Gold-bearing Minerals Research Articles

Mineralogy and Pretreatment of a Refractory Gold Deposit in Zambia

The technological mineralogy of a gold deposit located in North-Western province of Zambia was carried out by using X-ray fluorescence spectroscopy (XRF), X-ray diffraction spectroscopy (XRD), and scanning electron microscope (SEM). The results showed that gold was highly dispersed in gold-bearing minerals such as pyrite, arsenopyrite, and some gangues in the form of natural gold and electrum. The gold grade in the mineral was 15.96 g/t and the particle size distribution of gold was extremely uneven. Most of the gold particles were less than 10 μm and wrapped with gold-bearing minerals, making it difficult to achieve liberation during grinding. According to the characteristics of the refractory gold deposit, the gravity–flotation combined beneficiation process was used to recover the liberated coarse gold and the fine gold in the sulphides. The closed-circuit experiments obtained excellent indicators. The grade and recovery of gold in the gravity separation concentrates reached 91.24 g/t and 57.58%, respectively. The grade and recovery of gold in the flotation concentrates were 49.44 g/t and 33.36%, respectively. The total recovery of gold was 90.94%. The gravity–flotation combined beneficiation pretreatment process provided a feasible method for the refractory gold ore and ensured the effective recovery of gold.

Gold and other impurity elements in pyrite from the Berezovskoe deposit in the Middle Urals

Research subject. In this work, we investigated the crystals of pyrite, one of the key gold-bearing minerals, from the Berezovskoe (the Middle Urals) deposit using modern research approaches.Materials and methods. Samples for the analysis were collected from the ladder sulphide-quartz veins and related berezites in the Ilinskaya, Pervopavlovsk and Vtoropavlovsk dykes of the Berezovskoe deposit. The ores were studied using the methods of optical microscopy, X-ray microanalysis (PCMA), scanning electron microscopy (SEM) and LA-ICP-MS. The latter method was largely used to examine pyrite. Along with pyrite, the materials under study included faded ore, galena, and such rare occurring minerals as aikinite, cosalite, tetradymite and tsumoite. Results. According to the point and profile analysis, as well as grain mapping, the main impurity elements in the stu died samples are found to be Co, Ni and As. The distribution of these elements has shown a zonal character: the amounts of Co and Ni tend to increase and that of As tends to decrease towards the grain centre. In the pyrite samples, Cu, Zn and Pb occur either in the form of their sulphide micro-inclusions or as evenly distributed admixtures. The pyritic ore of later genera tions in the Pervopavlovsk dyke is established to contain gold in amounts of up to 22 g/t, with Au being zonally distributed. The goldbearing variety of pyrite is characterized by abnormally low contents of Co and Ni, as well as by an increased content of As (up to 8000 g/t). Conclusion. A common character of the distribution of main impurity elements in the pyritic ores in the studied dikes indicates similar conditions of their crystallization. The presence of late-generation pyrite with fine gold in the Pervopavlovsk dike evidences to a heterogeneous distribution of gold mineralization therein, likely due to the multistage character of the latter. This may also be an indicator of the concentration of ore columns, which fact requires further elucidation.

Mineral Types of Gold Deposits and Regularities of Their Localization in Southeastern East Sayan

