Stable isotope compositions of alteration fluids in low-grade Lower Palaeozoic rocks, English Lake District

Thomas, L. J.

doi:10.1180/minmag.1985.049.352.13

Cited by 14 publications

(6 citation statements)

References 24 publications

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“…17) (White et al, 1973;Magaritz and Taylor, 1976;Taylor, 1979 Clearly, the paths shown are strongly dependent on the parameters chosen for the model and are therefore only rough guides to the direction and magnitude of the isotopic shifts expected. (Halliday et al, 1980;Thomas et al, 1985) and from other published values (Savin and Epstein, 1970;Yeh, 1980;Taylor, 1979). The fractionation factors used (AR_w) are given in the Appendix.…”

Section: Implications For the Origin Of The Mineralizing Fluidsmentioning

confidence: 80%

Genesis of the Silvermines zinc-lead-barite deposit, Ireland; fluid inclusion and stable isotope evidence

Samson

Russell²

1987

Economic Geology

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The Silvermines zinc-lead-barite deposit occurs adjacent to a major normal fault system within a sequence of Mississippian (Tournaisian) sandstones, shales, limestones, and dolomites. It comprises large synsedimentary-syndiagenetic and smaller, underlying epigenetic orebodies.Fluid inclusions within the epigenetic minerals are dominated by a simple liquid-vapor type which in places contains one to five solid phases, the commonest of which is calcite. Single-phase liquid inclusions are commonest in barite; single-phase vapor and vapor-liquid inclusions are occasionally found in quartz, barite, and carbonates, although there is no indication of extensive boiling.Fluid inclusion salinities range from 8 to 28 equiv wt percent NaC1 with modes at 14 and 19 wt percent. Leachate studies show the fluids to have high sodium concentrations with lesser, variable amounts of potassium and calcium and uniformly low magnesium concentrations (K/Na = 0.03-0.23; Ca/Na = 0.03-0.28; Mg/Ca = 0.1-0.67). Fluid inclusions within synsedimentary-syndiagenetic barite are highly saline, indicating the possible presence of a brine pool at the site of ore deposition.Homogenization temperatures range from 50 ø to 260øC, with most between 140 ø and 220øC. There is a mode at 190øC and a subsidiary group at 140øC. Required pressure corrections are less than 5øC. If the pressure within the epigenetic ore zones was purely hydrostatic, as is reasonable, a minimum seawater depth of --•80 m is required to prevent boiling of some fluids.For the whole deposit there is a negative correlation between homogenization temperature and salinity for quartz-hosted inclusions, which is interpreted as the involvement of two (or possibly three) fluids in the mineralizing process. We suggest that high-temperature, 8 to 12 equiv wt percent NaC1 fluids mixed with lower temperature, 18 to 22 equiv wt percent NaC1 fluids, both within and below the ore zone during mineralization.Fluid inclusion waters have bD values of -24 to -49 per mil for quartz, -23 to -29 per mil for dolomite, -41 to -55 per mil for barite, -46 per mil for sphalerite, and -58 per mil for galena. The b•80 values of the mineralizing fluids, calculated from mineral values, range from 1.1 to 7.7 per mil for quartz and 1.8 to 5.7 per mil for dolomite. These data best represent aqueous fluids that have equilibrated with the geosynclinal sequence and granites underlying the deposit. They also suggest that local Carboniferous surface and ground waters may have contained a deuterium-depleted (meteoric?) component. The fluid inclusion evidence presented refutes a model involving the expulsion of Carboniferous formation waters and indicates little, if any, involvement of magmatic waters. The geologic, geochemical, and fluid inclusion evidence best fits a model involving the convection of Carboniferous surface waters in the putative thick geosynclinal sequence and associated granitoids below the deposit, with a contribution from lower Paleozoic formation waters.Mineral precipitation resulted from fluid mixing in...

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Section: Implications For the Origin Of The Mineralizing Fluidsmentioning

confidence: 80%

Genesis of the Silvermines zinc-lead-barite deposit, Ireland; fluid inclusion and stable isotope evidence

Samson

Russell²

1987

Economic Geology

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“…8; Taylor 1974). The surrounding orthogneisses have similar ~D(phengite) values as do the hydrated pyrope megacrysts Frey et al 1976;Margaritz and Taylor 1976;Rye et al 1976;Desmons and O'Neil 1978;Friedrichsen and Morteani 1979;Hoernes and Holler 1979;Friedrichsen 1978, 1980;Pineau et al 1981;Thomas et al 1985;Morikiyo 1986;Huebner et al 1986;Wickham and Taylor 1985;McCaig et al 1990 ( Table 1). The ~D(biotite ) value of -64%o in the orthogneiss are in isotopic equilibrium with the coexisting phengite (Suzuoki and Epstein 1976).…”

