Kimberlites: Mapping the Path to Diamonds
Human beings have been utilizing diamonds for millennia. Early humans used them as engraving tools; ancient civilizations placed them in religious iconography; and today, they are treasured gemstones used in jewelry and other adornments. Most diamonds come from the Earth’s mantle, transported to the surface via kimberlite pipes. Locating these pipes is essential to mining the approximately 26,000 kgs of diamonds annually across the globe.
Kimberlites are ultramafic-volcanic and sub-volcanic rocks often occurring in clusters along major crustal fracture zones. There are two types of kimberlite mineralogy. Group I kimberlites are CO2-rich, ultramafic-potassic, and are dominated by a mineral assemblage of Forsteritic Olivine, Mg-Ilmenite, Cr-Pyrope, Almandine-Pyrope, Cr-Diopside, Phlogopite, Enstatite, and Ti-poor Chromite. Group II kimberlites are dominantly H2O ultrapotassic peralkaline rocks rich in volatiles. These unique characteristics allow diamonds to reach the surface before they dissolve.
Not all kimberlite deposits contain diamonds. Discovering diamond-bearing kimberlite deposits can be difficult and time-consuming due to hindrances present in the surrounding environment. Geologists typically use chemically distinct indicator minerals to reveal the presence of kimberlite. Cr-Pyrope, Eclogitic Garnets, Cr-Diopside, Mg-Ilmenite, and Chromite, are some of the alteration mineral indicators sought out in the field. In addition to these minerals, G10 garnets can be used as an indicator for diamond potential within kimberlite deposits. G10 garnets have a diagnostic chrome feature in the visible range indicated by the arrow in Figure 1.
Full-range UV-Vis-NIR spectrometers such as the Spectral Evolution oreX-™ series use state-of-the-art detectors in the near-infrared to identify unique spectral signatures in minerals. These high-resolution spectrometers instantly reveal spectral features to the geologist that help distinguish between the alteration of indicator minerals of kimberlite. The oreX- series is engineered specifically for field use with a rugged, portable enclosure and robust accessories. Whether you are searching for diamonds, precious metals, or rare earth elements, field spectroscopy can lead you to your deposit quickly and effectively.
The oreXpress geological spectrometer with EZ-ID™ delivers:
- Full range NIR field spectrometer – 350-2500nm
- High resolution/high sensitivity scanning in a lightweight field package
- Rugged reliable design with all photodiode arrays – no moving optical parts
- Contact probe and two lithium-ion batteries for a full day of fast scanning in the field
- Fast and accurate identification of an unknown mineral to a known spectral library sample
- Simple, consistent user interface
- USGS, SpecMIN and GeoSPEC libraries available
- Weighted score for best matches
- Include or exclude spectral regions of interest for optimal results
- User-configurable batch processing and output to an Excel spreadsheet
- All data saved as ASCII files for immediate use with 3rd party software
Figure 1 Mineral spectra pointing out the chrome feature in G10 garnets.