Transport Of Gold Research Articles

Comparative evaluation of remaining dentin thickness and root canal transportation in curved canals with newer nickel–titanium single and multiple rotary file systems: A cone-beam computed tomography study

Abstract Context: The purpose of this study was to evaluate and compare the remaining dentin thickness and root canal transportation of WaveOne GOLD, XP-endo Shaper, and GenEndo file systems to assess their performance in curved canals using cone-beam computed tomography (CBCT) imaging. Materials and Methods: Seventy-five extracted maxillary first molars were selected with a curvature ranging between 15° and 30°. The samples were allocated into three groups (n = 25) and shaped using WaveOne GOLD, XP-endo Shaper, and GenEndo files. CBCT images were captured before and after instrumentation. Statistical Analysis: The remaining dentin thickness and root canal transportation were measured at 3, 5, and 7 mm from the apex in both mesiodistal and buccolingual directions. The data were statistically analyzed using one-way ANOVA followed by Tukey’s post hoc test. Results: GenEndo file system demonstrated greater preservation of remaining dentin thickness and resulted in less root canal transportation compared to the WaveOne GOLD and XP-endo Shaper systems across all three levels. Conclusions: GenEndo file system which comprises multiple files has removed less amount of dentin and canal transportation when compared to single file systems, i.e., WaveOne GOLD and XP-endo Shaper file systems.

Evaluation and Comparison of Dentin Thickness, Centering Ability, Canal Transportation, and Instrumentation Time of Pro AF Baby Gold and Pedoflex Files in Primary Root Canals Using a Cone Beam Computed Tomographic Analysis: An In Vitro Study.

Pediatric rotary systems have the advantage of improved canal centricity and conservative canal preparation with better obturation quality. Pro AF Baby Gold and Pedoflex files are two exclusive pediatric rotary file systems that were introduced in recent times. The aim of the present study is to compare and evaluate the dentine thickness, centering ability, canal transportation, and instrumentation time of Pro AF Baby Gold and Pedoflex files using cone beam computed tomography (CBCT). A total of 40 extracted human primary molar teeth with a minimum 7 mm root length were included in the study and randomly divided into two groups: group I, Pro AF Baby Gold; group II, Pedoflex files. Teeth were imaged preoperatively with CBCT, then root canal preparation was done in both groups with respective files, followed by postoperative CBCT imaging to evaluate the dentin thickness, centering ability, and canal transportation of both groups. Instrumentation time was noted using a stopwatch. There is a statistically significant difference in the instrumentation time; Pedoflex took a shorter time when compared to Pro AF Baby Gold files. Regarding canal transportation, there was no significant difference between the two files, with Pedoflex showing a better value than the other files. Regarding centering ability, there was no significant difference between the two files, with Pro AF Baby Gold having a better value than the other files (p < 0.001). From the findings of our present study, it was found that both systems were able to effectively shape curved root canals in terms of canal transportation and centering ability. Busi S, PJ N, Deoghare A, et al. Evaluation and Comparison of Dentin Thickness, Centering Ability, Canal Transportation, and Instrumentation Time of Pro AF Baby Gold and Pedoflex Files in Primary Root Canals Using a Cone Beam Computed Tomographic Analysis: An In Vitro Study. Int J Clin Pediatr Dent 2024;17(8):892-897.

Redistribution of fine gold from hydrothermal sources to sedimentary sinks, Rakaia River, Canterbury, New Zealand

ABSTRACT The Rakaia River in the South Island of New Zealand is a unique catchment in which to trace active detrital gold transport, deformation and concentration from near-coeval orogenic sources. The catchment hosts widespread small late Cenozoic hydrothermal alteration zones, some of which are gold-bearing, in actively rising and eroding mountain headwaters. Detrital gold liberated from the sources is distinctively porous with abundant micron-scale silicate inclusions, especially albite. Fine gold (∼200–100 µm) has been transported >100 km downstream, but coarse gold remains highly diluted in proximal fluvial sediments. Fine gold is also diluted by coarse fluvial sediments that form the upper kilometre of the Canterbury sedimentary basin southeast of the mountain front. Minor re-concentration of fine gold occurs in a bedrock gorge at the mountain front, and on steep ocean beaches beyond the river mouth. Despite the long-distance transport, the fine gold particles have been only superficially modified by surface smearing and minor flattening. The gold may have travelled in suspension in the river, buoyed by electrostatically adhering fine micas, in contrast to detrital garnets that were rounded in bed-load. In contrast, detrital gold on the western side of the mountains has been flattened to thin flakes during bed-load transport.

