Gold in 2000
THIS Gold in 2000volume is organized around a classification of hypogene gold deposits that emphasizes their tectonic setting and relative time of formation compared to their host rocks and other gold deposit types (e.g., Sawkins, 1972, 1990; Groves et al., 1998; Kerrich et al., 2000). The temporal division of orogenic gold deposits into Archean, Proterozoic, and Phanerozoic follows closely the recently published classification of orogenic gold deposits (Groves et al., 1998) which incorporates the previously identified “mesothermal” gold deposits. The newly recognized intrusion-related and sedex gold deposits represent new gold deposit classes even though their exact genetic classification remains open, with more research considered a priority. Proterozoic Au-only and Cu-Au-(Fe) deposits are also a relatively recently recognized class of structurally controlled epigenetic gold deposits. Particularly, the origin and classification of Cu-Au-(Fe) deposits (e.g., Olympic Dam) remains equivocal, as pointed out by Partington and Williams (2000). In fact, Kerrich et al. (2000) discuss the anorogenic iron oxide copper-gold deposits as one of six world-class gold deposit classes. Low- and high-sulfidation and hot spring epithermal gold deposits are dealt with as one genetic gold class. Alkalic epithermal and porphyry gold deposits are dealt with as a separate gold deposit class owing to their specific host-rock association and element enrichment (e.g., Mo, F, Be, Hg, W, and Sn).
The gold deposit classes are described from both industry and academic points of view, with emphasis on a balanced account of the descriptive geology, genetic interpretations, exploration significance, as well as open questions and future research avenues. The volume contains 13 papers covering 10 major classes of gold deposits and three summary papers, and was presented as a Society of Economic Geologists-sponsored short course held November 10 and 11, 2000, at Lake Tahoe, Nevada.
Orogenic gold ores are associated with regionally metamorphosed terranes of all ages (Kerrich and Cassidy, 1994) and are spatially linked to subduction-related thermal processes (Kerrich and Wyman, 1990)(Fig. 1). These metal concentrations formed during compressional to transpressional deformation processes at convergent plate margins in accretionary (oceanic-continental plate interaction) and collisional (continental-continental collision) orogens (i.e., Bohlke, 1982; Groves et al., 1998). In both cases hydrated marine sedimentary and volcanic rocks have been added to continental margins over a long period of collision (10 to >100 Ma). Accretionary or peripheral orogens contain gold deposits in the Archean of Australia, Canada, Africa, India, and Brazil and the Mesozoic and Cenozoic gold fields of western North America, i.e., the famous Mother Lode belt. Collisional or internal orogens contain gold deposits in the Proterozoic of Australia, North America, West Africa, and Brazil, and the famous Phanerozoic gold fields in the Variscan, Appalachian, and Alpine regions of North America and Europe. In Phanerozoic orogenic gold deposits, subduction- related thermal events, episodically raising geothermal gradients within the hydrated accretionary sequences, initiate and drive long-distance hydrothermal fluid migration.
The Geodynamics of World-Class Gold Deposits: Characteristics, Space-Time Distribution, and Origins
Published:January 01, 2000
Robert Kerrich, Richard Goldfarb, David Groves, Steven Garwin, 2000. "The Geodynamics of World-Class Gold Deposits: Characteristics, Space-Time Distribution, and Origins", Gold in 2000, Steffen G. Hagemann, Philip E. Brown
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There are six distinct classes of gold deposits, each represented by metallogenic provinces having hundreds to more than 1,000 tonnes (t) gold production. These deposit classes are as follows: (1) orogenic gold; (2) Carlin and Carlin-like gold deposits; (3) epithermal gold-silver deposits; (4) copper-gold porphyry deposits; (5) iron oxide copper-gold deposits; and (6) gold-rich volcanic-hosted massive sulfide to sedimentary-exhalative (sedex) deposits. This classification is based on ore and alteration mineral assemblages, ore and alteration metal budgets, ore fluid pressure(s) and compositions, crustal depth or depth ranges of formation, relationship to structures and/or magmatic intrusions at a variety of scales,...