Gold In Soils Research Articles

A Deep-Penetrating Geochemical Prospecting Experiment of Mahuagou Gold Deposit in the Core of the Huangling Anticline, Western Hubei, China

The Mahuagou gold deposit is among the most important gold deposits in the core of the Huangling Anticline. However, the geochemical exploration on the surface of the mining area presents challenges due to the thin overburden. This paper focuses on the overburden soil of the Fengxiangshugou (FXS)-Mahuanggou (MHG) section as the research object. It utilizes chemical form analysis of gold, soil halogen survey, and heat-released mercury survey to determine the key deep-penetrating geochemical methods for the mining area. The results indicated that Si and Al components of samples exhibit minimal variation, suggesting that drift loads did not influence the overburden soil. Based on the systematic clustering, As, Sb, Mo, Bi, W, and Hg emerge as ore-body or ore-belt front elements of hydrothermal gold deposits. In the study area, the predominant chemical form of gold in soil is the strong organic bond. Compared to the total amount, strong organic bound gold and heat-released mercury show higher anomaly contrasts, making them crucial indicators of faults, intrusions, and hidden ore bodies. Consequently, chemical form analysis of gold and heat-released mercury surveys can enhance the anomaly contrast, proving beneficial for geochemical prospecting for weak anomalies in this area.

Features of Copper and Gold Nanoparticle Translocation in Petroselinum crispum Segments.

The application of metal nanoparticles in industry and medicine results in their release into the environment, which can have a negative impact on human health. The effects of gold (AuNPs) and copper (CuNPs) nanoparticles at the concentration range of 1-200 mg/L on parsley (Petroselinum crispum) under conditions of root exposure and their translocation in roots and leaves were investigated in a 10-day experiment. The content of copper and gold in soil and plant segments was determined using ICP-OES and ICP-MS techniques, while the morphology of nanoparticles was analyzed using transmission electron microscopy. Differences in the nanoparticle uptake and translocation were observed: CuNPs mainly accumulated in soil (4.4-465 mg/kg), while accumulation in the leaves were at the control level. AuNPs mainly accumulated in soil (0.04-108 mg/kg), followed by roots (0.05-45 mg/kg) and leaves (0.16-53 mg/kg). The influence of AuNPs and CuNPs on the biochemical parameters of parsley was on the content of carotenoids, the levels of chlorophyll, and antioxidant activity. Application of CuNPs even at the lowest concentration led to a significant reduction in carotenoids and total chlorophyll content. AuNPs at low concentrations promoted an increase in the content of carotenoids; however, they also significantly reduced it at concentrations higher than 10 mg/L. To our knowledge, this is the first study of the effect of metal nanoparticles on parsley.

Microfunnel magnetic stirring-assisted liquid–liquid microextraction method for determination of trace amounts of gold after optimization employing response surface methodology

ABSTRACTA rapid, sensitive and simple technique was proposed for the preconcentration and determination of gold in the presence of N-methyl-N,N,N-trioctylammonium chloride (Aliquat 336) as ion pair forming agent employing microfunnel magnetic stirring-assisted liquid–liquid microextraction (MF-MSA-LLME) and flame atomic absorption spectrometry. Parameters were optimized by full factorial and Box-Behnken design. Under the optimum conditions, the calibration graph was linear in the range of 2.5–800.0 ng mL⁻1 (r2 = 0.998). Detection limit, enrichment factor and relative standard deviation were 0.6 ng mL⁻1, 240.0 and 1.4% (n = 7, C = 100 ng mL−1), respectively. This technique was successfully applied for the determination of gold in soil and water samples.

