The Organic Geochemistry of Gold, Platinum, Uranium, and Mercury Deposits
Gold, the platinum group elements, uranium, and mercury have been subjects of organic geochemical studies for the past few decades. This geochemical interest contrasts with their chemistry, as platinum and gold compounds were synthesized over 150 years ago. Gold and the platinum group elements are valued for their relative chemical inertness, in experimental bombs, for example. In organic and biochemical systems, however, they are reactive. Mercury occurs in ores as a native element or sulfide, but in the environment it is often a component of organic species.
Several approaches are combined in this review in order to highlight areas where there is good agreement between the perspective of a chemist and a geologist and areas where there are discrepancies. Initially, the concept of organometallic compounds is introduced, and a brief chemical or biochemical guide as to which metals would be expected to show strong or weak interactions with organic matter is presented. The ore deposits in which organic matter is present with each metal are then summarized in order to provide an initial comparison between chemical and biochemical predictions and geologic observations. To illustrate the stages during which metal-organic interactions take place, the occurrence of organosulfur and organonitrogen compounds is summarized, together with a brief summary of reduction mechanisms. Finally, the potential interactions between metals and organic matter are summarized in terms of the three general stages of ore deposit formation (source, transport, and precipitation).
In this paper, an unusual citation convention is used in reference to certain papers cited by Boyle (1987). This volume contains many key papers on gold, some of which were published in neither recent nor easily accessible original sources. Citations of papers considered difficult to obtain have been made therefore to Boyle (1987). The literature on the organic geochemistry of ore deposits has grown considerably in the past 20 years, especially with respect to uranium, so that a detailed review would be excessively long. As far as possible, therefore, references have been cited which permit the interested reader to follow a topic in more detail.