Late-stage Mineralization Research Articles

Geodynamic setting and ore formation of the Younusisayi thorium deposit in the Altyn orogenic belt, NW China

Thorium deposit related to alkaline/peralkaline magmatism is the dominant thorium source. Its ore-forming thorium mechanism has long been fascinating. The Younusisayi Th deposit, hosted in early Paleozoic alkali-feldspar granite in the South Altyn Complex, NW China, is an example to explore the Th mineralization processes in magmatic-hydrothermal systems. Zircon U-Pb dating shows that the ore-hosting alkali-feldspar granites are emplaced at 445.7–439.0 ± 1.3 Ma. The apatite that occurs concomitantly with thorite in the mineralized alkali-feldspar granites formed at are 442.0–438.0 ± 14 Ma, indicating Th mineralization temporally related to the magmatism. Four populations of fluorite exhibit distinct occurrences, the fluorite Ia and Ib are in intergrowth with thorite, but the fluorite IIa and IIb are not. Notably, four populations of fluorite are differentiated by their Th + U and HREE concentrations, fluorite Ia and Ib show higher Th + U contents and lower HREE contents than fluorite IIa and IIb. Th was extracted by magma during emplacement. As a strong incompatible element, thorium will not be enriched in rock-forming minerals. In the process of magmatic evolution, thorium is gradually enriched in the post-magmatic fluids which contains abundant volatile components. Thorium can be transported as F-Th complexes in F-rich fluids. As temperature decreased, thorium precipitated in the form of thorite, and fluorite Ia and Ib crystallized with a low HREE content. Fluorine from the decomposition of F-Th complexes, reacts with HREE in the fluids to form F-HREE complexes, which increases the HREE content in the fluid. Therefore, the fluorite IIa and IIb which formed in the late stage of mineralization have obviously higher contents of HREE. We propose that the Younusisayi deposit, with an average grade of 0.4 wt% ThO2, formed in a post-collisional extensional environment during the early Paleozoic. The Younusisayi deposit is best classified as a magmatic-hydrothermal deposit. Our results demonstrate the usefulness of geochemistry of fluorite for tracing the ore-forming process, thus establishing the ore formation model.

Fluid evolution of the Zhunuo porphyry Cu-Mo deposit in Gangdese Tract, Tibet, China: A fluid-inclusion investigation

The Zhunuo porphyry Cu-Mo deposit in the western part of south Gangdese porphyry copper belt (GPCB), Tibet, is a large porphyry system. The Cu-Mo mineralization of this deposit is mainly associated with a weakly aluminous I-type Miocene granite porphyry pluton that formed in a post-collisional extensional tectonic setting. Field observations and petrographic studies demonstrate that emplacement of the pluton took place in several intrusive pulses, each with associated hydrothermal activities. Early hydrothermal alteration produced a potassic assemblage, overprinted by later phyllic alteration. At least three main stages of mineralization have been identified: (1) early A stage quartz + K-feldspar + minor sulfide veins; (2) middle stage B1-subtype veins composed of quartz + molybdenite + sporadic sulfide and B2-subtype quartz + pyrite + chalcopyrite veins; and (3) late stage pyrite + quartz D veins.Three types of fluid inclusions (FIs) in quartz were identified in the early and middle stages (i.e., CO2 bearing-aqueous vapor (V)-type and liquid (L)-type, and solid (S)-type); only aqueous L-type FIs were observed in the late stage minerals. S-type FIs contain variable solid particles, including halite, calcite, anhydrite (or gypsum), and chalcopyrite, hematite, and an unidentified transparent crystal. Only halite was dissolved during heating. Halite-bearing S-type FIs were mainly homogenized by halite dissolution at 300–470°C (S2-type), corresponding to salinities of 38.9–56.3 wt% NaCl equiv.; and minor halite bearing S-type FIs were homogenized to liquid at 360–520°C via vapor disappearance (S1-type), with salinities of 31.9–56.7 wt% NaCl equiv. Other FIs in minerals of A, B1, B2 and D veins were homogenized at temperatures of 350–550°C, 303–500°C, 305–460°C, and 250–347°C with salinities of 3.4–20.9, 2.6–22.4, 4.8–21.8, and 4.7–18.2 wt% NaCl equiv., respectively. These data suggest that the ore fluids forming the Zhunuo deposit changed from high-temperature, low-moderate salinity, CO2-bearing magmatic fluids to low-temperature, low-salinity and CO2-poor meteoric fluids. Phase separation and cooling caused the precipitation of the abundant chalcopyrite in the middle stage B2-subtype veins. The molybdenite mineralization was caused mainly by the decrease of pressure due to the release of CO2, and by phase separation of fluid in the middle stage as recorded in the B2-subtype veins. This hydrothermal ore-forming system is different from other magmatic-hydrothermal systems in GPCB, but is similar to the typical Cu-Mo porphyry systems, which were initially CO2-bearing as indicated by the presence of abundant CO2-bearing, low-moderate salinity FIs and calcite-bearing S-type FIs.

