pXRF Data Research Articles

Tropical Soil Toposequence Characterization via pXRF Spectrometry

Variability of elemental composition in a toposequence of quartzite‐derived soils in a tropical environment was evaluated via portable x‐ray fluorescence (pXRF) spectrometry. The toposequence featured different degrees of weathering and variable soil formation processes. Specifically, this study aimed to: (i) use elemental composition obtained through pXRF as a tool to investigate the degrees of weathering–leaching and pedogenic processes; and (ii) correlate elemental data with physicochemical properties of soils. Four soil profiles (Lithic Ustorthent, Typic Ustorthent, Typic Dystrudept, and Xanthic Hapludox) were described and sampled. Laboratory analysis for soil physicochemical characterization and pXRF were performed. Soils featured high contents of SiO2 due to the predominance of quartz in the rock. However, pXRF analysis revealed that the soils showed a decrease in such content with depth. Potassium contents tended to be greater in the C horizons since they are less weathered and retained greater amounts of K‐bearing minerals, such as muscovite. Al, Fe, Ca, Ti, Cu, and Sr increased their contents with increasing clay content in soils, while Zr generally remained stable. Ba was leached out of soils during weathering. Both CaO and Sr were positively correlated with exchangeable contents of Ca2+ and Mg2+, base saturation, pH, and cation exchange capacity, while inversely correlated to Al3+ saturation. Fe, Al, Ti, Ca, K, Cu, Rb, and Zr accumulated in soil in comparison with the parent material. Variability of elemental contents in soils with differential degrees of weathering–leaching can be easily accessed with pXRF and such data correlate well with several soil physicochemical properties.Core Ideas Toposequence of quartzite‐derived soils variability assessed by pXRF. Soils presented varying weathering degrees, from Entisols to Oxisols. pXRF elemental data correlated well with soil physical and chemical properties. Soil mineralogy and pXRF data elucidated soils variability with weathering. Al, Fe, Ca, Ti, Cu, and Sr increased with increasing clay content.

Assessing copper fertility of intrusive rocks using field portable X-ray fluorescence (pXRF) data

Based on a global compilation of whole-rock geochemical data, Sr/Y and Sr/MnO are identified as effective discriminators between ore-forming and unprospective intrusions in the porphyry Cu setting. Intrusive rocks are classified into three fertility groups – prospective, unprospective and mixed-signal – designed to assist explorers as a discrimination tool, narrowing the exploration search space in porphyry Cu districts. Portable X-ray fluorescence (pXRF) data of Sr, Y and MnO were collected on pulp powders and rock slabs from six porphyry Cu (±Mo ± Au) districts. Pre- and post-mineralization intrusions from porphyry Cu districts have lower Sr/Y and Sr/MnO values than syn-mineralization intrusions from the same districts, although absolute values are variable between districts. pXRF data were compared to conventional whole-rock data to determine if pXRF data were appropriate substitutes for conventional whole-rock methods of evaluating the ore-forming potential of intrusive rocks. pXRF data collected on pulp material were found to be more accurate (within 16% of conventional methods) and more precise (<5% relative standard deviation (RSD)) than those collected on intact rock slabs (within 37% of conventional methods and <24% RSD). These differences are attributed to the grain size and mineral homogeneity of samples. Despite the low precision of pXRF analyses on individual rock slabs (mean RSD of 24% Sr/Y and 32% Sr/MnO), the mean values for each sample plot in the expected fertility field on the Sr/Y and Sr/MnO diagram. Our results demonstrate that in situ pXRF data collection provides an effective discriminator of Cu fertility, and represents a powerful field exploration tool. Supplementary material: Tabulated pXRF data for all samples including standards are available at https://doi.org/10.6084/m9.figshare.c.4447769

