REE geochemistry and Sr isotopic composition of silicate-carbonate rocks from the Zelentsovskaya mine (Kusa-Kopan intrusive complex, Southern Urals)

Geochemical characteristics of the Permian Changxing Formation reef dolomites, northeastern Sichuan Basin, China

Petrography, trace elements and oxygen and carbon isotopes of Gordon Group carbonates (Ordovician), Florentine Valley, Tasmania, Australia

Irradiance regulates genotype-specific responses of Rhizobium-nodulated soybean to increasing iron and two manganese concentrations in solution culture

The Aptian shallow-water carbonate platform of the Benassal Formation in eastern Spain (Maestrat Basin) contains facies dominated by scleractinian corals. Corals and coral reefs are widely used as environmental archives; however, the effects of their complex diagenetic evolution are a major factor impacting reliable reconstructions of the environments. This study addresses the environmental signatures (i.e. relative sea-level changes) and burial conditions that controlled the various diagenetic minerals present in the Aptian coral facies. A multiproxy approach including petrographic and geochemical evaluation reveals the diagenetic pathways, fluid compositions and timing accounting for the syn- to post-depositional history of this ancient coral facies. Cc1, which shows low Fe and Mn content and high Na content, precipitated within the primary porosity, alongside the replacement of coral skeletons, in a mixing zone dominated by marine waters. Cement Cc2, characterized by its higher Fe and Mn content and low Na values, precipitated in the mixing zone dominated by meteoric waters related to a relative sea-level drop. Cement Cc3, distinguished by low Fe and Mn content and high Na content, reflects a subsequent phase of increased marine influence, likely associated with a relative sea-level rise. Silica and isolated rhombohedral dolomite crystals formed concurrently in this mixing zone. During intermediate burial, saddle dolomite and cement Cc4 precipitated from high-temperature formation brines. Finally, during uplift, meteoric fluids caused the calcitization of previously formed dolomite rhombohedra.

Point analyses of natural calcite cements by SIMS confirm the earlier suggestions that 20 ppm Mn is required to activate luminescence, whereas Fe concentrations in excess of 1400 ppm quench it partly, independently of the Mn content. Below this Fe threshold, luminescence is bright at Mn concentrations in excess of 225 ppm. In the range 20-225 Mn, all types of luminescence--dull, luminescent, and nonluminescent--can occur. This undifferentiated domain is evident also from a compilation of literature data. The type of luminescence is not a simple function of Fe and Mn concentrations; other parameters influence CL. Sinc most diagenetic calcite cements have Fe and Mn concentrations that place them within the field of mixed cathodoluminescence, these results force reassessment of models that equate the type of luminescence with the redox state of the diagenetic environment.

Although health risk due to discoloured water is minimal, such water continues to be the source of one of the major complaints received by most water utilities in Australia. Elevated levels of iron (Fe) and/or manganese (Mn) in bulk water are associated with discoloured water incidents. The accumulation of these two elements in distribution systems is believed to be one of the main causes for such elevated levels. An investigation into the contribution of pipe wall biofilms towards Fe and Mn deposition, and discoloured water events is reported in this study. Eight laboratory-scale reactors were operated to test four different conditions in duplicate. Four reactors were exposed to low Fe (0.05 mg l−1) and Mn (0.02 mg l−1) concentrations and the remaining four were exposed to a higher (0.3 and 0.4 mg l−1 for Fe and Mn, respectively) concentration. Two of the four reactors which received low and high Fe and Mn concentrations were chlorinated (3.0 mg l−1 of chlorine). The biological activity (measured in terms of ATP) on the glass rings in these reactors was very low (∼1.5 ng cm−2 ring). Higher concentrations of Fe and Mn in bulk water and active biofilms resulted in increased deposition of Fe and Mn on the glass rings. Moreover, with an increase in biological activity, an increase in Fe and Mn deposition was observed. The observations in the laboratory-scale experiments were in line with the results of field observations that were carried out using biofilm monitors. The field data additionally demonstrated the effect of seasons, where increased biofilm activities observed on pipe wall biofilms during late summer and early autumn were found to be associated with increased deposition of Fe and Mn. In contrast, during the cooler months, biofilm activities were a magnitude lower and the deposited metal concentrations were also significantly less (ie a drop of 68% for Fe and 86% for Mn). Based on the laboratory-scale investigations, detachment of pipe wall biofilms due to cell death or flow dynamics could release the entrapped Fe and Mn into the bulk water, which could lead to a discoloured water event. Hence, managing biofilm growth on drinking water pipelines should be considered by water utilities to minimize accumulation of Fe and Mn in distribution networks.