Beach gold transport and aeolian concentration, southern New Zealand

ABSTRACT Aeolian concentration of iron-titanium oxides (black sand) is a common phenomenon on coasts around the world but associated aeolian detrital gold is relatively rare. In contrast, Holocene and active dunes at Waipapa beach on the coast of the southern South Island of New Zealand host aeolian black sand layers with locally abundant finely particulate (<200 µm) gold and platinum, some of which have been mined historically. Aeolian concentration of black sand, gold and platinum is driven by strong prevailing westerly winds (gusts >100 km/h) on annual or decadal time scales. Holocene fluvial recycling of aeolian sands has been important in upgrading the black sand, gold, and platinum contents. Surf concentration of black sand on the beach is minor and merely feeds the aeolian system, and this differs from other beach gold deposits around the world, which are surf-dominated. Most of the Waipapa beach gold (>90%) has flaky morphology with abundant superficial transport-related deformation reflective of fluvial transport, probably down the nearby Mataura River (∼200 km transport) between Miocene and Holocene. Minor distinctive wind-sculpted toroidal gold, and the platinum, arrived from the west (∼300 km transport) via the Waiau River and Foveaux Strait.

Solvation Properties of Neutral Gold Species in Supercritical Water Studied By THz Spectroscopy

AbstractSupercritical water provides distinctly different solvation properties compared to what is known from liquid water. Despite its prevalence deep in the Earth's crust and its role in chemosynthetic ecosystems in the vicinity of hydrothermal vents, molecular insights into its solvation mechanisms are still very scarce compared to what is known for liquid water. Recently, neutral metal particles have been detected in hydrothermal fluids and proposed to explain the transport of gold species to ore deposits on Earth. Using ab initio molecular dynamics, we elucidate the solvation properties of small gold species at supercritical conditions. The neutral metal clusters themselves contribute enormous THz intensity not because of their intramolecular vibrations, but due to their pronounced electronic polarization coupling to the dynamical supercritical solvent, leading to a continuum absorption up to about 1000 cm−1. On top, long‐lived interactions between the gold clusters and solvation water leads at these supercritical conditions to a sharp THz resonance that happens to be close to the one due to H‐bonding in liquid water at ambient conditions. The resulting distinct resonances can be used to analyse the solvation properties of neutral metal particles in supercritical aqueous solutions.

Solvent Extraction of Gold(III) by 2-Ethylhexanol and Modeling of Facilitated Transport across a Supported Liquid Membrane

The solvent extraction of gold(III) by undiluted 2-ethylhexanol or dissolved in toluene from a HCl solution has been investigated in this paper. The numerical analysis of gold distribution data suggests the formation of HAuCl4·L and HAuCl4·2L (L = 2-ethylhexanol) species in the organic phase, with formation constants K11 = 38 and K12 = 309, respectively. The results derived from gold(III) distribution have been implemented in a solid-supported liquid membrane system. The influence of several variables on gold transport has been considered: feed and receiving phases’ stirring speeds, HCl and gold concentrations in the feed phase, and carrier concentration in the membrane phase as well as the presence of base metals (Fe, Cu, Ni) and platinum-group metals (PGMs) in the feed phase. Gold transport is influenced by the stirring speed of the feed phase and the variation in HCl and gold (feed phase) and carrier (membrane phase) concentrations. Also, diffusional resistances to mass transfer are estimated, and the contribution of each resistance to gold transport is estimated. Gold is recovered as zero-valent nanoparticles.

Gold Migration and Precipitation as Collaurum in Orogenic Gold Deposits: Constrains from Microscopic Gold Particles Observed in the Alteration Zone in Shanggong Gold Ore, Henan, China

Aqueous complexation has long been considered the only viable means of transporting gold to depositional sites in hydrothermal ore-forming systems. Here, we present direct evidence supporting an alternative hypothesis, namely, the transport of gold as colloidal particles. We observed nano-scale gold particles adsorbed on halloysite and micro-scale gold particles in altered rocks by TEM and SEM in the Shanggong orogenic gold deposit. Based on this evidence, we propose a feasible model for the origin of microscopic gold particles in alteration zones. In the early stage of ore-forming fluid, gold may migrate in the form of collaurum, which is maintained by supercritical CO2 and colloidal silica. Low salinity and high pressure are conducive to the stable migration of colloidal gold. When the physicochemical conditions change, some collaurum is precipitated and adsorbed by the clay minerals produced by hydrothermal alteration, and some collaurum undergoes growth and evolves into micro-submicrometer-sized gold particles. This study highlighted the significance of collaurum in the formation of orogenic gold deposits.

