Free Gold Research Articles

Research into heap leaching technology of gold-bearing ores at the Vasilkovsky gold ore deposit (Kazakhstan)

Purpose. To study gold-bearing ores subjected to heap leaching technology to identify both free gold particles, as well as gold in aggregates and adhesions, which makes it possible to obtain data on the distribution of gold by its occurrence forms. Methodolgy. Leaching process studies are conducted at the laboratory setup of the Institute of Metallurgy and Ore Beneficiation of the Ministry of Education and Science of the Republic of Kazakhstan. The gold particles are studied using an AxioScope A1 optical microscope on the polished thin section surface. The sample materials are taken from the heap leaching site of the Vasilkovsky gold ore deposit. Findings. As a result of a microscopic test of a sample taken from the heap leaching site, ultrafine-dispersed and finely-dispersed gold particles have been found both in free form and in aggregates with waste rock and arsenical pyrite, as well as the fact of Au particles adhesions, accumulated on a grain of the host waste rock. The size class of detected Au particles varies from 0.35 to 9.5 m. Originality. For the first time, according to the samples of gold-bearing ores of the Vasilkovsky gold ore deposit, a pattern of the gold distribution according to the forms of its occurrence has been revealed. Practical value. The data obtained as a result of the research make it possible to predict the distribution of the gold form occurrence in other areas of the deposit. This can greatly simplify the conditions for its development, as well as adjust the technological process of leaching the gold-bearing ores and the main technological parameters of the heap leaching process.

Nature and genesis of the Zaglic Au deposit, NW Iran: Constraints from geochemical studies

The Zaglic Au deposit is located in a Late Oligocene magmatic arc within the Arasbaran Magmatic Belt of NW Iran, which formed during the subduction of Mesotethys oceanic crust. Country rocks comprise intermediate to mafic volcanic and volcanoclastics of andesitic to trachy–andesitic composition, and exhibit late granite plutonism. Host assemblages display medium– to high–K calc–alkaline affinities with fractionated REE profiles, including Nb and Ti depletion and Rb, Ba, Th, U enrichment, consistent with subducted terranes. Wall–rock alteration comprises multi–stage silicic, sericitic, argillic and/or propylitic domains, associated with (i) pre–, (ii) main–, and (iii) post–ore emplacement. Pyrite is the dominant sulfide with spatially associated chalcopyrite and bornite in quartz vein and veinlets, with free gold occurring as microscopic grains in quartz, or as inclusions in pyrite. Fluid inclusion analysis of pre– (quartz I), main– (quartz II) and post–ore stages (quartz III) identifies liquid–rich, multi–stage, and vapor–rich varieties with decreasing temperatures and salinities, with the following Th and NaCl wt% equivalent ranges: pre–mineralization: 230–382 °C and 6.1–8.2; main–ore: 179–311 °C and 0.35–3.22%; and post–ore: 150–195 °C and 2.2–2.9%. Stable isotope analysis identifies variable δ18Ofluid and δDfluid signatures, including: quartz I: 2–3.4‰; −86 to −78‰; quartz II: −0.6–0.2‰; −89 to −85‰; sericite: −0.2 to 3.4‰; −107 to −91‰; and chlorite: −0.6 to 1.4‰; −115 to −104‰. Such ranges imply a mixture of magmatic and meteoric fluids, characteristic of a wide range of epithermal Au deposits. Sulfur isotope composition (δ34S) of this deposit's two principal sulfide minerals is consistent with compositionally reduced mineralizing fluids including: pyrite: −1.4 to 2.7‰ and chalcopyrite: −2.6 to 1.8‰. Geochronological analysis records 40Ar/39Ar dating of biotite from andesite porphyry with a plateau Eocene age of 48.20 ± 0.73 Ma, together with ~8 Ma or Late Miocene ages from fine–grained sericite.