Formation of late-stage hydrothermal mineralization in the Mesoarchean Boula-Nuasahi ultramafic complex, Odisha, India: Constraints from arsenopyrite geothermometry and trace element data

The Mesoarchean Boula-Nuasahi ultramafic complex is situated in the south eastern flank of the Singhbhum Craton, India and consists mainly of gabbro-anorthosite, peridotite and pyroxenite litho-units that host a series of chromitite bodies. A contemporaneous but slightly younger magmatic event has structurally disturbed the area with intrusion of a coarse-grained gabbro unit known as the Bangur gabbro (∼3.1 Ga). This has caused extensive hydrothermal alteration of the original host rocks and is associated with hydrothermal sulphide- and Pt-Pd mineralizations. Petrographic study shows that well-crystallized and euhedral arsenopyrite crystals are associated with quartz and carbonates in veins aligned along the foliation planes/fractures in the host rocks. This vein assemblage (arsenopyrite + quartz + calcite) has formed during the late stage of hydrothermal mineralization. Electron probe micro-analysis and LA-ICP-MS analysis of arsenopyrite demonstrates that its chemical composition varies within narrow limits and that the concentrations of trace elements are below 900 ppm. The only trace element present in significant concentrations is Sb with an average value of 490 ppm. The As/S atomic ratio varies between 0.93 and 1.01 and As and S show a clear negative correlation according to the substitution FeAs1-xS1+x. The average composition is very close to the stoichiometric value. Because the arsenopyrite crystals are vein minerals, have very low concentrations of any impurities and do not show any compositional zoning, they were used for geothermometric calculations. Matching the measured As atom% with one of the experimentally calibrated isopleths in the established Fe-As-S phase diagram, calculated temperatures are in the range of 335–425 °C. This temperature range is in very good agreement with temperature estimates of 300–500 °C (based on cobaltite–gersdorffite compositions) for late-stage hydrothermal mineralization in the Boula-Nuasahi ultramafic complex available in the literature.

Alteration, uranium occurrence state, and enrichment mechanism of the Cretaceous Luohe Formation, southwestern Ordos Basin, western China

To ascertain the characteristics of mineral assemblages associated with uranium mineralization and enrichment mechanism of deep sandstone-type uranium deposits, drill-core logging, petrography and mineralogy, scanning electron microscopy (SEM), electronic probe micro analysis (EPMA), whole-rock analysis, X-ray diffraction (XRD) were used to identify the types, redox state of uranium minerals, and typical uranium-related mineral assemblages in the sandstone of the Cretaceous Luohe Formation, southwestern Ordos Basin. The results showed that the clastic grains in the gray and red uranium-bearing sandstone have undergone relatively strong alteration, while alteration of the clastic grains in the gray and red calcareous sandstone is relatively weak. The alteration minerals mainly include pyrite, anatase, kaolinite, chlorite, calcite, apatite, and feldspar. Uranium contents is highly consistent with S, P2O5, CaO, and FeO concentrations in the vertical direction and has a weak correlation with the total organic carbon. Uranium ores are mainly pitchblende and titanium-bearing uranium minerals. The Luohe Formation experienced transformation from a weak alkaline oxidation environment during the diagenetic stage to a weak acid reduction conditions in the early mineralization stage and then to a weak alkaline reduction environment in the middle–late mineralization stages. Typical alteration minerals associated with uranium ores include two types, which are formed in acid reduction and alkaline reduction redox stages, respectively. The alteration minerals related to acidic fluid process are pyrite, anatase, kaolinite, and apatite; those related to alkaline fluid mechanism consist of calcite and chlorite. Deep-seated uranium mineralization was formed by both acidic and alkaline reducing fluids, being dominated by acidic fluid conditions. In-depth investigation of the alteration and uranium ore minerals are of great scientific value to infer the fluid type of mineralization stage and reveal the enrichment mechanism of uranium deposits.

Metamorphism obscures primary taphonomic pathways in the early Cambrian Sirius Passet Lagerstätte, North Greenland

Abstract Correct interpretation of soft-bodied fossils relies on a thorough understanding of their taphonomy. While the focus has often been on the primary roles of decay and early diagenesis, the impacts of deeper burial and metamorphism on fossil preservation are less well understood. We document a sequence of late-stage mineral replacements in panarthropod fossils from the Sirius Passet Lagerstätte (North Greenland), an important early Cambrian Burgess Shale–type (BST) biota. Muscle and gut diverticula were initially stabilized by early diagenetic apatite, prior to being pervasively replaced by quartz and then subordinate chlorite, muscovite, and chloritoid during very low- to low-grade metamorphism. Each new mineral replicates the soft tissues with different precision and occurs in particular anatomical regions, imposing strong biases on the biological information retained. Muscovite and chloritoid largely obliterate the tissues’ original detail, suggesting that aluminum-rich protoliths may have least potential for conserving mineralized soft tissues in metamorphism. Overall, the fossils exhibit a marked shift toward mineralogical equilibration with the matrix, obscuring primary taphonomic modes. Sequential replacement of the phosphatized soft tissues released phosphorus to form new accessory monazite (and apatite and xenotime), whose presence in other BST biotas might signal the prior, more widespread, occurrence of this primary mode of preservation. Our results provide critical context for interpreting the Sirius Passet biota and for identifying late-stage overprints in other biotas.

