Geochemical Signatures Research Articles

Investigating Pre-Columbian Gold and Copper in Costa Rica – Ores, Mines and Artefact Production

The wealth of pre-Columbian gold, copper and guanín (an alloy consisting mainly of gold and copper; also tumbaga) artwork of Costa Rica suggests that exploitation of its abundant ore deposits goes back way before the Spanish conquest. The name of Costa Rica itself in fact alludes to the large numbers of golden metal objects worn by the indigenous peoples upon arrival of the conquistadors. Up to now, however, very little is known about pre-Columbian mining in the country or the raw material provenance of these artefacts.In a transdisciplinary project, we aim to reconstruct the metallurgical process chain by combining (mining) archaeological research with geochemical analysis of local ores and metal artefacts using a combination of different techniques. We identified four major gold and copper districts with different mineralisation types, which are the focus of our fieldwork-based research. They are surveyed for potential signs of pre-Columbian metal production and sampled for ores and their processing remains. On the other side of the process chain, we focus on the metal artefacts in museum collections. They are systematically registered in a database, which serves as a basis to identify correlations with the geochemical signatures of the artefacts, and to retrace potential links to possible areas of origin or different workshops. Once the necessary basic data have been collected, we will focus on economic and socio-cultural aspects of metal production and circulation. The results from Costa Rica will be put into perspective of New World early metallurgy and can provide a starting point for future research between Mesoamerica and the Isthmo-Colombian region.

Reevaluation of the K/Rb-Li Systematics in Muscovite as a Potential Exploration Tool for Identifying Li Mineralization in Granitic Pegmatites

A dataset of >1190 published compositional analyses of muscovite from granitic pegmatites of varying mineralogical types was compiled to reevaluate the usefulness of K-Rb-Li systematics of muscovite as a tool for distinguishing mineralogically simple pegmatites from pegmatites with potential Li mineralization. Muscovite from (i) common, (ii) (Be-Nb-Ta-P)-enriched, (iii) Li-enriched, and (iv) REE- to F-enriched pegmatites contain Li contents that vary between 10 and 20,000 ppm depending on the degree of pegmatite fractionation. Common pegmatites are characterized by low degrees of fractionation as exhibited by K/Rb ratios ranging from 618 and 25 and Li contents generally being <200 ppm but infrequently as high as 743 ppm in muscovite. Moderately fractionated pegmatites with Be, Nb, Ta, and P enrichment contain muscovite having K/Rb ratios mostly between 45 and 7 plus Li contents between 5 to >1700 ppm. Muscovite from moderately to highly fractionated Li-rich pegmatites exhibit a wide range of K/Rb ratios and Li values: (i) K/Rb = 84 to 1.4 and Li = 35 to >18,100 ppm for spodumene pegmatites, (ii) K/Rb = 139 to 2 and Li = 139 to >18,500 ppm for petalite pegmatites, and (iii) K/Rb = 55 to 1.5 and Li = 743 to >17,800 ppm for lepidolite pegmatites. Pegmatites that host substantial REE- and F-rich minerals may carry muscovite with K/Rb ratios between 691 to 4 that has Li contents between 19 to 15,690 ppm. The K/Rb-Li behavior of muscovite can be useful in assessing the potential for Li mineralization in certain granitic pegmatite types. The proposed limits of K/Rb values and Li concentrations for identifying spodumene- or petalite-bearing pegmatites as part of an exploration program is reliable for Group 1 (LCT) pegmatite populations derived from S-type parental granites or anatectic melting of peraluminous metasedimentary rocks. However, it is not recommended for application to Group 2 (NYF) pegmatites affiliated with anorogenic to post-orogenic granitoids with A-type geochemical signatures or that derived by the anatexis of mafic rocks that generated REE- and F-rich melts.

Late Jurassic Tethyan igneous records in North Sumatra: Geochronological and geochemical constraints

The Jurassic igneous rocks on Sumatra Island are important for investigating the Mesotethyan evolution and regional correlation in Southeast Asia. This paper presents new laser ablation−multicollector−inductively coupled plasma−mass spectrometry zircon U-Pb-Hf geochronological and isotopic, whole-rock elemental, and Sr-Nd isotopic data for the newly identified Glebruk dolerite and andesite in North Sumatra. New zircon dating results suggest that these mafic−intermediate volcanic rocks, with ages of 150−146 Ma, were formed during the Late Jurassic. The Glebruk dolerite and andesite belong to the calc-alkaline series, are enriched in the light rare earth elements, and exhibit depletion in Nb, Ta, and Ti. Thus, they resemble arc-like volcanic rocks. They have low (87Sr/86Sr)i ratios of 0.7038−0.7048 and strong positive εNd(t) and εHf(t) values of +6.4 to +7.5 and +4.8 to +18.6, respectively. Their geochemical signatures suggest that these Late Jurassic volcanic rocks were derived from a depleted mantle wedge that was metasomatized by the slab-derived melts. The Glebruk volcanic rocks were formed in a continental arc setting in response to the Late Jurassic northward subduction of the Woyla Ocean beneath West Sumatra. Our results and regional geological observations suggest that the Mesotethyan subduction-related igneous rocks could extend from South Qiangtang through West Yunnan to North Sumatra. The Woyla Ocean could represent the southern extension of the Mesotethyan Ocean.

