Earthquake faulting, induced fluid flow, and fault-hosted gold-quartz mineralization

Sibson, Richard H.

doi:10.1007/978-94-011-1614-5_42

Cited by 21 publications

(11 citation statements)

References 35 publications

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“…A vast literature on all aspects of fluid flow and geomechanics related to faults exists (Phillips, 1972;Knipe et al, 1988;Sibson, 1990Sibson, , 1992Sibson, , 2000Knipe, 1993;P. Gretener, 1996, personal communication;Fleming et al, 1998;Connolly and Cosgrove, 1999a, b;Eichhubl and Boles, 2000), going well beyond the scope of this article.…”

Section: Fluid Flow and Faultingmentioning

confidence: 94%

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Structurally controlled hydrothermal dolomite reservoir facies: An overview

Davies¹,

2006

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Section: Fluid Flow and Faultingmentioning

confidence: 94%

“…aquifers ( Figure 7) below platformal limestone sequences. This may allow periodic fluid recharge (fault valve: Sibson, 1990Sibson, , 1992 into the episodically active fault. 5.…”

Section: Strike-slip (Wrench) Preferencementioning

confidence: 99%

Structurally controlled hydrothermal dolomite reservoir facies: An overview

Davies¹,

2006

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“…[11] Samples were collected from several sites (Figure 2a) near two major faults in California: Little Pine fault and San Gabriel fault that were recently uplifted and exposed. This sampling was supplemented by collecting country rock samples within the Mother Lode vein system presumed to be associated at depth with fault-valve activity [Sibson et al, 1988]. These various examples allowed observation of crack sealing in rocks brought up from depths of several kilometers.…”

Section: Observation Of Natural Crack Sealing Mechanisms Near Active mentioning

confidence: 99%

Modeling fluid transfer along California faults when integrating pressure solution crack sealing and compaction processes

2003

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[1] Several models pertaining to earthquake cycles imply intermittent fluid flow through fault. During the interseismic period, increase in fluid pressure from hydrostatic to lithostatic values is a crucial parameter in mechanisms leading to earthquakes. To achieve such pressures, geodynamic processes (gouge compaction, fluid flow) and changes in permeability are required. Previous models have postulated that changes in permeability (by self-healing) are faster than the effects of geodynamic processes. We consider the different mechanisms and rates of crack sealing near active fault on the examples of uplifted Californian faults. We find that natural crack sealing is normally not achieved by a rapid self-healing process. Pressure solution, with mass transfer from solution cleavage to cracks, appears to be a more important mechanism for crack sealing and creep during postseismic deformation. The geometry of transfer path and experimental data have been used to model crack sealing rates by pressure solution which are estimated to be rather slow, similar to the recurrence time of some earthquakes. Such slow changes in permeability may be crucial factors in controlling the increase in fluid pressure and, consequently, the mechanism of critical failure in faults. Then, numerical modeling of fluid pressure and transfer around active faults has been performed integrating a slow change in permeability by crack sealing, gouge compaction, and fluid flow from depth. This modeling shows various location and evolution of fluid overpressure during the interseismic period depending on these processes and allows one to estimate the amount of fluid transferred from depth during interseismic periods.

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“…The main mechanism cited for the spatial distribution of gold mineralization at Round Hill is one of differential stresses imposed on the intrashear pelite during thrusting, causing variable scales of extension, or dilational jogs, and thus forming favorable depositional sites (Angus, 1993;Sibson, 1997). This is consistent, on a local scale, with higher concentrations of gold found in stockwork and ramp veins over flat veins.…”

Section: Discussionmentioning

confidence: 92%

Round Hill Shear Zone-Hosted Gold Deposit, Macraes Flat, Otago,New Zealand: Evidence of a Magmatic Ore Fluid

Ronde¹,

Faure²,

Bray³

et al. 2000

Economic Geology

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The 0.8-Moz Round Hill shear zone-hosted gold deposit is one of several located on, or near, the Hyde-Macraes shear zone, Macraes Flat, New Zealand. Field relationships show stockwork veins are the oldest part of the hydrothermal system, followed by flat and ramp veins. Hanging-wall shear veins formed early but have been modified by late deformation.Fluid inclusion microthermometric results for dominant type I inclusions show that flat and ramp veins have the same average wt percent NaCl equiv values (2.2 ± 0.6%) and were precipitated from the same fluid. Salinity data for these veins overlap with those from hanging-wall veins (average 1.3 ± 0.3%) and stockwork veins (1.6 ± 0.6% for vein margins; 0.9 ± 0.3% for vein centers), although both of the latter trend toward lower overall wt percent NaCl equiv values, suggesting mixing between relatively dilute and more saline end members. All of the above veins have similar temperatures of homogenization (T h ), ranging between 110°and 188°C. Fluid inclusion trapping temperatures are considered to be ~300°C, equating to a ~10-km depth of formation. Carbon dioxide dissolved in the hydrothermal fluid is responsible for up to one third of fluid inclusion apparent salinities. Stockwork and hanging-wall veins thus have true salinities of <1 wt percent NaCl equiv (<0.17 molal) and flat and ramp veins have true salinities of <2 wt percent (<0.34 molal).Fluid inclusion volatiles from Round Hill and other Macraes deposits are dominated by H 2 O (99.02-99.69 mol %), with lesser CO 2 (0.14-0.76 mol %), N 2 (0.03-0.32 mol %), and CH 4 (0.06-0.17 mol %). Noticeable concentrations of hydrocarbons occur in many of the samples. Fluid inclusion cation and anion data show few components of relatively low concentration are dissolved in the hydrothermal fluid, consistent with CO 2corrected microthermometric measurements.A range in fluid inclusion δD H 2 O values obtained for the Round Hill deposit is coincident with the different vein types and also indicates mixing between two fluids. One fluid is considered to be O isotope shifted meteoric water, as trapped by the early stockwork veins, and has the lowest δD H 2 O values of -80 per mil. The other fluid is represented by flat and/or ramp and hanging-wall veins that have δD H 2 O values up to -40 per mil. The Macraes δD H 2 O data show a trend toward the magmatic water end member for geothermal systems associated with convergent plate boundaries and are consistent with a 25 to 50 percent magmatic component in the Macraes hydrothermal system.

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Earthquake faulting, induced fluid flow, and fault-hosted gold-quartz mineralization

Cited by 21 publications

References 35 publications

Structurally controlled hydrothermal dolomite reservoir facies: An overview

Structurally controlled hydrothermal dolomite reservoir facies: An overview

Modeling fluid transfer along California faults when integrating pressure solution crack sealing and compaction processes

Round Hill Shear Zone-Hosted Gold Deposit, Macraes Flat, Otago,New Zealand: Evidence of a Magmatic Ore Fluid

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