Abstract China produces about 450 t Au per year and has government stated in-ground reserves of approximately 12,000 t Au. Orogenic gold, or gold deposits in metamorphic rocks, and associated placer deposits compose about 65 to 75% of this endowment, with lodes existing as structurally hosted vein and/or disseminated orebodies. The abundance of orogenic gold deposits reflects Paleozoic to Triassic closure of Paleo-Tethyan ocean basins between Precambrian blocks derived from Rodinia and Gondwana as well as late Mesozoic-Cenozoic circum-Pacific events and Cenozoic Himalayan orogeny. The deposits range in age from middle Paleozoic to Pleistocene. The Jiaodong Peninsula contains about one-third of China’s overall endowment, and large resources also characterize East Qinling, West Qinling, and the Youjiang basin. Although gold ores in Jiaodong postdate formation and metamorphism of Precambrian host rocks by billions of years, they are nevertheless classified here as orogenic gold ores rather than as a unique Jiaodong-type or decratonic-type of gold deposit. Similarly, although many workers classify the gold lodes in the Youjiang basin and much of West Qinling as Carlin-type gold, they show significant differences from gold ores in Nevada, United States, and are better defined as epizonal orogenic gold deposits. Although there are widespread exposures of Precambrian rocks in China, there are no significant Precambrian gold deposits. If large ancient orogenic gold deposits formed in Archean and Paleoproterozoic rocks, then they have been eroded, because these deep crustal rocks that are now exposed in China’s cratonic blocks have been uplifted from levels too deep for orogenic gold formation. The oldest large gold deposits in China are perhaps those of the Qilian Shan that were formed in association with Silurian tectonism along the present-day southwestern margin of the North China block. Closure of ocean basins in the outer parts of the Central Asian orogenic belt led to late Carboniferous to Middle Triassic orogenic gold formation in the Tian Shan, Altay Shan, Beishan, and northwestern North China block. Deformation associated with amalgamation of the North China block, northern Tibet terranes, South China block, and Indochina, as well as initial Paleo-Pacific subduction, can be related to Late Triassic orogenic gold formation in West Qinling, East Kunlun, Youjiang basin, West Jiangnan (Xuefengshan belt), Hainan Island, and Yunkaidashan gold provinces. In the middle Mesozoic, continued subduction along the Paleo-Pacific margin was associated with gold ores forming in East and Central Jiangnan, whereas early to middle Mesozoic deformation along the northern North China block formed important orogenic lodes in Precambrian basement (e.g., Jiapigou, Zhangjiakou, and Yanshan districts). Continued Yanshanian orogeny in the eastern half of the North China block led to extensive orogenic gold formation during the main period of decratonization and regional extension at ca. 135 to 120 Ma (e.g., Jiaodong, Liaodong, Chifeng-Chaoyang, Zhangbaling, Taihangshan, and East Qinling). At the same time, strike-slip events in central Transbaikal were associated with orogenic gold formation in both Russia and adjacent northeastern China and likely are the source for China’s most productive gold placers in the upper Heilongjiang basin. China’s youngest orogenic gold deposits formed in the Ailaoshan, Lanping basin, Ganzi-Litang belt, Daduhe district, and areas south of the Lhasa terrane in Tibet during the middle Cenozoic, as well as in the northern half of the Central Range of Taiwan during the Pliocene-Pleistocene.

The Blackbird cobalt-copper (Co-Cu) district in the Salmon River Mountains of east-central Idaho occupies the central part of the Idaho cobalt belt—a northwest-elongate, 55-km-long belt of Co-Cu occurrences, hosted in grayish siliciclastic metasedimentary strata of the Lemhi subbasin (of the Mesoproterozoic Belt-Purcell Basin). The Blackbird district contains at least eight stratabound ore zones and many discordant lodes, mostly in the upper part of the banded siltite unit of the Apple Creek Formation of Yellow Lake, which generally consists of interbedded siltite and argillite. In the Blackbird mine area, argillite beds in six stratigraphic intervals are altered to biotitite containing over 75 vol% of greenish hydrothermal biotite, which is preferentially mineralized. Past production and currently estimated resources of the Blackbird district total ~17 Mt of ore, averaging 0.74% Co, 1.4% Cu, and 1.0 ppm Au (not including downdip projections of ore zones that are open downward). A compilation of relative-age relationships and isotopic age determinations indicates that most cobalt mineralization occurred in Mesoproterozoic time, whereas most copper mineralization occurred in Cretaceous time. Mesoproterozoic cobaltite mineralization accompanied and followed dynamothermal metamorphism and bimodal plutonism during the Middle Mesoproterozoic East Kootenay orogeny (ca. 1379–1325 Ma), and also accompanied Grenvilleage (Late Mesoproterozoic) thermal metamorphism (ca. 1200–1000 Ma). Stratabound cobaltite-biotite ore zones typically contain cobaltite 1 in a matrix of biotitite ± tourmaline ± minor xenotime (ca. 