Trace Element and Isotope Systematics in Vent Fluids and Sulphides From Maka Volcano, North Eastern Lau Spreading Centre: Insights Into Three-Component Fluid Mixing

Back-arc spreading centres and related volcanic structures are known for their intense hydrothermal activity. The axial volcanic edifice of Maka at the North Eastern Lau Spreading Centre is such an example, where fluids of distinct composition are emitted at the Maka hydrothermal field (HF) and at Maka South in 1,525–1,543 m water depth. At Maka HF black smoker-type fluids are actively discharged at temperatures of 329°C and are characterized by low pH values (2.79–3.03) and a depletion in Mg (5.5 mmol/kg) and SO4 (0.5 mmol/L) relative to seawater. High metal (e.g., Fe up to ∼6 mmol/kg) and rare Earth element (REE) contents in the fluids, are indicative for a rock-buffered hydrothermal system at low water/rock ratios (2–3). At Maka South, venting of white smoke with temperatures up to 301°C occurs at chimneys and flanges. Measured pH values range from 4.53 to 5.42 and Mg (31.0 mmol/kg), SO4 (8.2 mmol/L), Cl (309 mmol/kg), Br (0.50 mmol/kg) and Na (230 mmol/kg) are depleted compared to seawater, whereas metals like Li and Mn are typically enriched together with H2S. We propose a three-component mixing model with respect to the fluid composition at Maka South including seawater, a boiling-induced low-Cl vapour and a black smoker-type fluid similar to that of Maka HF, which is also preserved by the trace element signature of hydrothermal pyrite. At Maka South, high As/Co (>10–100) and Sb/Pb (>0.1) in pyrite are suggested to be related to a boiling-induced element fractionation between vapour (As, Sb) and liquid (Co, Pb). By contrast, lower As/Co (<100) and a tendency to higher Co/Ni values in pyrite from Maka HF likely reflect the black smoker-type fluid. The Se/Ge ratio in pyrite provides evidence for fluid-seawater mixing, where lower values (<10) are the result of a seawater contribution at the seafloor or during fluid upflow. Sulphur and Pb isotopes in hydrothermal sulphides indicate a common metal (loid) source at the two vent sites by host rock leaching in the reaction zone, as also reflected by the REE patterns in the vent fluids.

Importance of the Spatial Distribution of Rare Earth Elements in the Bottom Sediments of Reservoirs as a Potential Proxy for Tracing Sediments Sources. A Case Study in the Dominican Republic

The geochemical composition of rare earth elements (REE) in the bottom sediments of two Dominican reservoirs and in soils from their catchments was studied to identify possible sources of the deposited materials. Knowledge of the origin of the sediments will serve to control the excessive rates of erosion and sedimentation that occur annually due to periodic extreme climatic events that promote excessive silting of the lakes, followed by loss of storage capacity and degradation of water quality. The REE contents of sediments and soils were normalized to the North American Shale Composite (NASC) and the ratio of light/heavy rare earths (LREE/HREE ratio), Ce and Eu anomalies, and some fractionation parameters were determined. The REE patterns are more homogeneous in the sediments, indicating uniform sedimentation in both deposits. The sediment data reflect depletion of REE from the sources, enrichment of light REE (LREE) and some middle REE (MREE), and positive Eu and Ce anomalies. All data were plotted in correlation diagrams between some fractionation parameters of light–middle–heavy REE and anomalies of Ce and Eu. The similarity of the ratios between these parameters in all samples and the overlap of data from soils and rocks on the sediment projection in the diagrams allowed a good discrimination of the main sources of the materials.

