Source Of Gold Research Articles

Morphological, thermoelectrical, geochemical and isotopic anatomy of auriferous pyrite from the Bagrote valley placer deposits, North Pakistan: Implications for ore genesis and gold exploration

The Bagrote valley in North Pakistan, belonging to the Kohistan island arc, is well-known for regional placer gold mining. However, no economically feasible in situ hydrothermal gold deposits have been discovered in this region due to rugged terrain and remote nature of its location in the western Himalaya. The streams draining the Main Karakoram Thrust (MKT)/Shyoke suture zone carry placer gold in sediments as well as old river terraces, although the primary source remains unknown. In this paper, we employ a multiparametric approach including, X-ray Diffraction (XRD) analysis, thermoelectricity, major and trace element geochemistry and isotopic characteristics of pyrite associated with placer gold with a view to identify the nature of the unknown deposits and ore forming fluids on the catchment of the Bagrote valley. Pyrite in the Bagrote valley placers is euhedral to subhedral indicating the proximal gold sources. The high rate of occurrence of N-type thermoelectric coefficients (89%) with low P-type (11%) and crystallization temperature (290 °C−380 °C) combined with chemical features indicate that the pyrite was derived from porphyry or epithermal type of magmatic hydrothermal gold deposits from the hinterlands of the Bagrote valley. The X-Ray elemental maps show that Fe, As, Mo and Ni are homogenously distributed from core to rim suggesting stable crystallization condition without any alteration by later fluids. The calculated chemical formula of pyrite of our samples is [Au0.0006Fe] S2.004], plots of Au-As and Au-Fe shows that gold occurs in pyrite as micro to nano inclusion as Au0. The δ34 SV-CDT values of pyrite range from – 0.6‰ to 0.9‰ with an average of −0.02‰, indicating the derivation of sulfur from a homogeneous magmatic source. The Pb isotope data indicates that the Pb was sourced from orogenic-type source, with minor contribution of lower crust. The narrow variations in 206Pb/204Pb and 208Pb/204Pb values suggest a single lead source. The low, medium and high Mo/Ni ratios reflect a mixed provenance for the auriferous pyrite. The average value of γ (71.8%), of pyrite computed from thermoelectric parameters (XnP), suggests that the dominant part of the primary source that contributes to the placers might have already been eroded. However, the proximal source and with high content of gold in the pyrite grains (up to 1160 ppm) suggest the possibility of significant economic mineralisation below the present erosion level of the deposits in the hinterlands of Bagrote Valley.

Effect of the mercaptan alkyl chain structure on the structure and electrochemical properties of Au-doped mesoporous carbon materials

A good chelating agent such as mercaptan plays an important role in the synthesis of gold nanoparticles (AuNPs) or Au-doped carbon nano-composites. Herein, a synchronous carbonization-reduction method was employed to synthetize stable and monodispersed AuNPs embedded in the mesoporous carbon framework. A phenolic resin, mercaptan, and HAuCl4 acted as a carbon source, coordination agent, and gold source, respectively. The effect of the mercaptan chain length on the size of AuNPs and the pore structure of the mesoporous carbon materials was systematically studied. Ultraviolet spectrum analysis revealed that the coordination shifted from Cl–Au to S–Au depending on the mercaptan added to the reaction system. The as-prepared gold nanoparticles@mesoporous carbon materials (AuNPs@MPCs) were characterized by transmission electron microscopy, dynamic light scattering, X-ray diffraction, and N adsorption–desorption. The size of the AuNPs (3.71–12.86 nm) was controlled by changing the alkyl chain length of the mercaptans. The specific surface areas of the obtained AuNPs@MPCs increased from 1440 to 1603 m2/g as the mercaptan chain length increased. Square-wave stripping voltammetry (SWASV) tests on a typical MPTMS-AuNPs@MPC/GCE modified electrode revealed good detection response towards Pb2+, with a limit detection as low as 1.96 nM (S/N = 3). This detection limit was significantly lower than the value provided by the World Health Organization. This electrode also showed a relative wide linear detection range (0–2 μM). This good performance was ascribed to the excellent conductivity of AuNPs and the high specific surface area of the carbon materials. This work provides a new research strategy for the one-step synthesis of AuNPs@carbon materials with controllable NP size by using mercaptans with different alkyl chain structure. It can be believe that this approach could be expanded to nano-metal materials other than Au.

