Single mineral dating by the PbPb step-leaching method: Assessing the mechanisms

Villa, Igor M.; Nägler, Thomas F.; Kramers, Jan D.; Przybyłowicz, W.J.; Prozesky, V.M.; Hofmann, Beda A.; Kamber, Balz S.

doi:10.1016/s0016-7037(96)00343-2

Cited by 108 publications

(31 citation statements)

References 33 publications

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“…Between 250 and 300 mg of powdered rock and 50 mg of K-feldspar were leached at 180°C in 3.5 ml of 7 M HCl and 1.5 ml of 14.4 M HNO 3 during $36 h in screw-sealed Teflon beakers. The aim of this strong leaching was not only to dissolve common secondary minerals (sulfides, sulfates, and carbonates), but also to remove radiogenic lead hosted by silicate minerals and in intergranular positions, with the exception of zircon (see also Deloule et al 1989;Erel et al 1994;Mattinson 1994;Frei et al 1997). This allows us to obtain the highest ratio of common to radiogenic lead in the residue fractions.…”

Section: Analytical Techniquementioning

confidence: 99%

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Separate lead isotope analyses of leachate and residue rock fractions: implications for metal source tracing in ore deposit studies

Chiaradia

Fontboté

2003

Miner Deposita

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ARTICLEMassimo Chiaradia AE Lluı´s FontboteŚ eparate lead isotope analyses of leachate and residue rock fractions: implications for metal source tracing in ore deposit studies Abstract Separate lead isotope analyses of leachate and residue fractions are applied to a broad spectrum of rocks commonly investigated in metallogenic studies. Resulting data highlight a systematic behavior of leachate and residue fractions with respect to lead isotope compositions, which essentially depends on the mineralogical composition of the rock. Granitoid and high-grade metamorphic rocks have residue compositions virtually identical to common lead. In contrast, low-grade metasedimentary rocks may have residue compositions swamped by radiogenic lead of leach-resistant zircons. Mafic magmatic rocks have residues that are often more radiogenic than leachates, depending on the ratio of leach-refractory zircons to common lead in the residual fraction of these rocks. Separate leachate and residue analyses of source rocks provide two lead isotope end members whose mixture may represent lead with the appropriate ore fluid composition. Our leaching experiments indicate that hot acid solutions (and by inference hydrothermal fluids) preferentially leach radiogenic lead from medium-to high-grade metamorphic and granitoid rocks, whereas they preferentially leach common lead from low-grade metasedimentary and mafic magmatic rocks. The method presented in this study provides a reliable alternative to other methods (i.e., age-correction of bulk-rock compositions) for the determination of the common lead signature of felsic to intermediate magmatic rocks. This may be preferable to age-corrected bulk-rock analyses, where ages to apply for corrections of bulk-rock data are not known or where moderately to highly altered rocks must be used. Case studies of orogenic gold and MVT districts of Peru (Pataz and San Vicente, respectively) show that separate leachate and residue lead isotope analyses carried out systematically on whole rocks allow a more thorough evaluation of metal source reservoirs than does the standard method of age-corrected or uncorrected bulk-rock analyses.

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Section: Analytical Techniquementioning

confidence: 99%

“…A leaching longer than 20 h (e.g., 36 h) allows reduction and extraction of most of the radiogenic lead oxidized to ''immobile'' Pb 4+ during alpha-recoil (Frei et al 1997 Frei et al 1997). 4.…”

Section: Analytical Techniquementioning

confidence: 99%

Separate lead isotope analyses of leachate and residue rock fractions: implications for metal source tracing in ore deposit studies

Chiaradia

Fontboté

2003

Miner Deposita

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“…sufficient U and Th, and relatively low common Pb (Frei et al 1997, Ketchum et al 1998, Aleinikoff et al 2002, and the crystals are large enough to allow for widespread distribution.…”

