Post‐magmatic hydrothermal circulation and the origin of base metal mineralization, Cornwall, UK

Gleeson, Sarah A.; Wilkinson, Jamie J.; Shaw, H. F.; Herrington, Richard

doi:10.1144/jgs.157.3.589

Cited by 34 publications

(23 citation statements)

References 25 publications

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“…at $5 km depth) during the early Mesozoic. Fluid inclusion studies indicate that much of the mineralisation occurred when the present land surface was at $3-4 km depth (Gleeson et al, 2000).…”

Section: Introductionmentioning

confidence: 96%

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Cenozoic uplift of southwest England

Westaway

2010

J Quaternary Science

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The uplift history of southwest England is inferred using a composite dataset including marine and fluvial terraces and karstic data. The estimated post-Mid-Pliocene uplift increases eastward from $130 m in west Cornwall and $135 m in south Devon to $150 m in the Hampshire Basin. The post-Early-Pleistocene uplift likewise increases eastward, from $55 m in west Cornwall to $60 m in south Devon and $80 m in Hampshire. Landscape and thermochronological evidence also indicates Eocene uplift, caused by the British Tertiary Igneous Province magmatism; this component tapers eastward from $300 m in west Cornwall to $50 m in south Devon, with subsidence in east Devon. This uplift accompanied magmatic underplating; the mafic layer added to the basal crust thins eastward from $6 km in west Cornwall to $2 km in south Devon, evidently tapering to zero farther east. The laterally variable crustal properties caused by this variation in underplating have affected the post-MidPliocene uplift; the study region is thus intermediate, in terms of crustal strength and landscape evolution, between central-southern England, with no underplating, and Ireland, where $10 km thick underplating has resulted in extreme Late Cenozoic landscape stability. The Eocene mantle-plumerelated uplift is distinct from the post-Mid-Pliocene phase which, the modelling indicates, has been driven by surface processes and, thus, by climate change.

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Section: Introductionmentioning

confidence: 96%

“…The region's metalliferous mineralisation is thought to have occurred over tens of millions of years following this intrusion, as a result of hydrothermal circulation driven by the radioactive heat production in the granite (e.g. Stone and Exley, 1986;Gleeson et al, 2000;cf. Clark et al, 1993).…”

Section: Introductionmentioning

confidence: 99%

Cenozoic uplift of southwest England

Westaway

2010

J Quaternary Science

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“…The salinity of aqueous inclusions that show final ice melting at the eutectic, and have hydrohalite as the final solid phase (e.g. Gleeson et al, 2000), is likely to be reasonably approximated by the algorithm. Because of the solute--independent nature of the metastability (Fig.…”

Section: Application Of the Metastable Freezing Methods For Estimationmentioning

confidence: 99%

Metastable Freezing: A New Method for the Estimation of Salinity in Aqueous Fluid Inclusions

Wilkinson

2017

Economic Geology

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On cooling during microthermometry, fluid inclusions invariably supercool before freezing under disequilibrium (metastable) conditions to form ice and hydrates. Measurements of fluid inclusions from the Irish Zn--Pb hydrothermal system reveal a strong linear correlation (R 2 = 0.968) between final ice melting temperature (TmI) and metastable freezing temperature (Tmf) of the form: TmI = 0.563 Tmf + 22.7 (+1.5/--3.5) The relationship is shown to be independent of heating--freezing stage model, host mineral, and largely of inclusion size, but is affected by the presence of CO2 and by cooling rate. The correlation shows that metastable freezing is predictable and in fact, in small droplets of pure solution, occurs at a well--defined, salinity--dependent temperature referred to as the homogeneous freezing point. This relationship allows salinity to be estimated in fluid inclusions where the optical recognition of final ice melting is not possible due to small inclusion size or cloudy samples, or where inclusions go into a metastable, vapor--absent, state because of collapse of the bubble on freezing. Using a cooling rate of 50°C/min, inclusion salinity is given by:Salinity (wt% NaCl equivalent) = --69.7 --2.617Tmf --0.02603Tmf 2 --0.0000994Tmf 3 The homogeneous freezing point is controlled by an equilibrium thermodynamic property related to the activity of water. In small droplets of pure solution, as approximated by fluid inclusions, freezing will occur when the water activity is 0.305 above that of the stable ice melting condition at the same temperature, independent of solute type. "Early" metastable freezing, at a temperature above the homogeneous freezing point may occur in very large inclusions, or those containing "seed" particles or CO2. In such cases, the salinity will be underestimated by the equation above. Introduction Fluid inclusion microthermometry has been long established as the only direct method for constraining the properties of paleofluids in the Earth's crust (e.g. Roedder, 1967a). In particular, the ability to constrain fluid density, trapping temperature and pressure, solute and volatile contents has provided many important tests of genetic models for hydrothermal ore formation (Roedder and Bodnar, 1997). It is also the basis for the more advanced techniques such as laser ablation ICP--MS that are providing fundamental new insights into metal transport and deposition from ore--forming fluids (e.g. Audetat et al., 1998Audetat et al., , 2008Heinrich et al., 1999;Ulrich et al., 1999;Wilkinson et al., 2009;Kouzmanov and Pokrovski, 2012).The basic principles of microthermometry by which fluid inclusions are investigated using a heating--freezing stage are well established (e.g. Roedder, 1984;Shepherd et al., 1985). Total homogenisation temperatures, typically by liquid--vapor homogenisation, can provide minimum constraints on trapping pressure and temperature. Measurements of halite, hydrate and ice melting temperatures can be used to estimate fluid salinity, assuming simple model systems...

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“…The crystals are strongly growth banded, with opaque and clear zones defined by the presence or absence of fluid inclusions. The fluid inclusions within a given growth zone are dominated by one population of primary inclusions and, thus, are suitable for bulk fluid inclusion studies (Gleeson et al, 2000). Microthermometric data suggests the quartz veins formed at temperatures of c. 200°C from dilute (0-5 wt% NaCl equiv.)…”

Section: Vein E-w Vein Samplesmentioning

confidence: 99%