Research Chemistry

Scientific Issue and Relevance

Mineral assessments, ore deposit models, and studies of environmental and human-health impacts of mineralization are all underpinned by the ability to accurately determine concentrations of elements, chemical species, and minerals in complex samples. Geoanalytical methods are analyses of geological and environmental samples, such as rocks, soils, and waters, to determine their properties and chemical makeup using specialized equipment and analytical techniques. While many geoanalytical methods have become routine and are outsourced to contract laboratories, there is a critical need to maintain state-of-the-art analytical capabilities and expertise within the Mineral Resources Program (MRP) for non-routine samples. These non-routine samples are often complex in mineralogy, aqueous matrix, and geologic/environmental context and so require significant analytical method adaptation or development. As a result, the success of many USGS projects funded by the Mineral Resources Program (MRP) and Energy and Minerals Mission Area relies on the ability to obtain high quality, defensible data which requires access to state-of-the-art instrumentation and methods of analysis as well as advanced analytical expertise that are beyond the scope and capability of most individual projects and contract laboratories.

Methods to Address Issue

Scientists supported by Research Chemistry respond to the analytical needs of MRP and other USGS projects by developing analytical methods and maintaining state-of-the-art facilities and expertise over a broad range of geoanalytical techniques. Project members also develop methods for specialized analyses via reimbursable projects for other DOI and U.S. government agencies. Advances in analytical methods and approaches are shared with the scientific community through presentations and publications.

Current Capabilities and Research Directions of Research Chemistry Facilities

Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)

LA-ICP-MS measures concentrations of multiple trace elements in the solid phase without need for extensive sample preparation such as acid digestion. Multi element analysis can be performed at micron scale resolution with low limits of detection, allowing a detailed look at the chemical story preserved in minerals, rocks, and biological and environmental samples. The USGS LTRACE laboratory can provide collaborators with analyses on submitted samples or guide them through the analysis of their own samples.

Solution Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES)

The task objective is to develop new and improved capabilities in measuring concentrations of multiple elements and chemical species in a wide range of aqueous samples to support MRP science goals. Both ICP-MS and ICP-OES have become the standard at contract labs that employ standard operating procedures, but there are numerous complex samples and emerging areas of instrumental analysis that are beyond the routine capabilities of commercial or contract laboratories. Examples of areas of developing needs include hydride/vapor generation methods to determine very low levels of critical elements from geological materials, and single particle ICP-MS methods to characterize colloidal chemistry of critical minerals, mineral deposits and
mine waste.

X-ray Methods

Task objectives are to improve current methods, develop new methods, and push the boundaries of X-ray mineral analysis in geological materials. Techniques included in this task are:

• Powder X-ray diffraction (XRD) for mineral identification and compositional analysis
• Wavelength dispersive X-ray fluorescence spectroscopy (WD-XRF) and Energy dispersive X-ray fluorescence spectroscopy (ED-XRF) for bulk elemental chemistry
• Portable X-ray fluorescence spectroscopy (pXRF) for portable screenting and in-field elemental analysis
• Handheld laser induced breakdown spectroscopy (LIBS) for portable screening and elemental analysis
• Specialized clay and amorphous (poorly-crystalline) phases analysis
• Development of USGS XRD analysis software and mineral database, RockJock 2.0

Routine Aqueous Analyses

The G3 Single Element Analysis Laboratory (G3SEAL) provides projects with anion and alkalinity analyses for routine aqueous samples. Analysis of routine aqueous samples submitted through the Analytical Chemistry Project uses ion chromatography for anions (fluoride, sulfate, chloride) and auto-titration for alkalinity. Secondary analyses of samples submitted to contract laboratories are performed when requested.

Topical Geoanalytical Collaboration

Task scientists provide synergistic innovations for the characterization of geological, environmental, and biological samples. Current priorities are to develop ideas and collaborative analytical and geoanalytical methods to mine waste characterization and critical mineral recovery.

Geochemical Reference Materials

Goals are to maintain the scientific expertise and laboratory capabilities to develop new powdered and microanalytical geochemical reference materials that provide the critical ability to calibrate and control existing and innovative geoanalytical methods and technologies within USGS and collaborator laboratories. Additionally, task scientists will work with USGS scientists and partners to identify needed gaps and develop and synthesize new reference materials to ensure the integrity of generated geochemical data to answer critical questions in the development and management of mineral resources.

Fluid Inclusion Reference Materials

This task will synthesize fluid inclusions in quartz at pressure and temperature conditions relevant to ore deposit formation. These synthetic inclusions will then be characterized and calibrated against existing synthetic fluid inclusions and the resulting material will be available to MRP and the wider analytical community. Production of these synthetic fluid inclusions will allow for validation of natural fluid inclusion measurements and lays the groundwork for more applied synthetic inclusion studies within the USGS laboratories.