Geochemical Datasets Research Articles

Crustal control on the petrogenesis of adakite-like rocks

Adakite-like rocks have attracted extensive interest as they record magmatic processes and mantle-crustal material recycling, and because they are associated with major porphyry Cu deposits. However, their petrogenesis is still under debate. In this study, we compiled ca. 7000 sets of whole-rock geochemical and Nd isotopic data of Phanerozoic adakite-like rocks worldwide from published literature, with the aim to characterize geochemically adakite-like rocks from subduction, collision, and post-collision settings. Statistical analysis highlights the different lanthanides + Y patterns from various types of juvenile and mature crust. Modelling of the statistically-processed data suggest that pure fractionation of amphibole and/or garnet cannot account for the lanthanides + Y patterns of adakite-like rocks, whereas partial melting of mafic protoliths is a possible mechanism. This study supports a adakite-like magma generation model by partial melting of the eclogitic lower crust. The melt was then mixed with depleted mantle-derived basaltic melt, and subsequently fractionated. Compared with the adakite-like magma formation from the juvenile crust, that from the mature crust is featured by higher degree of partial melting, greater depths and higher water content. Additionally, secular peaks of La/Yb value (which reflects the depth of magma source) of adakite-like rocks worldwide suggest that the period of magmatic activity in deep-level magma reservoirs could be used as the indicator of either the final stages of the Phanerozoic orogenesis, or craton activation by subduction.

Explosive eruptions at Stromboli volcano (Italy): a comprehensive geochemical view on magma sources and intensity range

A comprehensive understanding of the processes that occur during magmatic storage and pre-eruptive ascent—and of their associated timescales—is critical to identifying potential precursory signals, and to developing robust volcano early-warning systems. Stromboli’s persistent activity comprises continuous degassing and explosive activity that ranges from hourly, low-intensity “normal” activity to occasional, more violent, paroxysmal activity. While the magma source processes that drive normal and paroxysmal activity are reasonably constrained, eruptive activity intermediate in magnitude and intensity (i.e., major explosions) remains elusive in terms of classification, source region, and pre-eruptive timescales. Here, we investigate the 19 July 2020 major explosion that geophysical parameters place at the upper limit of the major explosions field, close to small-scale paroxysms such as the 2003 and 2007 events. The geochemical signatures of matrix glass, olivine, melt inclusions, and embayments—integrated with gas measurements—highlight important differences in eruption source, ascent behaviour, and pre-eruptive timescales of the studied event when compared to paroxysms. Melt inclusion volatile contents identify that magma rise begins from a slightly shallower source (~9.5 km below sea level, b.s.l.) than for paroxysms (11.4 km b.s.l.), with the activation of a shallower ponding zone at 5–6 km b.s.l.. This, in combination with intermediate matrix glass compositions, suggests complex ascent behaviour, characterised by CO2 buffering in the deep ponding region and magma self-mixing in the shallower zone. Fe–Mg-diffusion modelling in olivine indicates a system perturbation starting ~20–25 days before eruption onset, in agreement with the timescale of volcanic gas CO2/SO2 ratio changes observed in the plume, and significantly shorter than that observed prior to paroxysms (~4 months). The geochemical dataset provides insights into the processes controlling the steady-state conditions and the broad spectra in eruption magnitude and intensity at Stromboli and bears important implications for eruption forecasting.