Soil horizon delineation using vis-NIR and pXRF data

In this study, we evaluate the use of visible-near infrared (vis-NIR) and portable X-ray fluorescence (pXRF) for delineating soil horizons and how these are affected by soil moisture in a Mollisol (A, Ab, 2E, and 2Bt) profile of south-central Wisconsin. The soil profile was scanned in the field (moist) and soil samples were taken that were scanned in the laboratory (dry) using a vis-NIR spectrometer and a pXRF spectrometer. The CIE L*a*b* color was extracted from the vis-NIR spectra, and the elemental ratios and weathering indices were calculated from the pXRF data. The CIE L*a*b* color, elemental concentrations, elemental ratios, and weathering indices of the vertical transect were interpolated into 1-cm interval up to 100-cm soil depth for moist and dry measurements which were further used in the clustering analysis for identifying soil horizons. It was found that soil moisture decreased L*, a*, and b* color coordinates and the elemental concentrations. Soil moisture had little effect on the vertical distribution of the CIE L*a*b* color and pXRF measurements. Moisture effects can be partly reduced by taking elemental ratios and calculating weathering indices, or corrected by a linear function. The color variables (a* and b*), Ca, and Calcium/Titanium ratio (CTR) distinguished A horizons (Ap, A2, and Ab), whereas the Al, Fe, Ruxton index (R), and Sesquioxide ratio (Saf) distinguished 2E, 2Bt1, and 2Bt2 horizons. The CIE L*a*b* color and pXRF data were excellent variables for delineating soil horizons, and the measurements on moist soil samples performed better than those measured on dry soil samples.

Statistical artifacts: Critical approaches to the analysis of obsidian artifacts by portable X-ray fluorescence

In the past decade, chemical assay by portable X-ray fluorescence (pXRF) has become a common method of determining the geological origin of obsidian artifacts. We present source assignments made for 355 artifacts from the Late Postclassic site of Guadalupe, Honduras. Statistical studies of concentration data for six individual elements imply that obsidian from at least three sources (Güinope, La Esperanza, and Ixtepeque), and possibly two more (El Chayal and Otumba), was exploited in ancient times, but yield conflicting and ambiguous results for 5% of the collection. We argue that pXRF studies need to be conducted more critically and demonstrate how different statistical tools can yield contradictory source assignments for a significant portion of an obsidian collection. Visual sourcing supports discriminant function analysis over Mahalanobis distance assignments. Furthermore, element ratios imply that Otumba is not actually present. We are concerned that in obsidian studies, pXRF data are not consistently interpreted in ways that yield reproducible results. We propose an integrated methodology that employs pXRF, statistical analysis, visual sourcing, and—when needed and appropriate—destructive chemical assay to determine the source of “high-stake” artifacts.

Tracing tropical soil parent material analysis via portable X-ray fluorescence (pXRF) spectrometry in Brazilian Cerrado

Parent material (PM) type is crucial for understanding the distribution of soils across the landscape. However, such information is not available at a detailed scale in Brazil. Thus, portable X-ray fluorescence (pXRF) spectrometry can aid in PM characterization by measuring elemental concentrations. This work focused on mapping soil PM (specifically variations of phyllite) using pXRF data and evaluating which soil horizon (A, B, or C) provides optimal PM identification in the Brazilian Cerrado. A total of 120 soil samples were collected from A, B, and C horizons across the study area as well as associated PMs; all were subjected to pXRF analysis. Artificial neural network, support vector machine, and random forest were used to model and predict PMs through pXRF data to the entire area. The nine maps (3 soil horizons data × 3 algorithms) generated for PM prediction were validated through overall accuracy, Kappa coefficient, producer's, and user's accuracy. The most accurate PM maps were obtained by using C horizon information (overall accuracy of 0.87 and Kappa coefficient of 0.79) via support vector machine algorithm. Land use dramatically influenced the results. In sum, pXRF data can be successfully used to predict soil PMs by robust algorithms. Specifically, V, Ni, Sr, and Pb were optimal for predicting PM regardless of land use.

Synthesis of proximal sensing, terrain analysis, and parent material information for available micronutrient prediction in tropical soils