Geology and Genesis of the Unkurtash Intrusion-Related Gold Deposit, Tien Shan, Kyrgyzstan

Abstract Situated in the heart of the Tien Shan gold province, Unkurtash (3.5 Moz at 1.82 g/t) is a representative lode gold deposit that is hosted within the Carboniferous Andagul granodiorite in the Kassan district, western Kyrgyzstan. The Tien Shan gold province consists of porphyry and epithermal deposits, which are related to magmatic arcs, and lode gold deposits formed in the late stages of continent-continent collision that have been generally classified as mesothermal or orogenic type. Some of the lode gold deposits have been considered to be intrusion-related, but the genetic relationship between gold mineralization and the magmatic intrusions remains ambiguous in most cases due to lack of absolute timing of the gold mineralization. This paper addresses this problem through detailed geologic and petrographic studies of the Unkurtash gold deposit in conjunction with Re-Os, U-Pb, and 40Ar/39Ar dating along with S and Pb isotopes. The paragenesis of the Unkurtash deposit is divided into four stages. Stage 1 is related to pre-ore sheeted quartz veins outlined by narrow K-feldspar alteration envelopes. Stage 2 is characterized by quartz-molybdenite (±Au) veins with sericite and chlorite alteration assemblages. Stage 3 is the main gold mineralization stage and is characterized by gold-bearing quartz-ankerite veins and pervasive quartz ± K-feldspar ± rutile ± titanite alterations, with development of auriferous pyrite, free gold, electrum, galena, pyrrhotite, and minor chalcopyrite and arsenopyrite. Stage 4 is defined by the presence of abundant arsenopyrite in barren quartz-calcite veins associated with sericite ± muscovite ± carbonate alteration. Molybdenite from a single stage 2 vein yielded a weighted mean Re-Os age of 306.5 ± 1.7 Ma (n = 7). Auriferous pyrite from stage 3 yielded an Re-Os isochron age of 307.3 ± 8.0 Ma (n = 5) and a weighted mean age of 307.4 ± 3.1 Ma (n = 2; low-level highly radiogenic pyrite). 40Ar/39Ar ages of three hydrothermal K-feldspar samples from stage 3 veins returned younger plateau ages (ca. 293–289 Ma) that are possibly related to post-ore thermal events. The molybdenite and pyrite Re-Os ages are comparable with a newly obtained U-Pb zircon age of 305.1 ± 2.7 Ma for the Andagul granodiorite, providing unequivocal evidence for synchronous gold mineralization and magmatism. The similarity in δ34SVienna-Canyon Diablo Troilite (V-CDT) between auriferous pyrite (5.7–7.1‰, n = 10) and the Andagul granodiorite (7.0–8.9‰, n = 4) and their similarity in Pb isotopes, which are significantly different from those of the pre-Silurian metamorphic rocks and regional Devonian sedimentary rocks, support the hypothesis that the Andagul granodiorite was the main source of metals and sulfur for mineralization. These results, together with concentric development of proximal skarn and metamorphic rock-hosted Au-As-Bi deposits and distal Sb-Au-As-Hg deposits around the Andagul intrusion, provide a strong case for an intrusion-related gold system. The establishment of an intrusion-related model for the Kassan district broadens the window for additional discoveries of gold deposits in the Tien Shan and elsewhere in the Central Asian orogenic belt.

Petrogenesis of the late Tonian arc-related Um Balad gabbro-diorite complex (Egypt) and insight into its spatially related orogenic gold mineralization

ABSTRACT The gabbro-diorite complex of the Um Balad prospect hosts lode gold mineralization. The complex is dated at 723 ± 4 Ma using the LA-ICP-MS U-Pb zircon method and is correlated with the late Tonian-early Cryogenian subduction-related magmatic stage during the evolution of the Arabian-Nubian Shield. The gabbro-diorite complex evolved through the crystallization of a calc-alkaline magma and the subduction signature of this magma is verified by primitive mantle-normalized trace element patterns that show enrichment in large ion lithophile elements, U, and Th relative to high field strength elements as well as negative Nb and Ti anomalies. The high La/Ybcn (3.1–9.4) and Ta/Yb (0.12–0.41) ratios are consistent with a continental arc rather than an oceanic arc system. Amphibole chemistry indicates that this complex might have crystallized under a moderately oxidizing condition from a hydrous magma (>6 wt% water content) at temperature and pressure estimates of about 800°C and 3 kbar, respectively. Gold mineralization in the Um Balad prospect is confined to structurally controlled massive quartz±carbonate veins and surrounding alteration halos. Alteration in the prospect is represented by localized sericitization and carbonation as well as pervasive chlorite-sericite alteration. The alteration halos are characterized by enrichment in K and Rb and depletion in Ca and Sr compared to their host rocks. The veins of the prospect are related to lower order extensional fractures associated with the regional first order transpressional Najd Fault System. The high Fe contents of the gabbro-diorite complex represent a suitable chemical trap for gold through sulfidation of the host rocks. Supergene alteration resulted in the formation of goethite in association with atacamite and chrysocolla. Free mill gold is associated with these supergene phases, which were deposited in near neutral to slightly alkaline conditions.

