SRK completed a Feasibility-level hydrogeological investigation of a large gold and silver deposit in a recent hot springs environment in Nevada.
Major issues included the following:
- Characterization of pre-mining groundwater levels and flow directions in compartmentalized aquifers
- Evaluation of dewatering requirements for a large open-pit mine from discrete highly conductive faults and prediction of groundwater impacts during mining and post-mining periods
- Prediction of pit lake infilling conditions
- Definition of a water supply for the mine and proposed mill facilities
In addition, SRK worked closely with the client’s geological and environmental groups and third-party contractors who are providing geotechnical design and geochemical modeling.
SRK directed and managed a multi-year groundwater field program which included:
- installation of deep monitoring/pumping wells in high-temperature conditions with exsolving H2S gas;
- design and construction of deep, large-diameter prototype dewatering wells;
- conducting core hole packer tests and airlift tests in slim-hole monitoring wells; and
- conducting long-term, multiple-well pumping tests to evaluate aquifer compartmentalization and effectiveness of a structural-based dewatering strategy.
Following analysis of the groundwater system characterization data, and minimal revision to the conceptual hydrogeologic model, SRK developed a 3D numerical groundwater-flow model of the project and evaluated passive inflow and dewatering requirements to the proposed open-pit, estimated propagation of drawdown during mining, and predicted pore pressure distributions as input to a geotechnical slope stability analysis.
SRK predicted pit lake infilling, predicted potential impacts to the groundwater system during both mining and post-mining conditions, and defined components of a pit lake water balance as input for geochemical predictions of pit lake water quality.
In 2019, SRK updated the mine water supply predictions and dewatering requirements for a proposed expansion of the Hycroft Mine limited to heap-leach processing only. A GoldSim water balance was developed for the proposed mine plan, which included multiple heaps and solution ponds with a complex scheduling of oxidation, rinsing, pH adjustment followed by cyanide leaching. The model was used to predict water consumption and determine if the makeup water required by operations would consume the water produced by the required dewatering flows.
