Grade Gold Research Articles

Mineralogy and primary sources of gold in Davenda-Klyuchevsky ore-placer cluster (Eastern Transbaikalia)

The Davenda-Klyuchevsky ore cluster contains a large number of gold placers and ore occurrences, deposits of gold-sulfide-quartz and gold-bearing Mo-porphyry formations of stockwork and vein types. Judging by the morphology of gold, most placers are closely spatially related to ore sources, but data on the chemical composition of gold from placers and ores are very limited in the literature. A detailed mineralogical and geochemical study of placer gold, which is the subject of this work, provides important genetic information that can be used to predict and search for gold mineralization. It has been established that the fineness of placer gold is well comparable to the fineness of ore gold. In the autochthonous placers, that formed a distant aureole around the Klyuchevskoye deposit, are dominated by gold with a fineness of 900–950‰. Gold often contains inclusions of ore minerals and forms intergrowths with them. First of all, these are pyrite, galena and Bi minerals (tetradymite, Bi tellurides, Bi-containing sulfosalts, native Bi, bismuthine), less often – arsenopyrite, chalcopyrite, fahlores. In the autochthonous placers, located around the Davenda deposit, gold with a fineness of more than 950‰ predominates; inclusions of ore minerals (pyrite, galena, tetradymite, PbBiCuS mineral, arsenopyrite) in the gold of these placers are rare. The third type of gold (850–900‰) is less common in the above-mentioned placers, but predominates in the autochthonous placers of the Maly and Levy Amundzhikan rivers. In essentially allochthonous placers on the periphery of the Davenda-Klyuchevsky ore cluster and the Cherny Uryum River, lower grade gold is also common. In this group of placers, the mineral association of Au changes somewhat. Galena and Bi minerals are almost never found together in gold grains; hessite, acanthite, and petzite appear, associated with Bi minerals or pyrite. The heavy concentrates contain cinnabar. The fineness of placer gold and its associations with ore and nonmetallic minerals indicate telescoping mineralization in ore sources and the superimposed nature of placer-forming gold mineralization.

A comparison of dry and wet grinding on gold-bearing sulphide ore flotation

This study investigates the hypothesis that dry grinding prior to flotation can mitigate the adverse effects of galvanic interactions, improve the selectivity of gold flotation compared to wet grinding, and offer additional benefits due to water scarcity concerns and high water treatment costs. The effects of dry and wet grinding on the flotation behavior of gold-bearing sulphide ore were studied comparatively in terms of flotation test results and pulp chemistry parameters (pH, Eh, and dissolved oxygen). In addition, flotation tests without conditioning were also conducted following dry grinding in an attempt to minimize water contact further. Results demonstrated that dry grinding increased pulp potentials and dissolved oxygen levels, implying more oxidative conditions. Despite a lower mass pull with dry grinding, flotation recoveries and grades of gold and chalcopyrite were comparable to wet grinding, while dry grinding enhanced pyrite flotation at the rougher stage. Notably, flotation without conditioning effectively rejected pyrite and achieved higher grades for gold and chalcopyrite, indicating selective flotation. Therefore, dry grinding before flotation emerges as a viable alternative for gold and chalcopyrite flotation due to its improved selectivity while carefully optimizing flotation strategies and reagents to maximize recoveries.

Ore Characteristics and Distribution Based on Geological and Geophysical Features of the Tambang Sawah Low Sulfidation Epithermal Gold Prospect in Lebong District, Sumatra Island, Indonesia

Sumatra is recognized as one of the Indonesian islands with a big potential for mineral deposits particularly along the belt known as Neogene Sumatra gold axis. However, the publication of the gold resources is still restricted as regional/district scale maps or limited in some locations and internal company reports, hence, a detailed study on deposit scale remains limited. This study aims to document the deposit geology, ore characteristics and geophysical features of the Tambang Sawah prospect at Lebong district, Sumatra Island. The study was done by geological mapping, sampling, and analyzing of selected samples by petrographic, ore microscopic, X-Ray Diffraction, micro X-Ray Fluorescence and various geochemical analyses to identify ore characteristics. The geophysical survey was carried out using geomagnetic and induced polarization. Ore mineralization is manifested by various alteration types such as argillic, propylitic, and silicification, which suffered andesitic breccia and granite host-rocks. Gold mineralization is in the form of quartz veins with typical opening space filling textures such as colloform, crustiform, cockade, moss, comb, and brecciated. The main sulfides consist of pyrite, chalcopyrite, covelite, sphalerite and galena. Gold commonly occurs as free grains. Highest grade gold of up to 21.3 ppm is associated with colloform and cockade-crustiform quartz veins. Geophysical surveys indicate that gold mineralization is associated with low geomagnetic anomaly areas. The 3D modelling of the IP survey reveals that the ore mineralization may occur at 75m depth. Two target areas located at the northeastern and southwestern portions are recommended for a follow-up detailed exploration based on the mapped ore geology, ore characteristics, and geophysical anomalies.