Contribution of Precambrian basements to the Mesozoic ore-fluid system: An illustration using the Majiayao gold deposit, Jiaodong, China

In contrast to most Mesozoic granite-hosted gold deposits in the giant Jiaodong gold province (China), the Majiayao deposit represents a significant example hosted in the Archean high-grade metamorphic terrane. The mineralization is characterized by auriferous quartz-sulfide veins together with notable Fe-bearing carbonates (ankerite and siderite), iron oxides and barite. In this study, the comprehensive in-situ analyses of vein-hosted hydrothermal minerals (such as: xenotime U-Pb dating, ankerite Rb-Sr isotopes and monazite Sm-Nd isotopes) and sulfur isotopic analyses of gold-bearing sulfides are used to constrain the timing of mineralization and to better understand the ore genesis. The syn-ore hydrothermal xenotime yielded a U-Pb age of 120.0 ± 1.2 Ma marking timing of gold mineralization, which is much younger than wallrocks’ latest metamorphism at 1950 to 1850 Ma. The relatively higher and variable initial 87Sr/86Sr ratios (0.715809–0.718753) of ore-related ankerite may be leached from ore-hosting Archean metamorphic rocks and/or regional Neoproterozoic Penglai Group low-grade metasedimentary rocks via extensive fluid-rock interactions. This inference is also supported by the newly reported near-zero δ34S values (–1.2 to 1.4‰) of pyrite from altered wallrocks, which are significantly comparable to the surrounding Archean plagioclase amphibolite. The monazite has relatively homogenous εNd(t=120Ma) values ranging from –19.3 to –17.6, which are much higher than the Nd isotope compositions of the ore-hosting Archean high-grade metamorphic rocks. Combining the widespread mafic dykes and previous relevant geochemical studies, it is proposed that the ore-forming fluids were probably derived from deeply mantle-related contents, followed by intense interaction with Archean basements at the shallow crustal level. In addition, the progressive decrease of δ34S values of pyrite and more appearances of iron oxides and barite from early to late mineralization stages, are ascribed to gradual fluid oxidation by extensive carbonatization of Fe-rich Archean wallrocks.

C-C chemokine receptor type 6 modulates the biological function of osteoblastogenesis by altering the expression levels of Osterix and OPG/RANKL.

Circulating inflammatory factors affect osteoblast and osteoclast formation and activity in osteoporosis. Estrogen affects the migration of Th17 cells via the C-C chemokine receptor type 6 (CCR6) and C-C chemokine ligand 20 (CCL20) signaling pathways to modulate bone metabolism; however, it is unclear whether and how CCR6 modulates bone homeostasis. In the present study, CCR6 knockout (CCR6-/-) mice were selected to investigate the effects of CCR6 in the regulation of homeostasis of osteoblasts and osteoclasts. Primary osteoblasts were isolated from the calvarium of newborn CCR6-/- or wild-type mice, followed by osteoblastic differentiation culture in vitro. CCR6 deletion reduced osteoblast activity in terms of alkaline phosphatase (ALP) activity and inhibited osteoblast mineralization according to the results of Alizarin Red S staining, whereas it did not affect the proliferation of osteoblasts. CCR6 deletion inhibited Osterix mRNA expression in osteoblasts during the late stage of mineralization in vitro, while it did not affect mRNA expression levels of runt-related transcription factor 2 (Runx2) and Collagen-1. The ratio of osteoprotegerin (OPG) /receptor activator of nuclear factor κ-Β ligand (RANKL) mRNA level in osteoblasts was decreased by CCR6 deficiency in the culture treated with 1,25(OH)2D3/PGE2, while there was no effect observed in the normal culture environment. The results provide novel insights, such as that CCR6 deletion suppresses osteoblast differentiation by downregulating the expression levels of the transcription factor Osterix, and indirectly promotes osteoclast production by increasing transcription of RANKL. This may be one of the mechanisms via which CCR6 deletion regulates bone metabolism.

The relative solubilities of wolframite and scheelite in hydrothermal fluids: Insights from thermodynamic modeling