The genesis of the Baguamiao orogenic gold deposit linked to multistage ore-forming processes in Triassic tectonic transition of South Qinling, China

The Baguamiao gold deposit represents one of the largest Triassic orogenic gold deposits in the South Qinling metallogenic belt of central China. Here we investigate Ar-Ar dating of sericite and muscovite, fluid inclusion of quartz, the trace element and sulfur isotopic composition of pyrite from different mineralization stage in the Baguamiao gold deposit to gain insights into the ore genesis. The Ar-Ar dating results yield 40Ar/39Ar plateau ages of 217.5 ± 2.1 Ma, 209.2 ± 0.2 Ma and 208.8 ± 0.2 Ma, indicating a two-stage gold mineralization during the tectonic transition from the early metamorphic deformation (at ca. 218 Ma) to the late extension (ca. 209 Ma) in the post-collision environment. Fluid inclusion, trace element and sulfur isotopic analyses reveal that the two stages gold mineralization show different sources. The early mineralization period developed CO2-rich inclusions with medium temperature (317–413 °C) and medium–low salinity (4.62–18.81 wt% NaCleqv.), and is characterized by formation of Py1 and Py2 with depleted Au, Cu, Pb, Zn, Ag, Te and Bi. The sulfur isotope data of Py1 and Py2 are between 3.6 ∼ 10.5 ‰, suggesting that the sulfur source was mainly derived from the surrounding rock (Xinghongpu Group). The late mineralization period developed medium–high temperature (321–453 °C), medium–high salinity (3.3–19.62 wt% NaCleqv.) CO2-rich inclusions and high-temperature and high-salinity daughter crystal inclusions, and is characterized by formation of Py3 and Py4 with obviously higher arsenic and metal contents, such as Au, As, Cu, Pb, Zn, Ag, Cr, Ti, Mn, Sb. The δ34S values of Py3 and Py4 are 8.3 ∼ 18.8 ‰, suggesting a mixed fluid of the Xinghongpu Group and Gudaoling Group with deep magmatic-hydrothermal fluids. We propose that the two periods of gold mineralization in the Baguamiao deposit, in response to the collision assembly of Qinling Orogenic Belt, preserve evidence for diverse metal sources with the early mineralization period sourced from the metamorphism of the upper crust (Xinghongpu Group) in the compressional stage (ca. 218 Ma), and the late mineralization period characterized by the contribution of the Xinghongpu Group, Gudaoling Group and deep magmatic-hydrothermal fluids in a post-collisional extensional setting (ca. 209 Ma). The role of metamorphism and magmatic activity during the Triassic Qinling orogenic processes is considered to be important in the remobilization, transport and enrichment of sulfur, arsenic and gold (and potentially other trace elements) from the earlier formed seafloor exhalation sequence.

Likely gold transportation via organic complexes in sediment-hosted orogenic gold deposits in southern Tibet: From the perspective of thermodynamic modelling

Carbon dioxide and hydrocarbons, typically considered to be end products of organic matter (OM) in metasedimentary rocks and are commonly observed in the sediment-hosted orogenic gold deposits. It has been suggested that gold can be possibly transported via Au-organic complexes during gold mineralization, which, however, has been overlooked. However, whether gold can be transported via Au-organic complexes during gold mineralization has not been verified. In this study, we took the sediment-hosted orogenic gold deposits in southern Tibet as an example and applied thermodynamic modelling to test this hypothesis. The thermodynamic data for gold acetate is the only comprehensive set available for Au-organic complexes in current common thermodynamic datasets. Therefore, we examined the thermal stability of gold acetate in metamorphic ore-forming fluids at temperatures ranging from 150 to 350 °C at 800–5000 bar and 600 °C at 30000–70000 bar, which are the conditions of gold transportation and deposition in southern Tibet. Our thermodynamic modeling results show that OM begins to decomposition as pressure and temperature rise at 350 °C and 3000 bar. Acetate (CH3COO–) and acetic acid (CH3COOH) remain stable and form in large quantities under a lower geothermal gradient with temperatures below 450 °C and above 3000 bar. We additionally demonstrate that the organic compounds have strong stability in the lower crustal even the upper mantle rocks (pressures > 30000 bar). Simultaneously, gold can combine with acetate to form Au-organic complexes, such as Au(CH3COO) and Au(CH3COO)2- in the ore-forming fluids. As temperature increases at constant pressure, Au(CH3COO) and Au(CH3COO)2- gradually decompose, leading to an increase in CO2 and CH4 content. The findings suggest that organic matter (OM) can transport gold during mineralization processes in southern Tibet, indicating its potential for gold transportation under specific conditions.