A holistic model for the origin of orogenic gold deposits and its implications for exploration

The term orogenic gold deposits has been widely accepted, but there has been continuing debate on their genesis. Early syn-sedimentary or syn-volcanic models and hydrothermal meteoric-fluid models are now invalid. Magmatic-hydrothermal models fail because of the lack of consistent spatially associated granitic intrusions and inconsistent temporal relationships. The most plausible models involve metamorphic fluids, but the source of these fluids is equivocal. Intra-basin sources within deeper segments of the hosting supracrustal successions, the underlying continental crust, subducted oceanic lithosphere with its overlying sediment wedge, and metasomatized lithosphere are all potential sources. Several features of Precambrian orogenic gold deposits are inconsistent with derivation from a continental metamorphic-fluid source. These include the presence of hypozonal deposits in amphibolite-facies domains, their anomalous multiple sulfur isotopic compositions, and problems of derivation of gold-related elements from devolatilization of dominant basalts in the sequences. The Phanerozoic deposits are largely described as hosted in greenschist-facies domains, consistent with supracrustal devolatilization models. A notable exception is the Jiaodong gold deposits of China, where ca. 120-Ma gold deposits are hosted in Precambrian crust that was metamorphosed over 2000 million years prior to gold mineralization. Other deposits in China are comparable to those in the Massif Central and elsewhere in France, in that they are hosted in amphibolite-facies domains or clearly post-date regional metamorphic events imposed on hosting supracrustal sequences. If all orogenic gold deposits have a common genesis, the only realistic source of fluid and gold is from devolatilization of a subducted oceanic slab with its overlying gold-bearing sulfide-rich sedimentary package, or the associated metasomatized mantle wedge, with CO2 released during decarbonation and S- and ore-related elements released from transformation of pyrite to pyrrhotite at about 500 °C. Although this model satisfies all geological, geochronological, isotopic, and geochemical constraints, and is consistent with limited computer-based modeling of fluid release from subduction zones, the precise mechanisms of fluid flux are model-driven and remain uncertain. From an exploration viewpoint, the model re-emphasizes the ubiquitous occurrence of orogenic gold deposits in subduction-related orogenic belts and importance of continental-scale lithosphere-tapping fault and shear zones to focus large volumes of auriferous fluid. It confirms the importance of the consistent spacing between world-class deposits, broadly equivalent to the depth of the Moho, as derived from empirical observations.

Identifying the source of illicit gold from South America

Abstract Illicit trade in gold, mainly sourced from South America and Africa, is used to fund criminal activities such as the drug trade. Laundering money through the purchase of illicit gold, then having it refined and being paid for in clean funds is a major problem, and drives further growth in illicit mining. In order to restrict the influx of illicit gold into the legal domain, it is necessary to be able to identify the traded item as being of a licit or illicit nature. The only way that this can be done with any certainty is by determining, from its chemical composition, the source of the gold and the means by which it has been processed and upgraded. The example dealt with here shows how the use of compositional, processing and geological knowledge is able to discriminate gold from different origins. Data derived from a physical sample is far better able to constrain the source than a paper trail of certification, which can be manipulated.

Micro‐fabrics and Genesis of Pyrite from Zhaoyuan Golden Deposits in Shandong Province, North China

AbstractAs a widely‐developed mineral in various types of rocks, pyrite features important geological information such as temperature and pressure during its formation and evolution (An et al., 2014; An et al., 2018). It is an important geological formation for studying the origins of rocks, mineralization, and deposits (Xue et al., 2014; An et al., 2016). The study of the genesis of gold deposits is a research hotspot in current geology and mineral deposits not only because of high economic value, but also because of important practical significance (An et al., 2017; Yang et al., 2014). Shandong Zhaoyuan, as the third largest gold production area in the world, has important research significance of the origin and generation of gold‐bearing minerals (Xue et al., 2014; Wen et al., 2014). In this study, pyrite from augen granite (figure 1a), syenite (figure 1b), basite (figure 1c) and gold ore (figure 1d) at Zhaoyuan gold deposit Shandong Province, was selected as the research object. The morphological and structural micro‐fabrics were analysed by polarized light microscopy (PLM) and Raman spectroscopy to reveal the source and process of gold further.

Effect of quality-switched laser exposure in patients with history of edible gold consumption.

