Types Of Deposits Research Articles

The Role of Reductive Carbonaceous Surrounding Rocks in the Formation of Porphyry Mo Deposits

Porphyry Mo deposits are the most important type of Mo resource. They result from a high oxygen fugacity of the parent magma, which acts as an effective indicator for evaluating the mineralization. In the ore-forming system of porphyry Mo deposits, sulfur exists mainly as sulfate in highly oxidized magma but as sulfide in ores. What triggers the reduction in the mineralization system that leads to sulfide precipitation has not yet been determined. Most of the previous studies have focused on the origin and evolution of the ore-forming parent magma, and the effects of reductive surrounding rocks on porphyry mineralization have been ignored. In this study, a comprehensive geological–geochemical investigation and review have been performed on the typical porphyry Mo deposits, the Nannihu-Sandaozhuang, Yuchiling, and Shapingou deposits in China, and the Mt. Emmons deposits in America. Black carbonaceous sedimentary layers commonly surround porphyry Mo ores, which are widely altered and discolored during mineralization. CH4 is commonly present in fluid inclusions in the main mineralization stage, and the δ13CV-PDB values of calcite and fluid inclusions from the altered surrounding rocks and ore minerals are generally low and significantly different from those of marine sedimentary carbonate rocks, indicating that the involvement of reductive components from carbonaceous surrounding rocks might be key to the redox state transformation leading to mineral precipitation. On the other hand, the CH4 produced by the thermal decomposition of organic matter or carbonaceous reaction with H2O can diffuse into the ore-forming system along the structural fractures and reduce the SO42− in the ore-forming hydrothermal fluids to form sulfide precipitation without direct contact between the intrusion and the carbonaceous surrounding rocks. Moreover, the CH4 content controls the location of the orebody formation with the high content producing orebodies mainly in the porphyry intrusion, while the low CH4 content results in the orebodies mainly occurring at the contact zone between the porphyry and carbonaceous surrounding rocks. Compared to the magmatic stage of mineralization, the involvement of reductive components in the carbonaceous surrounding rocks during the hydrothermal stage is more favorable for forming giant/large Mo deposits. The highly oxidized porphyry with reductive carbonaceous surrounding rocks or Fe-rich volcanic rocks offers a new indicator for efficiently evaluating porphyry Mo mineralization.

Discovery of the large-scale Eocene Xiwu Pb–Zn–Ag deposit in the Tethyan Himalaya: Geochronology, geochemistry, and C–H–O–S–Pb–Sr–Nd isotopes

The known Pb–Zn–Sb–Au polymetallic deposits in the Himalaya mainly formed during the main-collisional convergence (65–41 Ma) and post-collisional crustal extension (25–0 Ma) tectonic settings. Here, we report the discovery and genesis of the large-scale Eocene Xiwu Pb–Zn–Ag deposit that formed during the late-collisional tectonic transition stage (40–26 Ma) in the eastern Himalaya. The surrounding ore-hosting rocks are mainly low-grade metamorphosed Jurassic clastic rocks and Early Cretaceous diabase. The most important ore-controlling structures are NE–SW thrust faults. The ore minerals include large amounts of galena, sphalerite, tetrahedrite and siderite, with minor chalcopyrite, pyrite, arsenopyrite, calcite and quartz. In this contribution, we analyzed the S–Pb isotopes of sulfides, fluid inclusions and the C–H–O–Pb–Sr–Nd isotopes of nonmetallic minerals. The results indicate that the ore-forming materials originated from deeper metamorphic rocks of the Greater Himalayan Crystalline Complex. This study infer that the source of ore-forming fluids was mainly metamorphic fluids with moderate temperatures and salinities, and S and C were mainly derived from microbial sulfate reduction and the decarboxylation of organic matter, respectively. The main ore-forming mechanism is fluid mixing between the deep ore-bearing metamorphic fluids and shallow formation waters. The Sm–Nd isotopic age of siderite is 37.4 ± 1.1 Ma, which is slightly younger than the zircon U–Pb age of the Zhunba leucogranite (38.9 ± 0.4 Ma) but is consistent with the main epoch of early prograde metamorphism (43–36 Ma) in the Himalaya. We propose a new metallogenic model for Himalayan Pb–Zn–Ag deposits that can greatly promote ore prospecting. The genetic type of the Xiwu deposit is a clastic-dominated subtype of sediment-hosted Pb–Zn deposits.

