Tin and tungsten-bearing veins, breccias and skarns occur in a 60 km long belt trending west from Keno Hill to the Tintina Fault. They are hosted by mid-Cretaceous felsic intrusions, or adjacent metasedimentary rocks of Upper Precambrian to Mississippian age. Tin occurrences are mainly associated with two-mica granites in the southern part of the belt, while the tungsten lodes are more commonly associated with biotite-hornblende granitoids. Tin- and silver-bearing veins are associated with the central granite phase of a zoned intrusion in the northwest part of the belt (the Syenite Range). The zoned intrusion ranges in composition from tourmaline orbicular granite to granite to quartz monzonite to syenite. Most skarns are tungsten-dominant, whereas most breccias and veins are tin-bearing. The skarns are calcic and reduced. Three stages of skarn mineral formation and associated minerals are recognized:: 1) isochemical contact metamorphism, including diopside, grossular, wollastonite, and tremolite; 2) metasomatic skarn formation including andradite, idocrase, hedenbergite, axinite, and some sulphide minerals; and 3) retrograde alteration including actinolite, chlorite, clinozoisite, epidote, calcite, biotite, scheelite, cassiterite and sulphide minerals. Sulphide minerals are mostly minor, with pyrrhotite and pyrite predominant. Breccias, veins and sheeted veins of tin and tungsten occur in steeply diping tabular bodies close to felsic intrusions. The veins consist of quartz, tourmaline or chlorite. Tin-bearing veins and breccias contain all three gangue minerals plus pyrrhotite, pyrite, sphalerite, chalcopyrite, arsenopyrite and galena. Tungsten is only found in quartz (~orthoclase) veins which contain minor pyrite and molybdenite. Sheeted vein systems consist of three mineral assemblages:: 1)quartz-orthoclase-scheelite, 2) quartz-orthoclase-cassiterite, and 3) tourmaline-cassiterite. The first assemblage is present both in the endo- and exocontact of felsic intrusions, whereas the second and third occur further away from the granite in metasedimentary rocks which generally lie outside the thermal aureole of the intrusion. Breccia clasts consist of quartzite, schist, and/or vein fragments (quartz, tourmaline, or chlorite). The breccias are either clast-supported with a matrix of rock flour, or matrix-supported with a matrix (groundmass) of crystalline quartz, tourmaline or chlorite similar to vein material. Geochemical studies of the McQuesten River occurrences indicate that:: 1) Some properties are exclusively tin or tungsten properties, but others contain both metals. There is a positive correlation between tungsten and tin in some tin-bearing rocks. 2) Silver is common in veins and skarns which contain over 50 ppm Sn. 3) Gold occurs in significant quantities in most skarns and in several veins. 4) There is a positive correlation between gold and bismuth in the skarns. Bismuth can be used as a pathfinder for gold in these skarns.

Mid-Cretaceous plutons in the McQuesten River region intrude Upper Proterozoic to Mississippian miogeoclinal metasedimentary rocks of Selwyn Basin. They form a belt trending east from the Tintina Trench which can be roughly subdivided into two parallel belts. Plutonic rocks fall into three main groups: 1) biotite-muscovite (two-mica) granite in the southernmost belt which follows the trend of the McQuesten Anticline; 2) biotite-hornblende quartz monzonite, granite and granodiorite in the northern belt which follows the thrust faulted contact of the Hyland Group (Grit Unit) with the Road River Formation; and 3) hornblende-biotite syenite and associated quartz syenite, quartz monzonite, granite and tourmaline-orbicular granite along the north edge of the northern belt. Tin-silver breccia veins and skarns are spatially associated with the two-mica granites, while tungsten-gold skarns and sheeted veins are associated with biotite-hornblende granite, quartz monzonite and granodiorite. The concentrically zoned syenite intrusion in the northern belt (ZETA) includes all the plutonic phases (two-mica granite, biotite-hornblende granitoids, and hornblende-biotite syenitoids), and links them cogenetically through the fractional crystallization process. The ZETA tin-silver veins are associated with the tourmaline orbicular granite, which is the most evolved phase of the concentrically zoned ZETA syenite intrusion. Plutons in the McQuesten region resemble those of the Selwyn and Tombstone Plutonic Suites. They are post to syntectonic, roughly circular in shape, and intrude miogeoclinal metasedimentary rocks of ancient North America. They show a concentric zonation and are surrounded by contact aureoles. The intrusive suite is bimodal, with a southern belt consisting of evolved two-mica granites and a northern belt consisting of less evolved biotite-hornblende granites. Lavas associated with the plutons are believed to be coeval.