In developing countries, the use of proximal and remotely sensed data is of critical importance as a less expensive means of obtaining soils information. While proximal sensor approaches such as portable X-ray fluorescence (pXRF) spectrometry are becoming increasingly used to predict soil properties worldwide, remotely sensed data has also been used for terrain analysis in recent decades with the aid of powerful interpretive algorithms. The aims of this work were to apply a random forest algorithm to model and predict the available contents of Fe, Cu, Mn, and Zn from pXRF data in addition to terrain attributes (TAs) with 5 and 10 m spatial resolution and parent material information. The data were used separately and together in an area with high variability of parent materials. Soil samples (n = 153) were collected, analyzed by pXRF, and subjected to laboratory analyses to determine the available contents of Fe, Cu, Mn, and Zn. Twelve TAs were generated from digital elevation models (DEM). These data were divided into five datasets (or random forest inputs): pXRF data; TA 5 m data; TA 10 m; pXRF + TA 5 m; and pXRF + TA 10 m. Predictions were performed to assess the importance of such variables. Models were validated with an independent set of samples. Finally, the best models were spatially rendered to cover the entire study area and maps were also validated. The combination of pXRF data and TA covariates in addition to parent material information allowed accurate predictions of available Fe, Mn, Cu, and Zn through the random forest algorithm. Parent material information improved the predictions. Pixel size of 10 m resolution promoted better results than 5 m resolution. Available Fe contents were better predicted using only TA data. For the spatial prediction of available micronutrients, validation of maps resulted in R2 of 0.88, RMSE of 59.97 mg kg−1 and ME of 24.00 mg kg−1 for Fe; 0.85, 29.65 mg kg−1, 9.70 mg kg−1 for Mn, 0.64, 3.11 mg kg−1, 0.71 mg kg−1 for Zn and 0.82, 1.17 mg kg−1, 0.43 mg kg−1 for Cu, respectively. Available micronutrient contents can be accurately predicted using pXRF data in association with terrain and parent material information.

Portable X-ray fluorescence (pXRF) spectrometry applied to the prediction of chemical attributes in Inceptisols under different land uses

ABSTRACT Portable X-ray fluorescence (pXRF) spectrometry has been increasingly adopted for varying studies worldwide. This work aimed at characterizing effects of soil management on the content of chemical elements detected by pXRF in managed and unmanaged areas of Inceptisols, and evaluating the potential of using pXRF data to generate prediction models for soil fertility attributes, evaluating the effect of land uses on such models. Samples were collected in A, B, and C horizons of soils under native forest, native Cerrado, coffee crops with 1 and 5 years of implantation and eucalyptus. Soil fertility attributes were determined through laboratory analyses, whereas, elemental contents were obtained through pXRF analysis. PXRF data were used for modeling (regressions) and validation of soil fertility attributes and necessity of lime (NL) application, with or without distinction between managed and unmanaged areas. Management practices on coffee crops increased the levels of Sr, CaO, P2O5, Cu, and Zn. CaO content was efficient for prediction of exchangeable Ca2+ contents (R2 = 0.91), pH (R2 = 0.88), base saturation (R2 = 0.89) in managed areas. General models presented adequate results to predict exchangeable Ca2+ (R2 = 0.92), pH (R2 = 0.85), and base saturation (R2 = 0.90). Models for unmanaged areas were less effective. PXRF detected modifications in elemental contents caused by management practices and provided reliable predictions of soil fertility attributes.

Maximising the value of Portable XRF data in exploration: An example from Marirongoe, Mozambique

Here we present a portable X-ray fluorescence (pXRF) dataset collected in situ ( n = 1591) and a laboratory dataset ( n = 226) from a soil sampling campaign in Marirongoe, Mozambique, to document the strength of rapid geochemical data collection in the field during mineral exploration. Real-time mapping of the geochemistry of underlying granite by utilising pXRF analysis of soil samples identified variation in granitic composition, thus allowing exploration to rapidly focus on the most prospective areas for Ta-Nb-U-REE mineralization. Principal components analysis and clustering protocols are applied to the centred log-ratio transform of a selection of eight elements (Ca, Fe, K, Rb, Sr, Ti, Mn, and Zr) to identify rocks of the same geochemical affinity a posteriori. Maps of these clusters reveal a map pattern that provides an interpretation of the underlying geology. One of the limitations of pXRF is false elemental concentrations being detected due to spectral overlaps between elements. We provide a possible solution to this problem through statistical data analysis using a probabilistic modelling approach. We propose a binary approach whereby the pXRF data for these elements, such as Sn, can be considered in the context of presence (detected; >150 ppm) or absence (not detected; <150 ppm) as comparison to laboratory data shows that the concentration of Sn is reliably detected at concentrations >150 ppm. A kernel density estimator and Bayes conditional probability can provide an effective method for calculating the probability of a sample having elevated content of elements, such as Sn, which may be variably detected by pXRF (depending on matrix and concentration). Utilising statistical approaches to treat large geochemical datasets, such as those that can be generated by pXRF, as they are collected, can provide timely and significant insights that might otherwise not have been apparent in elemental concentration maps alone.