Combined Effect of Organic Carbon and Arsenic on the Formation of Sediment-Hosted Gold Deposits: A Case Study of the Shahuindo Epithermal Deposit, Peru

Abstract Sediment-hosted gold deposits represent a significant portion of the world’s gold resources. They are characterized by the ubiquitous presence of organic carbon (Corg; or its metamorphosed product, graphite) and the systematic occurrence of invisible gold-bearing arsenian pyrite. Yet the role played by these features on ore formation and the distribution of gold remains a long-standing debate. Here, we attempt to clarify this question via an integrated structural, mineralogical, geochemical, and modeling study of the Shahuindo deposit in northern Peru, representative of an epithermal gold deposit contained in a sedimentary basin. The Shahuindo deposit is hosted within Lower Cretaceous fluvio-deltaic carbon-bearing sandstone, siltstone, and black shale of the Marañón fold-and-thrust belt, where intrusions of Miocene age are also exposed. The emplacement of the auriferous orebodies is constrained by structural (thrust faults, transverse faults) as well as lithological (intrusion contacts, permeable layers, anticlinal hinge in sandstone) features. The defined gold reserves (59 tons; t) are located in the supergene zone in the form of native gold grains. However, a primary mineralization, underneath the oxidized zone, occurs in the form of invisible gold in arsenian pyrite and arsenopyrite. Here, four subsequent pyrite generations were identified—namely, pyI, pyII, pyIII, and pyIV. PyI has mean Au concentrations of 0.3 ppm, contains arsenic that is not detectable, and is enriched in V, Co, Ni, Zn, Ag, and Pb compared to the other pyrite generations. This trace element distribution suggests a diagenetic origin in an anoxic to euxinic sedimentary basin for pyI. Pyrite II and pyIV have comparable mean Au (1.1 and 0.7 ppm, respectively) and As (2.4 and 2.9 wt %, respectively) concentrations and precipitated under conditions evolving from lower (pyrrhotite, chalcopyrite, sphalerite) to higher (enargite, digenite, chalcocite) sulfidation, respectively. The pyIII generation is the major gold event in the primary mineralization, with pyrite reaching 110 ppm Au (mean ~7 ppm) and 5.6 wt % As (mean ~1.8 wt %), while coeval arsenopyrite attains 460 ppm Au. Pyrite III is also enriched in other trace elements such as Se, Ge, Mo, In, Ga, and Bi compared to the other pyrite generations, which is indicative of a magmatic source. Bulk analyses of the surrounding unmineralized rocks show only parts per billion levels of Au and less than 25 ppm As. These data, combined with mass balance considerations, demonstrate that the sedimentary rocks could not be the sole source of gold, as they could only contribute a minor portion of arsenic and sulfur (and iron) to the deposit. Conversely, fluids exsolved from a pluton crystallizing at depth likely provided the great part of the gold endowment. Equilibrium thermodynamics simulations, using geochemical constraints established in this study, demonstrate that interaction between Au-As-S-Fe–bearing fluids and organic carbon-bearing rocks strongly enhanced the fluid ability to transport gold by maximizing its solubility as AuI hydrosulfide complexes via a combined increase of pH and aqueous sulfide concentration. This finding challenges the traditional qualitative view of organic matter acting exclusively as a reducing agent for AuI that should promote gold deposition in its native state (Au0) rather than enhance its solubility in the fluid. Our results have significant implications for the exploration of carbonaceous sedimentary environments. Such settings may provide a very effective mechanism for focusing gold transport. Subsequent scavenging of AuI from solution in a chemically bound form is promoted by the precipitation of arsenian pyrite in permeable structural and lithologic traps, bound by more impermeable units, similar to what occurs in petroleum systems. Our integrated study underlines the important potential of sedimentary Corg-bearing rocks in the formation and distribution of gold and associated metal resources.

Origin and evolution of gold-bearing fluids in a carbon-rich sedimentary basin: A case study of the Algamarca epithermal gold-silver-copper deposit, northern Peru

