Gold Inclusions Research Articles

Mineralogická charakteristika hydrotermální mineralizace ze starých těžebních pozůstatků v oblasti Mladoňov - Nový Malín (silezikum)

In the area north of Mladoňov, which is built by phyllites and quartzites of the Vrbno Group and granite-derived phyllonites of the Desná Group (Silesicum, northern part of the Bohemian Massif), there were found two types of hydrothermal ore mineralization in vein material sampled from remnants of old mining/prospection. The Cu(-Bi-Au) mineralization hosted by quartz gangue was found at the locality Husarčina šachta. A main ore mineral is chalcopyrite, which contains inclusions of pyrite, native bismuth, bismuthinite, a phase close to bismite, and native gold with fineness of 717 - 818. Baryte, recorded in part of collected samples, probably represents a significantly younger hypogene mineralization. Supergene minerals include malachite, azurite, a phase close to chrysocolla, bornite, Cu-sulphides, tenorite, native copper, limonite and probably also cuprite. A quartz-pyrite-pyrrhotite mineralization with accessory arsenopyrite and xenotime-(Y) and supergene limonite and baryte was recorded at localities Husarčina šachta and Kopka. Sporadically, Fe-sulphides contain elevated contents of Au (measurable by means of an electron microprobe), probably due to submicroscopic inclusions of native gold. Gold could be leached from wall rocks by ore fluids and/or remobilized from older mineralization to the younger one. The presence of traces of Cr, Co and Ni in some ore minerals implies for wider circulation of parent fluids involving probably also basic or ultrabasic rocks.

Comparative experiments on the activation cyanide and chloride re-leaching of gold from the secondary mineral material of heaps of Aprelkovo mine

This article presents the results of comparative experiments on the activation chloride and activation carbonate-cyanide leaching of gold from the secondary mineral material of heaps of Aprelkovo mine. A cyanide scheme with a gradual increase in the cyanide concentration in the pregnant solution was adopted as a control scheme for percolation leaching. To establish the maximum recovery of gold and associated components, preliminary experiments with agitational cyanide leaching were carried out. In the course of the experimental work, some of the problems of gold recovery according to the classical cyanide scheme applicable to this deposit were identified and, thanks to the use of activated solutions, were solved. The reasons for the insufficiently high recovery are clogging and limited access of the complexing agent to encapsulated and chemically bound gold inclusions due to their high dispersion in the crystal lattices of concentrating minerals and the presence in the ore of minerals that tend to absorb water with a pronounced hydration effect.

Mineralogical and geochemical features of pyrite nodules of sulfide turbidites from the Talgan Cu–Zn massive sulfide deposit (South Urals)

Pyrite nodules were found in thin-layered sulfide ores localized at the flanks of the Talgan Cu‒Zn massive sulfide deposit (South Urals). The nodules consist of (1) an inner core of microgranular pyrite with inclusions of authigenic sulfides and host rock minerals, (2) an intermediate zone of anhedral and subhedral pyrite metacrystals, (3) an outer zone formed by parallel subhedral pyrite crystals and (4) dioctahedral chlorite rimming the pyrite crystals of zone 3. Each zone exhibits specific trace element association, which is identified using LA ICP-MS micromapping. The trace element content of pyrite significantly (by 13 orders of magnitude) decreases in a range of microgranular pyrite of the core an- and subhedral pyrite crystals of the intermediate zone subhedral pyrite crystals of the outer zone (average values, ppm): 131069 Zn, 241001783 Pb, 1323134 As, 10271.81 Co, 4564 Ni, 39038 Ag, 0.10.01 Au, 550.6 Te, 9.80.6 Bi. The subhedral pyrite crystals of the outer zone are enriched (ppm, up to) in Cu (8367), Sb (1627) and Mn (734) relative to microgranular pyrite of the core. The extremely high trace element contents are related to the inclusions of authigenic chalcopyrite, sphalerite, fahlore, gold and silver minerals. The host rock components of the nodules include quartz, calcite, chlorite, illite and REE minerals. The ore clasts of distal sulfide turbidites mixed with hyaloclastites, which were altered during dia- and anadiagenesis, were the source of ore material for the nodules.

Plasmonic Metamaterial Gels with Spatially Patterned Orientational Order via 3D Printing.