Numerous silver-rich, galena- and sphalerite-bearing veins and stratabound lenses are located on both sides of the Yukon-British Columbia border in the Rancheria District. Some veins are within either the Cassiar Batholith or other mid-Cretaceous intrusions; some veins and lenses are near the Cassiar Batholith within early and middle Paleozoic carbonate rocks/and others are far from any exposed Cretaceous Batholiths. Green first thought that a distinctive type was defined by those associated with Lower Cambrian limestone. Gabrielse and Mulligan emphasized the well-defined stratigraphic and structural controls of those located near the Casssiar Batholith, and inferred that they were related to that intrusion. Stratabound lenses far from large intrusions are recent discoveries. Exploration geologists first considered them to be Paleozoic syngenetic/diagenetic deposits, but later exploration has revealed their epigenetic nature. No explanation has been offered for the origin of veins within the Cretacoeus intrusions. This report describes the characteristics of the deposits, and attempts to show that they comprise a distinct type with a common genesis. If so, the deposits are younger than and unrelated to mid-Cretaceous Batholiths. They are closely related to:: steeply dipping faults with a variety of strikes, mafic dykes, felsic dykes and breccias. The deposits, dykes, faults and breccais may all be related to regionally extensive, large scale, northwest-trending, dextral transcurrent faults that were active during Late Cretaceous and Early Tertiary time.

The Logan (MINFILE 105B 099) and YP (MINFILE 105B 001) zinc-lead-silver deposits are located in the Rancheria District, Yukon Territory. These deposits and numerous other occurrences occur in veins and breccia zones which cut clastic sedimentary rocks of Proterozoic and Palaeozoic age, along fracture zones cross-cutting Cretaceous granites and Eocene volcanic dykes of mafic and felsic composition, and form replacement bodies in Palaeozoic carbonates. At the Logan and YP deposits, four phases of mineralization can be distinguished. The main sulphide minerals are sphalerite, galena, pyrrhotite, pyrite, chalcopyrite and arsenopyrite. Silver is mostly confined to galena, but also occurs in tennantite-freibergite group minerals, stannite, Pb-Ag-Bi-sulphosalts of the matildite-galena series and lillianite homologues. Arsenopyrite geothermometry using the method of Kretschmar and Scott (1976) returned maximum formation temperatures of 465° - 490° C at YP and 335° - 385°C at Logan. Microthermometric investigations of fluid inclusions in quartz associated with the YP mineralization showed formation pressures corresponding to a depth of 2500 m. Fluid inclusion data from quartz suggest that mineralization at YP and Logan is caused by a mixture of magmatic and metamorphic fluids. The fluid inclusions have low salinities of 34 weight per cent NaCl equivalent, an unusally low value for fluids which have separated from acid magmas. The metamorphic fuids may have been derived from metamorphic dewatering of Palaeozoic sediments.