Defining iron-bearing rock sources in compositional data statistical analysis for provenance studies: A case study from South Africa

In iron-bearing rock provenance researches the definition of what is a source vary from an author to another. Issues might occur when the sources are associated with complex weathering profiles. How may the definition of the source influence the results of provenance studies when different types of iron-bearing rocks are encountered within the same weathering profile? In order to deal with this research question, we used a geochemical dataset previously obtained from the study of the ochre geological collection collected around Diepkloof rock shelter, South Africa. We tested the efficiency of Linear Discriminant Analyses (LDA, supervised analysis) and Principal Component Analysis (PCA, non-supervised analysis) in source discrimination and in the attribution of archaeological pieces to the right source. Different assumptions were made: sources were defined by separating or grouping the different lithologies (shale and ferricrete) encountered at the same location. The results show that grouping the different lithologies allows a good attribution of the archaeological pieces to the source it comes from when elements positively correlated with iron are used in the analysis. Separating the different lithologies do not allow a rate of success in archaeological pieces attribution as high as when the lithologies are grouped together. This result might be explained by a highest number of samples that define a source when the different lithologies are grouped together. Further research should be considered in this direction in order to define if this is a general trend.

Garnet Xenoliths in Andesitic Lavas of Lipari: New Geochemical Data to Provide Additional Information on the Metamorphic Basement Under the Aeolian Arc

The purpose of this paper is to discuss and interpret a comprehensive set of geochemical (major and trace elements) data for xenolithic garnets included in high-K andesites from Lipari Island (Aeolian Archipelago, Italy), with the aim to constraint the parent rocks. Since, among all the mineral phases, garnet has a high affinity for the heavy REE (Dy-Lu) and HFSE (Hf, Zr, Ti), we use it as petrogenetic indicator. The investigated xenoliths are mainly composed of cordierite, garnet and Al-silicates and are considered as fragments of the metamorphic Calabria-Peloritani Orogen inferred to be the basement beneath the Aeolian volcanoes. Xenolithic garnet from Lipari andesites and metamorphic garnets from rocks of Southern Calabria and Peloritani Mountains were sampled and analysed. Major elements were determined through ESEM, whereas trace elements were acquired using LA-ICP-MS. Two types of garnets were recognised on the base of major elements, one homogeneous and one zoned, whit an almandine-dominant composition. The comparison between major and trace elements data of xenolithic and metamorphic garnets allowed defining nature of the basement beneath Lipari Island, which is composed of: a) a metamorphic Unit similar to the kinzigitic ones for the unzoned crystals; b) a metamorphic unit similar to the Aspromonte and not outcropping in Sicily and in Calabria for the zoned garnets.

The influence of Cenozoic Eurasia-Arabia convergence on the Southeast Arabian Foreland Basin: new geochronological and geochemical constraints from syn-kinematic carbonate mineralization

The Cenozoic succession of the Jabal Hafeet anticline yields the most complete surface expression of the deformation that affected the Southeast Arabian Foreland Basin (SEAFB). The carbonate rocks of the Eocene Rus Formation comprise the core of the Jabal Hafeet anticline and host a network of fractures and carbonate veins associated with dynamic fracture opening and sealing events. These fracture networks developed during the propagation of compressional stresses from the Makran and Zagros fold-and-thrust belts into their foreland basin system (the SEAFB) and are associated with Arabia-Eurasia convergence. Syn-kinematic calcite veins associated with the Cenozoic folding events in the SEAFB were dated by U–Pb LA-ICP-MS carbonate geochronology and characterized further by Raman fluid-inclusion geochemistry. The U–Pb data show that Cenozoic compression linked to the propagation of the Makran fold-and-thrust belt into the SEAFB took place from c. 20 Ma (early Miocene) to c. 2 Ma (mid Pleistocene). Raman fluid-inclusion data reveal the presence of complex hydrocarbons within the parent carbonate-bearing fluids, reflecting a fluid transport pathway between the upper Cenozoic rocks and deeper hydrocarbon-bearing Mesozoic sequences. Combined isotopic and geochemical datasets show that the deformational history of the SEAFB is likely related to the reactivation of inherited deep-seated structures in the upper Cenozoic stratigraphic sequence due to the far-field stress propagation from the Makran belt into the Arabian peninsula, rather than the propagation of a thin-skinned deformation architecture.

