Gold Basin Research Articles

Hydrogeochemistry and Mercury Contamination of Surface Water in the Lom Gold Basin (East Cameroon): Water Quality Index, Multivariate Statistical Analysis and Spatial Interpolation

Artisanal and small-scale gold mining activities have an impact on natural resources and human health. This study addresses the assessment of surface water quality in the Lom gold basin. A combined approach of water quality index calculation, multivariate statistical analysis and spatial interpolation was used. Sampling was performed at 15 stations during low- and high-water periods in 2021 for classical physicochemical parameters and total mercury measurements. The results show that the physicochemical parameters were below drinking water standards for both periods, except for pH, total suspended solids and total mercury. These waters show a large cation deficit as well as an anion deficit. The water chemistry is controlled by precipitations and silicate dissolutions in rock that convert the water into the Ca-HCO3 and Ca-Mg-HCO3 types. The level of mercury contamination varied from acceptable to high due to high flow rates during high water that cause a dilution effect for the mercury concentration upstream and its accumulation downstream. The water quality varied from excellent to very poor with better quality during the high-water period. The Lom watershed is locally affected by physical and chemical pollution due to the abundance of suspended solids and mercury resulting from the different gold mining activities.

Landslide monitoring and runout hazard assessment by integrating multi-source remote sensing and numerical models: an application to the Gold Basin landslide complex, northern Washington

The landslide complex at Gold Basin, Washington, has been drawing considerable attention after a catastrophic runout of the nearby landslide at Oso, Washington, in 2014. To evaluate potential threats of the Gold Basin landslide to the campground down the slope, remote sensing and numerical modeling were integrated to monitor recent landslide activity and simulate hypothetical runout scenarios. Bare-earth LiDAR DEM (digital elevation model) differencing, InSAR (Interferometric Synthetic Aperture Radar), and offset tracking of SAR images reveal that localized collapses at the headscarps have been the primary type of landslide activity at Gold Basin from 2005 to 2019, and currently no signs indicative of movement of a large centralized block or a deep-seated main body were detected. The maximum horizontal deformation rate is 5 m/year occurring primarily from headscarp recession of the middle lobe, and the annual landsliding volume of the whole landslide complex averages 1.03 × 105 m3. From three-dimensional limit equilibrium analysis of generalized terrace structures, the maximum landslide volume is estimated as 2.0 × 106 m3. Simulations of hypothetical runout scenarios were carried out using the depth-averaged two-phase model D-claw with above-obtained landslide geometry constraints. The simulation results demonstrate that debris flows with volume less than 105 m3 only pose limited threats to the campground, while volumes over 106 m3 could cause severe damages. Consequently, the estimated maximum landslide volume of 2.0 × 106 m3 suggests a potential risk to the campground nearby. Adaption of our methodology could prove useful for evaluating other similar landslides globally for hazards prevention and mitigation.

Process network modelling of the geochemical reactions responsible for acid mine drainage emanating from the Witwatersrand tailings facilities

ABSTRACTAcid mine drainage (AMD) and associated metal(loid) and SO42- pollution of soil, surface water and groundwater is ubiquitously associated with tailings material generated by Au mining in the Witwatersrand Basin in South Africa. The individual geochemical processes responsible for the AMD generation in this tailings material are relatively well understood. What is less clear are how these different processes interact as a network within the tailings system. Process network modelling (PNM) is a tool that can be used to study such interactive and complex networks of geochemical processes, especially when stochastic methods, e.g. Monte Carlo simulation, are included in the model development. Secondary mineral phase supersaturation requirements from classical nucleation theory are also built into the model.A PNM was developed for a tailings facility in the Witwatersrand gold basin focussing on pH, Fe(total) and SO42- concentrations in the tailings pore water and the relationship of these parameters to the dissolution of pyrite, O2 diffusion into the tailings, oxidation of Fe2+ and the precipitation of secondary minerals, specifically goethite and jarosite. The model indicated that AMD conditions develop fairly rapidly after the sulphidic material is exposed to the Earth’s oxygenated atmosphere. The concentration of H+, and hence the pH, in the tailings pore water is controlled by a number of feedbacks. The positive feedback, implying addition of H+, is the dissolution of pyrite and the precipitation of the secondary Fe3+-bearing minerals goethite and jarosite. Jarosite precipitation was shown to increase the median H+ addition rate by ~2%. The negative feedback, i.e. decrease in H+, is the oxidation of Fe2+ to Fe3+. This feedback loop produces a net excess of H+. Together with the buffer effect of goethite and jarosite precipitation, system steady-state conditions are eventually achieved with respect to pH.The pore water SO42- concentration is controlled by the positive and negative feedback of pyrite dissolution and jarosite precipitation. This feedback loop produces a large excess of SO42- and steady state conditions can only be achieved if SO42- is physically removed from the tailings system, e.g. seepage to groundwater.Oxidation of the Fe2+ produced by pyrite dissolution to Fe3+ is the only positive feedback for tailings pore water Fe3+ concentrations. The negative feedbacks are precipitation of goethite and jarosite and the oxidation of pyrite by Fe3+. The former effect is delayed as these phases first have to achieve a certain level of supersaturation in the tailings pore water solution before they can form. The precipitation of jarosite and goethite, by removing Fe3+ from solution, decreases the effect of Fe3+ pyrite oxidation causing O2 to remain the dominant oxidation mechanism. This feedback loop produces a small excess of Fe3+ over time, however, the model is very sensitive to other factors, e.g. O2 diffusion deeper into the tailings facility.