The Geochemistry and Ecotoxicity of Offshore New Zealand Phosphorites

<p>The New Zealand offshore seabed hosts diverse resources including phosphate rich rocks. Phosphate rock deposits on the Chatham Rise have been the focus of previous investigations into their composition and mining potential; however, the diversity of the geochemistry of phosphate deposits, including their wider distribution beyond the Chatham Rise, their trace metal budget, and potential for ecotoxicity, remain poorly characterised. This study addresses some of these gaps by presenting a geochemical investigation, including trace metals, for a range of phosphate nodules from across the Chatham Rise, Bollons Seamount and offshore southeastern South Island. Elutriate and reconnaissance bioaccumulation experiments provide insights into the potential for ecotoxic trace metal release and effects on biota should sediment disturbance through mining activities occur. The bulk chemistry of Bollons Seamount phosphorite nodules have been characterised for the first time, and show significant enrichment in first row transition metals; Co, Ni, Cu, Zn, in addition to Sr, Y, Mo, U, MnO, CaO and P2O5, and depletion in TiO2, Al2O3, MgO, K2O, FeO, SiO2, Sc, Cr, Ga, Rb, Cs, Hf, and Th relative to average upper continental crust. The cores of these nodules are dominated by apatite, quartz and anorthoclase phases, which are cross cut by Mn rich dendrites. The abundant presence of these minerals results in the significant differences in chemistry observed relative to Chatham Rise phosphorite nodules. The nodules also contain a secondary authigenic apatite phase, with a Mn crust rim. Significant rare earth element enrichment (REE) is most likely due to efficient scavenging by the Mn crust, resulting in seawater REE patterns characterised by negative Ce and Eu anomalies and heavy rare earth element enrichment. The bulk geochemistry of the Chatham Rise and offshore South Island phosphorite nodules is characterised by enrichment in CaO, P2O5, Sr, U, Y, Mo and depletion in TiO2, Al2O3, MnO, MgO, FeO, K2O, Sc, Cr, Cu, Ga, Rb, Cs, Ba, Hf, Ta, Pb and Th relative to average upper continental crust. The low concentrations of Cd in Chatham Rise, offshore South Island, and Bollons Seamount phosphorites make them potentially suitable sources for direct application fertilizers. The New Zealand marine phosphorite nodule deposits formed by repeated cycles of erosive bottom currents and phosphogenesis, resulting in the winnowing and concentration of the deposits. The iron pump model is proposed as a mechanism for the formation of apatite and associated mineral phases, giving the nodules their characteristic concentric zoning. The migration of the nodules through the oxic, suboxic, and anoxic zones of the sediment profile led to the formation of glaucony, apatite (suboxic zone), goethite (oxic zone), and pyrite with associated U enriched (anoxic zone) minerals. Rare earth elements (REE) in the Chatham Rise phosphorite nodules are associated with the glaucony rim minerals, and indicate that since the formation of the rims, very little diagenesis has occurred, preserving seawater REE patterns characterised by negative Ce and Eu anomalies and heavy REE enrichment. Site specific enrichments in trace elements Ba, V, Co, Ni, Cu, Zn, Y, Cd and Pb are attributed to either differences in incorporation of material into precursor carbonate e.g. volcanic materials, or higher fluxes of organic matter, delivering high concentrations of essential metals from biota, especially Cu and Zn. Direct pore water measurements from surficial sediment of the Chatham Rise show high concentrations of dissolved Fe and Mn, along with Cu, indicating suboxic conditions. High Cu concentrations measured in sediment pore water suggest that Cu release requires monitoring should seafloor surficial sediments on the Chatham Rise be disturbed. However, the elutriate experiments were not able to resolve if Cu release by sediment disturbance would exceed Australian and New Zealand Environment Conservation Council (2000) environmental guideline trigger values. The surrogate amphipod species Chaetocorophium c.f. lucasi shows promise as a biomonitor for disturbed marine sediments. Elements enriched in surficial sediments and phosphorite nodules, Hg, Pb, Fe, U and V, were not observed to bioaccumulate. Site specific differences in chemistry were observed, specifically in the different total relative bioaccumulation of Mo between amphipods exposed to sediments from two different sites. This suggests that future monitoring of chemical release during marine sediment disturbance requires the full geochemical characterisation of the substrate. Furthermore, fresh sediment and deep water should be used for future elutriate experiments, as storage of material by freeze-thawing and/or refrigeration causes mobilisation of some key trace metals such as U, V, Mo, Mn.</p>