Basin circulation affecting sediment partitioning in a fine-grained carbonate–siliciclastic, subaqueous clinoform: the Upper Jurassic–Lower Cretaceous Vaca Muerta Formation, Neuquén Basin, Argentina

Fine-grained sediments deposited under oxygen-deficient conditions are enriched in organic matter and hold considerable economic interest as unconventional reservoirs. The present analysis integrates sedimentological, ichnological and geochemical datasets to understand depositional processes in the Upper Jurassic–Lower Cretaceous Vaca Muerta Formation (Argentina), the most important economic unconventional play outside North America. For this purpose, cores from eight wells and one outcrop were examined. The succession comprises 13 facies associations corresponding to marginal-marine, basin, drift and slope environments, deposited in a mixed carbonate–siliciclastic, shelf-margin, subaqueous clinoform system. Estuarine circulation during warm and humid climates produced a stable stratification. Sediment delivery was dominated by pelagic processes in the bottomset, and hemipelagic processes and fluid mud flows in the foreset. However, the typical estuarine circulation changed to weakened estuarine or anti-estuarine during cool and arid climates, triggering wind- and thermohaline-driven contour (bottom) currents that reworked and oxygenated the complete clinoform system. The analysis suggests that distal–proximal trends are of lesser importance for the delineation of sedimentary environments in settings with contrasting basin circulation regimes and provides several insights to understand sediment partitioning in fine-grained clinoform systems. Supplementary material : The stratigraphic context of the Vaca Muerta Formation, an example of facies distribution in a well, trace-fossil descriptions, and X-ray diffraction and total organic carbon geochemical data are available at https://doi.org/10.6084/m9.figshare.c.6294914

Fossil Diatoms Reveal Natural and Anthropogenic History of Jackson Lake (Wyoming, USA)

Jackson Lake supplies valuable cultural and provisioning ecosystem services to the Upper Snake River watershed in Wyoming and Idaho (western USA). Construction of Jackson Lake Dam in the early 20th century raised lake level by ∼12 m, generating an important water resource supporting agriculture and ranching, as well as tourism associated with Grand Teton National Park. Outlet engineering drastically altered Jackson Lake’s surface area, morphology, and relationship with the inflowing Snake River, yet the consequences for nutrient dynamics and algae in the lake are unknown. Here, we report the results of a retrospective environmental assessment completed for Jackson Lake using a paleolimnological approach. Paleoecological (diatoms) and geochemical datasets were developed on a well-dated sediment core and compared with available hydroclimate data from the region, to assess patterns of limnological change. The core spans the termination of the Little Ice Age and extends to the present day (∼1654–2019 CE). Diatom assemblages prior to dam installation are characterized by high relative abundances of plankton that thrive under low nutrient availability, most likely resulting from prolonged seasonal ice cover and perhaps a single, short episode of deep convective mixing. Following dam construction, diatom assemblages shifted to planktic species that favor more nutrient-rich waters. Elemental abundances of sedimentary nitrogen and phosphorous support the interpretation that dam installation resulted in a more mesotrophic state in Jackson Lake after ∼1916 CE. The data are consistent with enhanced nutrient loading associated with dam emplacement, which inundated deltaic wetlands and nearshore vegetation, and perhaps increased water residence times. The results of the study highlight the sensitivity of algal composition and productivity to changes in nutrient status that accompany outlet engineering of natural lakes by humans and have implications for water resource management.

Evaluation of Shale Oil Mobility for the Eocene Shahejie Formation in Liutun Sag, Dongpu Depression, Bohai Bay Basin