Development of the resource conservation concept of non-metallic minerals and remains of tailings

High technological loss of valuable ingredient during sand washing and low efficiency of waste use as the secondary raw materials reduces value for alluvial gold mining. It is proposed to improve the efficiency of combined low-waste technological schemes for free fine gold particles extraction and non-metallic clay and pebble products separation during mineral processing of hard- cleaning metalliferous sands. It is technological assessment of dump integrated use schemes for resource-saving technologies development which are used in gold mining objects. The purpose of using such technologies is producing construction materials and articles, road building, impervious screens making.

Deciphering multiple ore-forming processes of the Shuangqishan orogenic gold deposit, Southeast China by in situ analysis of pyrite

Gold deposits are characteristically formed via multiple mineralization and remobilization events. Inferences on the complex formation history of such deposits from ore textures can be ambiguous in the lack of chemical and isotopic evidence as exemplified by the Shuangqishan orogenic gold deposit in Southeast China. We, therefore, conducted LA-ICP-MS spot analysis coupled with LA-MC-ICP-MS sulfur and lead isotope analysis on texturally complex gold-bearing pyrite from the Shuangqishan deposit. Gold distribution in different syn- to late-ore pyrite generations indicate initial evenly deposition of nano- to micro-inclusions of Au-Ag-Pb-Bi tellurides within pyrite grains and subsequent Au remobilization following brittle deformation and fluid-mediated coupled dissolution-reprecipitation (CDR) reactions. Gold dissolved from the pyrite during the reworking event became re-concentrated and re-precipitated as visible gold either as inclusions in pyrite or larger free gold grains within microfractures of pyrite. The distribution of Bi-Te-Pb-Ag assemblage is comparable to that of Au, illustrating that these trace metals became redistributed in a similar fashion. Early, undeformed pyrite has the least radiogenic Pb isotopic compositions. Late, porous and inclusion-rich pyrite, brecciated pyrite, and recrystallized Te-Bi minerals have variable but in general more radiogenic Pb isotope ratios (higher 206Pb/204Pb and 207Pb/204Pb ratios), which are attributed to modification and precipitation from a more evolved crustal fluid during the re-precipitation of native gold. The Pb isotopic signature of the younger pyrite generations was likely inherited from Pb released during modification of earlier proto-pyrite and a second, crustal lead source that was involved in the hydrothermal system during later remobilization. The δ34S values for the early proto-pyrite and the reworked pyrite generations within the individual vein stage are broadly similar. The variations in sulfur isotope compositions reflect the change in physicochemical conditions (temperature and oxygen fugacity) during proto-ore formation. Our study highlights the importance of metal recycling from early proto-auriferous pyrite during later reworking and gold remobilization, which led to visible gold and high-grade ore shoot formation. The extensive variations of trace element concentrations and S-Pb isotope compositions of proto and reworked pyrites record the complicated Au mobilization and deposition processes and help to understand how gold ores evolved.

Повышение уровня извлечения золота при комбинированной переработке золотосодержащих свинцово-цинковых руд

The ore of the Novo-Shirokinskoye deposit is processed at the processing plant of JSC Novo-Shirokinskoye Mine according to the gravity-flotation scheme. The technological scheme for processing gold-containing lead-zinc ores consists of two nodes: 1 – gravity; 2 – flotation. The gravity node for the extraction of free gold (the extraction proportion of free gold into the gravity concentrate is not more than 30%) is realized with the help of jigging machines, screw separators and concentration tables. The flotation node includes: collective cycle, including the main, control and two partial operations; lead cycle, including the main, control and one recleaner operation; zinc cycle, which includes the main, control and three cleaning operations. The ore of the Novo-Shirokinskoye deposit belongs to the primary type, since the degree of its oxidation is 3 %. Final (marketable) products obtained at the factory during ore processing of the Novo-Shirokinskoye deposit are: combined lead concentrate of the LC-8 brand, corresponding to TU 1725-002-24722376-2011 "Lead concentrates"; zinc concentrate of the ZC-3 brand, corresponding to TU 1725-001-24722376-2011 "Zinc concentrate". Zinc flotation tailings are dump and stored in a tailings storage facility. Due to the tendency to reduce the lead content in the ore, the dependence of the reduction in the extraction of gold into the flotation concentrate is manifested. Considering the use of the traditional reagent of potassium butyl xanthogenate - C5H9OS2K (further BPX) as a collector, does not give the desired results, a search for combinations with new reagents is required. The object of research is gold–containing lead-zinc ores. The subject of the study is the modes of the flotation process of enrichment of gold–containing lead-zinc ores using the collector BPX and the new reagent Aeroflot BTF 15221 of the company "Kvadrat Plus". The main idea of the work is to increase the efficiency of flotation enrichment of gold–containing lead-zinc ores by determining the optimal combination of the known reagent of the collector BCC and the proposed Aeroflot BTF15221