Structural, Optical, and Chemical Characteristics of High‐Quality PbI2 Thin Films via Chemical Solution Deposition with Thermal Annealing

Herein, a synthesis method for obtaining lead iodide through chemical bath deposition, a type of chemical solution deposition without the use of organic solvents, is presented; the process consists of three stages. In the first stage, tin hydroxide films are produced which act as a seed layer allowing for a better adherence of the film that is to be deposited. The second stage consists of the synthesis of the lead iodide films. Finally, annealing is done (100, 150, and 200 °C) with the purpose of promoting the polytypic transitions of the material and to study the effect of these structures on the properties of the material. Assessment of the structural and optical properties of the films is done by means of scanning electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, optical spectroscopy, Raman spectroscopy, and transmission electron microscopy, where a direct influence of the annealing in the induction of polytypes is observed. The resultant PbI2 films have a large‐area coverage across the substrate, wide‐bandgap (2.38 eV), and a structure that belongs to the 2H and 4H polytypes. Hence, it is suggested from these results that the chemically deposited PbI2 thin films are promising candidates for large‐area optoelectronic applications.

The role of metallogenic research in predicting promising territories: From models to objects

The possibilities of academic basic metallogenic research in the forecast and search for various types of ore deposits are shown with the example of various academic institutes in the Siberian and Far East federal districts. Using a complex of mineralogical–geochemical and geological–structural methods, prospects for copper and gold in the Upper Indigirka and Kolyma regions and specific areas in Transbaikalia and the Bodaibo district of Irkutsk oblast have been studied. Problems in assessing and developing the mineral resource base of the regions are considered.

Middle Visean (Mississippian) conodonts from shallow-water deposits in the Yashui section, Guizhou, South China, and their stratigraphic significance

AbstractThe typical Mississippian shallow-water deposits of the Jiusi and Shangsi formations are well exposed in the Yashui section in southern Guizhou, South China. The strata are composed mainly of platform limestones intercalated with shales and sandstones. Conodonts obtained from the limestones are dominated by two assemblages of cavusgnathids: the Cavusgnathus aff. Cav. unicornis and Clydagnathus windsorensis assemblage from the upper Jiusi Formation and the Cavusgnathus unicornis assemblage from the lowest Shangsi Formation. Vogelgnathus campbelli (Rexroad, 1957) is reported for the first time in Eastern Paleotethys and is characterized by small lateral denticles. The evolutionary first occurrence of Cavusgnathus unicornis Youngquist and Miller, 1949 is recognized as a marker for the regional Shangsian stage. This biostratigraphic datum is interpreted to be correlative with other shallow-water conodont zones marked by Cavusgnathus unicornis s.l. and similar species from North America and Europe.

Laboratory experiments on the sublimation of methane through ice dust layers and applications to cometary activity

Context. Comets are small celestial bodies made of ice, dust, and rock that orbit the Sun. Understanding their behavior as they warm up at perihelion unveils many pieces of information about the interior and general morphology of the ices hidden under the dust. Aims. The goal of this research is to study the sublimation of CH4 through amorphous solid water (ASW), with a focus on the structural changes in water and the influence of a layer of indene (as a proxy of the crust) during a period of thermal processing, which we use in a controlled laboratory setting to simulate cometary environments. Methods. Ices at a CH4/H2O abundance ratio of about 0.01 are deposited and layered, or co-deposited, at 30 K and are heated until 200 K (or 140 K) with a ramp of either 1 or 5 K min−1. We use mass spectrometry and infrared spectroscopy to analyze the results. Results. Depending on the heating ramp and type of deposition, the sublimation of methane through ASW varies, being lower in intensity and higher in temperature when the co-deposited structure is considered. When two temperature cycles are applied, the second one sees less intense CH4 desorptions. When indene is placed above the ice mixtures, we find that the thicker its layer, the later the methane desorption. However, this later desorption sees a greater quantity of methane released due to water reorganization and higher desorbed material pressure. Conclusions. The structural changes of water ice drive volatile and hyper-volatile desorption because of the transition from high to low intrinsic density and transformation from amorphous to crystalline. This desorption indicates that such material has been deposited at low temperatures in agreement with previous theories on cometary ices formed in the pre-stellar cloud. During the two temperature cycles of our experiments, most of the released material is seen to be pristine and the processed part, if any, is of a negligible quantity, in agreement with dust-rock cometary studies.

