S. Leary, R. Sillitoe, Jorge Lema, Fernando Téliz, Diego Mena
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.
Fruta del Norte是一个完全隐蔽且保存极为完好的晚侏罗世浅成热液型低硫化和中硫化型金银矿床，位于厄瓜多尔东南部偏远的Subandean山脉。目前确定的指示资源量为2380万吨(Mt)，平均为9.61克/吨金，总禀赋为9.48万盎司金。该矿床以可见金矿和富矿品位普遍存在而著称，将在地下大规模开采。Fruta del Norte是在2006年的绿地勘探和概念地质模型的系统钻探测试中发现的，该模型预测含金矿脉将出现在安山岩火山岩中，这些火山岩被推断位于河流砾岩中砷和锑异常硅化带的下面。寄主安山岩火山岩、横切长石斑岩和伴生的潜水角砾岩是萨莫拉岩基顶板垂坠的一部分。它们都是中晚侏罗世大陆边缘火山-深成弧的产物。该矿床位于约16公里长的Suárez拉分盆地的北端，位于区域广泛的Las Peñas走滑断裂带内的陡峭二级断裂中。拉分盆地逐渐被河流砾岩、英灰质火成岩、细粒硅质沉积岩填充，最后是安山岩流。Fruta del Norte矿床包括一条长1.3公里、宽>300米的脉网，并伴有石英-伊利石-黄铁矿蚀变。矿床主要有两种脉型，南部以石英、碳酸锰为主，贱金属硫化物丰富;北部以缺锰、贱金属的石英、玉髓、方解石为主。两者都是一种次要的脉石矿物。这两种矿脉类型都突然向上和向西过渡到第三种重要的矿脉类型，其特征是强烈的硅化和玉髓脉状，并带有浸染状和脉状的黄铁矿(±黄铁矿)。广泛的硅质烧结层直接覆盖在安山岩上和/或在砾岩最下方20米处互层，因此，与下伏的金银矿体异常接近。大部分砾岩缺乏硅化作用，除了在矿床上方露出一个狭窄的、陡峭的倾斜带，这导致了它的发现。
{"title":"Chapter 21: Geology of the Fruta del Norte Epithermal Gold-Silver Deposit, Ecuador","authors":"S. Leary, R. Sillitoe, Jorge Lema, Fernando Téliz, Diego Mena","doi":"10.5382/sp.23.21","DOIUrl":"https://doi.org/10.5382/sp.23.21","url":null,"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.","PeriodicalId":12540,"journal":{"name":"Geology of the World’s Major Gold Deposits and Provinces","volume":"8 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87804643","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
N. Goryachev, A. Yakubchuk, I. S. Litvinenko, A. Lozhkin, Y. Pruss, V. Smirnov
The Upper Kolyma gold placers of northeastern Russia produced 2,700 metric tons (t) Au. Approximately 40% of this gold was extracted from just five placers, Chai-Yuria, Berelekh, Maldyak, Malyi At-Yuryakh, and Omchak, and their immediate tributaries. The placers were derived from Late Jurassic to Early Cretaceous lode deposits, formed during sinistral translation subsequent to the Kolyma-Omolon superterrane accretion to the Verkhoyansk passive margin of the Siberian craton. The metallogenic events produced either abundant and widespread small quartz veins or more localized large to superlarge quartz stockworks and disseminated gold deposits. These orogenic gold deposits acted as a principal hard-rock source during formation of the gold placers, beginning in the Late Cretaceous but most importantly during the Cenozoic. Tectonic, geomorphologic, and climatic factors at a triple junction of the North American, Eurasian, and Okhotsk lithospheric plates provided the ultimate controls on placer formation.