Sediment-hosted gold deposits account for the major part of economic gold in the Earth's crust. However, the origin of the gold-bearing fluid and its evolution in sedimentary basins in the presence of organic carbon and its metamorphosed products such as graphite are poorly known. In an attempt to clarify these issues, we performed an integrated mineralogical, geochemical, and fluid-inclusion study of the Algamarca epithermal Au-Ag-Cu deposit, hosted by Mesozoic sediments corresponding to an over-mature petroleum system within the Marañón fold and thrust belt (northern Peru). Results show that mineralization started with a pre-gold stage characterized by quartz veins containing gold-poor pyrite and chalcopyrite. Most gold was deposited afterwards, during the main gold stage in an “invisible” form within arsenian pyrite, followed by minor visible native gold with sulfosalts and chalcopyrite at a later stage. Fluid inclusions in quartz from the pre-gold and gold stages show features analogous to those observed in porphyry Cu-Au systems such as vapor–liquid immiscibility, enrichment in K, Rb, Cu, As, and Sb, a wide range of salinity (5–35 wt% NaCl eq.), and similar elemental (atomic) ratios (Zn/Pb ∼ 4, 0.1 < K/Na < 5, Br/Cl ∼ 0.06), all consistent with a fluid of magmatic origin. In addition, the fluid inclusions from the pre-gold stage are highly enriched in CO2 (∼60 mol% in gas phase), CH4 (∼10 mol%) and H2S (∼30 mol%). Such high volatile contents are rather unusual for typical porphyry-epithermal systems and likely reflect reactions between the magmatic fluid and carbon-bearing sediments. This conclusion is independently supported by the temperature values of graphite metamorphic peak determined by Raman spectroscopy, which are similar to those derived by fluid-inclusion microthermometry in quartz veins. Our findings imply that strong interactions of magmatic fluid with carbonaceous matter favored gold transport through the sedimentary basin and its subsequent concentration in arsenian pyrite. Furthermore, our results point to a possible presence of porphyry-style mineralization beneath the sedimentary sequence hosting the epithermal Algamarca deposit, thereby providing new potential for exploration.

Evaluation of Canal-centering Ability and Apical Transportation of Hyflex-EDM, OneShape, WaveOne Gold, and Reciproc Files: An Ex Vivo Study.

To evaluate and compare canal-centering ability (CCA), canal transportation (CT), and dentinal crack formation by using Hyflex-electrical discharge machining (EDM), OneShape, WaveOne Gold, and Reciproc single file system in the mesiobuccal root of maxillary first molar at coronal, middle, and apical third using cone-beam computed tomography (CBCT) and scanning electron microscopy (SEM). Mesiobuccal roots of 120 freshly extracted maxillary molar teeth were divided into four experimental groups; Hyflex-EDM, OneShape, WaveOne Gold, and Reciproc (n = 30/group). Preinstrumentation scanning was done using CBCT for all samples at coronal one-third (4 mm), middle one-third (8 mm), and apical one-third (12 mm). After cleaning and shaping with standard irrigation protocol, the specimens were again scanned. Canal-centering ability and CT were calculated using pre- and postinstrumentation CBCT values. A scanning electron microscope was used to identify dentinal crack formation. No significant difference was found for CCA by any of the systems at coronal, middle, and apical third, respectively. However, OneShape was found to have better CCA at the coronal third and WaveOne Gold at the middle and apical third. There was a significant difference in canal transportation at the apical third (p = 0.004) with WaveOne Gold having the least CT followed by Reciproc at the apical third. OneShape resulted in more dentinal cracks in the coronal and middle thirds. Also, Hyflex-EDM was better in the apical third. No difference in CCA was observed between the groups. The lowest values for CT were obtained for WaveOne Gold (similar to Reciproc) whereas both rotary files showed higher values for CT. Also, OneShape showed the most dentinal at all levels. Furthermore, Hyflex-EDM and WaveOne Gold produced the least dentinal cracks at all levels. Given that the Reciprocating file system had the least CT and least dentinal cracks, the clinical success rate of root canal treatment (RCT) with the Reciprocating file system can be a better choice to improve the longevity of root canal-treated teeth.

Interfacial adsorption of gold nanoparticles on arsenian pyrite: New insights for the transport and deposition of gold nanoparticles

Gold nanoparticles (AuNPs) are found extensively in the near-surface Earth system. The transport, aggregation, and deposition of AuNPs have been potentially recognized as an important process and even a fundamental intermediary step both in formation of high-grade gold deposits and in the dispersion of gold into the Earth's surface environment. The interfacial adsorption between AuNPs and sulfide minerals is a long-recognized process regulating transport and deposition of gold in hydrothermal fluids, and the occurance of Au and As in pyrite are often observed in various hydrothermal Au deposits. However, the adsorption behavior of AuNPs on sulfide minerals and the fundamental chemical mechanism for the AuAs relationship remain enigmatic. In this work, we selected citrate as a surrogate for typical natural organic compounds abundantly found in lower-temperature hydrothermal systems and Earth's surface environment, and experimentally investigated the adsorption of negatively charged AuNPs on pyrite and arsenian pyrite under anaerobic conditions. We demonstrate that pyrite and nanoparticle surface properties, and solution chemistry, control the adsorption process. Negligible adsorption of AuNPs on pyrite (absent of As) was verified under all experimental conditions likely due to high electrostatic repulsion. However, we observed AuNPs adsorption on arsenian pyrite and suggest that this interaction is due to negative charge-assisted hydrogen bonds ((−)CAHBs) between hydroxyl/oxyl groups on the surface of arsenian pyrite and carboxyl groups on the citrate capping agent of AuNPs. Also, the lower negative charge density of arsenian pyrite surfaces significantly reduces electrostatic repulsion between both negatively charged AuNPs and arsenian pyrite. The solution pH, coexisting organics (citrate) concentration, and ionic strength are demonstrated to play substantial roles in the adsorption of AuNPs on arsenian pyrite. However, the solution pH appears to be an overriding factor controlling the adsorption of AuNPs which decreases with the increase of pH. With respect to citrate concentration, the adsorption rates of AuNPs onto arsenian pyrite initially decreases, but only slightly, and then increases. Increased ionic strength also promotes the adsorption of AuNPs. Our findings highlight a potentially important role of AuNPs in transport and deposition processes of gold in aqueous mediums, and provide new insights on the geochemical behavior of metal nanoparticles in the hydrothermal systems and Earth's surface environment.

