Auriferous sheeted quartz veins and silicified shear zones occur along the margins and within adjacent hornfels zones of mid-Cretaceous Tombstone intrusions near the head of Clear Creek in the central Yukon. The lodes are the source for more than 120,000 ounces of downstream placer gold production. These lodes contain variable amounts pyrrhotite, pyrite, and arsenopyrite, with less abundant scheelite - alkali-feldspar, muscovite, biotite and tourmaline are common gangue phases. Grab samples of mineralization often contain gold grades in excess of 1 ounce per ton. Gold-to-silver ratios vary most commonly from 1:1 to 5:1. Gold-rich quartz veins cut all stocks, adjacent hornfels and associated lamprophyre dykes commonly contain greater than 1% arsenic. Bismuth, and less consistently tungsten and stibnite, characterize many of the most highly mineralized veins within and surrounding the stocks. Quartz veins along the intrusive-metasedimentary rock contact around the Pukelman stock are also enriched in lead and silver. R-mode factor analysis of multi-element geochemical data for 111 gold- and sulphide-bearing rock samples indicates that there are two geochemically distinct metal suites in the Clear Creek occurrences. The first is characterized by As-Au-Bi ± Sb, Te ore-related mineral association, which is typical of many intrusion-related deposits in the Tombstone gold belt. Less consistently, anomalous concentrations of Ag, Co, Cu, Fe, and Mo occur within these auriferous rocks. The second metal factor is defined by Ag-Bi-Pb ± As, Au and Te. It characterizes metalliferous vein samples that have uncommonly low Au: Ag ratios and may represent a second hydrothermal episode. Tungsten shows little consistent correlation with the metalliferous veins in either element suite.

The Hunker Creek area is located 30 km southeast of Dawson City, Yukon. Gold and sulphide-bearing quartz veins (MINFILE 115O 067, 068) crosscut metamorphic rocks of the Klondike Schist. The veins are enclosed by envelopes of sericitic (inner) and propylitic (outer) alteration. Locally, carbonatization occurs between propylitized and sericitized rocks. Three stages of vein mineralization can be distinguished:: (1) quartz, carbonates, gold, arsenopyrite, pyrite, pyrrhotite, chalcopyrite, and galena; (II) quartz, carbonates, chalcopyrite, sphalerite, tetrahedrite, freibergite, polybasite, 'polyargyrite', argentite, pyrostilbnite and galena; (III) quartz and gold. Fluid inclusion data indicate that stage I minerals precipitated from hydrothermal solutions containing CO2. Homogenization temperatures range from 260° to 390°C. Stage II aqueous fluid inclusions homogenize between 190° and 260°C. Stage III inclusions homogenize between 120° and 210°C. Salinities of the three stages range from 0 to 7.2 wt-% NaCl equiv. and show no significant changes with time. It is suggested that stage I mineralization was initiated by unmixing of an original single-phase H2O and CO2 bearing fluid, and that subsequent hydrothermal evolution was controlled mainly by decreasing temperature.

The Livingstone Creek area is located 100 km northeast of Whitehorse, Yukon Territory, Canada. Hydrothermal gold-sulphide mineralization (MINFILE 105E 001) occurs in quartz-carbonate veins and veinlets which cut Paleozoic metamorphic rocks of the Teslin Suture Zone. The metamorphic rocks are also cut by Cretaceous(?) feldspar-porphyry dykes with an average thickness of 2 m. The mineralization appears to be structurally controlled by NNE-striking faults and a set of NNW-trending joints. The vein minerals consist of gold, pyrite, chalcopyrite, galena, hessite/stuetzite, tetradymite, Au-Ag tellurides, tennantite, hematite, pyrrhotite, quartz, and carbonate. Gold occurs as: 1) "free gold" in cracks and interstices of quartz gangue, 2) inclusions in galena, usually rimmed by hessite, 3) minute grains associated with chalcopyrite and galena in aggregates of coarse-grained pyrite and 4) individual grains or fracture fillings in iron hydroxides. The coarse-grained gold in Livingstone Creek appears to be derived from gold-quartz veins in the metamorphic bedrock. This is indicated by: 1) similar silver and mercury contents in primary and placer gold 2) identical trace element composition of galena from gold-quartz veins and galena inclusions in placer gold, 3) similar telluride mineral assemblages in both gold-quartz veins and placer gold grains and 4) similar homogenization temperatures and salinities in fluid inclusions from both gold-quartz veins and placer nuggets. A limited amount of gold appears to have formed by supergene leaching and precipitation. This kind of gold occurs as irregular-shapd grains in the stream placers and in iron hydroxide along fractures in quartz veins. Relative to the pirmary gold it is enriched in silver and mercury.

