Factors controlling free thermal convection in faults in sedimentary basins: implications for the formation of zinc–lead mineral deposits

Yang, Jianwen; Large, Ross R.; Bull, SW

doi:10.1111/j.1468-8123.2004.00084.x

Cited by 57 publications

(51 citation statements)

References 30 publications

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“…However, when both faults only penetrate down to 10 km deep as discussed in the forth case study, a 'reversed' recharge-discharge pattern of hydrothermal fluid flow developed. The factors causing this change are not fully understood; nevertheless they are more likely controlled by the basin architecture and its spatial relation with the faults (e.g., Yang et al [13] ). Although noticing the fact that one fault behaves as the recharge conduit and the other as the discharge conduit, or vice versa, we do not intend to investigate the exact reasons leading to a certain recharge-discharge pattern of fluid flow.…”

Section: Discussionmentioning

confidence: 98%

“…Grid discretization of the faults can be found in Figure 1(b). Similar general geological structure of the Mount Isa-McArthur basin region has been also used in previous fluid flow models [12][13][14]18,22,23] . Like in the previous studies [22,23] , Fault 1 on the left is equivalent to the Mount Isa fault system, and Fault 2 on the right simulates a fault zone to farther north, such as the Termite Range fault at the Century deposit.…”

Section: Governing Equations and Finite Element Modelingmentioning

confidence: 98%

“…In addition, we assume c w =4174 J·kg −1 ·℃ −1 , c s =800 J·kg −1 · ℃ −1 , λ w =0.5 W·m −1 · ℃ −1 , ρ s =2630 kg/m 3 , ρ 0 =1000 kg/m 3 , and φ=10%. The upper boundary beside the faults, maintained at 20℃ following the previous numerical studies [12][13][14]18] , is at the seafloor and permeable to fluid flow. Over the top of the faults, the vertical temperature gradient is fixed at zero.…”

Section: Conceptual Hydrological Modelmentioning

confidence: 99%

“…framework for regional-scale fluid flow. The permeabilities and thermal conductivities assigned to the stratigraphic elements and faults are given in Table 1, following the previous numerical investigations in the Mount Isa-McArthur basin region [13,14,18,22,23] . We assume that the vertical permeability of the host rocks is two orders of magnitude less than the horizontal one due to bedded and stratified nature of these sedimentary rocks.…”

Section: Conceptual Hydrological Modelmentioning

confidence: 99%

“…Their numerical results exhibit a dominant recharge-discharge pattern controlled by syn-sedimentary faults and a subsurface sandstone aquifer. Yang et al [13] simulated timedependent fluid flow and developed criteria for efficient identification of potentially mineralizing discharge faults in sedimentary basis, and more recently Yang et al [14] investigated the effect of salinity on ore-forming processes and fluid flow patterns.…”

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confidence: 99%

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On the role of buoyancy force in the ore genesis of SEDEX deposits: Example from Northern Australia

Yang

Feng

et al. 2009

Sci. China Ser. D-Earth Sci.

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Finite element modeling on a highly conceptualized 2-D model of fluid flow and heat transport is undertaken to simulate the paleo-hydrological system as if the Mount Isa deposits were being formed in the Mount Isa basin, Northern Australia, and to evaluate the potential of buoyancy force in driving basin-scale fluid flow for the formation of sedimentary-exhalative (SEDEX) deposits. Our numerical case studies indicate that buoyancy-driven fluid flow is controlled mainly by the fault penetration depth and its spatial relation with the aquifer. Marine water recharges the basin via one fault and flows through the aquifer where it is heated from below. The heated metalliferous fluid discharges to the basin floor via the other fault. The venting fluid temperatures are computed to be in the range of 115 to 160℃, with fluid velocities of 2.6 to 4.1 m/year over a period of 1 Ma. These conditions are suitable for the formation of a Mount Isa-sized zinc deposit, provided a suitable chemical trap environment is present. Buoyancy force is therefore a viable driving mechanism for basin-scale ore-forming hydrothermal fluid migration, and it is strong enough to lead to the genesis of supergiant SEDEX deposits like the Mount Isa deposit, Northern Australia. hydrothermal fluid flow, finite element modeling, SEDEX deposits, Mount Isa basinSedimentary-exhalative (SEDEX) deposits are a major source of lead and zinc, and an important source of silver. On the global scale, they account for about 40% of zinc production and about 60% of lead production [1] . Geological and sulphide paragenetic studies suggest that this type of deposits may be formed by hydrothermal exhalative processes of metal-bearing brines discharging onto the basin floor. Despite this general understanding, geologists continue to debate the mechanisms of fluid migration, heat flow and mass transport for ore deposition.Several factors have been deemed responsible for basin-scale fluid flow, including topography, compaction, buoyancy, and deformation [2] . Among these, buoyancy driven flow is potentially of great importance because it can lead to fluid flow and mass transport over large distances and significantly shorter time scales, compared with diffusion alone. This is because diffusion results from molecular collision, representing a micro-scale process. In certain circumstances, buoyancy may become even more important than other forces in enhancing hydrodynamic mixing of the dense fluid with the less dense ambient groundwater [3] .A buoyancy force results from variations in fluid density due to spatial and temporal changes in temperature and salinity. Buoyancy driven fluid circulation is commonly termed free convection because of the lack of external inputs and outputs [4] . The importance of this type of fluid flow has long been recognized in mid-ocean ridge hydrothermal systems [5,6] , seawater intrusion [7,8] , and solute transport [9,10] . Recently, buoyancy-