Magmatic Native Gold: Composition, Texture, Genesis, and Evolution in the Earth’s Crust

Abstract —Here we report results of microforms’ studies of native gold and its alloys in igneous rocks, modified to varying degrees by secondary processes. We discuss the composition and occurrence of both the deep-seated magmatic gold-bearing alloys and the products of their transformation under conditions of the upper Earth’s crust. Gold-bearing Kamchatka adakites and ankaramites, Ildeus massif mafic-ultramafic intrusions and adakites from the Stanovoy fold system as well as dacites from the Bolivian Andes were formed during melting of either the suprasubduction mantle wedge or the subducted oceanic crust. In depleted peridotites from the Avachinsky Volcano in Kamchatka as well as suprasubduction ophiolites from Polar Urals, Eastern Sayan and the Western Mediterranean Betic–Rifean belt, the gold-bearing mantle was hybridized by subduction-related melts and high-temperature fluids. Volcanic rocks associated with the Lesser Khingan Fe–Mn deposits and Zolotaya Gora Au deposit in Southern Urals as well as Taragai ultramafic rocks in the South Khingan Range display subduction-related geochemical characteristics. Gold-bearing trachytes in the Virginian Appalachians (USA) represent felsic differentiates of mafic intraplate magmas. We propose that one of the principal forms of gold transport into the upper crustal environments is represented by Cu–Ag–Au alloys, which precipitated from mantle-derived silicate melt enriched in chalcophile and siderophile elements. Such Cu–Ag–Au alloy-rich magmatic rocks can either constitute primary sources of precious metals in the mantle-crust system or serve as geochemical precursors to the formation of native gold assemblages in epithermal and mesothermal ore deposits. Presence of magmatic gold particles in subduction-related igneous rocks and mantle restites hybridized by subduction-derived melts and high-temperature fluids suggest the existence of gold-rich horizons in the Earth’s mantle at depths comparable to typical depths of generation of primary convergent zone and some within-plate magmas.

Fluid-rock interaction modeling to constrain Au enrichment: Implication for the giant Jiaodong Au mineralization, eastern North China Craton

The devolatilization model of the metasomatized lithospheric mantle without pre-enriched gold has been proposed to account for the giant gold mineralization. An excellent example is the world-class Jiaodong gold province with >5000 tonnes Au resources in the eastern North China Craton. The auriferous fluid transport and gold enrichment during wallrock alterations are two vital processes to determine the giant gold mineralization formation in this province. However, the effects of the fluid-rock interaction with alterations on the auriferous fluid transport and gold enrichment still keep poor understanding, which leads the above model to be imperfect. The giant Jiaojia goldfield in this province recorded a wallrock alteration evolution from K-feldspar alteration to pyrite-sericite-quartz alteration, and some parts of the latter can become gold orebodies when the gold grade is >1 ppm. This study conducts thermodynamic fluid-rock interaction modeling to reveal auriferous fluid transport and coupled relationship between gold enrichment and alteration mineral assemblage based on the alteration-mineralization and ore fluid characteristics of the goldfield. The modeling of fluid-rock interaction with cooling indicates the transformation of Au-Cl complexes to Au-S complexes combined with the total sulfur concentration decrease by pyrite precipitation when cooling from ∼460 °C can trigger the dispersive gold precipitation, which should hinder the gold long-range transport to lower ambient temperature. The high oxygen fugacity at >400 °C can enhance Au-Cl complexes stability, and the low pH can maintain high total sulfur concentration in the auriferous fluid, both of which facilitate the long-range gold transport to a lower-temperature environment. The auriferous fluid would acquire higher pH by the buffering of feldspars or sericite, which was beneficial for the high-efficiency precipitations of pyrite and gold. The ankerite-siderite assemblage without pyrophyllite in the pyrite-sericite-quartz alteration zone indicates that a cumulative fluid to rock mass ratio (f/r) of 3.8–4.8 should be needed for the transformation from K-feldspar alteration to pyrite-sericite-quartz alteration according to the fluid-rock interaction modeling at 300 °C and 2000 bar. In the case of auriferous fluids with ≤200 ppb Au concentration, the single fluid-rock interaction can only elevate the gold grade to ≤0.69–0.87 ppm in the pyrite-sericite-quartz alteration zone at f/r 3.8–4.8. Therefore, the fracture-induced fluid flow coupled with fluid-rock interaction is proposed to the prerequisite to elevate the gold grade to >1 ppm in the pyrite-sericite-quartz alteration zone. The metasomatized lithospheric mantle volume for the required ore fluid and Au in the Jiaodong province is estimated according to the modeling results and alteration-mineralization characteristics, which provides a link between the mantle without abnormal Au enrichment and the alteration-mineralization processes.