1370–1320 Ma) ± minor chalcopyrite ± sparse allanite ± sparse microscopic native gold in cobaltite. Such cobaltite-biotite lodes are locally folded into tight F 2 folds with axial-planar S 2 cleavage and schistosity. Discordant replacement-style lodes of cobaltite 2 -biotite ore ± xenotime 2 (ca. 1320–1270 Ma) commonly follow S 2 fractures and fabrics. Discordant quartz-biotite and quartz-tourmaline breccias, and veins contain cobaltite 3 ± xenotime 3 (ca. 1058–990 Ma). Mesoproterozoic cobaltite deposition was followed by: (1) within-plate plutonism (530–485 Ma) and emplacement of mafic dikes (which cut cobaltite lodes but are cut by quartz-Fe-Cu-sulfide veins); (2) garnet-grade metamorphism (ca. 151–93 Ma); (3) Fe-Cu-sulfide mineralization (ca. 110–92 Ma); and (4) minor quartz ± Au-Ag ± Bi mineralization (ca. 92–83 Ma). Cretaceous Fe-Cu-sulfide vein, breccia, and replacement-style deposits contain various combinations of chalcopyrite ± pyrrhotite ± pyrite ± cobaltian arsenopyrite (not cobaltite) ± arsenopyrite ± quartz ± siderite ± monazite (ca. 144–88 Ma but mostly 110–92 Ma) ± xenotime (104–93 Ma). Highly radiogenic Pb (in these sulfides) and Sr (in siderite) indicate that these elements resided in Mesoproterozoic source rocks until they were mobilized after ca. 100 Ma. Fe-Cu-sulfide veins, breccias, and replacement deposits appear relatively undeformed and generally lack metamorphic fabrics. Composite Co-Cu-Au ore contains early cobaltite-biotite lodes, cut by Fe-Cu-sulfide veins and breccias, or overprinted by Fe-Cu-sulfide replacement-style deposits, and locally cut by quartz veinlets ± Au-Ag ± Bi minerals.

Abstract Lithoteetonic terranes thot are now the northwestern eoms of North America record more than 500 m.y. of ore-forming processes. Almost all of Alaska’s mineral deposits older than 150 Ma knuicd in oceanic environments in blocks of oceanic crust island areas, or isolated continental fragments distant from North America or in platforms and basins adjacent to the Paleozoic North American continental margin, Most and dle Cretaceous and vounger ore systems, especially those couccntinted in the soothern part of the slate are associated with processes attendant to terrain accretion Hydrothernial activity and commonly related magmatism were principally prodnets of oceanic plate subdnetinn beneath the southern Alaska continental margin. Few significant lode deposits in Alaska arc poslacerelionary, anorogenic systems that are clearly unrelated to Mesozoic and Cetiozoic plate convergence. Late Proterozoie th rough Silurian poly metallic volcauogcnic massive sulfide deposits, some broadly contemporaneous with Fe-Cu-Au starts, are the oldest recognized major mineral deposits in Alaska. These deposits were formed during submarine-arc magmatism distant from the North American continent and are now located in rocks of the accreted Alexander terraue in the southernmost part of southeastern Alaska. Shale- and carbonate-hosted base metal deposits and polymetallic volcanogenie massive sulfide deposits developed along the North American continental shelf in the Devonian and Carbonilcrous Extension and probably rift-related voleanism along the continental margin were coeval with Antler-Ellesnicii an orogenesis landward on the eraton. Resulting submarine hydrothernial activity formed the mineral deposits now exposed in rocks of the Arctic Alaska terrain- in the western and central Brooks Range. They include stratilorm, shale-hosted bo the s such as Red Dog, massive syngenelic barite carbonate-hosted copper systems such as Rubv Creek, and the voleanogenie massive sulfide occurrences of the Ambler district. The late Paleozoic continental margin strata of the Yukon-Tanaua lerrane, where exposed in east-central and southeastern Alaska, contain additional volcauogcnic massive sulfide bo the s that may be of similar origin. Triassic lifting along the east side of the Alexander terraue, still distal to North America, was responsible for a third episode of polymetalle volcauogemc massive sulfide formation. Resulting deposits include Creens Creek, in the northern part of southeastern Alaska, and Windy Craggy, in adjacent British Columbia. By the Late Triassic, the Alexander terrane was amalgamated with the Wrangellia, Peninsular, and northern Taku terrenes inlo the Wrangclltn superterrane. A second, prohahlv unrelated Triassic lifting event along the superterrane led to extrusion of thick snbaerjal basalt flows within the Wrangellia Iciitine. These basalts served as the metal source for Kelinecott-type copper deposits during terrane accretion to the eraton later in the Mesozoic. Jurassic arc inaginalisin in the Pacific basin included formation of a series of mineral deposits in terranes that were obducted onto of accreted to western Alaska during a period of 100 m.y. Podifonn chroinite bo the s formed in ultramnlicplutonie rocks that were later nbdnded in the Brooks Range and Ruby geanticline as parts of the Augavucliam lerrane and formed part of the Talkeetna arc in the Peninsular lerrane that is now part of south-central Alaska Coeval volcanisni in the Talkeclna arc was characterized bv many small but widespread metalliferous events and the formation of at least one significant Jurassic volcaoogenic