Geochemical and geochronological constraints on the gold-sulfide mineralization and host granitoid rocks in the Bulghah and Al-Maham prospects, central Arabian Shield, Saudi Arabia

Among several gold-sulfide deposits and prospects scattered in the Afif terrane of the Arabian Shield, the Bulghah and Al-Maham prospects are investigated to assess the spatial and temporal relationships between gold mineralization and the host lithologies and regional structures. Both prospects are hosted by the sulfide-bearing Hulayfah Group metavolcano-sedimentary successions, and are confined to cross-cutting granitoid intrusions. Tonalite-granodiorite and monzogranite from the two areas have geochemical characteristics of metaluminous to weakly peraluminous calc-alkaline I-type granitoids. Younger alkali feldspar granite in the Bulghah area exhibits geochemical features of A-type granite, likely formed in a post-collisional or transitional setting. ID-TIMS dating of zircons from two granodiorite samples from the Al-Maham prospect yielded 206Pb/238U ages of ∼662 and 651 Ma. A tonalite sample from the Bulghah mine area gave a concordia age of 674.8 ± 0.8 Ma (2σ; MSWD = 0.42), whereas the alkali feldspar granite sample has an age of ∼ 631 ± 1 Ma. The newly defined ages can be considered as the upper age limit of the auriferous quartz veins, evidently attendant to the Nabitah orogeny (∼680–640 Ma). Gold-bearing quartz veins in the two prospects are identical in terms of ore mineralogy, textures and paragenesis. Gold-bearing quartz veins are associated with intersecting veinlets and stockwork of arsenopyrite, pyrite, and less common pyrrhotite, chalcopyrite, and sphalerite. Recrystallized pyrite and arsenopyrite are ubiquitous in quartz veins, whereas pyrrhotite-chalcopyrite intergrowths in-fills or replacements prevail in the deformed host metavolcanic rocks. Free gold typically occurs as fine inclusions in quartz veins, commonly in deformed pyrite and arsenopyrite crystals. The sulfides of Al-Maham prospect have significantly higher Re-Os concentrations (ppb level), compared with those in the Bulghah prospect, and define an isochron with a Model-1 age of 360 ± 2 Ma and an initial 187Os/188Os ratio of 1.962 ± 0.032. The obtained Re-Os age and the crustal initial Os isotope ratio do not necessarily define the primary age of gold mineralization since ore textures indicate that pyrrhotite was a paragenetically late sulfide phase in both prospects. Alternatively, this age may be interpreted as the time of remobilization and recrystallization of older sulfides in response to Hercynian uplift and deformation (370–290 Ma), manifested as intermittently rejuvenated reverse faults elsewhere in the Arabian Shield.

Evaluating the effectiveness of fine gold extraction technologies on the example of titanomagnetite beach placers of the western coast of Kamchatka

The material on the gold content of coastal-marine deposits of the western coast of Kamchatka is analyzed and the resource potential is briefly characterized. A review of gold technological estimates obtained from the study of gold-bearing samples taken in promising areas of the coastal-marine strip, from the Bolshaya Vorovskaya River in the north to Cape Levashova in the south, is presented. Stock materials supplemented by our studies were used. Gold-bearing deposits with very fine (0.05-0.1 mm) and fine (0.1-1.0 mm) gold amounting to 94.6 % were tested, as well as samples with gold up to 2 mm and more in addition to fine gold The content of freely recoverable gold reached 91.9 %. In the case of significant gold reserves in placers, prospects for their commercial development open up. experiments on the enrichment of gold-bearing coastal-marine deposits of Western Kamchatka indicate the possibility of extraction of free gold and other valuable components from them. Gravity technologies and modern equipment developed by ОАО Irgiredmet and JSC ITOMAK are the most effective for their extraction. enrichment of gold-bearing formations with simultaneous extraction of several useful components from them, which is possible with the use of fluoride technology, can also become economically advantageous.

