Geochemistry is a frequently used term in geological studies that defines a discipline which has developed in importance over the past 40 years. The meaning of this term and the substance of the discipline is the relationship between the chemical properties of elements found in the geological sphere and their expression as minerals or other phases found in rocks. Essentially the elements that are the most common and abundant in surface materials are limited in number, such as Na, K, Mg, Ca, Al, Si, and Fe (called the major elements) with concentrations of elements such as Mn, P, S, C, Cl present in smaller amounts and considered as minor elements. The elements of industrial importance, such as the transition metals Cu, Cd, Co, Ni, Ti, and Au, among others, are of yet lesser abundance in rocks and most often occur as inclusions in phases dominated by major elements or as isolated concentrations due to special geological conditions. Other elements of low overall abundance in rocks such as As, Sb, and Sn are more difficult to classify in that their occurrence is limited to small and sporadic concentrations in rocks. In the classical geological chemical framework the elements found as gases in the atmosphere such as Ar, N, Ne, He, and others are little present. Some atmospheric elements such as C and O are present in both the realm of geological occurrence and the sphere of the surface atmosphere. Geochemistry is the study of the occurrence and reasons for these occurrences of different elements.

Geochemistry in Mineral Exploration is a pioneering text and reference book dealing with the newer phases of an ancient and important subject that has intrigued man ever since the days he began to use metals rather than stones for his weapons and implements.

It is now common parlance to refer to the Earth as a physical–chemical–biological system; but this is a relatively recent innovation. Until about 1950, geologists generally used the word ‘system’ to define geologic periods, or the several crystal classes, or the physical chemistry of multicomponent mixtures. Long before then, the word ‘system’ in its current usage had been a part of the vocabulary of a number of fields, including communication and control engineering.

Organic matter is associated frequently with several types of ore deposits. Examples   include   uranium  deposits,  Mississippi  Valley-type   (MVT) bad-zinc deposits, Carlin-typc disseminated gold deposits, and black shale deposits. This association has led to suggestions that the organic material has been involved in ore genesis for many metals and in differing geological environments. Until recently, however, organic geochemical studies have lagged behind inorganic geochemical approaches. The prime reason has been the analytical difficulty in resolving and identifying the range of organic compounds in geological systems. This problem was resolved in the 1960s by the successful coupling of a separation technique, gas chromatography, with a meth\od for determining molecular mass and structure, mass specttrometry. At the start of a metallogenic study, it is necessary to consider critically whether the organic matter could have been passive or active in ore genesis. If passive, considerable information still can be obtained on ore genesis. Organic matter is a sensitive recorder for many events affecting host rocks, including thermal maturation (Douglas et al., 1970), oxidation (McPhee and Nandi, 1981; Havens et al., 1983), leaching {Hunt, 1979) <...>