Post-orogenic exhumation triggers gold mineralization in the Trans-Hudson orogen: New geochronology results from the Lynn Lake greenstone belt, Manitoba, Canada

Metamorphic devolatilization is thought to be the critical process that can liberate gold from amphibolite facies source rocks to form orogenic gold deposits. However, a growing number of studies demonstrate that orogenic gold deposits are the product of multiple hydrothermal stages over 10 s to 100 s of Myr rather than one metallogenic event. Herein we report new geochronology results for orogenic gold deposits hosted within the Paleoproterozoic Lynn Lake greenstone belt (Manitoba, Canada) to address the knowledge gap. Garnet-hosted xenotime crystals, which occur in a folded pyrite veinlet with gold, yield a weighted average 207Pb/206Pb date at 1827 ± 8 Ma. This new and more precise age demonstrates that the earliest auriferous fluids at the MacLellan gold deposit coincided with the rapid burial of ca. 1836 Ma sedimentary rocks before regional metamorphism. New garnet-biotite geothermometry results further demonstrate that the earliest auriferous veins were preserved despite being metamorphosed to amphibolite facies conditions (505–689 °C). The peak metamorphic mineral assemblage is overprinted by: (1) the main xenotime- and gold-bearing deformation fabric (S2; 1790–1827 Ma); (2) an overprinting xenotime- and monazite-bearing S3 fabric that is also associated with gold-rich arsenopyrite (1769–1790 Ma); and (3) chlorite-hosted xenotime and gold (1747 ± 12 Ma) that are coeval with the oldest U-Pb apatite dates (1691–1740 Ma) and a prominent mode of 40Ar/39Ar biotite dates at ca. 1746 Ma. We suggest that the post-orogenic gold events are incompatible with the standard devolatilization model because they post-date subduction and peak-metamorphism by up to 80 Myr. Instead, the new geochronological results suggest that gold deposition at the MacLellan deposit was linked to burial and the subsequent exhumation of chemically reactive trap rocks through favourable temperature windows that allowed gold transport as sulphide complexes. Exhumation and far-field tectonics are interpreted as the most likely drivers of post-orogenic auriferous fluids rather than regional metamorphism and active subduction. This revised mineral systems model provides an explanation for the high prospectivity of high- and low-temperature mineral assemblages and suggests that mineral exploration should focus on the earliest ore-forming structures that are reactivated during multiple stages of orogenesis.

A mathematical model for cilia actuated transport of Gold–Silver hybrid nanofluid EMHD flow with activation energy phenomena

The advancement of nanobiotechnology is happening with leap and bound and the maneuvering in application of nanofluids in medical field is emerged as major research topic in recent times. Motivated by key applications in this direction, the current investigation embarks to explore the hybrid nanofluid dynamics in a ciliated inclined microchannel with various physical impacts, electromagnetohydrodynamic (EMHD), gyrotactic microorganisms, activation energy, and solar radiation. The pertinent equations of motion are tackled with low Reynolds number, long wavelength, and Debye–Huckel linearization approximations. The resulting equations of motion after simplifications tackled with the implementation numerical computations in Mathematica. The variations of pivotal physical parameters on the flow dynamics and thermal axiom are exhibited with graphical illustrations. It is worth mention here that the Hartmann, Grashof, electroosmotic, buoyancy, bioconvection parameters surged the hybrid nanofluid velocity adjacent to right wall. The temperature goes down with the thermal radiation and thermophoresis parameters. The radiation, Brownian motion, thermophoresis parameters reinforce the nanoparticle volume fraction, and motile microorganisms. The reported investigation has great significance for physiological fluid transport in the gastrointestinal tract, managing the bleeding by manipulating the magnetic field and in drug infusion mechanism.

