Abstract Giant gold deposits are defined as those containing > 200 metric tons Au, and bonanza deposits as those containing > 30 metric tons Au averaging at least 30 g/t (1 oz/t). Sixteen giant and/or bonanza gold deposits around the Pacific rim are compared and contrasted in an attempt to determine the factor(s) controlling their development in the epithermal environment. Metallogenic (regional) controlling factors seem to be excluded by the wide variety of tectonic, crustal, and petrochemical settings in which the deposits occur. The deposits are present in neutral, extensional, and, less commonly, compressive arcs. Extension may be concentrated within or behind principal arcs either during active subduction or immediately after cessation of subduction. Mineralized crust ranges from cratonic to primitive island arc. The petrochemisty of genetically related igneous rocks may be calc-alkaline or alkaline, with some extension-related suites being bimodal in character. Deposits are not confined to the proximity of major crustal faults or lineaments. The data base does suggest, however, that unusual arc settings characterized by tectonic complexity and relatively uncommon igneous rock compositions, especially the alkaline suite, are more prospective for giant and bonanza gold deposits than “normal”, andesite-dominated arcs. Deposit- or district-scale factors also cannot be isolated as unique controls of giant or bonanza status. All epithermal deposit types, both high and low sulfidation, may develop exceptional tonnages and/or grades. No single mineralization style or local structural or lithologic setting acts as a universal control. Most deposits are parts of volcanic centers, but these may be dome complexes, maar-diatreme systems, calderas, or stratovolcanoes. Nor do the number or sequence of mineralizing events, the depth of gold deposition, or the inferred mechanism of gold precipitation influence profoundly the formation of all giant and bonanza gold deposits. In the absence of any specific causative factor(s) of a regional or local character, it is difficult to avoid the empirical truism that supply of an unusually large amount of gold to the deposit site is the basic requirement. Large volumes of auriferous fluids may explain giant deposits, but exceptionally gold-rich fluids need to be invoked for generation of bonanzas. However, it is proposed that these fluid requirements must be combined with fortuitous geologic parameters or circumstances at the site of gold deposition if giant and/or bonanza rather than ordinary gold deposits are to develop in the epithermal environment.

Abstract Northeastern Nicaragua is host to three major precious and base metal deposits and numerous smaller prospects, representing a wide spectrum of deposit types. These include the Siuna gold-copper skarn, the Rosita copper-gold skarn, and the Bonanza gold and base metal vein system, as well as occurrences of massive sulfide of uncertain origin, disseminated gold manto-style mineralization, iron skarns, and podiform chromite. Other mineralization may await discovery. The region can be divided into at least two main tectonic units—a pre-Tertiary volcanic arc on continental basement that hosts the Bonanza deposit and a Cretaceous island arc and associated basins on oceanic crust, which host the Siuna and Rosita deposits. The region can also be divided into three major provinces centered on the three major mines, each with its own unique exploration potential. In the Bonanza province there is a potential for extensions of the vein system or other new volcanic-hosted vein systems not yet exposed by erosion. In the Rosita province there is a possibility of a gold-rich porphyry copper deposit, as well as disseminated gold manto mineralization. In the Siuna province there is a strong potential for additional Siuna-type bulk-minable disseminated gold deposits, as well as economic gold-rich massive sulfide mineralization.