The occurrence of either scheelite (CaWO4) or wolframite ([Fe,Mn]WO4) in tungsten deposits is generally explained by the Ca content of the host rocks, but scheelite/wolframite ratios in granitoids-hosted tungsten deposits are highly variable, ranging from scheelite-dominated to wolframite-dominated. Wolframite is also commonly replaced by scheelite or vice versa- among many granitoids-hosted tungsten deposits. To fill this gap in understanding the stabilities of wolframite and scheelite under hydrothermal conditions, the relative solubilities of scheelite and wolframite in hydrothermal fluids were constrained using two modeled chemical systems: W-Ca-Mn-Cl-Na-O-H and W-Ca-Fe-Cl-Na-O-H. The two modeled chemical systems can well reproduce the available experimental data for scheelite, ferberite, and hübnerite solubilities under hydrothermal conditions. The modeling results indicate that scheelite is more soluble than hübnerite and ferberite under most W-mineralizing conditions (300–400 °C, 500–1500 bars, and 1–3 mol/kg NaCl). Scheelite can replace ferberite (hübnerite) over a wide range of temperatures and pressures; therefore, the replacement of ferberite (hübnerite) by scheelite does not necessarily represent late stages of mineralization. Two mechanisms can cause scheelite to replace ferberite (hübnerite). The first mechanism is cooling with an increase in the ∑Ca∑Fe (∑Ca∑Mn) molality ratio in fluids, and the second mechanism is a decrease in fluid pressure with constant ∑Ca∑Fe (∑Ca∑Mn). Neither leaching Ca from Ca-rich wallrocks nor removing Fe (Mn) from hydrothermal fluids is required for the second mechanism. The second mechanism may account for vein-type or disseminated scheelite mineralization in host rocks whose Ca is low compared to carbonates.

Geochemistry of Rhenium and Other Trace Elements in Molybdenite, Sar Cheshmeh Porphyry Cu‐Mo Deposit, Iran

AbstractLA‐ICP‐MS analysis of molybdenite from the Sar Cheshmeh porphyry Cu‐Mo deposit (PCD), Iran, shows moderate concentration of Re (average ∼207 ppm) and low concentration of chalcogenides (average of Pb + Te + Bi, ∼31 ppm) as well as metalloids (average of As + Sb + Ge, ∼4.5 ppm). The early‐formed quartz–molybdenites associated with potassic alteration are characterized by moderately low concentration of Re (21–215 ppm with an average of 83 ppm), whereas the transitional quartz–molybdenite veins related to the sericitic stage of mineralization contain more Re (62–465 ppm, with an average of 207 ppm). In contrast, the late‐formed quartz–molybdenite veins associated with phyllic alteration show the highest concentration of Re (up to 1273 ppm with an average of 395 ppm). Gradual increase in Re content of molybdenites deposited throughout the evolution of the porphyry system is probably related to elevated ƒO2 and acidic conditions of the ore fluids governing the transitional and late stage of mineralization, when compared to the moderately low ƒO2 and basic conditions of the ore fluids precipitating the low‐Re molybdenites associated with potassic alteration. The mixed mantle/crustal source of the ore‐related magma and its fractionated composition in Sar Cheshmeh are consistent with magmatic conditions for the formation of Mo‐rich and Re‐poor PCDs in the world.

Geology, geochronology and tectonic setting of the Chaihulanzi gold deposit in Inner Mongolia, China

The Chaihulanzi is a Precambrian metamorphic rock-hosted gold deposit in the northern margin of the North China Craton (NCC). The local outcropping lithologies include mainly Archean metamorphic rock, Paleoproterozoic carbonatite, and Phanerozoic diorite, granite, aplite and mafic to felsic dikes. Due to the lack of data, the deposit was variably proposed to be orogenic, intrusion-related, or mesothermal type, and the mineralization was loosely constrained to be Paleozoic or Mesozoic. Based on field geology, petrological/mineralogical observations, whole-rock geochemistry, and zircon U-Pb-Hf isotopes of ore-related aplite, and sericite Ar-Ar dating of gold-ore veins, we discussed the ore-causative magmatism, and the age and tectonic setting of gold mineralization. Our results show the presence of an early (native gold-dominated) and a late (gold-silver telluride-dominated mineralization) stage: The early-stage gold mineralization was genetically linked to the Middle-Late Permian aplite (LA-ICP-MS zircon U-Pb age: 264.5 ± 1.3 Ma), whose ages are similar to the gold ore veins (sericite Ar-Ar age: 263.67 ± 0.99 Ma). The distinct negative zircon εHf (-18.31 to -15.45) and model age (TDMC = 2.1–2.4 Ga) indicate a crustal magma source, probably from partial melting of the NCC basement. The whole-rock trace element compositions and zircon U-Pb ages, together with the tectonic evolution of northern NCC margin imply a post-collisional extension setting (after the Paleo-Asian ocean closure) for the gold mineralization. The newly-discovered late-stage quartz-carbonate ore veins occur as fracture infill, and crosscut early-stage quartz-sericite veins and Mesozoic volcanic wallrocks, implying that the late-stage mineralization occurred in the Mesozoic or after. The two-stage gold mineralization overprinting makes Chaihilanzi and its periphery highly prospective for gold exploration.