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Section: Discussionmentioning

confidence: 98%

Section: Governing Equations and Finite Element Modelingmentioning

confidence: 98%

Section: Conceptual Hydrological Modelmentioning

confidence: 99%

Section: Conceptual Hydrological Modelmentioning

confidence: 99%

mentioning

confidence: 99%

See 3 more Smart Citations

On the role of buoyancy force in the ore genesis of SEDEX deposits: Example from Northern Australia

Yang

Feng

et al. 2009

Sci. China Ser. D-Earth Sci.

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Electrical imaging and fluid modeling of convective fingering in a shallow water-table aquifer

et al. 2014

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Unstable density-driven flow can lead to enhanced solute transport in groundwater. Only recently has the complex fingering pattern associated with free convection been documented in field settings. Electrical resistivity (ER) tomography has been used to capture a snapshot of convective instabilities at a single point in time, but a thorough transient analysis is still lacking in the literature. We present the results of a 2 year experimental study at a shallow aquifer in the United Arab Emirates that was designed to specifically explore the transient nature of free convection. ER tomography data documented the presence of convective fingers following a significant rainfall event. We demonstrate that the complex fingering pattern had completely disappeared a year after the rainfall event. The observation is supported by an analysis of the aquifer halite budget and hydrodynamic modeling of the transient character of the fingering instabilities. Modeling results show that the transient dynamics of the gravitational instabilities (their initial development, infiltration into the underlying lower-density groundwater, and subsequent decay) are in agreement with the timing observed in the time-lapse ER measurements. All experimental observations and modeling results are consistent with the hypothesis that a dense brine that infiltrated into the aquifer from a surficial source was the cause of free convection at this site, and that the finite nature of the dense brine source and dispersive mixing led to the decay of instabilities with time. This study highlights the importance of the transience of free convection phenomena and suggests that these processes are more rapid than was previously understood.

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Heat and Fluid Transport Induced by Convective Fluid Circulation Within a Fracture or Fault

Patterson¹,

Driesner²,

Matthäi

et al. 2018

JGR Solid Earth

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Natural water convection in subvertical fractures, fracture zones, or faults can perturb the temperature field around the fracture and enhance and focus vertical heat flow within. We investigate, by means of numerical simulation, the effects of convection in a deeply buried vertical fracture zone. Fracture zone transmissivity, defined as permeability times thickness of the permeable region, is found to be the primary control on convection style rather than fracture zone thickness or permeability alone. In an impermeable host rock, the convection‐induced thermal anomaly propagates solely via conduction, diminishing away from the fracture. Convective heat flow increases with fracture transmissivity up to ~10−8 m3, when a plateau in convective heat flow is reached, constrained by fracture size and the host rock's thermal conductivity. Permeable host rocks modify these results significantly. In a moderately permeable host rock (10−14 m2), convection in the fracture induces non‐Rayleigh fluid convection, while thermal effects and fluid exchange between host rock and fracture remain moderate. If the host rock is sufficiently permeable to allow porous medium Rayleigh convection to occur (10−13 m2), the convection patterns within the fracture are overprinted by the host's convective patterns. Fluid exchange between the fracture and the rock will be significant. Our findings provide insight into how thermal anomalies in the uppermost crust may relate to locally enhanced heat flow from convection in nonoutcropping fractures below. Furthermore, the results for permeable host rocks provide evidence for previously inferred hydrologic scenarios for the formation of certain hydrothermal, vein‐type mineral deposits.

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Factors controlling free thermal convection in faults in sedimentary basins: implications for the formation of zinc–lead mineral deposits

Cited by 57 publications

References 30 publications

On the role of buoyancy force in the ore genesis of SEDEX deposits: Example from Northern Australia

On the role of buoyancy force in the ore genesis of SEDEX deposits: Example from Northern Australia

Electrical imaging and fluid modeling of convective fingering in a shallow water-table aquifer

Heat and Fluid Transport Induced by Convective Fluid Circulation Within a Fracture or Fault

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