TRACING THE SOURCE OF FLUORINE IN THE FLUORITE MINERALIZATION OF THE SOUTHERN RIO GRANDE RIFT
In this study chlorine is being used as proxy for determining the source of the fluorine because chlorine, unlike fluorine, has more than one isotope and can be used as an isotopic tracer. Chlorine and fluorine exhibit chemically similar behavior, and therefore are likely to be derived from the same source. Samples of fluorite from seven RGRT deposits, as well as granites, basalts and limestones were collected throughout the southern RGR. Chlorine is isotopically distinct in the two hypothesized potential reservoirs (d37Cl mantle~+4.7; crust 0), therefore it should be possible to distinguish between crustal and mantle sources of chlorine (Banks et al., 1999). Complimentary to chlorine isotopic studies, Sr, Nd and Pb isotopes and Br/Cl ratios are also being applied as additional tracers.
Preliminary results indicate that the fluorites have 87Sr/86Sri=0.7314-0.7353, distinctly more radiogenic than local basalts (~0.7036) and carbonates (0.7266-0.7293). The radiogenic character of the fluorites indicates that the Sr was derived largely from a granitic source, possibly through interaction of the mineralizing fluids with the pre-Cambrian basement granites.