Origin and Characteristics of the Shwetagun Deposit, Modi Taung-Nankwe Gold District and the Kunzeik and Zibyaung Deposits, Kyaikhto Gold District in Mergui Belt, Myanmar: Implications for Fluid Source and Orogenic Gold Mineralization

The Mergui Belt of Myanmar is endowed with several important orogenic gold deposits, which have economic significance and exploration potential. The present research is focused on two gold districts, Modi Taung-Nankwe and Kyaikhto in the Mergui Belt comparing their geological setting, ore and alteration mineralogy, fluid inclusion characteristics, and ore-forming processes. Both of the gold districts show similarities in nature and characteristics of gold-bearing quartz veins occurring as sheeted veins, massive veins, stockworks to spider veinlets. These gold deposits are mainly hosted by the mudstone, slaty mudstone, greywacke sandstone, slate, and slaty phyllite of Mergui Group (dominantly of Carboniferous age). The gold-bearing quartz veins generally trend from NNE to N-S, whereas some veins strike NW-SE in all deposits. The gold-bearing quartz veins are mainly occurred within the faults and shear zones throughout the two gold districts. Wall-rock alterations at Shwetagun are mainly silicification, chloritization, and sericitization, whereas in Kyaikhto, silicification, carbonation, as well as chloritization, and sericitization are common. At Shwetagun, the gold occurred as electrum grains in fractures within the veins and sulfides. In Kyaikhto, the quartz-carbonate-sulfide and quartz-sulfide veins appeared to have formed from multiple episodes of gold formation categorizing mainly as free native gold grains in fractures within the veins or invisible native gold and electrum within sulfides. At Shwetagun, the ore minerals in the auriferous quartz veins include pyrite, galena, and sphalerite, with a lesser amount of electrum, chalcopyrite, arsenopyrite, chlorite, and sericite. In Kyaikhto, the common mineralogy associated with gold mineralization is pyrite, chalcopyrite, sphalerite, galena, pyrrhotite, arsenopyrite, marcasite, magnetite, hematite, ankerite, calcite, chlorite, epidote, albite, and sericite. At Shwetagun, the mineralization occurred at a varying temperature from 250 to 335°C, with a salinity range from 0.2 to 4.6 wt% NaCl equivalent. The Kyaikhto gold district was formed from aqueous–carbonic ore fluids of temperatures between 242 and 376°C, low to medium salinity (<11.8 wt% NaCl equivalent), and low CO2 content. The ore-forming processes of the Shwetagun deposit in the Modi Taung-Nankwe gold district and the Kyaikhto gold district are remarkably comparable to those of the mesozonal orogenic gold systems.

Developing the technology of associated gold recovery when concentrating copper-pyrite ore

Research objective is to address an up to date task of developing the technology of associated gold recovery from complex ore. Object of research is the gold-bearing copper-pyrite ore. Gold was recovered in laboratory conditions with the use of gravity methods of mineral separation. Research tools. Rational modes of machinery operation have been determined through mathematical planning of experiments including the obtained results processing by mathematical and statistical methods. Methods of research. Gold was recovered in the grinding-classification circuit based on a seriesinstalled short-cone hydrocyclone, a jigging machine and a shaking table. Research results. The developed jig mode differs from the existing ones by the closed-circuit of jig machine chambers: from the feed of the second (in the direction of the light fraction travel) jig chamber, the light fraction (tailings) and undersize product – fraction with the increased content of accessory minerals (rough concentrate) are separated. The rough concentrate in the second chamber is directed to the first chamber of the machine, where the finished jig concentrate is obtained in the form of an undersize product. The light fraction moves from the first chamber to the second and is removed from the machine through the tail board. When fine-tuning the heavy fraction of jigging on a shaking table, it is recommended to mix 1/2 part of the initial feed of the tables with the rough concentrate isolated from the other 1/2 of the original feed. The new jigging mode and the scheme of concentration on the tables provide an increase in the gold content in the initial feed of the apparatus, which is the reason for a decrease in gold losses with the tails of the gravity circuit. Research relevance. Gold recovery increment by 4.77% was obtained due to the use of all three recommended scientific and technical measures, namely sands concentration in a short head cone crusher on a jig, switching the jig chambers to a closed circuit, and jet motion of concentrates on shaking tables. Scope of the results. The results should be applied when concentrating ore containing free (amalgamable) gold, as well as gold-bearing pyrite.

