Determining the particle size of native gold based on fire assay results and its influence on the allowable discrepancy in the material balance

Recent research indicates that an enhanced coarse gold problem may be present in some gold deposits. This can be due to the presence of gold particle clusters that give the effect of individual coarse-gold particles and leads to a high constitution heterogeneity (CH). These clusters, which may be distributed on the centimetre-scale or greater, give rise to high assay variability in field samples. However, once a sub-sample is pulverised, the effect of the clusters may be removed if the individual gold particles making up the clusters are liberated. Thus any resulting pulp will tend to have a low variability, unless true coarse-gold particles exist. Clusters are readily recognised in coarse gold deposits where they accentuate existing high nugget effect and CH. Clusters may however also occur in fine gold deposits where they produce an apparent coarse gold style. This is signaled by an unexpectedly high nugget effect from variography and poor correlation between field sample duplicates. The Gy sampling equation is applied to model coarse and fine gold deposits with clustered and non-clustered gold grains. Case studies illustrating observed effects of clustering are presented. If clustered particles exist, then proper protocol design at the field and early laboratory stage is paramount. The sample characterisation stage should include an assessment of possible gold particle clustering, in addition to the standard descriptions of the gold particle size distribution.

The application of a mineral exposure model in a gold leaching operation

GOLD has been so large a factor in the prosperity and greatness of Australia, that the interesting subject of the origin of gold drifts and reefs must always possess to us something more than a purely scientific attraction. In the earlier days of the goldfields there was among the diggers much speculation, of a scientific and semi-scientific nature, as to the processes by which Nature had produced the accumulations of coarse and fine gold dust which it was their business to extract from the alluvial drifts. The most obvious explanation, of course, was that the grains of gold had an origin similar to that of the debris and detritus of various characters which made up the alluvium itself; and this explanation seemed to harmonize so completely with the general processes of Nature that at one time it was almost universally accepted as the correct one. But many thoughtful mining authorities had their doubts upon the subject, and these doubts were not founded, as so frequently happens, upon mere prejudice, but were fortified by the fact that certain phenomena characteristic of the occurrence of drift gold were not only not explained by the “detrital hypothesis,” as it is called, but were absolutely inconsistent with it. Chief among these objections may be mentioned the undoubted generalization that drift gold is nearly always purer than the gold in the reefs of the neighbourhood in which it occurs. No explanation as to the long distances to which grains of gold might be conveyed, or to the possible purifying effects of natural chemical action, made up any satisfactory explanation of the known facts, and accordingly under the detrital theory these facts had to remain shrouded in mystery. Then, again, it was a frequent occurrence for gold to be found so peculiarly embedded in pieces of wood, or in conjunction with natural crystals of minerals, such as the sulphides, that those who were constantly being brought into contact with such phenomena were firmly convinced that at all events there was a certain proportion of the gold found in alluvial drifts which had its origin in some other source than the breaking down of quartz reefs by the ordinary processes of Nature. The majority of those who held to this belief had at first but little scientific knowledge of natural reactions; and when questioned as to their theory on the subject, they were accustomed to say of the alluvial drift-gold, that it appeared to be actually growing—a statement which sometimes provoked, not unnaturally, a smile of pity for misplaced credulity.

The erratic and localized occurrence of gold is a feature of many gold-bearing veins. The term ‘ nuggety’ is often used to describe such deposits, where it refers to the erratic high gold values that may accompany low grades (low relative to the mean). The effect is a consequence of localized geologically controlled enrichment and the inclusion or exclusion of sparse gold grains because of the nature of the sampling process. 8 Nuggety deposits do not always contain visible or coarse gold (e.g. >100 µ m) and may be characterized by erratically distributed fine-grained gold. High-grade regions are generally extremely erratic with a low spatial continuity, but may make mineralization economic. Economic grades are generally contained within discrete oreshoots, which are surrounded by barren to low-grade material. A measure of ‘ gold grade potential’ based on trace-element ratios has been developed that allows the user to discriminate between barren, low-, medium- and high-grade mineralization. A preliminary report on the development of this discrimination index, the Gold Proxy Index (GPI), is presented here and the discussion of gold sampling in previous