Study on the PTX Parameters and Fractal Characteristics of Ore-Forming Fluids in the East Ore Section of the Pulang Copper Deposit, Southwest China

In this paper, the east ore section of the Pulang porphyry copper deposit is selected as the research object. The micro-thermometer and laser Raman spectroscopic technique are utilized to study the parameters of ore-forming fluids such as pressure, temperature, and compositions. In the meantime, the fractal models, including the perimeter-area (P-A) model and number-size (N-S) model, are introduced to quantify the shape of fluid inclusions, and distinguish the stages of ore-forming fluids, respectively. The results show that the types of fluid inclusions are diversified, namely two-phase liquid-rich type, two-phase vapor-rich type, three-phase CO2-rich type, three-phase halite-bearing type and pure liquid type. The fluids of main mineralization stage are characterized by medium-high temperature (170.2–421.4 °C), medium-high salinity (9.3 wt.%–33.3 wt.%), and low density (0.73–1.06 g/cm3). With the migration and evolution, the temperature, salinity, and pressure of ore-forming fluids gradually decrease, while the density of fluids increases. The liquid-phase compositions mainly include H2O, and the vapor-phase compositions consist of H2O, CH4, N2, and CO2, indicating the characteristics of reducing fluids and the mixing of atmospheric precipitation. In general, the characteristics of ore-forming fluids in the east ore section are similar to those of the first mining area, suggesting that the ore-forming fluids in the east ore section may not migrate from the first mining area. And the east ore section may be a relatively independent metallogenic system. Moreover, the fractal analysis results demonstrate that the shape of fluid inclusions formed in the same hydrothermal activity features self-similarity. The DAP values of fluid inclusions in B veins, ED veins, and D veins are 1.04, 1.06 and 1.10, respectively, showing a gradually increasing trend from the main stage to the late stage of mineralization. Meanwhile, the shape of fluid inclusions ranging from B veins to D veins becomes increasingly irregular. It also reveals that the homogenization temperature satisfies fractal distribution with four scale-invariant intervals, suggesting that all B veins, ED veins, and D veins have experienced at least four hydrothermal activities. Compared with histogram, the N-S fractal model is able to describe the distribution characteristics of the ore-forming fluids’ homogenization temperature more precisely. Therefore, it presents a potential tool for the stage division of ore-forming fluids. This research provides information about the characteristics of ore-forming fluids in the east ore section of the Pulang porphyry copper deposit, which is beneficial for further exploration in this region, and the extension of the application of fractal models in the study of fluid inclusions. However, further testing of fractal models on the fluid inclusion study is warranted to fully determine the universality.

Optimizing In Vitro Osteogenesis in Canine Autologous and Induced Pluripotent Stem Cell-Derived Mesenchymal Stromal Cells with Dexamethasone and BMP-2.

A growing body of work suggests that canine mesenchymal stromal cells (cMSCs) require additional agonists such as bone morphogenic protein-2 (BMP-2) for consistent in vitro osteogenic differentiation. BMP-2 is costly and may challenge the translational relevance of the canine model. Dexamethasone enhances osteogenic differentiation of human MSCs (hMSCs) and is widely utilized in osteogenic protocols. The aim of this study was to determine the effect of BMP-2 and dexamethasone on early- and late-stage osteogenesis of autologous and induced pluripotent stem cell (iPS)-derived cMSCs. Two preparations of marrow-derived cMSCs were selected to represent exceptionally or marginally osteogenic autologous cMSCs. iPS-derived cMSCs were generated from canine fibroblasts. All preparations were evaluated using alkaline phosphatase (ALP) activity, Alizarin Red staining of osteogenic monolayers, and quantitative polymerase chain reaction. Data were reported as mean ± standard deviation and compared using one- or two-way analysis of variance and Tukey or Sidak post hoc tests. Significance was established at P < 0.05. In early-stage assays, dexamethasone decreased ALP activity for all cMSCs in the presence of BMP-2. In late-stage assays, inclusion of dexamethasone and BMP-2 at Day 1 of culture produced robust monolayer mineralization for autologous cMSCs. Delivering 100 nM dexamethasone at Day 1 improved mineralization and reduced the BMP-2 concentrations required to achieve mineralization of the marginal cMSCs. For iPS-cMSCs, dexamethasone was inhibitory to both ALP activity and monolayer mineralization. There was increased expression of osteocalcin and osterix with BMP-2 in autologous cMSCs but a more modest expression occurred in iPS cMSCs. While autologous and iPS-derived cMSCs respond similarly in early-stage osteogenic assays, they exhibit unique responses to dexamethasone and BMP-2 in late-stage mineralization assays. This study demonstrates that dexamethasone and BMP-2 can be titrated in a time- and concentration-dependent manner to enhance osteogenesis of autologous cMSC preparations. These results will prove useful for investigators performing translational studies with cMSCs while providing insight into iPS-derived cMSC osteogenesis.

Primary inclusions of burbankite in carbonatites from the Fen complex, southern Norway

Carbonatites in the Fen intrusive complex (southern Norway) contain abundant burbankite (confirmed by Raman microspectroscopy) as inclusions in calcite, dolomite and, less commonly, fluorapatite and pyrochlore. Typically the inclusions occur in the core of calcite or dolomite grains relatively unaffected by subsolidus processes, and are associated with Fe-poor dolomite or Sr-rich calcite, respectively. Burbankite does not exceed 30 × 50 μm in size and is characteristically absent from the peripheral areas of carbonate grains affected by recrystallization or interaction with fluids. Compositionally, the mineral falls within the following range: (Na1.51–2.16Ca0.58–1.21)(Sr1.50–2.42Ca0.28–0.57LREE0.05–0.64Ba0.06–0.41)(CO3)5 and contains low Th, but no detectable Mg, Fe or F (LREE = light rare-earth elements: Ce > La > Nd > Pr > Sm). Burbankite inclusions at Fen are interpreted as primary and indicative of Na enrichment in their parental carbonatitic magma. Dissociation of burbankite during subsolidus re-equilibration of its host phases with fluids undoubtedly served as one of the sources of LREE for the development of late-stage mineralization in the Fen complex.