Injectable gold is known to deposit in the dermis for life, and such patients are at risk of developing chrysiasis post-laser exposure. It is unknown if patients with history of edible gold consumption would develop a similar reaction after quality-switched laser exposure. Our aim is to assess if patients with history of edible gold consumption develop chrysiasis after quality-switched laser exposure. This is a proof of concept pilot study conducted between September 2017 and September 2018 at two dermatology clinics in Riyadh, Saudi Arabia. Adult patients who have history of edible gold consumption were recruited to receive a spot test with different quality-switched lasers in a hidden, non-sun-exposed skin site. The test area was photographed before, immediately after, and 10min after laser exposure. The test area was examined by two independent investigators for the development of chrysiasis. A total of 10 patients (five male and five female) were enrolled. The mean age was 31.7years. Forty percent of subjects consumed edible gold more than once, and the duration of last intake ranged from 3weeks to 3months. Chocolate was the main source of edible gold. All participants had no chrysiasis reaction post-quality-switched laser exposure. Contrary to our hypothesis, all participants with history of short-term edible gold consumption did not develop chrysiasis after quality-switched laser exposure. Further controlled studies including more patients with longer duration and higher frequency of edible gold consumption are needed.

Exsolution depth and migration pathways of mineralising fluids in porphyry systems – examples from the Yerington District, Nevada

Porphyry copper deposits provide around 75% of the world’s copper and are an important source of gold and other metals (Sillitoe 2010). One aspect of porphyry deposit models that is poorly understo...

Ancient deep roots for Mesozoic world-class gold deposits in the north China craton: An integrated genetic perspective

The North China Craton (NCC) hosts some of the world-class gold deposits that formed more than 2 billion years after the major orogenic cycles and cratonization. The diverse models for the genesis of these deposits remain equivocal, and mostly focused on the craton margin examples, although synchronous deposits formed in the interior domains. Here we adopt an integrated geological and geophysical perspective to evaluate the possible factors that contributed to the formation of the major gold deposits in the NCC. In the Archean tectonic framework of the NCC, the locations of the major gold deposits fall within or adjacent to greenstone belts or the margins of micro-continents. In the Paleoproterozoic framework, they are markedly aligned along two major collisional sutures – the Trans North China Orogen and the Jiao-Liao-Ji Belt. Since the Mesozoic intrusions hosting these deposits do not carry adequate signals for the source of gold, we explore the deep roots based on available geophysical data. We show that the gold deposits are preferentially distributed above zones of uplifted MOHO and shallow LAB corresponding to thinned crust and eroded sub-lithospheric mantle, and that the mineralization is located above regions of high heat flow representing mantle upwelling. The NCC was at the center of a multi-convergent regime during the Mesozoic which intensely churned the mantle and significantly enriched it. The geophysical data on Moho and LAB upwarp from the centre towards east of the craton is more consistent with paleo-Pacific slab subduction from the east exerting the dominant control on lithospheric thinning. Based on these results, and together with an evaluation of the geochemical and isotopic features of the Mesozoic magmatic intrusions hosting the gold mineralization, we propose a genetic model that invokes reworking of ancient Au archives preserved in the lower crust and metasomatised upper mantle and which were generated through multiple subduction, underplating and cumulation events associated with cratonization of the NCC as well as the subduction-collision of Yangtze Craton with the NCC. The heat and material input along zones of heterogeneously thinned lithosphere from a rising turbulent mantle triggered by Mesozoic convergent margins surrounding the craton aided in reworking the deep roots of the ancient Au reservoirs, leading to the major gold metallogeny along craton margins as well as in the interior of the NCC.

Geological structure and mineralogy of the Mechnikovskoe gold deposit, thе Southern Urals

Subject. The article presents the results of study of Mechnikovskoe gold deposit associated with listvenites and beresites of the Miass region of the Southern Urals.Materials and methods. Materials were sampled during the field work of 2010– 2012. The chemical composition of rocks is analyzed by methods of classical chemistry (rock-forming oxides) and ICP MS (trace elements). The mineral composition is determined on an electron microscope with EDS.Results. The deposit is composed of tectonic sheets of serpentinites, carbonatized serpentinites and listvenites (sheet I), metadiabases and plagioclase metabasalts of the Irendyk Formation and beresites and volcanosedimentary rocks and metabasalts of the Karamalytash Formation (sheet II). In the central part of the deposit, the volcanic rocks are intruded by a dike of finegrained island-arc granites. Chromites of serpentinites are characterized (on average) by high Cr# (89) and low Mg# (29) values and low contents of Al2O3 (6.94 wt %) and MgO (5.5 wt %). Gold-bearing rocks include listvenites, beresites and carbonaceous shales. The major ore mineral is pyrite; accessory minerals are Au and Ag minerals, chalcopyrite, fahlores, galena, sphalerite, pyrrhotite, cubanite, vaesite, melonite, secondary copper sulfides, barite, rutile, monazite and xenotime. Gold of the deposit contains low Ag contents (3.52 wt %) and minor amount of Cu and Hg (<1 wt % in most analyses).Conclusions. The listvenites and beresites of the deposit were formed after ultramafic and mafic rocks, respectively. The discovery of gold in various rocks indicates that gold mineralization was deposited after the formation of the geological structure of the deposit. The source of gold was most likely related to a magmatic fluid.