Marine sediments: A sink for geogenic and anthropogenic metals, a case study of Ridge flank and near vent sediments in Carlsberg Ridge, Indian Ocean

<div>Marine sediments found in the Mid-Ocean Ridges serve as repositories for both naturally occurring (geogenic)</div><div>and human-generated (anthropogenic) metals. Understanding the geochemistry and processes of these sediments is crucial</div><div>for assessing their source, compositional end-members, and environmental impact. This study applied geochemical ratios</div><div>and proxies to representative samples from the Carlsberg Ridge, Indian Ocean, to determine the influence of hydrothermal</div><div>circulations on the near-vent hydrothermal sediments (NVS) and ridge flank sediments (RFS) and the potential effect of</div><div>toxic trace metals on the benthic ecosystems. The bulk chemical compositions of seven representative hydrothermal</div><div>indicator metals (Ca, Al, Ti, Fe, Mn, Cu, and Zn) and seven representative toxic trace metals (Pb, Ni, Co, Cr, As, Cd, and</div><div>Co) were analyzed at the A laboratory services in Guangzhou, China, by Agilent 7700 Inductively Couple Plasma Mass</div><div>Spectrometer (ICPMS). The geochemical signatures Fe/(Al + Fe + Mn) > 0.5; Al/(Al + Fe + Mn) < 0.3; (Fe + Mn)/Al ></div><div>2.5; and (Fe + Mn)/Ti > 25 affirm the proximity of the NVS and the distal position of RFS to the Wocan vent site in the</div><div>Carlsberg Ridge, Indian Ocean. The pollution indices, ecological risk index, and sediment quality guidelines showed low</div><div>to moderate contamination, low to moderate severity, and low to moderate ecological risk of As, Cd, Sb, Pb, Ni, Co, and</div><div>Cr to the benthic ecosystems at RFS. This is an indication of low to moderate anthropogenic influence from hydrothermal</div><div>venting to the ridge flank sediment (RFS). This study has shown that an understanding of background and threshold</div><div>concentrations can guide the development of strategies to reduce the impact of human activities on marine ecosystems.</div>

Late Mesozoic subduction-accretion in the southern Qiangtang: Insights from the Sumxi igneous complex of west-central Tibet

Knowledge of the evolution of the Bangong-Nujiang Tethyan Ocean is crucial for reconstructing the paleography of the Tethyan Realm, given its significance as a key component of the eastern Tethys. Nonetheless, there has been uncertainty regarding both the timing and the processes involved in the closure of this ocean. This study focused on a 110−106 Ma igneous complex comprising basalts−basaltic andesites, trachyandesites, and granodiorites from the Sumxi area in the western part of the Qiangtang terrane of west-central Tibet. The basalts−basaltic andesites have SiO2 contents of 52.5−58.7 wt% and MgO contents of 2.89−4.63 wt%, and exhibit some arc-like geochemical signatures. However, these rocks also have elevated Nb contents (>10 ppm) and Nb/La ratios (>0.5), as well as enriched Sr-Nd isotopic composition [εNd(t) = −7.40 to −6.00], implying that they are products of a mantle source metasomatized by adakitic melts. The trachyandesites are characterized by intermediate compositions (SiO2 = 63.6−65.2 wt%), high Mg number (40−60), and more enriched εNd(t) values (−8.37 to −7.49). Comparing their geochemical composition to that of mélange rocks, it is postulated that these trachyandesites were formed through the partial melting of a mantle source including mélange matrix rocks within a subduction zone. The granodiorites exhibit adakitic geochemical features (Sr = 830.14−1032.70 ppm, Y = 14.86−15.37 ppm, Sr/Y = 54−68), indicating that they originated from the partial melting of a thickened lower crust in a continental arc setting. Our results, in combination with a synthesis of tectonomagmatism along the Bangong-Nujiang suture zone, provide convincing evidence for subduction of an oceanic plateau and subsequent slab roll-back. The Sumxi igneous complex, with its clear arc affinity, suggests that the Bangong-Nujiang Tethyan Ocean, or at least its western part, remained open until the late Early Cretaceous (ca. 106 Ma).