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confidence: 99%

GRENVILLE SKARN TITANITE: POTENTIAL REFERENCE MATERIAL FOR SIMS U-Th-Pb ANALYSIS

Kennedy¹,

Kamo²,

Nasdala³

et al. 2010

The Canadian Mineralogist

130

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We have investigated the homogeneity, chemical composition, structure, degree of radiation damage, and post-formation evolution of titanite crystals from skarns of the Grenville Province of the Canadian Shield using SHRIMP, TIMS, Raman and PL spectroscopy, EBSD, and EPMA-WDS. These results are used to assess the potential of the titanite as Reference Material (RM) for micro-analytical U-Th-Pb age dating. The SHRIMP data show that these megacrysts (5-31g) have concordant U-Pb isotope systematics, 60 to 500 ppm U, 120 to 1200 ppm Th , 206 Pb/ 204 Pb between 500 and 2500, ages of ~1 Ga, and excellent homogeneity at the scale of the analytical volume of the ion probe. The ID-TIMS titanite data for OLT1, OLT2 and TCB show that these crystals are essentially concordant. Data for OLT1 and OLT2 show slight scatter (i.e., in excess of that expected from the uncertainty in an individual analysis). For OLT1, one of seven analyses shows Pb loss or, possibly, a younger period of growth. Crystals OLT1 and OLT2 have respective TIMS concordia ages of 1014.8 ± 2.0 Ma (2s, n = 6, MSWD = 1.8) and 998.0 ± 4.5 Ma (2s, n = 3, MSWD = 3.3) for domains that have not lost Pb. The TIMS analyses of TCB are tightly clustered and give a concordia age of 1018.1 ± 1.7 Ma (2s, n = 4, MSWD = 0.92). Raman and PL spectra show a low to moderate degree of accumulated radiation-induced damage in the Grenville Skarn Titanite crystals and uniform internal distributions of this damage. The EDSB contrast images indicate little or no crystallographic misorientation. The EMPA-WDS data show that the outer 50-100 mm of the OLT1 and TCB crystals are enriched in Al and F, and depleted in Fe and Nb, when compared with the interior. In spite of the variation in composition and degree of radiation damage amongst samples, there are no identifiable matrix effects in our SHRIMP data. Some Grenville skarn titanite (GST) crystals have potential as RM for micro-analytical U-Th-Pb age dating. Crystal TCB has excellent homogeneity of U-Th-Pb isotopic composition. Crystals OLT1 and OLT2 have minor TIMS age heterogeneity. However, this heterogeneity is smaller than that of the Khan titanite, our current in-house titanite standard. Careful selection of analysis areas during SIMS, and of chips for TIMS analysis, allows high-quality isotopic data to be obtained from these large crystals of titanite.

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“…The FeO content was determined via the volumetric method. The results of chemical analyses are reported in Table 1. The Sr, Nd, and Pb isotope ratios were determined at the Institut f€ u ur Geologie, Universit€ a at Bern (Switzerland) on a Nu Instruments ICP-Mass Spectrometer (Schoenberg et al, 2000 Pettke and Diamond (1995), Frei et al (1997), Kleinhanns et al (2002).…”

Section: Discussionmentioning

confidence: 99%

Pre-metamorphic melt infiltration in metasediments: geochemical, isotopic (Sr, Nd, and Pb), and field evidence from Serie dei Laghi (Southern Alps, Italy)

et al. 2008

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SummaryGradual transitions from K-feldspar free gneisses to K-feldspar bearing augengneisses are sometimes observed in metamorphic terranes. They have been explained with metasomatic porphyroblastic growth connected with regional metamorphism, or with pre-metamorphic presence of magmatic megacrysts. A transition of this kind can be observed in the Serie dei Laghi (Southern Alps, Italy), where coarse-grained metaarenites (Cenerigneiss) grade into Ceneri augengneisses with large K-feldspar porphyroclasts, and banded amphibolites of the ''Strona Ceneri Border Zone'' grade into Hbl augengneisses rich in K-feldspar.The Ceneri augengneisses are chemically indistinguishable from the Cenerigneiss, but have higher 87 Sr =86 Sr (0.7256-0.7258 vs. 0.7215-0.7233), similar to those of the Ordovician granites that were intruded, before the regional metamorphism, into the protoliths of both Cenerigneiss and amphibolites. The Cenerigneiss contains two types of zircons: (1) highly luminescent, rounded grains or fragments, yielding U-Pb SHRIMP ages from 0.43 to 1.0 Ga; (2) euhedral grains with oscillatory zoning (magmatic), with U-Pb SHRIMP concordant ages of 466 AE 13 Ma. This age coincides with the Rb-Sr whole rock emplacement age of the Ordovician granitoids (466 AE 5 Ma).Correspondence: L. Pinarelli, CNR -Istituto di Geoscienze e Georisorse, Sezione di Firenze, Via La Pira 4, 50121 Firenze, Italy e-mail: lapina@igg.cnr.itThe Hbl augengneisses form three groups with distinct geochemical patterns, whose distributions on inter-element diagrams trend towards the Ordovician metagranites and meta-aplites. In addition, the Hbl augengneisses have higher 87 Sr =86 Sr (0.7132-0.7147 vs. 0.7031-0.7046) and lower 143 Nd =144 Nd (0.51214-0.51219 vs. 0.51273-0.51297) than the amphibolites, suggesting the addition of an isotopically evolved component.The observed chemical and isotope patterns, as well as the vicinity of the augen gneisses to the Ordovician intrusions, lead us to conclude that the Ceneri augengneisses and Hbl augengneisses are the result of infiltration of residual hydrous magmas into the protolith of both the Cenerigneiss and the amphibolites at the time of Ordovician granite emplacement, long before the regional metamorphism in the Serie dei Laghi.

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Single mineral dating by the PbPb step-leaching method: Assessing the mechanisms

Cited by 108 publications

References 33 publications

Separate lead isotope analyses of leachate and residue rock fractions: implications for metal source tracing in ore deposit studies

Separate lead isotope analyses of leachate and residue rock fractions: implications for metal source tracing in ore deposit studies

GRENVILLE SKARN TITANITE: POTENTIAL REFERENCE MATERIAL FOR SIMS U-Th-Pb ANALYSIS

Pre-metamorphic melt infiltration in metasediments: geochemical, isotopic (Sr, Nd, and Pb), and field evidence from Serie dei Laghi (Southern Alps, Italy)

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