TRACE ELEMENT CONCENTRATIONS OF PEGMATITE GEMS: TRACERS OF PETROGENESIS AND TERRORIST FUNDING

Trace element concentrations of pegmatite minerals represent a record of magma composition. This study uses trace element concentration of beryl, feldspar, and muscovite to address two issues: 1) stopping use of gems as a terrorist funding source; and 2) understanding changes in magmatitc and aqueous process during pegmatite crystallization. Current open-source intelligence shows that gems, especially tanzanite, diamond, and emerald, are used as a terrorist funding source. Locating the source mine of these gems is critical to diminish terrorist funding.

In this pilot study, trace element concentrations of beryls, feldspars, and muscovite from the core, core margin, intermediate, and wall zones of six pegmatites from the Palermo district, North Groton, New Hampshire, are compared to each other and to nine beryls from seven countries (Afghanistan, Brazil, China, India, Mozambique, Namibia, and Pakistan). LIBS (Laser-Induced Breakdown Spectroscopy) and ICP-MS analyses provide complementary data and advantages. LIBS records the visible emission spectrum of a plasma produced by intense laser ablation pulses (10^-9s). Although LIBS quantitative analysis is still in development, LIBS has enormous potential because: 1) essentially no sample preparation is necessary; and 2) portable LIBS is now commercially available. For the current study, qualitative LIBS spectra are accompanied by quantitative ICP-MS analyses.

The following observations suggest that trace element ratios of pegmatite gems can be used to trace a gem to its source pegmatite. Preliminary LIBS element intensity ratios show that beryls from Palermo pegmatite #1 (n=11) have higher Fe/Ti (1.42-2.53), Fe/Mg (1.28 to 4.22), and Fe/Zr (1.27-9.99) than the world samples Fe/Ti (0.89 – 1.51), Fe/Mg (0.85 – 1.40), and Fe/Zr (0.70 – 1.60). Beryl from Palermo #2 (Fe/Ti=0.95, Fe/Mg=1.11, Fe/Zr=0.81) is also distinct from Palermo #1.

Element ratios vary slightly between beryls from different zones in Palermo #1. Beryls from the core margin have higher Fe/Ti and Fe/Mg, and lower Na/K than beryls in the surrounding intermediate and core zones, suggesting that trace element ratios in minerals are indicators of pegmatite processes. However, this variability needs to be fully assessed if this technique is to be used in the fight against terrorism.