Lithophile

From a geochemical viewpoint, U is an incompatible lithophile and refractory element. U exists in three distinct oxidation states in nature (Galas 1979) but the most common are ([Rn] 5f ) and ([Rn]). The most reduced form (metal) is never found in natural environments. At the surface of the earth, U is dominantly in the form. However, in a reducing environment, it will be in the state where it is insoluble and therefore generally far less mobile than U(VI). In the mantle, U is thought to occur in the... 

In summary, a key aspect to the utility of U-series isotopes in the study of arc lavas is that whereas Th and Pa are observed and predicted to behave as relatively immobile high field strength elements (HFSE), Ra and (under oxidizing conditions) U behave like large ion lithophile elements (LILE) and are significantly mobilized in aqueous fluids. Fluid-wedge interaction will only serve to increase these fractionations. Just how robust the experimental partition coefficients are remains to be established by future experiments. 

Note It is sometimes convenient to describe the element distribution between sulfides and oxides as chalcophiles (occurring in the Earth s crust as sulfides) and lithophiles (predominating as oxides and halides in the Earth s crust) (see Fig. 1.5). This geochemical classification includes also the siderophiles (remaining as metals or alloys, especially in the Earth s core) and the atmophiles (which occurs largely in volatile form in the atmosphere and dissolved in the oceans). 

Abstract strong commodity prices in the last few years have led to a remarkable renaissance of uranium exploration in Labrador, focused in a complex and geologically diverse region known as the Central Mineral Belt (CMB). Potentially economic epigenetic U deposits are mostly hosted by supracrustal rocks of Paleoproterozoic and Mesoproterozoic age, and are difficult to place in the traditional pantheon of uranium deposit types. Recent exploration work implies that structural controls are important in some examples, but the relationships between mineralization and deformation remain far from clear. Geochronological data imply at least three periods of uranium mineralization between 1900 and 1650 Ma. It seems likely that the Labrador CMB represents a region in which U (and other lithophile elements) were repeatedly and sequentially concentrated by hydrothermal processes. The current exploration boom lends impetus for systematic research studies that may ultimately lead to refined genetic models that may be applicable elsewhere. 

Uranium mineralization in the CMB is characterized by a diversity of style and host rocks, and it is naive to suppose that a single genetic model can explain all its variations. Like many metallogenic provinces in which incompatible (or lithophile ) elements are important, the CMB of Labrador seems to represent an area in which U has been repeatedly and perhaps sequentially concentrated, and... 

Schauble (2004) applied the theory of stable isotope fractionation to nontradi-tional isotope systems. He pointed out that, differences in coordination numbers among coexisting phases control isotope fractionation of cations. The hghter isotope preferentially occupies the higher coordinated site. Thus, differences in isotope composition of lithophile elements such as Mg, Ca, and Li are likely to reflect changes in coordination numbers... 

O, H, C, S, and N isotope compositions of mantle-derived rocks are substantially more variable than expected from the small fractionations at high temperatures. The most plausible process that may result in variable isotope ratios in the mantle is the input of subducted oceanic crust, and less frequent of continental crust, into some portions of the mantle. Because different parts of subducted slabs have different isotopic compositions, the released fluids may also differ in the O, H, C, and S isotope composition. In this context, the process of mantle metasomatism is of special significance. Metasomatic fluids rich in Fe +, Ti, K, TREE, P, and other large ion lithophile (LIE) elements tend to react with peridotite mantle and form secondary micas, amphiboles and other accessory minerals. The origin of metasomatic fluids is likely to be either (1) exsolved fluids from an ascending magma or (2) fluids or melts derived from subducted, hydrothermally altered crust and its overlying sediments. 

Iron oxides present in coal are generally stable for the relatively short period of time that they are exposed to combustion temperatures. Therefore, siderophile elements (e.g., Ni, Co, Mo, Pt, Pd, Au) that are incorporated within iron oxides are also expected to remain stable, and escape any significant thermal transformation reactions (Bums 2003). Similarly, lithophile elements (e.g., Ba, B, Cr, Mn, Sr, V) that are initially found in association with silicates and aluminosilicates in coal are expected to be incorporated within the glassy fraction of coal ash upon thermal transformation of their parent minerals (Bums 2003). 

A cosmochemical periodic table, illustrating the behavior of elements in chondritic meteorites. Cosmic abundances are indicated by symbol sizes. Volatilities of elements reflect the temperatures at which 50°/o of each element would condense into a solid phase from a gas of solar composition. As in Figure 1.2, the chemical affinities of each element, lithophile for silicates and oxides, siderophile for metals, and chalcophile for sulfides, are indicated. Some of the most highly volatile phases may have remained uncondensed in the nebula. Stable, radioactive, and radiogenic isotopes used in cosmochemistry are indicated by bold outlines, as in Figure 1.2. Abundances and 50% condensation temperatures are from tabulations by Lodders and Fegley (1998). 

Distinguish between the following terms lithophile, siderophile, chalcophile, atmophile. 

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