Material composition analysis and process flow development for the porphyry copper ores of the Yoshlik-1 deposit

The purpose of this research was to analyze the material composition of porphyry copper ores of the Yoshlik-1 deposit (Uzbekistan) and select a cost-effective processing technology for them. It has been found that the deposit has gold- and molybdenum-bearing ores, composed by 83.84–87.68 % of lithophilic components with a distinct silica prevalence (51.6 %). The mass fractions of quartz and feldspars in the sample are 17 and 40 %, respectively. The total mass fraction of alkali and alkaline earth metals is 16.03 %. The mass fraction of carbon is 0.25 %. All carbon is found in carbonates. The mass fraction of iron is 5.12 %, with oxidized iron being the predominant form. According to the sieve analysis data, the mass fraction of copper in the ore samples is 0.34 %. The grain-size analysis showed a sample gold grade of 0.38 g/t. The valuable components are copper, molybdenum, gold, and silver with the grades of 0.34 wt%, 0.0054 wt%, 0.38 g/t and 0.73 g/t, respectively. A centrifugal concentrator was used for a preliminary assessment of free gold recovery into the gravity concentrate. A series of flotation experiments were carried out to select the collector types and rates for the flotation of ore ground to the 70 % passing –0.074 mm class. Potassium butyl xanthate, 442F, and MX5125 were used as collectors at various rates. Based on the results of the studies, a combined gravity/flotation concentration process was recommended for the ore of the Yoshlik-1 deposit.

Epithermal gold-bearing sulfide ore deposit Tulallar: Structure, structural geology and mineralization patterns

In the latest decades, the characteristic of geology and mineralization in Somkhito–Karabakh island–arc paleosystem undergoes cardinal rethinking. This article describes epithermal gold-bearing sulfide ore deposit Tulallar in the Lesser Caucasus in Azerbaijan. The deposit adjoins a partly eroded volcano-tectonic depression and localizes in the east–westward striking Upper Jurassic andesite-dacitic and andesite strata more than 500 m thick. In the center, the Tulallar Fault splits the structure into three blocks — Western, Central and Eastern, which hold the same-name zone of gold-bearing ore lodes and veins. The main concentrators of finely dispersed and free gold are chalcopyrite and pyrite. The essential tectonic structures which govern distribution of the mineralization are the bordering branches of the Tulallar–Chiragdar–Toganaly fault. The test deposit is the volcanic epithermal shallow and medium-depth cluster within the structurally isolated wedge-like junction of the regional northwestern and northeastern faults. Based on the revealed localization patterns of the mineralization, the prognostic estimation procedure is developed for different-scale ore potentials. The direct and indirect signs of a mineralization are identified. The type, spatial location and intensity of these signs are assumed as the estimation criteria. Regarding the lithological criterion, these are the volcano-clastic facies and the same-age sub-volcanic Kimmeridgian bodies. The types of folds are considered as different values of folding structures. The same principle is used to differentiate between two types of faulting (strike-slip faults and thrustfaults). The information content of the criteria was assessed by the relative weights found empirically during filed operations, and by the method of analogy.

Diversity of supergene gold expressions and implications for gold targetting in an equatorial regolith (AMG's Couriège Exploration Prospect, French Guiana)

Abstract The Couriège prospect (French Guiana) provides key examples of the diversity of gold distribution related to supergene processes. The nature of gold in two contrasted weathering profiles is examined as a function of the weathering lithofacies. The autochthonous profile hosts weathered Au-bearing quartz veins whereas the pediment profile is enriched in free gold issued from dismantled gold-bearing quartz veins. The gold distribution is controlled by: (1) the preservation of primary gold as free gold in both transported and autochthonous horizons and as electrum inclusions in detrital pyrite; and (2) the formation of secondary gold through dissolution/precipitation processes, expressed as gold spherulites on the free gold grain surface, an Ag-depleted rim around transported free gold grains and Ag-depleted gold micro-inclusions hosted by oxidized autochthonous pyrite. Gold enrichment through supergene chemical processes remains limited within the truncated autochthonous profile. A new conceptual model is proposed for the area, defining the role of chemical and physical processes in gold endowment and accounting for the geomorphological context. The overall evolution includes (1) deep weathering and peneplenation, (2) dismantlement and transport of lateritic material and (3) the development of a latosol cover. This study highlights that gold exploration in tropical environments must consider the residual v. transported nature and the inheritance of targeted pedogenic horizons.

