The Tombstone, Mayo and Tungsten plutonic suites of granitic intrusions, collectively termed the Tombstone-Tungsten Belt, form three geographically, mineralogically, geochemically and metallogenically distinct plutonic suites. The granites (sensu lato) intruded the ancient North American continental margin of the northern Canadian Cordillera as part of a single magmatic episode in the mid-Cretaceous (96-90 Ma). The Tombstone Suite is alkalic, variably fractionated, slightly oxidised, contains magnetite and titanite, and has primary, but no xenocrystic, zircon. The Mayo Suite is sub-alkalic, metaluminous to weakly peraluminous, fractionated, but with early felsic and late mafic phases, moderately reduced with titanite dominant, and has xenocrystic zircon. The Tungsten Suite is peraluminous, entirely felsic, more highly fractionated, reduced with ilmenite dominant, and has abundant xenocrystic zircon. Each suite has a distinctive petrogenesis. The Tombstone Suite was derived from an enriched, previously depleted lithospheric mantle, the Tungsten Suite is from the continental crust including, but not dominated by, carbonaceous pelitic rocks, and the Mayo Suite is from a similar sedimentary crustal source, but is mixed with a distinct mafic component from an enriched mantle source. Each suite has a distinctive metallogeny that is related to the source and redox characteristics of the magma. The Tombstone Suite has a Au-Cu-Bi association that is characteristic of most oxidised and alkalic magmas, but also has associated, and enigmatic, U-Th-F mineralisation. The reduced Tungsten Suite intrusions are characterised by world-class tungsten skarn deposits with less significant Cu, Zn, Sn and Mo anomalies. The Mayo Suite intrusions are characteristically gold-enriched, with associated As, Bi, Te and W associations. All suites also have associated, but distal and lower temperature Ag-Pb- and Sb-rich mineral occurrences. Although processes such as fractionation, volatile enrichment and phase separation are ultimately required to produce economic concentrations of ore elements from crystallising magmas, the nature of the source materials and their redox state play an important role in determining which elements are effectively concentrated by magmatic processes.

Abstract The Tintina gold province comprises numerous (>15) individual gold belts and districts throughout interior Alaska and Yukon and has a recently defined lode gold resource of ~35 Moz and past placer-lode production of ~33 Moz Au. This recently defined province is underlain by a diverse geology comprising the following: (1) highly deformed and polymetamorphosed Neoproterozoic and Paleozoic schists and meta-igneous rocks of the pericratonic Yukon-Tanana terrane in eastern Alaska and western Yukon, (2) deformed continental margin Neoproterozoic and Paleozoic clastic rocks and limestones of the Selwyn basin in eastern Yukon, and (3) weakly deformed flysch of the Cretaceous Kuskokwim basin in western Alaska. Most gold lodes show a spatial and temporal association with mid-Cretaceous plutons in the former two areas and with Late Cretaceous plutons in the latter area. These calc-alkaline, reduced, radiogenic intrusions were emplaced within a wide variety of tectonic settings along the Cretaceous margin of North America. Significant lode gold resources, newly defined during the last decade, include those at Fort Knox (5.4 Moz), Donlin Creek (12.3 Moz), Pogo (5.8 Moz), True North (0.79 Moz), and Brewery Creek (0.85 Moz) Mineralization styles throughout the Tintina gold province are extremely varied. Most deposits are well defined as zones surrounding a central causative pluton. Sheeted quartz-feldspar veins are a distinctive ore style where ore is localized in the apical parts of plutons or in immediately adjacent hornfels, and they are typically characterized by a Te-W-Bi-Au geochemical signature. Polymetallic replacement bodies, auriferous breccias, and disseminated ores occur farther out within thermal aureoles; gold-rich skarns develop where reactive carbonate units are part of the surrounding country rock sequence. Other ore styles, although spatially and temporally associated with intrusions, continue to require more data before a definitive genetic link to magmatism can be assured. These styles include the epizonal fracture networks within carbonaceous sedimentary rocks and/or intruded dikes and sills, which have a consistent As-Au-Hg-Sb signature (e.g., Brewery Creek, Donlin Creek, True North). Also of uncertain origin are the shear-zone—related veins (e.g., Ryan Lode, Longline, Pogo) that have more abundant sulfide minerals (2—3 vol %) than other styles, common crack-seal textures, ductile and brittle features, and little metal zoning. Recognition in 1992 that an old prospect, known since 1913 at the site of the presently producing Fort Knox deposit, could be a world-class gold deposit changed precious metal exploration strategies in the northern North American Cordillera. Bulk tonnage orebodies with economic grades <1 g/t Au were for the first time seen as conventional milling or heap leaching targets. The resulting exploration boom throughout the 1990s in interior Alaska and Yukon led to four years of recent gold production at Brewery Creek, the present mining at True North, and the large defined resource at Donlin Creek. In addition, the Pogo deposit was discovered in the mid-1990s; it has ore grades (~18 g/t Au) about one order of magnitude greater than those of the other new resources in the Tintina gold province. Regional stream geochemistry followed by soil geochemistry has been most effective in discovering new orebodies in this vast region (e.g., Brewery Creek, Pogo), although the application of the intrusion-related deposit model to areas with known mineral deposits has also been successful (e.g., Fort Knox, True North, Donlin Creek). The notable characteristics of the Tintina gold province deposits pertinent to exploration (such as vast, remote under explored areas, unallocated regions with variable oxidation depths, and discontinuous permafrost), in combination with an evolving geologic model, create exploration challenges that can be overcome with the pragmatic application of selected exploration techniques and strategies.

Geologic and isotopic data suggest a depositional link between granitic plutons of northern Stikinia and the adjacent Jurassic Laberge Group sedimentary rocks of the Whitehorse Trough. U/Pb zircon dating of granitic cobbles in Lower Jurassic Laberge Group conglomerate of the Mesozoic Whitehorse Trough suggests clast derivation from a source terrane containing Late Triassic (ca. 215–208 Ma) granitic plutons. Initial strontium ratios are primitive and paleocurrent data show that detritus comprising Laberge Group conglomerate was westerly derived. A string of small, isotopically unevolved plutons of Late Triassic to earliest Jurassic age intrude the Lewes River volcanic arc rocks along the western margin of the Whitehorse Trough and are interpreted as the probable western source for the clasts. Dates and initial strontium values of the clasts rule out previous suggestions that the clasts were derived from the Early Jurassic Klotassin suite batholiths which intrude Nisling Terrane rocks. The deposition of extremely coarse Early Jurassic boulder conglomerate on top of Late Triassic carbonate facies represents a dramatic change in depositional style. Sudden uplift incised a Lower Jurassic erosional disconformity into arc and arc-flanking shelf deposits along the western margin of the Whitehorse Trough. Episodic uplift periodically maintained extreme paleotopographic relief in the arc, sufficient to prograde coarse-grained debris flows into the basin and erode the plutonic roots of the arc throughout Early and early Middle Jurassic time. Initial Sr isotopic ratios of the granitic clasts average 0.7045 and suggest that they were derived from unevolved island-arc magmas. U/Pb systematics do not indicate the presence of inherited zircon xenocrysts. These data suggest that the plutons which acted as the source for the clasts had limited, if any, interactions with isotopically evolved continental crust and likely intruded oceanic or transitional crust. The source of metamorphic clasts in Laberge Group conglomerate is presumed to be the Nisling Terrane, suggesting that Nisling and Stikinia were linked by Middle Jurassic time.