Optical properties can be programmed on mesoscopic scales by patterning host materials while ordering their nanoparticle inclusions. While liquid crystals are often used to define the ordering of nanoparticles dispersed within them, this approach is typically limited to liquid crystals confined in classic geometries. In this work, the orientational order that liquid crystalline colloidal hosts impose on anisotropic nanoparticle inclusions is combined with an additive manufacturing method that enables engineered, macroscopic three-dimensional (3D) patterns of co-aligned gold nanorods and cellulose nanocrystals. These gels exhibit polarization-dependent plasmonic properties that emerge from the unique interaction between the host medium’s anisotropic optical properties defined by orientationally ordered cellulose nanocrystals, from the liquid crystal’s gold nanorod inclusions, and from the complexity of spatial patterns accessed with 3D printing. The gels’ optical properties that are defined by the interplay of these effects are tuned by controlling the gels’ order, which is tuned by adjusting the gels’ cellulose nanocrystal concentrations. Lithe optical responsiveness of these composite gels to polarized radiation may enable unique technological applications like polarization-sensitive optical elements.

Source and evolution of the Luanling gold deposit in the Xiong'ershan region, western Henan Province: Constraints from pyrite trace elements, in situ sulfur isotopes, and He–Ar isotopes

The Luanling gold deposit is a lode gold deposit in the Xiong'ershan region located on the southern margin of the North China Craton. Based on typical mineral assemblages and relative Au contents, the pyrites in the Luanling deposit can be divided into four types: Py1‐s, pyrite with abnormally high levels of Au in pyrite–quartz veins; Py1, pyrite with low levels of Au in pyrite–quartz veins; Py2‐1, pyrite intergrowth with molybdenite; and Py2‐2, pyrite with higher concentrations of Au in association with molybdenite. Inductively coupled plasma mass spectrometry analyses reveal that the gold mainly occurs as “visible gold” (either native gold or electrum) inclusions and disseminations. “Invisible gold” is only hosted in the Py2‐2 pyrite grains, and Py1 and Py2‐1 contain low levels of Au concentrations (Py1 ≤ 6.563 ppm; Py2‐1 ≤ 8.377 ppm). Interestingly, As shows a strong correlation with gold concentrations in Py2‐2. The δ34S values of Py1 from Stage I span from −7.4‰ to −5.1‰. At Stage II, the δ34S values of Py2‐1 exhibit a range of −11.0‰ to −7.5‰. Pyrite in Py2‐2 shows δ34S values from −12.6‰ to −11.0‰. In situ sulfur isotope analyses of pyrite show an obvious decreasing trend, which is a result decreasing ore‐forming temperatures during the ore‐forming process. The He–Ar isotope data indicate that the ore‐forming fluids were derived from a mantle‐fluid mixing source. The metallogenesis in the Luanling deposit is closely related to the lithospheric thinning and the destruction of the North China Craton.

Electron back-scattered diffraction and LA-ICP-MS analysis of pyrite from the Dahu lodegold deposit, southern North China craton: Insights into geochemistry and distribution of trace element connection to microstructure of pyrite

The Dahu lodegold deposit is situated in the Xiaoqinling district, hosted in the east-west-trending shear zones, and characterized by auriferous quartz vein-type. Based on the morphology and paragenetic assemblage, three generations of pyrite (termed as first-generation pyrite (Py1), Py2, and Py3) can be classified. The Py2 can be further identified as brittle fractured pyrite (Py2-B) and ductile deformed pyrite (Py2-D). The different generations of pyrites feature distinct contents and distribution patterns of Au and other trace elements. The coarse-grained, euhedral Py1, disseminating in the early formed pyrite-poor quartz veins, contained negligible to extremely low levels of Au and associated trace elements, probably indicating a slow growth rate from a hydrothermal fluid unsaturated with respect to Fe, S, and Au and other trace elements, such as Cu, Pb, Bi, and Te, during the early orestage. Py2, occurring as laminations in the auriferous quartz veins, consistently contained significant amounts of Au, Bi, and Te, with a strong positive correlation between these elements, probably indicating a rapid growth rate and concentrated precipitation process of pyrite due to a hydrothermal fluid supersaturated with respect to Fe, S, Au, and other trace elements during the pyrite-rich auriferous quartz veining. Py3, which precipitated in the polymetallic sulfide orestage, contained a small amounts of Ag and a dramatically decreased content of Au, Bi, Te, and ratios of Bi/Ag. The results of electron back-scattered diffraction analysis on the Py2 revealed that Py2-B was characterized by predominantly brittle deformation with a limited local plastic deformation by dislocation glide on a simple slide system, whereas the Py2-D displayed a significant crystal plastic deformation through a lattice rotation on two separate 〈1 0 0〉 axes and local dislocation creep. Microscopic petrography and laser ablation inductively coupled plasma mass spectrometry analyses revealed that the brittle fracturing-dominated Py2-B generally displayed homogenous distribution patterns of Au and other trace elements and scarce visible gold grains, whereas the plastically deformed Py2-D generally exhibited an inhomogeneous distribution pattern of trace element and commonly contained fine-grained irregular-shaped visible native gold and other sulfide inclusions in the low-angle boundaries and dislocation sites within Py2-D, possibly suggesting the significant influence of ductile deformation on remobilization and reprecipitation of Au and associated trace elements once locked in Py2. The corrosion of Au-Te-Bi-bearing Py2 by the late polymetallic sulfide assemblage led to a liberation of invisible Au and other trace elements and reprecipitation of visible native gold and other Bi–Pb minerals. The results indicate that brittle deformation exhibited no essential effects on the crystal structure and chemical component of pyrite, whereas the plastic deformation can cause the readjustment of crystal lattices and liberation of impurities (e.g., Au, Te, Bi, and Cu) from the crystal lattices of pyrite. The plastic deformation and dissolution–remobilization of pyrite are the important mechanisms responsible for the visible discrete gold grain formation in auriferous quartz veins. Macroscopically, a preferred constant E–W extending orientation and typical lamination structure of the auriferous quartz veins suggest a channeled fluid flowing along the closed and connected fractures under a syn-mineralization S–N oriented extensional tectonic regime related to the Xiaoqinling metamorphic core complex. Here, we report that the microstructures of ductile deformation and brittle fracturing of the auriferous quartz veins are probably indicative of the continuous shearing activation of the ore-hosting normal fault.

