Introducing Field Characterization of White Micas using the ASD TerraSpec Halo

The ASD TerraSpec Halo mineral identifier can be used to rapidly identify alteration minerals with a single pull of a trigger. In addition to mineral identities, the ASD TerraSpec Halo also monitors and reports on subtle spectral shifts due to geochemistry changes (called “scalars”) that can be used as supplementary exploration vectors to mineral deposits.

One such group of minerals that the ASD TerraSpec Halo identifies and provides associated scalars for are the white micas.

What are white micas?

“The white micas are a diverse group of common fine-grained phyllosilicate minerals that include the true micas paragonite, muscovite, and phengite, as well as the K-deficient mica illite. This group often serves as a useful exploration vector as they provide an indicator of geothermal and geochemical conditions at the time of their formation. Using the Al-OH scalar reported by the ASD TerraSpec Halo mineral identifier, it is possible to track geochemical conditions while the Illite Spectral Maturity (ISM) scalar (Doulblier et al. 2010) reported by the ASD TerraSpec Halo provides an indicator of thermal maturity.

How are white micas identified?

The white micas contained in the mineral library used by the ASD TerraSpec Halo are organized by composition. The true white micas are represented by the potassium white micas muscovite and phengite, and the sodic white mica paragonite. The muscovite—phengite series is characterized by increasing substitution of Mg+2 or Fe+2 and Si+4 for Al+3. The illites are classified similarly. Thus, a shift in mineralogy from muscovite and/or illite (labeled as K-Illite in the Halo mineral library) to paragonite and/or paragonitic illite (labeled as Na-Illite in the Halo mineral library) is indicative of increasingly sodic conditions. Similarly, a shift in mineralogy to phengite and/or phengitic illite (labeled as Mg-Illite in the Halo mineral library) is usually indicative of increasingly magnesium-rich conditions.”

Learn more about how the ASD TerraSpec Halo identifies white mica group minerals and associated scalars, providing the means to map geochemical and geothermal gradients in many economically important geologic systems. Download the rest of our free whitepaper “Field Characterization of White Micas Using the TerraSpec Halo,” written by Dr. Brian Curtiss.