The layered gabbroic intrusion in the Southern Eastern Desert of Egypt: Implications for Fe-Ti-rich magmatism at the end of the East African Orogeny

The Rahaba layered intrusion in the Southern Eastern Desert of Egypt is mainly composed of pyroxene hornblende-, and hornblende gabbros. It hosts thick FeTi oxide ore layers that are composed of titanomagnetite with subordinate ilmenite and magnetite. To understand the petrogenesis of the FeTi rich gabbroic rocks, the nature of their parent high-Fe primitive mantle melts and condition of FeTi oxide layer formation, we obtained new mineral chemistry and whole-rock major and trace element compositions. The geochemical characteristics of the gabbroic rocks resemble those of picro-basalts, suggesting generation from picritic basaltic-like melts of tholeiitic affinity. Their high-Fe-Ti-Mg nature (TiO2, ∼1.91 wt%; MgO, ∼11.0 wt%; Fe2O3, ∼14 wt%) probably indicates elevated mantle potential temperatures due to upwelling of hot asthenospheric mantle. Rare earth elements (REEs) of clinopyroxene show flat patterns with depletion in LREEs, similar to those of the host gabbros and picritic basaltic lava, suggesting a mantle origin for their parental melts. Moreover, clinopyroxene compositions show differentiation trends similar to low-pressure igneous intrusions, and reveal a rift-related origin. Chemistry of plagioclase (An45–62), clinopyroxene (Wo38.4–45.3, En39.9–43, Fs14–19.3; Mg#: 0.71–0.92) and olivine (Fo56–80) shows wide compositional ranges due to variable degrees of crystal fractionation. The calculated equilibrium temperature for the Rahaba Fe-Ti-rich gabbros is mainly 820–1000 °C, at pressure below 5 kbar, reflecting depth of rock solidification of <15 Km. These rocks show both subduction-like and rift-related geochemical signatures comparable to other post-collisional layered intrusions in the Arabian-Nubian Shield. The low average Ce/Pb (8.3) and high Ba/Nb (391) ratios together with the enriched large-ion lithophile elements (Cs, Ba, K and Sr) and depleted high-field strength elements (Th, Nb, Ta and Zr) reflect the contribution from a preceding subduction event. The lineament map, structural lineament and lineament density map reveal main WNW-ESE and NW-SE structural trends of the Najd System in the Rahaba area. The Rahaba FeTi rich gabbroic intrusion was likely formed by initial impact of a mantle plume head with Fe-rich streaks at the base of metasomatized lithospheric mantle during an extensional phase associated with activity of the Najd-related strike-slip faults, at the end of the East African Orogeny. The resultant mantle-derived melt compositions and Najd-related structures possibly controlled the distribution of FeTi ore deposits during this Orogeny. The Rahaba gabbroic intrusion was emplaced during post-collisional extension after slab break-off and lithospheric delamination following collision of accreted island-arcs with the Saharan Metacraton.

Offshore evidence of historic and prehistoric tsunamis on the north shore of Tutuila (American Samoa)

Although research dealing with the geological evidence of past tsunamis has increased significantly in the last two decades, studies of tsunami deposits emplaced during the backwash phases are still underrepresented. Here, we provide the first investigation of tsunami backwash deposits all around an island (Tutuila Island, American Samoa), in the southwest of the Pacific Ring of Fire. We decipher the sedimentary record preserved offshore an open bay (Fagafue) and within a sheltered bay (Masefau) on the north shore of Tutuila. Backwash deposits of three historic tsunamis, namely the 2009 South Pacific, 1960 Valdivia and 1917 Tonga Trench tsunamis, were identified in sediment cores, based on sedimentological, geochemical and chronological data. Deposits were characterized by a geochemical terrestrial signature (Ti/Ca and K), while the grain size characteristics differed, being finer offshore the open bay and coarser within the sheltered bay. The 2009 South Pacific and the 1960 Valdivia tsunamis are recorded on both the north (Masefau and off Fagafue bays) and south (Pago Pago Bay) shores of Tutuila, providing the first correlation of tsunami backwash deposits all around an island. Furthermore, the present study presents the first geological evidence of backwash associated with a large 15–16th century tsunami, which also affected many parts of the South Pacific, as well as that of an older event between the 11th and 14th century. Studies of tsunami backwash deposits provide means to extend the geological record of these high energy events, due to the generally good preservation potential of the deposits.

Depositional age and formation conditions of Archean banded iron formations, Bundelkhand Craton, Central India: Geochemistry, neodymium isotopes and U-Pb zircon geochronology

In this study, we present major and trace element concentrations, U-Pb zircon geochronology as well as neodymium isotopic compositions of the banded iron formations (BIFs) from the Bundelkhand Craton, India. The study aims to constrain the source characteristics, depositional age and evaluate the paleoenvironmental implications of the Meso-Neoarchean seawater from which the BIF precipitated. The presence of a 2898 ± 26 Ma rounded zircon grain in the Girar BIFs indicates their maximum depositional age, which is consistent with the reported age of the metabasalts (2989 ± 190 Ma). Bearing in mind the errors, we consider the age of the studied BIFs to be ca. 2850 Ma. The BIFs from Mauranipur are associated with 2810 Ma dacite and formed at the same time. They have zircon with ages of 2718 ± 22, 2573 ± 66, 2070 ± 29 and 1934 ± 39 Ma. The BIFs from Babina are associated with 2540 Ma felsic volcanics and can be considered of the same age. Our study shows that the sedimentation of BIF in the Girar and Mauranipur greenstone belts took place in the Mesoarchean between ca. 2850 and 2810 Ma, respectively, and in the Babina greenstone belt in the Neoarchean at ca. 2540 Ma.A positive correlation between TiO2 and Zr, Al2O3 and Zr, Zr and Th/U, Y and Zr, Ni and Cr, as well as Hf and Zr, may suggest a detrital component to the BIF derived from terrigenous mafic and felsic sources. The PAAS-normalized REE patterns of the Bundelkhand BIFs are characterized by depleted LREEs, positive La, Eu, Y anomalies and Y/Ho ratios mostly ranging between 18 and 47. The studied BIFs are broadly similar to worldwide BIF occurrences at the time with the exception of the Mauranipur BIFs, which show elevated MnO concentrations (0.92 to 4.82 wt%). The studied BIF samples from the Bundelkhand Craton display a wide range of εNd(t) ranging from −6.57 to + 4.12. The broad range of isotopic values along with the above-noted geochemical signatures suggest that the BIF from the Bundelkhand Craton had significant inputs from submarine hydrothermal sources as well as pre-existing continental crust. The elevated manganese concentrations in BIFs from Mauranipur may imply the availability of free oxygen in seawater on the Bundelkhand Craton during the Mesoarchean.