A Nanoscale Investigation of Carlin-Type Gold Deposits: An Atom-Scale Elemental and Isotopic Perspective

Abstract Carlin-type gold deposits are one of the most important gold mineralization styles in the world. Despite their economic importance and the large volume of work that has been published, there remain crucial questions regarding their metallogenesis. Much of this uncertainty is due to the cryptic nature of the gold occurrence, with gold occurring as dispersed nanoscale inclusions within host pyrite rims that formed on earlier formed barren pyrite cores. The small size of the gold inclusions has made determining their nature within the host sulfides and the mechanisms by which they precipitated from the ore fluids particularly problematic. This study combines high-resolution electron probe microanalysis (EPMA) with atom probe tomography (APT) to constrain whether the gold occurs as nanospheres or is dispersed within the Carlin pyrites. APT offers the unique capability of obtaining major, minor, trace, and isotopic chemical information at near-atomic spatial resolution. We use this capability to investigate the atomic-scale distribution of trace elements within Carlin-type pyrite rims, as well as the relative differences of sulfur isotopes within the rim and core of gold-hosting pyrite. We show that gold within a sample from the Turquoise Ridge deposit (Nevada) occurs within arsenian pyrite overgrowth (rims) that formed on a pyrite core. Furthermore, this As-rich rim does not contain nanonuggets of gold and instead contains dispersed lattice-bound Au within the pyrite crystal structure. The spatial correlation of gold and arsenic within our samples is consistent with increased local arsenic concentrations that enhanced the ability of arsenian pyrite to host dispersed gold (Kusebauch et al., 2019). We hypothesize that point defects in the lattice induced by the addition of arsenic to the pyrite structure facilitate the dissemination of gold. The lack of gold nanospheres in our study is consistent with previous work showing that dispersed gold in arsenian pyrite can occur in concentrations up to ~1:200 (gold/arsenic). We also report a method for determining the sulfur isotope ratios from atom probe data sets of pyrite (±As) that illustrates a relative change between the pyrite core and its Au and arsenian pyrite rim. This spatial variation confirms that the observed pyrite core-rim structure is due to two-stage growth involving a sedimentary or magmatic-hydrothermal core and hydrothermal rim, as opposed to precipitation from an evolving hydrothermal fluid.

Morphological and chemical assessment of alluvial gold grains from Ako'ozam and Njabilobe, southwestern Cameroon

Placer gold is widely distributed in southwestern Cameroon but no known lode sources have been uncovered possibly because of intense weathering. In this study, the morphology and microchemistry of alluvial gold from Ako'ozam and Njabilobe were investigated to understand the nature of the source mineralization. SEM, QEMSCAN and EMPA methods were employed to characterize morphology, mineral associations, alloy composition and mineral inclusions of placer gold in both localities. The gold grains exhibited angular to sub-rounded shapes, complex outlines and possessed surface textures such as striations, pits and cavities. These morphological parameters indicated a close source. Major mineral associations included clays and quartz with minor monazite, zircon, pyrite, ilmenite, rutile, chlorite and Fe oxide minerals. Gold in the area is essentially alloyed with Ag. Mineral inclusions included quartz, rutile, Fe-oxide and mica. Gold chemistry indicates interaction of the mineralization with basic rocks notably amphibolite and metadolerite in the area. The wide compositional span of Ag indicated that gold mineralization in the area resulted from multiple source deposit. Similarity in chemical character of gold from Ako'ozam and Njabilobe pointed to the same mineralizing event that sourced the placers in both localities. Gold chemistry suggested an orogenic style of mineralization in which gold occur as free gold in quartz veins. Liberation properties of gold within the Ako'ozam-Njabilobe area weighed in favor of physical gravity-based ore recovery methods which are environmentally friendly.