PURPOSE. The paper studies the material composition of the ore from the Jamgyr deposit located in the Chatkal region of the Jalal-Abad district of the Kyrgyz Republic and determines the expediency of its gravity concentration. The ore belongs to the quartz low sulfide type. Its main valuable component is gold, the content of which averages 8.5 g/t. METHODS. Complex mineralogical analysis was performed using X-ray phase, optical and microscopic analyzes. Sulphide minerals and gold were studied using the method of selective dissolution of natural minerals. X-ray phase analysis was carried out on a portable X-ray diffractometer D2 PHASER (CuKa) of Bruker AXS design in the range of 20 angles from 5 to 80°. The obtained diffractograms were processed in the DIFFRAC.EVA program. A qualitative X-ray phase analysis was performed via comparison of standards (ICDD PDF-2) and diffractograms. A semiquantitative analysis of the sample was carried out using the DIFFRAC.TOPAS program according to Rietveld method. The content of gold was determined on the atomic absorption multielement spectrometer AGEP-0,1 by the assay atomic absorption analysis. RESULTS AND THEIR DISCUSSION. Having studied the morphology of particles of free gold, we have found that the shape of coarse gold is mainly dendritic, small-size gold has the shape of a drop in pyrite. The data on the granulometric distribution of gold show that the percentage of coarse gold is about 70%. The phase analysis data show that the percentage of free gold is 64.37%. The ore study has allowed to substantiate the use of gravity concentration through the GRG test at a hydraulic pressure of 25-12 kPa, ore feed rates from 1000 g/min to 400 g/min, stage-by-stage reduction in size from 100% of 85 μm to 80% of 75 μm. The technique of performing the stage-by-stage gravity concentration conducted in three stages on Knelson concentrator is given and the GRG test determination diagram is presented. The results of each stage and the total result of the GRG test are provided. According to the GRG test result 19.86% of free gold is extracted at the first stage, 35.83% - at the second stage, and 17.65% - at the third stage. The total recovery is 73.34%. CONCLUSIONS. The morphology and release of gold on the concentrates obtained by gravitation on a centrifugal separator are studied. The degree of gold release is determined as well as the gold grain size in I, II, III stage concentrates and relative amounts of free gold grains. The final determination is given to the main shape of gold grains: it is either dendritic or flake. It is also noted that stage-by-stage decrease in the grind size causes changes in the gold grain shape: the particles of isometric forms are expanded into flat grains.

Influence of particle size on the electrocatalytic oxidation of glycerol over carbon-supported gold nanoparticles

Characteristics and origin of coarse gold in Late Pleistocene sediments of the Cariboo placer mining district, British Columbia, Canada

Naturally occurring heavy radioactive elements in the geothermal microcosm of the Los Azufres (Mexico) volcanic complex

Beach placer gold has been mined around the world historically, but extraction of fine (~ 100 µm) gold particles is notoriously difficult. This study illustrates morphological and mineralogical changes that transform fine gold during aeolian processes on windy beaches and contribute to mine concentration inefficiencies. Sandblasting on exposed beaches in southern New Zealand has caused extreme attenuation of edges of gold flakes that were previously transported in rivers for > 200 km. Flakes have been transformed into complex but compact toroids and spheroids with thin (~ 20 µm) internal and external strands of attenuated gold. Most of the gold within the attenuated strands has recrystallised to fine (micron-scale) undeformed grains with little or no Ag (< 1 wt%). Some coarse (> 40 µm) gold grains remain from the precursor fluvial particles, and these retain original Ag contents (1–10 wt%). These coarse grains show substantial internal crystallographic deformation and sub-grain formation, although some of these strain effects may have been inherited from fluvial transport. Co-existing detrital platinum minerals are much less malleable than gold during sandblasting and have only minor (10-µm scale) toroidal deformation on edges of fluvial flakes. The complex frameworks of the fine toroidal and spheroidal gold particles can include air, water, and clay, which lowers their average density and so they commonly float on water and are readily entrained with other heavy minerals. The fine particle size, compact shapes, and clay coatings also resist mercury amalgamation.

The Transbaikal Region holds a large stockpile of gold reserves in placers. Gold placers differ in structural tectonics, morphology and parameters of productive strata, their specific mineralogical and geochemical composition, grain-size composition and shape of gold grains, roundness and fineness of gold particles, etc. The drop in the gold content and thickness of productive sand at placers being currently mined necessitates studying refractory gold, including encapsulated, dispersed and chemically bound gold. This article discusses new patent-protected methods for identifying nanoscale gold. New geotechnologies for gold extraction from placer sands using solutions with active chloride complexes pumped into productive formations via wells are presented. Alongside with pumping out pregnant solutions, it is proposed to use the electro-diffusion deposition of dissolved gold from a conventionally immobilized pore solution onto ion-exchange resins placed together with submersible cathodes in wells. The authors express their gratitude to Professors A. I. Trubachev, V. S. Salikhov, Yu. I. Rubtsov and Cand.Eng.Sci. Yu. S. Shevchenko from the Chita Division of the Institute of Mining, SB RAS, and to Cand.Eng. Sci. N. V. Zykov, Director of the Transbaikalia Mining College, for their help in the pilot trials of the electro-diffusion leaching technology. The studies were carried out using the scientific lab equipment and instruments of the Center for Processing and Storage of Scientific Data of the Far Eastern Branch of the Russian Academy of Sciences, supported by the Ministry of Science and Higher Education of Russia under Agreement No. 075-15-2021-663. The production research and chemical analyses were implemented at the Center of Mineralogical Research of the Khabarovsk Research Center, Far Eastern Branch of RAS.