Geochemical signatures of metapelites in the Highland Complex, Sri Lanka and Trivandrum Block, India: Implications for provenance, nature and tectonic setting of their source protoliths

AbstractThe investigation of whole‐rock major and trace element geochemical data from metapelites, incorporating analyses from both previous studies and new localities within the Highland Complex (HC) of Sri Lanka and the Trivandrum Block of India (TB), aimed to discern the nature and tectonic setting of their provenance. Examination of chondritic REE distribution and K versus K/Rb diagrams suggests that the geochemistry of the studied metapelites closely resembles typical Post Archaean Australian Shale (PAAS), North American Shale Composite (NASC), and Upper Continental Crust (UCC), indicating minimal modification during high‐grade metamorphism. Predominantly, the protoliths of the metasediments appear to be shales and greywackes derived from Proterozoic felsic to intermediate sources. Tectonic discrimination diagrams reveal that most metapelites correspond to active continental margins and continental island arcs. These geochemical characteristics suggest that the majority of studied metapelites in the HC and TB originate from felsic to intermediate sources, likely deposited within a continental arc setting. Subsequently, these sediments likely accreted in an accretionary prism and underwent metamorphism during continental‐continental collision. The congruence in geochemical signatures between metapelites in the HC and TB, along with established tectonic, geochronological, petrological, mineralogical, and geophysical correlations, implies that precursor sediments of metasedimentary rocks were likely deposited within a laterally extensive Neoproterozoic sedimentary basin.

Petrography and Geochemistry Study of the Madharam Lamprophyre Dyke, Western Margin of the Proterozoic Pakhal Basin Within Eastern Dharwar Craton, Khammam, Telangana, India

Various lamprophyre types are prevalent throughout the Cuddapah Igneous Province (CIP) and Prakasam Alkaline Province (PAP) in the Eastern Dharwar Craton (EDC), located in southern India. This study focuses on a newly identified lamprophyre dyke situated near the Madharam area in Khammam District, Telangana, India (coordinates 80°15ʹ:17°32ʹ) on the northeastern edge of the EDC. The paper provides an in-depth analysis of the petrography and geochemistry of this lamprophyre. The study area predominantly comprises granitoids from the Peninsular Gneissic Complex (PGC) within the EDC. Geographically, it is flanked by the Proterozoic sedimentary basins of Pakhal to the east and Cuddapah to the south. The Madharam lamprophyre exhibits a characteristic porphyritic-panidiomorphic texture, with clinopyroxene phenocrysts occurring alongside feldspar in the groundmass. Amphiboles present in the rock are of calcic variety (mainly actinolite group). Clinopyroxene is found to be diopside in nature (Wo48-50 En40-41 Fs9-10) and the feldspars show albitic (Or0Ab85-92 An 6-14) nature. Lower TiO2 content in the amphibole and clinopyroxene suggests the nature of the lamprophyre is calc-alkaline. The geochemical signatures, such as variable Ba/La ratios and low Nb/La values, suggest minimal to no crustal contamination in the lamprophyre magma. These findings are significant for understanding the evolution of the EDC and provide important constraints on the geodynamics of southern peninsular India.

Differences in Geochemical Characteristics and Tectonic Settings between Hai Van Granitic Rocks in Da Nang Province and Van Canh Plutonic Rocks in Quang Nam Province, Central Vietnam