Investigating the benefits of using HPGR prior to cyanidation of low grade gold ore

AbstractIt is known that the cracked structure of the particles has positive effects in leaching processes. In this respect, high pressure grinding rolls (HPGR) provides some advantages such as increasing leaching efficiency and reducing leaching time by creating more cracked particles compared to other crushers. Although there are studies on the advantages of HPGR on different ores, these have not been fully demonstrated in low grade gold ores, and leaching kinetics have not been examined in detail in the studies conducted in this context. In this study, first of all, crack formation in a low grade gold ore by crushing with HPGR and jaw crusher was investigated. Then, bottle roll tests were performed in different size fractions and different cyanide concentrations along with column leaching of the pelletized ore in a single test condition. As a result of the studies, it was determined that 2–3 times more cracked particles were formed in HPGR depending on the particle size. It was shown that the modified Kelsall model explains the kinetics better than other kinetic models tested. In summary, it was revealed that maximum gold extractions are almost same for HPGR and jaw crushers. However, the fast dissolution kinetic constant was found to be around 25% higher for HPGR than for the jaw crusher in bottle roll tests while this ratio was approximately 30% higher in column leaching tests, suggesting a distinct influence of the crushing method on the dissolution kinetics.

Development of an affordable microRNA electrochemical biosensor for identification and monitoring of obstructive sleep apnea and its associated comorbidities

Obstructive sleep apnea (OSA) is a growing and common disorder found in a large global population. Unfortunately, many tend to neglect this disorder without anticipating its chronic and serious health consequences. In this work we demonstrate a prototype portable, low-cost and facile sensing platform that can identify microRNA based molecular markers of OSA including monitoring its severity. An affordable commercial grade gold coated copper cladded laminate sheet was used for fabricating the electrochemical biosensor. The electrode surface was nanotextured to extend a dense and high surface area to significantly improve the sensitivity. A limit of detection of 0.7 nM could be obtained for mir-21 target with a very promising stability of more than 600 days at − 20 °C storage. Clinical utility of the fabricated sensor was established with a rsd of 7.3 % using RNA extracted from PBMC isolated blood samples of various (n = 12) OSA patients and healthy individuals (n = 7). The electrochemical sensing results were compared and satisfactorily validated with ΔCt values obtained from RT-PCR and AHI values from Polysomnography test. Clinical validation not only indicated potentials for an easy portable sensing technology but also a method to monitor patient’s severity of the disorder. These test results have been further supported by statistical analysis that enabled prediction of correlation of OSA with other common lifestyle disorders such as Obesity, liver disorder and diabetes. Overall, the proposed platform holds a strong potential as a reliable alternative to the existing OSA detection technology like Polysomnography that is complex and requires long data acquisition time.

Imputation of Gold Recovery Data from Low Grade Gold Ore Using Artificial Neural Network

In a multivariate database, the missing data can be obtained through several imputation techniques, which are particularly useful for data that are difficult to obtain, for any reason, or have high uncertainties or scarce variables. A Self-Organizing Maps (SOM) neural network is an effective tool for the analysis of multidimensional data applied for the imputation of data. In this paper, data from drilling were used for training, testing, and validation using the variables: total Au recovery (%), which means gold recovery from a gravity concentration plus hydrometallurgical process, Au (g/t), As (ppm), S (%), Al2O3 (%), CaO (%), K2O (%), and MgO (%). After training, the partial omission of Au content and recovery was carried out, from 10% to 50%, to evaluate the data imputation performance for those variables. The results imputed by the SOM were compared with the original data values and evaluated according to descriptive statistics; the results indicated a determination coefficient of 85% when 50% of the data were omitted and 93% when 10% of the data were omitted. Once demonstrated, the correlation between the original data and SOM imputation analysis can help geologists and metallurgists to obtain results with a high degree of reliability of metallurgical recovery through related chemical variables, making it possible to implement SOM analysis as a powerful tool to input analytical data. One of the practical applications of the proposed model is to produce a pattern of imputed data that can be a good alternative in the construction or generation of a synthetic geometallurgical database with missing data.