The Fazenda Nova gold deposit, Goiás Magmatic Arc: Late neoproterozoic intrusion-related auriferous mineralization controlled by intracontinental strike-slip faulting

The Fazenda Nova gold deposit (with an inferred resource of 650 koz at 4.0 g/t Au, cut-off grade of 2.0 g/t Au) consists of stockwork Au-As mineralization hosted in late Neoproterozoic dikes in the Goiás Magmatic Arc, central Brazil. The dikes, which host the mineralization, consist of a set of post-collisional ilmenite-bearing gabbros, dolerites, trachyandesite porphyry, trachyandesite, and trachyte porphyry (known as the Bacilândia Intrusions). U-Pb dating indicates at least two pulses of dike intrusions: the first pulse consists of small-volume dikes with ages varying from 593 ± 5 to 590 ± 5 Ma, and the second pulse comprises a large volume of dikes with ages from 574 ± 7 to 572 ± 5 Ma. Three veining or hydrothermal alteration stages are identified in the Fazenda Nova deposit. The first is the early or main stage, which comprises the pervasive biotitization of mafic minerals and a stockwork of quartz associated with a disseminated sulfide assemblage of arsenopyrite-pyrrhotite-stibnite, in addition to hydrothermal siderite, scheelite, rutile and apatite. The most common sulfide in this stage is a fine-grained, acicular arsenopyrite hosting inclusions of gold, galena and pyrite grains. The temperature estimated for acicular arsenopyrite, pyrrhotite and gold is 340 °C, based on the arsenopyrite geothermometry. The intermediate stage is represented by a stockwork of calcite-quartz veins associated with hydrothermal sericite, chlorite, tourmaline, epidote, and titanite, and a sulfide assemblage of pyrrhotite-arsenopyrite-pyrite. The arsenopyrite at this stage displays a tabular texture with no inclusions of sulfides or gold. The crystallization temperature of the tabular arsenopyrite-pyrite was estimated to be 305 °C. The C-O isotope data from the calcite veins of the second stage provided δ13C values ranging from −9.68 to −11.57‰, and δ18O values range from 12.87 to 13.84‰. These values are equivalent to those of hydrothermal mantle/magmatic carbonates. The late stage is represented by veining and brecciation infilled by monotonous calcite-ankerite with cockade and colloform vein textures and no gold mineralization.The dikes and gold mineralization present a strong relationship with the crustal-scale strike-slip Bacilândia Fault. This is a second-order crustal-scale fault that branches out of the major crustal-scale Moiporá-Novo Brazil Shear Zone (MNBSZ) along a NNW direction. The Bacilândia Fault played an important role in channeling melts and mineralizing hydrothermal fluids to the upper crust. The major activity of this fault occurred at ∼572 Ma with the emplacement of the second pulse of dikes and, most likely, the development of hydrothermal stages in the Fazenda Nova deposit. The collectively evidence allows Fazenda Nova to be classified as an epizonal, reduced intrusion-related deposit following that: i) the mineralization developed in a post-collisional tectonic setting above previously metasomatized subcontinental lithospheric mantle; ii) the dikes crystallized from metaluminous magmas with a primary oxidation state, which formed the ilmenite-series intrusions iii) the ore deposition had relatively high temperatures (340°–300 °C), and vein textures formed only at shallow depths (<4 km); iv) the metal association of Au-As-W-Sb; v) the volatile saturation induced by magmatic processes, such as fractional crystallization or magma mixing; vi) the CO2 hydrothermal veins with C-O isotopes displaying magmatic/mantle fluid affinities.

Evaluation of ferrocenyl phosphines as potent antimalarials targeting the digestive vacuole function of Plasmodium falciparum.