Screening the edible parts of low-cadmium (Cd) and high-nutrient crop cultivars is an effective method for reducing Cd intake and enhancing the absorption of beneficial elements for humans. In a hydroponic experiment with Cd toxicity treatment (5 μmol/L CdCl2), we analyzed the differences in the absorption and transport characteristics of Cd and mineral nutrients in 30 rapeseed (Brassica napus L.) cultivars during the seedling stage, as well as the correlations between various elements. Firstly, Pearson correlation analysis indicated that Cd content in the shoot parts of 30 rapeseed cultivars was not correlated with the Cd uptake ability of the roots and was obviously positively correlated with the Cd translocation coefficient from root to shoot (r = 0.452 *, p < 0.05). Hierarchical clustering selected 26 cultivars with lower Cd content in the shoots, and correlation analysis of Cd and other nutrient element contents in the shoots of the 26 cultivars revealed significant negative correlations (r = −0.40 *, p < 0.05; r = −0.45 *, p < 0.05) between iron (Fe) and magnesium (Mg) content and Cd content, while potassium (K), calcium (Ca), manganese (Mn), and zinc (Zn) content had no correlation with Cd content. Then, hierarchical clustering screened 19 cultivars with higher dry weight, 4 cultivars with higher K content, 1 cultivar with higher Ca content, 8 cultivars with higher Mn content, and 3 cultivars with higher Zn content. Finally, a Venn diagram identified four superior rapeseed cultivars with lower Cd and higher nutrients in the shoots, namely, OJ114 (lower Cd, higher Mn and K content), BN365 (lower Cd, higher Mn, Fe, and Zn content), BN275 (lower Cd, higher Ca, Zn, Mn, and Fe content), and BN112 (lower Cd, higher K, Mg, Fe, and Mn content).

ABSTRACTPetrography demonstrates the presence of three types of fibrous calcite cement in buildup deposits of the Kullsberg Limestone (middle Caradoc), central Sweden. Translucent fibrous calcite has intrinsic blue luminescence (CL) indicative of pure calcite. This cement has 2–5 mol% MgCO3, low Mn and Fe (≤ 100 p.p.m.), and is considered to be slightly altered to unaltered, primary low‐ to intermediate‐Mg calcite. Grey turbid fibrous calcite has variable but generally low MgCO3 content (most analyses <2 mol%) and variable CL response, with Mn and Fe concentrations up to 1200 and 500 p.p.m., respectively. The heterogeneous characteristics of this variety of fibrous calcite are caused by diagenetic alteration of a translucent fibrous calcite precursor. Light‐brown turbid fibrous calcite has low MgCO3 (near 1 mol%) and variable Mn (up to 800 p.p.m.) and Fe (up to 500 p.p.m.) concentrations, with an abundance of bright luminescent patches, which formed during alteration caused by reducing diagenetic fluids. The δ13C and δ18O values of all fibrous calcite form a tight field (δ13C=1·7 to 3·1‰ PDB, δ18O= − 2·6 to − 4·1‰ PDB) compared with fibrous calcite isotope values from other units. Fibrous calcite δ18O values are larger than adjacent meteoric or burial cements, which have δ18O δ − 8‰ PDB. Consequently, most diagenetic alteration of Kullsberg fibrous calcite is interpreted to have occurred in the marine diagenetic realm. First‐generation equant and bladed calcite cements, which pre‐date fibrous calcite, are interpreted as unaltered, low‐Mg calcite marine cements based on δ13C and δ18O data (δ13C = 2·3 to 2·7‰ PDB, δ18O= − 2·8 to − 3·5‰ PDB). Unlike fibrous cement, which reflects global sea water chemistry, first‐generation equant and bladed calcite are indicators of localized modification of seawater chemistry in restricted settings. Kullsberg abiotic marine cements have larger δ18O values than most Caradoc marine precipitates from equatorial Laurentia. Positive Kullsberg δ18O values are attributed to lower seawater temperatures and/or slightly elevated salinity on the Baltic platform relative to seawater from which other marine precipitates formed.