Abstract Epithermal Au and Ag deposits of both vein and bulk-tonnage styles may be broadly grouped into high-, intermediate-, and low-sulfidation types based on the sulfidation states of their hypogene sulfide assemblages. The high- and low-sulfidation types may be subdivided using additional parameters, particularly related igneous rock types and metal content. Most high-sulfidation deposits are generated in calc-alkaline andesitic-dacitic arcs characterized by near-neutral stress states or mild extension, although a few major deposits also occur in compressive arcs characterized by the suppression of volcanic activity. Rhyolitic rocks generally lack appreciable high-sulfidation deposits. Highly acidic fluids produced the advanced argillic lithocaps that presage high-sulfidation mineralization, which itself is due to higher pH, moderate- to low-salinity fluids. Similar lithocaps in the Bolivian Sn-Ag belt, some mineralized with Ag and Sn, accompany reduced, ilmenite series magmatism. Intermediate-sulfidation epithermal deposits occur in a broadly similar spectrum of andesitic-dacitic arcs but commonly do not show such a close connection with porphyry Cu deposits as do many of the high-sulfidation deposits. However, igneous rocks as silicic as rhyolite are related to a few intermediate-sulfidation deposits. These deposits form from fluids spanning broadly the same salinity range as those responsible for the high-sulfidation type, although Au-Ag, Ag-Au, and base metal-rich Ag-(Au) subtypes reveal progressively higher ore-fluid salinities. Most low-sulfidation deposits, including nearly 60 percent of the world's bonanza veins, are associated with bimodal (basalt-rhyolite) volcanic suites in a broad spectrum of extensional tectonic settings, including intra-, near-, and back-arc, as well as postcollisional rifts. Some low-sulfidation deposits, however, accompany extension-related alkaline magmatism, which, unlike the bimodal suites, is capable of generating porphyry Cu deposits. Extensional arcs characterized by active andesitic-dacitic volcanism do, however, host a few low-sulfidation deposits. Low-sulfidation deposits genetically linked to bimodal volcanism are formed from extremely dilute fluids, whereas modestly saline contributions account for the low-sulfidation deposits in alkaline centers. Early lithocap-forming and high-sulfidation fluids, as well as low-sulfidation fluids in deposits associated with alkaline igneous rocks, display clear evidence for a close genetic relationship to magmatism and, although the linkage is less intimate, late high-sulfidation fluids responsible for much of the Au introduction along with similar intermediate-sulfidation fluids also seem to owe much to their magmatic parentage. Where ascending intermediate-sulfidation fluids enter lithocaps, they evolve to high-sulfidation fluids. Eventual neutralization and lowering of sulfidation state by wall-rock interaction can convert high- back to inter-mediate-sulfidation fluids, as confirmed by both spatial and paragenetic transitions from high- to interme-diate-sulfidation mineralization. In contrast, low-sulfidation fluids other than those of alkaline affiliation lack such clear-cut connections to magmatism, although Giggenbach's work on the geothermal fluids associated with the Taupo Volcanic Zone in New Zealand suggests that a deep magmatic source different from that of fluids in andesitic arc terranes is probable. In addition, at least in some regions, there appears to be a correlation between the reduced sulfide assemblages of low-sulfidation deposits and the reduced nature of the volcanic rocks with which they are associated. Therefore, it may be argued that the defining characteristics of epithermal deposits are related directly to their magmatic roots, notwithstanding the existence of important unanswered questions, especially regarding the source of low-sulfidation fluids. This review puts forward several exploration guidelines for epithermal precious metal deposits. Exploration activity in andesitic-dacitic arcs should be restricted to high- and potentially related intermediate-sulfidation deposits containing Au and/or Ag, whereas a variety of rift-related bimodal suites and convergent-margin alkaline rocks offer the prime environments for Ag-deficient, low-sulfidation Au deposits (Ag/Au <∼15). Bonanza Au veins are more likely to be of the low-sulfidation type and to be discovered at relatively shallow paleodepths in bimodal rift settings, where rhyolitic and/or basaltic rocks may be proximal to Au ore. Even tholeiitic basalts in emergent mid-ocean ridge or hot-spot settings might possess underappreciated epithermal Au potential. Subaerial extensions to some volcanic-hosted massive sulfide (VMS) belts may possess low-sulfidation Au potential because of the broadly similar volcanotectonic settings for both deposit types. The reduced, ilmenite series volcanic rocks of the Bolivian Sn-Ag belt are unfavorable for epithermal Au. Deficiency of volcanic rocks in epithermal provinces is typical of highly compressive arcs (high- and intermediate-sulfidation deposits) and some rifts swamped by fluviolacustrine sedimentation with silica sinter occurrences (low-sulfidation deposits). In contrast to high- and intermediate-sulfidation deposits, exploration for low-sulfidation Au deposits, even where exposed, may be hampered by the visually subtle nature of many outcropping examples.