Polyphase gold mineralization at the Yaou deposit, French Guiana

Abstract The Yaou deposit, located in French Guiana within the Guiana Shield, is one of the most promising gold deposits of the regional Paleoproterozoic greenstone belt. It displays numerous quartz monzodiorite bodies aligned along a sinistral shear zone where a five-deformation phases model is established at the camp scale. The ductile D 1/2YA phase is responsible for the main penetrative foliation while the D 3YA phase is related to shearing. An intrusive event is identified as being pre to syn-D 3YA . The following phase D 4YA represents a brittle quartz-carbonate veining set hosted preferentially within intrusive bodies and along the shear zone. A local D 5YA brecciation event crosscuts the D 4YA veins. Among this deformation history, two auriferous events (D 3YA and D 4YA ) control the overall grade of the Yaou gold deposit. More specifically, most of the Au grade is associated with the main economic D 4YA veining event, where the gold is visible and linked to Py 4 within an ankerite/hematite rich alteration halo. At the microscopic scale, results of in situ analyses using LA-ICP-MS on pyrite show that metasediment-hosted Py 0 is a primary source of submicroscopic gold having a low contribution to the total endowment. Py 3 shows some gold content due to possible remobilization of Au D0YA . Gold in Py 4 is found as submicroscopic gold, as micro-inclusions and as infilling fractures in association with elements such as Te, Ag and Bi. Most contribution to the Au grade is from micro-inclusions and, to a lesser extent, from free and submicroscopic gold. The ore shoot locations are lithologically controlled for Au D0YA (metasedimentary unit-hosted), structurally controlled (shear zone-hosted) for Au D3YA and rheologically controlled for the Au D4YA (intrusion-hosted). The deposit is clearly polyphase both at the macroscopic and the microscopic scales, invisible gold is associated with As whereas visible gold is observed as inclusions in pyrite with high contents of Ag, Te and Bi. We define an early low-grade enrichment of Au D0YA to Au D3YA followed by a later high-grade event, Au D4YA supporting polyphase mineralization processes. This study confirms that orogenic gold deposits can be formed by remobilization and/or new gold inputs during multiple deformation, veining and hydrothermal events.

Formation temperature and ages of the True North ‘orogenic’ gold deposit in Manitoba, Canada

Abstract The True North orogenic gold deposit is situated in the 2.99–2.70 Ga Rice Lake greenstone belt near Bissett (Manitoba, Canada). This belt is the western equivalent of northern Ontario's Abitibi gold-producing region. The lithology and alteration, structural control, geochronological framework, and ore geology of the True North orogenic gold deposit have been addressed, but its formation temperature and age are poorly constrained. The deposit's gold-bearing veins are composed mostly of quartz (40 to 80%), ankerite (20 to 30%), and albite (5 to 25%), with minor muscovite, sericite, chlorite, and calcite. Sulfide minerals are dominated by pyrite and chalcopyrite and with minor pyrrhotite; native gold appears as inclusions in sulfides or as free gold. In general, most of the major minerals, the sulfides, and gold all precipitated during the main ore stage. The oxygen isotopic composition of co-existing quartz–albite and quartz–ankerite couples were used to calculate a formation temperature of approximately 230°C for these minerals, which is comparable to the nearby 007 gold deposit. These temperatures are on the low end of the temperature range reported for orogenic gold deposits. 40 Ar/ 39 Ar geochronology (single grain laser fusion of muscovite and sericite) revealed the presence of two age groups, at 2441.2 ± 8.8 Ma and 2483.1 ± 10.2 Ma, approximately 200 myr lower than the age of the main collision-related deformation within the Rice Lake belt. These ages indicate that the True North deposit was clearly post-orogenic, similar to vein gold deposits elsewhere, and was likely produced by the emplacement of the Huronian Supergroup and the thermal effects of the Matachewan large igneous province, which has the same ages. It is suggested that the True North deposit may belong to a descriptive category of post-orogenic low-temperature quartz–carbonate–albite vein gold deposit, more in line with recent developments in classification schemes.