Section: Rock Protolith and Fluid Originmentioning

confidence: 90%

“…Published 6~80(q,,r~,) values for metamorphic rocks and average value for the Dora Maira samples (vertical dashed line). Sources of data: Taylor and Epstein 1962;Taylor et al 1963;Garlick and Epstein 1967;Taylor and Coleman 1968;Wilson et al 1970;Schwarcz et al 1970;Wilson and Green 1971;Perry and Tan 1972;Fourcade and Javoy 1973;Black 1974;Hoernes and Friedrichsen 1974, 1980Honma and Sakai 1975;O'Neil and Ghent 1975;Frey et al 1976;Margaritz and Taylor 1976;Rye et al 1976;Desmons and O'Neil 1978;Rumble 1978;Friedrichsen and Morteani 1979;Hoernes and Hoffer 1979;McNaughton and Wilson 1980;Pineau et al 1981;Brown and O'Neil 1982;Manhews and Schliestedt 1984;Valley and O'Neil 1984;Whelan et al 1984;Robert et al 1985;Thomas et aL 1985;Wickham and Taylor 1985;Huebner et al 1986;Jiang et al 1988;Sharp et al [988;Burkhard and Kerrich 1988;Baker 1990;Hoffbauer et al 1992;Vennemann and Smith 1992 pegmatites, eclogites, blueschists and greenschists, quartzites, quartz veins, marbles and calc-silicates have 8t80 values that are significantly higher than those of the Dora Maira whiteschists. Sediments, particularly those of authigenic origin, have a much higher 6180 value than the whiteschists from Dora Maira (e.g.…”

Section: Rock Protolith and Fluid Originmentioning

confidence: 99%

Stable isotope geochemistry and phase equilibria of coesite-bearing whiteschists, Dora Maira Massif, western Alps

Sharp

Essene

Hunziker

1993

Contr. Mineral. and Petrol.

123

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retrograde talc + chlorite after pyrope may be fluids evolved locally during retrograde melt crystallization. The similar 6D, but dissimilar 8180 values of the coesitebearing whiteschists and hosting orthogneiss suggest that the two were in hydrogen isotope equilibrium, but not oxygen isotope equilibrium. The unusual hydrogen and oxygen isotope compositions of the coesite-bearing unit can be explained as the result of metasomatism from slab-derived fluids at depth.

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“…In fact the problem is the reverse. A cover of Windermere Supergroup is adequate to produce prehnite-pumpellyite facies metamorphism in the Borrowdale Group (Thomas, Harmon & Oliver, 1985;Millward et al 2000) but extra cover is required over the younger Silurian rocks to raise them to anchizone grade, and this could only have been provided by Lower Devonian strata.…”

Section: B Critique Of the Flexural Model In Northwest Englandmentioning

confidence: 99%

The lost Lower Old Red Sandstone of England and Wales: a record of post-Iapetan flexure or Early Devonian transtension?

Soper

Woodcock

2003

Geol. Mag.

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Illite crystallinity data from the Silurian slate belts of England and Wales indicate anchizone to low epizone metamorphism during the Acadian deformation in late Early Devonian time. This metamorphic grade implies a substantial overburden, now eroded, of Lower Devonian non-marine sediments of the Old Red Sandstone (ORS) magnafacies. A minimum 3.5 km pre-tectonic thickness of ‘lost’ ORS is estimated in the southern Lake District and comparable thicknesses in North Wales and East Anglia. Tectonically driven subsidence of the underlying Avalonian crust is required to accommodate such thicknesses of non-marine sediment. One proposed mechanism is flexure of the Avalonian footwall during convergence that continued from Iapetus closure in the Silurian until Acadian cleavage formation in the Emsian. The evidence for this model in the critical area of northwest England is reviewed and found to be unconvincing. An alternative model is developed following a recent suggestion that the Early Devonian was a period not of continued convergence but of orogen-wide sinistral transtension. Transtensional accommodation of the lost ORS is evidenced by Early Devonian extensional faults, by synchronous lamprophyric magmatism, and by compatibility with previously diagnosed sediment provenance patterns. A summary of Siluro-Devonian tectonostratigraphy for Britain south of the Highland Border emphasizes that, unlike the Scottish Highlands, this area was not affected by the Scandian Orogeny, but was by the Acadian. An important period of sinistral transtension in the Early Devonian (c.420–400 Ma) was common to both regions. This was a time of high heat flow, lamprophyric and more evolved magmatism, and major southward sediment transport, involving mainly recycled metamorphic detritus from the Highlands and from contemporaneous volcanicity. Old Red Sandstone, deposited in coalescing transtensional basins over much of Britain from the Midland Valley to the Welsh Borders, was largely removed and recycled southward during Acadian inversion.

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Stable isotope compositions of alteration fluids in low-grade Lower Palaeozoic rocks, English Lake District

Cited by 14 publications

References 24 publications

Genesis of the Silvermines zinc-lead-barite deposit, Ireland; fluid inclusion and stable isotope evidence

Genesis of the Silvermines zinc-lead-barite deposit, Ireland; fluid inclusion and stable isotope evidence

Stable isotope geochemistry and phase equilibria of coesite-bearing whiteschists, Dora Maira Massif, western Alps

The lost Lower Old Red Sandstone of England and Wales: a record of post-Iapetan flexure or Early Devonian transtension?

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