Research was conducted on plutonic rocks, previously referred to as the Hai Van granitic rocks, distributed in Da Nang and Quang Nam provinces in Central Vietnam. The granitic rocks in Da Nang Province have low magnetic susceptibilities and have geochemical signatures typical of S-type. Additionally, a negative Eu anomaly suggests that the source rock is an organic matter-bearing sedimentary rock. The granitic rocks were likely formed during the collision between the Indochina and South China blocks. In contrast, plutonic rocks in Quang Nam Province have high magnetic susceptibilities and have geochemical signatures of I-type. No Eu anomaly was observed, and they are adakitic rocks in nature. Based on these findings, the plutonic rocks in Quang Nam Province are distinctly different from the Hai Van granitic rocks in Da Nang Province, but they are Van Canh plutonic rocks. The Hai Van granitic rocks in Da Nang Province and the Van Canh plutonic rocks in Quang Nam Province are located in the Truong Son Fold Belt. The Van Canh plutonic rocks are located farther away from the Song Ma Suture Zone than the Hai Van granitic rocks. The Van Canh plutonic rocks were generated due to the subduction of the hot Song Ma Ocean beneath the Indochina Block. The Hai Van granitic rocks are understood to have been generated in a compressional field where the Song Ma Ocean was pushing against the Indochina Block; however, the Van Canh plutonic rocks are supposed to have been generated in an extensional field, like in a back-arc-like environment generated by the subduction of the Song Ma Ocean beneath the Indochina Block.

Cold climatic snaps during the Eocene-Oligocene transition in the central Tibetan Plateau: Implications for ice-induced sedimentary structures and isotope geochemistry

The Eocene-Oligocene transition was a time of major climate instability and a shift from an ice-free world to a predominant icehouse climate. Identifying the ancient glacial deposits and their associated sedimentary structures are of paramount significance for understanding the Earth's climate in the Cryogenian Period. Ice-induced sedimentary structures (IISS) are considered as types of primary structures preserved on surfaces and in upper parts of unconsolidated sediments by physical cryospheric processes of seasonal ice freezing and thawing, and therefore sensitive not only to climate, but also to paleogeography, hydrology, and type of environment. Despite the common occurrence of modern IISS in a wide variety of environments, from high-latitude regions to low-latitude areas of high altitude, available records from ancient geologic archives are scarce. Herein, we integrated sedimentological and geochemical proxies to study IISS and geochemical signals as reliable indicators of cold climate in an outstanding example of the Eocene-Oligocene interval from the Niubao Formation in the Lunpola Basin, central Tibet. Detailed field sedimentological, petrographic microscopic investigations, and bulk carbonate oxygen (δ18Ocarb) and carbon (δ13Ccarb) isotope geochemistry were conducted in this lacustrine succession. Seven sets of IISS are represented by ice crystal marks, frozen cracks, ice-frozen bubbles, ice-expanding laminae, ice-rafted debris (dropstones), ice water pea-like, and ice water pits. They are classified into three groups based on major deriving mechanisms: ice-related crystal marks, deformation-related ice structures, and gravitational fall IISS. Positive δ18Ocarb excursions at the Eocene-Oligocene transition provide evidence of a shift toward cold or near-freezing climatic snaps in response to global cooling episodes at this time. Integrating the paleogeomorphic scenario of central Tibet with the stratigraphically reported IISS and glendonite clusters, the results support that the Lunpola lake sustained cold or near-freezing conditions at Eocene-Oligocene transition. These findings provide one of the most comprehensive sedimentological and isotopic analyses of ancient IISS and a more direct spatial-temporal constraint for the regional climate system of central Tibet.

Hammerscale and slag inclusions: New insights into metal supply during the early iron Age in Western Europe

Understanding the nature and origin of iron processed in ancient smithing workshops is essential for unraveling procurement strategies and, more broadly, the circulation of iron. Studying smithing slags traditionally proves complex due to their diverse compositions influenced by hearth substances. Another technique, analyzing slag inclusions in metallic fragments, offers direct insights into the iron's chemical nature. However, the scarcity or absence of these fragments poses challenges in assessing sample representativeness. An alternative approach studies hammerscale, hot iron waste from hammering, providing insights into iron's chemical composition and source. At Weyersheim, an early Iron Age site in France, extensive analysis of 300 hammerscale samples and 77 slag inclusions in 6 iron scraps unveiled a unique geochemical signature. This signature showcases enrichment in Vanadium (V > 800 ppm), Chromium (Cr > 400 ppm), Rare Earth Elements (REE) (∑REE + Y > 1500 ppm), especially Heavy Rare Earth Elements like Yb (>100 ppm), and High Field Strength Elements (HFSE) (e.g., U > 30 ppm). The remarkable chemical uniformity observed in various hammerscale samples, and the slag inclusions indicates that the majority of the processed iron originates from a singular source. Comparison with known iron artifacts, particularly the bi-pyramid iron bars revealed similarities. This source exhibited uncommon enrichment and partitioning patterns of REEs, hinting at a rare geological deposit or a closely associated group of deposits. Plausibly sourced from weathered peralkaline rocks, the iron ore's geological origins potentially link to regions like Vosges and the Black Forest massifs. Nevertheless, identifying the geological formations accountable for these distinctive iron traits remains challenging, as there have been no findings of deposits or iron slag with similar compositions to aid in identification.