Mississippi Valley-type (MVT) deposits contain about 20% of global zinc resources and host critical raw materials crucial to the development of green technologies. Despite their economic and strategic importance, there is a lack of consensus on the duration of mineralizing fluid flow events in MVT systems. This study couples in-situ U-Pb dating with Sr-isotope and trace element analysis of syn- and post-ore gangue carbonates to establish: (1) timing and duration, (2) redox evolution, and (3) flow rates of mineralizing fluids in the world-class San Vicente Zn-(Pb) deposit (Peru). New radiometric ages bracket the crystallization of syn-mineralization dolomite, characterized by high Fe and Mn contents and Sr isotopic values overlapping with that of host carbonates, between 103.2 ± 4.1 Ma and 70.6 ± 5.6 Ma. This age interval reveals a direct genetic relationship between flow of mineralizing fluids and late Cretaceous Andean compressional tectonics. Basinal fluid expulsion coeval with known tectonic events continues in the district until Pliocene times, driving episodic crystallization of post-ore hydrothermal carbonates between 61.6 ± 9.3 and 2.7 ± 0.2 Ma. The low Mn and Fe content and high 87Sr/86Sr values characteristic of these post-ore, bedding-parallel and cross-cutting carbonate veins indicate a colder, oxidized environment. Our findings highlight the contribution of paired carbonate geochemistry and U-Pb geochronology in drawing links between tectonic events, fluid expulsion and the waxing and waning of mineralization potential in foreland basins. The results of this study challenge our understanding of timescales in MVT systems and imply that anomalous metal enrichment in basinal fluids over a short temporal interval is not a necessary precondition to form economic-sized, sediment-hosted Zn-Pb deposits. Rather, it is the coexistence of a focused fluid flow in an interconnected aquifer with suitable metal depositional mechanisms over a prolonged period of time (106–107 yr) that allows precipitation of economic amount of base metals at a specific site in the upper crust.

Thermodynamic zonation in the black shale facies based on iron-manganese-vanadium content

The high REE contents (57,23-561,2 ppm) of thin-layered sulfide ores of the Talgan Cu-Zn massive sulfide deposit (South Urals) are related to the presence of REE minerals: galgenbergite, parisite, bastnesite, synchysite and xenotime, which were found for the first time in massive sulfide deposits of the Urals. These minerals occur in quartz-carbonate-chlorite matrix of sulfide layers, as well as pyrite nodules and sub- and euderal crystals. The chondrite-normalized REE patterns are enriched in LREEs relatively to HREEs and the presence of weak negative cerium and positive europium anomalies. The LREE contents decrease by an order of magnitude and the LREE and HREE contents become similar with decreasing amount of hyaloclastic material in sulfide layers. The REEs for the formation of REE minerals are derived from mixed carbonate-hyaloclastic and ore material during the formation of layered sulfide ores.