The gold-bearing deposits of southeastern East Sayan have been categorized according to mineral composition. The most important classification criterion is the composition of productive ore mineral assemblages specific to each of the distinguished types, whereas the use of other criteria results in the inevitable overlap of different structural, compositional, or genetic features of deposits. Eight mineral types of deposits have been determined, which characterize the main gold-bearing mineral ore parageneses: gold-polysulfide, gold-quartz, gold-telluride, gold-tetradymite, gold-antimony, gold-bismuth-sulfosalt, gold-pyrrhotite, and gold-fahlore. The regional metallogenic units are structural-metallogenic zones somewhat differing by the nature of mineralization. Thus, in the Bokson-Gargan metallogenic zone, the gold-quartz, gold-polysulfide, and gold-pyrrhotite types of deposits prevail, while in the western part of the zone, the gold-telluride and gold-bismuth-sulfosalt types are widespread. In the Ilchir zone, gold-fahlore deposits are developed, while in the Khamsarinskaya zone, gold-tetradymite and gold-stibnite. It has been established that the mineral types of deposits depend on the composition of the host rock complexes: gold-quartz, gold-polysulfide, and gold-pyrrhotite types form in association with ophiolites and Archean basement rocks. At granitoid-massif-related deposits, base-metal minerals assume the leading role: Bi sulfosalts, stibnite, tetradymite, and tellurides. The gold-fahlore type forms in carbonate sequences. The proposed classification makes it possible to group all of the known gold-bearing deposits of southeastern East Sayan; it can also be applied to adjacent regions.

Analysis of the spatial patterns in localization of gold mineralization relative to the system of deep faults in the Chortomlyk greenstone structure of the Ukrainian shield

The results of analysisof the patterns of the spatial relationship between hydrothermal gold ore formations and the zones of metasomatites and systems of deep faults within the Chortomlyk greenstone structure of the Middle Pridniprovie megablock in the Ukrainian Shield are given. As a result of studying the localization conditions of gold mineralization, it was established that the gold-bearing mineralization is confined to tectonically fractured zones and is localized among metasomatically altered rocks. The hydrothermal series of metasomatites in the Chortomlyk greenstone structure is represented by greisens, propylites, amphibole-carbonate metasomatites and listvenite-berezites. The mineralization of Au and Mo is associated with metasomatites of the greisen type. The study of spatial relationship between the fields of metasomatites and the gold mineralization and zones of deep faults revealed that the closest relationship is expressed with systems of faults with azimuths of 0° and 270°, 17° and 287°, 77° and 347°. The results of the studies allowed us to develop a newprospecting criterion, which, in turn allows us to state that the gold mineralization within the Chortomlyk greenstone structure is spatially confined to metasomatites related to the schistosity, fracture, millonitization, and cataclase zones with high content of sulphide mineralization. These zones are localized in nodes of intersecting faults of the first order of the system 77° and 347° with discontinuous violations of high orders of azimuths of 0° and 270°, 17°and 287°. The results of the research can be used to develop a set of predictive criteria and the allocation of promising sites of hydrothermal mineralization of gold within the Chortomlyk greenstone structure of the Middle Pridniprovie megablock in the Ukrainian shield.

The Olimpiadinskoe Gold Deposit (Yenisei Ridge): Temperature, Pressure, Composition of Ore-Forming Fluids, δ34S in Sulfides, 3He/4He of Fluids, Ar–Ar Age, and Duration of Formation1

Abstract —New thermobarogeochemical and isotope-geochemical data are presented, which show the intricate and long history of the formation of the unique Olimpiadinskoe gold deposit with predicted gold reserves of >1000 tons on the Yenisei Ridge. Metal-bearing oxidized water–carbon dioxide and reduced carbon dioxide–hydrocarbon fluids participated (at the same time or successively) in the formation of the deposit at 220–470 °C and 0.6–2.5 kbar. Fluids of gold-bearing mineral assemblages include CO2, hydrocarbons, and S-, N-, and halogen-containing compounds capable of transporting ore elements, including gold. Highly mobile carbon dioxide–hydrocarbon fluids were responsible for the appearance of disseminated gold mineralization in large bodies of quartz–carbonate–mica schists serving as geochemical barriers in the Olimpiadinskoe deposit. The deposit formed in the period from 817 to 660 Ma, which fits the time interval from crystallization to cooling (868–721 Ma) of the most proximal multiphase Chirimba granitoid pluton. The hydrothermal activity of the fluids that formed the Olimpiadinskoe deposit lasted at least 100–150 Myr year.

