Hydrothermal Vesuvianite: A U-Pb Dating Mineral

Since mineral deposits are the products of multiple hydrothermal pulses, in many circumstances, selecting a robust mineral to date the different mineralization events precisely is important. Vesuvianite, usually known as a rock-forming or accessory silicate mineral typically found in metasomatic and regional metamorphic calcsilicate rocks, has the potential to be a dating mineral. Vesuvianite crystallized entirely from saturated boiling hydrothermal fluid has not been previously reported. Here, we report a new occurrence of hydrovesuvianite, which yields a reliable U-Pb isotope age, is associated with quartz and zircon in hydrothermal veins in central Madagascar. The hydrovesuvianite and associated minerals entirely crystallized from a boiling hydrothermal fluid with relatively low salinities at 290-320 degrees C and 70 bars. The hydrovesuvianite has cell parameters of a 15.6254(5), c 11.8870(9) & Aring;, and space group P4/nnc. The chemical composition of the hydrovesuvianite is similar to vesuvianites of metamorphic origin, and they have LREE-enriched chondrite-normalized rare earth element (REE) patterns and negative Eu anomalies. The hydrovesuvianite crystallized at 526.7 +/- 3.6 Ma. Hydrothermal vesuvianite is an ideal U-Pb isotope dating mineral for hydrothermal mineralization and vesuvianite-bearing metamorphic rocks.