Previous studies have shown that shale oil mobility depends on the relative content of free oil and adsorbed oil. However, the research on how to establish a shale oil mobility evaluation is relatively insufficient. This study aims to use pyrolysis data before and after extraction to accurately identify the content of free oil and adsorbed oil, analyze the influencing factors of shale oil mobility, characterize the hydrocarbon generation and expulsion process, and evaluate shale oil mobility. We utilized an integrated mineralogical and geochemical dataset from the PS18-1 well in the Liutun Sag, Dongpu Depression, Bohai Bay Basin. The results show that the adsorption capacity of type I organic matter (OM) on shale oil is greater than that of type II OM, the OM abundance is of great significance to shale oil mobility, and that quartz and feldspar can promote shale oil mobility. The Tmax corresponding to the threshold of hydrocarbon expulsion is 438~440 °C, and the oil saturation index (OSI) is about 158 mg/g TOC. There are four small intervals: a (3257 m~3260 m), b (3262 m~3267 m), c (3273 m~3278 m), and d (3281 m~3282 m) meeting the conditions of hydrocarbon expulsion. Large-scale hydrocarbon expulsion occurred in interval a, a small amount of hydrocarbon expulsion in interval b, a large amount of hydrocarbon expulsion in interval c, and almost no hydrocarbon expulsion in interval d. Based on the crossplot of S1 and TOC, combined with other parameters such as OSI, hydrocarbon generation potential (HGP), and free and adsorbed oil, we established an evaluation chart of shale oil mobility and divided it into five categories: A, B, C, D, and E. While categories A and C have good mobility and great resource potential, categories B and D have relatively poor mobility and medium resource potential, and category E has little mobility and is an invalid resource.

Major elements concentration in soils. A case study from Campania Region (Italy)

In this study, 500 bottom soils and 7300 topsoils samples were collected to determine the major elements concentrations and to evaluate the correspondence of soil chemical contents and the local geology and to better identify background values. The <2 mm fraction of each sample was analysed for a total of 52 elements combining ICP-MS and ICP-ES techniques. This study focuses on the concentration and distribution of major elements: Al, Ca, Fe, K, Mg, Mn, Na, P and Ti. A combined methodological approach, which involved compositional data analysis, multifractal data interpolation, as well as enrichment factor analysis, was applied to the geochemical dataset. Results indicate that the compositional approach in the multivariate data analysis allows to better interpret the behaviour of elements in natural environment and in geochemical processes as compared to raw data and to improve the quality of related maps. The study has shown that the soils of the Campania region generally contain higher concentrations of investigated major elements than those assessed for European and Italian agricultural soils. In Campania, both bottom soils and topsoils contain higher concentrations of Al, K, Na, P and Ti in volcanic areas. Limestone and dolostone are responsible for higher Ca and Mg contents, while soils formed on siliciclastic deposits generally contain higher levels of Fe and Mn. P and Na concentrations are higher in volcanic soils, but the contribution of fertilizers, which is evident in some areas, should not be underestimated. Weathering processes play an essential role in the distribution of elements in soils, and this appears very evident mostly in volcanic areas. The observations are consistent with the results of the enrichment factors analysis.

Protracted oxygenation across the Cambrian-Ordovician transition: A key initiator of the Great Ordovician Biodiversification Event?

Fluctuations in marine oxygen concentrations have been invoked as a primary driver for changes in biodiversity throughout Earth history. Expansions in reducing marine conditions are commonly invoked as key causal mechanisms for mass extinctions, while increases in marine oxygenation are becoming an increasingly common causal mechanism invoked for biodiversification events. Here we utilize a multiproxy approach to constrain local and global marine paleoredox conditions throughout the late Cambrian-Early Ordovician from two drill core successions in Baltoscandia. Local paleoredox proxies such as manganese concentrations and iron speciation reveal that both sites in the Baltic paleobasin had persistently anoxic and predominantly euxinic (anoxic and sulfidic) bottom water conditions throughout the study interval. Corresponding trace metal datasets indicate nuanced contraction and expansion of global anoxic and euxinic conditions along continental margins during the late Cambrian-Early Ordovician. Lastly, thallium isotope data from these locally reducing sections suggest a global expansion of oxygenated shelf and deeper marine environments from the late Cambrian into the Early Ordovician. This evidence for increasingly oxic marine environments coincides with increases in burrowing depth and tiering in marine animals, as well as diversification of body fossils throughout this ~8-million-year interval. The collective geochemical datasets provide some of the first direct paleoredox evidence for an increase in marine oxygen concentrations as a key mechanism for the Ordovician radiation of marine life.