Origin of calcite cements in the Permian Lucaogou Formation tight reservoirs, Jimsar sag, Junggar basin, NW China: Constraints from geochemistry

Understanding the diagenetic evolution of carbonate cementation in hydrocarbon reservoirs is critical to better reconstruct the history of fluid flow during petroleum accumulation. The extensive occurrence of carbonate cements within the lower Permian Lucaogou Formation tight reservoirs is regarded as a major diagenetic factor that causes strong hydrocarbon reservoir heterogeneities. Petrographic and geochemical analyses, including optical microscopy fitted with cathodoluminescence, scanning electron microscopy, carbon and oxygen stable isotopes, in situ rare earth element, as well as fluid inclusion microthermometry, were carried out to decipher the origin of calcite cementation and understand its control on reservoirs quality. Petrography shows that the precipitating cements mostly consist of pore-filling blocky/mosaic calcite, with a dull orange luminescence color. Chondrite-normalized rare earth element (REE) patterns and C–O isotopic compositions of these calcite cements exhibit strongly negative Eu and Tb anomalies, enrichment in light REE, positive carbon (δ13CPDB = 0.58‰–7.45‰) and negative oxygen (δ18OPDB = −11.38‰ to −8.61‰) isotopic values, similar to the dolostone and micritized peloidal grains, suggesting that the calcite-precipitating fluids were derived from dissolution of lacustrine depositional carbonates. The relative timing of calcite precipitation in reservoirs was constrained based on the thermal-burial history of the study region and precipitation temperatures obtained from fluid inclusions. The results show that this cementation episode mainly occurred during the Late Triassic to Early Jurassic, which was synchronous with the tectonic uplift event. Moreover, homogenization temperatures of fluid inclusions and geochemical signatures of the calcite cement are similar to those of the fracture-fillings, suggesting that these two calcite phases may be genetically related and form coevally within one fluid flow system. It can be interpreted as a response to the compressional tectonic deformation given by the collision of the Qiangtang Block with the Eurasia Plate. This tectonic deformation event is regarded as the driver for calcite precipitation during the early burial stage, resulting in a considerable reduction of reservoir quality. Calcite cementation is pervasive and may play a main role in halting hydrocarbon migration through some of the permeable pathways in reservoirs.

The genetic link between lode and disseminated gold ores and relationship between hypozonal and mesozonal deposits: A case study of the Yanzigou orogenic gold deposit, northwestern Yangtze Craton, China

The process controlling the formation of orogenic lode and disseminated gold ores is the basis for understanding the complexity of the orogenic gold system. The mesozonal Yanzigou gold deposit, located in the Danba ore district of the northwestern Yangtze Craton, is hosted by Devonian carbonaceous slate with coexisting fault-hosted lode and strata-bound disseminated gold ores. Three types of pyrite (PyI-q, PyII-q and Pyd) were formed during two stages of hydrothermal evolution. PyII-q in quartz-polymetallic veins and the rims of Pyd in disseminated ores have the highest Au and As contents, contrasting to distal sedimentary pyrite that have low Au and As contents. This implies that the Devonian host sequences are incapable of providing ore elements to the ore fluid. Pyd and associated quartz have intermediate isotopic values (δ34S = -1.7∼+0.8 ‰; δ18OH2O = 10.6 ∼ 12.7 ‰) between the quartz-vein ores (δ34S = 8.5 ∼ 10.7 ‰; δ18OH2O = 9.0 ∼ 10.1 ‰) and wall-rocks (δ34S ≈ −5‰; δ18OH2O ≈ 12 ‰), implicating a critical role of fluid-rock reaction in the formation of the disseminated gold ores and preservation of original ore fluid characteristics in the lode gold ores. The 40Ar/39Ar dating of hydrothermal muscovite from auriferous quartz veins at Yanzigou yields a total fusion age of 118.4 ± 0.4 Ma, later than ∼ 185 Ma for the nearby hypozonal Danba gold deposit. However, both deposits have common geological, geochemical, and isotopic signatures, suggesting a multi-stage orogenic gold mineralization on the Mesozoic dome margins associated with episodic reactivation of metasomatized mantle lithosphere during the continued crustal uplift.

Nb-Ta-Sn Oxides from Lithium-Beryllium-Tantalum Pegmatite Deposits of the Kolmozero–Voronja Belt, NW Russia: Implications for Tracing Ore-Forming Processes and Mineralization Signatures

