ANATOMY OF A HIGH-TEMPERATURE HYDROTHERMAL QUARTZ VEIN

The Shuteen Mineralised Complex (SMC; South Gobi District, Mongolia), comprises an extensive, silicified hydrothermal breccia zone, with anomalous Cu- and Mo values, and corresponds to an intensely leached, sub-volcanic, high-sulphidation breccia-pipe complex, or high-level parts of a porphyry copper deposit with associated breccia pipes. The volcano-plutonic hosted SMC provides a field analogy to study (i) fluid-rock interactions in high-temperature magmatic-hydrothermal systems, and (ii) energy (thermal) extraction from rock masses hotter and/or deeper than conventional geothermal utilisation. Key factors for utilisation of gEnhanced Geothermal Systemsh is the maintenance of a large surface area for heat exchange, at conditions where fluid-rock interactions preserve the heat exchange surface, as quartz precipitation may decrease permeability to an extent that there is little fluid convection.

Detailed SEM-Cathodoluminescence (CL) microtextural imaging and petrography of quartz veins at SMC, cutting Carboniferous (310 +/- 15Ma) granodiorite on the periphery of the main alteration zone, containing gold values up to 57g/t, reveals mineral-fluid relationships that point to a high-temperature, epithermal origin. SEM-CL imaging of the quartz veins have revealed a complex history of crystal growth, dissolution and microfracturing, and enabled specific alteration events that formed the veins to be gfingerprintedh, thus constraining the timing discrete fluid inclusion populations were trapped in the quartz. We have taken our SEM-CL imaging SMC investigation further, using fluid inclusion and trace element profiling/distribution studies, to examine primary quartz from non-mineralised Quaternary Takidani Granodiorite (Japan) and synthetic quartz grown in laboratory experiments (up to supercritical conditions) to reveal quartz precipitation-dissolution and microfracturing processes at elevated temperature-pressure conditions, and the nature of rock-fracture permeability in deep-seated, magmatic-hydrothermal systems.