Open Fissure Mineralization at 2600 m Depth in Long Valley Exploratory Well (California) – Insight into the History of the Hydrothermal System

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Journal Article: Open Fissure Mineralization at 2600 m Depth in Long Valley Exploratory Well (California) – Insight into the History of the Hydrothermal System

Abstract
Long Valley Exploratory Well, drilled into the Resurgent Dome at Long Valley Caldera (California) to explore the potential of geothermal power in an active magmatic system, achieved temperatures of only ca. 100°C at 2500–3000 m depth, well below the range expected atop an active magma chamber. Open fissures encountered at 2600 m depth are coated by mm-sized idiomorphic quartz crystals with first- and second-order growth discontinuities. Specific growth defects indicating rapid crystallization reflect sudden changes in SiO2 supersaturation. Fluid inclusions contain low salinity (0–5 wt% NaCl) and low CO2 (<3 mole%) aqueous fluids, with V–L homogenization temperatures of 300–350°C, indicating trapping at more than 200°C above the ambient temperatures measured within the borehole today. Fluid composition and inclusion density varies between and within the growth zones, reflecting progressive changes in the hydrothermal system during crystallization. Episodic crystallization from supersaturated fluids is interpreted to reflect sudden changes in the convection pattern, presumably induced by seismic activity, with a more recent and dramatic reorganization resulting in convective cooling. The quartz crystals are sensitive recorders of the earlier higher temperature history, unaffected by the present-day situation.

Authors 
M. Fischer, K. Röller, M. Küster, B. Stöckhert and V.S. McConnell








Published Journal 
Journal of Volcanology and Geothermal Research, 10/2003





DOI 
10.1016/S0377-0273(03)00176-8

Online 
Internet link for Open Fissure Mineralization at 2600 m Depth in Long Valley Exploratory Well (California) – Insight into the History of the Hydrothermal System

Citation

M. Fischer, K. Röller, M. Küster, B. Stöckhert, V.S. McConnell. 10/2003. Open Fissure Mineralization at 2600 m Depth in Long Valley Exploratory Well (California) – Insight into the History of the Hydrothermal System. Journal of Volcanology and Geothermal Research. 127(3-4):347-363.