Upper temperature limits of orogenic gold deposit formation: Constraints from TiO2 polymorphs in the Dongyuan Au deposit, Jiangnan Orogen, China

Abstract Gold (Au) deposits have formed in orogenic belts throughout Earth’s history. However, the upper temperature limits of orogenic Au vein formation are difficult to constrain because measurements made on fluid inclusions focus on intermediate to late-stage minerals (e.g., quartz and calcite) or are based on P-T estimates for the metamorphic mineral assemblages of the host rocks. We conducted a study of TiO2 polymorphs that are among the earliest minerals that grew in Au-bearing veins of the Dongyuan deposit, Jiangnan orogenic Au belt, South China. Based on Raman analyzes, we identified TiO2 polymorphs of anatase (with Raman peaks at 396, 515, and 638 cm−1), rutile (with Raman peaks at 235, 447, and 613 cm−1), and anatase–rutile intergrowths. Transmission electron microscope (TEM) confirmed the polymorphs identifying the [111] zone axis of anatase, [110] zone axis of rutile, and [111] and [111] zone axes of rutile–anatase intergrowths. The TiO2 polymorphs in the Dongyuan Au veins constrain a temperature range for early mineral precipitation in the veins of 450–550 °C. The results show that ore-forming fluids for this orogenic Au deposit emplaced in the shallow crust originated from deeper and hotter crustal levels (e.g., high-grade metamorphic rocks in the middle to lower crust).

Evolution of Multistage Hydrothermal Fluids in the Luoboling Porphyry Cu-Mo Deposit, Zijinshan Ore Field, Fujian Province, China: Insights from LA-ICP-MS Analyses of Fluid Inclusions

Abstract The Luoboling Cu-Mo deposit, with 1.4 million tons (Mt) Cu and 0.11 Mt Mo, is the largest porphyry deposit in the Zijinshan district of southeast China. Mineralization at Luoboling is divided into premineralization, synmineralization, and late-mineralization stages. Consistent Cs/(Na + K) ratios in fluid inclusions suggest that the mineralizing fluids originated from a common source—the Luoboling granodiorite porphyry. The absence of initial supercritical fluid inclusions and abundant coexisting vapor and brine fluid inclusions imply that the fluids exsolved at low-pressure two-phase conditions, with temperatures of 250° to 600°C and salinities of 30 to 60 wt % NaCl equiv (brines) and &amp;lt;10 wt % NaCl equiv (vapors). The deposit formed at ~120 to 800 bar, corresponding to the depths of ~1.2 to 3.2 km (assuming a transition from lithostatic to hydrostatic load). Metals such as Mo (up to 77 ppm), Pb (up to 8,800 ppm), Zn (up to 13,000 ppm), and Ag (up to 130 ppm) migrated mainly in brines. Although vapor inclusions have high concentrations of Cu (up to 20,000 ppm), hypersaline fluid was the major medium for Cu transport and precipitation. The successive precipitation of Mo and Cu occurred when fluids cooled to ~500°C and ~350° to 450°C, respectively. The late-stage quartz-pyrite veins with phyllic alteration were formed by Cu-rich magmatic hydrothermal fluids. The Zijinshan epithermal Cu-Au deposit and the Luoboling porphyry Cu-Mo deposit originated from independent hydrothermal systems. Nonetheless, the increasing trends of Pb, Zn, and Ag concentrations in different stage inclusions from Luoboling imply potential for distal Pb-Zn-Ag mineralization.

The geology, magnetite geochemistry, and oxygen isotopic composition of the Akesayi skarn iron deposit, Western Kunlun Orogenic Belt, Xinjiang, northwest China: Implications for ore genesis