Сomposition and structure features of the Vikulov productive deposits (Krasnoleninsky arch) and their influence on reservoir properties

Both sedimentological factors and secondary processes of lithogenesis influenced the formation of porosity and permeability properties of the reservoir rocks of the Vikulov suite of the Krasnoleninskoe field. The former includes the conditions of sedimentation of the deposits of the Vikulov suite, which at the initial stages of its formation were controlled by the development of a system of incised river valleys, the stages of filling of which, like their composition, have their own characteristics. Also, various genetic types of deposits were formed here. The formation of the upper part of the Vikulov suite took place in a shallow-marine setting, in conditions of storm and wave shallow water, which affected the thin-layered structure of the VK1-3 reservoir. On the other hand, in the sections of a number of wells, dense interlayers are noted, the formation of which is associated with both sedimentation and superimposed processes in lithogenesis, including the formation of hydrocarbon deposits. Therefore, the prediction of the distribution of productive reservoir rocks is the main task when creating a petrophysical model of the field, and to solve this problem, the methods of lithofacies and staged core analysis are used in the work.

DEPOSIT OPERATIONS AS THE BASIS OF SUCCESSFUL BANKING: THEORETICAL ASPECT, REALITIES AND PROSPECTS OF DEVELOPMENT IN UKRAINE

The paper considers the peculiarities of Ukraine’s deposit market functioning in 2020–2023 under the influence of force majeure factors. The current state of the respective market was analysed in terms of types of deposits by duration, namely fixed and demand, by types of currencies in which funds are placed on deposits, by ranges of the size of the deposits themselves, etc. Approaches to the interpretation of the “deposit operation” concept were systematized. Having analysed the definitions it is possible to define a “deposit operation” as an operation involving the deposit institution’s attraction of funds (in national or foreign currency, in cash or non-cash form) or bank metals of depositors to deposit bank accounts under the terms of the concluded agreement and following the current legislation of Ukraine. A comprehensive analysis of the dynamics of the deposit portfolio of the banking system was carried out. The dynamics of deposits of individuals in the banking system of Ukraine were analysed. The dynamics of interest rates on deposit deposits in terms of subjects, currencies and duration are highlighted. The increase in deposit rates contributed to the recovery of the growth of fixed deposits of individuals which volume increased for the first time since the beginning of the war. The permission of the National Bank to buy foreign currency to open fixed currency deposits contributed to their growth in dollar equivalent. The peculiarities of the activity of the Deposit Guarantee Fund in Ukraine during the period of martial law were identified, and the impact on the level of public trust in banks was investigated. The obtained results of the conducted research made it possible to determine the main trends in the development of the deposit market of Ukraine and to outline proposals for improving the deposit policy of Ukrainian banks.

Methodology for a better estimation of the reserves and resources of minor metals exemplified by selenium in different copper deposit types

Methodology for a better estimation of the reserves and resources of minor metals exemplified by selenium in different copper deposit types

Tool life and wear mechanisms of CVD coated and uncoated SiAlON ceramic milling inserts when machining aged Inconel 718