In this paper we present textural and compositional data for columbite group minerals (CGMs) and associated Nb-Ta-Sn oxides from lithium-beryllium-tantalum pegmatite deposits of the Kolmozero–Voronja belt, NW Russia, with the aim of deciphering these characteristics for minerals from deposits with different mineral signatures and lithium ore grade. Minerals from four deposits, including two of world-class (Kolmozero and Polmostundra), are examined. The main controlling factors for CGM compositional ranges are the diversity and rate of magmatic fractionation, hydrothermal overprint and mineral paragenesis, following the specific geochemical signature of the different pegmatite deposits. CGM from Kolmozero include several mineral species (columbite-(Fe), columbite-(Mn), tantalite-(Fe), and tantalite-(Mn)), showing large compositional variations, mainly controlled by Nb-Ta fractionation (Ta/(Ta + Nb) = 0.16–0.70; Mn/(Mn + Fe) = 0.45–0.63). Textural patterns are various (oscillatory, homogeneous, and patchy); spongy domains and overgrowing Ta-rich rims are also observed somewhere. This indicates the involvement of numerous magmatic and hydrothermal processes. The Polmostundra CGMs are represented by columbite-(Fe) with Ta/(Ta + Nb), ranging from 0.05 to 0.39; some crystals are homogenous, and others present normal, oscillatory, mottled and reverse-zoning patterns. The Okhmylk CGMs are irregular normal, patchy and homogeneous columbite-(Fe) and columbite-(Mn), with Ta/(Ta + Nb) = 0.09–0.24 and Mn/(Mn + Fe) = 0.29–0.92, indicating the suppressed magmatic fractionation and iron drop due to precipitation of Fe minerals. Columbite-(Fe) and columbite-(Mn) from the Be-Ta Shongui deposit are less evolved, with Ta/(Ta + Nb) = 0.07–0.23 and Mn/(Mn + Fe) = 0.31–0.55. The minerals are characterized by progressive normal, oscillatory, homogeneous and irregular reverse patterns. Associated pyrochlore minerals occur both as early magmatic (Kolmozero) and late hydrothermal (Polmostundra, Okhmylk). Cassiterite is found only in the Okhmylk dykes, and is apparently of hydrothermal origin. CGM from Li pegmatites have impurities of Ti (0.01–0.05 apfu) and W (up to 0.02 apfu), whereas CGM from Be pegmatites contains elevated Ti (up to 0.09 apfu). The mineral system analysis presented here is relevant for exploration.

In-depth characterization of sediment contamination in stormwater infiltration basins

Abstract Managing stormwater in infiltration-based systems enables the interception of runoff suspended solids. Accumulated particles form a layer of stormwater sediments, the contamination of which presents a critical challenge for maintenance operations but is still insufficiently understood. This study therefore aims to characterize the main contamination patterns of stormwater sediments. Sediments were sampled from 18 infiltration basins encompassing a diversity of catchments. Eighty-five substances, including metals and six families of organic micropollutants, were targeted, almost all of which were consistently quantified. A significant accumulation relative to baseline levels was ascertained in all sites. The geochemical signature of stormwater sediments was relatively close to that of road dust, but different from continental and marine sediments, revealing the contribution of urban-specific sources of contaminants. Common emission and transfer dynamics were inferred from strong correlations between metals; same observations were made for alkylphenols and the group formed by polycyclic aromatic hydrocarbons, polychlorinated biphenyls, dioxins, and furans. The predominant land use was generally insufficient to explain the inter-site variability of sediment contamination, which could still be understood from an in-depth study of each catchment and the identification of site-specific emission sources. These results constitute a milestone toward stormwater sediment reuse as a resource.

Impact of seawater sulfate concentration on sulfur concentration and isotopic composition in calcite of two cultured benthic foraminifera

Abstract. Marine sediments can be used to reconstruct the evolution of seawater [SO42-] and δ34S over time, two key parameters that contribute to refine our understanding of the sulfur cycle and thus of Earth's redox state. δ34S evolution can be measured from carbonates, barites and sulfate evaporites. [SO42-] variations can be reconstructed using fluid inclusions in halites, a method that only allows a low-resolution record. Reconstruction of the past sulfur cycle could be improved if carbonates allowed the tracking of both seawater δ34S and [SO42-] variations in a sole, continuous sedimentary repository. However, most primary carbonates formed in the ocean are biogenic, and organisms tend to overprint the geochemical signatures of their carbonates through a combination of processes often collectively referred to as vital effects. Hence, calibrations are needed to allow seawater δ34S and [SO42-] reconstructions based on biogenic carbonates. Because foraminifera are important marine calcifiers, we opted to focus on calcite synthesized by individuals of rosalinid benthic foraminifera cultured in the laboratory under controlled conditions, with varying seawater [SO42-] (ranging from 0 to 180 mM). Our experimental design allowed us to obtain foraminiferal asexual reproduction over several generations. We measured bulk carbonate-associated sulfate (CAS) content and sulfur isotopic composition (δ34SCAS) on samples of tens to hundreds of specimens from a selection of culture media, where [SO42-] varied from 5 to 60 mM. Increasing or decreasing [SO42-] with respect to modern-day seawater concentration (28 mM) impacted foraminiferal population size dynamics and the total amount of bioprecipitated carbonate. Foraminiferal CAS concentration increased proportionally with [SO42-] concentration from 5 mM up to 28 mM and then showed a plateau from 28 to 60 mM. The existence of a threshold at 28 mM is interpreted as the result of a control on the precipitation fluid chemistry that foraminifera exert on the carbonate precipitation loci. However, at high seawater sulfate concentrations (&gt; 40 mM) the formation of sulfate complexes with other cations may partially contribute to the non-linearity of the CAS concentration in foraminiferal tests at high increases in [SO42-]. Yet, despite the significant effect of seawater [SO42-] on foraminiferal reproduction and on CAS incorporation, the isotopic fractionation between CAS and seawater remains stable through varying seawater [SO42-]. Altogether, these results illustrate that CAS in biogenic calcite could constitute a good proxy for both seawater [SO42-] and δ34S and suggests that sulfate likely plays a role in foraminiferal biomineralization and biological activity.

