Development of our nation's mineral resources depends on finding new deposits, evaluating the scale of new and existing resources, and developing extractive procedures that can remove the desired resource from its host rock in an economical manner. Geochemistry plays an important role in all stages of this process.
Most of this nation’s surficial mineral deposits have already been found and exploited, so geologists need to hunt for clues that indicate the presence of resources hidden underground. The geochemical analysis of rock outcrops, soils, and stream sediments can point to areas favorable for the discovery of new mineral resources. This exploration effort is typically followed by drilling programs that pinpoint the location and size of a deposit. Critical to all of this work is the reliable chemical/mineralogical analysis of collected samples. The availability of well characterized geochemical reference materials is an important part of any analysis program. Having reference materials that are similar in composition to the unknown samples provides the highest degree of reliability.
The USGS in collaboration with industry partners is developing a series of geochemical reference materials in support of the shale gas and rare earth element industries. The shale gas reference materials are designed to assist the industry in identifying optimal drilling zones in subsurface shale gas formations. Materials collected from outcrops associated with the five major domestic shale gas formations will be transformed into geochemical reference materials which will be characterized for their mineralogical and elemental composition.
Efforts in the area of rare earth element resource development are focused on Arkansas phosphate formations. USGS studies have identified selected domestic phosphate deposits as potential rare earth element resources. Rare earth elements are used in a variety of military and commercial products that are integral parts of our economy. With our current reliance on China for most rare earth element supplies, it is important to determine if domestic resources can supply future demand. Development of Arkansas phosphate reference materials will have two purposes. The first will be to develop instrument calibration materials designed to instantaneously provide laboratory quality analyses in the field. The second will focus on development of extraction procedures that optimize the extraction of rare earth elements while producing a phosphate product that could be integrated into the phosphate industry supply stream. The ability to produce two important products while minimizing waste is an important aspect of this work.
Proper use of shale gas reference materials will allow the energy sector to efficiently identify optimal horizontal drill zones for fracking which can lower development costs and increase well production. The materials will also assist in the identification of new shale gas formation around the world which may have substantial impact on domestic and international energy markets.
Exploitation of phosphate ore deposits could play a major role in increasing available rare earth element resources internationally. Optimizing rare earth element and phosphate extraction procedures using the Arkansas phosphate ore would be a first step in evaluating if these resources can be efficiently developed. Given the estimated domestic phosphate resources and the ease with which rare earth elements can be extracted this resource could have a positive impact on the availability of these technologically important elements.
Technological advances in emerging defense and energy-related technologies are critically dependent on the availability of reliable supplies of heavy rare earth elements. Currently, more than 95% of the world’s supply of these is produced in China, but a potential domestic source of heavy rare earth elements has been identified in the Love Hollow phosphate deposit of north-central Arkansas. We will develop a set of geochemical standards specific to this deposit that will characterize its mineralogy and heavy rare earth element content. These standards can be used to calibrate instrumentation used for assaying additional samples from Love Hollow to determine its overall heavy rare earth element content. Another avenue of research is the development of new technologies that will merge commercial phosphate production and an economic extraction of heavy rare earth elements from their phosphate host material.
Unconventional petroleum resource development has boomed in the U.S. over the last 10-15 years, primarily from the Bakken Formation in the northern Great Plains and the Eagle Ford Shale in southern Texas. The chemistry and mineralogy of these black shales are key parameters in the decision-making process affecting horizontal drilling and hydraulic fracturing operations. However, the wide diversity of formation age, mineralogy, chemistry, organic matter, and water content makes development of comprehensive or unified models difficult.
We will develop geochemical reference materials for a variety of black shale gas resources. These matrix-matched reference materials will provide for a more accurate calibration of instruments, thereby improving the reliability of data needed to address a wide range of analytical quality control issues challenging the petroleum industry.
Stephen A. Wilson
Crustal Geophysics and Geochemistry Science Center