Multiple linear regression and random forest to predict and map soil properties using data from portable X-ray fluorescence spectrometer (pXRF)

ABSTRACT Determination of soil properties helps in the correct management of soil fertility. The portable X-ray fluorescence spectrometer (pXRF) has been recently adopted to determine total chemical element contents in soils, allowing soil property inferences. However, these studies are still scarce in Brazil and other countries. The objectives of this work were to predict soil properties using pXRF data, comparing stepwise multiple linear regression (SMLR) and random forest (RF) methods, as well as mapping and validating soil properties. 120 soil samples were collected at three depths and submitted to laboratory analyses. pXRF was used in the samples and total element contents were determined. From pXRF data, SMLR and RF were used to predict soil laboratory results, reflecting soil properties, and the models were validated. The best method was used to spatialize soil properties. Using SMLR, models had high values of R² (≥0.8), however the highest accuracy was obtained in RF modeling. Exchangeable Ca, Al, Mg, potential and effective cation exchange capacity, soil organic matter, pH, and base saturation had adequate adjustment and accurate predictions with RF. Eight out of the 10 soil properties predicted by RF using pXRF data had CaO as the most important variable helping predictions, followed by P2O5, Zn and Cr. Maps generated using RF from pXRF data had high accuracy for six soil properties, reaching R2 up to 0.83. pXRF in association with RF can be used to predict soil properties with high accuracy at low cost and time, besides providing variables aiding digital soil mapping.

INTERREGIONAL OBSIDIAN EXCHANGE DURING THE LATE INITIAL PERIOD AND EARLY HORIZON: NEW PERSPECTIVES FROM CAMPANAYUQ RUMI, PERU

Campanayuq Rumi is a large civic-ceremonial center located in the south-central highlands of Peru. Founded in the late Initial Period (1100–800 BC), Campanayuq Rumi became an important center within the Chavín Interaction Sphere in the Early Horizon (ca. 800–400 BC). In particular, Campanayuq Rumi is significant because of its geographical proximity to Quispisisa, the most important and widely circulated obsidian source during the Early Horizon. Portable X-ray florescence (pXRF) was used to geochemically source a sample of 370 obsidian artifacts from Campanayuq Rumi. Though obsidian from Quispisisa dominates the assemblage throughout the site's history, diachronic analysis indicates that the diversity of obsidian sources increases markedly in the Campanayuq II Phase (700–450 BC). The pXRF data lead us to conclude that Campanayuq Rumi was the locus of obsidian distribution to other locations in highland and coastal Peru within the Chavín Interaction Sphere, and functioned as a regional center of worship and interaction.

Geochemical fingerprinting as a tool for repatriating poached dinosaur fossils in Mongolia: A case study for the Nemegt Locality, Gobi Desert

Over the past two decades, illegal poaching of vertebrate fossils from the well-known Cretaceous exposures in Mongolia's Gobi Desert has reached epidemic proportions. Following recent efforts led by the Mongolian government to stem the flow of illegal fossils on the black-market, numerous important specimens have now been seized from private collectors. A tandem objective has been to identify and document poached quarries in the field, which is now allowing scientists to evaluate which areas and stratigraphic intervals are more intensively targeted and impoverished by poachers. Although illegal specimens are now being returned and becoming available for research, the question of provenance still remains of both scientific and political concern. To address this issue, we investigated the geochemistry of the fossil-rich Baruungoyot and Nemegt formations in the Nemegt Basin, including both sediments and associated fossils, using portable X-ray fluorescence (pXRF). Field data were collected using a stratigraphic criterion and are representative of several localities across the Nemegt Basin, although the most complete datasets come from the Nemegt and nearby Khulsan localities. Secondarily, pXRF data were acquired from specimens housed in Ulaanbaatar, including type, recently described, and poached specimens. The final dataset includes approximately 700 pXRF readings. We used a combination of multivariate analysis and data mining techniques to match known with unknown sample provenances, and to determine the most informative elements from the geochemical array available for doing so. Results indicate that the chemical compositions of the Baruungoyot and Nemegt formations largely overlap with calcium being the most informative element for determining provenance from either bones or sediments. However, data arranged by geographic and stratigraphic occurrence (thus reflecting different facies and palaeoecological settings) resulted in more discriminant clusters. The newly developed methodology represents the first systematic attempts to provide an innovative and rapidly-implementable tool to support legal and scientific assumptions.