In this study, an investigation has been conducted to fully characterise for the first time the tribological benefits of adding two different types of chemical vapour deposition (CVD) coatings to silicon aluminium oxynitride milling inserts with a chemical composition of (Si3N4 + Al2O3 + Y2O3), known by the trade abbreviation ‘SiAlON’, typically used to cut difficult to machine materials such as Inconel 718. The experimental tests compared the tool life, material removed and wear resistance of the two different CVD coated inserts against that of uncoated SiAlON ceramic milling inserts. Coating A was a multilayer CVD coating and had a composition of (TiN + TiCN + Al2O3), Coating B was a bilayer CVD coating and had a composition of (Al2O3 + TiN). It was determined that at 900 m/min the uncoated SiAlON ceramic milling inserts exhibited the least amount of wear and variation in cutting force when milling precipitation hardened Inconel 718 samples. Coating A demonstrated significantly lower adhesion to the SiAlON substrate but had higher tool life and material removal rates, Coating B demonstrated excellent adhesion to the SiAlON substrate. The interfacial bonding of Coating B allowed for much higher adhesion to the substrate, but it suffered from much lower tool life and higher rates of rake and flank face wear. The flank wear measurements concluded a cutting speed of 900 m/min to be the optimum cutting speed for machining Inconel 718 with uncoated SiAlON ceramic milling inserts.

40Ar-39Ar dating, fluid inclusion, and isotopic constraints on the timing, fluid evolution, and deposition of the polymetallic Nuocang Pb–Zn deposit in the western Nyainqêntanglha belt

The Nyainqêntanglha polymetallic belt (NPB) is western China's foremost skarn Pb–Zn metallogenic belt. Significant progress has been made in determining these ore deposits' age and origin. However, the precipitation mechanisms and mineralization controls for these deposits remain unresolved. 40Ar/39Ar dating, fluid inclusion (FI), and H-O-S-Pb isotopic data are presented for the Nuocang deposit, a newly discovered polymetallic Pb-Zn skarn deposit in the western NPB, with the goal to trace age and, especially, the major fluid processes associated with hydrothermal evolution leading to the precipitation of ore. The muscovite yields an 40Ar-39Ar plateau age of 59.68 ± 0.60 Ma, which closely resembles typical skarn deposits within the NPB, indicating that it formed during the main collisional stage of the India–Eurasia continent. In the Nuocang base-metal skarn deposit, three ore-related stages can be discerned and subdivided: 1) the pre-ore stage, containing the prograde and early retrograde metasomatic skarn minerals, 2) the syn-ore stage, including the late retrograde metasomatic minerals and sulfides, and 3) the post-ore stage of quartz, calcite, and chlorite alteration. Correspondingly, three types of FI (L, V, and S type) have been identified. The ore-forming fluids evolved from moderate to high temperature between 340 and 440 °C primarily, but up to 571 °C, and moderate to high salinity (concentrated ∼8–18 wt% NaCl-equiv., but up to 48.1 wt% NaCl equiv.) in the pre-ore stage. During the syn-ore stage, the fluids were at low to moderate temperature (between 200 and 320 °C) and low salinity (∼2 to 12 wt% NaCl-equiv.) and developed in low temperature (∼120–200 °C) and low salinity (∼2–8 wt% NaCl equiv.) in the post-ore stage. The calculated δDH2O values of the transparent minerals were −180 to −106 ‰ during the pre-ore stage, −141 to −59 ‰ during the syn-ore stage, and −152 to −105 ‰ during the post-ore stage. The δ18OH2O values were −1.2 to 3.8 ‰ during the pre-ore stage, −4.7 to −2.3 ‰ during the syn-ore stage, and −10.9 to −5.0 ‰ during the post-ore stage, respectively.Based on these results, the magmatic fluids appeared to have gradually evolved into meteoric. Meteoric water is believed to play a significant role in metal deposition within magmatic-hydrothermal systems. Locally, boiling is also considered another key mechanism for ore precipitation. The S-Pb isotope values of the sulfide metals indicate that the metallogenic materials were predominantly derived from an upper crustal source mixing with minor amounts of mantle–derived components. This study suggests that the fluid mixing is related to geostatic pressure variations and infiltration of meteoric waters into the hydrothermal system and are key mechanisms triggering Pb-Zn ore deposition in the NPB.

