As Pointed out by Boyle (1974) in his comprehensivecoverage of element associations of mineral deposits, rarely does a single element concentrate in the Earth's crust• to form a mineral deposit. Generally mineral deposits consist of a suite of elements which have been concentrated because of certain intrinsic chemical properties which depend essentially on each element's electronic configuration and therefore position in the periodic table of the elements (Boyle, 1974).

Goldschmidt (1923, see also Levinson, 1974) recognised the systematic behaviour of element. groups 'and established a classificationschemeI now the most widely used one, based on the early history of the Earth. once completely molten, on cooling three phases separated in the Earth: a metal phase, a sulphide phase, and a silicate phase. Goldschmidt obtained trace element data relevant to these phases by study of natural materials such as
meteorites, rocks and ores, and artificial material such as slag.
Observational data showed the natural groupings, Table 1, which are:
(1) Siderophile, with affinity for iron, concentrated in the Earth's core;
(2) Chalcophile, affinity for• sulphur, concentrated in sulphides;
(3) Lithophile, affinity for silicates, concentrated in the Earth's crust;
( 4) Atmophile, present . as gas in the atmosphere,and ( 5 ) •Biophile, occu_rring as biological material. Some of these groups have been further subdivided, for example by szadeczky-Kardon (see Rossler and Lange, 1972) where the chalcophile elements are divided into the more chalcophile, •sulpho•
chalcophile• , and the less chalcophile, 'oxy-chalcophile.'

Tin, for
example, in the oxy-chalcophile group, frequently is present in many sulphide ore associations and may occur _either as the oxide cassiterite or the sulphide stannite. The classificationof elements in schemes like that in Table 1 shows a close but not always exact relationshipto position on the periodic table. Though one cannot in every case predict an •eleme~t•s geochemical behaviour some general trends are understood. For example ions such as Nb+s, Ta+s, zr+4, w+4,+6 with their high charge are difficult to acconunodate in major rock forming minerals and are therefore concentratedin residual fluids. These crystallize generally at the pegmatite stage.

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