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Adularia, a low-temperature form of K-feldspar, has been dated, but as of yet, there are insufficient data to confirm the suitability of this mineral.
These minerals do not usually have potassium in their theoretical formulae, but may carry minor amounts (usually %) as impurities or as substitutions for sodium (e.g., in plagioclase).
The differing half-lives for the radioactive U means that two systems can be used to calculate ages and when plotted against each other provide a test for closed system behaviour; i.e.
when there is concordancy of the two uranium-lead ages, giving rise to a conventional concordia diagram (a plot of The main advantage of the uranium-lead technique rests with the resistance of accessory phases, notably zircon, to post-crystallization disturbances and alteration.
ESTIMATING RATES OF RECENT GEOMORPHOLOGICAL PROCESSES affecting Cenozoic igneous rocks (e.g., uplift, denudation, laterite, silcrete and duricrust formation).
The K-Ar method is most suited to this application and the error, for Cenozoic rocks, can be less than 1 Ma so that relatively short episodes can be distinguished; All radiometric dating methods are based on the assumption of closed system behaviour of the sample throughout geological time; i.e.
The determination of the ages of rocks and minerals by the measurement of radioactive elements and their decay products, and the measurement of the isotopic abundances of strontium and lead have become accepted tools for mappers, researchers and exploration geologists in oil and metals exploration.
Carbonates deposited from, and calcareous organisms living in these waters will have distinctive The presence of uranium-rich accessory minerals (e.g., zircon, monazite, sphene and apatite) in acid to intermediate igneous and metamorphic rocks enables the uranium-lead technique to be applied to the problems of precisely defining crystallization ages of such minerals.Minerals in this group are hornblende, plagioclase and pyroxene.Hornblende is excellent for dating, but the other minerals, particularly plagioclase and pyroxene, are not always suitable for K-Ar dating.Even though lead may be lost from the system, in most cases a cogenetic suite of zircons will preserve the age of crystallization.Measurement of lead isotope ratios in whole-rocks, minerals and ores has long been recognized as an important technique in studying the origins of igneous and metallogenic suites.
Hence, Precambrian galenas from a massive sulphide deposit will have a characteristic lead isotopic signature that will be reflected in material derived from a massive sulphide source.