Uranium-bearing minerals

It should also be remarked that uranyl complexes tend to emit a bright green fluorescence under UV irradiation, from the first excited state. This is used by geologists both to identify and to assay uranium-bearing minerals in deposits of uranium ores. 

Some of the earliest attempts at dating uranium-bearing minerals were made by measuring the accumulation of helium in crystals from the a-decay of uranium and thorium. Two efforts that immediately predated the development of modem geochronology were Hurley (1954) and Damon (1957). Because of the ease of helium diffusion, however, the dates calculated were shown to be too young in most cases and the technique was soon abandoned in favor of... 

The decay of radioactive nuclides with known half-lives enables geochemists to measure the ages of rocks from their isotopic compositions. Suppose that a uranium-bearing mineral was deposited some 2 billion (2.00 X 10 ) years ago and has remained geologically unaltered to the present time. The in the mineral decays with a half-life of 4.51 X 10 years to form a series of short-lived intermediates, ending in the stable lead isotope ° Pb (Fig. 19.6). The fraction of uranium remaining after 2.00 X 10 years should be... 

At current prices of uranium ( 30 to 50/lb U30g) ores containing around 0.1 percent UgOg or more are being mined pritrrarily for their uranium content. The principal uranium-bearing minerals found in such ores are listed in Table 5.15, classified according to the type of treatment needed to extract the uranium. 

The first group, minerals containing high concentrations of uranium, mostly in the tetravalent state, can be concentrated by specific gravity methods when in massive form. Frequently, however, the particle size is so small that the uranium-bearing mineral must be dissolved in sulfuric acid or sodium carbonate leach liquors. In either case, an oxidant must be added to bring uranium to the soluble, hexavalent state. 

In an area where the crust is being uplifted, the fission-track dates of apatite increase with increasing elevations of the collecting sites and record the time that has elapsed since the samples cooled through the 60°C isotherm. All of the fission-track dates in the Transantarctic Mountains post-date the intrusion of the sills of Ferrar Dolerite which had already cooled before the apatites and other uranium-bearing minerals began to accumulate fission track. 

Uranium is composed of three naturally occurring radioactive isotopes having the mass numbers 238, 235, and 234 all of which decay by emitting alpha particles from their nuclei. All of the naturally occurring isotopes of uranium can also decay by spontaneous fission, but virtually all spontaneous fission events in a uranium-bearing mineral are due to which is by far the most abundant isotope of uranium at 99.2745% by number. 

The temperature is an important variable because uranium-bearing minerals anneal fission tracks at elevated temperatures and retain them quantitatively only after the temperature has decreased below the level at which all tracks are preserved. Therefore, the fission track date of a mineral or glass is the time that has elapsed since the specimen cooled through the track-retention temperature for the last time. In other words, fission track dates are equal to the age of a specimen of mineral or glass only in cases when the specimen cooled to the track-retention temperature immediately after it was formed. The fission-track method appears to be straightforward in principle but is, in fact, quite labor intensive and demanding (Faure and Mensing 2005). 

In addition to uranium-bearing minerals such as autunite and torbernite, reported uranium salts include... 

Concordia plots allow the interpretation of the geological histories of uranium/lead systems and provide information on the past disturbances of these systems. Several concordia models have been developed in order to interpret the discordancy of the U/Pb dates of uranium-bearing minerals. 

Uranium undergoes spontaneous fission as well as radioactive a decay and this produces fissiogenic xenon and krypton that accumulate in uranium-bearing minerals through... 

Hiess, J., Condon, D.J., McLean, N. et al. (2012). 238U/235U systematic in terrestrial uranium bearing minerals. Science 335, 1610-1616. 

Non-refractory primary uranium minerals are rare, but uranothorianite has been reported from Palabora" and uraninite from Lake Nipissing, Ontario, Canada. Most car-bonatite uranium-bearing minerals me refractory phases. Uranium occurs as a minor or trace element in zircon, apatite, baddeleyite, perovskite, monazite, pyrochlore minerals, goyazite, bastnaesite, allanite, anatase, rutile, etc. The secondary mineral autunite occurs in soil covering the Araxa carbonatite. " ... 

The other variety of orebody is represented by mica-epi-syenite bodies, usually developed at the intersections of east-west and north-south fractures. This brittle and vesicular rock forms extremely irregular three-dimensional bodies able to exceed significantly 100 m in height. Fig. 9 shows such a typical body of the Margnac deposit of the La Crouzille district. They are sometimes vertically interrupted (Fig. 10). The main uranium-bearing minerals are pitchblende and coffinite. 

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