The Geochemistry and Ecotoxicity of Offshore New Zealand Phosphorites

<p>The New Zealand offshore seabed hosts diverse resources including phosphate rich rocks. Phosphate rock deposits on the Chatham Rise have been the focus of previous investigations into their composition and mining potential; however, the diversity of the geochemistry of phosphate deposits, including their wider distribution beyond the Chatham Rise, their trace metal budget, and potential for ecotoxicity, remain poorly characterised. This study addresses some of these gaps by presenting a geochemical investigation, including trace metals, for a range of phosphate nodules from across the Chatham Rise, Bollons Seamount and offshore southeastern South Island. Elutriate and reconnaissance bioaccumulation experiments provide insights into the potential for ecotoxic trace metal release and effects on biota should sediment disturbance through mining activities occur. The bulk chemistry of Bollons Seamount phosphorite nodules have been characterised for the first time, and show significant enrichment in first row transition metals; Co, Ni, Cu, Zn, in addition to Sr, Y, Mo, U, MnO, CaO and P2O5, and depletion in TiO2, Al2O3, MgO, K2O, FeO, SiO2, Sc, Cr, Ga, Rb, Cs, Hf, and Th relative to average upper continental crust. The cores of these nodules are dominated by apatite, quartz and anorthoclase phases, which are cross cut by Mn rich dendrites. The abundant presence of these minerals results in the significant differences in chemistry observed relative to Chatham Rise phosphorite nodules. The nodules also contain a secondary authigenic apatite phase, with a Mn crust rim. Significant rare earth element enrichment (REE) is most likely due to efficient scavenging by the Mn crust, resulting in seawater REE patterns characterised by negative Ce and Eu anomalies and heavy rare earth element enrichment. The bulk geochemistry of the Chatham Rise and offshore South Island phosphorite nodules is characterised by enrichment in CaO, P2O5, Sr, U, Y, Mo and depletion in TiO2, Al2O3, MnO, MgO, FeO, K2O, Sc, Cr, Cu, Ga, Rb, Cs, Ba, Hf, Ta, Pb and Th relative to average upper continental crust. The low concentrations of Cd in Chatham Rise, offshore South Island, and Bollons Seamount phosphorites make them potentially suitable sources for direct application fertilizers. The New Zealand marine phosphorite nodule deposits formed by repeated cycles of erosive bottom currents and phosphogenesis, resulting in the winnowing and concentration of the deposits. The iron pump model is proposed as a mechanism for the formation of apatite and associated mineral phases, giving the nodules their characteristic concentric zoning. The migration of the nodules through the oxic, suboxic, and anoxic zones of the sediment profile led to the formation of glaucony, apatite (suboxic zone), goethite (oxic zone), and pyrite with associated U enriched (anoxic zone) minerals. Rare earth elements (REE) in the Chatham Rise phosphorite nodules are associated with the glaucony rim minerals, and indicate that since the formation of the rims, very little diagenesis has occurred, preserving seawater REE patterns characterised by negative Ce and Eu anomalies and heavy REE enrichment. Site specific enrichments in trace elements Ba, V, Co, Ni, Cu, Zn, Y, Cd and Pb are attributed to either differences in incorporation of material into precursor carbonate e.g. volcanic materials, or higher fluxes of organic matter, delivering high concentrations of essential metals from biota, especially Cu and Zn. Direct pore water measurements from surficial sediment of the Chatham Rise show high concentrations of dissolved Fe and Mn, along with Cu, indicating suboxic conditions. High Cu concentrations measured in sediment pore water suggest that Cu release requires monitoring should seafloor surficial sediments on the Chatham Rise be disturbed. However, the elutriate experiments were not able to resolve if Cu release by sediment disturbance would exceed Australian and New Zealand Environment Conservation Council (2000) environmental guideline trigger values. The surrogate amphipod species Chaetocorophium c.f. lucasi shows promise as a biomonitor for disturbed marine sediments. Elements enriched in surficial sediments and phosphorite nodules, Hg, Pb, Fe, U and V, were not observed to bioaccumulate. Site specific differences in chemistry were observed, specifically in the different total relative bioaccumulation of Mo between amphipods exposed to sediments from two different sites. This suggests that future monitoring of chemical release during marine sediment disturbance requires the full geochemical characterisation of the substrate. Furthermore, fresh sediment and deep water should be used for future elutriate experiments, as storage of material by freeze-thawing and/or refrigeration causes mobilisation of some key trace metals such as U, V, Mo, Mn.</p>