Technology of Gold-Containing Technogenic Raw Materials Processing Using the Electric Explosion Method

The paper shows fundamental possibility of processing of gold-bearing technogenic raw materials using the method of electric explosion. A series of experiments using a laboratory and pilot-production high-voltage pulsed discharge (HVPD) installation for the processes of enrichment of gold-bearing mineral raw materials of Komsomolsk mine tailings in Kemerovo region is conducted with a relatively low energy electrical discharge in the pulse of up to 112.5 Joules and the cost of electric power of about 1.5 kW/ton of raw material, that allows complete destruction of clay components agglomerations to less than 0.045 mm (micron and submicron sizes). Solid minerals such as quartz are simultaneously destroyed by defects in the grains and withdrawn from the installation with water, thus increasing gold degree of the concentrate. The results of particle-size and X-ray structural analyses of gold-bearing mineral raw materials of Komsomolsk mine tailings in Kemerovo region obtained by the method of electric explosion are discussed.

ON THE INFLUENCE ORGANIC COMPONENTS OF THE EXTRACT OF HERACLEUMON FLOTATION OF GOLD-BEARING SULPHIDES

The complexing, sorption and flotation properties of the organic extract of the green mass of Heracleum Sosnovsky (BO) containing sulphide gold-bearing minerals were investigated. The sorption and elemental composition of the surface of the minerals before and after contact with the reagent BO were studied on polished sections using an LEO 1420VP analytical scanning electron microscope (ASEM) equipped with an X-ray energy dispersive microarray analyzer INCA 350 and a KEYNCE laser microscope with VK-9700. The sorption of furocoumarines on the surface of chalcopyrite and gold particles after their contact with the organic extract of BO was determined by a spectrophotometric method and thin-layer chromatography (TLC). By flotation studies using monomineralic powders FeS2 and CuFeS2, as well as minerals with artificially deposited gold (FeS2Au and CuFeS2Au), the flotation activity of the BO extract with respect to the gold-bearing pyrite and chalcopyrite was revealed. When flotation gold-bearing sulphide ore with the use of BO as an additional collector, an increase in the quality of the concentrate with respect to gold content up to 10.8 g / t and gold recovery into concentrate to 82.69% was found, which is 3% higher than in the base experiment. The obtained results give grounds to talk about the possibility of using the flotation of a poisonous species of Heracleum after isolation from it of natural chemical compounds possessing surface-active properties with respect to gold-bearing sulfide minerals. The extraction of an extract containing furocoumarines from the Heracleum is not a problem.

Structure–activity relationship of xanthates with different hydrophobic groups in the flotation of pyrite

Xanthate collectors have been industrially used for the flotation of pyrite in the gold mining industry because pyrite is the most common gold-bearing mineral. However, after reviewing the structure-activity relationship study of flotation collectors, the influence of hydrophobic groups on the flotation performance of collectors remains underexplored. In this paper, using density functional theory (DFT) method, the quantum chemical properties of xanthate derivatives ROC = SS- (R = ethyl, isobutyl or amyl) and their interactions with Fe3+, Fe(OH)2+, Fe(OH)2+ and pyrite cluster were evaluated in the context of solvation effects. The flotation performance of substituted xanthates was experimentally investigated for a gold–pyrite ore. Based on the values of frontier orbital energies and electronic chemical potential, the flotation performance of the alkyl xanthates was predicted to be amyl xanthate > isobutyl xanthate > ethyl xanthate. The results showed that the direct chemisorption of the ferric hydroxo xanthates on the pyrite surfaces was thermodynamically possible. The flotation performance of the xanthate collectors matched with the theoretically predicted trend. This study could offer some theoretical insights into the mechanism of pyrite flotation and provide novel guidelines for rational selection/design of hydrophobic groups of flotation collectors.