Recycling of Paleoplacer Gold through Mechanical and Postdepositional Mobilization in the Neoarchean Black Reef Formation, South Africa

The source of gold in the ca. 2.66 Ga Black Reef Formation (BRF) has been investigated and constrained through petrographic, mineralogical, geochemical, and high-resolution three-dimensional reflection seismic data combined with drill core and underground geological mapping. The BRF is a strong seismic marker and consists of carbonaceous shale, quartz arenite, and conglomerate. Gold grade in the BRF is primarily controlled by the nature of the host conglomerates. Most of the gold in the BRF conglomerate occurs in native form, and its morphology is highly heterogeneous. Gold was initially introduced through mechanical recycling of underlying Witwatersrand reefs, followed by short-range (millimeter- to centimeter-scale) postdepositional alteration/remobilization associated with the Bushveld Complex and the Vredefort meteorite impact. Although the BRF was subjected to high postdepositional fluid circulation facilitated by high fracture density, the volume of dissolved gold was probably too small to form a large gold deposit, except in areas around the Black Reef/Witwatersrand reefs subcrop positions. Findings from this study demonstrate the importance of both sedimentological controls and impact-related structures in the formation of paleoplacer gold deposits during Neoarchean times.

Preparation and catalytic performance of polymer gold nanocomposites

The development of efficient heterogeneous catalysts for reductive conversion of 4-nitrophenol (4-NP) is of vital significance for environmental remediation, dyestuff industry, pharmaceutical industry. We reported that Au@D201, a polymer gold nanocomposite of gold nanoparticles loaded on D201 resin, was prepared using macroporous styrenic ion exchange resin D201 as carrier, chloroauric acid as gold source and sodium borohydride as reducing agent. The average diameter of gold nanoparticles in Au@D201 composites is 5 nm, which has excellent catalytic properties for the reduction of 4-nitrophenol. The Au@D201 was characterized by ultraviolet–visible spectroscopy, X-ray diffraction, mercury injection instrument, transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). The results reveal that some of the gold nanoparticles were loaded on the surface of the resin, and most of the gold nanoparticles were in the resin pores. A strong chemical interaction, between the gold nanoparticles and the resin, is similar to the cross-linking action of the macromolecules. The gold nanoparticles provide a new cross-linking point for the resin, increasing the degree of cross-linking of the resin and causing some degree of resin ordering to occur. XPS shows that the electron density of the outer layer of the gold atom increases, indicating that there are some conjugated interactions between the resin and gold atoms. Conjugated interactions and the gold quantum size effect are the main reasons for improving the catalytic effect of the composite material. When the gold nano-loading amount is 0.1%, it still has an excellent catalytic effect on the reduction reaction of 4-nitrophenol.

A nucleophilic gold complex.

Solid-state auride salts featuring the negatively charged Au- ion are known to be stable in the presence of alkali metal counterions. While such electron-rich species might be expected to be nucleophilic (in the same manner as I-, for example), their instability in solution means that this has not been verified experimentally. Here we report a two-coordinate gold complex (NON)AlAuPtBu3 (where NON is the chelating tridentate ligand 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) that features a strongly polarized bond, Auδ--Alδ+. This is synthesized by reaction of the potassium aluminyl compound [K{Al(NON)}]2 with tBu3PAuI. Computational studies of the complex, including quantum theory of atoms in molecules charge analysis, imply a charge at gold (-0.82) that is in line with the relative electronegativities of the two metals (Au: 2.54; Al: 1.61 on the Pauling scale). Consistently, the complex is found to act as a nucleophilic source of gold, reacting with diisopropylcarbodiimide and CO2 to give the Au-C bonded insertion products (NON)Al(X2C)AuPtBu3 (X = NiPr, 4; X = O, 5).