Orogenic gold: is a genetic association with magmatism realistic?

Many workers accept a metamorphic model for orogenic gold ore formation, where a gold-bearing aqueous-carbonic fluid is an inherent product of devolatilization across the greenschist-amphibolite boundary with the majority of deposits formed within the seismogenic zone at depths of 6–12 km. Fertile oceanic rocks that source fluid and metal may be heated through varied tectonic scenarios affecting the deforming upper crust (≤ 20–25 km depth). Less commonly, oceanic cover and crust on a downgoing slab may release an aqueous-carbonic metamorphic fluid at depths of 25–50 km that travels up-dip along a sealed plate boundary until intersecting near-vertical structures that facilitate fluid migration and gold deposition in an upper crustal environment. Nevertheless, numerous world-class orogenic gold deposits are alternatively argued to be products of magmatic-hydrothermal processes based upon equivocal geochemical and mineralogical data or simply a spatial association with an exposed or hypothesized intrusion. Oxidized intrusions may form gold-bearing porphyry and epithermal ores in the upper 3–4 km of the crust, but their ability to form economic gold resources at mesozonal (≈ 6–12 km) and hypozonal (≈ > 12 km) depths is limited. Although volatile saturation may be reached in magmatic systems at depths as deep as 10–15 km, such saturation doesn’t indicate magmatic-hydrothermal fluid release. Volatiles typically will be channeled upward in magma and mush to brittle apical roof zones at epizonal levels (≈ < 6 km) before large pressure gradients are reached to rapidly release a focused fluid. Furthermore, gold and sulfur solubility relationships favor relatively shallow formation of magmatic-hydrothermal gold systems; although aqueous-carbonic fluid release from a magmatic system below 6 km would generally be diffuse, even if in cases where it was somehow better focused, it is unlikely to contain substantial gold. Where reduced intrusions form through assimilation of carbonaceous crustal material, subsequent high fluid pressures and hydrofracturing have been shown to lead to development of sheeted veins and greisens at depths of 3–6 km. These products of reduced magmatic-hydrothermal systems, however, typically form Sn and or W ores, with economic low grade gold occurrences (< 1 g/t Au) being formed in rare cases. Thus, whereas most moderate- to high-T orogens host orogenic gold and intrusions, there is no genetic association.

The role of competitive fluid-rock interaction processes in the formation of high-grade gold deposits

Although forming one unified class, orogenic gold deposits may be associated with a range of ore mineral assemblages controlled by a variety of gold deposition processes that have a direct impact on gold grade. Whereas, a better understanding of the deposition process may be critical for effective targeting of highly-endowed gold deposits, it is challenging to establish a direct comparison between mineral systems formed under different conditions. Accordingly our ability to predict whether contrasted mineral associations may be more or less prospective for high grade mineralization remains poor. In this paper, we compare fluid-rock interaction processes that led to the coeval formation of two contrasting gold mineral assemblages within the world-class Callie orogenic gold deposit. Stratabound and vein-hosted lodes formed within the same structural framework but with contrasting grades (∼3 g/t Au and ∼8 g/t Au, respectively). The stratabound mineralization consists of bedding-parallel sulfides in which gold is preserved in arsenopyrite micro-fractures. The vein-hosted mineralization consists of locally very high-grade (up to 10,000 ppm Au) visible gold concentrated in quartz veins. Both mineralization styles are hosted within different metasedimentary stratigraphic horizons with contrasting compositions. The stratabound mineralization occurs in iron-oxide rich siltstones whereas the vein-hosted mineralization occurs in carbonaceous siltstones. We investigate the fluid-rock interaction mechanisms of the two styles of mineralization at the Callie deposit by combining petrographic observation with whole-rock geochemistry, quantitative chlorite and gold analyses and thermodynamic modeling. Our results show that the stratabound mineralization occurred in response to sulfidation of the host-rock whereas decarbonation alteration, associated with the vein-hosted mineralization, records oxidation of the host-rock. Our investigation shows that gold deposition induced by oxidation of the host-rock produces the valuable, locally very-high grade visible gold mineralization whereas the sulfidation process lead to the formation of lower grade gold mineralization disseminated within the sulphide ore assemblage. We conclude that the nature of the host-rock applies a first-order control on the gold deposition efficiency in metasedimentary-hosted gold deposits.