A new indicator mineral methodology based on a generic Bi-Pb-Te-S mineral inclusion signature in detrital gold from porphyry and low/intermediate sulfidation epithermal environments in Yukon Territory, Canada

Porphyry-epithermal and orogenic gold are two of the most important styles of gold-bearing mineralization within orogenic belts. Populations of detrital gold resulting from bulk erosion of such regions may exhibit a compositional continuum wherein Ag, Cu, and Hg in the gold alloy may vary across the full range exhibited by natural gold. This paper describes a new methodology whereby orogenic and porphyry-epithermal gold may be distinguished according to the mineralogy of microscopic inclusions observed within detrital gold particles. A total of 1459 gold grains from hypogene, eluvial, and placer environments around calc-alkaline porphyry deposits in Yukon (Nucleus-Revenue, Casino, Sonora Gulch, and Cyprus-Klaza) have been characterized in terms of their alloy compositions (Au, Ag, Cu, and Hg) and their inclusion mineralogy. Despite differences in the evolution of the different magmatic hydrothermal systems, the gold exhibits a clear Bi-Pb-Te-S mineralogy in the inclusion suite, a signature which is either extremely weak or (most commonly) absent in both Yukon orogenic gold and gold from orogenic settings worldwide. Generic systematic compositional changes in ore mineralogy previously identified across the porphyry-epithermal transition have been identified in the corresponding inclusion suites observed in samples from Yukon. However, the Bi-Te association repeatedly observed in gold from the porphyry mineralization persists into the epithermal environment. Ranges of P-T-X conditions are replicated in the geological environments which define generic styles of mineralization. These parameters influence both gold alloy composition and ore mineralogy, of which inclusion suites are a manifestation. Consequently, we propose that this methodology approach can underpin a widely applicable indicator methodology based on detrital gold.

Physicochemical model for the genesis of Cu-Ag-Au-Hg solid solutions and intermetallics in the rodingites of the Zolotaya Gora gold deposit (Urals, Russia)

In this contribution we examine the compositions of solid solutions and intermetallics of the system Cu-Ag-Au-Hg and the physicochemical conditions of their formation in rodingites from the Zolotaya Gora gold deposit (Southern Urals, Russia). Thermodynamic calculations, modeling the formation of mineral assemblages of rodingite and Cu-Ag-Au-Hg mineralization, were carried out using a “Selektor-C” software package. Two probable models for the genesis of Au-Ag-Cu-Hg solid solutions and Au-Cu intermetallics in rodingites are: 1) hydrothermal; the result of single-stage discharge in open space of deep-sourced gold-bearing fluid with the composition corresponding to rodingite, taking into account its interaction with host serpentinites. 2) metasomatic; deep-seated gold-bearing fluid (W) rising to the surface interacts with early formed rodingite (R) at different ratios (W/R). T and P-conditions of modeling: 450 °C, 3 kbar; 350 °C, 2 kbar; 250 °C, 1 kbar. Results of the calculations on the “hydrothermal” and “metasomatic” models showed different degrees of similarity of natural and theoretical model associations of rodingites. The metasomatic model is better for corresponding to real mineral compositions and mineral paragenesis in the natural Cu-Ag-Au-Hg system observed at the deposit. In this model the chlorite-garnet-pyroxene rodingite is replaced by a chlorite-rich rock with increasing W/R. In this case all gold minerals of Zolotaya Gora deposit (Au-Cu intermetallics and Au-Ag solid solutions) are formed at 250–450 °C. Gold-copper solid solution formed at a temperature of 450 °C (W/R >10). Au-Ag-Hg solid solutions and native copper are formed only at 250 °C. According to the hydrothermal model native copper and AuCu3 were absent phases, but other Au-Cu intermetallics (AuCu, Au3Cu) precipitate if gold concentration in the solution is higher than 0.5 ppm. Thermodynamic calculations proved the possibility of formation of equilibrium assemblages of rodingite minerals and gold-bearing minerals with the participation of water-chloride complexing and low CO2 fluids. At a temperature <350 °C the main status of gold in solution are Au(HS)2− and AuHS0, while at higher temperatures it occurs as AuOH0. Formation of Au-Cu intermetallics occurred under the effect of weak-acid hydrothermal solutions (pH = 3.5 ÷ 5) with low fugacity of O2 and S2: log fO2 = −26 ÷ −47, log fS2 = −8 ÷ −20. Both models (hydrothermal and metasomatic) explain the formation of Au-bearing rodingites and can be used for predicting potential gold-bearing rodingite targets.