Dynamics of Rare Earths and associated major and trace elements during Douglas-fir (Pseudotsuga menziesii) and European beech (Fagus sylvatica L.) litter degradation

Given the diverse physico-chemical properties of elements, we hypothesize that their incoherent distribution across the leaf tissues, combined with the distinct resistance to degradation that each tissue exhibits, leads to distinct turnover rates between elements. Moreover, litter layers of different ages produce diverse chemical signatures in solution during the wet degradation. To verify our hypothesis, Na, K, Mg, Mn, Ca, Pb, Al and Fe were analysed together with the Rare Earth Elements (REE) in the solid fractions and in the respective leachates of fresh leaves and different humus layers of two forested soils developed under Pseudotsuga menziesii and Fagus sylvatica L. trees. The results from the leaching experiment were also compared to the in situ REE composition of the soil solutions to clarify the impact that the litter degradation processes may have on soil solution chemical compositions. Our results clearly show that REE, Al, Fe and Pb were preferentially retained in the solid litter material, in comparison to the other cations, and that their concentrations increased over time during the litter degradation. Accordingly, different litter fractions produced different yields of elements and REE patterns in the leachates, indicating that the tree species and the age of the litter play a role in the chemical release during the degradation. In particular, the evolution of the REE patterns according to the age of the litter layers allowed us to deliver new findings on REE fractionation and mobilization during litter degradation. In particular, the LaN/YbN ratio highlights differences in litter degradation intensity between both tree species, which was not shown with major cations. We finally showed the primary control effect that litter degradation can have on the REE composition of the soil solution, which presents a positive Ce anomaly associated with the dissolution and/or transportation of Ce-enriched MnO2 particles accumulated onto the surface of the old litter due to white fungi activity. Similar MREE and HREE enrichments were also found in the leachates and the soil solution, probably due to their higher affinity to the organic acids, which represent the primary products from the organic matter degradation.

Petrographic and geochemical features of Gimo marble, Gole area, Kurdistan Region, Iraq: constraints on its protolith's origin and depositional environment

It is essential to identify marbles' petrographic and geochemical characteristics to determine the palaeo-environmental settings where their carbonate protoliths formed. The petrogenesis of massive Gimo marbles in the Gole area, Kurdistan Region of northeast Iraq, was investigated in this study through a combination of field mapping, petrographic, and geochemical techniques. Petrographic examination of these marbles reveals that mineral compositions are similar in all samples, with both homeoblastic and mosaic textures occurring, in addition to opaque grains that provide evidence of mineralization. Geochemical analyses show that the average calcium carbonate content of the marble is 94.96%; hence, the marble is lithologically characterized as a pure calcite marble. In most samples, the silica content was below 2 wt.%, with high values related to quartz veinlets. A range of geochemical indices and Post-Archean Australian Shale (PAAS–normalized rare earth element (REE) patterns) suggest that the limestone protolith was deposited in a shallow, near-shore marine environment on a continental margin, with very low input of detrital material. The negative Ce anomalies indicate that the protoliths of the Gimo marbles were carbonate rocks of a sedimentary origin.

