Pressure fluctuations, phase separation, and gold precipitation during seismic fracture propagation

Wilkinson, Jamie J.; Johnston, Joseph

doi:10.1130/0091-7613(1996)024<0395:pfpsag>2.3.co;2

Cited by 148 publications

(75 citation statements)

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“…The trapping pressure of these fluid inclusions is lower than from inclusions from the other assemblage types. Similar trapping mechanisms have been reported by Wilkinson and Johnston (1996) for gold mineralization in western Ireland. Mapping at Telfer revealed structures such as horizontal extension and shear veins with dilatant jogs along bedding plane (Hewson, 1996, Miller and Batt, pers. comm.)…”

Section: Precipitation Mechanism and Fluid Dynamicssupporting

confidence: 85%

“…The fluid overpressure at one point can trigger the failure of faults with a rapid decrease in pressure leading to phase separation of the ore forming fluid and precipitation of metals (c.f., Sibson et al, 1988;Wilkinson and Johnston, 1996). Fluid inclusion assemblage type 3 represents fluid inclusions trapped during phase separation of ascending hydrothermal fluids during fault failure (Fig.…”

Section: Precipitation Mechanism and Fluid Dynamicsmentioning

confidence: 99%

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Magmatic Hydrothermal Fluids at the Sedimentary Rock-Hosted, Intrusion-Related Telfer Gold-Copper Deposit, Paterson Orogen, Western Australia: Pressure-Temperature-Composition Constraints on the Ore-Forming Fluids

et al. 2016

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The Neoproterozoic Telfer A -copper deposits is located in the Paterson Orogen. Several highly differentiated calc-alkaline to alkali-calcic peraluminous granites intruded the metasedimentary rocks near (5-20 km) Telfer contemporaneous with structurally controlled gold-copper mineralization.Fluid inclusion assemblages with different fluid inclusion types were identified in samples from a range of different vein types. These inclusion types range from three phase aqueous Laq+Vaq+Shalite, high salinity N C C inclusions to two phase aqueous or two phase aqueous carbonic, low to moderate salinity (2 -22 wt % NaCl equiv.), moderate to high 480°C) fluid inclusions.Fluid inclusion trapping mechanisms, and interpreted precipitation mechanisms for gold and copper include: (1) This interpretation is supported by the observation that the highest base metal contents occurs in the highest salinity fluid inclusion.Potassium/Ca ratios of >1 in most assemblages, the high homogenization C in many fluid inclusion assemblages, and the high trace element contents (e.g., Fe, Mg, K, Na) in most of the fluid inclusion assemblages is compatible with

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Section: Precipitation Mechanism and Fluid Dynamicssupporting

confidence: 85%

Section: Precipitation Mechanism and Fluid Dynamicsmentioning

confidence: 99%

Magmatic Hydrothermal Fluids at the Sedimentary Rock-Hosted, Intrusion-Related Telfer Gold-Copper Deposit, Paterson Orogen, Western Australia: Pressure-Temperature-Composition Constraints on the Ore-Forming Fluids

et al. 2016

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“…At Croagh Patrick auriferous quartz veins are associated with shear zones in greeschist facies quartzites. Gold deposition was associated with unmixing of a H 2 O-CO 2 -NaCl fluid at 240 to 320°C (Wilkinson and Johnston, 1996).…”

Section: Orogenic Goldmentioning

confidence: 99%

Atypical Gold Mineralization in an Orogenic Setting--The Bohaun Deposit, Western Irish Caledonides