Trace Element Compositions of Pyrite from the Shuangwang Gold Breccias, Western Qinling Orogen, China: Implications for Deep Ore Prediction

The Shuangwang gold deposit, located in the Fengxian-Taibai fore-arc basin in the western Qinling Orogen of Central China, has yielded over 70 tons of gold. It is an orogenic gold deposit occurring in an NW-trending breccia belt. Most of the ores are hydrothermal breccia type containing fragments of adjacent strata cemented by ankerite and pyrite. Pyrite is the most abundant metallic mineral and the major gold-bearing mineral in the ores. A total of 58 pyrite samples from main ore bodies of the Shuangwang gold deposit have been analysed for 44 trace elements by HR-ICP-MS. Sb, Ba, Cu, Pb, Zn, Bi, Mo, Co are selected as indicator elements to investigate the potential usefulness of trace elements in pyrite as an indicator in gold exploration. The results show that the supra-ore halo elements Sb and Ba, which may have been more active than other near-ore halo elements and sub-ore halo elements, are best to characterize the shape of ore bodies. Five target areas are pointed out for deep ore exploration based on a comprehensive study of supra-ore, near-ore and sub-ore halos. This study provides evidence that trace elements in pyrite can be used to depict the deep extension of ore bodies and to vector towards undiscovered ore bodies.

Finely Dispersed Micro- and Nano-Gold Recovery Using Thermomorphic Polymer with Diphenylphosphine

The article reports test data on adsorption and flotation characteristics of thermomorphic polymer joined with diphenylphosphine—TMPD. The test materials are natural pyrite and arsenopyrite, and models of gold-bearing sulfide minerals. Electron microscopy and X-ray structure analysis prove that reductive adsorption of gold at the surface of sulfide minerals from HAuCl4 solution allows modeling natural aggregates of sulfides and finely dispersed gold. UV spectrophotometry proves selective adsorption of TMPD at gold. Laser scanning microscopy shows connection of TMPD with micro- and nano-size gold on polished sections of pyrite and arsenopyrite. During monomineral flotation, joint use of TMPD and butyl xanthate at a ratio of 1:1 doubles the yield of gold-bearing sulfides and enables maximum recovery of gold minerals at the total consumption of reagents reduced by 30–50%. It is found that TMPD is selective relative to gold-bearing minerals and its combination with xanthate ensures a considerable increment in gold-bearing mineral recovery by flotation.

Geological and technological evaluation of gold-bearing mineral material after photo-electrochemical activation leaching

The paper reports the lab test results on simulation of heap leaching of unoxidized rebellious ore extracted from deep levels of Pogromnoe open pit mine, with different flowsheets and photo-electrochemically activated solutions. It has been found that pre-treatment of rebellious ore particles –10 mm in size by photo-electrochemically activated solutions at the stage preceding agglomeration with the use of rich cyanide solutions enhances gold recovery by 6%.

Optimizing a Knowledge-driven Prospectivity Model for Gold Deposits Within Peräpohja Belt, Northern Finland