Granite Pluton at the Panasqueira Tungsten Deposit, Portugal: Genetic Implications as Revealed from New Geochemical Data

Core samples recovered from exploration boreholes and granite/greisen outcrops at the Panasqueira world-class tungsten deposit in central Portugal were subjected to chemical analyses and petrographic studies. We present a geochemical dataset and the trace element compositions of quartz and micas from a large part of the unexposed Panasqueira granitic pluton. Our data suggest that the hidden granite body is more complicated than previously believed. It consists of a flat cupola of porphyritic granite with only traces of mineralization at Rio and a steep stock of greisenized leucogranite surrounded by a swarm of flat quartz–muscovite veins rich in wolframite between Barroca Grande and Panasqueira. The contents of W (Sn, Nb, Ta) in muscovite markedly drop at a transition from the unmineralized greisen body to quartz veins. The W deposit was formed in three principal stages: (1) intrusion of porphyritic two-mica granite accompanied with local near-contact greisenization and uncommon quartz–wolframite veinlets; (2) intrusion of a more strongly fractionated leucogranite and formation of the cupola and apophyses; (3) circulation of hydrothermal fluids from deeper parts of the granite body into the cupola, greisenization, hydraulic fracturing and opening of flat structures in and outside the cupola and formation of ore veins.

Genome-resolved metagenomics reveals depth-related patterns of microbial community structure and functions in a highly stratified, AMD overlaying mine tailings

Acid mine drainage (AMD) is a worldwide environmental problem, yet bioremediation is hampered by a limited knowledge of the reductive microbial processes in the AMD ecosystem. Here, we generate extensive metagenome and geochemical datasets to investigate how microbial populations and metabolic capacities driving major element cycles are structured in a highly stratified, AMD overlaying tailings environment. The results demonstrated an explicit depth-dependent differentiation of microbial community composition and function profiles between the surface and deeper tailings layers, paralleling the dramatic shifts in major physical and geochemical properties. Specifically, key genes involved in sulfur and iron oxidation were significantly enriched in the surface tailings, whereas those associated with reductive nitrogen, sulfur, and iron processes were enriched in the deeper layers. Genome-resolved metagenomics retrieved 406 intermediate or high-quality genomes spanning 26 phyla, including major new groups (e.g., Patescibacteria and DPANN). Metabolic models involving nitrogen, sulfur, iron, and carbon cycles were proposed based on the functional potentials of the abundant microbial genomes, emphasizing syntrophy and the importance of lesser-known taxa in the degradation of complex carbon compounds. These results have implications for in situ AMD bioremediation.

Hydrated komatiites as a source of water for TTG formation in the Archean

The preserved Archean continental crust is dominantly comprised of tonalite-trondhjemite-granodiorite (TTG) suites associated with less abundant low-grade greenstone belts. The exact processes that form TTGs, as well as the source rock they are derived from, are difficult to constrain from the sparse Archean geological record. However, studies show that the water-present partial melting of metamorphosed basalt at temperatures of 750–950°C is required to produce large volumes of partial melt with TTG compositions. In this contribution, we investigate if hydrated komatiites — a constituent of greenstone belts — played a vital role in TTG genesis. Using petrology, mineral chemistry and phase equilibria modelling of representative komatiite samples, combined with analysis of a global geochemical dataset of komatiites and basaltic komatiites, we show that during metamorphism hydrated komatiites can release at least 6 weight % mineral-bound water. Up to 5 weight % of this water is released by breakdown of chlorite and tremolite at temperatures between 680 and 800°C, regardless of the P–T path (i.e., tectonic scenario) experienced by the komatiitic rocks. As the temperatures of komatiite dehydration are above the water-saturated basalt solidus, the released water can trigger voluminous partial melting of basalt to ultimately create TTG batholiths. This considerable hydration potential of komatiites is due to their high XMg (XMg = molar Mg/[Mg+Fe]), which stabilises water-rich minerals during oceanic alteration on the seafloor, but also extends the stability of Mg-rich chlorite to high temperatures. During prograde metamorphism, the XMg, CaO and Al2O3 content of the reactive rock composition determines the proportion of chlorite vs amphibole, and therefore the volume of water which can be transported to temperatures of >750°C. Despite the low abundance of komatiites in greenstone belts, they potentially played a vital role in crustal formation and the Earth's early water cycle.