Deep‐water sand transfer by hyperpycnal flows, the Eocene of Spitsbergen, Arctic Norway

AbstractFlood‐generated hyperpycnal flows are dense, sediment‐laden, turbulent flows that can form long‐lived, bottom‐hugging turbidity currents, which undoubtedly transport large volumes of fine‐grained sediments into the ocean. However, their ability in transferring sand into deep‐water basins is debated. This study presents sedimentological evidence of sandy hyperpycnal flow deposits (hyperpycnites) in a series of basin floor lobe complexes associated with a progradational shelf margin in the Eocene of Spitsbergen, Arctic Norway. Four coexisting types of sediment gravity flow deposits are recognized: (i) sandy hyperpycnites deposited by quasi‐steady hyperpycnal flows; (ii) turbidites deposited by waning, surge‐type turbidity currents; (iii) hybrid event beds deposited by transitional flows; and (iv) mass transport deposits emplaced during rare slope failures. The abundance of thick‐bedded massive sandstones, frequent bed amalgamation, the distribution of hyperpycnites across the lobes and the abundance and systematic occurrence of plant‐rich hybrid event beds and associated climbing ripple cross‐laminated beds in the lobe fringes, suggest that hyperpycnal flow was the most important mechanism driving lobe progradation. Shelf‐edge positioned fluvial channels linked to the basin floor lobe complexes via deeply incised, sandstone‐filled slope channels, suggest that rivers fed directly onto the slopes where their dense, sand‐laden discharges readily generated quasi‐steady hyperpycnal flows that regularly reached the basin floor. The composite architecture and complex waxing–waning flow facies configuration of the hyperpycnites is consistent with sustained and concomitant suspension and traction deposition under fluctuating subcritical to supercritical conditions. Similar sandstone beds occur on the clinoform slopes, indicating that the hyperpycnal flows operated likewise on the slope. Plant‐rich hybrid event beds indicate transformation of initially turbulent flows by relative enrichment of clay and plant material via progressive sand deposition to such an extent that it suppressed turbulence. The multi‐faceted character of the hyperpycnites reported here, challenges traditional beliefs that hyperpycnites assumingly preserve the waxing–waning signal of single‐peaked floods.

Analysis of hydrocarbon solvents for the removal of various types of asphalt, resin and paraffin deposits

In this work the physical-chemical properties of asphaltene-resin-paraffin deposits are studied. Their component composition was determined. The results obtained are the basis for the selection of effective solvents and the choice of the method of removing deposits from oil reservoirs. Two hydrocarbon solvents with the brands “TSK А” and “TSK B” were tested. The solvent ability of solvents was tested.

A Review of the Metallogenic Mechanisms of Sandstone-Type Uranium Deposits in Hydrocarbon-Bearing Basins in China

As a valuable mineral resource, uranium is extensively utilized in nuclear power generation, radiation therapy, isotope labeling, and tracing. In order to achieve energy structure diversification, reduce dependence on traditional fossil fuels, and promote the sustainable development of energy production and consumption, research on the metallogenic mechanisms and related development technologies of uranium resources has been one of the focuses of China’s energy development. Sandstone-type uranium deposits make up approximately 43% of all deposits in China, making them the most prevalent form of uranium deposit there. Sandstone-type uranium deposits and hydrocarbon resources frequently coexist in the same basin in China. Therefore, this study summarizes the spatial and chronological distribution, as well as the geological characteristics, of typical sandstone-type uranium deposits in China’s hydrocarbon-bearing basins. From the perspectives of fluid action, geological structure, and sedimentary environment, the metallogenic mechanisms of sandstone-type uranium deposits in hydrocarbon-bearing basins are explored. According to the research, the rapid reduction effect of oil and gas in the same basin is a major factor in the generation of relatively large uranium deposits. Additionally, ions such as CO32− and HCO3− in hydrothermal fluids of hydrocarbon-bearing basins, which typically originate from dispersed oil and gas, are more conducive to uranium enrichment and sedimentation. This study provides guidance for efficient sandstone-type uranium deposit exploration and production in hydrocarbon-bearing basins and helps to achieve significant improvements in uranium resource exploitation efficiency.