et al. 2011

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The Bohaun gold deposit in County Galway, western Ireland is located in the Caledonian orogenic belt, proximal to a major accretionary boundary. The mineralization is hosted in a normal extensional fault, representing a zone of repeated extension and vein infilling of open cavities, within clastic sedimentary rocks, which have only reached the late diagenetic zone of low-grade metamorphism.The mineralization consists of undeformed veins, stockworks and breccias. Quartz dominates all the veins and commonly displays multiple growth stages and a variety of classic epithermal textures, including comb, plumose and banded, indicative of low confining pressures. The veins have a simple mineralogy comprising quartz-sericite-chlorite with minor sulfides, hematite, rare visible gold, with a high silver content (up to 41 wt %), and late barite and dolomite.Vein quartz is associated with two fluids compositions: Type I with moderate to high salinity (8.0-23.6 wt % NaCl equiv) and Type II with low to moderate salinity (0.0-7.8 wt % NaCl equiv). CO 2 contents in both fluid types are <3.5 wt percent. The majority of fluid inclusion homogenization temperatures range from 126 to 257 o C and geologically constrained depth estimates (≤5 km) indicate maximum fluid inclusion trapping temperatures between 175 and 245°C.The geodynamic setting of Bohaun, which comprises a deformed continental margin of an allochthonous terrane, is typical of orogenic gold deposits. However, an orogenic association for the Bohaun mineralization is discounted on the basis of fluid inclusion evidence, atypical vein textures, gold grain composition and undeformed veins. While vein textures locally resemble those found in epithermal quartz-adularia mineralization, there is no obvious magmatic association and alteration is restricted to the veins and immediate host rocks. The origin of the gold at Bohaun remains enigmatic. However, we favor an association with widespread Carboniferous or later mineralizing fluids and a model which involves transport and deposition of gold from a basinal brine type fluid, in a similar fashion to red-bed Au-Pd mineralization. Bohaun provides further evidence that low temperature brines may be capable of generating economic grade gold mineralization, independent of other fluids.3

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“…Au is almost always found within sulphides and so this is an unusual scenario that would require detailed high resolution microscopy (TEM for example) to image any Au-sulphide association and is beyond the scope of this study. The effects of extreme pressure cycling in gold deposits often caused by seismic events (Sibson et al, 1988;Wilkinson and Johnson, 1996;Weatherley and Henley, 2013) are clearly associated with the initiation and efficacy of the mineralising process. The increasing metal concentrations are a reflection only of the effectiveness of the mineralising process at different locations and/or times.…”

Section: Deposition Of Gold and Silvermentioning

confidence: 99%

The importance of supersaturated silica deposition for base-metalAu–Ag mineralisation in western Turkey

Bozkaya¹,

Banks²

2015

Turkish J Earth Sci

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In the Arapuçandere LS-IS epithermal deposit in western Turkey, either well crystallised euhedral quartz or milky amorphous silica occurrences are associated with the precious and base-metal mineralisation. This study has determined the relative importance of the processes precipitating both of these in relation to the deposition of the ore. Analysis by LA-ICPMS of euhedral quartz and amorphous silica show that the latter is associated with much higher metal concentrations and suggests that the process responsible is more important for deposition of ore in the deposit. Mineralisation at Kumarlar and Koru may be similar. Slow cooling precipitates euhedral quartz and some ore but flashing of hydrothermal fluids causes drastic decreases in both T and P, sufficient to quantitatively deposit base metals and Au. In amorphous silica bands base metals reach concentrations of 1000's of ppm compared with a few 10's ppm in euhedral quartz; Au can reach over 1 ppm compared with a few 10's ppb in quartz. The drastic pressure change from lithostatic to sub-hydrostatic could reasonably be caused by opening of faults and fractures by seismic events.

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Pressure fluctuations, phase separation, and gold precipitation during seismic fracture propagation

Cited by 148 publications

References 0 publications

Magmatic Hydrothermal Fluids at the Sedimentary Rock-Hosted, Intrusion-Related Telfer Gold-Copper Deposit, Paterson Orogen, Western Australia: Pressure-Temperature-Composition Constraints on the Ore-Forming Fluids

Magmatic Hydrothermal Fluids at the Sedimentary Rock-Hosted, Intrusion-Related Telfer Gold-Copper Deposit, Paterson Orogen, Western Australia: Pressure-Temperature-Composition Constraints on the Ore-Forming Fluids

Atypical Gold Mineralization in an Orogenic Setting--The Bohaun Deposit, Western Irish Caledonides

The importance of supersaturated silica deposition for base-metalAu–Ag mineralisation in western Turkey

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