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.

Depositional Environment and Genesis of the Nabeba Banded Iron Formation (BIF) in the Ivindo Basement Complex, Republic of the Congo: Perspective from Whole-Rock and Magnetite Geochemistry

The Nabeba high-grade iron deposit (Republic of the Congo) is hosted by banded iron formation (BIF) in the Ivindo Basement Complex, which lies in the northwestern part of the Congo Craton. The Nabeba BIF is intercalated with chlorite-sericite-quartz schist and comprises two facies (oxide and a carbonate-oxide). In this study, whole-rock and LA-ICP-MS magnetite geochemistry of the BIF was reported. Magnetite samples from both BIF facies had fairly similar trace element compositions except for the rare earth element plus yttrium (REE + Y) distribution patterns. The high V, Ni, Cr, and Mg contents of the magnetite in the Nabeba BIF could be ascribed to the involvement of external medium-high temperature hydrothermal fluids during their deposition in relatively reduced environment. The Post-Archean Australian Shale (PAAS)-normalized REY patterns of the Nabeba BIF magnetite were characterized by LREE depletion coupled with varying La and positive Eu anomalies. Processing of the information gathered from the geochemical signatures of magnetite and the whole-rock BIF suggested that the Nabeba BIF was formed by the mixing of predominantly anoxic seawater (99.9%) with 0.1% of high-temperature (>250 °C) hydrothermal vent fluids, similar to the formation mechanism of many Archean Algoma-type BIFs reported elsewhere in the world.

Paleogeographic Characteristics of the Mengyejing Formation in the Simao Basin during Its Depositional Period and Its Indication of Potash Mineralization: A Case Study of MZK-3 Well

In China, pre-Quaternary solid potash deposit has only been discovered in the Simao Basin, and the Lower Cretaceous Mengyejing (MYJ) Formation (Fm.) is the productive layer of potash deposit. In this study, we investigated the clay conglomerates which are distributed in upper and lower members of the potash-bearing salt rock layer. We analyzed the relative contents of major elements (Al2O3, Fe2O3T, MgO, CaO, Na2O, K2O) and trace elements (B, Ba, Co, Cr, Cu, Ga, Mn, Ni, Rb, Sr, V, Zn, Zr) in the samples. The results show that MgO and CaO in the major elements are rich relative to Post Archean Australian Shale (PAAS), whose average enrichment factor values of the MgO (EFMgO) is 2.61 and CaO (EFCaO) is 4.57, and the others major elements are relatively minor; trace elements (B, Ga, Mn, Zr) are rich relative to PAAS, and the others trace elements are minor relative to PAAS. The study of paleogeographic conditions using various parameters shows that the paleoclimate is generally dry and hot during the period of clay conglomerate deposition, but it was warm and humid in certain periods; the main sedimentary environment is weak oxidation condition with strong oxidation conditions in individual periods; the average value of paleosalinity is ~21‰, and the highest is no more than ~92‰. The significance of the paleogeographic characteristics of MYJ Fm. to potash mineralization are as follows: (1) they indicates that the clay conglomerates of MYJ Fm. are not clastic sediments in brine formed by seawater, because the paleosalinity of clay conglomerates deposition period is obviously lower than that of seawater; (2) MYJ potassic salt ore is not formed by evaporation and concentration of seawater in clay conglomerates in the sedimentary basin, because there is no carbonate rock and sulfate rock of corresponding scale after the deposition of clay conglomerates in the basin; (3) clay conglomerates of MYJ Fm. were deposited in continental shallow water basin; (4) the matter source of potash minerals is deep marine strata; (5) in the MYJ Fm. sedimentation period, deep source salt moved to the surface under the background of extensional structure, and the subsequent sedimentary clastic rock formed a protective layer of potash-bearing rock, thus completing the “deep source and shallow mineralization” metallogenic process.

