The Chemical Composition of Metasomatic Fluids in the Crust

Yardley, B. W. D.

doi:10.1007/978-3-642-28394-9_2

Cited by 21 publications

(21 citation statements)

References 121 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Yardley, 2013) shows the variation in the K/Na ratios of crustal fluids and demonstrates a particularly large range in the composition of formation waters. Brines derived by dissolution of evaporites have very low K contents and K/Na ratios, while bittern brines have exactly the opposite characteristics.…”

Section: Mass-limited Fluidsmentioning

confidence: 99%

“…Not all the fluids are from host rocks that contained coexisting plagioclase and K-feldspar, but while the high temperature data generally follow the equilibrium trend, sedimentary formation brines can deviate from it very significantly according to their origin and whether they have been able to interact with sufficient feldspar in the subsurface. As a result, different basinal brines could cause either albitisation or K-feldspathisation in the sub-surface (modified from Yardley, 2013).…”

Section: Figure 212mentioning

confidence: 99%

“…Aqueous fluids from these sources can carry dissolved loads exceeding 25 wt% and can continuously exchange with the wall rock as the fluid:rock system attempts to maintain equilibrium as fluids move. Metasomatic modification of rock compositions by moving fluids (infiltration metasomatism) occurs in a wide range of settings, although primarily in the upper crust, where fluid fluxes are largest (Yardley, 2013). Any fluid that moves from one rock type into another with contrasting mineralogy, or simply flows along a single unit to a region with different temperature and pressure, will react with the wall rocks along the way, causing metasomatism.…”

Section: Geological Settings Of Crustal Fluidsmentioning

confidence: 99%

“…An example of how prograde metamorphic fluids evolve from basin brines by continuing cation exchange and release (occasionally incorporation) of water or gases is provided by the low-grade metamorphic fluids in the emerald-bearing veins from Colombia (Banks et al, 2000). These have Br-poor signatures typical of basinal brines derived from halite dissolution, but show more evidence of cation exchange with their host rocks compared to most basinal fluids (Yardley, 2013;Fig. 4.4), for example they are much richer in Ca than sedimentary brines with comparable Br/Cl ratios.…”

Section: Metamorphic Fluidsmentioning

confidence: 99%

See 3 more Smart Citations

Fluids in the Continental Crust

Yardley¹,

Bodnar²

2014

GeochemPersp

222

View full text Add to dashboard Cite

Section: Mass-limited Fluidsmentioning

confidence: 99%

Section: Figure 212mentioning

confidence: 99%

Section: Geological Settings Of Crustal Fluidsmentioning

confidence: 99%

Section: Metamorphic Fluidsmentioning

confidence: 99%

See 2 more Smart Citations

Fluids in the Continental Crust

Yardley¹,

Bodnar²

2014

GeochemPersp

222

View full text Add to dashboard Cite

“…If sediments containing such concentrated brines begin to undergo metamorphism, it seems likely that the brines will migrate and progressively become equilibrated with new host rocks, perhaps causing albitization or other metasomatic changes in the process. Figure 2 is from Yardley (2012) and shows the relationship between the proportion of Ca to Na in sedimentary brines and their Cl/Br ratios. Redissolved evaporite brines are very low in both Br and Ca, but low-grade metamorphic brines associated with emerald deposits from Columbia (Banks et al 2000), although clearly derived by halite dissolution (very high Cl/Br) are much richer in Ca than similar sedimentary brines.…”

Section: The Chemical Composition and Evolution Of Metamorphic Fluidsmentioning

confidence: 99%

The role of metamorphic fluids in the formation of ore deposits

Yardley

Cleverley

2013

Self Cite

View full text Add to dashboard Cite

Many ore deposits are hosted by metamorphic rocks, and metamorphic fluids have been invoked as a source for various deposits, especially gold deposits. Metamorphic fluid compositions reflect original sedimentary environment: continental shelf sequences yield saline metamorphic fluids with little dissolved gas while metasediments from accretionary and oceanic settings host less saline fluids with significant CO 2 contents.The principal difficulty in reconciling ore deposits with a metamorphic origin is that many form quickly (c. 1 Ma), whereas metamorphic heating is slow (c. 10-208/Ma). Gravitational instability means that fluid cannot be retained. Metamorphic ores may nevertheless form by: (a) segregation leading to enrichment of pre-existing concentrations; (b) infiltration of water-rich fluids from schists into marbles at high temperature overstepping decarbonation reactions and allowing fast reaction that locally draws down temperature; and (c) rapid uplift driving dehydration reactions owing to pressure drop.Some orogenic lode gold deposits fit well with a purely metamorphic origin during rapid uplift, but others are problematic. At Sunrise Dam, Western Australia, anomalies in Sr-isotope ratios and in apatite compositions indicate a partial mantle/magmatic source. Low salinity, H 2 O-CO 2 fluids commonly associated with hydrothermal gold reflect the effect of salt on gas solubility, not the origin of the fluid.Gold Open Access: This article is published under the terms of the CC-BY 3.0 license.Many hydrothermal ore deposits are hosted by metamorphic rocks, and so the possibility that ore deposits may form from metamorphic fluids has been discussed for many years. In this paper we will review what is known about metamorphic fluids from a chemical perspective, and the implications that this may have for their ore-forming potential, and then put this in the context of the history of regional metamorphism and the physical supply of fluid to possible ore systems. Possible natural examples of metamorphic fluids giving rise to ore deposits are also discussed with an emphasis on gold mineralization, because this is the type of mineralization for which metamorphic fluids have been most widely invoked.The term metamorphic fluid is used here in the strict sense to denote fluids present during prograde metamorphism. They will commonly include a component of pre-metamorphic formation waters as well as fluid released by breakdown of volatilebearing minerals, all modified by ongoing interactions with host rock. This definition is much more restrictive than that often used in stable isotope studies, which embraces all fluids that have isotopically equilibrated with metamorphic rocks, irrespective of their origin.Despite some clear evidence to the contrary (e.g. Roedder 1972), until recently crustal fluids were generally assumed to carry only small amounts of potential ore metal in solution. Thus the problem of understanding ore deposits was seen as one of accounting for extensive focussing of fluid flow. With the ...

show abstract

References

2012

Crustal Permeability

View full text Add to dashboard Cite

A simple predictive model of quartz solubility in water-salt-C02 systems at temperatures up to 1000 ∘ C and pressures up to 1000 MPa. Geochimica Cosmochimica Acta, 76, 1597-1608. Allen DM, Grasby SE, Voormeij DA (2006) Determining the circulation depth of thermal springs in the southern Rocky Mountain Trench, southeastern British Columbia, Canada using geothermometry and borehole temperature logs.

show abstract

The Chemical Composition of Metasomatic Fluids in the Crust

Cited by 21 publications

References 121 publications

Fluids in the Continental Crust

Fluids in the Continental Crust

The role of metamorphic fluids in the formation of ore deposits

References

Contact Info

Product

Resources

About