Surface structure of Amur region high grade native gold

The purpose of the research is to study the surface structure of high grade gold. The subject of research is gold ore fields in the Amur region. The object of the study is samples of native high grade gold grains from these fields. The study uses the methods of thermodynamics and X-ray electron microscopy. The study results in revealing a multilayer structure of the surface of high grade minerals of the Amur region native gold with the following levels: a boundary layer with zero oxidation degree Au0 in the form of yellow metallic gold; an oxide layer with the oxidation degree Au+1in the form of purple Au2O; an oxide layer with the oxidation degree Au+3in the form of a yellow-brown Au2O3; a hydrated oxide layer with the oxidation degree Au+3in the form of a red-yellow-brown Au(OH)3. The methods of electron microscopy have allowed to identify external surface structures – dense oxide layers of the form of Au2O3and loose hydrated layers of the form of Au(OH)3, whereas the inner layers of metallic and monovalent gold are not visible. Important thermodynamic characteristics of the presented levels are the values of standard oxidation-reduction potentials (E°), which determine their physicochemical properties: for metallic gold E° = +1.68 V; for the oxide layer with the oxidation degree Au+1in the form of Au2O – E° = +0.32 V; for the oxide layer with the oxidation degree Au+3in the form of Au2O3– E° = +1.36 V; for the hydrated oxide layer with the oxidation degree Au+3in the form of Au(OH)3– E° = +0.7 V. The results of the conducted studies indicate that the surface structure has several layers that lower the oxidation-reduction potential, which explains the generation and formation of migratory forms of gold in humid hypergene conditions of natural environment.

K–Ar geochronology of orogenic gold mineralization in the Vangtat gold belt, southeastern Laos: Effect of excess argon in hydrothermal quartz

AbstractThe Thongkai‐Ok gold deposit is one of several actively mined deposits in a newly discovered orogenic gold belt in southeastern Laos. At a district scale, gold mineralization occurs within the Vangtat shear zone, one of the tectonic structures of the Poko suture zone that marks the collision between the Indochina Terrane and the Kontum Massif in southern Laos‐central Vietnam. High grade gold mineralization is associated with quartz–pyrite–white mica veins and silicified zones up to 10 m thick, hosted by strongly deformed and sheared pelitic schist. Lower‐grade gold mineralization occurs in a graphite–carbonate–quartz–sulfide hydrothermal alteration envelope that grades into sub‐economic/barren altered pelitic schist. The objective of this study is to establish the age of mineralization in the Vangtat orogenic gold belt by K–Ar dating of hydrothermal white mica in the gold‐bearing quartz‐sulfide veins in order to better understand its spatial and temporal relation to other gold deposits in Southeast Asia and to regional tectonic events. Three‐white mica bearing quartz–pyrite samples were collected from the open pit at Thongkai‐Ok. The dominant white mica phase in the samples is 2M1 muscovite and the K2O content measured by electron microprobe techniques in individual white mica crystals ranged between 8.61 and 9.79 wt%. Two of the three vein samples were separated by gravity settling into four size fractions, &lt;2, 2–4, 4–10, and 10–40 μm, respectively. The results of potassium measurements by flame photometry in the K–Ar sample aliquots show a range in potassium content which reflects the amount of quartz present in each sample as an impurity. With one exception, a correlation was observed between potassium concentration in the samples, including the size fraction separates, and the calculated K–Ar age. The large range of calculated ages, from 348 to 206 Ma, is interpreted to reflect excess argon contained in fluid inclusions in the hydrothermal quartz present in the analyzed samples. We interpret the youngest age of the quartz‐free samples, 206 ± 4 Ma, as closest to the age of mineralization in the Vangtat gold belt. The age could be as young as ~170 Ma if the age versus potassium content relation is extrapolated to the average potassium content of white mica in the samples analyzed.