Fluid regime of Olimpiada gold deposit formation

The PTX-parameters of the fluids formed the Olympiada gold deposit were determined using microthermometry and Raman spectroscopy of carbonic (CO2-N2-CH4) and aqueous-carbonic inclusions in quartz. Weakly gold-bearing metamorphic pyrrhotite-quartz veinlets were formed by oxidized (СО2 / СН4 = 10-100) nitrogen-carbon dioxide fluid at temperatures of 410-360 °C and a pressure of 2,4 ± 0,2 kbar. Gold-arsenopyrite mineralization was formed by deep-seated reduced (СО2 / СН4 ~ 1) methane-carbon dioxide-nitrogen fluid in the temperature range of 360-300 °C and pressure of 1,2 ± 0,1 kbar. Gold-antimonite mineralization was formed by nitrogen-methane fluid at temperatures 290-240 °C and pressure 0,8 ± 0,1 kbar. Gold transport was carried out in a boiling environment in carbonic phase.

Centering ability and root canal transportation of protaper gold and v taper gold using cone-beam computed tomography: An in vitro study

Introduction: This study aimed to evaluate the central ability and root canal transportation of two types of rotary files in curved molar canals using cone-beam computed tomography (CBCT) in mesiodistal (MD) and buccolingual (BL) directions.Method and Material: A total of 40 mesiobuccal root canals of mandibular first molars with an angle of 25-35 degrees and radius curvature of 5 millimeters were randomly divided into two groups of 20 canals each. Group A was prepared with Pro Taper Gold (PTG), and Group B with V Taper Gold (VTG). Pre- and post-instrument CBCT scans were recorded. Images were reconstructed, then cross-sections were detected corresponding to distances of 3, 6, and 9 mm from the anatomic apex using Gambill’s method. Statistical analysis was performed with T-test and repeated measure ANOVA. P-value was set at 0.05.Results: There was a significant difference in centering ratio and canal transportation at all three levels of 3-, 6-, and 9- mm, mesiodistally. PTG has higher centering ability in 6 mm and 9 mm sections with more canal transportation at 3 mm and 6 mm. In the BL direction, no statistically significant difference in central ability was observed among the PTG and VTG groups. The centering ability of both groups became higher from the apex to the coronal part. The last and the most canal transportation in both PTG and VTG groups was reported at 6 mm level and 9 mm level, respectively.Conclusion: Both rotary instruments efficiently cleaned and shaped curved canals. ProTaper Gold had better centering ability, while V Taper Gold showed less canal transportation.

Ore fluid characteristics and depositional processes of the hydrothermal gold mineralisation at Damang, Southwestern Ghana

Gold mineralisation at Damang in the southwestern part of Ghana occurs in two types of geological settings: (1) as paleoplacer in the Banket Series conglomerates of the Tarkwaian system and (2) in hydrothermal sheeted quartz vein system that crosscuts all the Tarkwaian lithologies including the palaeoplacer units. This paper focused on the second type because not much research has be conducted on the fluid inclusion and stable isotope characteristics of the Damang deposit to reveal the nature of the hydrothermal ore-forming associated the quartz veins and gold deposition. Microthermometry measurements of fluid inclusions in mineralised quartz veins indicated two sets of temperature-salinity variations: a relatively low temperature (142–292 °C) and moderate salinity aqueous fluids that range from 2.4 to 8.9 wt% NaCl equivalent, and a high temperature (210–393.6 °C) with low salinity aqueous-carbonic fluids with the salinity ranging from 1.0 to 2.6 wt% NaCl equivalent. These fluids are inferred to have unmixed from a homogeneous fluid with an average salinity of 3.85 ± 2.42 wt % NaCl equivalent. Laser Raman spectroscopic data on the fluid inclusions confirmed an aqueous-carbonic (H2O–CO2–NaCl) composition of the fluids with minor amounts of H2S, CH4 and SO2 as volatile species. The temperature of gold precipitation based on overlapped temperatures of chlorite, fluid inclusions and stable isotope geothermometers, indicated a mean temperature of 324.7 ± 20 °C and corresponding pressures from 1.1 to 3.5 kbar. The calculated oxygen isotopic composition of the ore fluids, δ18Ofluid using the estimated mineralisation temperature indicated average values of 9.3 ± 1.2‰. This isotopic range and the low salinity of the fluids (<10 wt % NaCl equiv.) are suggestive of metamorphic origin, which may be attributed to devolatisation reactions in the underlying Birimian greenstones. This is consistent with orogenic lode gold mineralisation in many Precambrian greenstone belts worldwide. The close association of gold with sulphides is consistent with gold transport as bisulphide complexes. A combination of factors including sulphidation and phase separation, concomitant with temperature decrease are inferred to be the principal factors that controlled the hydrothermal gold precipitation at Damang.