Translation of the function of hydrothermal mineralization-related focused fluid flux into a mappable exploration criterion for mineral exploration targeting

Formation of hydrothermal mineralization is related to the late stages of, or immediate following, orogenic compressional regimes that have been superimposed on arc magmatism. For instance, mineralization-related fluid flux mechanisms of porphyry Cu formation deal with how magmatic fluids are transferred from the corresponding source chambers to the environment of stock emplacement related to porphyry systems. In this paper, firstly, we review the imperative physicochemical processes of mineralizing fluid flux mechanisms, e.g., the function of intrusive, metalliferous compounds, and permeable structures, and then assemble them to translate the mechanism of forming focused fluid flux into 2D mappable criteria for mineral exploration targeting. According to the review and the ensuing knowledge and idea, we propose a simplifying approach by focusing on a geological point feature - inferred sites of strongly concentrated ore fluid flux - that represents a critical, if not the most critical, geological element in mineral exploration targeting. We demonstrate that this point feature can be derived as a mappable criterion and that there are stronger spatial and thermal relationships between the location of hydrothermal mineral deposits and this proposed point feature relative to the existing point and line features (e.g., intrusive contacts, fault density, fault intersections, and proximity to faults), which have been widely used in the procedure of prospectivity analysis for mineral exploration targeting. We illustrate the procedures of generating mineral exploration targets, proposed in this paper, using geochemical and geological data sets of porphyry Cu deposits of Iran.

Petrogenesis and tectonic setting of TTG rocks from the Katoro area, Sukumaland Greenstone Belt, NW Tanzania: Evidence from zircon U-Pb geochronology, Lu-Hf isotopes, whole-rock geochemistry, and Sr-Nd isotopes

The northern part of the Tanzania Craton is mainly comprised of several low-grade metamorphic granite-greenstone belts that are exposed on the east and south shores of Lake Victoria. Due to their gold-endowment, these greenstone belts have been the main focus of research and were interpreted to form in various tectonic settings involving back-arc basin, island arc or continental arc, and oceanic plateau. However, the TTG gneiss, as the dominant component of Archean crust, has received far less attention from the scrutiny of modern analytical methods than its counterpart, the mafic volcanics of the greenstone belts. Here, we present a comprehensive geochemical dataset including zircon U-Pb age, zircon Lu-Hf isotope results, as well as bulk-rock geochemical compositions and Sm-Nd isotopic analyses for TTG suites from the Katoro area in northwestern part of Tanzania. Zircon U-Pb dating for three TTG samples yielded 207Pb/206Pb ages of 2688 ± 19 Ma, 2717 ± 19 Ma and 2695 ± 15 Ma, respectively, and the results fall within the peak crustal growth period in northern part of the Tanzania Craton. The Katoro TTGs have relatively high contents of SiO2 (70.77–74.69 %) and Na2O (4.74–5.16 %), high ratios of Sr/Y (59.49–167.25) and (La/Yb)N (17.27–50.72), but low MgO (0.24–0.70 %) and K2O (1.71–3.26 %) contents, low Nb/Ta ratios (8.50–16.60), and most of them belong to the trondhjemitic series rocks. They are characterized by strong enrichment of LILEs and LREEs with slightly positive Eu anomalies (Eu/Eu*=1.05–1.38), but depleted in Nb-Ta and Ti, as well as heavy REEs and Y. They have positive εHf(t) values (average εHf(t) = +1.90 ± 0.50 or + 2.07 ± 0.33) and εNd(t) values (+1.19 to + 2.40) but lower than the contemporaneous depleted mantle, which is inconsistent with a subducting slab signature, and it is proposed that the Katoro TTGs most likely originated from partial melting of rutile-free, garnet- and amphibole-bearing lower mafic crust of an oceanic plateau. The results presented here suggest that the tectonic evolution in this part of Tanzania Craton needs to invoke a scenario in which crustal growth caused by subduction-related modification of an oceanic plateau.

