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The Anvil Mining District contains the most westerly exposures of the off-shelf basinal facies (Selwyn Basin) of the Cordilleran miogeocline, a prism of sedimentary rocks of Precambrian to Jurassic age deposited along the relatively stable, passive continental margin of western North America. Anvil District is immediately northeast of the Slide Mountain and Yukon-Tanana Terranes, the most easterly of the allochthonous suspect terranes which were amalgamated with North America starting in Jurassic time. The total interpreted stratigraphic thickness of the metasedimentary rocks of North American affinity is greater than 7400 m, ranging in age from latest Precambrian or earliest Cambrian through Devonian. These metasedimentary rocks consist predominantly of fine clastic sediments deposited in an off-shelf marine basin with local occurrence of euxinic carbonaceous shales and coarser sandstones and conglomerates. Extensive Ordovician within-plate basaltic submarine volcanic rocks and associated epiclastic breccias are indicative of localized rifting along the continental margin.

The Anvil district contains the most westerly off-shelf basinal facies of the Cordilleran miogeocline, a prism of sedimentary rocks of Precambrian to Jurassic age deposited along the relatively stable continental margin of western North America. The district is part of Selwyn basin, a large area of central Yukon in which deep water clastic rocks, chert, and minor carbonate accumulated along the ancient North American continental margin during Neoproterozoic and early Paleozoic time (Gabrielse, 1967).

Includes a geological cross section, mineral occurrences, isotopic age dates and fossil samples.

Cambrian (?) schist and phyllite of the Anvil Range, Yukon, host three large stratabound lead-zinc deposits: Faro, Vangorda, and Swim. Because geological exploration is limited by a thick cover of glacial overburden, geochemical techniques were tested in the area. These include bedrock sampling for primary halos and geochemical marker horizons, and glacial overburden sampling for secondary dispersion patterns. Multi-element geochemistry of bedrock indicates that the schist and phyllite are not distinctive in one or any combination of the trace elements analyzed. However, some younger rocks are enhanced in various elements: amphibolite in Ni, Cr, Co, and Cu; rhyolite in Pb and Sn; and granite in Sn. Despite presence of glacial overburden, the trace element content of bedrock is reflected in soils. Soils overlying magnetic greenstones are enriched in Ni and Cu, whereas soils overlying granite are slightly enriched in Sn content. Detailed bedrock, overburden and soil sampling at the Faro deposit reveals that primary Pb, Zn, Mo, and Ba halos exist about the ore zone. Mo parallels the visible alteration envelope, but Pb and Zn extend into the hanging wall and the footwall. Ba extends into the hanging wall but is not detected in the footwall. Secondary dispersion patterns are primarily related to the proximity of the Faro ore zone and type of parent material sampled. Till deposits have higher background and threshold values for Cu, Pb, and Zn than those of glaciofluvial deposits. Bath Pb and Zn distributions in overburden delineate the Faro #2 ore body; Zn extends to surface whereas Pb, in some cases, does not. This is a reflection of the type of overburden sampled. In general, Zn is the more consistent indicator of ore. The Zn anomaly is primarily hydromorphic in origin, cxZn having higher anomalous/threshold contrast than total Zn (11.1 for cxZn vs 4.8 for total Zn). The nature of the Pb anomaly is not understood. This thesis is available online at https://open.library.ubc.ca/cIRcle/collections/ubctheses/831/items/1.0302661. A copy of this thesis is available at the EMR library – TN27.Y8 M677.

Till geochemistry and glacial geology have rarely been integrated into Yukon mineral exploration. In the Anvil District, thick glacial deposits have consistently hampered exploration. From the initial (massive sulphide) discovery in Vangorda Creek, twenty years elapsed before the Grum deposit was discovered only two kilometres to the northwest. This work examines the utility of till geochemistry as a method to trace mineralized soil/till samples back to their source rocks in the Anvil District. The Anvil District was last glaciated during the McConnell glaciation, which had a significant impact on the local terrain. The relatively swift-flowing Cordilleran ice sheet deposited thick sequences of till in low-lying areas and eroded southeast-facing slopes and hill summits in the Swim Basin and Vangorda Plateau. This type of glacial history is conducive for till geochemical exploration. A 12 km 2 till grid was sampled northwest of the Faro deposit to map the glacial dispersion train. The till geochemistry on the -230 mesh fraction (silt and clay) indicated a broad dispersion plume for lead, zinc, and copper, extending more than 5 km west of the Faro Pb/Zn deposit. A section of the dispersion train may have a palimpsest origin. The soil geochemistry on the -80 mesh fraction, from 1964 data, indicated a much narrower dispersion plume extending directly from the Faro deposit. Till geochemistry, particularly on the fine fraction, has applications to similar drift-covered terrain, such as the Finlayson Lake massive sulphide district to the southeast.