Gold distribution and source of the J4 gold-bearing breccia pipe in the Qiyugou district, North China Craton: Constraints from ore mineralogy and in situ analysis of trace elements and S-Pb isotopes

The Qiyugou district is one of the most important gold deposit distribution areas in the Xiong’ershan region, North China Craton. These deposits are hosted in Archean Taihua Supergroup rocks as gold-bearing breccia pipes. Here, we report a detailed in situ analysis of trace elements and S-Pb isotopes in sulfides from different ore stages, in combination with electron probe microanalysis of ore minerals from the gold-bearing J4 breccia pipe in the Qiyugou district, to unravel the gold distribution and their textural relationships to pyrite, the metal sources and S-Pb isotopic composition variations during the ore-forming processes. The Qiyugou breccia pipes hosted gold ore (over 70 t Au, average grade of 2–5 g/t) that formed in four mineralization stages, i.e., an early K-feldspar-biotite-magnetite-quartz-pyrite (Py-1) stage (I) that can be further divided into two substages, namely the Ia K-feldspar-biotite-magnetite stage and the Ib quartz-pyrite stage; a gold-pyrite (Py-2)-quartz stage (II); a gold-quartz-polymetallic sulfide (Py-3) stage (III); and a late quartz-carbonate stage (IV). The visible native gold and electrum grains occur as small inclusions and disseminations in the fractures within Py-2 and Py-3. Tellurides and Bi-Pb-minerals are widespread in the stage II stockworks and veins, as is intergrowth with visible native gold and Py-2. In situ LA-ICP-MS trace element analysis reveals the presence of invisible gold hosted in three types of pyrite with extremely low Au content (Py-1 ≤ 0.05 ppm; Py-2 ≤ 0.03 ppm; Py-3 ≤ 0.02 ppm). Concentrations of Te, Bi, and Pb in pyrite are high and correlate well with Au concentrations, but As content is low. Therefore, the Te, Bi and Pb played a significant role in gold mineralization in As-deficient ore fluids in the J4 gold-bearing breccia pipe from the Qiyugou district.High-precision in situ laser ablation multiple collector inductively coupled mass spectrometry (LA-MC-ICP-MS) lead isotope analyses indicate that the sulfides have 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios from 17.250 to 17.629, from 15.401 to 15.621, and from 37.649 to 38.290, respectively, which are similar to the granite porphyry in the district and indicative of their similar lead sources. High-precision in situ LA-MC-ICP-MS sulfur isotope analyses of pyrite show a large δ34S variation (e.g., from −18.1 to −11.1 per mil for Py-1, from −12.2 to − 6.6 per mil for Py-2, and from −4.9 to −1.6 per mil for Py-3) with a remarkable increasing trend from stage I, stage IIto stage III. This trend may record a decreasing oxygen fugacity of the ore-forming fluids during mineralization.

Microchemical characterization of placer gold grains from the Meyos-Essabikoula area, Ntem complex, southern Cameroon

Gold occurs as a native metal, usually containing silver, and in some cases mercury, copper, and palladium. It may also occur as inclusions within sulfur-rich minerals, such as pyrite and arsenopyrite. The style and variety of gold mineralization is influenced by the geological setting, chemistry of the ore fluids, and the nature of their interactions with rocks. Gold grains liberated from bedrock into surficial sediments during weathering and erosion are chemically stable and may be characterized according to their mineralogy: i.e the alloy composition and suite of mineral inclusions revealed within polished sections, characteristics faithful to gold from the hypogene source. This approach has been applied to placer gold grains from the Meyos-Essabikoula area, Cameroon, where the source of gold is not yet confirmed due to poor outcrop exposure.A total of 221 alluvial gold grains from 10 sites, tributaries of Sing and Bivele River over the Ntem Complex have been studied using Electron Probe Micro-Analysis (EMPA) to determine the concentration of minor alloying metals, (notably Au, Ag, Cu, and Hg) and Scanning Electron Microscopy (SEM) in order to evaluate the assemblage of mineral inclusions within the gold. Most of the grains are sub-rounded with pitted surfaces and inclusions of pyrrhotite, acanthite, and chalcopyrite were observed. The grains are AuAg alloys ranging from 54.4 to 99.8 wt% Au, 0.1–48.4 wt% Ag, 0.1–0.8 wt% Hg and 0–0.3 wt% Cu. The presence of Fe oxide (magnetite) inclusions containing Cr and V (to around 5 wt %) has not been reported elsewhere and suggests a strong interaction between hot reducing ore fluids and local mafic lithologies.

