.3 and 383.4 ± 8.9 Ma (Kinkel Quarry); 383 ± 15 Ma (185th St. and Harlem River Drive); and 372 ± 10 Ma (Fort George). A partial metamict zircon (“cyrtolite”) from the Kinkel Quarry yielded a weighted average U-Pb age of 376.9 ± 4.3 Ma. The Neoacadian ages obtained agree with those determined by thermal ionization mass spectrometry (TIMS) for zircon from Lithium-Cesium-Tantalum (LCT) pegmatites from Connecticut and Maine. No pegmatites temporally associated with the Taconic orogeny were found. The size, lack of common Pb, uniform U concentrations across crystal cross-sections, sufficient but moderate uranium concentrations, lack of metamictization, and consistency in U-Pb isotopic ratios for columbite samples BCB-COL, NYSM #25232, and NYSM #525.8 suggests they show promise as potential standards for oxide mineral LA-MC-ICP-MS geochronological analyses, however, additional characterization using ID-TIMS would be necessary to develop as such.

Syn-tectonic sulphide remobilization and trace element redistribution at the Falun pyritic Zn-Pb-Cu-(Au-Ag) sulphide deposit, Bergslagen, Sweden

Mineralization types at the Palaeoproterozoic Falun base metal sulphide deposit are predominantly pyritic Zn-Pb-Cu-rich massive sulphide mineralization, disseminated to semi-massive Cu-Au mineralization, auriferous quartz veins, and mineralized shear zones of talc-chlorite-dominated schist. The massive and disseminated to semi-massive sulphide mineralization types were subject to polyphase ductile deformation (D1 and D2) and metamorphism under low-P, lower-amphibolite facies conditions, which led to the development of ore textures and paragenetic relationships indicating both mechanical and chemical remobilization of sulphides. In the massive sulphide mineralization, rare inclusion-rich pyrite occurs as relic cores inside inclusion-poor metamorphosed pyrite. Imaging and spot analysis using multielement laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) reveal that inclusion-poor pyrite was depleted in trace elements, which were originally present as non-stoichiometric lattice substitutions or in mineral inclusions. The inclusion-rich pyrite was shielded from depletion and, at least partly, retained its initially higher trace element concentrations, including Au.Gold is also associated with chalcopyrite in the disseminated to semi-massive Cu-Au mineralization and in the system of auriferous quartz veins hosted therein, the latter being also affected by the D2 ductile strain. It is inferred that emplacement of the vein system took place after the peak of metamorphism, which occurred between D1 and D2, but prior to and possibly even shortly after completion of the D2 deformational event. Similarities in trace element signatures in chalcopyrite are compatible with the interpretation that the quartz veins formed by local chemical remobilization of components from the Cu-Au mineralization. Transport of liberated Au from pyrite during grain growth in the massive sulphide mineralization may have upgraded the Au endowment in the quartz veins, leading to the additional formation of native gold in the veins. A strong correspondence between elements liberated from pyrite (e.g. Pb, Bi, Se and Au) and those forming discrete and characteristic mineral phases in the quartz veins (Pb-Bi sulphosalts, native gold) supports this hypothesis.Trace element signatures for the main sulphide minerals pyrite, chalcopyrite, sphalerite and galena are similar to previously published data from other metamorphosed massive sulphide deposits. The association of the Falun mineralization with elevated Bi is reflected by its occurrence in sulphide minerals (e.g. galena) and in abundant mineral inclusions of Pb-Bi sulphosalts (e.g. weibullite), especially in the disseminated to semi-massive Cu-Au mineralization. Elevated Sn concentrations in the lattice and/or as cassiterite inclusions in chalcopyrite, sphalerite and galena are compatible with a hot, acidic and reducing fluid during formation of the syn-volcanic, base metal sulphide mineralization and associated host-rock alteration.