Latest (?) Proterozoic to Earliest Cambrian and Devonian to (?) Mississippian strata, and a Cretaceous or Early Tertiary porphyry dyke underlie the Plata-Inca property. The sedimentary rocks are part of the dominantly clastic assemblage that makes up the other part of the northern Cordilleran miogeocline. The sedimentary rocks are folded and cut by thrust faults and younger (?) normal faults. Steep normal faults with a variety of orientations cut all other structures. These faults host most of the veins and are well exposed in the mine workings. Most veins contain galena, sphalerite, and tetrahedrite in a gangue of siderite and quartz with minor barite and calcite. Silver-lead ratios determined from the grade of ore shipments range from 55.5 g/t Ag : 1% Pb to 137.1 g/t Ag : 1% Pb The age and origin of the gold-silver veins in the Plata-Inca camp is unclear. They are most likely related to a buried intrusion, although the only evidence for one is the small porphyry dyke at the northwest end of the property. There are no other intrusions nearby, but the deposits are at the northern margin of the belt of mid-Cretaceous intrusions that belong to the Selwyn Plutonic Suite.

Epithermal vein and porphyry-related gold-silver deposits in the Mount Nansen area are mainly hosted in Paleozoic Yukon-Tanana Terrane metasedimentary rocks and Early Jurassic Big Creek Batholith intrusive rocks. Mineralization is spatially, and probably temporally, related to a northwest-trending belt of mid-Cretaceous hypabyssal felsic intrusions and dykes along the Mount Nansen Trend. The proximal relationship between the veins and mid-Cretaceous intrusive rocks suggests that mineralization may be genetically related to felsic magmatism. The Dickson stock yields a U-Pb zircon age of 108.3 ± 0.7 Ma, and proximal dykes in the Flex, Dickson, Brown-McDade and Weber zones give ages of 107.9 ± 0.9 Ma to 109.0 ± 0.7 Ma, similar to the age of the Mount Nansen Group volcanic rocks. Granodiorite that hosts the Dickson deposit gives a U-Pb titanite age of 191.5 ± 2.9 Ma, and is likely part of the Big Creek Batholith. Previous studies indicated two periods of mineralization in the Dawson Range: mid-Cretaceous and Late Cretaceous. Dating indicates that Mount Nansen mineralization is associated with the mid-Cretaceous emplacement of the high-level felsic intrusions.

Alpine glaciers from cirques of Granite and Albert creeks have deformed and reworked sediments in the Granite Creek valley and deposited locally sourced gold. Placer mining operations in the valley allowed detailed study of sedimentary deposits. The main units identified are from at least two glacial episodes which advanced farther than the previously mapped limits. Thick sequences of advance and retreat outwash blanket the till and represent high energy depositional environments. At least one proglacial lake formed due to ice-damming of lower Granite Creek by the Cordilleran Ice Sheet. We provide a stratigraphic record extending approximately 130 000 years and have correlated alpine till units to MIS 4, which has not been identified elsewhere in central Yukon. Multiple gold-bearing sedimentary units are found in the stratigraphy, representing glacial, interglacial/interstadial, and modern processes. This work highlights processes important to gold concentration that can be applied to other alpine glaciated areas with proximal gold mineralization.

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.

The Tintina Gold Province (TGP) of east-central Alaska, Yukon Territory, and the southwestern Northwest Territories comprises a very large number of gold (± base metal) deposits and occurrences that are spatially and temporally related to mid-Cretaceous intrusions. Intrusions in the eastern Selwyn Basin, south of MacMillan Pass and east of Frances Lakes, include some of the largest bodies within the TGP and are the focus of this study. Magmatic rocks of the TGP have been divided into individual plutonic suites on the basis of crystallization age, lithology, mineralogy, geochemistry, and spatial distribution, as well as metallogenic association. From -111 Ma to -99 Ma, magmatism is thought to reflect the formation of a southwest-facing continental magmatic arc, represented by the Whitehorse - Coffee Creek suite, and that the coeval Anvil and Cassiar suites formed in a back-arc environment. The younger Tay River, Tungsten and Tombstone plutonic suites successively stepped inboard between 99 Ma to 89 Ma. However, the processes leading to such volumetrically significant magmatism remains poorly understood. Intrusions within the study area range in composition from granite to granodiorite with subordinate diorite and are characteristically calc-alkaline, peraluminous to weakly metaluminous, relatively reduced, and typically contain only biotite as the dominant mafic phase. Sixteen new U-Pb ages, ranging from ~107 Ma to -91 Ma, constrain a temporal framework for plutonism across the region that is consistent with the progressively "inboard younging" pattern of magmatism observed in the northern and western portions of the TGP. - Geochemical (major, trace and rare earth elements) characteristics, together with geochronology indicate that the Anvil, Tay River, Tungsten, and Tombstone plutonic suites as originally defined farther to the northwest do continue southeastward and into the southwestern Northwest Territories. Initial Sr ratios and epsilon Nd values (n=20; age corrected for T = 100 Ma) range from 0.70853 to 0.72243 and -6.0 to -17.5, respectively. Lead isotopic compositions (n=20) show relatively narrow ranges for 2 0 6Pb/2 0 4Pb, 2 0 7Pb/2 0 4Pb, and 2 0 8Pb/2 0 4Pb ratios of 19.397 to 19.772, 15.697 to 15.829, and 39.461 to 39.883, respectively. All radiogenic isotope systematics indicate that these magmas have interacted extensively with or were derived entirely from continental crust. Several spatial and temporal trends are apparent in the data including an increase in overall REE abundance and sNd values, and a decrease in Srjnit ai, values with decreasing age (broadly moving from west to east). These trends may reflect differences in the nature of the underlying basement, potential magma source(s), and/or the melt producing processes that were involved. Lead isotope compositions of feldspars from various intrusions and sulphides from associated precious- and base metal deposits and occurrences define narrow and overlapping ranges indicating that the metals in many of the mineral deposits (and prospects) in the region are mostly derived from the mid-Cretaceous TGP intrusions.

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.

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.

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.

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 Flex Gold-Silver deposit is a multiple vein epithermal system found within the Mount Nansen precious metal trend. High-grade gold and silver values are associated with north-northwesterly trending, sulphide-rich quartz veins that infill structures associated with regional shearing. BYG has stripped and mapped the deposit to prepare advanced exploration and mining design plans. The mineralization is typically epithermal with extensive wall rock alteration including argillic and phyllic zones. Gold - silver values occur with sulphide-rich quartz veins, breccia veins, and silicified zones. Gold values up to 34 grams per tonne and silver values up to 1416 grams per tonne were obtained from the sulphide-rich veins.