Incorporating the genetic and firefly optimization algorithms into K-means clustering method for detection of porphyry and skarn Cu-related geochemical footprints in Baft district, Kerman, Iran

For the purpose of multi-element geochemical modeling of stream sediment data, we investigate the use of unsupervised clustering analysis (CA). For the various reasons including straightforward implementation, fast computation, and scaling to big dataset, the K-means (KM) algorithm was implemented to cluster the geochemical data to reveal anomalous populations linked to porphyry and skarn Cu deposits in Baft district, NE Iran. However, one of the biggest disadvantages of KM method is the randomly selection of cluster centroids which may increase the systemic uncertainty in unsupervised geochemical modeling and also run time. To address this, genetic (GA) and firefly (FA) metaheuristic optimization algorithms were incorporated into the KM method (namely GKM and FKM models) for determination of cluster centroids, and then, optimal definition of geospatial patterns of anomaly-background classes using clr-transformed values of stream sediment geochemical data. To do so, sample catchment basins (SCBs) of anomalous geochemical dataset were used to spatially map the anomaly populations derived from KM, GKM and FKM methods. We have used the advantages of quantitative evaluation measures namely normalized density index (NDI) and success-rate curves to assess the effectiveness of multi-element geochemical anomaly in determining exploratory targets. The results not only affirms that CA is a useful method to decompose the geochemical anomaly-background populations, but also hybridization of clustering methods via optimization algorithms can efficiently increase the certainty of mineralized zones to be used in further exploration stages.

Applying neural networks-based modelling to the prediction of mineralization: A case-study using the Western Australian Geochemistry (WACHEM) database

Geochemical data collected and stored by government and private sectors are becoming increasingly complex and too large for manual interpretation. The use of automatic methods for identification of potentially spurious data and estimation of missing values in very sparse geochemical datasets can significantly improve our understanding of geological systems. Deep neural networks have recently achieved remarkable success in a wide range of applied problems. These methods do not require manual feature engineering and significantly outperform traditional machine learning algorithms when applied to large datasets. We present a deep learning based method for estimation of unknown sample analytes in geochemical data. This approach is entirely data-driven and, once the network is trained, delivers the results in real time by predicting the distribution of an unknown analyte in a single step. A case study on the Western Australian Geochemistry (WACHEM) database demonstrates the efficiency of the method. Base metals as well as many other metals show good predictive capability (average symmetric mean absolute percentage errors range from 20% to 26.1%). Silver, platinum and especially gold are found to be more difficult to predict. The estimation of rock types from geochemical data allows for validation of existing datasets and prediction of rock types directly from geochemical data when there is no other existing information. The results of this study can benefit mineral explorers by indicating exploration targets and highlighting gaps in existing data.