High REE and Y Concentrations in Mo-Au Ores of the Kis-Kuel IOCG Deposit, East Yakutia (Russia)

This paper presents the results of an updated from 2008-2019 study of the Kis-Kuel promising area and is devoted to the discovered unusual molybdenite + gold bearing mineralizing system of the Kis-Kuel Iron Oxide Copper-Gold deposit in Eastern Yakutia (Russia). Economic mineralization is localized within the apical zone of a granodiorite-diorite stock and represented by hematite, goethite, quartz, chalcopyrite, molybdenite, arsenopyrite, pyrite, native gold and bismuth (no signs of any ore mineralization were found outside the Kis-Kuel intrusive). The intrusive has a Late Cretaceous crystallization age (K-Ar) of 103 Ma. The Mo-bearing quartz vein yields a mineralization age (Ar-Ar) of 99.9±1.1 Ma and genetically relates to the granodiorite. Kis-Kuel breccia complex (KKBC) consists of a manto-type irregular shaped breccia body with arrays of variably mineralized veins and veinlets inside. The KKBC has a complete gradation from hematite-goethite altered granodiorites and more locally -diorites to intensely brecciated and hematite-goethite breccias. Multiple episodes of brecciating and veining with Fe-oxide-Cu-Au±Ag, porphyry Cu-Au±Bi, Ag-Pb and Mo+REE±Au mineralization occur in Kis-Kuel intrusive. In order to obtain more resources, the research Kis-Kuel target with IOCG mineralization was studied for molybdenum and rare earth minerals. Mainly, ore is quartz-bearing, Mo-Au-mineralized and strongly enriched in the rare earth elements (REE) material. The textures of REE minerals indicate crystallisation of monazite-(Ce) and xenotime as hydrothermal phases together with molybdenite and arsenopyrite. Analysis of quartz-molybdenite ore from the Kis-Kuel diorite-granodiorite intrusive shows previously unknown high concentrations of REE and Y, averaging 4.76 wt percent ∑REE + Y. Ore additionally contains 2.42 wt percent Mo, 8.8 g/t Au and 231 g/t Ag. We propose that one of the basic factors for mineralization styles at Kis-Kuel consists in the granitoids evolution and strongly differs from unevolved and mantle compatible compositions to highly evolved and fractionated intrusive rocks. The calc-alkaline evolution trend of the Kis-Kuel magmatic rocks is influenced by the accumulation of iron in ore. A significant part of the iron did not fractionated into high-iron melts, and separated into hydrothermal solutions with high grade gold concentrations. An extensively revised paragenetic model for Kis-Kuel deposit incorporates next four stages. Stage 1 dominated by widespread brecciating and iron metasomatism, which converted granodiorite rocks to Fe-oxide-Cu-Au ore. Stage 2 comprises chloritic and sericitic alteration and associated systems of linear quartz veins with Cu-Au-porphyry and Au-Bi mineralization. Stage 3 includes sericitic alteration and veining with quartz-molybdenite-native gold-REE minerals. Stage 4 consists of Ag-Pb veins.

KARAKTERISTIK ALTERASI DAN TEKSTUR URAT KUARSA PADA PIT BARANI, CEBAKAN EMAS MARTABE, KABUPATEN TAPANULI SELATAN, PROVINSI SUMATRA UTARA

Pit Barani merupakan bagian dari wilayah kontrak karya PT Agincourt Resources yang terletak di Kelurahan Aek Pining, Kecamatan Batangtoru, Kabupaten Tapanuli Selatan, Sumatra Utara. Pit Barani berupa tambang terbuka, dengan tipe cebakan epitermal berupa urat-urat yang menjadi tempat konsentrasi lebih banyak unsur logam. Penelitian bertujuan untuk mengetahui karakteristik alterasi dan variasi tekstur urat kuarsa yang banyak terdapat pada daerah Pit Barani dan mengidentifikasi tekstur urat kuarsa pembawa mineralisasi yang ekonomis. Pengambilan conto batuan dilakukan pada saat pemetaan pit dan identifikasi mineral alterasi menggunakan analisis laboratorium berupa analytical spectral devices (ASD), serta analisis geokimia untuk mengetahui kadar unsur Au, Ag, dan Cu. Hasil penelitian menunjukkan zona alterasi yang berkembang terdiri dari zona alterasi argilik (kaolinit+illit+smektit), argilik lanjut (kuarsa+kaolinit+dikit), dan silisifikasi (kuarsa+kalsedon+kaolinit). Tekstur urat kuarsa yang berkembang pada daerah penelitian terdiri dari masif, crustiform, crustiform-colloform, brecciated, bladed, dan saccharoidal. Tekstur urat kuarsa pembawa mineralisasi dengan kadar emas tinggi berupa crustiform-colloform, banded diikuti oleh massive quartz oxide, dan lattice bladed. Urat kuarsa tersebut berasosiasi dengan mineral lempung kaolinit+dikit dengan tingkat oksidasi sedang sampai tinggi, serta berasosiasi dengan sulfida abu-abu yang mengandung kadar tertinggi mencapai Au 76,65 ppm dan Ag 34 ppm.