The Akesayi skarn iron (Fe) deposit is hosted by the Huangyangling Group within the Tianshuihai Terrane of the Western Kunlun orogenic belt, Xinjiang, China, and consists of several orebodies that formed along contacts between Miocene syenogranite, diorite porphyry dykes and late Paleozoic carbonate rocks. Manganese-bearing skarn minerals are common within the deposit. The ore-forming process can be divided into five stages: Prograde skarn stage (I), retrograde skarn stage (II), oxide stage (III), quartz-sulfide stage (IV), and carbonate stage (V), with this evolution being typical of Fe skarns. Magnetite, which formed mainly during the retrograde skarn and oxide stages, includes banded (BO), disseminated (DO), and massive (MO) magnetite. Backscattered-electron images indicate that magnetite within the massive ores can be further classified as primary (MO-1) and secondary (MO-2) magnetite.Magnetite within all ore types exhibits a strongly negative correlation between Si and Fe3+ contents, indicating that Si was incorporated into intra-crystalline sites of magnetite by substitution of Si4+ for Fe3+. Positive correlation among Al, Mn, Mg, and Si contents indicate that these elements behaved similarly during magnetite formation. The δ18OV-SMOW values of MO-1 magnetite range from 4.3‰ to 4.7‰, higher than magmatic magnetite (1‰–4‰), while the BO and DO magnetite have lower δ18OV-SMOW values of 1.7‰ to 2.4‰ and 1.8‰ to 2.5‰ respectively. Its anomalous oxygen isotopic composition indicates that most magnetite in the Akesayi Fe deposit precipitated from evolved ore-forming fluids formed by reaction between country rocks and primary magmatic fluids during the early stages of mineralization, with input from meteoric water during the later stages of mineralization. Trace-element patterns indicate that the different types of magnetite share a common source, with variations in the magnetite geochemistry amongst the different ore types of the Akesayi Fe deposit reflecting variations in the extent of fluid-rock interaction, dissolution-reprecipitation, mineral precipitation, temperature, and oxygen fugacity (ƒO2). The different types of magnetite of the Akesayi skarn Fe deposit form distinguishable populations in (Ca + Al + Mn)-(Ti + V) and (Ni/(Cr + Mn))-(Ti + V) discrimination diagrams, with the range of compositions possibly indicating more variable magnetite compositions in skarn deposits than previously thought.

Geochemical and Isotopic Signature of Pyrite as a Proxy for Fluid Source and Evolution in the Candelaria-Punta del Cobre Iron Oxide Copper-Gold District, Chile

Abstract Pyrite is ubiquitous in the world-class iron oxide copper-gold (IOCG) deposits of the Candelaria-Punta del Cobre district, documented from early to late stages of mineralization and observed in deep and shallow levels of mineralized bodies. Despite its abundance, the chemical and isotopic signature of pyrite from the Candelaria-Punta del Cobre district, and most IOCG deposits worldwide, remains poorly understood. We evaluated in situ chemical and isotopic variations at the grain scale in a set of pyrite-bearing samples collected throughout the district in order to characterize and further understand the nature of mineralization in this IOCG system. Our multianalytical approach integrated synchrotron micro-X-ray fluorescence (μ-XRF) mapping of pyrite grains with electron probe microanalysis and laser ablation-inductively coupled plasma-mass spectrometry data, and sulfur isotope determinations using secondary ion mass spectrometry (SIMS) complemented with bulk sulfur isotope analyses of coeval pyrite, chalcopyrite, and anhydrite. Synchrotron μ-XRF elemental concentration maps of individual pyrite grains reveal a strong zonation of Co, Ni, As, and Se. The observed relationships between Ni and Se are interpreted to reflect changes in temperature and redox conditions during ore formation and provide constraints on fluid evolution. Co and Ni concentrations and ratios suggest contributions from magmas of mafic-intermediate composition. Pyrite chemical concentrations reflect potential stratigraphic controls, where the sample from the upper part of the stratigraphy diverges from trends formed by the rest of the sample set from lower stratigraphic levels. The SIMS δ34S values of pyrite (and chalcopyrite) range between –2 up to 10‰, and bulk δ34S values of pyrite range between 4 up to 12‰. The majority of the δ34S analyses, falling between –1 and 2‰, indicate a magmatic source for sulfur and, by inference, for the hydrothermal ore fluid(s). Variation in the δ34S signature can be explained by changes in the redox conditions, fluid sources, and/or the temperature of the hydrothermal fluid. The Se/S ratio combined with δ34S values in pyrite is consistent with mixing between a magmatic-hydrothermal fluid and a fluid with a probable basinal signature. The results of this study are consistent with the hydrothermal fluids responsible for mineralization in the Candelaria-Punta del Cobre district being predominantly of magmatic origin, plausibly from mafic-intermediate magmas based on the Ni-Co content in pyrite. External fluid incursion, potentially from a basinal sedimentary source, occurred late in the evolution of the system, adding additional reduced sulfur as pyrite. There is no evidence to suggest that the late fluid added significant Cu-Au mineralization, but this cannot be ruled out. Finally, the data reveal that trace element ratios coupled with spatially resolved sulfur isotope data in pyrite are powerful proxies to track the magmatic-hydrothermal evolution of IOCG systems and help constrain the source of their contained metals.

A cold-water trap as an essential process for the generation of low-sulfidation epithermal deposits: Geological and numerical studies of the Hosokura deposit, northern Japan