ABSTRACT The Bonanza King Formation of the southern Great Basin is composed of 150 to 250 carbonate parasequences (0.5 to 7 m thick) that provide a remarkable "strip chart" of Middle to Late Cambrian third-order accommodation history. Six superb exposures of the Banded Mountain Member of the Bonanza King Formation were logged on a decimeter scale and correlated to generate a detailed platform-to-basin transect. These cyclic carbonates were deposited on a flat-topped, fully-aggraded platform that extended approximately 250 to 300 km across the early Paleozoic passive margin of southern Nevada and eastern California. The Banded Mountain Member ranges from 400 to 1330 m in thickness and forms a westward-thickening wedge from craton margin facies in the eastern Mojave to shelf-edge and base-of-slope facies in the Last Chance Range. Thick successions of meter-scale carbonate parasequences show systematic changes in parasequence type, dominant lithofacies, and thickness vertically through the cyclic interval that were governed by long-term, third-order changes in accommodation. Fischer plots provide a graphic illustration of changes in accommodation space through time, and appear to be a valuable tool for correlating sequence boundaries and systems tracts. Similar patterns of positive and negative slopes on Fischer plots of the five platform sections of the Banded Mountain Member define four major sets of long-term increases in accommodation followed by long-term decreases in accommodation that correspond to four distinct depositional sequences. Translating sequence stratigraphic principles originally defined for seismic-scale siliciclastic systems to outcrops of cyclic carbonates requires a deemphasis of stratal geometries and an increased awareness of correlative vertical changes in stacking patterns of component parasequences. Sequence boundaries and transitions between systems tracts on flat-topped platforms, such as the Bonanza King, are believed to be zones rather than distinct horizons because of the effect of the higher frequency sea-level signal superimposed on the long-term, third-order event. Sequence boundary zones bracketing the four depositional sequences within the Banded Mountain Member are characterized by thin, tidal-flat dominated parasequences exhibiting abundant evidence for repeated episodes of exposure. Transgressive systems tracts in the Banded Mountain Member are characterized by a lower succession of parasequences composed of subequal amounts of tidal-flat and subtidal lithofacies passing upward into thicker parasequences with higher percentages of deeper subtidal facies. Highstand systems tracts in the Banded Mountain Member are characterized by thinning-upward stacks of parasequences showing progressively shallower peritidal conditions within the component lithofacies.

Abstract Fruta del Norte is a completely concealed and extremely well-preserved, Late Jurassic epithermal gold-silver deposit of both low- and intermediate-sulfidation type, which is located in the remote Subandean mountain ranges of southeastern Ecuador. Currently defined indicated resources are 23.8 million metric tons (Mt) averaging 9.61 g/t Au and the total endowment is 9.48 Moz Au. The deposit, notable for the widespread occurrence of visible gold and bonanza grades, will be bulk mined underground. Fruta del Norte was discovered in 2006 during greenfield exploration and systematic drill testing of a conceptual geologic model, which predicted that auriferous veins would occur in andesitic volcanic rocks inferred to underlie a zone of arsenic- and antimony-anomalous silicification in fluvial conglomerate. The host andesitic volcanic rocks, crosscutting feldspar porphyry, and associated phreatic breccia are part of a roof pendant in the Zamora batholith. Together, they are products of a continental-margin volcanoplutonic arc of Middle to Late Jurassic age. The deposit lies beneath the northern extremity of the ~16-km-long, Suárez pull-apart basin where it is localized by steep, second-order faults within the regionally extensive Las Peñas strike-slip fault zone. The pull-apart basin was progressively filled by fluvial conglomerate, dacitic ignimbrite, finer grained siliciclastic sedimentary rocks, and, finally, andesite flows. The Fruta del Norte deposit comprises a 1.3-km-long and up to >300-m-wide vein stockwork associated with quartz-illite-pyrite alteration. The deposit comprises two principal vein types, one in the south dominated by quartz, manganoan carbonates, and abundant base metal sulfides and the other in the north dominated by manganese- and base metal-poor quartz, chalcedony, and calcite. Adularia is a minor gangue mineral in both. Both vein types are abruptly transitional upward and westward to a third important ore type characterized by intense silicification and chalcedony veining, with disseminated and veinlet marcasite (± pyrite). An extensive silica sinter horizon directly overlies the andesitic rocks and/or occurs as interbeds in the lowermost 20 m of the conglomerate and, consequently, is in unusual proximity to the underlying gold-silver orebody. Much of the conglomerate lacks silicification except for a narrow, steeply inclined zone exposed above the deposit, which led to its discovery.