Distinguishing different classes of mass-transport deposits in LPIA strata exposed in eastern Paraná Basin, Brazil

Ice age mass-transport deposits (MTD) occur in multiple stratigraphic intervals within the Permocarboniferous Itararé Group, in the Paraná Basin, and are exposed in several disconnected quarries and road cuts around the region of Mafra, southern Brazil. The most typical deposits are diamictites with muddy matrix, but silty-sandy diamictites and metric intercalations of deformed layers of sandstones and siltstones occur subordinately. Similar MTD facies have been described from better exposed and time equivalent successions in western Argentina. There, because of the km-scale exposures, MTDs can be mapped in their plenitude, giving better insights about their emplacement. In this paper, we describe the Brazilian MTDs and infer their modes of transport and deposition supported by comparisons with published Argentinean examples. Based on matrix constitution, presence of coherent blocks and rafts, and sedimentation phases, at least four types of MTDs can be identified: 1) Mud-rich MTD and isolated sandstone blocks; 2) Resedimented MTD represented by diamictites with folded blocks of diamictite, possibly corresponding to two phases of remobilization; 3) Sand/silt-rich MTD (evolved stage), and formed by deformed bands of sandstones and siltstones (mature stage); and 4) MTD with rafts of heteroliths and sandstone blocks. Usually MTDs rest on and scour into a fine-grained substrate such as thin-bedded turbidites and shale. The regional geological setting at Mafra points to an open embayment. The collapse of inclined depositional slopes related to high sediment supply associated with deglaciation was the major control on MTD development. However, the inferred proximity of the ice margin during slope failure was variable, suggesting MTD formation during different stages of a glacial cycle.

Fertigation and Carboxymethyl Cellulose Applications Enhance Water-Use Efficiency, Improving Soil Available Nutrients and Maize Yield in Salt-Affected Soil

Conventional organic soil amendments and drip irrigation are insufficient for mitigating soil salinization. The development of a more potent soil amendment with higher water retention capability is critical. Carboxymethyl cellulose (CMC) has excellent water retention and adsorption properties and is suitable for soil water retention and amendment; however, its effects on water and salt distribution, soil nutrients, and maize yield have not been clearly investigated. We set up five treatments with flood irrigation (CK), drip irrigation (W), drip irrigation combined with 100 kg CMC ha−1 (WC1), drip irrigation combined with 200 kg CMC ha−1 (WC2), and drip irrigation combined with 300 kg CMC ha−1 (WC3). Our findings demonstrate that the application of CMC in conjunction with drip irrigation led to a significant surge in soil water content within the 0–40 cm layer, ranging from 3.73% to 16.46%, while simultaneously inducing a reduction in salt content of 4.08% to 16.61%. Consequently, this resulted in a desalination rate spanning from 10.32% to 12.93%. The salt was gradually washed down and formed a desalination area with the drip emitter as the center, and the salt distribution characteristics shifted from a surface accumulation type to a bottom deposition type. The drip irrigation and CMC application also increased the content of available nutrients, reduced surface evaporation, underground water loss, and maize evapotranspiration, and improved water-use efficiency, thus increasing the aboveground biomass and grain yield. In summary, CMC had a significant effect on water retention, desalination, and yield increases. It can serve as a novel soil amendment for salt-affected soil.

The graph attention network and its post-hoc explanation for recognizing mineralization-related geochemical anomalies

Deep learning algorithms have become a cutting-edge technology for mining geochemical survey data to identify geochemical patterns related to mineralization. Similarities in the origins of the same types of mineral deposits may result in similarities in the observed geochemical anomalies to some extent. However, image-based models have limited ability to model the relationships between samples because fixed-size pixel patches are not connected. Graphs have enormous potential to capture spatial information, which can model the complex nonlinear spatial relationship between vertices and edges and effectively measure the spatial relationships between metallogenic information and geochemical survey sites. The graph-based model considers both labeled and unlabeled data as inputs, allowing the relationships between individual samples to be incorporated into the network. In this study, we used a graph-based model, the graph attention network (GAT), to recognize geochemical anomalies associated with gold mineralization in the Xiaoqinling–Xiong'ershan region of the western Henan Province, China. The GNNExplainer, a method for explaining the predictions of graph-based deep learning tasks, was used to determine the importance of the input features of the trained GAT model. The results indicated that the model regards Bi, Cd, Mn, Zn, and Mo as important geochemical elements for mineralization. Meanwhile, a comparative study of GAT with a convolutional neural network suggests that the graph-based model can be applied to effectively identify mineralization-related geochemical patterns, and geochemical anomalies recognized by GAT are more representative of gold mineralization.