{"title":"Chapter 37: Giant Placers of the Upper Kolyma Gold Fields, Yana-Kolyma Province, Russian Northeast","authors":"N. Goryachev, A. Yakubchuk, I. S. Litvinenko, A. Lozhkin, Y. Pruss, V. Smirnov","doi":"10.5382/sp.23.37","DOIUrl":"https://doi.org/10.5382/sp.23.37","url":null,"abstract":"The Upper Kolyma gold placers of northeastern Russia produced 2,700 metric tons (t) Au. Approximately 40% of this gold was extracted from just five placers, Chai-Yuria, Berelekh, Maldyak, Malyi At-Yuryakh, and Omchak, and their immediate tributaries. The placers were derived from Late Jurassic to Early Cretaceous lode deposits, formed during sinistral translation subsequent to the Kolyma-Omolon superterrane accretion to the Verkhoyansk passive margin of the Siberian craton. The metallogenic events produced either abundant and widespread small quartz veins or more localized large to superlarge quartz stockworks and disseminated gold deposits. These orogenic gold deposits acted as a principal hard-rock source during formation of the gold placers, beginning in the Late Cretaceous but most importantly during the Cenozoic. Tectonic, geomorphologic, and climatic factors at a triple junction of the North American, Eurasian, and Okhotsk lithospheric plates provided the ultimate controls on placer formation.","PeriodicalId":12540,"journal":{"name":"Geology of the World’s Major Gold Deposits and Provinces","volume":"24 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79751702","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Boddington is a giant, enigmatic, and atypical Archean Au-Cu deposit hosted in a small, remnant greenstone belt within granite-gneiss and migmatite of the Southwest terrane of the Yilgarn craton, Western Australia. Primary Au and Cu (and Mo) mineralization consists of a network of thin fractures and veins, controlled by shear zones, and dominantly hosted by early dioritic intrusions and their immediate wall rocks, which comprise felsic to intermediate-composition volcanic and volcaniclastic rocks. The pre-~2714 Ma host rocks are typically steeply dipping and strongly deformed, with early ductile and overprinting brittle-ductile fabrics, and have been metamorphosed at mid- to upper greenschist facies. Features consistent with porphyry-style mineralization, classic orogenic shear zones, and intrusion-related Au-Cu-Bi mineralization are all recognized, giving rise to a variety of genetic interpretations. It is clear that Boddington does not fit any classic Archean orogenic gold deposit model, having a general lack of quartz veins and iron carbonate alteration, a Cu (Mo and Bi) association, zoned geochemical anomalism, and evidence of high-temperature, saline ore-forming fluids. Detailed petrographic, geochemical, and melt inclusion studies suggest a late-stage ~2612 Ma, monzogranite intrusion as one of the principal sources of the mineralizing fluids. However, there is also local evidence for older, perhaps protore, porphyry-style Cu (±Au) in the dioritic intrusions and patchy, locally high-grade, orogenic-style gold mineralization associated with enclosing shear zones and brittle-style deformation, which was focused on the relatively competent dioritic intrusions. The relative contributions of metals from these components to the system may not be resolvable. It appears that the Boddington deposit has been a locus for multiple episodes of intrusion, alteration, and mineralization over an extended period of time, as has been demonstrated in a number of other large Canadian and Australian gold deposits, including the Golden Mile near Kalgoorlie.
{"title":"Chapter 13: Boddington: An Enigmatic Giant Archean Gold-Copper (Molybdenum-Silver) Deposit in the Southwest Yilgarn Craton, Western Australia","authors":"S. Turner, Graeme Reynolds, S. Hagemann","doi":"10.5382/sp.23.13","DOIUrl":"https://doi.org/10.5382/sp.23.13","url":null,"abstract":"Boddington is a giant, enigmatic, and atypical Archean Au-Cu deposit hosted in a small, remnant greenstone belt within granite-gneiss and migmatite of the Southwest terrane of the Yilgarn craton, Western Australia. Primary Au and Cu (and Mo) mineralization consists of a network of thin fractures and veins, controlled by shear zones, and dominantly hosted by early dioritic intrusions and their immediate wall rocks, which comprise felsic to intermediate-composition volcanic and volcaniclastic rocks. The pre-~2714 Ma host rocks are typically steeply dipping and strongly deformed, with early ductile and overprinting brittle-ductile fabrics, and have been metamorphosed at mid- to upper greenschist facies. Features consistent with porphyry-style mineralization, classic orogenic shear zones, and intrusion-related Au-Cu-Bi mineralization are all recognized, giving rise to a variety of genetic interpretations. It is clear that Boddington does not fit any classic Archean orogenic gold deposit model, having a general lack of quartz veins and iron carbonate alteration, a Cu (Mo and Bi) association, zoned geochemical anomalism, and evidence of high-temperature, saline ore-forming fluids. Detailed petrographic, geochemical, and melt inclusion studies suggest a late-stage ~2612 Ma, monzogranite intrusion as one of the principal sources of the mineralizing fluids. However, there is also local evidence for older, perhaps protore, porphyry-style Cu (±Au) in the dioritic intrusions and patchy, locally high-grade, orogenic-style gold mineralization associated with enclosing shear zones and brittle-style deformation, which was focused on the relatively competent dioritic intrusions. The relative contributions of metals from these components to the system may not be resolvable. It appears that the Boddington deposit has been a locus for multiple episodes of intrusion, alteration, and mineralization over an extended period of time, as has been demonstrated in a number of other large Canadian and Australian gold deposits, including the Golden Mile near Kalgoorlie.","PeriodicalId":12540,"journal":{"name":"Geology of the World’s Major Gold Deposits and Provinces","volume":"5 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80790472","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Cortez district is in one of the four major Carlin-type gold deposit trends in the Great Basin province of Nevada and contains three giant (>10 Moz) gold orebodies: Pipeline, Cortez Hills, and Goldrush, including the recently discovered Fourmile extension of the Goldrush deposit. The district has produced >21 Moz (653 t) of gold and contains an additional 26 Moz (809 t) in reserves and resources. The Carlin-type deposits occur in two large structural windows (Gold Acres and Cortez) of Ordovician through Devonian shelf- and slope-facies carbonate rocks exposed through deformed, time-equivalent lower Paleozoic siliciclastic rocks of the overlying Roberts Mountains thrust plate. Juxtaposition of these contrasting Paleozoic strata occurred during the late Paleozoic Antler orogeny along the Roberts Mountains thrust. Both upper and lower plate sequences were further deformed by Mesozoic compressional events. Regional