EVOLUTION OF POTASH MINING STRATEGIES IN THE US

Potash is necessary, mostly as an agricultural fertilizer but also for use in industrial applications. In 2018, the USGS listed potash as a critical mineral, as the U.S. is more than 90 percent reliant on imported potash, mostly from Canada but also from Belarus and Russia. Research done for the USGS Mineral Deposit Database (USMIN) project has provided a window into the evolution of potash mining in the U.S. Early mining efforts sought potash sources at the surface, such as brines (e.g., Searles Lake, CA), saline lakes (e.g., western NE), and alunite (e.g., Marysville, UT). In the 1930’s, the discovery of potash in relatively shallow (<550 m deep), subsurface evaporite deposits determined what would become the dominant source for potash production. Now, as the shallow evaporite deposits become depleted, solution mining is being used or considered to reach deeper (e.g., MI basin) and/or more complex (e.g., Paradox basin, UT) targets and to enhance extraction from the remnants of older workings (e.g., HB mine, NM). This has the added advantages of eliminating the hazards of underground mining and reducing costs. Although mining near surface brines for potash has been an important contributor to U.S. potash production since the 1900’s, future projects are anticipated to use even more of these resources. Furthermore, alunite deposits, which have not been exploited since World War I, are once again being considered for development.

As of 2020, calculated potash resources for current and potential mines where potash is the primary objective are: solution mining 903 Mt, conventional underground mining 222 Mt, alunite mining 71 Mt, and brine mining (including Great Salt Lake) 48 Mt. If we consider calculated potash resources for active mines only, they are: brine mining (including Great Salt Lake) 42 Mt, conventional underground mining 30 Mt, and solution mining 6 Mt. Note that brine resources are often underreported due to their dependence on recharge from meteoric waters and may be greatly affected by climate change. These data suggest that for the U.S. to reduce its dependence on potash imports and maintain its >5.5 Mt consumption per year, it will need to continue to develop less conventional resources.