Influence of support surface basicity and gold particle size on catalytic activity of Au/γ-AlOOH and Au/γ-Al2O3 catalyst in aerobic oxidation of α,ω-diols to lactones

Following a successful investigation on the Central Zone sample, a cyanidation study was conducted on an ore sample from the AD-MW Zone of Clarence Stream Property, owned by Freewest Resources Canada, to develop a leaching strategy to extract gold. At a grade of 6.48 g/t, gold is present in the forms of aurostibite, free gold and electrum. The ore contains 4.3% berthierite/gudmundite, 1.3% pyrrhotite, 0.7% pyrite, 0.07% stibnite and 0.9% arsenopyrite. Similar to the Central Zone, the extraction of gold from the AD-MW Zone can be performed at atmospheric pressure, pH 10.5 and with a low concentration of cyanide. The grind size had no effect on gold extraction between a P80 of 28 to 71 μm. The oxygen and cyanide requirement significantly increased with a finer grind. Consequently, a very close control of cyanide addition is required to minimize passivation of gold. Lead nitrate, added in the pretreatment, increased the extraction of gold by 2.3%. Leaching at pH < 10 improved gold extraction but increased the cyanide consumption by 5%. Passivation of gold occurred when the pretreatment was longer than 2 hours. A longer pretreatment reduced the cyanide consumption by 5%. Mineralogical characterization of the leach residue with no gravity pretreatment prior to leaching indicated the presence of unleached gold grains and passivated gold grains. Removal of coarse gold by gravity increased the extraction by 2.8% (leach residue at 0.74 g/t Au). Increasing the DO to 16 ppm or the lead nitrate from 500 to 1,000 g/t increased the overall gold extraction to 90.4% (leach residue at 0.62 g/t), which is the maximum gold extraction obtained. The leaching parameters were 800 ppm NaCN, DO 16 ppm and pH 10.5 for a duration of 120 hours. The associated cyanide consumption was 4.0 kg/t. Gold leaching was not sensitive to cyanide concentration. Reducing the cyanide concentration to 250 ppm resulted in a gold extraction of 89.5% with a cyanide consumption of 2.6 kg/t.

Visible gold in arsenian pyrite at the Shuiyindong Carlin-type gold deposit, Guizhou, China: Implications for the environment and processes of ore formation

Technogenic placers are characterized by a chaotic distribution of gold and other valuable components, which restricts their industrial mining for gold. The development of an effective mining method for technogenic placers is therefore of great national economic importance. The study is aimed at creating a new type of technogenic placer deposits with high gold grade zones, to be formed through the preferred vertical migration of high-density particles under the influence of natural and industrial factors. The resulting enriched zone shall have higher gold grades as compared to the original technogenic mass, with a thickness equal to 45&ndash;60 % of the thickness of the technogenic placer. This will reduce the volume of sand to be washed and significantly cut the related operating costs. This technology will allow mining technogenic placer deposits that have been previously considered unprofitable. The study is aimed at finding the optimal parameters of rock mass cyclic flooding and drainage that would ensure the most intensive migration of gold particles, as well as at assessing the effect of rock mass grain-size distribution on the intensity of gold migration. The data obtained facilitate a significant expansion in the theoretical knowledge on gold particle migration and identification of migration intensity patterns for various gold particle sizes, depending on the seepage flow parameters and mining and geological characteristics of the rock mass in respective technogenic placers.The work was carried out with the financial support of Government&nbsp;of the Khabarovsk Territory under the program &laquo;On the provisionof grants in the form of subsidie s from the regional budget for the&nbsp;implementation of projects in the field of scientific research in the&nbsp;direction of natural, technical, humanitarian and social sciences&raquo;.The research was carried out using the resources of the Center for&nbsp;Collective Use of Scientific Equipment &laquo;Center for Processing and&nbsp;Storing Scientific Data of the Far Eastern Branch of the Russian Academy&nbsp;of Sciences&raquo;, funded by the Ministry of Science and Higher Education&nbsp;of the Russian Federation under project No. 075-15-2021-663.Experimental studies, sample preparation, determination of gold&nbsp;content were carried out on the basis of the Center for Collective Use&nbsp;&laquo;Center for Research of Mineral Raw Materials&raquo; of the Khabarovsk&nbsp;Federal Research Center of the Far Eastern Branch of RAS.

Laminar mixed convection of humid air in a vertical channel with evaporation or condensation at the wall