Structural and geochemical studies of the Palaeozoic granites from Dalhousie region of Himachal Himalaya: Implications on petrogenesis and deformation of strongly peraluminous S‐type granites

The Palaeozoic granites forming the Dalhousie pluton occur as an elongated body intruded into the core of an antiform in Salkhala metasedimentary rocks and are referred to herein as Dalhousie granites (DG). The studied mesoscopic structures, for example, well‐developed and randomly distributed megacrysts of K‐feldspar at the core part of massif, show undeformed porphyritic nature, whereas augen along with the mylonitic foliation and parallelly aligned feldspar megacrysts are dipping towards north‐north‐east (NNE) in the marginal part. The presence of aplite veins is evidence of final stage crystallization, where these rocks rapidly crystallized from siliceous residual fluids/solutions that escaped along fractures in the granites. Moreover, the granites show intrusive as well as thrusted contact with the Chamba metamorphics. The microscopic study from the marginal parts shows the dynamic recrystallization of quartz along with the fractures filled with secondary material oriented opposite to the top‐to‐the‐SW. Whereas euhedral quartz grains with undeformed grain boundaries, compositional zoning in plagioclase, and magmatic (perthite) texture of K‐feldspar are present in the core of Dalhousie pluton. In addition, a new whole‐rock geochemical dataset of DG is presented and investigated to elucidate the petrogenesis and tectonic environment. The geochemical data shows that DG (dominantly monzogranites) are formed from a pelitic source‐derived, (molar Al2O3/CaO + Na2O + K2O &gt; 1.1) strongly peraluminous (S‐type) calc‐alkaline magma. This magma was generated by muscovite vapour absent dehydration melting. Harker bivariate plots indicate that fractional crystallization was a dominant process during the evolution of these granites. The tectonic discrimination diagrams suggest that DG were generated in syn‐collisional setting. Exceptionally high Pb in DG occurred due to primary melt generation at low‐temperature during partial melting (low‐degree melting) of the pelitic source rock. Trace and rare earth elements characteristics, such as positive anomaly of Zr show a notable amount of zircon as one of the accumulating phases. A pronounced negative Eu anomaly (EuN/Eu* = 0.04–0.66), along with high silica content and highly varied trace element ratios in these rocks, show that these are fairly evolved granites.

Portable X-ray Fluorescence (pXRF) as a Tool for Environmental Characterisation and Management of Mining Wastes: Benefits and Limits

Portable X-ray fluorescence (pXRF) is one of the main geochemical techniques employed in multi-elemental analysis screening for contaminated sites management. As the confidence of pXRF analyses are matrix-specific, efforts are made to provide studies of pXRF quality on different geochemical datasets, focusing on less investigated elements such as mercury (Hg) and antimony (Sb), to help both new and experienced users. The analysis of environmental solid samples from two decommissioned mining sites in NE Italy, characterised by Pb-Zn and (Hg-rich) Cu-Sb ore deposits, were prepared with two different protocols and compared with traditional destructive analyses. Sample composition was found strictly dependent to the occurrence of false positives and overestimation at low concentrations. In contrast, milling the sample did not produce major variations in the overall quality. Lead (Pb), Sb, and Zn reached the definitive data quality in at least one of the two datasets. Consequently, as far as a thorough QA/QC protocol is followed, pXRF can rapidly produce chemical data that is as accurate as that produced by destructive standard laboratory techniques, thus allowing to identify potential sources of contamination that could be reprocessed for the extraction of valuable elements and mitigating the dispersion of contaminants and ecological or health risks.

A resource for automated search and collation of geochemical datasets from journal supplements

This article presents a resource for automated search, extraction and collation of geochemical and geochronological data from the Figshare repository using web scraping code. To answer fundamental questions about the Earth’s evolution, such as spatial and temporal evolution and interrelationships between the planet’s solid and surficial reservoirs, researchers must utilize global geochemical datasets. Due to the volume of data being published, these datasets become quickly outdated. We present a resource that allows researchers to rapidly curate and update their own databases from existing published data. We use open-source Python code to web scrape the Figshare repository for journal supplementary files using the application programming interface, allowing for the collection and download of hundreds of supplementary files and metadata in minutes. Use of this web scraping tool is demonstrated here by collation of a zircon geochronology and chemistry database of >150,000 analyses. The database is consistent in reproducing trends in other published zircon compilations. Providing a resource for automated collection of Figshare data files will encourage data sharing and reuse.