The pit lake iterative simulation model (PLISM) is an iterative water-balance simulator that was developed in Microsoft Excel®. The PLISM workbook has a user-friendly interface that incorporates all natural and mine-related inflows and outflows to and from a pit lake. PLISM differs from previous water-balance approaches in data tabulation, pit-lake representation, and the solution method. User-defined data inputs can differ in time from PLISM time steps of lake stage and volumes. Unlike traditional pit-lake water balance models, PLISM is a transient model that simulates pit-lake stages and volumes by solving iteratively for changes in stage and volume at the end of each user-defined time step, rather than solving with forward differences. Stages and volumes are interpreted as a continuous function from the pit-shell geometry (i.e. stage-area-volume relation). PLISM also simulates highwall runoff as a function of pit-lake stage, where potential runoff from the catchment outside of the lake surface decreases as the lake stage increases. Highwall runoff is estimated with the curve number approach, which provides a physically defensible and climate-responsive framework for highwall runoff, greatly reducing uncertainty in this user-defined parameter. A simplified form of the Jacob and Lohman (1952) equation simulates groundwater exchange. PLISM was validated with the development of pit-lake models in semi-arid (Lone Tree Mine, Nevada, USA) and humid (Buzwagi Mine, Tanzania) climates, as examples. PLISM robustly simulates any site-specific pit-lake condition and an unlimited number of water-management scenarios that account for future climatic uncertainty.
In gold mines, carbonaceous materials (CMs) adsorb gold during gold mine recovery cyanidation, preg-robbing the gold and reducing the amount of gold that can be recovered. Here, we analyze CMs in refractory gold ore by conventional chemical testing methods to better understand preg-robbing. This study investigated the preg-robbing capacity and strength differences of CMs from four selected Nevada ore samples by loading solution gold onto solids and then competing with fresh granular activated carbon. Results were validated by the micro-XRF imaging of 10 CM particles per sample, showing a cross-sectional view of gold composition in the CM particle. Raman spectroscopy was used to analyze CMs in all the samples, using different laser wavelengths and the effect of contacting gold cyanide. A correlation between deconvoluted bands from the Raman spectra of CMs and their preg-rob ability has been observed. Raman spectral analysis of the four samples reveals increasing graphitic disorder in the CMs, which follows the known trajectory of carbon amorphization.
The Yalea gold deposit, the largest individual orebody discovered to date within the Paleoproterozoic Loulo gold district, hosts almost a third of the 30Moz gold endowment within the camp, and remains open both along strike and at depth. The Yalea orebody has been well studied from a geological and structural perspective, with associated controls on high-grade localisation along the +7.5km mineralised structure related to geometric complexities (e.g., bends and steps) and intersections along the host shear zone, having nucleated along a weaker carbonate-rich horizon. In contrast, the geochemistry of the deposit has been less well studied to date. The first full-lab (ultra-trace level method) pilot study was recently completed, with the aim being to develop an additional exploration targeting tool to assist with drill testing deeper, blind targets along numerous fertile structures present in the Loulo district, by understanding what a "near- miss" might look like from drilling results. Results show that the Yalea orebody is associated with a polymetallic signature consisting of Au-AsW +/- Sb +/- Bi +/- Ag +/- Co +/- Mo +/- Cu +/- Pb, with what appears to be systematic spatial zonation of the element concentrations about the core of the system. This conclusion is supported by multivariate (PCA) analysis of the dataset.