This paper combines knowledge- and data-driven prospectivity mapping approaches by using the receiver operating characteristics (ROC) spatial statistical technique to optimize the process of rescaling input datasets and the process of data integration when using a fuzzy logic prospectivity mapping method. The methodology is tested in an active mineral exploration terrain within the Paleoproterozoic Perapohja Belt (PB) in the Northern Fennoscandian Shield, Finland. The PB comprises a greenschist to amphibolite facies, complexly deformed supracrustal sequence of variable quartzites, mafic volcanic rocks and volcaniclastic rocks, carbonate rocks, black shales, mica schists and graywackes. These formations were deposited on Archean basement and 2.44 Ga layered intrusions, during the multiple rifting of the Archean basement (2.44–1.92 Ga). Younger intrusive units in the PB comprise 2.20–2.13 Ga gabbroic sills or dikes and 1.98 Ga A-type granites. Metamorphism and complex deformation of the PB took place during the Svecofennian orogeny (1.9–1.8 Ga) and were followed by intrusions of post-orogenic granitoids (1.81–1.77 Ga). The recent mineral exploration activities have indicated several gold-bearing mineral occurrences within the PB. The Rompas Au-U mineralization is hosted within deformed and metamorphosed calc-silicate veins enclosed within mafic volcanic rocks and contains uranium-bearing zones without gold and very high-grade (>10,000 g/t Au) gold pockets with uraninite and uraninite-pyrobitumen nodules. In the vicinity of the Rompas, a magnesium skarn hosted disseminated-stockwork gold mineralization was also recognized at the Palokas-Rajapalot prospect. The exploration criteria translated into a fuzzy logic prospectivity model included data derived from regional till geochemistry (Fe, Cu, Co, Ni, Au, Te, K), high-resolution airborne geophysics (magnetic field total intensity, electromagnetic, gamma radiation), ground gravity and regional bedrock map (structures). The current exploration licenses and exploration drilling sites for gold were used to validate the knowledge-driven mineral prospectivity model.

Features of the geological structure and gold mineralization of the ore occurrence Yuzhnoe (the Yenisei Ridge)

The relevance of the discussed issue is caused by the need to detect new gold ore deposits within the Yenisei ridge to replenish mineral resources of gold ore in Russia. The main aim of the study is to explore the features of geological structure and gold ore mineralized zones of ore occurrence Yuzhnoe in order to forecast gold ore bodies, and to substantiate the continuation of geological exploration. The methods used in the study. The exploration is implemented by the express method of prospecting gold ore deposits in difficult mountain-taiga landscapes using a complex of lithogeochemical sampling for secondary dispersion halos, schlich, point and trench sampling; spectrochemical analysis for determining gold content, ICP-MS, atomic-and-absorption, X-ray phase analysis and isotope-geochemical methods were used. The results. The complex of prospecting methods allowed the author to reveal ore-controlling zone of fold-discontinuous deformations and localize within it the ore occurrence Yuzhnoe. The latter is located in the south-eastern part of Sredne-Ishimbinskaya area in the zone of dynamic influence of Ishimbinskiy deep fault system. The gold ore mineralized zones were revealed within the ore occurrence. They are presented by a series of lode gold stockwork subparallel bedding zones with low average gold content. A detection of gold ore bodies is forecasted within the most wide and lengthy zone Centralnaya, where the geological exploration is recommended to be continued. The author hascompared the ore occurrence with model objects and determined a set of common criteria and indicators of the ore occurrence with lode gold-sulfide deposits of the Yenisei ridge - Olimpiadninskoye, Veduginskoye, etc. and with «carlin» type deposits. Conclusions. For the first time in the region the gold ore mineralized zones in carbonate-terrigenous carbonaceous sediments of kartochki and aladyinskaya series of the Middle Riphean were detected. The perspectives of gold-bearing mineralization of the eastern slope of the Yenisei ridge are defined.

Structural Controls on an Orogenic Gold System: The World-Class Siguiri Gold District, Siguiri Basin, Guinea, West Africa