The integration of till geochemistry and glacial geology into Yukon mineral exploration has been largely underused. In the Anvil district, thick glacial deposits have consistently hampered exploration. From the time of the initial discovery made in Vangorda Creek, it took an additional 20 years before the Grum deposit was discovered only 2 km to the northwest. This work examines the utility of till geochemistry as a method to trace mineralized soil/till samples back to their source rocks in the Anvil district. The Anvil district was last glaciated during the McConnell glaciation, which had a significant impact on the local terrain. The relatively swift-flowing Cordilleran ice sheet deposited thick sequences of till in low-lying areas and eroded southeast-facing slopes and hill summits in the Swim basin and Vangorda plateau. This type of glacial history is conducive for till geochemical exploration. Evidence for a late glacial Cordilleran re-advance is discussed and has implications on prospecting in the district. A 12-km2 till grid was sampled northwest of the Faro deposit to map the glacial dispersion of mineralized sediment. The till geochemistry on the -230 mesh fraction (silt and clay) indicated a broad dispersion plume for lead, zinc and copper extending more than 5 km west of the Faro Pb/Zn deposit. A section of the dispersion train may have a palimpsest origin. The soil geochemistry on the -80 mesh fraction, from 1964 data, indicated a much narrower dispersion plume extending directly from the Faro deposit. The geochemical changes at depth in the till stratigraphy were examined at the Vangorda mine. Results showed that anomalous lead concentrations, unlike zinc concentrations, were found throughout the 20-m till column. Regional till sampling was carried out in three areas peripheral to the known massive sulphide deposits. Results from these sampling programs highlighted anomalies in lead, zinc and copper. Overall, the application of till geochemistry proved to be successful in the Anvil district. Applying similar techniques to drift-covered terrain elsewhere in the northern Cordillera would be beneficial.

Between the Cretaceous granitic rocks (Hake Batholith on the west; Cassiar Batholith to the east) are three belts of metamorphic rocks, collectively part of Yukon-Tanana terrane. These are remnants of oceanic and continental volcanic arcs, and marginal basin sediments of Early to mid-Paleozoic age. At the head of Borden Creek are thick carbonate and andesitic volcanic rocks correlated with Klinkit Group. The Ram Creek fault and Hidden Lake fault are not exposed but deduced to be steeply dipping brittle structures with northeastward thrust or transpressional offset, based upon more complete exposure to the southeast in 105B/3 map area. The former is likely of Cretaceous age; the latter was active between mid-Permian and Early Jurassic time.

The Finlayson Lake district in southeastern Yukon is a remnant of a Late Paleozoic arc–back-arc system that consists of metamorphosed volcanic, plutonic, and sedimentary rocks of the Yukon-Tanana and Slide Mountain terranes. These rocks host more than 40 Mt of polymetallic resources in numerous occurrences and styles of volcanogenic massive sulphide (VMS) mineralization. Geochemical data from these rocks support previous interpretations that volcanism and plutonism occurred in arc–marginal arc (e.g., Fire Lake formation) and continental back-arc basin environments (e.g., Kudz Ze Kayah formation, Wind Lake formation, and Wolverine Lake group) where felsic magmatism formed from varying mixtures of crust and mantle-derived material. The rocks have elevated high field strength element (HFSE) and rare earth element (REE) concentrations in VMS-proximal stratigraphy relative to VMS-barren assemblages, suggesting that the petrogenetic conditions that generated felsic rocks likely played a role in the localization of VMS mineralization. Future work aims to constrain magmatic processes and outline prospectivity criteria for delineating productive VMS assemblages within the district, and in similar geodynamic settings globally.