Gold in Plant: A Biogeochemical Approach in Detecting Gold Anomalies Undercover- A Case Study at Pelangio Gold Project at Mamfo Area of Brong Ahafo, Ghana

Many plants have the ability to take up gold from soils and accumulate them in their tissues. Their concentrations and distributions reflect the nearby gold deposits masked by complex regolith. The 50 vegetation samples collected at Pelangio Tepa concession recorded low and subtle gold (Au) concentrations of 0.2 to 10.4 ppb at Pokukrom target, 0.3 to 28.3 ppb at Nfante East target and 0.1 to 1.7 ppb at Subriso target. Each target area had different concentration populations enough to distinguish the anomalous areas from the background contrary to Au-geochemical expressions derived from the gold in soils. So many uncertainties were placed on the soil-Au-geochemistry because the defined anomalies were not strong and generally appear patchy, weak and subtle that led to the assumption of no associated bedrock mineralisation. The gold in plant samples confirmed the Pokukrom anomaly that has been drilled and known to relate to underlying mineralisation. Much better and robust anomaly was defined by the biogeochemical Au data in plants sampled and analysed for Au at Nfante East target and isolated high patchy anomalies were identified at Subriso area. The case study at Pelangio Mamfo project reveals and recommends the significant application of biogeochemistry in mineral exploration particularly in the field of gold prospecting at the regional exploration stage and endorses it as being practically feasible in regolith-dominated terrains where regolith-landform modifications may impact on the true geochemistry in anomaly delineation. Keywords: Biogeochemistry, Regolith-Dominated-Terrain, Plant, Gold, Pelangio

Gold and pathfinders metalloorganic forms in podzol soil at the area of Novye Peski gold deposit (South Karelia)

Gold and natural organic matter interaction, including the interaction with humic and fulvic acids, is the most important part in migration and precipitation of that chemical element in supergene zone. Research into elementorganic forms of gold and related elements, which are often associated with gold deposits (As, Cu, Ag, Ni, Zn, Pb, Te, Bi, Se, Mo, Sb), allowed us to learn the groups of elements bounding preferably to one or the other humus acids and the most enriched with that element’s soil horizons. Complexation of gold and nickel are with both humic and fulvic acids; zinc, silver and antimony bound preferably to humic acids, arsenic and copper — with fluvic acids. More detailed research of different mobile forms of gold in soil profiles allowed us to identify the features of gold forms related with the type of soil horizon and location of soil profile in relation to the ore zone.

Development of the Diffusive Gradients in Thin Films Technique for the Measurement of Labile Gold in Natural Waters

Gold is a precious metal that exists in most soils, sediments, and natural waters at extremely low concentrations (<1 μg/kg). The diffusive gradients in thin films (DGT) technique, used extensively for measuring trace metal concentrations in soils, sediments, and waters, has potential for geochemical exploration for gold, but has not been developed for this metal. This work investigates the possibility of measuring labile gold using DGT by introducing a new binding layer based on activated carbon. The performance of this new technique was assessed using gold(III) chloride in solution by: (1) determining the diffusion coefficient of gold(III) in hydrogels; (2) determining the uptake of gold(III) chloride by the new activated carbon binding layer; (3) determining an elution methodology for the binding layer and evaluating its efficiency; (4) assessing the capacity of the activated carbon binding layer to adsorb gold; (5) determining the effect of pH and ionic strength (as NaCl) on performance, and (6) assessing the selectivity of the new binding layer for gold. It was found that the diffusion coefficient of gold(III) increased as solution pH decreased. The diffusion coefficient also increased at high ionic strength (≥0.1 M NaCl). Accounting for these phenomena, the DGT technique behaved predictably under all tested conditions. The technique can potentially be used as a geochemical exploration tool for gold in soils and in aqueous environments, with method detection limits as low as 0.9 ng/L for a 7-day deployment.