Stratigraphy and lithogeochemistry of the Goldenville horizon and associated rocks, Baie Verte Peninsula, Newfoundland

The Goldenville horizon in the Baie Verte Peninsula is an important stratigraphic horizon that hosts primary (Cambrian to Ordovician) exhalative magnetite and pyrite and was a chemical trap for younger (Silurian to Devonian) orogenic gold mineralization. The horizon is overlain by basaltic flows and volcaniclastic rocks, is intercalated with variably coloured argillites and cherts, and underlain by mafic volcaniclastic rocks; the entire stratigraphy is cut by younger fine-grained mafic dykes and coarser gabbro. Lithogeochemical signatures of the Goldenville horizon allow it to be divided into high-Fe iron formation (HIF; >50% Fe2O3), low-Fe iron formation (LIF; 15-50% Fe2O3), and argillite with iron minerals (AIF; <15% Fe2O3). These variably Fe-rich rocks have Fe-Ti-Mn-Al systematics consistent with element derivation from varying mineral contributions from hydrothermal venting and ambient detrital sedimentation. Post-Archean Australian Shale (PAAS)-normalized rare earth element (REE) signatures for the HIF samples have negative Ce anomalies and patterns similar to modern hydrothermal sediment deposited under oxygenated ocean conditions. The PAAS-normalized REE signatures of LIF samples have positive Ce anomalies, similar to hydrothermal sediment deposited under anoxic to sub-oxic conditions. The paradoxical Ce behaviour is potentially explained by the Mn geochemistry of the LIF samples. The LIF have elevated MnO contents (2.0-7.5 weight %), suggesting that Mn from hydrothermal fluids was oxidized in an oxygenated water column during hydrothermal venting, Mn-oxides then scavenged Ce from seawater, and these Mn-oxides were subsequently deposited in the hydrothermal sediment. The Mn-rich LIF samples with positive Ce anomalies are intercalated with HIF with negative Ce anomalies, both regionally and on a metre scale within drill holes. Thus, the LIF positive Ce anomaly signature may record extended and particle-specific scavenging rather than sub-oxic/redox-stratified marine conditions. Collectively, results suggest that the Cambro-Ordovician Taconic seaway along the Laurentian margin may have been completely or near-completely oxygenated at the time of Goldenville horizon deposition.

Stratigraphy and lithogeochemistry of rocks from the Nugget Pond Deposit area, Baie Verte Peninsula, Newfoundland

Stratigraphic and lithogeochemical data were collected from selected drill core from the Nugget Pond gold deposit in the Betts Cove area, Newfoundland. The stratigraphy consists of a lower unit of basaltic rocks that are massive to pillowed (Mount Misery Formation). This is overlain by sedimentary rocks of the Scrape Point Formation that consist of lower unit of turbiditic siltstone and hematitic cherts/iron formations (the Nugget Pond member); the unit locally has a volcaniclastic rich-unit at its base and grades upwards into finer grained volcaniclastic/turbiditic rocks. This is capped by basaltic rocks of the Scrape Point Formation that contain pillowed and massive mafic flows that are distinctively plagioclase porphyritic to glomeroporphyritic. The mafic rocks of the Mount Misery Formation have island arc tholeiitic affinities, whereas Scrape Point Formation mafic rocks have normal mid-ocean ridge (N-MORB) to backarc basin basalt (BABB) affinities. One sample of the latter formation has a calc-alkalic affinity. All of these geochemical features are consistent with results and conclusions from previous workers in the area. Clastic sedimentary rocks and Fe-rich sedimentary rocks of the Scrape Point Formation have features consistent with derivation from local, juvenile sources (i.e., intra-basinal mafic rocks). The Scrape Point Formation sedimentary rocks with the highest Fe/Al ratios, inferred to have greatest amount of hydrothermally derived Fe, have positive Ce anomalies on Post-Archean Australian Shale (PAAS)-normalized trace element plots. These features are consistent with having formed via hydrothermal venting into an anoxic/ sub-oxic water column. Further work is needed to test whether these redox features are a localized feature (i.e., restricted basin) or a widespread feature of the late Cambrian-early Ordovician Iapetus Ocean, as well as to delineate the role that these Fe-rich sedimentary rocks have played in the localization of gold mineralization within the Nugget Pond deposit.

