Abstract The association of organic matter with ore minerals, gangue, and host rock in many low-temperature (<120°C) to moderate-temperature (120°-350°C) ore deposits is a well-known phenomenon (Saxby, 1976; Leventhal, 1986; Parnell et al., 1993; Giordano, 1996; Giże, 1999) and was recognized early in the twentieth century (Siebenthal, 1915; Harder, 1919; Schneiderholm, 1923; Bastin, 1926; Fowler, 1933). The study of organic constituents in ores, particularly if coupled with studies of other ore components and conditions, can provide much information on both active and passive roles of organic matter before, during, and after ore genesis, and in some cases can lead to the development of valuable exploration techniques. By the 1950s, it was recognized that biological sequestering of metals, sulfide production by sulfate-reducing bacteria, biological precipitation of metals, sorption of metals by organic colloidal particles, modification of geochemical environments by organic processes, and the mobilization of metals by metal-organic complexes were all potentially important roles played by organic matter in the concentration of metals to form metalliferous shales and certain types of ore deposits (Berger, 1950; Krauskopf, 1955). By the 1960s, it was recognized that dead organic matter (organic matter not in living organisms) may be a powerful reducing agent for sulfate and thus may provide a source of sulfide for ore-forming systems (Barton, 1967; Skinner, 1967). Roedder (1967) reported the presence of hydrocarbons and sulfate in fluid inclusions from ore deposits. This observation was cited by Barton (1967) as strong evidence that organic matter was present at the time of ore formation and that thermodynamic equilibrium (which predicts hydrogen sulfide and carbon dioxide) was not attained in the ore fluid because of sluggish kinetics at the low temperature of ore formation. Hoering (1967) summarized his pioneering work on organic matter associated with gold and uranium in the Carbon Leader Formation of the Witwatersrand district, South Africa. Because it was relatively immature Precambrian organic matter (rather than graphite), it was suitable for analysis of simple and complex chemical compounds and led the way for future studies of organic matter in ore deposits and Precambrian rocks (Leventhal et al., 1975).

Abstract The objective of this review is to introduce some organic analytical methods that may be used to study organic matter in ore deposits. It is not a comprehensive guide to all techniques. The underlying theme is to guide the interested reader toward an analytical strategy that is appropriate for the information sought. Some of the background issues that an analyst has to consider are initially introduced, with a brief summary of the thermal maturation of organic matter. Following an introduction to sample preparation, the remainder of the chapter summarizes general and spectroscopic methods that provide a general indication of organic composition, followed by physical techniques that ultimately yield information at a molecular scale. Each analytical technique will be introduced, followed by its applications. Where applicable, a case study will be described. The hydrothermal alteration of organic matter from immature precursors to mature products is used as an analog of a process responsible for the maturation of organic matter found in ore deposits. The intention is to indicate how information obtained from these analytical methods can be used to solve problems stemming from the occurrence of organic matter in ore deposits. In order to understand the applicability and limitations of organic analytical techniques, it is first necessary to understand the forms in which organic matter can be present in and around ore deposits (see Giże, 2000; and Leventhal and Giordano, 2000). The simple reason is that all organic analytical methods are constrained by the organic matter form, such as phase (solid, liquid, or gas) and, often, by the molecular structure and molecular weight. To date, a single analytical method that provides a complete analysis of organic matter exists only in science fiction films. Consequently, part of the analyst' s consideration is in rendering the organic material into a form that can be analyzed by the techniques and instruments available without losing the information sought.

Abstract Within various types of ore deposits, both syngenetic and epigenetic, elemental or reduced carbon can be observed. Since the recognition of a possible role of organic matter in the formation of Carlin-type and black shale-hosted deposits, the ability to recognize organic residues associated with ore deposits and to identify, interpret, and manipulate the data from these residues are becoming important. Organic geochemical studies are one approach that has become increasingly popular during the past two decades. Organic petrographic studies applied to ore deposits are rare in the literature, but petrographic techniques are more rapid, less costly, and reflected light microscopes are probably more easily available than organic geochemical laboratories. An especially favorable aspect of microscopy is that it offers resolution on a finer scale than organic geochemical techniques, enabling immediate recognition of sample heterogeneity. Historically, organic petrography developed from ore microscopy during the first half of the twentieth century. As a result of the importance of organic petrography in hydrocarbon exploration, several techniques (especially ultraviolet fluorescence microscopy) have been developed which are of potential use to ore microscopists.