ZIRCON TRACE ELEMENT GEOCHEMISTRY AS AN INDICATOR OF MAGMA FERTILITY IN IRON OXIDE COPPER-GOLD PROVINCES

Extrusive and intrusive felsic magmas occur throughout the evolution of silicic-dominated large igneous province magmatism that is temporally related to numerous economically significant iron oxide copper-gold (IOCG) deposits in southern Australia. We investigate zircon trace element signatures of the felsic magmas to assess whether zircon composition can be related to fertility of the volcanic and intrusive suites within IOCG-hosted mineral provinces. Consistent with zircon forming in oxidizing magmatic conditions, the rare earth element (REE) patterns of zircon sourced from both extrusive and intrusive magmatic rocks are characterized by light REE depletions and a range of positive Ce and negative Eu anomalies. The timing of the major phase of IOCG mineralization overlaps with the early part of the first phase of Lower Gawler Range Volcanics magmatism (1593.6–1590.4 Ma) and older intrusive magmatism of the Hiltaba Suite (1593.06–1590.50 Ma). Zircon in these mineralization-related intrusives and extrusives is distinguished from zircon in younger, mineralization-absent rocks by higher Eu/Eu*, Ce/Ce*, and Ti values and separate magma evolution paths with respect to Hf. These zircon characteristics correspond to lower degrees of fractionation and/or crustal assimilation, more oxidizing magmatic conditions, and higher magmatic temperatures, respectively, in magmas coeval with mineralization. In this respect, we consider higher oxidation state, lower degrees of fractionation, and higher magmatic temperatures to be features of fertile magmas in southern Australian IOCG terrains. Similar zircon REE characteristics are shared between magmas associated with southern Australian IOCG and iron oxide-apatite (IOA) rhyolites from the St. Francois Mountains, Missouri, namely high Ce/Ce* and high Dy/Yb, indicative of oxidized and dry magmas, respectively. The dry and more fractionated nature of the IOCG- and IOA-associated magmas contrasts with the hydrous and unfractionated nature of fertile porphyry Cu deposit magmas. As indicated by high Ce/Ce* ratios, the oxidized nature is considered a key element in magma fertility in IOCG-IOA terrains. In both IOCG and IOA terrains, the trace element compositions of zircon are able to broadly differentiate fertile from nonfertile magmatic rocks.

Supplemental Material: Apatite fingerprints on the magmatic-hydrothermal evolution of the Daheishan giant porphyry Mo deposit, NE China

Figure S1: Harker diagrams illustrating major elemental variations of the porphyry and wall rock. QGP—Qiancuoluo granodioritic porphyry; QBG—Qiancuoluo biotite granodiorite; Figure S2: (a) Chondrite-normalized REE patterns and (b) primitive mantle (PM)-normalized spider diagrams of the porphyry and wall rock. Normalizing values are taken from S. Sun and McDonough (1989); Table S1: Whole-rock major and trace element compositions of the Qiancuoluo granodioritic porphyry (QGP) and Qiancuoluo biotite granodiorite (QBG) granites; Table S2: Whole-rock Sr-Nd compositions of the Qiancuoluo granodioritic porphyry (QGP) and Qiancuoluo biotite granodiorite (QBG); Table S3: Apatite major and trace elements (ppm) of the Qiancuoluo granodioritic porphyry (QGP) and Qiancuoluo biotite granodiorite (QBG); Table S4: Apatite Sr and Nd isotope data of the Qiancuoluo granodioritic porphyry (QGP) and Qiancuoluo biotite granodiorite (QBG); Table S5: Apatite U-Pb isotope data of the Qiancuoluo granodioritic porphyry (QGP) and Qiancuoluo biotite granodiorite (QBG).

Supplemental Material: Apatite fingerprints on the magmatic-hydrothermal evolution of the Daheishan giant porphyry Mo deposit, NE China

Figure S1: Harker diagrams illustrating major elemental variations of the porphyry and wall rock. QGP—Qiancuoluo granodioritic porphyry; QBG—Qiancuoluo biotite granodiorite; Figure S2: (a) Chondrite-normalized REE patterns and (b) primitive mantle (PM)-normalized spider diagrams of the porphyry and wall rock. Normalizing values are taken from S. Sun and McDonough (1989); Table S1: Whole-rock major and trace element compositions of the Qiancuoluo granodioritic porphyry (QGP) and Qiancuoluo biotite granodiorite (QBG) granites; Table S2: Whole-rock Sr-Nd compositions of the Qiancuoluo granodioritic porphyry (QGP) and Qiancuoluo biotite granodiorite (QBG); Table S3: Apatite major and trace elements (ppm) of the Qiancuoluo granodioritic porphyry (QGP) and Qiancuoluo biotite granodiorite (QBG); Table S4: Apatite Sr and Nd isotope data of the Qiancuoluo granodioritic porphyry (QGP) and Qiancuoluo biotite granodiorite (QBG); Table S5: Apatite U-Pb isotope data of the Qiancuoluo granodioritic porphyry (QGP) and Qiancuoluo biotite granodiorite (QBG).