extension, commencing in the Eocene, opened high- and low-angle structural conduits for mineralizing solutions and resulted in gold deposition in reactive carbonate units in structural traps, including antiforms and fault-propagated folds. The Pipeline and Cortez Hills deposits are located adjacent to the Cretaceous Gold Acres and Jurassic Mill Canyon granodioritic stocks, respectively; although these stocks are genetically unrelated to the later Carlin-type mineralization event, their thermal metamorphic aureoles may have influenced ground preparation for later gold deposition. Widespread decarbonatization, argillization, and silicification of the carbonate host rocks accompanied gold mineralization, with gold precipitated within As-rich rims on fine-grained pyrite. Pipeline and Cortez Hills also display deep supergene oxidation of the hypogene sulfide mineralization. Carlin-type mineralization in the district is believed to have been initiated in the late Eocene (>35 Ma) based on the age of late- to postmineral rhyolite dikes at Cortez Hills. The Carlin-type gold deposits in the district share common structural, stratigraphic, alteration, and ore mineralogic characteristics that reflect common modes of orebody formation. Ore-forming fluids were channeled along both low-angle structures (Pipeline, Goldrush/Fourmile) and high-angle features (Cortez Hills), and gold mineralization was deposited in Late Ordovician through Devonian limestone, limy mudstone, and calcareous siltstone. The Carlin-type gold fluids are interpreted to be low-salinity (2–3 wt % NaCl equiv), low-temperature (220°–270°C), and weakly acidic, analogous to those in other Carlin-type gold deposits in the Great Basin. The observed characteristics of the Cortez Carlin-type gold deposits are consistent with the recently proposed deep magmatic genetic model. Although the deposits occur over a wide geographic area in the district, it is possible that they initially formed in greater proximity to each other and were then spatially separated during Miocene and post-Miocene r
{"title":"Chapter 16: Giant Carlin-Type Gold Deposits of the Cortez District, Lander and Eureka Counties, Nevada","authors":"M. Bradley, L. Anderson, N. Eck, Kevin D. Creel","doi":"10.5382/sp.23.16","DOIUrl":"https://doi.org/10.5382/sp.23.16","url":null,"abstract":"The Cortez district is in one of the four major Carlin-type gold deposit trends in the Great Basin province of Nevada and contains three giant (>10 Moz) gold orebodies: Pipeline, Cortez Hills, and Goldrush, including the recently discovered Fourmile extension of the Goldrush deposit. The district has produced >21 Moz (653 t) of gold and contains an additional 26 Moz (809 t) in reserves and resources. The Carlin-type deposits occur in two large structural windows (Gold Acres and Cortez) of Ordovician through Devonian shelf- and slope-facies carbonate rocks exposed through deformed, time-equivalent lower Paleozoic siliciclastic rocks of the overlying Roberts Mountains thrust plate. Juxtaposition of these contrasting Paleozoic strata occurred during the late Paleozoic Antler orogeny along the Roberts Mountains thrust. Both upper and lower plate sequences were further deformed by Mesozoic compressional events. Regional extension, commencing in the Eocene, opened high- and low-angle structural conduits for mineralizing solutions and resulted in gold deposition in reactive carbonate units in structural traps, including antiforms and fault-propagated folds. The Pipeline and Cortez Hills deposits are located adjacent to the Cretaceous Gold Acres and Jurassic Mill Canyon granodioritic stocks, respectively; although these stocks are genetically unrelated to the later Carlin-type mineralization event, their thermal metamorphic aureoles may have influenced ground preparation for later gold deposition. Widespread decarbonatization, argillization, and silicification of the carbonate host rocks accompanied gold mineralization, with gold precipitated within As-rich rims on fine-grained pyrite. Pipeline and Cortez Hills also display deep supergene oxidation of the hypogene sulfide mineralization. Carlin-type mineralization in the district is believed to have been initiated in the late Eocene (>35 Ma) based on the age of late- to postmineral rhyolite dikes at Cortez Hills. The Carlin-type gold deposits in the district share common structural, stratigraphic, alteration, and ore mineralogic characteristics that reflect common modes of orebody formation. Ore-forming fluids were channeled along both low-angle structures (Pipeline, Goldrush/Fourmile) and high-angle features (Cortez Hills), and gold mineralization was deposited in Late Ordovician through Devonian limestone, limy mudstone, and calcareous siltstone. The Carlin-type gold fluids are interpreted to be low-salinity (2–3 wt % NaCl equiv), low-temperature (220°–270°C), and weakly acidic, analogous to those in other Carlin-type gold deposits in the Great Basin. The observed characteristics of the Cortez Carlin-type gold deposits are consistent with the recently proposed deep magmatic genetic model. Although the deposits occur over a wide geographic area in the district, it is possible that they initially formed in greater proximity to each other and were then spatially separated during Miocene and post-Miocene r","PeriodicalId":12540,"journal":{"name":"Geology of the World’s Major Gold Deposits and Provinces","volume":"14 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88145091","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Mesoarchean Witwatersrand Basin in the central Kaapvaal craton, South Africa, has been the largest gold-producing province in history. Although mining has reached a very mature state, this ore province remains the biggest regional gold anomaly in the world. Most recent research on the Witwatersrand gold deposits has focused on postdepositional processes, often on a microscale, thereby constraining conditions of gold transport in the host conglomerates. Here we review past and current observations on the geologic setting of the orebodies and first-order controls on gold mineralization, all of which strengthen the argument for a primarily syngenetic model. The Witwatersrand deposits are regarded as remnants of a gold megaevent at 2.9 Ga when environmental conditions are suggested to have been suitable for intense gold flux off the Archean land surface and early photosynthesizing microbes could act as trap sites for riverine and possibly shallow-marine gold. Sedimentary reworking of gold-rich microbial mats led to rich placer deposits which, in turn, became sources of younger placers higher up in the stratigraphy. The same gold concentration mechanism most likely operated on all Mesoarchean land masses, not only on the Kaapvaal craton. The uniqueness of the Witwatersrand gold province is explained by exceptional preservation of these easily erodible, largely continental sediments beneath a thick cover of flood basalt and a later impact melt sheet in the middle of a buoyant craton, with little tectonic overprint over the past two billion years.