Formic acid oxidation reaction on Au(111) electrodes modified with 4-mercaptopyridine SAM

The formic acid oxidation reaction (FAOR) on Au(111) electrodes modified by a 4-mercaptopyridine self-assembled monolayer (SAM) was studied with electrochemical techniques and surface-enhanced Raman spectroscopy (SERS). The adsorption of 4,4’-dithiodipyridine on Au(111) leads to a tremendous enhancement (up to 31-48 times) in electrocatalytic activity for FAOR, which is unique compared to other SAM molecules. The influence of 4,4’-dithiodipyridine and similar aromatic SAM molecules on Au(111) towards formic acid oxidation was studied systematically as a function of coverage and electrolyte composition. Several parameters such as position and availability of the pyridine nitrogen, adsorption and configuration of the SAM molecules, and the number of free gold sites exert a distinct effect on the formic acid oxidation on SAM-modified Au(111) electrodes and result in different enhancement of electrocatalytic activity. While various coverages of 4-mercaptopyridine enhance the activity towards FAOR on Au(111), the striped (5×3) SAM shows a tremendous activating effect after the addition of HCOOH to HClO4. In this way, 4-mercaptopyridine efficiently prevents the adsorption of strongly bound, non-reactive formate. The unique enhancement of this specific striped 4-mercaptopyridine adlayer renders FAOR a convenient test reaction to monitor self-assembly processes on Au(111).

Feasibility assessment of dry pre-concentration for gold-bearing ore

The present research is intended to estimate efficiency of dry preconcentration of ores originated from Gurbey deposit, the Irkutsk Region, as a case study and to develop a rational flowsheet to process ores bearing free gold. The dry preconcentration of Gurbey gold-bearing ores is studied at semi-industrial equipment including DKD-300 combined impact crusher, CMBU-800 centrifugal mill, and POS-2000 pneumatic separator designed at Chersky Mining Institute of the North, SB RAS. The test specimen is subjected to two crushing cycles and four grinding cycles followed by the pneumatic separation cycle. The circulating load consisted of +12 mm fraction after DKD-300, the return mill feed is the sized product of +3 mm as well as products of classification of -3+1 mm POS-200 concentrate. The follow-on recleaning treatment of the preconcentrated products at tables, Moseley mineral analyser, magnetic separator, heavy-medium separator (tribromomethane CHBr3) yielded 23.93 g of free gold. Thereto, it is established that the complete release and recovery of gold up to 100 µm in size can be gained at POS-2000 pneumatic separator at 60% gold recovery into the primary concentrate. The present research data were used as the basis to develop the principal dry preconcentration scheme to process Gurbey ores, bearing “free” gold.

Anticancer effects against colorectal cancer models of chloro(triethylphosphine)gold(I) encapsulated in PLGA\u2013PEG nanoparticles

Chloro(triethylphosphine)gold(I), (Et3PAuCl hereafter), is an Auranofin (AF)-related compound showing very similar biological and pharmacological properties. Like AF, Et3PAuCl exhibits potent antiproliferative properties in vitro toward a variety of cancer cell lines and is a promising anticancer drug candidate. We wondered whether Et3PAuCl encapsulation might lead to an improved pharmacological profile also considering the likely reduction of unwanted side-reactions that are responsible for adverse effects and for drug inactivation. Et3PAuCl was encapsulated in biocompatible PLGA–PEG nanoparticles (NPs) and the new formulation evaluated in colorectal HCT-116 cancer cells in comparison to the free gold complex. Notably, encapsulated Et3PAuCl (nano-Et3PAuCl hereafter) mostly retains the cellular properties of the free gold complex and elicits even greater cytotoxic effects in colorectal cancer (CRC) cells, mediated by apoptosis and autophagy. Moreover, a remarkable inhibition of two crucial signaling pathways, i.e. ERK and AKT, by nano-Et3PAuCl, was clearly documented. The implications of these findings are discussed.

Prodrug Activation by Gold Artificial Metalloenzyme-Catalyzed Synthesis of Phenanthridinium Derivatives via Hydroamination.

An emerging approach in the field of targeted drug delivery is the establishment of abiotic metal-triggered prodrug mechanisms that can control the release of bioactive drugs. Currently, the design of prodrugs that use abiotic metals as a trigger relies heavily on uncaging strategies. Here, we introduce a strategy based on the gold-catalyzed activation of a phenanthridinium-based prodrug via hydroamination under physiological conditions. To make the prodrug strategy biocompatible, a gold artificial metalloenzyme (ArM) based on human serum albumin, rather than the free gold metal complex, was used as a trigger for prodrug activation. The albumin-based gold ArM protected the catalytic activity of the bound gold metal even in the presence of up to 1 mM glutathione in vitro. The drug synthesized via the gold ArM exerted a therapeutic effect in cell-based assays, highlighting the potential usefulness of the gold ArM in anticancer applications.