Isotopic Composition and Distribution of Lead, Uranium, and Thorium in a Precambrian Granite

Tilton, G. R.; Patterson, Clair C.; Brown, Harrison; Inghram, Mark G.; Hayden, Richard J.; Hess, David C.; Larsen, Esper S.

doi:10.1130/0016-7606(1955)66[1131:icadol]2.0.co;2

Cited by 139 publications

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“…by Tilton, Patterson, et al (1955), Starik (1956, and Tilton (1956) uranium fractionation from the principal mineral of each concentrate. Unfortunately, documentation on the freedom of the concentrates from minor soluble minerals such as thorite is difficult to obtain, and certainly was not provided in these papers (see, e.g., Tilton, 1956, p. 230).…”

Section: Evidence On the Nature Of The Disturbance Mechanismsmentioning

confidence: 99%

“…The chemical procedures followed in the isotopic analysis of the mineral separates are generally similar to those developed by Til· ton and Patterson (Tilton et al, 1955;Tilton et al, 1957). The specific procedure is described in Silver, McKinney, Deutsch, and Bolinger (1963).…”

Section: Isotopic Studiesmentioning

confidence: 99%

“…They proposed the so-called lead-a method, or Larsen method, a non-isotopic method of age determination. Tilton, Patterson, et al (1955) and, in particular, Tilton et al (1957, and numerous other publications) demonstrated that precise and significant isotopic measurements could be made on the zircons of many different rocks. Tilton's work more than any other to date has defined the applicability and problems of U-Th-Pb systems in zircons in age-determination studies.…”

Section: Introductionmentioning

confidence: 96%

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Uranium-Lead Isotopic Variations in Zircons: A Case Study

Silver¹,

Deutsch²

1963

The Journal of Geology

253

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Zircons in a single 250-pound block of Precambrian Johnny Lyon granodiorite from the Dragoon Quadrangle in Cochise County, Arizona, have been concentrated with special attention to yield and nature of impurities. Morphology, zoning, color, inclusions, size distribution, radioactivity, refractive indexes, cell dimensions, and other properties have been compared with the isotopic properties in the U-Pb system (and to a less precise degree in the Th-Pb system). It has been observed: (1) Uranothorite impurities, while less than 1 per cent in abundance, contribute much more than 50 per cent of the activity in conventionally prepared concentrates. The presence of uranothorite drastically affects the apparent ages in the zirons. (2) The uranothorite can be satisfactorily removed by an appropriate acid-washing procedure. (3) The uranothoritefree zircon concentrates are not homogeneous and show systematic variations in radioactivity and various isotopic properties as a function of average crystal size. (4) Individual zircons show internal variation in radioactivity and may differ in specific activity from other individuals by as much as an order of magnitude. (5) It is possible to strip outer layers experimentally from an aggregate of zircons to determine variations in composite internal isotopic properties. (6) The family of uranium-lead systems distinguished in the inhomogeneous zircon suite may be utilized to establish patterns of isotopic ratio variations that yield much more useful geochronological information than any single system. (7) All systems in this rock appear to have formed 1,655 million years ago and to have been profoundly disturbed by an event 90 million years ago. There is no evidence of any type of disturbance other than this simple episodic pattern. (8) While the mechanism of disturbance is not directly established, it is evident that radioactivity and radiation damage strongly influence susceptibility of the systems to disturbance. (9) It is possible to offer reasonable explanations for some of the puzzling discrepancies between uranium-lead and thorium-lead ages determined on a single mineral concentrate. (10) Recognition of the existence of families of uranium-lead systems among the variable members of a single mineral species, or in associated mineral species, in a single typical granitic rock provides a powerful tool for investigation of the processes and conditions that have influenced the age-dating systems. (11) The systematic variations in U and Th provide interesting information on the role of some trace elements and accessory minerals in the crystallization history of the rock. (12) The Johnny Lyon granodiorite is the oldest igneous rock dated in Arizona thus far and places a minimum age of 1,655 ± 20 million years on the orogeny called Mazatzal Revolution.