Owing to their lipophilic nature and chemical stability, ferrocene and its derivatives have been widely explored as antimicrobial agents, in combination with other active chemical 'war heads'. A prime example is ferroquine, an analogue of chloroquine obtained by covalently bonding ferrocene to 4-aminoquinoline, which possesses superior efficacy against multi-drug resistant malaria parasites. Herein, we explored the possibility of combining the ferrocenyl moiety with a phosphine unit and the subsequent inclusion of gold(i) to derive a molecular framework with demonstrated potential in inhibiting parasitic diseases. A library of 24 compounds consisting of 5 non-functionalized ferrocenyl enones and 19 ferrocenyl phosphine derivatives were synthesized, verified and tested against Plasmodium (P.) falciparum, which allowed us to identify compounds with low micromolar potency against both normal and chloroquine-resistant strains. Through flow cytometry combined with microscopic examination of Giemsa-stained thin smears, we observed that most of the active compounds interfered with trophozoite development as well as schizont maturation. The gold complex, namely G3, derived from the hydrophosphination of the terminal furan bearing an enone substrate showed the highest inhibitory potential. We demonstrate that G3 is affecting the parasite's metabolic processes as evident from the swollen digestive vacuole. Furthermore, G3 significantly affected heme de-toxification as determined through the β-hematin assay, which caused apparent oxidative stress on parasites leading to death. Collectively, these results point out the potential of gold-conjugated ferrocenyl phosphine derivatives as antimalarials targeting the digestive vacuole function and metabolism of parasites.

Микротопохимия конкреций пирита в кремнистых алевропелитах Юбилейного медноколчеданного месторождения (Южный Урал) по данным LA-IСP-MS

Object . The zonal pyrite nodules and metacrystals from siliceous siltstones of ore-bearing horizon of the Second ore body from the Yubileynoe massive sulfide deposit are studied. Materials and methods . We used 9 samples and 15 polished sections of siliceous siltstones with pyrite mineralization. Analysis of chemical composition minerals was determined by Tescan Vega 3 with an energy dispersive microprobe Oxford Instruments X-act (Institute of Mineralogy UB RAS, Miass). Quantitave LA-ICP-MS analysis of pyrite for major and trace elements was carried out using New Wave Research UP-213 laser microprobe coupled to an Agilent 7500 quadrupole ICP-MS housed (University of Tasmania, Australia). Results. Microtopochemistry was established that the diagenetic core of the nodule is characterized by trace elements of typical poikilites of quartz (Si) and alumosilicates (Si, Al, Mg, V, Cr, K, Na, Ca), rutile and titanite (Ti), inclusions of chalcopyrite (Cu), sphalerite (Zn), galena (Pb, Sb, Bi), tetrahedrite-tennantite (As, Sb), native gold, petzite, hessite (Au, Ag, Te), tellurobismuthite, altaite, and coloradoite (Te, Bi, Pb). Cobalt and Ni substitute for Fe 2+ . The rim of subhedral pyrite is depleted in most trace elements except for Ni and As. Subhedral pyrite became rich in chalcophile (Au, Ag, Sb, Bi, Cu, Zn, Hg) and lithophile (Ca, K, Na, Cr) elements at the final stage of growth of the nodule. Similar mineralogical and geochemical zonation is typical of the pyrite metacrystals, where a micro-grained core concentrates Pb, Bi and Te, and a rim of subhedral pyrite is depleted in most trace elements. Similarly to the nodules, the outer rim of pyrite metacrystals is enriched in most trace elements (Pb, Au, Ag, Sb, Cu, As, Mo, Cr, etc.). The nodules and metacrystals were formed from diagenetic micronodule of poikilite pyrite. Conclusions. It is suggested that mineralogical and geochemical differences in pyrite metacrystals and nodules are caused by the greater degree of development of rims of subhedral pyrite.

About the assessment of gold concentrations in tiny inclusions within sulfide mineral matrix: An electron microprobe study

A method for estimating the native gold composition in micron‐ and submicron‐sized inclusions in the matrix of a sulfide mineral with electron probe X‐ray microanalysis is proposed. Such inclusion sizes are comparable with or less than the X‐ray generation volume, and therefore, the analytical signal is a mixture of signals from the matrix elements and the inclusion elements, which significantly complicates the quantification. The proposed procedure is based upon the extrapolation of the trend of the dependence of the measured elemental contents in the inclusions, for example, Au or Ag, versus the content of matrix elements, namely, S, Fe, and As. To define the influence of the inclusion size on the intensity of the excited X‐rays, the trajectories of the electrons in a sample were simulated by the Monte Carlo method. It was found that the trends in the behavior calculated by the Monte Carlo method are consistent with the data measurements of an artificial pyrite sample with a sprayed pure gold layer (approximately 1 μm thick) arranged perpendicular to the sample surface. The measurements were performed on a Superprobe JXA‐8200 microanalyzer. The proposed method was demonstrated by analyzing natural, finely dispersed gold inclusions in arsenopyrite. This approach made it possible to evaluate the Au and Ag contents in the approximately 1 μm inclusions and assess the uncertainty of the measurement.