Abstract One aspect of ore deposit studies is their potential application in prospecting for new deposits. That application has been considered in this volume (e.g., Leventhal and Giordano, 2000; Wood, 2000) and elsewhere. Heroux et al. (1996), for example, integrated organic reflectance and clay mineralogy to delineate alteration zones associated with mineralization. Both ore and petroleum deposits are a result of fluid migration, and from this viewpoint it can be expected that organic and inorganic fluids may use similar lithological pathways (Giże and Barnes, 1994). This chapter will briefly introduce organic maturation modeling as an approach to predicting both the age and relative timing of ore and petroleum fluids. The thermal maturation of sedimentary organic matter is primarily a function of time and temperature. Simplistically, if two of the parameters (organic maturity, temperature, and time) are known, then the third can be derived. If organic maturity can be determined (using optical properties such as vitrinite or bitumen reflectance, or using geochemical parameters such as isomer ratios or elemental ratios), as well as temperature (fluid inclusions), then time (e.g., duration of heating event) can be estimated. A close association between organic matter and some ore deposits has been noted throughout this and other volumes. The association may reflect genetic links (e.g., reduction or complexing), or maysimply reflect genetically unrelated aqueous and hydrocarbon fluids using the same aquifer. Petroleum, or petroleum-derived bitumens, have been reported as inclusions in ore minerals from many ore deposits (Roedder, 1984). If the time-temperature dependence of organic matter can be used to estimate when the petroleum stage of organic maturation occurred, then a potential dating method for the age of the ore deposit is also established. The use of organic modeling of the petroleum stage of organic maturation is shown for the Carlin (Nevada) disseminated gold deposit and the Bowland basin, United Kingdom, an historical district of renewed interest following the discovery of the Irish base metal deposits. The Carlin deposit provides an example of the use of organic modeling as a means of ascertaining whether or not organic matter was mobile at the time of mineralization, thus providing evidence to support or refute specific genetic concepts. The Bowland basin example will show that the integration of modeling, fluid inclusion data, and field observations can provide constraints on the probable age of mineralization.

Abstract Organic compounds generated by biological processes, either at the surface or within the Earth' s crust, are incorporated into many types of geologic materials and undergo numerous transformations driven by changes in temperature, pressure, and composition. These transformations reflect the energetic response of compounds that are transported by geologic processes into conditions where they are far from equilibrium. The active geochemical processes and the geologic variables that influence the course of organic alteration can be identified by evaluating the energy differences between the starting compounds and their alteration products in deeply buried sedimentary rocks, ore deposits, petroleum, and elsewhere. Thermodynamic calculations provide quantitative assessments of these energetic differences, and it is the purpose of this review to illustrate how such calculations can reveal the driving forces of organic transformations. This type of approach can be useful in the study of ore deposits because oxidation-reduction reactions dictate the course of organic alteration. These redox reactions can couple to inorganic redox processes that enhance metal transport or trigger ore deposition. As always, thermodynamics indicates the possible, and cannot, on its own, reveal the mechanisms through which the transformations may occur. Nevertheless, thermodynamics provides the means to assemble plausibility arguments based on geologic information and to test those arguments with an independent set of data.

Abstract Since the widespread occurrence of low-molecular-weight organic ligands in subsurface waters of sedimentary basins began to be recognized about 20 years ago (Willey et al., 1975; Carothers and Kharaka, 1978), their origin, distribution, and significance has become an intensively studied field in geochemistry (Gautier et al., 1985, Gautier, 1986; Pittman and Lewan, 1994). Acetate and propionate (for the International Union of Pure and Applied Chemistry (IUPAC) names and chemical structure, see Appendix II of this volume) are generally the most abundant organic ligands reported in oil-field waters, although a variety of additional monocarboxylic, dicarboxylic, and other reactive organic species are present (Germanov and Mel'kanovitskaya, 1975; Willey et al., 1975; Carothers and Kharaka, 1978; Workman and Hanor, 1985; Hanor and Workman, 1986; Kharaka et al., 1986; Fisher, 1987; Means and Hubbard, 1987; Fisher and Boles, 1990; Lundegard and Kharaka, 1990, 1994; Lundegard and Trevena, 1990; MacGowan and Surdam, 1990a; Giordano and Kharaka, 1994). The highest concentrations (close to 10,000 mg/L) are present in formation waters obtained from relatively young (Tertiary-age) reservoir rocks at temperatures of approximately 80° to 140°C (Carothers and Kharaka, 1978; Lundegard and Kharaka, 1994).