A detailed evaluation of structure and alteration related to gold- and silver-rich, base metal-bearing veins was completed at the Skukum property as part of the 2002 mineral exploration program. The structural setting is an east-trending sinistral strike-slip system bounded by the Berney Creek and Goddell faults to the south and north, respectively. The deposit comprises northeast-trending quartz-sulphide mineral shear veins that formed during syn-tectonic intrusion of rhyolite and andesite dykes related to the Eocene Mount Skukum caldera complex. A genetic relationship between mineralization and certain rhyolite dykes is indicated by patterns of alteration and mineralization. Dilational, northeast-trending structures interconnect and splay off the controlling faults, and host extensional quartz-sulphide mineral veins. At Skukum Creek the main gold-silver-bearing minerals are electrum and freibergite, which precipitated with late galena-stibnite mineralization, whereas refractory gold in arsenopyrite is the main style at Goddell. A geological model is proposed that facilitates identification of prospective structures within the property.

The Mount Nansen and Stoddart Creek map areas (NTS 115 I/3, 6) are in the southern part of the Dawson Range. They contain a number of porphyry and vein related mineral occurrences which have been undergoing extensive re-evaluation for precious metals potential. Basement rocks are part of the Yukon Crystalline Terrane and include metamorphosed and deformed sedimentary, volcanic and plutonic rocks of uncertain age. These are intruded by two suites of foliated plutonic rocks, the Upper Triassic to Jurassic Klotassin Suite, mainly hornblende-biotite granodiorite, and the Jurassic Big Creek Suite, including K-feldspar porphyritic syenite, quartz syenite and monzonite. Latest metamorphism of basement rocks is likely related to emplacement of these suites. Latest lower Cretaceous was marked by intrusion of the Dawson Range Batholith, consisting of the regionally exposed Casino Granodiorite and the more localized Coffee Creek Granite. The Mount Nansen Volcanics, mainly andesite with a lesser felsic component, are possibly cogenetic with these intrusives. Numerous intermediate to felsic porphyry stocks and dikes may be of Mount Nansen age in part, but they are at least in part younger. The Bow Creek Granite is a newly defined, high level, granophyric pluton with related, peripheral quartz-feldspar porphyry dikes. These rocks appear to cut the Mount Nansen volcanics and may be as young as the Carmacks volcanism. The Caribou Creek Conglomerate is a very localized sedimentary sequence which underlies the Carmacks volcanics. The Carmacks Volcanic Suite, uppermost Cretaceous in age, is relatively flat-lying and has been subdivided into three units. The lowermost consists of felsic pyroclastic rocks and associated glassy domes or plugs. The middle unit, which appears to be quite thin in the map area, consists of andesite flows and pyroclastics with minor basalt. The most extensive is the upper unit, which consists mainly of basalt flows. Mineral deposits are of four main types, including porphyries, veins, skarns and placer. Transitional varieties are associated with brecciation and porphyry dike emplacement. The porphyries are low grade copper-molybdenum deposits with local gold enrichment in the upper parts. Breccias with elevated precious metal values occur within the porphyries and also peripherally associated with quartz-feldspar porphyry dikes. Gold and silver-bearing quartz veins occur in dilational fracture systems which are also peripheral to the porphyries. In the presence of calcareous meta-sediments of Yukon Crystalline Terrane, gold-bearing, iron-rich skarns have formed. Base metal-rich veins are rare and distal from the porphyry centres. Mineralization controls are recognised as follows:: 1. Proximity to major regional structures such as the Big Creek Fault and the Minto Linear which extends north-northeasterly through the map area. 2. Local structures, ranging in trend from northwesterly to northeasterly, are important as hydrothermal channelways and vein sites. 3. Presence of a favourable host, including Mount Nansen volcanics, siliceous meta-sediments and Casino Granodiorite. 4. Proximity to porphyry stocks or quartz-feldspar pophyry dikes.

