In the vast goldfields of northern Nevada, large-scale, open-pit mining has been a way of life for decades. With so much mining activity concentrated in one area, many experts are studying the potential environmental impacts of these mines over the long-term.
Water management is one of the key issues facing the mining industry in Nevada. As large open-pit mines are developed, companies must pump the groundwater out of adjacent aquifers in order to operate the pits safely. Much of this water is re-injected back into the ground, while some is used in mineral processing and surface irrigation.
Pumping large quantities of groundwater has scientists trying to determine what, if any, the long-term effects will be.
Barrick Gold’s Goldstrike mine in Nevada is home to one of the largest open pit operations in the world. Currently, the company pumps 17,000 gallons of groundwater per minute to maintain the water table below the bottom of Goldstrike’s underground mine.
In the meantime, Barrick Gold is harnessing an innovative technology to monitor and assess the impact of mining on the area’s water resources. It’s called Interferometric Synthetic Aperture Radar (InSAR). It will allow Barrick Gold scientists to accurately map the potential effects of mining on water resources in the regional aquifer. The results will be shared with other mining companies, local communities and government regulators.
Traditionally, the Environment team at Goldstrike has relied on its extensive surface and groundwater monitoring program, which covers approximately 1,600 square kilometers with more than 110 regional monitoring wells and 20 stream monitoring stations.
InSAR gives them the big picture, literally. Here’s how it works. Special satellites orbiting the earth record sophisticated radar images of the area by sending out roughly 1,700 pulses per second. A suitable baseline is created over time. Appropriate images from different time periods are selected and “interfered” over each other, lining up exactly. Experts then use computer modeling to simulate a fl at topography. Subtle changes between the two images are recorded and color-coded to create an interferogram. This image can show changes to the earth’s surface over time, within millimeters.
How does this help with water monitoring? In certain geological formations, when mines draw water from the subterranean aquifer, the surface above actually sinks, although imperceptibly to the human eye. When water flows back into those aquifers, the earth’s surface is pushed up. InSAR provides a useful tool for measuring these very small changes in the earth’s crust. In doing so, it helps to illustrate just how mining affects groundwater resources in the region, and how much water is contained in subterranean aquifers.
It has been a very effective tool, according to Dr. Johnny Zhan, Barrick Gold’s senior manager of Hydrology. He explains how measuring deep-level subterranean aquifers can be difficult using traditional methods. At Goldstrike, that means drilling monitoring wells up to 4,000 feet deep, at a cost of up to $300,000-$500,000 per hole. And there is no guarantee your hole will hit the aquifer you’re looking for. Barrick Gold has been able to use data from InSAR to confirm the company’s groundwater monitoring results at Goldstrike and its projections from the regional groundwater flow model.
The technology has a wide range of applications for mining companies today. Barrick Gold is considering using InSAR to study the stability of rock storage facilities, large reclamation projects and tailings dams. In each case, examining changes to the earth’s surface over time can reveal vital information.
The InSAR satellite images can also provide excellent data for the study of soil moisture, evaporation, wetlands and vegetation. Geologists can even use the images to assess the mineral potential of a given area.