Arbitrary scaling in ISOCON method of geochemical mass balance: An evaluation of the graphical approach

Mukherjee, Pinaki; Gupta, Pankaj

doi:10.2343/geochemj.42.247

Cited by 17 publications

(9 citation statements)

References 10 publications

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“…Note the sharpness of the contact. Some larger quartz globules found in the granite can be traced into the whiteschist at this location and initial rocks, one additional equation is needed to mathematically obtain a unique solution (Gresens 1967;Grant 1986;Baumgartner and Olsen 1995;Ague and Haren 1996;Mukherjee and Gupta 2008). Typical assumptions leading to this additional equation might include constant volume or immobile elements such as Al or Zr (Dipple et al 1990;Baumgartner and Olsen 1995;Ague 2003).…”

Section: Whole-rock Geochemistry and Stable Isotope Compositionsmentioning

confidence: 99%

Whiteschist genesis through metasomatism and metamorphism in the Monte Rosa nappe (Western Alps)

Luisier

Baumgartner

Putlitz

et al. 2021

Contrib Mineral Petrol

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Whiteschists from the Monte Rosa Nappe were examined in the field as well as with petrographic, geochemical, and isotopic methods to constrain the controversial origin of these rocks in their Alpine metamorphic context. Whiteschists occur as ellipsoidal-shaped, decametric-sized bodies, within a Permian metagranite, and consist mainly of chloritoid, talc, phengite, and quartz. The transition from whiteschist to metagranite is marked by multiple sharp mineralogical boundaries defining concentric zones unrelated to Alpine deformation. The development of reaction zones, as well as the geometry of the whiteschist suggest a pervasive fluid infiltration, facilitated and canalized by reaction fingering. Whole-rock compositions of whiteschists and metagranites indicate an enrichment in MgO and H2O and depletion of Na2O, CaO, Ba, Sr, Pb, and Zn in the whiteschist relative to the metagranite. Trace- and rare-earth elements, together with all other major elements, notably K2O and SiO2, were within uncertainty not mobile. Such a K and Si saturated, Na undersaturated fluid is not compatible with previous interpretations of fluids derived from ultramafic rocks, evaporites, or Mg-enriched seawater due to mantle interactions. Together with the large variations in δD and δ18O values, this indicates large fluid fluxes during metasomatism. Calculated δD and δ18O values of fluids in equilibrium with the whiteschist support a magmatic–hydrothermal fluid source, as does the chemical alteration pattern. Bulk rock 87Sr/86Sr ratios in whiteschists confirm a pre-Alpine age of fluid infiltration. The 87Sr/86Sr ratios in whiteschists were subsequently partially homogenized in a closed system during Alpine metamorphism. In conclusion, the granite was locally affected by late magmatic–hydrothermal alteration, which resulted in sericite–chlorite alteration zones in the granite. The entire nappe underwent high-pressure metamorphism during the Alpine orogeny and the mineralogy of the whiteschist was produced during dehydration of the metasomatic assemblage under otherwise closed-system metamorphism. While each whiteschist locality needs to be studied in detail, this in-depth study suggests that many whiteschists found in granitic bodies in the Alps might be of similar origin.

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Section: Whole-rock Geochemistry and Stable Isotope Compositionsmentioning

confidence: 99%

Whiteschist genesis through metasomatism and metamorphism in the Monte Rosa nappe (Western Alps)

Luisier

Baumgartner

Putlitz

et al. 2021

Contrib Mineral Petrol

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“…It is very critical to identify the immobile elements as reference frame for successful execution of mass-balance estimations. We prefer to follow the isochemical volume factor (ICVF; F 0 v ) approach as outlined in Mukherjee and Gupta (2008); Marquer (1989) and Potdevin and Marquer (1987) for identification of conserved elements. The essential condition for conserved elements is that the F 0 v for such elements are nearly identical owing to residual enrichment or depletion (Gresens 1967).…”

Section: Whole Rock Geochemistrymentioning

confidence: 99%

“…(a) Isochemical volume factor (ICVF) plot(Mukherjee and Gupta 2008) for the alteration of fresh granite to mylonitic granite. The cluster of elements (encircled and shaded) in the terrace with a narrow range of ICVF values are taken as immobile reference frame for the massbalance computations.…”

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confidence: 99%

Fluid–rock interaction across the South Tibetan Detachment, Garhwal Himalaya (India): Mineralogical and geochemical evidences

et al. 2012

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The Malari Leucogranite in the Garhwal Himalaya is cut across by a continental-scale normal fault system called the South Tibetan Detachment (STD). A mineralogical, geochemical and fluid inclusion study of samples from the fault zone of the Malari Granite was performed to reveal the imprints of fluid-rock interaction. Fluid inclusion assemblages observed in the alteration zone indicate the presence of NaCl-dominated aqueous fluids with varied salinity of 6-16 wt.% of NaCl equivalent. Mineralogical changes include the alteration of feldspar to muscovite and muscovite to chlorite. This alteration took place at temperatures of 275 •-335 • C and pressures between 1.9 and 4.2 kbars as revealed by the application of chlorite thermometry, fluid isochores, and presence of K-feldspar+muscovite+chlorite+quartz mineral assemblage. Geochemical mass-balance estimates predict 32% volume loss during alteration. An estimated fluid/rock ratio of 82 is based on loss of silica during alteration, and reveals presence of a moderately low amount of fluid at the time of faulting. Results of fluid inclusion and alteration mineralogy indicate that the Malari Leucogranites were exhumed due to normal faulting along the STD and erosion from mid-crustal levels. Most of the leucogranites in the Himalayas occur along the STD and possibly a regional-scale fluid flow all along the STD might have caused similar alteration of leucogranites along this tectonic break. Regional fluid flow was probably concentrated along the STD and channelized through mesoscopic fractures, microcracks and grain boundaries.

