Geochemical affinities

In coastal environment, detrital and authigenic Fe and Mn oxides, which accumulate in oxic surface sediments, play a pivotal role in determining the geochemical behaviour of arsenic (Mucci et al., 2000) and selenium (Belzile et al., 2000). Arsenic and selenium differ in their affinities for metal oxide surfaces. Although both adsorb onto iron oxides, arsenate (As(V)) adsorbs more strongly than arsenite (As(lll)), and selenite (Se(IV)) adsorbs more strongly than selenate (Se(VI)) (Belzile et al., 2000). 

The rare earths (see table II) have a marked geochemical affinity for fluorine, calcium, titanium, niobium, zirconium, and the phosphate and carbonate ions. The most important, from an economic viewpoint, are the carbonatites and the phosphates. 

Goldschmidt (32) also introduced the concept of a geochemical classification of elements, in which the elements are classified on the basis of their affinities and tendencies to occur in minerals of a single group. The chalcophile elements are those which commonly form sulfides. In addition to sulfur, they include Zn, Cd, Hg, Cu, Pb, As, Sb, Se, and others. When present in coals, these elements would be expected to occur, at least in part, in sulfide minerals. Sulfides other than pyrite and marcasite have been noted in coals, but, except in areas of local concentration, they occur in trace or minor amounts. 

Many data on trace elements in coal are included in the chapter. The emphasis is on the geochemistry of the trace elements, with discussions of the concentration levels of trace elements in coals, the organic (or inorganic) affinities of the trace elements, and the geochemical controls of associations of elements. This and the following significant review article are contained within a single volume. 

Unlike silicon and germanium, tin and lead belong to the family of chalcophile elements (according to the Goldshmidt geochemical classification), which have a high affinity to sulfur. In this connection the stability of the stannathiane Sn—S bond (in the Sn—S—Sn... 

Klein E. M. and Karsten J. L. (1995) Ocean-ridge basalts with convergent-margin geochemical affinities from the Chile Ridge. Nature 374, 52-57. 

Ferrara G., Innocent F., Ricci C. A., and Serri G. (1976) Ocean-floor affinity of basalts from north Apennine ophiolites geochemical evidence. Chem. Geol. 17, 101-111. 

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