Effect of resident microbiota on the solubilization of gold in soil from the Tomakin Park Gold Mine, New South Wales, Australia

The processes influencing the solubilization and observed mobility of Au in soil were studied using a combination of geochemical and microbiological techniques. In this study, we demonstrate for the first time that biotic processes mediated by the resident microbiota are likely to control the mobilization of Au in auriferous soils and other regolith materials. Microcosms with auriferous soils from the Tomakin Park Gold Mine in temperate south eastern New South Wales, Australia, were incubated under biologically active versus inactive (sterilized) conditions. The soils were incubated oxic and anoxic, unamended and Au pellet- or cycloheximide amended for 70 days in a 1:4 (w:v) aqueous slurry at 25 °C in the dark. In biologically active unamended Ah- and B-horizon microcosms up to 80 wt.% of total Au was detected in solution after 45 days of incubation. In biologically active Au pellet amended microcosms Au was liberated from the soil and also from added Au pellets. Scanning electron microscopy and nucleic acid staining combined with confocal stereo laser microscopy revealed the presence of bacterial biofilms on Au pellets incubated in the biologically active microcosms. The biologically inactive microcosms displayed no or significantly reduced Au solubilization. After 40–50 days of incubation Au was generally re-adsorbed to the solid soil fractions. The results of sequential extractions conducted with dried slurry samples collected from the biologically active Ah-horizon microcosms after 0, 10, 20, 30, 40, and 68 days of incubation indicated a continuous microscale solubilization and re-adsorption of Au. In samples taken after 40 days of incubation more than 80 wt.% of the Au was extracted from the operationally defined organic fraction, which appears to act as a final re-adsorption site for Au in the soil. In samples taken after 10 days of incubation from microcosms amended with 100 μg g −1 (d.w. soil) of Au as AuCl 4 − 95 wt.% of the Au was associated with the organic fraction. To establish a mechanistic link between Au dissolution and re-adsorption with the activity of the heterotrophic bacterial community, analysis of the community structure based on carbon utilization patterns using was conducted. The bacterial community structure changed from a carbohydrate- and polymer-utilizing to a carboxylic- and amino acid utilizing community concurrently with the change from Au solubilization to re-adsorption. The bacterial community in the early stages of incubation (0–30 days) apparently produced an excess of amino acids, which are known to form stable amino acid Au complexes. The bacterial community in the later stages of incubation (after 40–50 days) metabolized these Au complexing ligands and Au, which apparently became unstable in the solution, was re-adsorbed to the solid soil fractions.

Slurry sampling for the determination of silver and gold in soils and sediments using electrothermal atomic absorption spectrometry

Procedures for determining silver and gold in soil and sediment samples using electrothermal atomic absorption spectrometry are discussed. Slurries are prepared from the samples and fast-program methodology is used for the heating cycle. To determine silver, suspensions are prepared by weighing 5–200 mg of sample and adding 25 ml of a solution containing 3% v/v concentrated nitric acid, 50% v/v concentrated hydrogen peroxide and 25% v/v concentrated hydrofluoric acid. For gold determination, slurries are prepared by weighing up to 200 mg of sample and then adding 1 ml of concentrated hydrofluoric acid. For both cases, the slurries are submitted to a 10 min mild heating stage. After cooling to ambient temperature, the suspensions are introduced directly into the atomizer. No modifier other than hydrofluoric acid and hydrogen peroxide (for silver determination) are required and calibration is carried out using aqueous standards. The detection limits are 0.02 and 0.01 mg kg −1 for silver and gold, respectively.

Integration of Sparse Geologic Information in Gold Targeting Using Logistic Regression Analysis in the Hutti–maski Schist Belt, Raichur, Karnataka, India—a Case Study

Logistic regression has been used in the study to integrate indicator patterns for estimation of the probability of occurrence of gold deposits in a part of the auriferous Archaean Hutti–Maski schist belt. Data used consist of categorical and continuous variables obtained from a coded lineament map and geochemical anomaly maps of the pathfinder elements of gold in soil and groundwater. Main effects and interactions of the variables studied were used in formulating the logistic regression model. Regression models using lineament-proximity data, combined with soil and groundwater geochemical anomalies were tested on parts of the schist belt with data not used in estimation of model parameters. Predicted probabilities greater than 0.9 identified known deposit locations in the area.