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Section: Evidence On the Nature Of The Disturbance Mechanismsmentioning

confidence: 99%

Section: Isotopic Studiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

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Uranium-Lead Isotopic Variations in Zircons: A Case Study

Silver¹,

Deutsch²

1963

The Journal of Geology

253

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“…4.468 billion years respectively. U-Pb geochronology was initially developed in the mid-1950s [1][2][3] and only made possible by earlier advances in mass spectrometry [4]. Thermal Ionization Mass Spectrometry (TIMS) is the method of choice for studies requiring the highest precision U-Pb data.…”

Section: Introductionmentioning

confidence: 99%

Chemical Abrasion Applied to LA-ICP-MS U–Pb Zircon Geochronology

et al. 2014

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Zircon (ZrSiO 4 ) is the most commonly used mineral in U-Pb geochronology. Although it has proven to be a robust chronometer, it can suffer from Pb-loss or elevated common Pb, both of which impede precision and accuracy of age determinations. Chemical abrasion of zircon involves thermal annealing followed by relatively low temperature partial dissolution in HF acid. It was specifically developed to minimize or eliminate the effects of Pb-loss prior to analysis using Thermal Ionization Mass Spectrometry (TIMS). Here we test the application of chemical abrasion to Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) by analyzing zircons from both untreated and chemically abraded samples. Rates of ablation for high alpha-dose non-treated zircons are up to 25% faster than chemically abraded equivalents. Ablation of 91500 zircon reference material demonstrates a ca. 3% greater down-hole fractionation of 206 Pb/ 238 U for non-treated zircons. These disparities necessitate using chemical abrasion for both primary reference material and unknowns to avoid applying an incorrect laser induced fractionation correction. All treated samples display a marked increase in the degree of concordance and/or lowering of common Pb, thereby illustrating the effectiveness of chemical abrasion to LA-ICP-MS U-Pb zircon geochronology. OPEN ACCESSMinerals 2014, 4 504

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“…com., 1976) that TILTON et al (1954), using cold 6N HC1, leached "• 29% of the uranium, 'r 42% of the thorium and -40% of the nonradiogenic lead from pulverized granite . Furthermore, BROWN and SILVER (19.55) leached -30 mesh granite rocks with 1 N HN03 for 50min and extracted 20-100 times the amounts of U and Th compared with the original rock.…”

Section: Volcanicsmentioning

confidence: 99%

Lead isotope results of acid leaching experiments on acid volcanics and black shales in an ore environment.

Gulson

1977

Geochem. J.

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In the volcanogenic Woodlawn Cu-Pb-Zn deposit, where pyrite is the dominant sulphide phase in the ore and a ubiquitous mineral in the host volcanics and shales, leaching experiments using HN03-HC1 to overcome the ore/rock lead dominance, resulted in highly complex lead isotopic data, dependent mainly on the original lead concentration in the rock. For samples with higher (> 5 ppm) lead concentrations, the acid leaches are less radiogenic than the rocks or residues whereas for samples with < 5ppm lead, the acid leaches are more radiogenic than the rocks or residues. In those samples with > 15 ppm lead, the data arrays. are those expected for a dominance of ore/rock lead. In all except the very high lead samples (> 100ppm), lead is derived from sources other than sulphides. Furthermore, in only the highest lead sample is the acid leach isotopic value compatible with that of the ore lead. As found in previous leaching investigations, the dominant component of lead and uranium is extracted in the acid leach.

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Isotopic Composition and Distribution of Lead, Uranium, and Thorium in a Precambrian Granite

Cited by 139 publications

References 0 publications

Uranium-Lead Isotopic Variations in Zircons: A Case Study

Uranium-Lead Isotopic Variations in Zircons: A Case Study

Chemical Abrasion Applied to LA-ICP-MS U–Pb Zircon Geochronology

Lead isotope results of acid leaching experiments on acid volcanics and black shales in an ore environment.

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