Placer gold deposits are widespread throughout the largely unglaciated Stewart River and southern part of the Dawson map areas. These deposits include the world famous Klondike goldfields, the historic Fortymile and Sixty Mile goldfields, and well known placers along Black Hills, Scroggie, Thistle and Kirkman creeks. Although the deposits have been mined for over 100 years and have produced an estimate 311 tonnes of gold, they still account for about 85% of Yukon's annual placer gold production. The placer deposits are classified into three levels of gravel with four main units: high-level gravel, which usually forms prominent, continuous high-level terraces and is subdivided into the White Channel Gravel (which is locally subdivided into a lower White Gravel and an upper Yellow Gravel unit) and Klondike Gravel; intermediate-level gravel, which mostly forms relatively small, irregularly distributed intermediate to low-level terraces; and low-level gravel, which represents alluvium along present day creeks, gulches and rivers. The White Channel Gravel, is up to 46 m thick and characterized by a predominance of quartz clasts (which are generally more abundant in the White Gravel than in the Yellow Gravel). It is considered Early Pliocene to earliest Late Pliocene in age (~5 to 3 Ma). The Klondike Gravel, not considered an economical placer, is up to 53 m thick and is distinguished by chert clasts derived from the Ogilvie Mountains, located northeast of the map areas. It was deposited as glaciofluvial outwash during the end of the initial and most widespread of the pre-Reid glaciations, and is probably latest Early Pliocene to earliest Late Pliocene (~3 Ma). The intermediate-level gravel, the least important economically, is up to 9 m thick. The low-level gravel, historically the most important gold-bearing unit, is 5 m thick in creeks and up to 20 m thick in rivers. The intermediate-level and low-level gravel have similar amounts of quartz, igneous and metamorphic rock particles, although locally, the low-level gravel contains sedimentary rock particles. The intermediate-level gravel is thought to be Late Pliocene to Early Pleistocene (~3 Ma to 750 Ka) in age and the low-level gravel is considered Late Pleistocene to Holocene in age. Practically all of the placers are fluvial in origin and were deposited primarily in braided streams that flowed parallel to the present day streams along which the deposits occur. Gold recovered from the various levels of gravel is detrital in origin and was mainly derived from early Mesozoic auriferous quartz veins. The concentration of gold in the gravel is related to a hierarchy of physical scales: at the lithofacies scale (metres), bed roughness determined sites of gold deposition; at the element scale (tens of metres), gravel bars were preferentially enriched in gold; at the reach scale (hundreds of metres), stream gradient was an important factor; at the system scale (hundreds of kilometres), braided river environments transported large amounts of gold; and at the sequence scale (thousands of kilometres), economic placers formed initially in the high-level White Channel Gravel and later in the intermediate- and low-level gravel.

The upper Sixtymile River area is located approximately 128 km west of Dawson City, Yukon. Lithology in this area consists of Precambrian to Paleozoic metamorphic rocks, Paleozoic ultramafic rocks, Middle Jurassic pegmatite and aplite dykes, Late Cretaceous porphyritic dykes and volcanic rocks with intercalated sedimentary rocks, Quaternary alkaline basaltic dykes and Quaternary alluvial sediments. Gold bearing, mesothermal quartz-(carbonate)-sulphide veins which trend NNE-SSW are hosted by metamorphic rocks north and south of Sixtymile River. The mesothermal quartz-(carbonate)-sulphide veins are surrounded by successive envelopes of sericitic, K-feldspar and propylitic alteration. Two stages of vein mineralization are recognized in the northern part of the area, and three stages are recognized in the south part. In the northern veins, pyrite, arsenopyrite, pyrrhotite and quartz are intergrown and formed first. These minerals are fractured and healed by second stage minerals, which include galena, sphalerite, chalcopyrite, pyrite, carbonate and minor quartz. Stage I mineralization in the southern veins is represented by quartz, and pyrite containing inclusions of other sulphides. Stage II is the main stage of precious metal enrichment, represented by arsenopyrite and galena which contain tetrahedrite, miagyrite and polybasite exsolutions. Stage I and II minerals are tectonically fractured, and healed by pyrite, sphalerite, chalcopyrite, freibergite and quartz of stage III. In both vein systems, gold enrichment is associated with arsenopyrite and silver enrichment is associated with galena. The evolution of hydrothermal fluids in the northern area is characterized by decreasing temperature (330°C to 280°C), salinity (12.8% wt.-% to 6 wt.-% NaCI equiv.), oxygen activity (log a(O2) = -30 to log a(O2) = -35), and sulphur activity (log a(S2) = -10 to log a(S2) = -12), as well as a slight increase in pH range (from >3.1 - <5.2 to >3.3 - <5.4). In the southern vein system the fluid evolution characterized by a decrease in temperature (330°C to 150°C), salinity (18.3 wt.-% to 10 wt.-% NaCI equiv.), oxygen activity (log a(O2) = -29 to log a (02) = - 52), and sulphur activity (log a(S2) = -9 to log a(S2) = -18, as well as a slight increase in pH range (>3.2 - <5.3 to >4.1 - <5.9). The following conclusions can be drawn about the fluid composition and mineral enrichment process in the fossil geothermal system of the Sixtymile River area. Deep seated fluids which circulated in the metamorphic rocks were characterized by high temperatures (above 300°C), high salinities (about 18 wt.-% NaCI equiv.) and pH values between 3.1 and 5.2. These fluids are similar to alkaline chloride fluids of active geothermal systems. Arsenic was transported as H3AsO3°-complex, gold as Au(HS)2- and lead, zinc, iron, copper as MeCl2° complexes. The first stage mineralization resulted from reaction of this deep-seated fluid with the wall rock. Second and third stage mineralization is believed to result from the mixing of two fluids with different physico-chemical characteristics.