The mobility of gold in tropical rain forest soils

The complex mineralogical and chemical system of a tropical rain forest weathering profile at the Ashanti mine, Ghana, was characterized to evaluate the role of inorganic and organic processes with the potential to mobilize gold in the rain forest soils. The concentration of gold has been measured in bulk saprolite, soil samples, and in pore-water extractions from the saprolite and soil horizons from the Sansu prospect at Ashanti. Gold concentration in the ground waters varied from below the detection limit (0.01 mu g/l) to a maximum of 84.4 mu g/l at the water table. Average gold concentration in the soil pore waters is 3.6 mu g/l. The gold in the pore waters is present as either soluble gold or as suspended particles less than 0.45 mu m in size.Despite the presence of significant gold concentrations in the soil pore waters, gold concentration in soils over the auriferous shear zones is up to 400 times greater than over the nonauriferous country rocks suggesting a limited gold mobility. Similarly, a close correlation between gold held in the solid soil fraction and in soil pore waters reveals very little in the way of supergene gold enrichment. Conversely, the gold is dissolved and reprecipitated over a range of a few centimeters. The high concentration of gold in the soil pore waters at Ashanti is a reflection both of the high gold content of the hypogene ore and of the efficiency of supergene fluids in the tropical rain forest environment to leach the gold but not retain it in a mobile form. Solubility calculations indicate that gold complexing in the soils appears to be dominated by AuOH(H 2 O), Au(CN) 2 (super -) , Au(S 2 O 3 ) 2 (super -3) , Au(NH 3 ) 2 (super +) , and a gold fulvate complex. Selective extraction of gold from organic and inorganic soil fractions reveals that the element is largely concentrated as native gold. A significant proportion (up to 28%) is concentrated in the light organic fraction of the near-surface soils which is dominated by fulvic acid. The role of gold adsorption by clays and hydrous Fe-Mn oxides appears to be small with less than 1 percent of the gold being present in an easily exchangeable form.Gold appears relatively immobile in the lower saprolite with gold values in solution being below the detection limit (0.01 mu g/l). Higher up in the saprolite, gold appears to be dissolved by hydroxide and thiosulfate complexes in the upper saprolite and by fulvate, cyanide, and hydroxide complexes in the soils. Due to the in situ nature of gold dissolution and reprecipitation, even short-lived species such as thiosulfate and cyanide can play an important role in the supergene chemistry of gold in the Ashanti soils. Halide complexes are not considered important owing to their low concentration in the ground waters (Cl, <9 mg/l) and the unrealistically high Eh-low pH conditions required. Humic acids are also not considered important in the dissolution of gold as they are only sparingly soluble in the pH range of the Ashanti soils (4.2-6.8).

Distribution and behavior of gold in soils and tills at the Nickel Plate Mine, southern British Columbia, Canada

The Nickel Plate deposit, in which gold occurs as <25 μm blebs associated with arsenopyrite in garnet-pyroxene skarns, is in the subalpine zone near the southern limit of the Thompson Plateau. During the last glaciation the Cordilleran ice sheet moved south-southwest across the deposit and deposited a stony basal till. A dispersion train with anomalous concentrations of gold in tills and soils now extends 2 km down ice from the deposit. Gold contents of samples of humus (LFH horizon) and the −212 μm fraction of mineral soils (A, B and C horizons) was determined by instrumental neutron activation and fire assay-atomic absorption, respectively. Selected samples were examined in detail to determine distribution of gold between different size and density fractions. Despite erratic variability, Au contents of the −212 μm fraction generally decrease from 200–400 ppb close to the mine site to <50 ppb at distal sites. At most sites there is also a twofold increase of gold values down the soil profile. Within samples concentrations of Au in the −420 + 212 μm, −212 + 106 μm, −106 + 53 μm and −53 μm fractions are usually roughly constant. However, because of its abundance, the −53 μm fraction contains more than 70% of the gold. Amenability of gold in this fraction to cyanidation suggests that it is largely free gold. For size fractions > 53 μm the contribution of the heavy mineral (SG > 3.3) fraction to total gold content increases with decreasing grain size. Distribution of gold between size and density fractions is consistent with its release from the bedrock or pre-glacial regolith by glacial abrasion. The bulk of the gold was incorporated into the fine fractions of the till at or close to the source. However, differences between down ice dilution ratios for gold in different heavy mineral size fractions suggest that comminution of host minerals continued to transfer gold to the finer size fractions during glacial transport. For exploration purposes, B and C horizon samples provide the best anomaly contrast. Estimates of the abundance of gold particles in different size fractions indicate that the nugget effect, which causes erratic gold values in the −212 μm fraction, can be avoided by analysis of 30 g of −53 μm material.