Although low-sulfidation epithermal deposits, including the Hosokura deposit (Ag–Pb–Zn) in the Miyagi Prefecture, northern Japan, are globally significant metal sources, their ore deposition mechanisms are not thoroughly understood . This study aimed to construct a genetic ore deposition model for this deposit by focusing on the richest vein, the Fuji, and test the model using a numerical simulation of the formation and transitions of this fossil geothermal system. It was proposed that the mixing of neutral hydrothermal fluids (~260 °C) ascending through the vein with oxygenated cold groundwater caused early stage mineralization and the transport of hydrothermal fluids into the surrounding host rocks, forming a hydrothermal alteration halo around the vein that results in silicification, adularia alteration, and argillization. The progress of this alteration decreased the permeability of the halo and generated a mushroom-shaped low-permeability alteration halo (LPAH) in permeable zones surrounding the vein. The low-permeability and insulating properties of the LPAH increased the fluid temperature, the vein fluid boiled, and consequently the middle stage mineralization occurred. After a further decrease in LPAH permeability, hydrothermal brecciation resulting from increasing fluid pressure occurred at the top of the vein, resulting in late-stage mineralization. A TOUGH2 numerical simulation tested these proposed processes: early stage cooling of hydrothermal fluids by mixing with groundwater, the development of vapor in the vein by the formation of an LPAH during the middle stage, and an increase in fluid pressure leading to hydrothermal brecciation during the late-stage. The results of the simulation confirmed that a cold-water trap is an essential process for the generation of low-sulfidation epithermal deposits. Mushroom-shaped LPAHs, silicification zones, and brecciated veins caused by cold-water traps have been found in representative low-sulfidation epithermal deposits in Japan, such as the richest Au deposit, the Hishikari. Therefore, identification of cold-water-trap footprints can contribute to the exploration of this type of deposit.

Fluid inclusion, H–O–S isotope and rare earth element constraints on the mineralization of the Dong’an Sb deposit, South China

Systematic geochemical study on the Cambrian strata-hosted Dong’an Sb deposit in the Central Hunan Sb belt would provide key information on the origin of the low-temperature mineralization in South China. In this study, microthermometric, H–O isotopic and fluid composition analyses on ore-bearing quartz, S isotopic analyses on sulfides, and rare earth element (REE) analyses on wall-rocks and monominerals (stibnite, pyrite and quartz) in ores were conducted to constrain the genesis of the Dong’an Sb deposit. Two major stages of mineralization were identified in the Dong’an deposit: (1) an early pyrite-stibnite-quartz stage mineralization with intense wall-rock alteration occurring at depth of the deposit, and (2) a late quartz-stibnite stage mineralization occurring at shallow depths. Microthermometric analyses reveal a low temperature (150 to 230 °C), low salinity (4.5–7.0 wt% NaCl equiv.), low density (0.88–0.96 g/cm3), low pressure (4.5 MPa) and weakly acid (pH = 5.74) fluid for the Sb mineralization. Compositional analyses for fluid inclusions show that the main ion compositions are Na+, K+, Mg2+, Ca2+, F−, Cl− and SO42−, while the gas compositions are dominated by H2O and CO2. This suggests that the ore-forming fluids were enriched in alkali metals, sulfur and halogen. The H–O isotopic compositions (δ18OH2O = 2.52‰ to 7.13‰, δ2HH2O = −88.6‰ to −58.3‰) of fluid inclusions in quartz suggest a mixture of magmatic water, metamorphic rocks-derived brine and meteoric water. The δ34S values of stibnite (−1.32‰ to +2.86‰) and pyrite (+17.4‰ to +23.6‰) are very different, suggesting multi-sulfur sources involving buried magmatic rocks, ore-bearing meta-sedimentary rocks and deep basement rocks. The decreasing of REE contents from early to late mineralization stages reflects a decrease of temperature, reduction of fluid-rock interaction and input of meteoric water along with the stibnite precipitation. We propose that Precambrian strata that underwent regional metamorphism during Early Paleozoic acted as a Sb source bed, whereas strong tectono-magmatism in the early Mesozoic provided thermal driving force for the Sb mineralization occurring under a tensile stress in secondary faults at the shallow crust. This study highlights the use of multi-geochemical methods to constrain the genesis of large-scale Sb mineralization in South China.

Simvastatin induces adverse effects on proliferation and mineralization of human primary osteoblasts

BackgroundFrequently statins were administered to reduce the LDL-concentration in circulating blood. Especially simvastatin (SV) is an often prescribed statin. Pleiotropic effects of these drugs were reported. Thus, the aim of this study was to evaluate effects of SV on osteoblastic mineralization.MethodsAfter informed consent primary osteoblasts were collected from tissue surplus after treatment of 14 individuals in the Department of Cranio-Maxillofacial Surgery, University Hospital Münster. The cells were passaged according to established protocols. Viability, mineralization capability and osteoblastic marker (alkaline phosphatase) were determined at day 9, 13 and 16 after adding various SV concentrations (0.05 μM, 0.1 μM, 0.5 μM, 1.0 μM). Statistical analysis was performed using the Kruskal-Wallis-test.ResultsThe cell cultures showed a time and dose-dependent significantly decreased viability (p < 0.01) and a significantly increased mineralization (p < 0.01) in a late mineralization stage after adding SV. The typical alteration of the alkaline phosphatase (ALP) levels during osteogenic differentiation was not recognizable.ConclusionsThe pleiotropic effects found for different SV concentrations were possibly originated from other mineralization pathways beside the ALP induced one. Additionally, possible alterations of protein expression levels during mineralization and investigation of possible deviating application of SV in other treatment fields can be considered after gaining a deeper insight in the affected mechanisms.