In-situ sulfur isotope analysis of pyrite from the Pangjiahe gold deposit: Implications for variable sulfur sources in the north and south gold belt of the South Qinling orogen

The sedimentary- and granite porphyry-hosted Pangjiahe gold deposit is located in the north belt of the South Qinling Orogen, with a proven reserve of 38 t Au at 6.3 g/t. A total of 26 samples, from various rock types and locations from the Panjiahe deposit, were taken in order to determine the paragenesis, sulfur source and absolute age of mineralization. Magmatic activities of ca. 240 Ma occurred around the whole study area, which is common in the northwest part of the West Qinling orogen. Field observations confirm that the emplacement of granite porphyry dykes is earlier than the gold mineralization, because they were both altered and mineralized. Moreover, post ore stage diabase dykes, which cut cross the ore bodies, display an age of ca. 220 Ma. Zircons from strongly mineralized granite porphyry samples show typical hydrothermal trace element characteristics. Theses zircons return a concordia age at ca. 230 Ma. Therefore, we infer that the ore-forming age of the Pangjiahe deposit is at ca. 230 Ma.Optical microscopy, EMPA and LA-(MC)-ICPMS have been used to determine the physical and chemical features of pyrite. Five stages of pyrite have been identified in mineralized phyllite and granite porphyry rocks. Diagenetic pyrite in phyllite, Py1-P, displays a wide range of δ34S (−1.5% to +9.4%). The magmatic pyrite in the granite porphyry, Py1-G, display relatively narrow range of δ34S (+2% to +5%) consistent with magmatic sulfur. The main ore stage pyrite in both rocks, Py2 (Py2-P and Py2-G), is the most common sulfide in the deposit. Py2 grains predominantly show oscillatory zoning and either replace or overgrown the Py1-P and Py1-G, or occur as individual fine grains. Arsenopyrite is typically associated with Py2. Pyrite grains in late stage quartz (Qz) veins that cross cut phyllite and granite, Py-Qz, display weak oscillatory zoning. Native gold is commonly observed as inclusions in the Py-Qz grains or within/proximal to quartz veins. Py3 pyrite (Py3-P and Py3-G), which also belong to the later ore stage and can be distinguished by the native gold inclusions in them, all occur as the outer rims that overgrown or replace on Py2. The ore stage Py2, Apy, Py-Qz and Py3 have a similar narrow range in sulfur isotopic composition, from +8% to +10%. This range is slightly lower than the age equivalent SEDEX Pb-Zn deposits situated in graben basins to the East, but totally different from the earlier Py1-P and Py1-G. EMPA element mapping and spot analyses, and in-situ sulfur isotope analyses indicate that the ore stage pyrites in both phyllite and granite rocks have similar major element chemistry and sulfur isotopic composition, indicating that they are likely sourced from the same ore fluids. Therefore, we propose that prograde metamorphism of the underlying Devonian sedimentary sequences during the seafloor exhalation, which are thought to be enriched in Au, As, Sb, B, F and S, may have released H2S that forming these auriferous sulfides.Gold mineralization in the south belt of the South Qinling orogen shows the same mineralization style as observed in the North belt. However, mineralization is younger and the δ34S values of the hydrothermal ore stage sulfide are consistent with magmatic sulfur, which is consistent with intense magmatic activities within the South Qinling orogen. The δ34S values in the South Belt are distinctly different from those of gold deposits in the north belt. We propose that the source of the sulfur and gold in north belt came from the Devonian graben basins, and in the south belt came from a deep magmatic source. More focused studies of the gold and Devonian graben basin hosted SEDEX Pb-Zn deposits are required to further prove or develop this hypothesis.

Geology and Mineral Chemistry of Gold Mineralization in Mirge‐Naqshineh Occurrence (Saqez, NW Iran): Implications for Transportation and Precipitation of Gold

AbstractThe Mirge‐Naqshineh gold district is situated at northwest of Iran with a NW‐trending brittle‐ductile shear zone. It is hosted by Precambrian meta‐sedimentary and meta‐volcanic units traversed by mineralized quartz veins. In terms of cross‐cutting relationships and sulfide content three types of quartz veins are identified in the region. Among those, parallel to bedding quartz vein (type I) is the main host for gold mineralization. Gold is found in three different forms: 1) submicrometer‐size inclusions of gold in arsenian pyrite, 2) as electrum and 3) in the crystal lattice of sulfides (pyrite, galena and chalcopyrite). Six types of pyrite (Py1‐Py6) were identified in this ore reserve. Py3 coexists with arsenopyrite and contains the greatest As‐Au concentrations. There is a negative correlation between the As and S contents in Py2 and Py3, implying the substitution of sulfur by arsenic. Pyrites and mineralized quartz veins were formed via metamorphic‐hydrothermal fluid and reflect the gold‐transportation as Au(HS)−2 under reducing and acidic conditions. The gold precipitation mainly controlled by crystallization of arsenian pyrite during fluid/rock interactions and variation of fO2. The volcanic host rock has played an important role in gold concentration, as Py3 in this rock contains inclusion of gold particles, but gold is within the lattice of pyrite in phyllite or other units.