LA-ICP-MS U-Pb dating, chemical composition and evolution of oscillatory zoned andradite from the Chengmenshan Cu-Au deposit, Jiangxi province

The Chengmenshan Cu-Au deposit is a typical porphyry-skarn deposit in the Middle-Lower Yangtze River Valley Metallogenic Belt (MLYRMB), developing abundant oscillatory zoned andradite. However, the physiochemical conditions, hydrothermal evolution and age of skarn formation is unknown. This paper presents BSE image, EMPA point analyses, LA-ICP-MS point analyses and mapping, U-Pb isotope data for andradite from the Chengmenshan Cu-Au deposit. From core to rim, three generations of andradite could be identified (Grt-1, Grt-2, Grt-3). Grt-1 (Adr73-88) exhibit compositional variations as oscillatory zoning. Grt-2 (Adr93-100) is almost pure andradite, with smooth surface. Grt-3 (And71-93) occur as halo surrounding earlier andradite, with broken surface. Incorporation of REE and U into all generations of andradite mainly follows coupled YAG-type substitution mechanism and the coupled substitution of [U4+]VIII + 2[Fe3+, Al3+]Ⅳ – [Ca2+] – 2[Si4+]Ⅳ in the dodecahedral position, respectively. Their associated intrusions, mineral assemblages and consistent positive Eu anomalies indicate an acidic, oxidizing and low salinity forming conditions. From core to rim, the contents of REE and HFSE are decreasing, and the REE patterns evolve from flatted, through LREE-enriched, HREE-depleted, to REE-depleted. The chemical composition and evolution of oscillatory zoned andradite suggest that the fluids in Chengmenshan deposit experienced the sequences of pore fluid-mixed, through magmatic-hydrothermal dominated, to meteoric water influx. In this process, the temperature, pH and fluid compositions varied. U contents are closely correlated with REE contents, especially LREE contents. The andradite samples yield Tera-Wasserburg lower intercept 206Pb/238U ages of 140.1 ± 2.6 Ma (MSWD = 1.8), representing the age of Cu-Au mineralization. These results indicate the evolutionary characteristics of hydrotheraml fluids and precisely date the Cu-Au skarn formation, which may serve as a useful indicator in the exploration of similar skarn deposits and point selection for U-Pb dating.

Sedimentology, stratigraphy and glacial genetic model of the coromandel phosphate deposit, Vazante group, central Minas Gerais state, Brazil

The Coromandel sedimentary phosphate deposit is inserted at the external zone of the Brasília Fold Belt geological context, more specifically in the Retiro Formation, basal unit of the Vazante Group. Compared to the world-class Rocinha Formation deposits, widely studied due to high economic interest, the Coromandel Deposit is the one that most lacks studies focused on the main rocks description, faciological characterization and proposal of a plausible metallogenetic model according to the depositional environments. Thus, from the detailed field description of outcrops, geological cartography, microscopic petrography and X-ray diffraction and fluorescence analysis, it was possible to contribute to a better understanding of the deposit. The Retiro Formation is characterized by a glaciogenic facies association that comprises polymictic diamictite, conglomeratic sandstone, fine whitish arkosean, massive and laminated siltstone, besides phosphate facies, including phosphate siltstone, laminated phosphorite and brecciated phosphorite. The phosphatic facies occur in straight relation to the glaciogenic sediments and not rare directly over diamictite, which matrix can be phosphated as well. These rocks P2O5 contents range from 2% to 34% and the succession suggest an establishment of a glaciotransitional environment responsible to constrain favorable alkalinity, temperature and oxi-reduction conditions to directly chemical precipitation of fluorapatite in a mechanism analogue as the cap dolomites, supporting an idea of “cap phosphorites”. The phosphate source is related to the glacial sedimentary supply of continental origin (granite, carbonatite and other alkaline bearing rocks). In addition, the input of cold water, as result of ice melting episodes, became a limiting development factor for phosphorus metabolizing organism which improves the P2O5 system enrichment. For the unique genetic conditions, this phosphatic deposit has been called as the Coromandel Deposit Type.