Economic Potential of Gold in Batouri (Eastern Cameroon)

The aim of this work is the valorization of the economic potential of gold in the Batouri region. The study is undertaken on five sites of which two alluvials (Djengo and Mongonam localities) made up of flat and river gold, two eluvials (Kambele and Bote) containing gold of veins in quarries, and one semi mechanized exploitation (METALICON) working on the two previous&amp;nbsp; types. Laboratory works consist of traditional melting, determination of the various grades of gold through densimetry and spectrometry analysis and refining using the Miller Chloration method. The main results from these analyses are: i) recovery concentration is low, (about 0.5 g/t) for the traditional mining and higher with the semi mechanization (1.5-2 g/t). Densimetry and spectrometry analyses show that gold of semi mechanized sites has an average grade of about 24 carats, 22 carats and 20 for alluvial and eluvial gold respectively. ii) For 26 kg of gold refined, a weight of 16.681 kg is obtained at a cost of 4 051 946 (four million fifty one thousand and nine hundred forty six) CFA F. Spectrometry analyses reveal the presence of silver and copper impurities, elements that can still be valorized through the presence of a gold refining unit. Hence, the absence of a gold refining unit in our country leads to poor transformation of its ores and loss of devices.

3D mineral potential modelling of gold distribution at the Tampia gold deposit

A 3D mineral potential model was developed for the Tampia Gold Project in Western Australia to help constrain resource estimation, understand the distribution of gold grades from the resource estimation techniques with respect to geological and physiochemical continuity, and predict the location of new gold mineralisation for future exploration drilling to expand the gold resource at Tampia.The 3D mineral potential model was generated using predictive maps based on a local granulite-facies orogenic gold mineral system model. These were generated from regional scale data and data collected during a 40 m by 40 m resource drilling programme, and included lithology, structure, rock property data and geochemical data. The predictive capacity of each map was tested for the spatial correlation with training data from high grade gold drill intersections, using the weights of evidence technique. There were 44 predictive maps created that can be used as proxies to map the physical and chemical processes active in the orogenic mineral system at Tampia. Of these, 11 were chosen for the final model that had the highest spatial correlation with the training data and did not duplicate map patterns.A closely spaced infill drilling programme was subsequently undertaken over an area where the post probability results indicated high and continuous probability for gold mineralisation, while the resource model estimated less continuous and lower grade gold mineralisation. This infill drilling aimed to compare the gold continuity at a 10 m by 10 m drill spacing with the resource estimate gold grades and post probability distribution developed from 40 m by 40 m spaced resource drilling. The results from the 10 m by 10 m spaced drilling were thereby used to test the performance of both the resource and prospectivity models, and assess the utility of mineral potential modelling for use in developing geological domains to constrain resource estimation.Results from the first phase of infill drilling, which only covers 4% of the total model area, confirm the continuity of the post probability values and suggests that the mineral potential model predicts the location and distribution of gold mineralisation within the area drilled. The results were also better and more continuous than predicted by the resource estimate. Importantly, these results confirm that geological and physiochemical controls on gold mineralisation can be numerically measured and mapped at the scale of an orebody. This allows mineral potential modelling to be considered as an option to constrain and help inform the results of geostatistical techniques used in resource estimation.

Alluvial-Placer Gold of Northwestern Salair: Composition, Types, and Mineral Microinclusions