Mineral chemistry, bulk rock geochemistry, and S‐isotope signature of lode‐gold mineralization in the Bétaré Oya gold district, south‐east Cameroon

Lode‐gold mineralization in the Bétaré Oya gold district is related to a series of quartz–sulphide veins that define a steeply dipping NNE–SSW‐trending brittle–ductile shear zone. The veins transect metasedimentary sequences in the vicinity of small granitic intrusions. Quartz veins range from barren (massive quartz) to mineralized with textures that vary from foliated, sheared, vuggy, fractured, and sugary to brecciated with inclusions of altered wall rock. They contain gold, pyrite, and galena in addition to chalcopyrite and both hypogene and supergene haematite and covellite. Parameters that consistently define primary gold mineralization in the area include silicification, sulphidation, sericitization, K‐feldspar alteration, haematitization, and carbonatization. Gold grains recovered from heavy mineral concentrate and grains that occur as inclusions in pyrite were characterized by microchemical methods. The gold grains are zoned and exhibit a simple internal structure of partly deformed and leached rims and high‐purity intragranular veinlets. Gold is alloyed with Ag; gold fineness varies between 859 and 877 in the core and from 958 to 997 in the leached rims. Inclusions of gold in pyrite cluster between 875 and 900. Pyrite has up to 0.59 wt% Au, and other trace elements occur in low quantities but for Pb (0.13 wt%), Ag (1.36 wt%), and Sb (1.63 wt%). The bulk trace element signature of the veins is characterized by Au, Ag, As, Bi, Ba, Cr, Cu, Mn, Pb, Sb, Sr, V, W, Zn, and Zr. This depicts a geochemical association of Au ± Cu ± Bi ± As ± Pb. The occurrence of Au as well as elevated Pb and Zn could suggest a granitic source for the ore‐bearing fluid. The auriferous quartz veins are characterized by a widespread in δ34S from 2.8 to 14.9‰ pointing to multiple sources of sulphur in the system, perhaps a mixture of sulphur from the metasedimentary and the granitic rocks.

Using a cover layer to improve the damage resistance of gold-coated gratings induced by a picosecond pulsed laser

The chirped pulse amplification (CPA) technology is the main approach to achieve high-intensity short-pulse laser. Diffraction gratings are good candidates for stretching and compressing laser pulses in CPA. In this paper, a kind of gold-coated grating has been prepared and its laser damage experiment has been performed. The results reflect that the gratings laser damage was dominated by thermal ablation due to gold films or inclusions absorption and involved the deformation or eruption of the gold film. Based on these damage phenomena, a method of using a cover layer to prevent gold films from deforming and erupting has been adopted to improve the gold-coated gratings laser damage threshold. Since the addition of a cover layer changes the gratings diffraction efficiency, the gratings structure has been re-optimized. Furthermore, according to the calculated thermal stress distributions in gratings with optimized structures, the cover layer was demonstrated to be helpful for improving the gratings laser damage resistance if it is thick enough.

Gold in Accessory Zircon (the Kozhim Massif, Subpolar Urals)

The crystals of zircon due to their resistance to external impact of various processes can reveal information about the environment of their formation and the inclusions observed of them. Zircon contains different mineral inclusions: biotite, plagioclase, quartz, apatite, etc. However, there is no information about gold inclusions in the zircons from granites of the Sudpolar Urals. The study results of the inclusions of gold in accessory zircon of the Kozhim granitic massif are presented in this paper. The studied mineral is a dark-brown translucent short-prismatic crystal containing the inclusion of gold and the allocations of quartz. According to studies, the inclusion of gold formed during the growth of zircon and it is the gold covered with a thin film of oxide gold. It was confirmed that the crystallization of the studied zircon occurred at a temperature of 800°C and above on the stage of formation of granites of Kozhim massif. The assumption is made about the additional temperature in the course of which was caused by decreasing of temperature up to 700° C and below during postmagmatic stage.