Multi-stage and multi-sourced fluid and gold in the formation of orogenic gold deposits in the world-class Mana district of Burkina Faso – Revealed by LA-ICP-MS analysis of pyrites and arsenopyrites

Mana is a world-class Paleoproterozoic orogenic gold district (∼8.0 Moz) that includes five gold deposits (Fofina, Nyafé, Siou, Wona-Kona and Yaho) hosted in various rocks in the northern part of the Birimian Houndé greenstone belt, western Burkina Faso. The gold deposits recorded different styles of mineralization associated with sulfides during polyphase deformation events. Detailed petrographic and LA-ICP-MS analyses of pyrites and arsenopyrites from the main mineralization of each deposit provide new information on the potential gold and arsenic sources and timing of fluids responsible for mineralization at Mana. Four hydrothermal fluid events associated with two distinct source reservoirs and at least two hydrothermal systems were recognized. The first hydrothermal fluid event was generated during the Eoeburnean D1MD (MD for Mana district) shortening event (∼2172 Ma), evidence of which is preserved in the Fofina and Siou deposits, and occurred under greenschist metamorphic facies conditions. Economic gold deposits at Fofina are associated with metamorphic disseminated pyrite (Py1F) in black shale, zoned pyrite (Py2F) enriched in As, Ni, Cu, Ag, Sb, W, Au and Pb, and arsenopyrite in folded V1F quartz-carbonate veins. In contrast, the Siou deposit exhibits Au in porous pyrite cores (Py1S), which are associated with Ag, Bi, Te and W (±Sb) in V1S quartz veins hosted in the Siou granodiorite. These two trace element suites are interpreted as having been induced by a metamorphic source in the Fofina deposit and by a local contribution of a magmatic source in the Siou deposit. The second hydrothermal fluid event occurred during the Eburnean D3MD transpressional event (2113–2090 Ma) in the Nyafé deposit. This event is defined by Au-As-rich rims in hydrothermal pyrite (Py3N) and by the co-precipitation of Au-rich arsenopyrite in the V3N quartz veinlets (V3N) controlled by a second-order dextral shear zone. The third and main hydrothermal fluid event during the D4MD transpressional event (∼2090 Ma) is characterized by the development of strong silicification and by zoned pyrites (Py3WK and Py2Y) and Au-rich arsenopyrite in the Wona-Kona and Yaho deposits. However, the same late Au-As-rich rims in hydrothermal pyrite are observed in both deposits and in the Nyafé deposit, and these rims are interpreted to be related to the same economic gold source related to the Lower Birimian metamorphic reservoir, composed of black shale (diagenetic framboidal pyrite) and tholeiitic basalts. The diagenetic framboidal Py1WK in black shale (Lower Birimian group) is enriched in Au (median of 0.8 ppm), low in As (median of 70 ppm), with other trace elements (Ni, Cu, Zn, Ag, Sb and Pb). The last hydrothermal event is associated with free gold remobilization in late microfractures in the Wona-Kona and Siou deposit during the reactivation of major transcurrent shear zones during the D4MD event or the D5MD shortening event (as late as 2022 Ma). A binary diagram of As/Ag vs. Sb/Bi appears to be effective at separating the diagenetic, magmatic and metamorphic pyrites and could be used in orogenic gold exploration to ascertain potential gold endowment at the district scale.

Mineralogical and geochemical characterization of mining wastes: remining potential and environmental implications, Muteh Gold Deposit, Iran.