The Triassic pelagic carbonates of the Lagonegro Basin Units from the Southern Apennines fold and thrust belt (Italy) are often replaced by dolomites, which in some cases show fabric and petrographic characteristics typical of late burial saddle dolomites displaying zebra-like structures (Iannace et al., in press). The aim of this thesis was to carry out a systematic regional study on Lagonegro dolomites, both on outcrops and on subsurface samples (cuttings from oil wells), in order to define dolomites extent, timing relative to Southern Apennines tectonic history, and fluids origin, by means of a combination of field work, and petrographic and geochemical investigations. The Lagonegro Basin succession, together with the Apennine Platform successions, is now imbricated in a pile of nappes of the Southern Apennines chain. This latter is a NE-directed fold and thrust belt, formed by progressive collision between Afro-Adriatic and Eurasian plates during the Neogene (Mazzoli and Helman, 1994, and references therein), with the Apulian promontory representing the orogenic foreland. The classical restorations of the pre-orogenic (Triassic to Paleogene) palaeogeography of the Southern Apennines show that the African (Apulian) passive margin was characterized by the Meso-Cenozoic pelagic Lagonegro Basin, located between two coeval carbonate platforms, Apennine and Apulian platforms (Pescatore and Tramutoli, 1980; Mostardini and Merlini, 1986). The evolution of the Lagonegro Basin was punctuated by two massive dolomitization events, which generated two distinct dolomite types displaying different petrographic and geochemical features. A fine crystalline and fabric preservative dolomite crops out in the northern area (Molise, Campagna and San Fele-Mount Pierno), whereas a coarse crystalline and fabric destructive dolomite, showing zebra-like and hydrofracturing structures is present in the southern area (from Pignola to the high Val d’Agri). Geochemical data (enrichment in 18O in respect with typical Upper Triassic seawater values, high Sr and low Mn and Fe content, Sr isotopes consistent with Upper Triassic seawater) allow to interpret dolomites of the northern area as the result of an early replacement caused by cold, marine and oxidizing fluid, in a shallow burial. It is proposed that dolomitizing fluids were expelled through a reflux from the Norian Apenninic carbonate platform toward the proximal Lagonegro Basin, or alternatively they were put into motion through a Kohout convection of seawater, heated thanks to a geothermal anomaly. Dolomites located in the southern area, display a depletion in 18O compared to Upper Triassic seawater values and show lower Sr, higher Mn and Fe contents, and higher Sr isotopes ratios in respect with early dolomites of the northern area. It is suggested that the southern area was affected, during Neogene time, by a late burial dolomitization, which was the result of a large scale “squeegee” fluid flow during Southern Apennines fold and thrust belt formation. The geochemistry of saddle dolomite samples indicates an origin by warm fluids (105-125 °C). Integration with available thermal data (Corrado et al., 2005; Mazzoli et al., 2008) into the regional deformation history, by assuming a fluid in thermal equilibrium with the host rocks, suggests that the fluid flow took place after maximum burial, in early stages of exhumation, between 5 and 4 Ma and under 3-4 km of burial. The dolomitizing fluids of southern area dolomites had salinities in the range of slightly modified to normal marine seawater (1.9-6.4 eq. wt % NaCl with a mean of 3.7) and oxygen isotopic composition typical of saline formation waters. Two possible sources for such fluids can be envisaged. They could be formation waters, diluted with fresh waters delivered during the smectite-illite transformation at depth, squeezed out from the surrounding Triassic and Cretaceous fine-clastic formations or Miocene marine pore-waters expelled from the melange zone that separates the allochthonous wedge from the buried Apulian platform. The fluid flow event was a major phenomenon affecting the fold and thrust belt and it could be expected that the dolomite bodies which are reported in the Apulian subsurface (Murgia et al., 2004) might have the same origin of Lagonegro dolomites from the southern area. As the carbonates of the Apulia platform host major oil fields of continental Europe, the fluid flow that took place along with Southern Apennines belt formation could be of economic significance, providing secondary porosity development.

Massive dolomitization does not commonly occur in deep-water carbonates. However, this regional study on outcrops and subsurface samples of Triassic Lagonegro basinal carbonates from the southern Apennines fold and thrust belt (Italy) shows that the evolution of the Lagonegro basin was punctuated by two events of massive dolomitization. These processes resulted in two distinct dolomite types, displaying different petrographic and geochemical features. A medium-crystalline and fabric-preservative dolomite in the northern area (Molise, Campagna, and San Fele–Mount Pierno) contrasts with a medium- to coarse-crystalline and fabric-destructive dolomite in the southern area (from Pignola to the high Val d'Agri). Geochemical data (increase in δ18O with respect to typical Late Triassic seawater values, high Sr and low Mn and Fe content, Sr isotopes consistent with Late Triassic seawater) indicate that the dolomite in the northern area is the result of an early replacement caused by a marine and possibly oxidizing fluid during shallow burial. Dolomitizing fluids likely were expelled through reflux from the Norian Apenninic carbonate platform towards the proximal Lagonegro basin. This reflux was promoted by the Norian peculiar paleoceanographic and climatic conditions in the Tethyan region, and affected only the proximal basinal facies. Dolomites in the southern area display a decrease in δ18O compared to Late Triassic seawater values and show lower Sr, higher Mn and Fe contents, and higher Sr isotope ratios compared to the early dolomites of the northern area. Fluid-inclusion microthermometry reveals homogenization temperatures between 70 and 120°C and salinities of 1.9 to 6.4 wt % NaCl eq. for saddle dolomites. These geochemical signatures indicate that the southern area was affected by late diagenetic burial dolomitization, interpreted to be the result of large scale tectonically driven fluid flow during the second compressional phase characterizing the southern Apennines fold and thrust belt emplacement. The dolomite distribution across the Lagonegro basin (northern and southern) is possibly controlled by the paleogeographic distribution of the facies (proximal vs. distal) as well as by their proximity to thrust faults. The Lagonegro case study demonstrates that basinal successions may undergo multiple dolomitization episodes in a manner similar to carbonate platform successions, from early shallow to deep-burial diagenesis. One of the relevant implications is that in areas of restricted oceanographic circulation, during periods of aridity, reflux dolomitization may extend beyond the platform margin, into deep-water carbonates, having the potential to alter their reservoir quality.

