Fluid mixing from below in unconformity-related hydrothermal ore deposits

Bons, Paul D.; Fußwinkel, Tobias; Gomez‐Rivas, Enrique; Markl, Gregor; Wagner, Thomas; Walter, Benjamin F.

doi:10.1130/g35708.1

Cited by 92 publications

(54 citation statements)

References 32 publications

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“…However, such a system can only work when the fluid pressure gradient is close to hydrostatic. Otherwise, fluids will not be delivered at high pressures (see discussion in Bons et al 2012;Bons & Gomez-Rivas 2013;Bons et al 2014). Alternatively, other mechanisms that can account for the release of overpressured and hot fluids from below are: (a) fluids resulting from dehydration reactions (e.g.…”

Section: Potential Mechanisms Of Overpressured Fluid Flowmentioning

confidence: 99%

Activation of stylolites as conduits for overpressured fluid flow in dolomitized platform carbonates

Martín‐Martín

Gomez‐Rivas

Gómez‐Gras

et al. 2017

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Section: Potential Mechanisms Of Overpressured Fluid Flowmentioning

confidence: 99%

Activation of stylolites as conduits for overpressured fluid flow in dolomitized platform carbonates

Martín‐Martín

Gomez‐Rivas

Gómez‐Gras

et al. 2017

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“…Such "mobile hydrofractures" thus propagate together with their contained fluid and can reach velocities in the order of m/s [16,22,23]. Possible fluid sources which may generate the necessary fluid pressure for hydraulic brecciation and hydraulic fracturing are fluid released by igneous intrusions [24], fluid release due to decompression [25,26] or mineral dehydration reactions [27]. Dehydration of the mineral biotite appears to be the main fluid source in case of Hidden Valley [4].…”

Section: Introductionmentioning

confidence: 99%

Transport efficiency and dynamics of hydraulic fracture networks

2015

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Intermittent fluid pulses in the Earth's crust can explain a variety of geological phenomena, for instance the occurrence of hydraulic breccia. Fluid transport in the crust is usually modeled as continuous Darcian flow, ignoring that sufficient fluid overpressure can cause hydraulic fractures as fluid pathways with very dynamic behavior. Resulting hydraulic fracture networks are largely self-organized: opening and healing of hydraulic fractures depends on local fluid pressure, which is, in turn, largely controlled by the fracture network. We develop a crustal-scale 2D computer model designed to simulate this process. To focus on the dynamics of the process we chose a setup as simple as possible. Control factors are constant overpressure at a basal fluid source and a constant "viscous" parameter controlling fracture-healing. Our results indicate that at large healing rates hydraulic fractures are mobile, transporting fluid in intermittent pulses to the surface and displaying a 1/f α behavior. Low healing rates result in stable networks and constant flow. The efficiency of the fluid transport is independent from the closure dynamics of veins or fractures. More important than preexisting fracture networks is the distribution of fluid pressure. A key requirement for dynamic fracture networks is the presence of a fluid pressure gradient.

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“…These deposits are fault-and fracture-hosted veins and seem to be directly linked to brittle deformation processes. Formation ages indicate hydrothermal activity in the Black Forest area since Variscan times, with a peak in the Jurassic (Bons et al 2014). But NNE alignment of the veins close to the escarpment fault may also indicate correlation of Cenozoic rifting and origin of hydrothermal circulation along this fault.…”

Section: Geological Setting At the Wilhelminenstollenmentioning

confidence: 99%

“…This may indicate that hydrothermal circulation and mineral precipitation took place at both conjugated shear angles during active normal faulting. The epigenetic ore deposits in the study area mainly consist of lead-bearing quartz-barite veins and were formed by mixture of fluids of different origin (Bons et al 2014;Kneer 2006). The distribution of the inflow of water into the tunnel and the high Ba concentration of 442.3 µg L −1 indicate a clear link between the barite-filled fractures and fluid pathways.…”

Section: Geological Setting At the Wilhelminenstollenmentioning

confidence: 99%

“…On the local scale, detailed geochemical studies of post-Variscan mineralised veins indicate a mixture of ascending and descending fluids during mineral formation in fault zones (e.g. Bons et al 2014). Radiometric dating of minerals originating from hydrothermal alteration of crystalline basement rocks and Permo-Triassic cover rock successions as well as of minerals originating from fault-related, mineralised veins reveal multiple and complex postVariscan phases of pervasive and localised fluid-rock interactions (Brockamp et al 2015;Zuther and Brockamp 1988;Glodny and Grauert 2009).…”

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confidence: 99%

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Criteria and geological setting for the generic geothermal underground research laboratory, GEOLAB

et al. 2016

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High flow rate injection and related hydromechanical interaction are the most important factors in reservoir development of Enhanced Geothermal Systems (EGS). GeoLaB, a new generic geothermal underground research laboratory (URL), is proposed for controlled high flow rate experiments (CHFE) to address limited comprehension of coupled processes connected to EGS reservoir flow conditions. As analogue for typical EGS development, CHFE require specific hydromechanical conditions including a connected fracture network in crystalline basement rock, sufficient hydraulic fracture transmissivities, a strike-slip to normal faulting tectonic regime, controllable hydraulic boundary conditions, and hydrothermal alteration fracture fillings that improve conditions for hydromechanical interaction. With the aim to identify most appropriate areas for future site selection, four criteria have been established based on the EGS reference site of Soultz. Two URLs in crystalline basement worldwide approximate the requirements of a new generic GeoLaB and may be used for accompanying experimentation. Besides favourable geological, hydraulic, and stress conditions, the vicinity to long-term EGS production favours the southern Black Forest as potential region for GeoLaB. Therefore, an exemplary site assessment has been carried out at "Wilhelminenstollen" in the southern Black Forest (Germany). New remote sensing, hydrochemical, and geophysical analyses as well as reactivation potential, and stress modelling were added to complement existing geological and hydrogeological information. At this site, reactivation potential analysis reveals two local maxima prone for shear reactivation as strike-slip faults. The highest lineament density is observed for the N110°E strike direction that is associated with both slip and dilation tendency maxima. Clay minerals occur in fractures and the matrix. Local, partly water-bearing fractures, when partly filled with ore minerals, were connected to veins in the tunnel using shallow geophysical methods. Hydrochemical data reveal infiltration of the tunnel water from at least 500 m above the tunnel. The results suggest a crystalline basement with a fracture network that is regionally connected and water-conducting. Hydraulic conductivity in the southern Black Forest granite is estimated to amount to about 4.5·10 −8 m s −1 at 500 m depth. The hydraulic boundary conditions exclude unknown drainage. Analyses of the influence of topography on orientation and magnitude of the maximum stress indicate a minimum overburden of about 500 m for regional reactivation to be valid. In conclusion, the southern Black Forest and in particular "Wilhelminenstollen" offers favourable condition for CHFE. Final decision on the GeoLaB site is to be drawn from forthcoming exploration wells.

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Fluid mixing from below in unconformity-related hydrothermal ore deposits

Cited by 92 publications

References 32 publications

Activation of stylolites as conduits for overpressured fluid flow in dolomitized platform carbonates

Activation of stylolites as conduits for overpressured fluid flow in dolomitized platform carbonates

Transport efficiency and dynamics of hydraulic fracture networks

Criteria and geological setting for the generic geothermal underground research laboratory, GEOLAB

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