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“…Normalization of each element, such that the squared sum of concentrations of altered and least altered rocks equals 1, makes the identification of conservative elements less biased ( Fig. 14A-B; Humphris et al, 1998), by avoiding the arbitrary scaling used in isocon diagrams (Mukherjee and Gupta, 2008). Elements that display similar chemical behavior remain in clusters during progressive alteration, and define a fan with the point of origin in normalized C0 (protolith)-Ca (altered) diagrams ( Fig.…”

Section: Mass Transfer During Alteration Of Host Rocksmentioning

confidence: 99%

Lithology and Hydrothermal Alteration Control the Distribution of Copper Grade in the Prominent Hill Iron Oxide-Copper-Gold Deposit (Gawler Craton, South Australia)

Schlegel

Heinrich

2015

Economic Geology

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The Prominent Hill iron oxide-copper-gold (IOCG) deposit, located in the Gawler craton of South Australia, contains ca. 278 Mt of ore at 0.98 % Cu, 0.75 g/t Au, and 2.5 g/t Ag. In contrast to the predominantly granite-hosted Olympic Dam IOCG deposit, Prominent Hill is mainly within unmetamorphosed sedimentary rocks comprising coarse clastic to laminated argillaceous lithologies with some volcaniclastic components and variable carbonate, including local massive dolomite. Essentially unmetamorphosed sedimentary rocks and structurally underlying mafic to intermediatecomposition lavas, inferred to be members of the lower Gawler Range Volcanics, host the economically mineralized hematite breccias. The volcanic-sedimentary package was downfaulted and tilted along a major E-W fault, north of which similar but regionally low-grade metamorphosed rocks were affected by subeconomic skarn mineralization, and (on a more regional scale of the Mount Woods domain) intruded by granitic and gabbroic bodies. Hydrothermal alteration and mineralization at Prominent Hill involved pervasive and texturally-destructive replacement of formerly calcareous, dolomitic, and siliciclastic breccia components. Hydrothermal alteration minerals comprise hematite, magnetite, siderite, ankerite, quartz, sericite, chlorite, kaolinite, fluorapatite, fluorite, barite, REE-U minerals (including monazite), uraninite, and coffinite, together with Cu sulfides including chalcopyrite, bornite, and chalcocite in the highest-grade ore. Brecciation and replacement caused mechanical mixing as well as chemical alteration of primary lithologies, such that sedimentary contacts became obscured. Mass-balance calculations identify Al, Ti, Si, and Zr as least-mobile components during hematite-chlorite-sericite to weak hematite-quartz alteration. Because Zr was not regularly assayed in drill cores, we use concentration ratios of Ti, Al, and Si from the deposit-scale assay database to delineate the distribution of lithochemical units prior to hydrothermal alteration and Cu mineralization. The resulting lithochemical model, based on one horizontal and five vertical cross sections, is used as a basis for mapping alteration patterns calculated 2 from molar (Fe+Si)/(Fe+Si+Al), K/Na, and K/Al ratios. These chemical patterns, in conjunction with mineral stoichiometry, indicate that the spatial distribution of hematite, chlorite, variably phengitic sericite (and /or illite) ± kaolinite ± quartz-bearing alteration is superimposed on the pattern of interpreted lithological contacts. The alteration patterns confirm visual logging results showing that hematite enrichment correlates only partially with the distribution of Cu grades of >0.25 wt %. A subvertical body of complete replacement by hematite and quartz with consistent but subeconomic gold enrichment forms a Cu-barren core in the central and eastern parts of the deposit. Zones of increasing K/Al and K/Na ratios extend upward and westward from this Cu-barren core, transgressively overprinting lithological contacts. The degree...

show abstract

Arbitrary scaling in ISOCON method of geochemical mass balance: An evaluation of the graphical approach

Cited by 17 publications

References 10 publications

Whiteschist genesis through metasomatism and metamorphism in the Monte Rosa nappe (Western Alps)

Whiteschist genesis through metasomatism and metamorphism in the Monte Rosa nappe (Western Alps)

Fluid–rock interaction across the South Tibetan Detachment, Garhwal Himalaya (India): Mineralogical and geochemical evidences

Lithology and Hydrothermal Alteration Control the Distribution of Copper Grade in the Prominent Hill Iron Oxide-Copper-Gold Deposit (Gawler Craton, South Australia)

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