Muteh Gold Deposit is the biggest active gold district in Iran consisting of two mines, Senjedeh and Chah-Khatoun, and seven mineral occurrences. Senjedeh has been mined about 20years ago and was recently closed because of the depletion of the reserves. Chah-Khatoun went into operation few years ago. During the previous decades, more than 22Mt of low-grade wastes has been produced from both mines. The wastes are assumed to be a possible source of gold, especially with recent increase in the world gold prices. In this research, 62 surface and subsurface samples were taken from four waste dumps in Senjedeh and two dumps in Chah-Khatoun mines. The optical mineralogy, XRD, ICP-MS analysis, SEM, and electron probe microanalysis (EPMA) studies were carried out to investigate the mineralogical and geochemical characteristics of the waste rocks. In addition to identification of major and minor primary and secondary phases, the mode of occurrence of minerals and also the content of precious and economic elements have been studied. The main opaque mineral was found to be pyrite. Among the economic elements, Au was recognized in the pyrite lattice as well as electrum. The Au grades are higher than 0.5mg/kg in some waste piles. Zinc and Cu revealed concentrations above 5000 and about 1400mg/kg, respectively. It is for the first time that electrum is reported in Muteh. Therefore, regarding the economically recoverable content of Au, the studied waste rocks may be considered as potential ores of coming years. Among the environmentally significant elements, As showed concentrations of up to 25mg/kg which may be of pollution concerns.

Geological-structural control and criteria of forecasting the types of primary sources of placer gold on the East of Siberian platform

Identification of indicators on placer gold allowed predicting formation types of primary sources of gold and their location in the East Siberian platform, overlapped by thick cover of Meso-Cenozoic deposits, where traditional methods of prospecting of gold deposits are ineffective. Each gold-ore formation is known to have the corresponding geological-structural control. Based on study of mineralogical-geochemical features of placer gold and regularity of its distribution, it has been determined that primary sources of low-sulfide gold-quartz, gold-copper-porphyritic, gold-ferruginous-quartzite, gold—rare-metal and gold-platinoid formations are confined to basement outcrops and their framings; gold-sulfide-quartz formation — to metasomatites, developed within the zones of deep faults, tracing the terrigenous-carbonate series; and manifestations of gold-silver formation are localized in the zones of intracontinental paleorifts. In general, identification of geological-structural location of specific types of gold sources favors more correct selection of prospecting methods for gold deposits in areas with thick sedimentary cover, and evaluating their potential.

The Raigorodok stockwork gold-sulfide-quartz deposit in the North Kazakhstan gold ore province

The Raigorodok stockwork gold-sulfide-quartz deposit is located in the contact zone of a monzogabbro-diorite intrusion belonging to the Stepnyak complex (442 Ma). Two main ore formation stages have been established: early, with disseminated gold-bearing pyrite-chalcopyrite mineralization related to skarn, propylite, and K-feldspar formation, and late, with productive mineralization. The late stage was accompanied by the formation of beresite, sericite, and quartz and comprised two substages: (1) quartz-gold-pyrite-chalcopyrite mineralization and (2) quartz-carbonate-gold-polysulfide mineralization. The 40Ar/39Ar ages of beresites and sericites are 422.9 ± 4.3 Ma and 416.7 ± 4.3 Ma, respectively, which is 19-22 Myr younger than the age of the host intrusion. The deposit ores formed stepwise, at temperatures of 112-335 °C and fluid salinity of 0.7-21.2 wt.% NaCl equiv. Sulfur for skarns, propylites, beresites, and ores might have been provided by a deep magma chamber, and the carbonaceous shales of the Vendian Sharyk Formation might have been the source of gold. The isotope and geochemical data and the results of fluid inclusion study suggest that Raigorodok is an intrusion-related deposit. At the same time, the deposit has a number of signs of porphyry-epithermal ore-magmatic systems.

Silver Isotopes as a Source and Transport Tracer for Gold: A Reconnaissance Study at the Sheba and New Consort Gold Mines in the Barberton Greenstone Belt, Kaapvaal Craton, South Africa☼

Silver Isotopes as a Source and Transport Tracer for Gold: A Reconnaissance Study at the Sheba and New Consort Gold Mines in the Barberton Greenstone Belt, Kaapvaal Craton, South Africa☼

Fluidolites as a Source of Primary Gold–Platinum Mineralization in the Poperechnoe Deposit (Malyi Khingan Range, Russia)

A genetic relationship is shown for the noble-metal mineralization (up to 11.3 g/t of Pt and platinoids and 2.58 g/t of Au) discovered in the Poperechnoe Fe–Mn deposit and the fluid–explosive breccias. The composition of platinoid minerals is in agreement with the characteristics of ore and placer formations of the Ural–Alaskan type and corresponds to the isoferroplatinum–osmium igneous paragenesis. The noble metals were crystallized at the conditions that should take place at the crust–mantle boundary under partial melting of the slab rocks. The near-surface occurrence of these metals is caused by the rising of high-mobile fluid flows. The data obtained testify to the expedience of searches for noble metals associated with occurrences of fluidolites.