Alteration paragenesis and the timing of mineralised quartz veins at the world-class Geita Hill gold deposit, Geita Greenstone Belt, Tanzania

The world-class Geita Hill deposit is one of the largest gold deposits located within the Geita Greenstone Belt in NW Tanzania. The deposit is hosted within a complexly deformed sedimentary package dominated by ironstone and intruded by diorite dykes. The gold mineralisation is spatially associated with the Geita Hill Shear Zone which, is a NE-trending, moderately NW dipping deformation zone consisting of a network of discontinuous shear fractures that record early thrusting overprinted by later strike-slip and normal events. The regional metamorphic assemblage in the meta-sediments is characterised by biotite+chlorite+actinolite+K-feldspar+magnetite±pyrrhotite±pyrite indicating upper greenschist facies conditions. The gold-related alteration overprints the regional metamorphic assemblage, and is characterised by silicification and sulfidation fronts that generally extend out from the mineralised zone by no more than one meter. The alteration assemblage includes sub-vertical, mineralised quartz veins that trend approximately E-W. The mineralised quartz veins are accompanied by alteration halos of quartz+biotite+K-feldspar+pyrite which overprints the peak metamorphic assemblage. Gold is closely associated with secondary pyrite and occurs as free gold and gold tellurides (sylvanite, calaverite and nagyagite). It occurs mainly as inclusions in pyrite and as invisible gold in pyrite but also as gold inclusions in biotite and along quartz grain boundaries. Two distinct textural styles of auriferous pyrite can be distinguished: inclusion rich subhedral pyrite, hosting invisible gold, and inclusion free euhedral pyrite, hosting visible gold grains. It is common for the inclusions rich pyrite to have thick rims of inclusion free pyrite. The mineralising alteration is overprinted by barren, multiphase quartz-carbonate, and carbonate-chlorite veins. This alteration is characterised by the assemblage calcite+siderite+chlorite±quartz±pyrite±barite. Palaeostress analysis of mineralised shear fractures along the Geita Hill Shear Zone are indicative of sigma 1 being vertical and sigma 3 trending N-S, indicating N-S extension, which is consistent with the orientation of the mineralised quartz veins.

Using in situ SHRIMP U-Pb Monazite and Xenotime Geochronology to Determine the Age of Orogenic Gold Mineralization: An Example from the Paulsens Mine, Southern Pilbara Craton

Paulsens is a mesothermal orogenic gold deposit located in the Wyloo Inlier on the southern margin of the Pilbara craton of Western Australia. Gold occurs in quartz-sulfide veins hosted within a folded and faulted gabbro dike, from which baddeleyite yields a U-Pb crystallization age of 2701 ± 11 Ma. Monazite and xenotime in the veins and from hydrothermally altered country rocks yield three distinct U-Pb dates of ca. 2400, 1730, and 1680 Ma. Textural relationships between euhedral xenotime and pyrite with rounded native gold inclusions from within the quartz-sulfide veins show that the primary gold mineralization was synchronous with xenotime crystallization at 2403 ± 5 Ma, and coeval with pervasive alteration of the host rocks, which yield monazite ages of 2398 ± 37 and 2403 ± 38 Ma. Regional-scale hydrothermal events at ca. 1730 and 1680 Ma are linked to the growth of monazite within phyllitic rocks at 1730 ± 28 and 1721 ± 32 Ma, carbonate veining at 1655 ± 37 Ma, and gold remobilization or introduction of new gold at 1680 ± 9 Ma. The ca. 2400 Ma age for mineralization and hydrothermal alteration does not correspond with any known deformation event in the region, indicating a significantly different and more complicated low-temperature tectonothermal evolution for the southern Pilbara region than previously recognized. The in situ secondary ion mass spectrometry dating of monazite and xenotime employed here will lead to better targeting of orogenic gold deposits in the northern Capricorn Orogen, and these techniques can be utilized for orogenic gold exploration worldwide.

Compositional variation of glauconites in Upper Cretaceous-Paleogene sedimentary iron-ore deposits in South-eastern Western Siberia

Glauconite occurs either as unaltered greenish or as altered brownish variety in Upper Cretaceous-Palaeocene sediments in the southeastern corner of Western Siberia. Studied section within the Bakchar iron-ore deposit includes Ipatovo, Slavgorod, Gan'kino and Lyulinvor formations, which are represented by sandstones, siltstones, claystones and oolitic ironstones of coastal-marine facies. The origin of unaltered glauconite is explained by the “verdissement theory”. Transgressions during Lower Coniacian, Santonian and Campanian favored the formation of unaltered glauconites in dysoxic to anoxic conditions. Subaerial exposure of glauconite resulted in leaching of potassium, oxidation of iron and formation of iron hydroxides in Upper Coniacian, Maastrichtian and Palaeocene. Glauconite ultimately converts to leptochlorite and hydrogoethite by this alteration. Abundant microscopic gold inclusions, besides sulphides, sulphates, oxides and silicates characterize this glauconite. Mineral inclusions include precious, rare metals and non-ferrous metals. The concentration of gold in glauconite may be as high as 42.9ppb. Abundant inclusions of various compositions in glauconites indicate enrichment of marine sediments in precious and non-precious metals. While major element composition of glauconites is affected by subaerial exposure, the broadly similar micro-inclusions in both altered and unaltered varieties are possibly related to the comparatively immobile nature of REE and trace elements.