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.

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.

A bimodal volcanic suite of rhyolite intrusions and flows and columnar olivine basalt, basaltic tuff and tuff breccia occurs along and immediately north of the Tintina Fault from near Faro to Tuchitua in east-central Yukon. The results of recent fieldwork and geochronometry over the northern part of this belt expands the known areal distribution of rhyolitic volcanics and confirms their age as late Paleocene to Eocene. Basalt formerly thought Quaternary is also of Eocene age. The concordance of dates between the mafic and felsic volcanics indicates a single Paleogene bimodal volcanic province. Such bimodal suites are commonly linked to crustal extension and normal faulting, which in this case are presumably related to transcurrent slip along Tintina Fault. The connection between Paleogene volcanism and the geographical extent of placer gold in this area is more than circumstantial. The recent lode gold discovery at Grew Creek appears to be intimately associated with Paleogene felsic volcanism. Hydrothermal systems associated with similar felsic volcanic centres elsewhere in the region, perhaps unmapped or buried by drift, may be the ultimate source of the placer gold.

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The Ketza River gold deposits, in central Yukon, are gold-bearing, massive sulphide mantos and chimneys in Lower Cambrian limestone. Mining is presently confined to oxidized portions of the deposits. The deposits are bounded on three sides by silver-rich veins. Metal zoning corresponds to a pronounced domal uplift that is thought to be related to a buried Cretaceous intrusion. The zoning may partly reflect stratigraphic control, but distance from the buried intrusion is considered the prime control.

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.

A copy of this thesis is available at the EMR library – TN785 L42 1973. This thesis is available online at http://hdl.handle.net/2429/32084.

A copy of this thesis is available at the EMR library – QE195.K57 1982.

A copy of this thesis is available at the EMR library – QE195 C56, This thesis is available online at https://archive.org/details/Cholach1969/mode/2up.

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.