{"title":"Chapter 31: Geologic Evidence of Syngenetic Gold in the Witwatersrand Goldfields, South Africa","authors":"H. Frimmel, G. Nwaila","doi":"10.5382/sp.23.31","DOIUrl":"https://doi.org/10.5382/sp.23.31","url":null,"abstract":"The Mesoarchean Witwatersrand Basin in the central Kaapvaal craton, South Africa, has been the largest gold-producing province in history. Although mining has reached a very mature state, this ore province remains the biggest regional gold anomaly in the world. Most recent research on the Witwatersrand gold deposits has focused on postdepositional processes, often on a microscale, thereby constraining conditions of gold transport in the host conglomerates. Here we review past and current observations on the geologic setting of the orebodies and first-order controls on gold mineralization, all of which strengthen the argument for a primarily syngenetic model. The Witwatersrand deposits are regarded as remnants of a gold megaevent at 2.9 Ga when environmental conditions are suggested to have been suitable for intense gold flux off the Archean land surface and early photosynthesizing microbes could act as trap sites for riverine and possibly shallow-marine gold. Sedimentary reworking of gold-rich microbial mats led to rich placer deposits which, in turn, became sources of younger placers higher up in the stratigraphy. The same gold concentration mechanism most likely operated on all Mesoarchean land masses, not only on the Kaapvaal craton. The uniqueness of the Witwatersrand gold province is explained by exceptional preservation of these easily erodible, largely continental sediments beneath a thick cover of flood basalt and a later impact melt sheet in the middle of a buoyant craton, with little tectonic overprint over the past two billion years.","PeriodicalId":12540,"journal":{"name":"Geology of the World’s Major Gold Deposits and Provinces","volume":"12 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84679417","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Porgera is a ~974-metric ton (t) Au, low-sulfidation, alkalic, epithermal gold deposit located in Papua New Guinea. The deposit is spatially associated with 6 Ma stocks of the mafic alkalic Porgera Intrusive Complex, which were emplaced within Cretaceous carbonaceous mudstones in a transpressional orogenic setting linked to continent-island arc collision. As with many other major magmatic-hydrothermal ore deposits in New Guinea, deep-seated, arc-normal transfer structures have been suggested as controls on intrusion emplacement through the creation of a localized extensional environment favorable for magma ascent. Gold mineralization occurred in two distinct phases, both within ≤0.2 m.y. of emplacement of the Porgera Intrusive Complex. Stage 1 mineralization of intrusion-related carbonate-base metal association consists of extensional vein swarms dominated by coarse intergrown pyrite ± galena and sphalerite, generally hosted within or proximal to the intrusive bodies of the Porgera Intrusive Complex. These veins represent the lowest grade and economically least significant mineralization phase. Overprinted high-grade epithermal Stage 2 mineralization consists of roscoelite, pyrite, and quartz veins and breccia veins ± subordinate amounts of barite, marcasite, sphalerite, tetrahedrite, galena, hematite, and tellurides. Gold mineralization is commonly associated with the roscoelite-rich coatings on vein walls or breccia clasts. Stage 2 mineralization is controlled by a deposit-scale extensional fault-fracture mesh and displays a variety of textural styles including: (1) <5-mm veinlets dominated by roscoelite, pyrite, and gold; (2) thicker veins up to 10 cm wide with roscoelite, pyrite, and gold on the margins with central bands of alternating crustiform quartz and thin layers of roscoelite-pyrite-gold; (3) hydrothermal breccias with roscoelite, pyrite, and gold coating breccia margins and internal clasts, with crustiform quartz forming the matrix. The giant endowment of the Porgera gold system is attributed to its favorable tectonic location and local extensional setting, its vertical extent, the oxidized nature of the mineralizing fluids, and highly efficient gold precipitation.