Abstract —On the territory of the Egor’evsk district, 3500 results of probe microanalyses of surface gold particles taken from 17 placers, weathering crusts, and orebodies were processed and summarized. High-fineness and mercury-containing gold is predominantly found within mother lodes and placers, and medium- and low-fineness gold is distributed in subordinate and dramatically subordinate quantities, especially in the placers. A unique feature of the gold composition, rarely occurring in other districts, is the constant and commonly simultaneous presence of mercury and copper impurities. Analysis of Ag, Hg, and Cu content variations has enabled us to identify five main grades of gold. The mother lodes of the predominant gold grades are metasomatites with beresite and listwaenite compositions, which are developed primarily after lower Cambrian volcanoterrigenous-carbonate rocks and ore-bearing mafic dikes. Mercury-containing gold is characteristic of beresites, but copper-bearing gold is typical of listwaenites. The relationship between corresponding grades of surface and ore gold is confirmed by the presence of microinclusions in the gold grains. Nonconformity between the content of gold from mother loads, weathering crusts, and placers is explained by the losses of Hg and Ag impurities by endogenous gold under subsurface hypergene conditions. Identification of mineral-geochemical properties of surface gold is of exceptional practical importance in ore-grade gold mineralization prediction.

The Discovery of the Edna Beryl Gold Deposit – a journey with the destination of multiple mineral discoveries

The discovery of the greater Edna Beryl mineralisation marks a successful journey of systematic, science based exploration over a nine-year period. It is as much about the tenacity of the Emmerson exploration team and the quest for unlocking the geological code as the capability of the Board to secure funding to support this aggressive exploration during the usual peaks and troughs of the capital markets. Like most successful endeavours, the journey has always been with a clear business focus around effective and efficient exploration, taking into account the probabilities of discovery whilst using the failures as the fertiliser for improvement. The Tennant Creek Mineral Field is famous in terms of hosting some of the highest-grade gold and copper deposits in Australia, the majority successfully discovered by either surface prospecting or, some innovative modelling of the various magnetic geophysics - the obvious “tool of choice” considering the host to the gold and copper is predominantly hydrothermal magnetite (locally termed ironstone). In 2008 when Emmerson commenced exploration in Tennant Creek, it was recognised that most if not all of the obvious magnetic anomalies had been tested, thus leading Emmerson on a very different journey that was predicated on refining the exploration models with a more holistic view of the entire mineral system across all geological scales. Emanating from this was the hypothesis that oxidised fluid sources played a far more important role in the genesis of these deposit types and that these fluids were in fact instrumental in the deposition of ultra-high grades of gold and copper. Thus much of the research and data collection is specifically aimed at trying to better understand the role of these fluids, their possible connection to the Tennant Event and their pathways via refining the 3D structural framework. Ultimately this approach has been successful in discovery of the Goanna and Monitor copper-gold systems, the Mauretania gold and the more recent, ultra-high-grade Edna Beryl gold mineralisation. All displaying the common theme of an association with highly oxidised, hematite rich fluids and typically associated with little or at best very weak magnetic signatures. This has opened up the entire Tennant Creek Mineral Field to a new generation of predominantly hematite hosted deposits which by virtue of their different geophysical signature, remain largely untested by previous explorers.

Ore genesis of the Bake gold deposit, southeastern Guizhou province, China: Constraints from mineralogy, in-situ trace element and sulfur isotope analysis of pyrite

The Bake gold deposit is exceptional for its high native gold abundance relative to the other orogenic gold deposits in the southeastern Guizhou district. The grades of gold can be up to 2 to 3 wt% in bonanza ore, and native gold preferentially occurs within voids and fractures in pyrite, arsenopyrite and quartz. Gold content can be up to 6.9 ppm in hydrothermal pyrite, however, the majority of the pyrite analyses have Au contents less than 1 ppm (mean = 0.32 ppm) based on LA-ICPMS analyses. Meanwhile, EMPA reveals that arsenopyrite has a maximal Au content of up to 0.14 wt%, but most analyses are below detection limit (0.01 wt%). Moreover, native gold grains in cataclastic pyrite and arsenopyrite are commonly high-purity with fineness ranging from 949 to 977. Given that paragenetically early hydrothermal pyrite and arsenopyrite contain variable but relatively high gold concentrations than later generations of sulfide, it is suggested that early invisible gold may have been remobilized to form at least part of the microscopic visible gold. Post-mineralization shear zones, which cut the vein-bearing anticline, may have led to the deformation of the lode quartz vein system on the macro level, and microscopically, sulfide fragmentation and elemental remobilization. Although diagenetic pyrite from unaltered host rocks is enriched in invisible gold with mean values at 0.83 ppm, evidence supporting the release of Au from them is weak. Corresponding evidence comes from the distinct sulfur isotope signatures in different pyrite generations. Diagenetic pyrite has δ34S values in the narrow range of +9.27‰ to +10.75‰, whereas hydrothermal pyrite shows a broad range (+6.81‰ to +17.42‰), based on LA-MC-ICPMS analyses. The Mesoproterozoic Lengjiaxi Group underlying the Xiajiang Group is most likely the source region, on the basis of geological background and assuming the metamorphic devolatilization model.