massive sulfide system at the Johnson River prospect. Are inagiuatisni that formed the Coodnews and Togiak terranes included crystallization of Fe-, Ti-. and Pt-rich zoned nllramafic bo the s. During the Quaternary, erosion of bo the s in the forniei lerrane led to major placer platinum aee-umulatktns that represent the largest resource of the metal in the United States. Middle to Late Cretaceous terraine accretion and magmatism were associated with vvidespread metalliferous events. Copper porphyries and Fe-Cu-Au-bearing skarns formed in rocks of ihe W’ rangcllia lerrane and in rocks of the inboard Gravina flysch basin soon afterttheir accrelinn along soutb-central Alaska and were coeval with continuing suhduction along the southern margin of these leiraues. The associated thermal event probably aLso drove fluid circulation that led to deposition of Keuneeott-type copper ores in littoral to supralitloral carbonate units above the Triassic rift basalts of the Wrangellia terrane. In the Gravina flysch basin in southeastern Alaska, and dle Cretaceous arc luaginalism included development of the Klukwan-Duke bell of Fe-rieh. Alaska-type zoned ultramafic bo the s. Late Cretaceous are magmatism in southwestern Alaska, also inboard of the accreted Wrangellia superterrane, is temporally associated with formation of einnabar-hearing epithermal lodes and Au-rieh voleano-piutonic completes. Farther north. Albian gold veins in the Seward and Arctic Alaska terrain’s could lie products of extensional events in compressional orogens or could be the result of simple, broad-scale erustal thinning. In contrast, early Late Cretaceous gold veins in the Yukon-Tanana terraue show a (lose genetic association with subdution-related plutons that were likelv derived from the underplaring of Gravina flysch. Late Gretaceous exlensiomil magmatism caused emplacement of tin granites on the Seward Peninsula. Collisional tectonics conlinued to direct Alaskan mineral deposit formation in the Cenozok, Plate eonvergepce and associated snbduetion led to the widespread development of Alaska’s productive mesothernial gold vein systems throughout the southeastern and south-central fere are, Metamorpliie fluid flow, in many cases aided by changing Eocene plate motions in the Pacific basin, resulted in lode gold formation in the Chichagof district, the Juneau gold belt, and the Willow Creek district and across the Kenai-Chugach mountain range, Beginning in the late Eocene, growth of the Meshik and Aleutian arcs in southwestern Alaska was associated with the formation ol Cu-Mo porphyry bo the s and related epithermal gold vein occurrences. In contrast to collision-driven ore genesis, localized late Oligocene and early Miocene extension in southeastern Alaska included crystallization of the Quartz Hill molybdenum porphyry and formation of Zn-Pb and tin skams in the Groundhog basin area.

Abstract Gold, bismuth, and copper mineralization at Tennant Creek is hosted by magnetite-hematite replacement bodies in lower Proterozoic sediments of the Warramunga Group. The sediments have been folded about east-west axes, are characterized by a pervasive axial-plane slaty cleavage, and are intruded by pre- and postfolding granites. Marked structural and stratigraphic control yields lines of lode (ironstones) that can be traced for distances of up to 40 km. Ironstone lodes are restricted to the magnetite-rich Black Eye Member of the Carraman Formation and concentrate adjacent to argillaceous banded iron-formations. They are aligned parallel to the regional axial-plane cleavage, commonly lying in the cores of third-order folds, especially in areas of fold hinge plunge reversal. Faulting and shearing parallel to the cleavage may also play a role in the localization of some lodes. Gold, bismuth, and copper mineralization and associated alteration form a late-stage overprint on the magnetite lodes, with gold typically concentrated toward the footwall of the ironstone or at its margins in distinct pods associated with chlorite and muscovite. Copper and bismuth mineralization occurs in overlapping zones around these pods, and this zonation is complemented by gangue mineralogy, and trace element and sulfur isotope zonation patterns. A model for the formation of the ironstone lode involves the movement of hot connate brines into developing fold axes during regional deformation of the Warramunga Group. The fluids in equilibrium with the magnetite in the sedimentary pile reacted with more oxidized horizons (e.g., hematite shales), resulting in the deposition of hematite (or a hydrated precursor) that was subsequently converted to magnetite as equilibrium was restored. Economic mineralization is associated with faulting and fracturing of the ironstone lodes and introduction of hot, saline, relatively reduced and sulfur-bearing solutions. Reaction of these solutions with chlorite in the lodes resulted in its replacement by muscovite with a consequent increase in pH and reduction in f O2 of the fluid. This reaction is likely to have controlled gold, bismuth, and copper deposition. The relative availability of sulfur, metals, and fluid between ironstone lodes is thought to be responsible for the spectrum from unmineralized to copper- and gold-rich ironstone lodes.