Apatite can be used as an archive of processes occurring during the evolution of granitic magmas and as a pegmatite exploration tool. With this aim, a detailed compositional study of apatite was performed on different Variscan granites, pegmatites and quartz veins from the Central Iberian Zone. Manganese in granitic apatite increases with increasing evolution degree. Such Mn increase would not be related to changes in the fO2 during evolution but rather to a higher proportion of Mn in residual melts, joined to an increase in SiO2 content and peraluminosity. In the case of pegmatitic apatite, the fO2 and the polymerization degree of the melts seem not to have influenced the Mn and Fe contents but the higher availability of these transition elements and/or the lack of minerals competing for them. The subrounded Fe-Mn phosphate nodules, where apatite often occurs in P-rich pegmatites and P-rich quartz dykes, probably crystallized from a P-rich melt exsolved from the pegmatitic melt and where Fe, Mn and Cl would partition. The low Mn and Fe contents in the apatite from the quartz veins may be attributed either to the low availability of these elements in the late hydrothermal fluids derived from the granitic and pegmatitic melts, or to a high fO2. The Rare Earth Elements, Sr and Y are the main trace elements of the studied apatites. The REE contents of apatite decrease with the evolution of their hosting rocks. The REE patterns show in general strong tetrad effects that are probably not related to the fluids’ activity in the system. On the contrary, the fluids likely drive the non-CHARAC behavior of apatite from the most evolved granitic and pegmatitic units. Low fO2 conditions seem to be related to strong Eu anomalies observed for most of the apatites associated with different granitic units, barren and P-rich pegmatites. The positive Eu anomalies in some apatites from leucogranites and Li-rich pegmatites could reflect their early character, prior to the crystallization of feldspars. The increase in the Sr content in apatite from Li-rich pegmatites and B-P±F-rich leucogranites could be related to problems in accommodating this element in the albite structure, favoring its incorporation into apatite. The triangular plots ΣREE-Sr-Y and U–Th–Pb of apatites, as well as the Eu anomaly versus the TE1,3 diagram, seem to be potentially good as petrogenetic indicators, mainly for pegmatites and, to a lesser extent, for granites from the CIZ.

Boggulakonda gabbroic complex (BKGC) (E 80°00'30, N 15°44'04) in the Prakasam Igneous Province (PIP) (southern India) is studied in detail using major, trace, REE and PGE geochemistry to understand its geochemical evolution. It shows sharp contact relationships with the Precambrian quartzofeldspathic mica schist and granite gneisses. It is one among the several gabbroic complexes, occurring to the east of Cuddapah basin, along the eastern margin of Nellore schist belt. It is predominantly composed of gabbro and gabbronorite with melanocratic to leucocratic variations. Petrographic studies show cumulus, poikilitic and porphyritic textures, micro-deformation features and symplectites/replacement textures. Magnetite and ilmenites are dominant opaques with subordinate pyrite and chalcopyrite. Cumulus phases of plagioclase, Cpx, are essential minerals whereas olivine, opx, amphibole and opaques appear as intercumulus phases. These rocks are classified as sub-alkaline, low Ti-tholeiitic gabbros. The normative compositions indicate that these rocks are quartz, plagioclase and pyroxene normative. The differentiation index (D.I.) determined from the norm compositions are in the range of 11.4 to 20.9 indicating that they are early-middle stage basaltic differentiates. These studies also indicate fractional crystalization was a dominant process of their genesis. The major, incompatible trace and REE geochemistry of BKGC rocks show LILE-LREE enrichment and HREE-HFSE depletion, pronounced Eu-positive anomalies, negative Nb anomalies relative to Th and low Ti/V ratios. Based on the above and other binary plots, it can be inferred that the BKG rocks are the products of ∼5-15% partial melting of depleted mantle source strongly modified by the melt enrichment and addition of slab derived fluids in a subduction zone environment and emplaced as tholeiitic island arc magmas. BK gabbroic rocks indicate low abundances of PGE. PPGE's are greater than IPGE; Pd/Ir and Pd/Pt ratios are greater than primitive mantle and chondrites. PGE geochemistry correlate well with the petrogenesis and tectonic discrimination studies made by using major, trace and REE geochemistry.