Bedrock underlying the Slab iron oxide-copper-gold occurrence consists of fine-grained sedimentary rocks and schist of the Fairchild Lake Group (oldest unit of the Early Proterozoic Wernecke Supergroup), intermediate to mafic Slab volcanics, dioritic Bonnet Plume River Intrusions, and Early Proterozoic Wernecke Breccia that crosscuts all other units. The Wernecke Breccia was divided into two units: Type 1 and Type 2. Type 1 is limited in extent and consists of sedimentary and locally abundant massive magnetite clasts in a carbonate-magnetite matrix. Type 2 cuts Type 1 and comprises sedimentary clasts in a micro-breccia matrix. Iron oxide-copper-gold mineralization is associated with Wernecke Breccia. It occurs disseminated in quartz-carbonate veins cutting metasomatized sedimentary rocks, as sulphide veins that cut Type 1 breccia, as sulphide clasts in Type 2 breccia, as well as disseminated in the matrix of Type 2 breccia, and finally as sulphide veinlets crosscutting Type 2 breccia.

The upper Sixtymile River area is located approximately 128 km west of Dawson City, Yukon. Lithology in this area consists of Precambrian to Paleozoic metamorphic rocks, Paleozoic ultramafic rocks, Middle Jurassic pegmatitic and aplitic dikes, Upper Cretaceous porphyritic dikes and volcanic rocks with intercalated sedimentary rocks, Quaternary alkaline basaltic dikes and Quaternary alluvial sediments. Precious metal occurrences in these volcanic rocks are divided into two types, based on differences in local distribution, petrology and wall rock alteration: a gold-bearing pyrite-arsenopyrite type and a silver-bearing galena-sphalerite type. Both types are characterized by four stages of mineralization.

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A new widespread, structurally controlled gold mineralizing system has been identified during the 2010 exploration drilling program at the Coffee Project, west-central Yukon. The Coffee Creek area is underlain by a sequence of shallowly to moderately south to southwest-dipping Paleozoic metamorphic rocks that are considered to be part of the Yukon-Tanana terrane and are intruded by the Cretaceous Coffee Creek granite along a west to northwest-trending contact. During the 2010m drilling program, structurally controlled gold mineralization was discovered in all major lithological units underlying the Coffee property. Importantly, these mineralized zones correspond to a number of discrete structural corridors. The gold zones are steeply dipping and characterized by extensive silicification in addition to sericite and clay alteration accompanied by variable As-Ag-Sb-Ba-Mo enrichment. Polyphase breccias of both hydrothermal and tectonic origin, in addition to andesitedacite dykes, are common within the gold-bearing structural corridors. The dominant sulphide is pyrite, although trace arsenopyrite, chalcopyrite and stibnite are observed locally. The similarity of breccia textures and alteration/sulphide mineralogy between all gold zones currently defined on the Coffee property implies a common mineralizing event.

Quantitative mineralogy, U-Pb geochronology of zircon and monazite, 40Ar/39Ar geochronology of muscovite and sericite, and Pb isotopes from galena in veins and feldspar in plutons provide insight into the age of metamorphism, mineralization, intrusion emplacement and the sources of metals at the Plateau South (MINFILE 105N 034, 035, 036) occurrences in central Yukon. Orogenic mineralization and metamorphism is ca. 110 Ma to 100 Ma, and possibly as old as ca. 130 Ma. Following deformation and regional metamorphism, two biotite-muscovite plutons, the Russell stock and Armstrong pluton, were emplaced at 95.39 ± 0.03 Ma and 95.51 ± 0.03 Ma, respectively. These plutons are here reassigned to the Tungsten suite based on mineralogy, chemistry and age. Coeval with these plutons are contact metamorphism and possibly intrusion-related mineralization. Lead isotopic data from galena cluster into two groups: Group 1 is enriched in thorogenic Pb with 206Pb/204Pb values between 18.31 and 18.14, 207Pb/204Pb between 15.62 and 15.55 and 208Pb/204Pb between 38.77 and 38.30. Group 2 is isotopically evolved with 206Pb/204Pb values between 19.13 nd 18.91, 207Pb/204Pb between 15.78 and 15.63 and 208Pb/204Pb between 39.24 and 39.07. We suggest that late Early Cretaceous mineralization is related to large-scale orogenic fluids that tapped primitive (deep?) metal sources and early Late Cretaceous mineralization, coeval with local intrusions, sourced isotopically distinct metals from the intrusions. Alternatively, all mineralization could relate to Early Cretaceous orogenic fluids but with heterogeneous, locally derived metal sources and thermal resetting of Ar ages near the intrusions.