Abstract The formation of all ore deposits can be linked to three fundamental processes (Fig. 1): (1) mobilization of elements in one or several source regions; (2) transport of ore and non-ore constituents from a source region to the site of deposition and beyond; and (3) concentration of ore constituents, normally at the site of deposition. All three processes are interrelated, particularly in the case of hydrochemical deposits in which specific chemical mechanisms responsible for keeping metals in the ore fluid (chemical transport) also play a key role in the processes of mobilization and deposition. For example, a metal may be leached from a source rock and enter the ore solution as a metal-organic complex (in this case, metal-organic complexing is the chemical transport mechanism). It can then be transported physically by the ore fluid as a metal-organic complex, and finally, the metal can be precipitated by the breakdown of the metal-organic complex. Thus, for many hydrothermal, residual, and chemical sediment deposits, an understanding of the chemical transport mechanism is a key to understanding the related processes of mobilization and deposition. In this chapter, the focus is on the role of organic matter as a chemical transport agent in aqueous ore-forming systems (i.e., hydrothermal, residual, and chemical sediment deposits). In these systems, ore and nonore constituents are carried primarily by aqueous fluids. The transport of ore metals in ore fluids can take place as dissolved aqueous species (e.g., metal-organic complexes), or within a suspension in which metals are bound to organic particles, or within a crude oil phase (liquid petroleum). Of these possibilities, only chemical transport in solution will be considered in the following sections. First, the role of dissolved organic matter as a metal-transport agent in aqueous ore fluids will be discussed at some length. Next, our current understanding of ore-metal transport via petroleum is reviewed. Finally, the relative importance of inorganic and organic mechanisms of ore-metal transport will be briefly commented upon.

Abstract Supergene enrichment and dispersion involve similar chemical and physical processes operating near the surface of the Earth. In both cases, elements are mobilized from their source, transported and fixed at some new site. In supergene enrichment, elements are concentrated by these processes. Supergene enrichment is of importance because it can upgrade otherwise uneconomic primary deposits to ore grade. During dispersion, elements are spread over a greater volume of space and diluted. In this chapter, use of the term dispersion is restricted to what Rose et al. (1979, p. 17) referred to as “secondary dispersion,” i.e., the redistribution of elements by processes occurring after the main ore-forming event, usually in the surficial environment. Dispersion often results in anomalous elemental concentrations in rocks, soils, lake and stream sediments, plants, or natural waters in the vicinity of ore deposits, and thus impacts on geochemical exploration by increasing the probability that a geochemical survey will uncover the anomaly. Giordano (2000) summarized the various roles of organic matter as transport agents in ore-forming and related systems. The inorganic geochemical processes which govern supergene enrichment and dispersion have been given considerable attention. Somewhat less attention has been paid to the role of organic matter. However, the potential roles for organic matter in supergene enrichment and dispersion are numerous and include (see also Schnitzer and Khan, 1972, 1978; Reuter and Perdue, 1977; and Wood, 1996): (1) increasing the solubility of minerals or decreasing the amount of sorption of ions onto mineral surfaces as a result of the formation of aqueous metal-organic complexes and/or increased acidity; (2) increasing metal mobility via coating and protection of colloids from coagulation; (3) metal fixation, either by reduction or through sorption onto solid organic material; (4) modification of the sorption-ion exchange properties of mineral surfaces; and (5) alteration of the rates of sorption, dissolution, and precipitation.

Abstract Organic matter provenance Organic matter in sedimentary basins, usually marine and either of Recent or geologically old origin, is derived from the syngenetic residues of posthumus biogenic debris (Simoneit, 1982a; Tissot and Welte, 1984; Hunt, 1996). This material is composed of both autochthonous detritus and allochthonous residues derived from continental sources (Simoneit, 1982a). Aquatic sediments receive allochthonous organic detritus primarily by river wash-in and eolian fallout particles, with ice-rafting and sediment recycling as minor contributing processes (Simoneit, 1975, 1978). Organic matter that accumulates in contemporary sediments represents the residues from primary biological carbon fixation and its degradation (remineralization; Table 1). The nature of this immature organic material is described below, followed by a general description of more mature organic matter formed as a result of maturation in subsiding basins. Nature of immature organic matter in sedimentary basins Gas : Interstitial gas in recent sedimentary environments consists primarily of methane, carbon dioxide, and sometimes hydrogen sulfide (Claypool and Kaplan, 1974; Claypool and Kvenvolden, 1983). The biogenic hydrocarbon gases usually have CH 4 /(C 2 H 6 + C 3 H 8 ) ratios greater than 1,000, while those of a thermogenic origin have ratios less than 50 (Bernard et al., 1976). For example, the C 1 /(C 2 + C 3 ) ratios for shallow sediment gases from Guaymas basin, Gulf of California range from 41 to 150 and thus indicate a mixed origin of biogenic (CH 4 ) and thermogenic (C 1 -C 8 ) hydrocarbons (Simoneit et al., 1979). The depth range where biogenic gas can be found is variable but generally shallow (∼100 m) and depends on microbial production and environmental conditions in the sediments.