The White River copper deposit, in upper Triassic Nikolai Greenstone of southwestern Yukon, is representative of the native copper-basalt association. Native copper and chalcocite are the association. Native copper and chalcocite are the most abundant ore minerals, but a substantial amount of bornite is known, as well as lesser amounts of chalcopyrite, pyrite, digenite, covellite, cuprite and native silver. These minerals are found in crosscutting fractures, amygdules, gas release tubes, small crackle zones, and as local disseminations in basalt; and although concentrated near the margins of a single glomeroporphyritic unit, are neither confined to that unit nor to a single zone within it. Two stages of copper mineralization are postulated: Stage I mineralization is thought to account for most of the native copper as a product of continental weathering of Nikolai basalts. Stage II mineralization is a much later event characterized by copper sulphides in crosscutting structures. Native copper and copper sulphides of Stage II appear to form a stable and primary product of a low grade (regional) metamorphism indicated by such minerals as chlorite, epidote, prehnite, pumpellyite, calcite analcite and apophyllite which have essentially the same mode of occurrence as primary copper minerals. Consequently, metamorphism (prehnite-pumpellyite facies) is interpreted to have been the mineralizing process. Whole-rock potassium-argon dating suggests an age no older than 120 million years for the metamorphic mineralizing event; hence, stage II mineralization post-dated host rock formation by at least 80 million years. It is probabe that many other copper occurrences in Nikolai Greenstone have formed in a similar manner. Also, it is likely that some of these mineralizing fluids could have moved higher in the stratigraphic sequence and precipitated copper minerals in other units.

Magmatism in the Nahanni region, which defines the eastern extent of the Tintina Gold Province, is generally associated with tungsten mineralization and/or gold-copper-antimony-bismuth-lead-zinc metal occurrences. Intrusions are subalkaline, granitic to granodioritic, and contain several types of textural variations and highly evolved phases. The intrusions range from large composite batholiths to small stocks with associated felsic dykes and veins. Initial U-Pb and Ar-Ar geochronology reveals ages of 97.5-95 Ma with short (0.5-1.5 m.y.) cooling periods, although the intrusion associated with the Cantung tungsten-skarn orebody cooled over a relatively long period (3 m.y.). Magmatism in the area has been interpreted as crustally derived, however, the rare earth element primitive-mantlenormalized profile revealed negative niobium, tantalum and titanium anomalies suggesting an arctype setting. Furthermore, the granites lack volumetrically significant, primary peraluminous mineralogies characteristic of S-type granites.

Gold mineralization at the Mt. Skukum deposit occurs in nearly vertical quartz-carbonate veins which crosscut flat-lying andesites with a NNE trend. The mineralized veins represent the second stage of a two stage hydrothermal system, the first of which resulted in emplacement of thin chalcedonic veinlets. These two stages of veins are probably indicative of an evolving hydrothermal fluid rather than being representative of two separate events. Vein emplacement is one of the latest of a series of events which began with volcanism, producing felsic and andesitic volcanic rocks which overlie basement in this area. Subsequent periods of tectonism produced large faults along which rhyolitic dykes were emplaced. Continued tectonism resulted in reactivation of old faults along which andesitic and dacitic dykes were injected, crosscutting rhyolite dykes in many cases. As volcanic activity waned, the faults remained active, leaving zones of high permeability which acted as conduits for the still active hydrothermal circulation. Veins appear to have been emplaced at low temperature in a circulating hydrothermal system driven by a heat source at depth associated with dykes present in the area. Circulating hydrothermal fluids may have leached gold from the surrounding andesitic volcanics during propylitization. Permeability may have been controlled by faulting, brecciated flow tops and bottoms, and lapilli tuff horizons. Gold was precipitated in highly permeable conduits, such as the Main Fault Zone and breccia bodies.

Sphalerite and tetrahedrite occur with arsenopyrite and minor chalcopyrite and galena in a tabular, fault-bounded body which cuts granitic rocks of the Cassiar batholith. Diamond drilling between 1986 and 1988 outlined a deposit 1100 m long and 50-100 m wide containing geological reserves of 12.3 million tonnes grading 6.17% Zn and 26 g/t Ag. These reserves are amenable to open pit mining and the deposit is open to depth.