A carbon, nitrogen, and multi-isotope study of basalt glasses near 14°N on the Mid-Atlantic Ridge. Part B: Mantle source heterogeneities

Geochemical variations along mid-ocean ridges reveal the heterogeneous nature of the convecting upper mantle and geodynamic evolution of our planet (e.g., Hofmann, 2007; Parai et al., 2012). Although the occurrence of incompatible element and isotopically enriched mid-ocean ridge basalts (E-MORB) commonly arises from interaction with nearby mantle plumes, the source of E-MORBs far from known hotspots is debated. A well-known example of an enigmatic geochemical enrichment is found at 14°N on the Mid-Atlantic ridge (MAR). This is also one of the few locations worldwide where volatile-saturated E-MORBs, often referred to as “popping rocks” (PR), have been recovered. Although the mechanism(s) involved in popping rock generation remain elusive, compressional regimes associated with the exhumation and formation of oceanic core complexes (OCC) may be required to produce popping rocks via protracted volatile accumulation. However, the geochemical signature of OCC samples and their potential relationship to local geochemical enrichments associated with popping rock-affiliated MORBs remain unknown. Here, we present a comprehensive volatile characterization of popping rocks and associated MORBs (n = 19) sampled at 14°N on the MAR, including (n = 2) normal MORBs (N-MORB) from an oceanic core complex (OCC) and (n = 17) E-MORBs (Bekaert et al., Part A). We use isotopic and abundance data for volatile (carbon, nitrogen, noble gases) and radiogenic (Pb, Sr, Nd) elements, as well as the abundances of major and trace elements, to elucidate on the source(s) of E-MORBs at 14°N and discuss the potential origin(s) of geochemical heterogeneities within the upper mantle. We observe co-variations of helium and radiogenic element isotopes, suggesting potential contributions from a young HIMU-type (high μ = time-integrated 238U/204Pb) component in the OCC mantle source. The mantle source of the OCC samples is clearly distinct from that of PR-affiliated samples, suggesting no genetic relationship between OCC samples and E-MORBs. In addition, elevated Dy/Yb in OCC samples likely point to the incorporation of a subducted crustal component that is not observed in the mantle source of other MORB samples analyzed in this study. We report mantle source 40Ar/36Ar variations at 14°N, which, in line with previous studies, are interpreted as primarily reflecting variations in the amounts of recycled atmospheric Ar. Despite extensive evidence for drastic geochemical heterogeneities at 14°N on the MAR, we observe no significant δ15N variation (average δ15N = -4.49 ± 1.40 ‰) across N-MORB and E-MORB samples. This is a fundamental constraint, as the absence of significant N isotope variations across the upper mantle may imply that sedimentary N (with a typical δ15N ∼+6‰) is not extensively introduced within this reservoir during subduction. We investigate several scenarios that could explain this observation, including a significant contribution of altered oceanic crust to the overall budget of subducting slabs, quantitative return of subducting sedimentary N to the Earth's surface by arc volcanism, and/or preferential transport/preservation of sedimentary N in the lower mantle source of oceanic island basalts.

Redox conditions across the Upper Cambrian of eastern Laurentia: Implications from geochemical proxies

The lower part of the Martin Point section (∼ 110 m - rhythmites) spans the uppermost Shallow Bay and lowermost Green Point formations (uppermost Franconian–lowermost Trempealeauan) of the Cow Head Group (western Newfoundland, Canada). It records two post-SPICE (Steptoean Positive Carbon Isotope Excursion) events marked by negative δ13Ccarb excursions (NL1 and NL2) that were also documented in South China. The petrographic and chemical screening of the investigated carbonate samples proves the preservation of at least near-primary geochemical signatures. The proxies of weathering (e.g., Mn, Fe, Al, and ∑REE), bioproductivity (e.g., δ13Corg, TOC, P, Ni, Zn, and Cu), and paleoredox (e.g., Cr, Th/U, Ce/Ce*) have been utilized to reconstruct the paleoenvironmental conditions during the post-SPICE events. The TOC, P, Ni, Cu, Cr, ∑REE, Mn, Fe, and U Ca-normalized profiles exhibit a positive pulse at the base of NL2 (upper negative δ13Ccarb excursion), followed by a drop. This might have resulted from shoaling organic-rich anoxic waters into an oxygenated shallow environment during transgression, which led to a negative shift in the δ13Ccarb and a decrease in TOC contents as well as an increase in the δ13Corg. The correlated enrichment in Zn and δ15Norg values and the Ce/Ce* around unity are consistent with the shoaling scenario. A similar scenario seems to be consistent with NL1 (lower negative δ13Ccarb excursion) although the lower resolution of correlated proxy variations makes the interpretations based on a few points and to be therefore taken with caution.