Orebodies in the Siguiri district, a world-class Paleoproterozoic orogenic gold camp located in the Birimian of northeastern Guinea, are typically represented by cryptic subvertical damage zones that host a high density of mineralized veins. Although no large regional fault system was recognized, observations from five representative deposits of the Siguiri district (Sanu Tinti, Bidini, Kami, Kosise, and Sintroko PB1) show that these orebodies are locally controlled by incipient structures and spread across three distinct structural and lithostratigraphic domains. Two shale-dominated peripheral domains adjoin a central domain whose lithostratigraphy is dominated by medium- to coarse-grained graywacke and this domain hosts the bulk of the gold endowment of the district. The three domains exhibit similar structural elements that can be described within a four-stage deformation scheme. The first deformation event (D 1S ) is poorly constrained and interpreted to have been an N-S compressional event. It included development of minor folds with W- to WNW-gently plunging fold axes without a clear axial planar cleavage. The main and second deformation event (D 2S ) is interpreted to have been associated with E-W to ENE-WSW- directed compression. The D 2S event was responsible for forming the dominant N-trending structural grain of the district and creating interference patterns between F 1S and F 2S folds. The third event (D 3S ) developed progressively from D 2S compression into an early-D 3S E-W- to ENEWSW-directed transpression and a late-D 3S NNW-SSE-directed-transtension responsible for most of the gold mineralization in the Siguiri district. The fourth and last event (D 4S ) was an NW-SE-oriented compressional event responsible for the localized overprinting of veining by a steep to shallowly dipping NNE-SSW ductile cleavage. Late-D 3S gold-bearing mineral occurrences formed along subvertical N-S reverse faults, NE-trending dextral shear zones, WNW-trending sinistral faults, and E-trending normal relay faults developed or reactivated early-D 3S . Mineralization is expressed as mineralized shear zones or subvertical damage zones, characterized by a 10- to 15-m-wide zone of dense quartz-carbonate-sulfide veining, or disseminated gold-bearing sulfides. The mineralized veins consistently strike ENE-WSW, are steeply dipping, and commonly have a conjugate geometry at the mesoscale. Finite strain analysis of deformation, including analysis of folds, faults, and conjugate mineralized vein sets, is consistent with a stress switch from a compressional (D 2S ) to transpressional deformation (termed early-D 3S ). Results of paleostress analysis on conjugate mineralized vein sets that formed late during D 3S indicate that the stress field ranged from extensional to strike-slip, sometimes within the same vein locality. The late-D 3S deformation is interpreted to have been a transtensional event. The first change in the orientation of the principal stress axes is related to a switch from a far field-dominated to a body force-dominated stress field reducing the deviatoric component on the stress tensor. The second change in the orientation of the principal stress axes, from early-D 3S transpression to late-D 3S transtension, suggests that σ 1 and σ 2 were similar in magnitude, which facilitated localized stress switches. In the Siguiri district, the early-D 3S and late-D 3S stress switches, which occurred at both a local and regional scale, enhanced the fracture permeability and were critical for the establishment of active fluid pathways leading to the formation of a world-class gold system.

Las leyes de minería en Ecuador a fines del siglo XIX: la reconfiguración de la propiedad minera

Reflecting on both the Mining Code of 1886 and the subsequent amendments administered to said code in 1892, this investigation endeavors to evaluate the immense impact that its implementation caused in Ecuador’s geographic space. These laws inaugurated criteria for the demarcation of mining properties; noteworthy acts that strengthened the state’s dominion over subsoil and the obtention of perks concerning concessionaires. The adoption of new mining law principles facilitated the arrival of foreign investors interested in the exploitation of gold-bearing mineral deposits. This investigation’s conclusions reveal that mining legislation was formed by dynamically integrated protagonists from distinct ranks who restructured Ecuador’s geographic space in the areas where these valuable mineral deposits could be found. Furthermore, this piece explores the tension between the needs of economical liberalism, at the national level, and the expansion of the mineral extraction industry, at the regional level, towards the end of the 19th century. &nbsp

New data on the age of gold mineralization of the Lugokan ore cluster (Eastern Transbaikalia)

The Lugokan ore cluster is located in the southeastern part of Transbaikalia within the Aga–Borzya structural–formational zone of the Mongol–Okhotsk orogenic belt. The 40Ar/39Ar dating of K-bearing minerals of syngenetic to ore parageneses has been carried out applying stepwise heating technique: it has been demonstrated that the earliest gold-ore mineral associations are Au–pyrite–arsenopyrite (163 ±1.9 Ma) and Au–chalcopyrite (160 ±2 Ma). The later parageneses encompass the Au–polymetallic (156.3 ± 1.8 Ma) and Au–Bi (155.9 ± 4.5 Ma) one. By their ages and position in the general scheme of the Late Jurassic magmatism of Eastern Transbaikalia, the Lugokan’s ore cluster gold-bearing mineral associations corresponds to the time of intrusion of the Shakhtama pluton (161 Ma) and the Porphyry Complex (159–155 Ma).