Reservoir-river-sea system sediment geochemistry in Fiumi Uniti catchment from Apennines to Adriatic Sea

<p>Sediment samples were collected in 2019 from Fiumi Uniti catchment in Italy in an area between the Romagna Apennines and the Adriatic Sea. The sampling phase included the collection of sediments from the Ridracoli reservoir, a large artificial basin located at 480 m a.s.l. made by construction of a dam on the Bidente river and used as the main drinking water supply of the region and for hydropower production, as well as river sediments within the whole catchment that includes the dam (Bidente, Ronco and Fiumi Uniti rivers and tributaries) and marine sediments from the Adriatic sea. In addition, we collected in the reservoir area rock and soil samples to define the element behaviour during weathering and transport.</p><p>Here we report data on chemical concentrations from different matrices within the area of Ridracoli reservoir as well as chemical characterization of sediments downstream the dam along the rivers. The chemical analyses were carried out at the State Key Laboratory of Marine Geology in Shanghai, where samples underwent a two-step digestion to assess the mobile and residual fraction using a first leaching step with 1N HCl and a second one with pure HNO<sub>3</sub> and HF, respectively.</p><p>The chemical differences between rock, soils and sediments inside the reservoir showed a system of element mobility that can be compared to the geochemistry of surrounding sediments to assess pathways of geochemical cycles of elements. The ratio between concentrations of different matrices shows an enrichment in soils compared to rock for some elements (>1.3; Li, V, Cr, Mn, Sr, Cd, U) and slightly depletion in lake sediments compared to rocks (0.8-0.9). The REE ratio between lake sediments and other matrices (i.e., rocks, soils, and stream sediments) equals to 0.7-0.8, while for other trace elements (Li, V, Mn, Fe, Ni) is 1.1-1.2 showing an opposite behaviour.</p><p>More mobile elements assessed using the ratio between the first step of leaching and the total composition, are Mn (0.7 of extractability) and Sr (0.8) followed by Co, Cu, Se Cd and Pb (around 0.3-0.4). The more stable elements (higher in the residual) are Ti, Rb, Zr, Cs (max 0.015). Cu and Pb seems to be more mobile in sediments than rock and soil, whereas the mobility of other analytes doesn’t seem to be affected by the different matrices. REE are quite mobile showing good extractability for Eu, Gd, Tb, Dy. Spider diagrams of REE were normalized to PAAS (Post Archean Australian Shale) and show similar shapes with Gd peaks. A difference can be seen between rocks (values around 0.8 and 1.2) and sediments, with the latter showing higher values (1.2 and 1.4).</p><p>The importance of this study relies on the implications that human activities have on river systems thanks to sediment quality and on the functioning of the river-sea system in Romagna and specifically in Ridracoli reservoir catchment.</p>

Particulate Rare Earth Element behavior in the North Atlantic (GEOVIDE cruise)

Particulate concentrations of the fourteen Rare Earth Elements (PREE), yttrium and 232-thorium have been measured in two hundred samples collected in the epipelagic (ca. 0–200 m) and the mesopelagic (ca. 200–1000 m) zones of the North Atlantic, during the GEOVIDE cruise (May/June 2014, R/V Pourquoi Pas ?, GEOTRACES GA01). Particulate cerium (PCe) concentrations vary from 0.2 pmol L−1 to 16 pmol L−1, particulate neodymium (PNd) ones from 0.09 pmol L−1 to 6.1 pmol L−1 and particulate ytterbium (PYb) ones from 0.01 pmol L−1 to 0.5 pmol L−1. PREE concentrations are higher close to the Iberian margin and on the Greenland shelf, where PREE concentrations normalized to Post Archean Australian Shale (PAAS) display a positive Ce anomaly between 0.3 and 3, and a light REE (LREE) enrichment compared to heavy REE (HREE) illustrated by high PNdN/PYbN ratios (normalized to PAAS). The lithogenic fraction of the particulate REE concentration is closely related to the margin morphology and the hydrodynamic context: off the Iberian margin, up to 100 % of the PREEs are lithogenic and this lithogenic input spreads westward along isopycnals as intermediate nepheloid layers (INL) up to 1700 km away. Lithogenic inputs are also observed along the Greenland and Newfoundland margins, although the circulation stacks them along the coasts. PREE distributions are also controlled by the biological uptake in the surface layers and remineralization processes deeper. Low surface concentrations and some normalized REE patterns displaying a negative Ce anomaly and HREE enrichment indicate freshly formed biogenic particles. A significant relationship between biogenic silica (BSi) and PHREE is also observed in the diatom blooms occurring in the Labrador and Irminger seas. PHo/PY ratio was calculated in order to identify processes independent of the ionic radius. However, we could not firmly assess the role of the iron hydroxides in the scavenging prates of these elements.