Geochemical dispersion of gold related to copper-gold mineralization in northeastern Thailand

The nature of gold dispersion in soils and stream sediments associated with a copper-gold-mineralized system in northeastern Thailand has been investigated as a basis for identifying appropriate geochemical exploration techniques for the search for comparable deposits in similar environments. Soils were collected with varying relationships to mineralization as a basis for determining sample representativity, size distribution of gold, variation with soil horizon and possible pathfinder elements. Similarly, stream sediments were collected to estimate sample representativity, size distribution of gold, variation of gold with depth in the stream sediment profile and to compare the relative recoveries of gold in field-panned and laboratory-prepared heavy-mineral concentrates. Samples were analyzed for Au and potential indicator elements by a variety of methods but mostly by instrumental neutron activation analysis. Results indicate the consistent distribution of fine-grained gold in soils which allows Au analysis of relatively small samples from B-horizon soils to be used effectively and reliably to identify the surficial patterns of gold mineralization in the study area. Anomalous patterns of other indicator elements, Co, As, Cu, Sb, W, Pb, Zn, Ag, Fe and Mn, may contribute additional information regarding type of mineralization. This finding indicates the effectiveness of soil surveys in gold exploration, particularly in areas of deep weathering where fresh bedrock exposures are infrequent. Unlike soils, size distributions of gold in stream sediments, as a result of the local flow regime, vary both between sampling sites and at depths within a sampling site. Exploration requires Au analysis of the fine fraction (minus 63 μm) of active stream sediments to reduce the problem of sampling representativity. The presence of coarse-grained gold in the stream channel has drawn attention to the possible benefit of using the conventional field-panning method as a semiquantitative technique for providing immediate results. However, highly erratic distribution of pannable gold on a very local scale together with variable proportions of the total gold recovered in field-panned or heavy-mineral concentrates highlights a potentially serious drawback of the method. Combination of analysis of the minus 63 μm fraction and field panning appears warranted to cover the possible existence of gold of a wide size range in stream sediments. The overall results indicate the utility of geochemical exploration techniques in the search for gold mineralization. However, particular care is necessary in the design and implementation of geochemical techniques to ensure maximum reliability of exploration.

Weathering effects on supergene gold in soils of a semarid environment, Gentio do Ouro, Brazil

Weathering effects on supergene gold in soils of a semarid environment, Gentio do Ouro, Brazil

Orientation studies for gold in the central pediplain of the Saudi Arabian shield

Abstract Orientation studies were carried out by the BRGM mission in Saudi Arabia between 1982–1986 to investigate the dispersion of gold in soils and wadi sediments and to define the optimum sample medium around eight prospects in the central Arabian pediplain. A comparison of gold distribution in several sieved fractions with various pedologic horizons shows that the distribution of gold changes abruptly from the coarser sizes near the source to the finest sizes 150 m downstream. The coarse fraction recommended by previous workers is not representative and yields erratic results in the specific environment of the pediplain. Gold is enriched and more homogeneously distributed in the minus 80 μm fraction of the skeletal soils and wadi sediments. Regional geochemical survey can be effective using a sensitive analytical method for gold and the minus 80 μm fraction of the brown gravelly sediment with a minimum density of 2 samples per km 2 . Geochemical halos in the 30–50 ppb range indicate gold mineralization 500 to 1000 m upstream, depending on relief. In a first follow-up stage, continued use of the same size of the upper argillaceous layer with a regular reg sampling grid gives more contrasted and more extensive anomalies than using a coarse material. These anomalies may be slightly offset by the present arid erosion. A second follow-up stage is then recommended at a closer grid and sampling the brown blocky layer below the surficial reg pavement. Again, the use of the finest fraction at this exploration stage has given the best probability of finding a blind gold target. Optical determination of gold on a nonmagnetic fraction of heavy panconcentrate is not recommended, because nugget growth is practically absent in the present arid conditions and flour-sized gold particles are lost in desliming samples.