Sulfide Minerals Bio-Oxidation of a Low-Grade Refractory Gold Ore

This paper describes the oxidative dissolution kinetics of sulfides with gold occlusion within pyrite and arsenopyrite. Shake flasks tests and column leaching of a low grade gold ore from China were carried out with domesticated mixed acidophiles isolated from acid mine drainage. Both test show that the main factors accelerating sulfide oxidation was mainly temperature and redox potential. Column bio-oxidation of mineral with a particle size less than 10 mm at 60°C resulted in higher mineral decomposition, finer fractions and eventually higher sulfide oxidation than that at 30°C. Sulfide-S dissolution increased from 58% to 77% from 30°C to 60°C after 247 ds of bio-oxidation. Further investigation into microbial community attached to the ore surface and in the leachate during the bio-oxidation was done by Real-time PCR assays. Organism of genera Acidithiobacillus was the most dominant species in both leachate and ore surface at lower temperature. For the Archaea, the iron oxidizing microbial Ferroplasma showed its predominance of 60°C. Mineral dissolution kinetics and microbial community in bio-oxidation was lucubrated in this work and suggestions were provided for pre-treatment of refractory gold ore.

Geology and geochemical constrains on the origin and depositional setting of the Kpwa–Atog Boga banded iron formations (BIFs), northwestern Congo craton, southern Cameroon

The Kpwa–Atog Boga (KAB) area lies within the Paleoproterozoic Nyong unit which defines the northwestern edge of the Archean Congo craton in southern Cameroon. Rock types in the area are mainly comprises of garnet gneiss associated with banded iron formations (BIFs). The BIFs and its host rocks were subjected to amphibolite facies metamorphism. The Rare Earth Elements (REE) patterns and the discrimination ratios (e.g., Al2O3/TiO2 Cr/Th Th/Sc La/Sc) of the garnet gneiss suggest that they are metasedimentary rocks derived from a felsic parent sources that have undergone intensive weathering. The KAB BIFs exhibit significant concentration of TFe2O3 + SiO2 (>93 wt%), and lower Al2O3 and TiO2 contents and high field strength elements (e.g., Hf, Nb, Ta, and Zr). This involves little contamination with continental detritus at their depositional environment. The Post Archean Australian Shale (PAAS)-normalized REE patterns of the KAB BIFs show enrichment in heavy REE and the depletion in light REE with positive La anomalies, which imply that these BIFs precipitated in ambient seawater. Moreover, the contribution of low-temperature hydrothermal fluids during the deposition of the studied BIFs were highlighted through their high superchondritic Y/Ho ratio (mean: 31.48), weak positive Eu/Eu∗(SN) ratio (mean: 1.83) and the low contents of transition metals. This suggests that the geochemical characteristics of the KAB BIFs and those of the Paleoproterozoic superior-type BIFs are almost similar. In summary, low-temperature hydrothermal fluids mixed with seawater contributed to the deposition of the KAB BIFs on the continental margin. This depositional setting similar to its host rocks is consistent with the Paleoproterozoic geological history recorded within the Nyong unit. This preliminary study reveals that the KAB BIFs are associated with low grade gold (<5 ppb), which could constitute further prospective mineralization besides the iron ore in the KAB area.

Determining an optimal interstitial filling condition: An Attainable Region approach

In this article, we present yet another application of the Attainable Region (AR) method to data from a laboratory scale milling of a low grade gold ore. In this particular case, we investigate how to optimize the amount of material in a desired size class for a scenario where the boundaries of the desired size class of interest are changed. The AR approach has never been applied in such a scenario before. Using a mono sized feed of −1700+850μm, two desired product size classes of interest (−850+150μm and −150+75μm) are selected in order to determine the optimum interstitial filling (U) to be used in the mill. Two different values of U, 1.75 and 1.0 respectively, are obtained as optimal. Our results also show that optimal operating conditions are different for different objective functions. We demonstrate that the AR may be used to specify optimal conditions that may be used for particle size reduction processes. We also illustrate how an AR boundary for optimization purposes can in certain cases be extended using the ‘mixing principle’.