{"title":"Chapter 27: Geology of the Porgera Gold Deposit, Papua New Guinea","authors":"Jonathan P. Hay, M. Haydon, F. Robert","doi":"10.5382/sp.23.27","DOIUrl":"https://doi.org/10.5382/sp.23.27","url":null,"abstract":"Porgera is a ~974-metric ton (t) Au, low-sulfidation, alkalic, epithermal gold deposit located in Papua New Guinea. The deposit is spatially associated with 6 Ma stocks of the mafic alkalic Porgera Intrusive Complex, which were emplaced within Cretaceous carbonaceous mudstones in a transpressional orogenic setting linked to continent-island arc collision. As with many other major magmatic-hydrothermal ore deposits in New Guinea, deep-seated, arc-normal transfer structures have been suggested as controls on intrusion emplacement through the creation of a localized extensional environment favorable for magma ascent. Gold mineralization occurred in two distinct phases, both within ≤0.2 m.y. of emplacement of the Porgera Intrusive Complex. Stage 1 mineralization of intrusion-related carbonate-base metal association consists of extensional vein swarms dominated by coarse intergrown pyrite ± galena and sphalerite, generally hosted within or proximal to the intrusive bodies of the Porgera Intrusive Complex. These veins represent the lowest grade and economically least significant mineralization phase. Overprinted high-grade epithermal Stage 2 mineralization consists of roscoelite, pyrite, and quartz veins and breccia veins ± subordinate amounts of barite, marcasite, sphalerite, tetrahedrite, galena, hematite, and tellurides. Gold mineralization is commonly associated with the roscoelite-rich coatings on vein walls or breccia clasts. Stage 2 mineralization is controlled by a deposit-scale extensional fault-fracture mesh and displays a variety of textural styles including: (1) <5-mm veinlets dominated by roscoelite, pyrite, and gold; (2) thicker veins up to 10 cm wide with roscoelite, pyrite, and gold on the margins with central bands of alternating crustiform quartz and thin layers of roscoelite-pyrite-gold; (3) hydrothermal breccias with roscoelite, pyrite, and gold coating breccia margins and internal clasts, with crustiform quartz forming the matrix. The giant endowment of the Porgera gold system is attributed to its favorable tectonic location and local extensional setting, its vertical extent, the oxidized nature of the mineralizing fluids, and highly efficient gold precipitation.","PeriodicalId":12540,"journal":{"name":"Geology of the World’s Major Gold Deposits and Provinces","volume":"40 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85486838","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hemlo combines several rare to unique features in the spectrum of Archean greenstone gold deposits. It is an isolated, approximately 800-metric ton (t) gold system in a region of otherwise limited known gold endowment. The geology of Hemlo is dominated by deformed and metamorphosed sedimentary, felsic volcanic, and volcaniclastic units, a premineral coherent felsic porphyry, and a swarm of mainly postmineral, intermediate, feldspar-phyric dikes. Ore is dominantly in the form of gold-bearing lenses of pyritic, feldspathic schist derived from deformation of both the clastic rocks and the felsic porphyry. The deposit and its host rocks were metamorphosed at moderate pressures to assemblages diagnostic of the mid-amphibolite facies, followed by progressive retrogression to those of the greenschist facies. The result is a wide range of silicate mineral species in ambiguous textural relationships. The gold system itself is known for ore and related alteration minerals with significant concentrations of Mo-As-Sb-Hg-Tl-V-Ba-K-Na. The inferences derived from lithologic mapping, structural chronology, U-Pb geochronology, and mineral paragenesis favors an interpretation of Hemlo as a deformed and metamorphosed gold system formed from oxidized hydrothermal fluids in an upper crustal setting. Uncertainty remains as to the exact nature and geometry of that ore-forming hydrothermal system, however, and the role subsequent metamorphism and deformation have played in the local remobilization of ore constituents into their present paragenetically late structural sites.