Comparison of the native antimony-bearing Paiting gold deposit, Guizhou Province, China, with Carlin-type gold deposits, Nevada, USA

The Paiting gold deposit, Guizhou Province, China, has been regarded as a Carlin-type gold deposit by several researchers. Alteration and ore-related minerals from the Paiting deposit were examined, and results were compared with the Cortez Hills Carlin-type gold deposit, Nevada, USA. Similarities include the structural and stratigraphic controls on the orebodies in both deposits and the occurrence of invisible gold ionically bound in arsenian pyrite. Significant differences include the following: (1) The gold-bearing mineral in Nevada is arsenian pyrite. However, gold-bearing minerals in the Paiting deposit include arsenopyrite, arsenian pyrite, and trace pyrrhotite. Also, euhedral or subhedral gold-bearing arsenian pyrite at Paiting contains significantly less As, Cu, and Hg than gold-bearing pyrite from Nevada. (2) Alteration in the Paiting deposit displays significantly less decarbonatization. Instead, dolomite precipitation, which has not been described in Nevada deposits, is associated with deposition of gold-bearing sulfide minerals. (3) Stibnite and minor native antimony typify Paiting late-ore-stage minerals, whereas in Nevada, realgar, orpiment, and calcite are common late-ore-stage minerals. Precipitation of native antimony in the Paiting deposit reflects the evolution of a late-ore fluid with unusually low sulfur and oxygen fugacities. Some characteristics of the Paiting gold deposit, including formation of ore-stage dolomite and precipitation from CO2-rich ore fluids at temperatures in excess of 250 °C, are more typical of orogenic deposits than Nevada Carlin deposits. The presence of similarities in the Paiting deposit to both Carlin type and orogenic deposits is consistent with formation conditions intermediate to those typical of Carlin type and orogenic systems.

GEOLOGY, PETROGEOCHEMISTRY OF AKHMEROVSKY GRANITE MASSIF AND ORE MINERALIZATION IN ITS FRAME

The article considers the geological structure, composition and geochemical features of Akhmerovsky granite massif, which is an integral and central part of zonal beloretsk metamorphic complex. It is shown that the massif consists mainly of granite and diorite, which in mineral composition meet the standard granites. The source rocks for beloretsk complex are sandy-clayey and carbonate rocks with thick interlayers of carbonaceous formations. On the characteristic geochemical diagrams granites of Akhmerovsky massif form a compact field in the area of intraplate granitoids. They are comagmatic the mashak volcanic rocks and their paleotectonic regime corresponds to stable consolidated structures of platform type. The formation of the main phase granites of Akhmerovsky massif belongs to the early phase of the middle Riphean and corresponds to the time of formation of Berdyaushsky, Ryabinovsky and Kusinsko-Kopansky intrusions. It is studied the carbonaceous deposits within the beloretsk metamorphic complex on the gold. It is shown that the largest manifestations of gold are confined to tectonically intensively deformed, silicified and sulfidation rocks of black-shale formation, located in an external high-temperature zone of the greenschist facies of metamorphism, which is an important exploration indicator for carrying out further work on the periphery of the beloretsk metamorphic dome. In such geological setting was revealed the gold manifestation of Otnurok, where was tested the carbonaceous formations which allowed us to identify a member of ore-bearing rocks. This zone of gold-bearing mineralization was traced in a north-easterly direction for several kilometres along strike, but not delineated, that allow us to continue research work in this direction.