Gold uptake by perennial ryegrass: The influence of humates on the cycling of gold in soils

An experiment in which perennial ryegrass (Lolium perenne L.) was grown in solution cultures containing various forms of radioactive gold (198Au) is described. Uptake of labelled Au from solutions containing either Au chloride or various Au-humic acid (HA) complexes is compared. In each case concentrations of Au in the plant roots were several fold higher than in the plant shoots. However, the Au concentration in roots from some of the Au-HA preparations was only about 5% of that from the Au-HA solutions. High voltage electrophoresis studies indicate the presence of several Au-HA complexes in the solution cultures. The relevance of these findings to the cycling of Au within soils is discussed.

Crystalline gold in soil and the problem of supergene nugget formation: Freezing and exclusion as genetic mechanisms

Many of the world's richest gold placer deposits now occur in cold regions despite differences in their climatic history. It therefore seems possible that there may be some fundamental connection between freezing climates and the local chemical behavior of gold in the weathering cycle. This hypothesis, along with the problematical occurrence of gold as euhedral crystals in arctic gravel and soil placers, has led me to review low temperature phenomena that may bear on the geochemistry of gold. Several effects which may influence the weathering of natural gold-bearing rocks, the chemical complexation of gold, and its subsequent mobility and deposition appear to be strongly connected with freeze action. The exclusion of dissolved solutes, solute gases, and particles from ice, subjects rock and soil minerals to increased corrosion from thin, unfrozen, adsorbed water films which remain at particle surfaces throughout the freezing of rocks and soils. The preferential exclusion of cations (over anions) from growing ice crystals creates charge separations and measurable current flow across waterice phase boundaries in freezing soil — a phenomenon which leads to troublesome seasonal electrolytic corrosion of pipelines buried in soil; this phenomenon may also favor the dissolution of normally insoluble metals such as gold during geologic time periods. The ice-induced accumulation of clays, organic acids, bacteria, and other organic matter at mineral surfaces may also speed chemical attack by providing a nearby sink of alternate cation-binding sites and hence rapid removal of liberated cations from solution. The latter mechanism may be operative in both the dissolution and redeposition of gold. These physical, chemical, and electrical effects are favorable to the dissolution of rocks (in addition to frost shattering) and to the dissolution, mobilization, and redeposition of gold and other noble metals and must therefore contribute significantly to the behavior of gold at low temperatures. The occurrence of large numbers of gold placer deposits in northern Canada, Alaska, and Siberia may thus be due in part to the low temperatures common to these regions.

Selective extraction of organically bound gold in soils, lake sediments and stream sediments

The extraction of organically bound gold from surficial materials is accomplished by using a solution of 5% sodium hypochlorite. A 10-g sample is digested at least twice with 50 mL of hypochlorite solution. The recovery of gold from the organic phase is nearly quantitative for lake sediments and stream sediments high in organic content. For stream sediments and soils low in organics, the recovery of gold is complicated by the sorption of released gold onto inorganic sample components. For these materials, recoveries as low as 70% of the organically bound gold are possible. For a stream sediment sample containing 53.4 ppb gold, the precision of the method is approximately 6% for a 10-g sample and 14% when a 5-g sample of stream sediment is used. The results obtained for all materials tested indicate that a substantial fraction of the gold found in sediments and soils exists as organically bound gold.

The determination of gold in soil with Brilliant green

The determination of gold in soil with Brilliant green