{"title":"Chapter 4: Hemlo Gold System, Superior Province, Canada","authors":"K. H. Poulsen, R. Barber, F. Robert","doi":"10.5382/sp.23.04","DOIUrl":"https://doi.org/10.5382/sp.23.04","url":null,"abstract":"Hemlo combines several rare to unique features in the spectrum of Archean greenstone gold deposits. It is an isolated, approximately 800-metric ton (t) gold system in a region of otherwise limited known gold endowment. The geology of Hemlo is dominated by deformed and metamorphosed sedimentary, felsic volcanic, and volcaniclastic units, a premineral coherent felsic porphyry, and a swarm of mainly postmineral, intermediate, feldspar-phyric dikes. Ore is dominantly in the form of gold-bearing lenses of pyritic, feldspathic schist derived from deformation of both the clastic rocks and the felsic porphyry. The deposit and its host rocks were metamorphosed at moderate pressures to assemblages diagnostic of the mid-amphibolite facies, followed by progressive retrogression to those of the greenschist facies. The result is a wide range of silicate mineral species in ambiguous textural relationships. The gold system itself is known for ore and related alteration minerals with significant concentrations of Mo-As-Sb-Hg-Tl-V-Ba-K-Na. The inferences derived from lithologic mapping, structural chronology, U-Pb geochronology, and mineral paragenesis favors an interpretation of Hemlo as a deformed and metamorphosed gold system formed from oxidized hydrothermal fluids in an upper crustal setting. Uncertainty remains as to the exact nature and geometry of that ore-forming hydrothermal system, however, and the role subsequent metamorphism and deformation have played in the local remobilization of ore constituents into their present paragenetically late structural sites.","PeriodicalId":12540,"journal":{"name":"Geology of the World’s Major Gold Deposits and Provinces","volume":"29 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81336313","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R. Seltmann, R. Goldfarb, B. Zu, R. Creaser, A. Dolgopolova, V. Shatov
Muruntau in the Central Kyzylkum desert of the South Tien Shan, western Uzbekistan, with past production of ~3,000 metric tons (t) Au since 1967, present annual production of ~60 t Au, and large remaining resources, is the world’s largest epigenetic Au deposit. The host rocks are the mainly Cambrian-Ordovician siliciclastic flysch of the Besapan sequence. The rocks were deformed into a broadly east-west fold-and-thrust belt prior to ca. 300 Ma during ocean closure along the South Tien Shan suture. A subsequent tectonic transition was characterized by left-lateral motion on regional splays from the suture and by a massive thermal event documented by widespread 300 to 275 Ma magmatism. The Besapan rocks were subjected to middle to upper greenschist-facies regional metamorphism, an overprinting more local thermal metamorphism to produce a large hornfels aureole, and then Au-related hydrothermal activity all during early parts of the thermal event. The giant Muruntau Au deposit formed in the low-strain hornfels rocks at ca. 288 Ma at the intersection of one of the east-west splays, the Sangruntau-Tamdytau shear zone, with a NE-trending regional fault zone, the Muruntau-Daugyztau fault, which likely formed as a cross fault during the onset of left-lateral translation on the regional splays. Interaction between the two faults opened a large dilational zone along a plunging anticlinorium fold nose that served as a major site for hydrothermal fluid focusing. The Au ores are dominantly present as a series of moderately to steeply dipping quartz ± K-feldspar stockwork systems surrounding uncommon central veins and with widespread lower Au-grade metasomatites (i.e., disseminated ores). Pervasive alteration is biotite-K-feldspar, although locally albitization is dominant. Sulfides are mainly arsenopyrite, pyrite, and lesser pyrrhotite, and scheelite may be present both in preore ductile veins and in the more brittle auriferous stockwork systems. The low-salinity, aqueous-carbonic ore-forming fluids probably deposited the bulk of the ore at 400° ± 50°C and 6-to 10-km paleodepth. The genesis of the deposit remains controversial with metamorphic, thermal aureole gold (TAG), and models related to mantle upwelling all having been suggested in recent years. More importantly, the question as to why there was such a focusing of so much Au and fluid into this one location, forming an ore system an order of magnitude larger than other giant Au deposits in metamorphic terranes, remains unresolved.
{"title":"Chapter 24: Muruntau, Uzbekistan: The World’s Largest Epigenetic Gold Deposit","authors":"R. Seltmann, R. Goldfarb, B. Zu, R. Creaser, A. Dolgopolova, V. Shatov","doi":"10.5382/sp.23.24","DOIUrl":"https://doi.org/10.5382/sp.23.24","url":null,"abstract":"Muruntau in the Central Kyzylkum desert of the South Tien Shan, western Uzbekistan, with past production of ~3,000 metric tons (t) Au since 1967, present annual production of ~60 t Au, and large remaining resources, is the world’s largest epigenetic Au deposit. The host rocks are the mainly Cambrian-Ordovician siliciclastic flysch of the Besapan sequence. The rocks were deformed into a broadly east-west fold-and-thrust belt prior to ca. 300 Ma during ocean closure along the South Tien Shan suture. A subsequent tectonic transition was characterized by left-lateral motion on regional splays from the suture and by a massive thermal event documented by widespread 300 to 275 Ma magmatism. The Besapan rocks were subjected to middle to upper greenschist-facies regional metamorphism, an overprinting more local thermal metamorphism to produce a large hornfels aureole, and then Au-related hydrothermal activity all during early parts of the thermal event. The giant Muruntau Au deposit formed in the low-strain hornfels rocks at ca. 288 Ma at the intersection of one of the east-west splays, the Sangruntau-Tamdytau shear zone, with a NE-trending regional fault zone, the Muruntau-Daugyztau