Using portable XRF to infer adularia halos within the Waihi Au-Ag system, New Zealand

Waihi Au-Ag mineralization is vein hosted within a relatively homogeneous andesite body. Geochemical exploration targets adularia and pathfinder (As, Sb, Hg etc.) anomalies. Adularia is formed as an alteration product of feldspars during hydrothermal alteration and occurs in anomalous concentrations near Au-Ag mineralization. This paper aims to test the potential of portable X-ray fluorescence (pXRF) to infer and map adularia and As anomalies. The pXRF was first tested on standards (CRM and ILD), it yielded accurate and precise data for most of the elements of interest (r 2 > 0.9 and APD < 10%). The second stage applied the pXRF directly on core, most elements were negatively affected, but still to a usable degree of accuracy. As was particularly effected due to its heterogeneous distribution (APD 46%). Lastly, we applied the pXRF to a suite of 300 Favona samples, their K/Al value were used as a proxy for adularia presence. XRD analysis carried out on 60 samples was used to validate adularias presence or absence. When combined with pXRF data we found a K/Al value above 0.4 generally indicated a sample contained adularia. Therefore, with further work, the pXRF could be independently used to infer adularia alteration in the Waihi setting.

Geochemical Methods for Sourcing Lava Paving Stones from the Roman Roads of Central Italy

This paper documents the results of in situ analysis of 306 lava paving stones and 74 possible source rocks using pXRF. Data were collected from sites both in the city of Rome—on major roads beyond the city (including the Viae Flaminia, Cassia, Clodia, Praenestina and Appia)—and in the city of Ostia. Comparison of the pXRF data with lava compositional data from the geological literature allows broad identification of possible sources. The results point to quite distinctive patterns of exploitation for the city of Rome and Ostia, utilizing the Alban Hills lava flows, and the roads of the middle Tiber Valley, drawing on lava flows associated with the Vico and Sabatini volcanoes. The results show the potential of pXRF to produce data to elucidate the exploitation of lava flows for paving the Roman roads.

Reducing risk and increasing confidence of decision making at a lower cost: In-situ pXRF assessment of metal-contaminated sites.

This study evaluates the in-situ use of field portable X-ray Fluorescence (pXRF) for metal-contaminated site assessments, and assesses the advantages of increased sampling to reduce risk, and increase confidence of decision making at a lower cost. Five metal-contaminated sites were assessed using both in-situ pXRF and ex-situ inductively coupled plasma mass spectrometry (ICP–MS) analyses at various sampling resolutions. Twenty second in-situ pXRF measurements of Mn, Zn and Pb were corrected using a subset of parallel ICP–MS measurements taken at each site. Field and analytical duplicates revealed sampling as the major contributor (>95% variation) to measurement uncertainties. This study shows that increased sampling led to several benefits including more representative site characterisation, higher soil-metal mapping resolution, reduced uncertainty around the site mean, and reduced sampling uncertainty. Real time pXRF data enabled efficient, on-site decision making for further judgemental sampling, without the need to return to the site. Additionally, in-situ pXRF was more cost effective than the current approach of ex-situ sampling and ICP–MS analysis, even with higher sampling at each site. Lastly, a probabilistic site assessment approach was applied to demonstrate the advantages of integrating estimated measurement uncertainties into site reporting.