Geology, sulphide geochemistry and geochronology of the Romsås Ni-Cu-Co mineralisation, Norway: Implications for ore formation and regional prospectivity

The Romsås intrusion, located in the southern portion of the Idefjorden lithotectonic unit, is part of a cluster of small to medium-sized mafic intrusive bodies which host NiCu sulphide mineralisation, referred to as the Indre Østfold metallogenic area. The Romsås is an almost 1 km-long intrusion with rounded shape, comprising undifferentiated quartz-norite with local orbicular texture. The assemblage, comprising cumulus orthopyroxene and plagioclase, is partly recrystallised and altered, thus orthopyroxene is partly replaced by amphibole, whereas plagioclase is locally replaced by epidote. Locally, garnet, amphibole, plagioclase and magnetite define a granoblastic texture as product of amphibolite-facies metamorphism. Several sulphide-rich lenses, normally up to 5 m wide, occur within the Romsås intrusion and display a sharp contact with the host noritic rocks. The textures vary from disseminated, net-textured and massive sulphides. The sulphide assemblage is homogeneous within the deposit and consists mainly of pyrrhotite, followed by pentlandite, and minor chalcopyrite, with variable alteration of pentlandite.This contribution provides the first systematic characterisation of the Romsås Ni-Cu-Co mineralisation and constraints for its formation and geodynamic setting. We have measured the concentrations of S, PGE, TABS+ (Te, As, Bi, Sb and Se) and other chalcophile elements in both whole rock and sulphide minerals from different ore textures, and UPb and Hf isotope systematics in zircon. The Ni and Cu concentrations in 100% sulphides are around 2% and 1%, respectively. The PGE concentrations in all sulphide-bearing samples are low, generally below 0.3 ppm, with Pt and Pd displaying a broad positive correlation and Pt/Pd ratios varying from 1 to 2. Different ore types are modelled to have formed from a mantle-derived parental magma with higher Cu/Pd ratios and lower Pd contents than mantle values, interpreted as the result of 5% prior crystallisation under sulphide-saturated conditions. Negative mantle-normalised Nb anomalies relative to Th, As and Sb suggest around 10% of assimilation of a component similar to lower crust by the parental magmas. Moreover, S/Se ratios greater than mantle values likely reflect the combined effect of Se depletion during early sulphide removal and external S addition upon crustal assimilation. The Romsås Ni-Cu-Co mineralisation likely formed as a result of sulphide segregation in response to external S addition during several magma pulses. The composition of the sulphide ores can be modelled by an R-factor of around 500. A significant budget of the chalcophile elements is not hosted by sulphide minerals and must be thus accounted for other discrete phases, such as platinum-group minerals. Nevertheless, trace elements distribution in sulphides supports only local remobilisation of chalcophile elements and records compositions comparable to sulphides from pristine NiCu deposits worldwide. Sulphide alteration may have led to exsolution of a parcel of chalcophile elements from sulphide lattice. A UPb zircon crystallisation age of 1551 ± 10 Ma, εHft values between ca. 3.5 and 6, and regional geological considerations suggest that the intrusion formed as part of an arc or back-arc rift setting in the Idefjorden lithotectonic unit. The Romsås sulphide mineralisation represents another example of magmatic sulphide deposit formed at an arc-related geodynamic setting, normally unconventional for the formation of this type of deposit. Therefore, our findings support that arc-related settings in Idefjorden lithotectonic unit, southern Norway, should also be regarded as potential for the formation of Ni-Cu-PGE deposits.