Abstract A review of representative metallogentic provinces brings out present trends in the interpretation of ore deposits and touches upon many major problems of ore deposition. The individual provinces vary in size from single mining districts to regions several hundred miles in extent; the limits usually are difficult to place. The great molybdenite deposits of Climax, Colorado, may be classed as a single molybdenite province or it may be considered as a part of the larger, more varied Front Range mineral belt. The ore deposits of the Peruvian Andes contrast with those of the Eastern Cordillera of Bolivia, yet gradations exist that suggest a certain unity to the mineralization. Some geologists describe the copper deposits of Northern Rhodesia and Katanga as a well-defined metallogenetic province, whereas others look upon these deposits as a part of the larger mineralized region that includes the uranium-copper-cobalt ores of Shinkolobwe and the copper-zinc ores of Kipushi. The association of the ores of Sudbury, Cobalt and Keweenaw Point with basic igneous rocks of late Precambrian age suggests a logical grouping of the deposits as a unit, although the processes of ore deposition may be quite distinct. Among the larger metallogenetic provinces that seem to be well established are those of the Coast Range of British Columbia and Alaska, the Sierra Nevada, and the copper belt of Chile and southern Peru. Of somewhat smaller size, the gold province of South Africa is more sharply defined. The age of ore deposition constitutes a major problem in many of the metallogenetic provinces under review. Some districts may permit a close dating of the ores and may give evidence of more than one metallogenetic epoch. In many districts, however, the age of the mineralization is fixed only within broad limits and is based largely on indirect evidence. This may lead to a difference of opinion as to the age of the mineralization and the number of epochs that are represented. In the San Juan region of Colorado, two distinct metallogenetic epochs are clearly established. In the Arizona-New Mexico province the deposition of copper took place during more than one metallogenetic epoch, although some question remains as to the exact age of certain deposits. The varied ore deposits of Idaho, grouped as a single metallogenetic province, illustrate the difficulty in the dating of ores. The principal deposits may be of Nevadan or of Laramide age; the ores of shallow type may represent one or two subsequent epochs of metallization. Studies elsewhere in the West suggest that the metallogenetic epochs are not so sharply defined as previously supposed. The close connection between basic magmas and the chromite, nickel-copper and titaniferous iron Ores is well established, although relatively few deposits are of strictly magmatic type. The possible connection between ore deposits and nearby granitic intrusions has been the subject of closer analysis. In the Precambrian districts of Canada, for example, the distribution of the massive sulfide deposits suggests that they are more closely related to the Keweenawan basic intrusions than to the Algoman granites. Ore deposits occurring in regions that show little evidence of intrusive igneous activity are difficult to explain. To account for these deposits, several theories have been stressed as alternatives to the hydrothermal theory and have been applied to the uranium ores of the Colorado Plateau, the copper deposits of Northern Rhodesia, the gold deposits of South Africa, and the iron ores of metamorphic terranes. Metallogenetic provinces outlined by deposits of sedimentary origin are well illustrated by the iron-formations of Precambrian age; there is substantial agreement that these formations represent chemical sediments. The possible correlation between epigenetic ore types and tectonic environments is being given increased attention. Characteristic of the highly metamorphic Precambrian terrane are deposits of high to moderate intensity, including gold-quartz veins, massive sulfide deposits, and various types of iron ores. Some of these can be duplicated in the more deeply eroded orogenic belts of later age, such as the Sierra Nevadas and Appalachians. In less deformed Precambrian rocks, ores of lower intensity prevail, as illustrated by the uranium, copper-cobalt and native copper deposits. In the younger mountain ranges, the ores are more varied and represent a wide temperature range, with many examples of lateral zoning. The ores correlated with the post-tectonic period of volcanism are perhaps the most distinctive: the gold-silver ores of the bonanza type, mixed base-metal ores, and uncommon metal combinations which reflect a high degree of telescoping. At the low-temperature end of the sequence are deposits characteristic of the stable regions: the lead-zinc, copper-cobalt, uranium, barite and fluorite deposits, many of which lie far from exposed igneous rocks. In many districts, careful study has revealed highly significant stratigraphic and structural controls in ore deposition that are not readily apparent. This is true not only of the complex metamorphic areas of the Precambrian and the highly deformed belts but also of areas of mild deformation where details of stratigraphy may be of utmost importance. The continued application of the principles of geochemistry, geophysics and geology, combining field and laboratory study, should be of value not only in determining the origin of the ores but also in explaining the metallogenetic provinces.

Abstract Epithermal gold deposits are the principal source of gold in Japan, and mesothermal vein gold or by-product gold from skarn deposits, VMS (the Kuroko type and the Besshi type), and polymetallic veins contribute historically only 10 percent of domestic gold production. Gold production from epithermal gold deposits of Kyushu amounts to 284 tonnes and comprises about 40 percent of total Japanese gold production, 576 tonnes, from the Meiji Restoration (1868) to present (1999). The silver/gold ratio of ores in Kyushu is less than three and differs from the value that exceeds 10 in other areas ( Fig. 1 ). The Yamagano mine in the Edo era and later the Taio and Kushikino mines were the largest gold-silver mines in Kyushu before the discovery of the Hishikari deposit. At present the Hishikari underground operation and three opencut mines of the Nansatsu-type gold deposits at Kasuga, Iwato, and Akeshi are producing gold. The major gold deposits in Kyushu, typically of the low- sulfidation vein type and locally the high-sulfidation Nansatsu type, occur in extinct or waning geothermal systems of the Pliocene and Pleistocene volcanic areas. The young formation ages relate to the well-preserved shallow bonanza zones and overlying thick argillic alteration zones, and in places surface expression of hydrothermal activity, such as sinters and nearby acid alteration related to steam- heated acid hot springs. This contribution aims to present supplementary data to a previous review paper ( Izawa and Urashima, 1989 ), which described the relationship