Geochemical characteristics of Upper Jurassic – Lower Cretaceous platform carbonates in Hazine Mağara, Gümüşhane (northeast Turkey): implications for dolomitization and recrystallization

The Upper Jurassic – Lower Cretaceous Berdiga Formation of the Eastern Pontides, Turkey, represents a carbonate platform succession composed of pervasively dolomitized intra-shelf to deep-shelf facies. In this area, polymetallic deposits occur as veins and lenses within the Berdiga Formation in close proximity to its upper contact with the overlying formation. Three different types of replacive dolomites occur in the formation: (i) microcrystalline dolomite, (ii) fabric-preserving dolomite, and (iii) fabric-destructive dolomite. Replacive dolomites are Ca rich and nonstoichiometric (Ca56–58Mg42–44) and are characterized by a pronounced negative shift in oxygen (–11.38‰ to –4.05‰ Vienna Pee Dee Belemnite (VPDB)), δ13C values of 0.69‰ to 3.13‰ VPDB, radiogenic 87Sr/86Sr ratios (0.70753 to 0.70884), and extremely high Fe (2727–21 053 ppm) and Mn (1548–27 726 ppm) contents. All dolomite samples have low Y/Ho ratios (23–40), and they also contain highly variable contents of rare earth elements (REE) (7–41). REE patterns of dolomites normalized to Post-Archean Australian shale show a distinct positive Eu anomaly (1.3–2.1) and slightly flattened Ce anomalies (0.8–1.1). Integration of petrographic and geochemical studies reveals the history of a variety of diagenetic processes highly affected by hydrothermal alteration, which include dolomitization, recrystallization, dissolution, silicification, and pyrite mineralization associated with the emplacement of the polymetallic mineralization.

Iron and silica enrichments in the middle Albian neptunian dykes from the High-Tatric Unit, Central Western Carpathians: an indication of hydrothermal activity for an extensional tectonic regime

Studies dealing with the response of subaqueous volcanic and hydrothermal activities to carbonate sedimentation in hemipelagic environments affected by tectonic processes are comparatively rare. Here, a microfacies record with combined chemical data from the neptunian dykes found at an intrabasinal ridge (Tatric Ridge; Carpathian domain of the Western Tethys), close to a source of alkaline volcanism with possible hydrothermal vents (Zliechov Basin), is presented. The characteristic features of the neptunian dykes, up to 20 cm thick, in the middle Albian echinoderm-foraminiferal limestones (Tatra Mountains, Inner Carpathians) are their red fillings. Microprobe and x-ray diffraction analyses show that this reddish material, partly mixed with sparitic clasts coming from the host limestone, consists mainly of hematite crystals which are associated with low crystalline silica and quartz. The microfacies data suggest that the reddish infillings of the dykes is partly related to dissolution processes inside the fissures that could have taken place during the transport of FeCl3 fluids together with silica gel. The fluids could have been derived from hydrothermal vents occurring along the extensional faults in the neighbouring Zliechov Basin. Rare Earth element (REE) signatures of the reddish infill (i.e. low values of total REE content, chondrite- and Post-Archean Australian Shale-normalized REE + Y patterns with negative Ce anomaly) and a high Y/Ho ratio suggest authigenic removal of REEs from the water column. This suggests that the fissures were open to the sea bottom and were in contact with sea water during their filling.