Abstract 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.

Abstract Some of the world' s most important mineral resources occur in shales. Deposits at Shaba in the Congo, White Pine in the United States, and Lubin in Poland each hold or originally contained greater than 500 million tons of high-grade Cu ore and those at Meggen in Germany, the Selwyn basin in Canada, and Red Dog in Alaska contain multimillion-ton Pb-Zn sedimentary-exhalative (sedex) ores hosted by black shales and related beds (e.g., Rentsch, 1974; Brown, 1978; Gustafson and Williams, 1981; Carne and Cathro, 1982; Lange et al., 1985; Goodfellow and Jonasson, 1987; Sangster, 1990; Maynard, 1991a, b; Giże, 2000; Pratt and Warner, 2000). Moreover, recent discoveries in China (Fan et al., 1973) have led to small-scale production of shale-hosted Ni and Mo from an entirely new sort of bedded sulfide ore containing values for precious metals totaling several hundred parts per billion Au, Pt, and Pd. Together with similar deposits from the Devonian of the Yukon, the Chinese ores raise hopes for discovery of important new resources for Pt, Au, and ferroalloy metals (Fan 1983; Coveney and Chen, 1991). On the other hand, despite high tenors, shales from some enriched deposits such as the Mo-rich Pennsylvanian Mecca Quarry shale of North America and the Proterozoic HYC McArthur River Pb-Zn-Ag prospect of Australia are presently unmineable because of inadequate thickness and difficulties with beneficiation of fine-grained host phases. In addition to their economic value as ores of base metals, organic-rich shales have been important sources of solid fuels and hydrocarbons, clays, and uranium. Moreover, organic-rich shales have had adverse economic significance because of their tendencies to expand and disintegrate as a result of the growth of sulfate crystals or swelling of clays disrupting the foundations of buildings and the roofs of mines (Coveney and Parizek, 1977; Rudy, 1982). Metalliferous black shales also may have more general environmental significance. For example, they no doubt contribute heavy metals to soils, ground water, and surface waters (Bailey, 1995; Forseh, 1997) and therefore their presence may dictate the need for baseline geochemical studies in road construction projects, for example. Because of their high U contents, black shales have been suspected as sources of gas (e.g., Coveney et al., 1987).

Abstract Base metals are incorporated into diverse sedimentary rocks as a result of routine biogeochemical processes during primary production, heterotrophic consumption, bacterial diagenesis, burial maturation, and hydrothermal alteration. In most cases, concentrations of organic carbon and base metals in sedimentary strata are below minimum levels for economic development of energy and/or mineral resources. Major ore deposits are linked, in many cases, to unusual basinal conditions that focus metal-bearing solutions into sedimentary facies containing reactive organic constituents inherited from the original sedimentary inventory or enriched by secondary fluid migration. This chapter examines the chemical and physical role of reactive organic matter in base metal deposits associated with carbonate and shale sequences. The discussion of selected well-studied deposits is organized on the basis of the dominant metals and the sedimentary facies hosting the orebody. Three groups of ore deposits are discussed in this chapter: (1) carbonate-hosted lead-zinc-barium deposits; (2) shale-hosted zinc-lead deposits; and (3) shale-hosted copper deposits. Diverse roles of organic materials in the genesis of sediment-hosted base metal deposits are evident from recent publications on the Mississippi Valley Viburnum trend, Canadian Pine Point, French Massif Central, Canadian Selwyn basin, Australian McArthur River region, Alaska Red Dog mine, European Kupferschiefer, and Michigan Nonesuch shale. Although several important types of sediment-hosted base metal ores are not considered in this paper, the selected examples provide a framework for understanding how modern organic geochemical techniques can be applied in an interdisciplinary approach to exploration and development of a wide range of base metal deposits. Additional discussions of shale- and carbonate-hosted base metal deposits can be found in Coveney (2000), Giże (2000), Kettler (2000), Leventhal and Giordano (2000), and Simoneit (2000).