Comparison between inductively coupled plasma and X-ray fluorescence performance for Pb analysis in environmental soil samples

Comparison of two conventional analytical techniques such as X-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP-MS) for measuring Pb concentrations in soil samples was achieved using field and laboratory work. Seventy-three samples were collected from urban areas surrounding the large lead smelter at South Australia, as an indicator of the environment impact of smelter activity. Soil Pb concentrations were determined using hand-held XRF analyser under laboratory conditions. ICP-MS analysis on digested soils (using a microwave-assisted nitric acid digestion-extraction) was applied to validate p-XRF data. The analysis showed that Pb concentrations determined by XRF correlated with high linearity with Pb concentrations determined by ICP-MS measurements (R2 = 0.89). Statistical test (t test) was applied to the data of both methods applied without any significant difference between the two techniques. These results indicated that ICP-MS corroborated XRF for Pb soil measurements and suggests that XRF was a reliable and quick alternative to traditional analytical methods in studies of environmental health risk assessment, allowing for much larger sampling regimes in relatively shorter times and could be applied in the field.

GEOCHEMICAL ANALYSIS OF MICA SOURCE SPECIMENS AND ARTIFACTS FROM THE ABBOTT FARM NATIONAL HISTORIC LANDMARK (28ME1)

The Abbott Farm National Historic Landmark is one of the more significant Woodland-period sites in the Northeast. Numerous Hopewellian cultural traits (copper artifacts, cremated burials, exotic cherts, and mica) have been identified at the site. Numerous potential geological sources for the mica artifacts exist in the Mid-Atlantic region. We explore two analytical methods to evaluate the most likely geological sources of the mica artifacts. Source and artifact specimens were analyzed using pXRF as well as neutron activation. Our pXRF data are suggestive, but show high analytical uncertainty. We make several recommendations relevant to future attempts that would use this kind of instrument to study sheet mica. Our neutron activation results are promising and suggest that geochemical sourcing of mica has much potential. Results of both assays suggest that most of the artifact specimens recovered from Abbott Farm share a similar chemistry, and this composition is very similar to mica from southeastern Pennsylvania. A cut-and-drilled pendant exhibits a chemical makeup distinctly different from all other artifacts and source specimens evaluated here. Although our results are preliminary, the application of modern analytical methods to extant archaeological collections has the potential to provide significant new information.

Ceramic production and provenance in the Yiluo Basin (Henan, China): Geoarchaeological interpretations of utilitarian craft production in the Erlitou state

Petrographic and portable X-ray fluorescence (pXRF) analysis performed on late Neolithic/early Bronze Age utilitarian ceramic assemblages from three high-level centers in the Yiluo River valley (Henan, China) – Erlitou, Huizui, and Shaochai – have identified discriminating features which serve as a basis for inferring community-level production loci on an intra-basinal scale. Principal among these are 1) a volcanic and sulfide-silica “Luo River” inclusion signature seen at Erlitou and Shaochai, 2) a metamorphic (amphibole gneiss and schist) signature seen almost exclusively in sherds from Huizui, and 3) a predominantly fine-grained siliciclastic and carbonate sedimentary lithic “Songshan Mountain” signature observed among sherds at both Huizui and Shaochai. The pXRF data help to further refine these petrographic provenance assignments. Identification of overwhelmingly “local” production signatures suggests that wares were not widely exchanged between the Erlitou urban core and the surrounding centers with much frequency during the Erlitou period (ca. 1900–1500BCE). Domestic wares may have been produced for systems of local exchange among regional centers and surrounding rural potting communities utilizing ceramic raw materials found within shared geological resource zones. The persistence of local production signatures throughout the Yangshao (ca. 5000–3000BCE), Longshan (ca. 3000–2000BCE), and Erlitou periods at Huizui suggests that systems of localized ceramic production and exchange within the Yiluo basin were not significantly altered in response to processes of urbanism and regional economic integration characterizing formation of the Erlitou state.

Petrogeochemical assessment of rock units and identification of alteration/mineralization indicators using portable X-ray fluorescence measurements: Applications to the Fire Tower Zone (W-Mo-Bi) and the North Zone (Sn-Zn-In), Mount Pleasant deposit, New Brunswick, Canada