Mineralogy and heavy metal content of secondary mineral salts: A case study from the Witwatersrand Gold Basin, South Africa.

Secondary minerals associated with acid mine drainage play an important role in metal cycling and may pose a geochemical hazard. The occurrence of secondary minerals indicates prevailing and past geochemical conditions. Detecting and characterising secondary minerals is necessary to the planning of remediation programmes. This paper investigates the mineralogical and heavy metal contents of mineral salts associated with acid mine drainage in the East Rand area of the Witwatersrand Basin. Powdered X-ray diffraction was used to identify and quantify mineralogical phases and a scanning electron microscope was used to determine the morphology of the identified minerals. Major cations and anions were determined using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Ion Chromatography (IC). Geochemical modelling was used to predict the saturation of the minerals. Efflorescent crusts contained high levels of trace metals. Enrichment of trace metals, electrical conductivity and sulphate were highest in white salts. A high metal content was associated with low pH values in mineral salts. The salts were dominated by quartz and clay minerals of the smectite group. Tamarugite, apjohnite and jarosite were the predominant sulphate minerals in the salts. These minerals are very acidic and will accelerate weathering in the surrounding soils. Geochemical modelling yielded precipitated hydrated sulphate, halite and goethite. The information gathered during this study will be useful in managing salinity and high metal contents in receiving waters and soils associated with gold mining activities.

Influence of Rock Glaciers on Stream Hydrology in the La Sal Mountains, Utah

While valley glaciers have received considerable attention for their contributions to summer runoff during the past decade, the contributions of rock glaciers to summer runoff patterns have largely been ignored, especially in the western United States. This article examines summer runoff from two basins in the La Sal Mountains, Utah: the non—rock glaciated Wet Fork and rock glaciated Gold Basin. Runoff events were analyzed for volume of stormflow, stormflow duration, and peak flow duration. Four events were recorded in Wet Fork (n = 4), five events were recorded in Gold Basin (n = 5), and six events at a flume immediately adjacent to the Gold Basin rock glacier (n = 6). Wet Fork hydrographs are dominated by baseflow throughout the summer and a small proportion (0.13%–0.31%) of precipitation leaves the basin as stormflow during storms. Gold Basin hydrographs are characterized by early season snowmelt with flood peaks associated with summer storms. Runoff from the gaged rock glacier represents 15%–30% of total basin runoff and is inversely related to precipitation and directly related to rainfall intensity. Removal of rock glacier hydrographs from total basin hydrographs indicates that there is increased surface runoff from alpine drainage basins that contain rock glaciers, suggesting rock glaciers act as impervious surfaces. This short-term study in Utah suggests that alpine drainage basins with rock glaciers could have greater surface runoff and higher flood peaks than drainage basins that lack rock glaciers. While the long-term effects of rock glaciers on summer water resources is still unknown, this investigation demonstrates rock glaciers may profoundly influence hydrographs in alpine drainage basins.

The complex exposure history of the Jiddat al Harasis 073 L‐chondrite shower

Abstract— We measured the concentrations and isotopic compositions of He, Ne, and Ar in 29 bulk samples from 11 different strewn field fragments of the large Jiddat al Harasis (JaH) 073 L6 chondrite shower, including 7 samples from known locations within the main mass. In addition, we measured the concentrations of cosmogenic 10Be, 26Al, 36Cl, and 41Ca in 10 samples. All fragments of this shower are characterized by low 10Be concentrations (7.6–12.8 dpm/kg), high 26Al/10Be ratios (3.5‐5), large contributions of neutron capture 41Ca (200–1800 dpm/kgCa), low 3He/21Ne ratios (1.5‐3.0), large variations in cosmogenic 21Ne (1.2–12) × 10−8cm3STP/g, and significant contributions of neutron‐capture 36Ar. Stepwise heating experiments show that neutron‐capture produced 36Ar is predominantly released between 1000–1200 °C. All these results are consistent with a first‐stage exposure of ˜65 Ma within ˜20 cm of the surface of the L‐chondrite parent body, followed by ejection of a 1.5‐2 m large object, which was then delivered to Earth within about 0.5 and 0.7 Ma. The cosmogenic nuclide data in JaH 073 thus corroborate the trend that many of the large chondrites studied so far experienced a complex exposure history. The observed 3He/21Ne ratios of 2.5‐3.0 in the most shielded samples (including those of the main mass) are lower than predicted by model calculations, but similar to the lowest values found in the large Gold Basin L‐chondrite shower. The Bern plot, which gives a linear correlation for 3He/21Ne versus 22Ne/21Ne, is evidently not valid for very high shielding. Some of our measured 22Ne/21Ne ratios in JaH 073 are lower than 1.06, which is not well understood, but might be explained by loss of cosmogenic neon from shocked sodium‐rich plagioclase during terrestrial weathering. The amount of trapped atmospheric argon in the JaH 073 fragments varies by almost two orders of magnitude and shows only a weak correlation with the size of the fragments, which range from <100 g to >50 kg. Finally, low concentrations of radiogenic 4He and 40Ar indicate incomplete degassing < 1 Ga ago, probably at the main collision event on the L‐chondrite parent body ˜480 Ma ago.