fault, which likely formed as a cross fault during the onset of left-lateral translation on the regional splays. Interaction between the two faults opened a large dilational zone along a plunging anticlinorium fold nose that served as a major site for hydrothermal fluid focusing. The Au ores are dominantly present as a series of moderately to steeply dipping quartz ± K-feldspar stockwork systems surrounding uncommon central veins and with widespread lower Au-grade metasomatites (i.e., disseminated ores). Pervasive alteration is biotite-K-feldspar, although locally albitization is dominant. Sulfides are mainly arsenopyrite, pyrite, and lesser pyrrhotite, and scheelite may be present both in preore ductile veins and in the more brittle auriferous stockwork systems. The low-salinity, aqueous-carbonic ore-forming fluids probably deposited the bulk of the ore at 400° ± 50°C and 6-to 10-km paleodepth. The genesis of the deposit remains controversial with metamorphic, thermal aureole gold (TAG), and models related to mantle upwelling all having been suggested in recent years. More importantly, the question as to why there was such a focusing of so much Au and fluid into this one location, forming an ore system an order of magnitude larger than other giant Au deposits in metamorphic terranes, remains unresolved.","PeriodicalId":12540,"journal":{"name":"Geology of the World’s Major Gold Deposits and Provinces","volume":"49 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73093748","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
N. Oliver, A. Allibone, M. Nugus, C. Vargas, R. Jongens, R. Peattie, V. Chamberlain
Obuasi, with a total mineral resource plus past production of 70 Moz, is the largest gold deposit in West Africa, and one of the largest in the world. It is hosted by ~2135 Ma siliciclastic rocks of the Eburnean Kumasi Basin, which were obliquely shortened along an inverted boundary with the older Eoeburnean Ashanti belt to the east. Greenschist facies metamorphism was coeval with mineralization and related alteration at ~2095 Ma. The steeply dipping, ENE-plunging lodes extend over an 8-km strike length and to depths of >2.5 km. They include paragenetically complex gold-rich quartz veins surrounded by refractory auriferous arsenopyrite and closely associated carbonate-muscovite alteration halos in deformed carbonaceous phyllites and subordinate metaigneous host rocks. Gold and arsenic were initially precipitated during deformation-assisted interaction with reduced host rocks at ~350°C and 100 to 200 MPa. The mineralizing fluids were derived primarily from deeper, As-rich metasedimentary sources by basinal fluid expulsion and metamorphic devolatilization triggered by inversion and shortening, followed by transpression. Continued fluid injection during and after the metamorphic peak produced changes in gold fineness, sulfide assemblages, repeated dissolution (stylolites) and reprecipitation of mineralized veins, and a change from early deformed shear-related, sulfide-rich lodes to later quartz-rich lodes that plunge down or across the axes of younger transpressional folds. Channelized fluid flow due to reactivation of basin-edge transfer structures, and/or irregularly distributed gold source rocks, may explain the variation in gold endowment along the former basin boundary.
{"title":"Chapter 6: The Supergiant, High-Grade, Paleoproterozoic Metasedimentary Rock- and Shear Vein-Hosted Obuasi (Ashanti) Gold Deposit, Ghana, West Africa","authors":"N. Oliver, A. Allibone, M. Nugus, C. Vargas, R. Jongens, R. Peattie, V. Chamberlain","doi":"10.5382/sp.23.06","DOIUrl":"https://doi.org/10.5382/sp.23.06","url":null,"abstract":"Obuasi, with a total mineral resource plus past production of 70 Moz, is the largest gold deposit in West Africa, and one of the largest in the world. It is hosted by ~2135 Ma siliciclastic rocks of the Eburnean Kumasi Basin, which were obliquely shortened along an inverted boundary with the older Eoeburnean Ashanti belt to the east. Greenschist facies metamorphism was coeval with mineralization and related alteration at ~2095 Ma. The steeply dipping, ENE-plunging lodes extend over an 8-km strike length and to depths of >2.5 km. They include paragenetically complex gold-rich quartz veins surrounded by refractory auriferous arsenopyrite and closely associated carbonate-muscovite alteration halos in deformed carbonaceous phyllites and subordinate metaigneous host rocks. Gold and arsenic were initially precipitated during deformation-assisted interaction with reduced host rocks at ~350°C and 100 to 200 MPa. The mineralizing fluids were derived primarily from deeper, As-rich metasedimentary sources by basinal fluid expulsion and metamorphic devolatilization triggered by inversion and shortening, followed by transpression. Continued fluid injection during and after the metamorphic peak produced changes in gold fineness, sulfide assemblages, repeated dissolution (stylolites) and reprecipitation of mineralized veins, and a change from early deformed shear-related, sulfide-rich lodes to later quartz-rich lodes that plunge down or across the axes of younger transpressional folds. Channelized fluid flow due to reactivation of basin-edge transfer structures, and/or irregularly distributed gold source rocks, may explain the variation in gold endowment along the former basin boundary.","PeriodicalId":12540,"journal":{"name":"Geology of the World’s Major Gold Deposits and Provinces","volume":"62 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77588548","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Neoarchean Abitibi greenstone belt in the southern Superior Province has been one of the world’s major gold-producing regions for almost a century with >6,100 metric tons (t) Au produced and a total endowment, including production, reserves, and resources (measured and indicated), of >9,375 t Au. The Abitibi belt records continuous mafic to felsic submarine volcanism and plutonism from ca. 2740 to 2660 Ma. A significant part of that