The Mount Pleasant polymetallic deposits are located along the southwestern margin of the Late Devonian Mount Pleasant Caldera Complex in southwestern New Brunswick, Canada. The Fire Tower Zone (W-Mo-Bi) and the North Zone (Sn-Zn-In) comprise the main mineralized zones within the Mount Pleasant deposit. The rock units examined at surface in both zones are highly altered and are surface weathered to some extent. In order to classify these rock units with confidence, the Olympus X-5000 portable X-ray Fluorescence (pXRF) spectrometer was used in this study to rapidly obtain the geochemical composition of these rocks, identify lithologic discriminants, and find alteration/mineralization indicators in these areas. The immobile elements Ti, Zr, Nb, Y, and Th were selected to discriminate among various rock types. The Little Mount Pleasant Formation has the highest Ti and Zr and the Mount Pleasant Granitic Suite (MPGS, GI and GII) contains the highest Y, Nb, and Th. The McDougall Brook Granitic Suite (MBGS) has an intermediate composition between them. The element ratios of Zr/Ti, Nb/Ti, Y/Ti, and Th/Ti effectively discriminate these rock units and increase from the Little Mount Pleasant Formation, to the MBGS, and then to the MPGS.Greisen and propylitic alteration are reflected by strong depletion of K and Rb in some samples. The Fe and Mn typically are leached out of the mineralization system during the greisen alteration. Principal component analysis (PCA) was performed on the pXRF datasets. The first principal component (PC1) of the pXRF data from both the Fire Tower Zone and the North Zone mainly extracts information on Ti, Zr, Ce, Cr, V, Nb, Y, U, and Th, and thus represents different rock units. The PC2 is characterized by high-positive loadings of K, Rb, Fe, and Mn and negative loading of As and Mo. It is interpreted as the W-Mo mineralization indicator showing by the enrichment in Mo and depletion of K, Rb, Fe, and Mn associated with quartz+topaz+sericite+fluorite alteration. The PC3 consists of positive loadings of Sn, Zn, Cu, and S and slightly negative loadings of Sr and Ba, and thus represents the Sn-Zn mineralization in this area.

Using handheld pXRF to study medieval stained glass: A methodology using trace elements

ABSTRACTThe surfaces of 30 pieces of glass from panel 3b of the Great East Window of York Minster (1405-1408 CE) were analyzed by handheld portable X-ray fluorescence (pXRF) and small samples from the same pieces were analyzed by electron microprobe (EPMA). Comparison of the two methods reveals significant divergences which are not systematic, particularly for elements lighter than Ti. Rather than a problem with pXRF calibration or correction software, the non-systematic error is attributable to the presence of a thin surface layer of weathered glass. Analysis of the depths of X-ray generation indicate that virtually all X-rays characteristic of Ca and K are generated within the top 50 µm of the glass. However, for heavier elements such as Rb, Sr and Zr, most emitted X-rays are generated below 100 µm. Using pXRF data for the heavier elements, it is possible to replicate the compositional groupings identified by quantitative EPMA. White glass in the window is likely to have originated in England, while colored glasses were probably obtained from the Continent. The alkali contents of the green and yellow glasses appear to have been manipulated to generate their colors. Glass which is medieval in technology but not original to the panel was identified. In particular, zirconium proved a useful indicator of glassmaking regions, and rubidium and strontium were more sensitive to differences between batches, which has interesting implications for future work.

PXRF calibrations for volcanic rocks and the application of in-field analysis to the geosciences

Advances in portable X-ray fluorescence (pXRF) technologies have made such instruments an attractive choice for geologists who wish to collect chemical data in the field. The acceptance of pXRF data for research purposes such as, for example, petrogenetic studies by the geologic community has been hampered by a perception of poor quality. Here, we show that current-generation pXRF instruments can yield high-quality data when deployed either in the laboratory, or as a base-camp field instrument. We have developed four calibrations for major, minor and trace elements in geological materials using minimal sample preparation: one for the broad range of geologic compositions (0–100% SiO2) using rock powders, and three with an emphasis on volcanic rock samples: rock billets ranging from primitive basalt to rhyolite, basalt rock powder, and rhyolitic pumice powder. The calibrations use influence coefficients to correct for absorbance and secondary enhancement of one element by X-rays of other elements present in the sample. Nugget effects can have a significant influence over the determination of the concentration of elements such as Zr if proper care in sample homogenization is not taken. We evaluate data quality for each element in each calibration, and find that for several elements (Ti, Mn, Fe, Ca, K, P, Cr, Ni, Zn, Rb, Sr, Y, Zr, Nb), precision and accuracy approach those obtainable from full-size wavelength-dispersive XRF analysis. Maximization of data quality is achieved by matching of calibration material types and unknowns.