The Kibali gold district, located on the Congo Craton, comprises a Neoarchean gold resource exceeding 28.7 Moz. The district is located within a westerly-verging stacked fold-and-thrust belt associated with a compressional tectonic regime active from ca. 2.64 - 2.60 Ga. Deposits are hosted by a major fault zone that consists of a complex series of smaller thrust faults, shear zones, and folds, which extend over 60 kilometers. Gold deposits are primarily hosted in BIF and clastic sedimentary rocks. The gold and associated sulfides are in veins and disseminated in NE- to NNE-trending ore shoots within the deformed and metamorphosed volcanosedimentary rocks. Pyrite is the dominant sulfide mineral and hosts both solid solution gold and free gold. Because of its strong association with the gold mineralization, our study focusses on unravelling the metallogeny of the area by considering pyrite textural analyses, in situ trace element analyses using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), and S isotopic composition (δ34S) analyses using Secondary Ion Mass Spectrometry (SIMS).Eight distinct pyrite types were identified, including microcrystalline sooty (py-0a), small grains (< 40 μm) (py-0b), aggregate recrystallized (py-1), core-rich inclusion (py-2), vein-like (py-3), non-zoned (py-4a), oscillatory As-bands zoned (py-4b), and cubic euhedral (py-5) pyrite. The ore-forming processes occurred over a polyphase evolution. Syn-diagenetic pyrite py-0a in volcaniclastic layers of older basin sediments served as the primary repository of Au (15.6 ppm median) with a near-zero δ34S value. Late diagenetic or early metamorphic pyrite (py-0b) was found in younger basin sediments. Py-1 resulted from solid-state recrystallization of py-0a and py-0b. During the early ore stage, porous py-2 with high Au concentrations (3.1 ppm) and various trace element enrichments precipitated due to fluid-rock interaction. Metal precipitation occurred through sulfidation and carbonation of wall rock with a relatively reduced fluid undergoing 34S-depletion. However, py-3 displayed notable trace element depletion and a complex mineral association. In a second ore stage, py-4a and zoned py-4b deposition occurred, dominated by an over-pressured fluid fracturing brittle rock. Py-4b, rich in Au (5.5 ppm) concentrated in oscillatory zoned As-rich bands, resulted from interactions during pulsed fluid flow. This process involved fluid phase separation, non-equilibrium conditions, 32S-depletion, and precipitation of py-4b with a high δ34S value (6.4 ‰ mean). Subsequently, pyrite (0 to 4) generations underwent deformation during a later ductile deformation event, leading to the remobilization and concentration of invisible gold into adjacent gold grains within the high-grade shoot plunging NE. This process involved shearing, boudinaging, and folding ore minerals in tightly folded structures. Late-stage py-5 formed under gold-poor fluid conditions or inefficient gold depositional conditions. Brittle fracturing of these grains later provided local sites for remobilized gold. The study contributes insights into the origin and evolution of gold mineralization in the Kibali gold district, supporting a multistage ore-forming fluid system.
Permitting and regulatory obligations require mine operators to periodically report the spatial extent of mine-induced water-level changes, and to provide water-level monitoring data for review, along with explanations of all hydrologic stresses causing water-level trends. This study couples a baseline-estimation method with a curve-fitting trend-analysis approach to determine all natural, mining, and non-mining aquifer stresses affecting water levels in wells. The approach was applied to the Twin Creeks Mine monitoring network in north-central Nevada, USA. Stresses identified in wells were used to delineate the approximate extent of pumping effects and indicated that drawdowns had not coalesced between mining and non-mining pumping areas. Trend-analysis results indicated that 10 study-area well hydrographs have natural trends, and statistical methods identified three of these wells as having statistically significant downward trends. Thus, caution should be used when interpreting the meaning of statistically significant downward trends, because the downward trend may be climate driven rather than pumping related. The curve-matching approach requires the development of a baseline water-level trend to understand expected natural fluctuations. The baseline trend assumes a dynamic-equilibrium natural condition, where long-term net changes in groundwater levels are zero. The baseline trend and trend analysis require a recharge proxy for the study area. This study developed recharge proxies using winter precipitation data, peak reservoir-storage volumes, and metered mine-water discharge to a surface-water channel. The curve-matching approach also can be used to identify and remove erroneous data, reconcile water-level and pumping datasets, or build hydrologic conceptualizations.