gold is synvolcanic and/or synmagmatic and was formed during the volcanic construction of the belt between ca. 2740 and 2695 Ma. However, >60% of the gold is hosted in late, orogenic quartz-carbonate vein-style deposits that formed between ca. 2660 and 2640 ± 10 Ma, predominantly along the Larder Lake-Cadillac and Destor-Porcupine fault zones. This ore-forming period coincides with the D3 deformation, a broad north-south main phase of regional shortening that followed a period of extension and associated crustal thinning, alkaline to subalkaline magmatism, and development of orogenic fluvial-alluvial sedimentary basins (ca. <2679–<2669 Ma). These sedimentary rocks are referred to, in the southern Abitibi, as Timiskaming-type. The tectonic inversion from extension to compression is <2669 Ma, the maximum age of the D3-deformed youngest Timiskaming rocks. In addition to the quartz-carbonate vein-style, stockwork-disseminated-replacement-style mineralization is hosted in and/or is associated with ca. 2683 to 2670 Ma, early-to syn-Timiskaming alkaline to subalkaline intrusions along major deformation corridors, especially in southern Abitibi. The bulk of such deposits formed late-to post-alkaline to subalkaline magmatism and the largest deposits are early- to syn-D3 (ca. 2670–2660 Ma), whereas the bulk of the quartz-carbonate vein systems formed syn- to late-D3 and metamorphism. At belt scale, these illustrate a gradual transition, as shortening increases, in ore styles in orogenic deposits throughout the duration of the D3 deformation event along the length of the Larder Lake-Cadillac and Destor-Porcupine faults. The sequence of events, although similar in all camps, was probably not perfectly synchronous at belt scale, but varied/migrated with time and crustal levels along the main deformation corridors and from north to south. The presence of high-level alkaline/shoshonitic intrusions, which are spatially associated with Timiskaming conglomerate and sandstone, large-scale hydrothermal alteration, and numerous gold deposits along the Larder Lake-Cadillac and Destor-Porcupine faults indicates that these structures were deeply rooted and tapped auriferous metamorphic-hydrothermal fluids and melts from the upper mantle and/or lower crust, late in the evolution of the belt. The metamorphic-hydrothermal fluids, rich in H2O, CO2, and H2S were capable of leaching and transporting gold to the upper crust along the major faults and their splays. Although most magmatic activity along the faults predates gold, magmas may have
{"title":"Chapter 32: Gold Deposits of the Archean Abitibi Greenstone Belt, Canada","authors":"B. Dubé, P. Mercier-Langevin","doi":"10.5382/sp.23.32","DOIUrl":"https://doi.org/10.5382/sp.23.32","url":null,"abstract":"The Neoarchean Abitibi greenstone belt in the southern Superior Province has been one of the world’s major gold-producing regions for almost a century with >6,100 metric tons (t) Au produced and a total endowment, including production, reserves, and resources (measured and indicated), of >9,375 t Au. The Abitibi belt records continuous mafic to felsic submarine volcanism and plutonism from ca. 2740 to 2660 Ma. A significant part of that gold is synvolcanic and/or synmagmatic and was formed during the volcanic construction of the belt between ca. 2740 and 2695 Ma. However, >60% of the gold is hosted in late, orogenic quartz-carbonate vein-style deposits that formed between ca. 2660 and 2640 ± 10 Ma, predominantly along the Larder Lake-Cadillac and Destor-Porcupine fault zones. This ore-forming period coincides with the D3 deformation, a broad north-south main phase of regional shortening that followed a period of extension and associated crustal thinning, alkaline to subalkaline magmatism, and development of orogenic fluvial-alluvial sedimentary basins (ca. <2679–<2669 Ma). These sedimentary rocks are referred to, in the southern Abitibi, as Timiskaming-type. The tectonic inversion from extension to compression is <2669 Ma, the maximum age of the D3-deformed youngest Timiskaming rocks. In addition to the quartz-carbonate vein-style, stockwork-disseminated-replacement-style mineralization is hosted in and/or is associated with ca. 2683 to 2670 Ma, early-to syn-Timiskaming alkaline to subalkaline intrusions along major deformation corridors, especially in southern Abitibi. The bulk of such deposits formed late-to post-alkaline to subalkaline magmatism and the largest deposits are early- to syn-D3 (ca. 2670–2660 Ma), whereas the bulk of the quartz-carbonate vein systems formed syn- to late-D3 and metamorphism. At belt scale, these illustrate a gradual transition, as shortening increases, in ore styles in orogenic deposits throughout the duration of the D3 deformation event along the length of the Larder Lake-Cadillac and Destor-Porcupine faults. The sequence of events, although similar in all camps, was probably not perfectly synchronous at belt scale, but varied/migrated with time and crustal levels along the main deformation corridors and from north to south. The presence of high-level alkaline/shoshonitic intrusions, which are spatially associated with Timiskaming conglomerate and sandstone, large-scale hydrothermal alteration, and numerous gold deposits along the Larder Lake-Cadillac and Destor-Porcupine faults indicates that these structures were deeply rooted and tapped auriferous metamorphic-hydrothermal fluids and melts from the upper mantle and/or lower crust, late in the evolution of the belt. The metamorphic-hydrothermal fluids, rich in H2O, CO2, and H2S were capable of leaching and transporting gold to the upper crust along the major faults and their splays. Although most magmatic activity along the faults predates gold, magmas may have ","PeriodicalId":12540,"journal":{"name":"Geology of the World’s Major Gold Deposits and Provinces","volume":"120 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77192652","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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