Noble gases and cosmogenic radionuclides in the Gold Basin L4 chondrite shower: Thermal history, exposure history, and pre‐atmospheric size

Abstract— We measured the concentrations of the cosmogenic radionuclides 10Be, 26Al, 36Cl, and 41Ca in the stone and metal fractions of 15 fragments of the Gold Basin L4 chondrite shower, as well as noble gases in 18 Gold Basin fragments. A comparison of 10Be, 26Al, and 41Ca concentrations with calculated production rates from two different models indicates that the Gold Basin samples came from depths of about 10 cm to more than 150 cm in an object with a radius of 3–5 m. As was predicted by recent model calculations, the noble gases show a reversal of the 22Ne/21Ne ratio at very high shielding. The 21Ne/10Be and 21Ne/26Al ratios in most samples are constant and correspond to a 4π exposure age of 18 ± 2 Myr. However, three Gold Basin samples show a 30–120% excess of 21Ne implying that they were previously exposed close to the surface of the parent body, whereas the other samples were buried several meters deeper. Concentrations of neutron‐capture 36Ar in most samples are consistent with measured concentrations of neutron‐capture 36Cl and an exposure age of 18 Myr. Large excesses of neutron‐capture 36Ar were found in those samples with an excess of 21Ne, providing additional evidence of a first‐stage exposure on the parent body. The excess of spallation‐produced 21Ne and neutron‐capture‐produced 36Ar in these samples indicate a first‐stage exposure of 35–150 Myr on the parent body. The radiogenic 4He and 40Ar concentrations indicate a major impact on the parent body between 300 and 400 Myr ago, which must have preceded the impacts that brought the Gold Basin meteoroid to the surface of the parent body and then expelled it from the parent body 18 Myr ago.

Gold Basin meteorite strewn field, Mojave Desert, northwestern Arizona: Relic of a small late Pleistocene impact event

Abstract— Over 4450 meteorite specimens with a total mass of 168 760 g have been found in the Gold Basin (L4) strewn field over an area of 225 km2. The meteorite is a breccia, composed only of fragments of L‐chondrite materials. The parent meteoroid had a kinetic energy equivalent to ∼5 to 50 ktons when it hit the top of the atmosphere. Cosmogenic nuclide studies indicate the meteorite has a terrestrial age of 15 000 ± 600 years, corresponding to the Late Pinedale portion of the Wisconsin Glaciation. Conditions in the Gold Basin, which is now part of the Mojave Desert, were wetter and cooler at the time of the fall. Mössbauer analyses indicate the sample is 30 to 35% oxidized. This is less than that in meteorites with similar ages found in eastern New Mexico, but comparable to that found in meteorites from the Sahara and the Nullarbor Region. Oxidation is likely to have occurred soon after the fall, when exposure to precipitation was at its maximum. Four other new meteorites were also found in the Gold Basin strewn field.

Patch dynamics ofGlaucopsyche lygdamus (Lycaenidae): correlations between butterfly density and host species diversity.

Glaucopsyche lygdamus egg densities were surveyed over a 2000-m section of Gold Creek and at 30 different isolated patches in the Gold Basin drainage in Colorado. Host plant numbers and diversity were quantified, as well as other variables potentially influencing butterfly population size, such as patch size and isolation. Egg densities correlated significantly only with measures of host species diversity. Patches consisting of a single host species, no matter how large, did not support high butterfly densities, but patches of multiple, equitably distributed host species did. The most likely explantation, in light of oviposition preference and larval performance data accumulated for this butterfly species, is that host species diversity is necessary for the persistence ofG. lygdamus populations, because alternative host species buffer population losses during poor or unusual years. The dependence of both ovipositing butterflies and developing larvae on the ephemeral, young, host plant flowers make the butterfly especially vulnerable to year-to-year variation in host plant availability and quality.

Control of gold mineralization at the Cyclopic Mine, Gold Basin District, Mohave County, Arizona

Control of gold mineralization at the Cyclopic Mine, Gold Basin District, Mohave County, Arizona