for a copy of this paper please contact the Yukon Geological Survey; geology@gov.yk.ca.

not_specified

The Tummel fault zone, a northwest-trending belt of rocks of uncertain age and/or tectonic affinity, separates Paleozoic miogeoclinal strata of Cassiar Terrane from Yukon-Tanana Terrane metavolcanic and metasedimentary rocks. Northeast of the fault, Cassiar Terrane comprises pelitic and semipelitic rocks with rare amphibolite, which are correlated with the Kechika Group. These are overlain by carbonate correlated with the Askin Group. Southwest of the fault, in Yukon-Tanana Terrane, Devono-Mississippian siliciclastic rocks are overlain by Mississippian arc volcanic rocks. Granodiorite and diorite of the Telegraph Plutonic Suite (348-350 Ma) intrude the siliciclastic rocks. Foliated greenstone, leucogabbro intrusions, serpentinite and chert occur in the Tummel fault zone. The Early Cretaceous Glenlyon Batholith intrudes strata of Cassiar Terrane. Contact metamorphism recognized across the Tummel fault zone is interpreted to have been imposed by the Glenlyon Batholith. If correct, this interpretation requires that post-mid-Cretaceous displacement across the Tummel fault zone has been minimal (~5 km).

Upper Devonian and Lower Mississippian metavolcanic rocks of Yukon-Tanana Terrane in southern Finlayson Lake and Frances Lake map areas occur in three thrust sheets, locally modified by a Cretaceous normal fault. The lower thrust sheet, the Big Campbell sheet, comprises the Upper Devonian to Lower Mississippian metavolcanic stratigraphy that hosts the main volcanichosted massive sulphide (VHMS) deposits of the district. Metavolcanic rocks in the middle thrust sheet, the Money Creek sheet, include the Upper Devonian Waters Creek and Early Mississippian Tuchitua River formations. The former comprises primarily felsic metavolcanic rocks and carbonaceous phyllite and is extensively intruded by sheets of comagmatic porphyry. The latter comprises primarily intermediate metavolcanic, volcaniclastic and epiclastic rocks. The upper thrust sheet, the Cleaver Lake sheet, is in part made up of Late Devonian calc-alkaline basalt and rhyolite, the Cleaver Lake formation, and comagmatic felsic to ultramafic plutonic rocks. Of these, the Waters Creek formation and the formations in the Big Campbell sheet have the highest potential to host VHMS deposits.

for a copy of this paper please contact the Yukon Geological Survey; geology@gov.yk.ca.

Yukon-Tanana Terrane in Little Kalzas Lake area consists of a lower quartzite package and an upper metavolcanic package. The lower quartzite package includes a discontinuous metavolcaniclastic and mafic metavolcanic unit. The upper metavolcanic package consists predominantly of intermediate to felsic metavolcanic rocks in the northern part of the map area. These rocks pass southward into a clastic-dominated metavolcanic assemblage. A conspicuous crinoidal marble occurs in the middle of the upper metavolcanic package and can be traced between the northern and southern domains. The layered metamorphic rocks are intruded by the multi-phase Little Kalzas orthogneiss complex in the northeastern part of the map area along the southwestern side of Tintina Trench. The Little Kalzas orthogneiss complex, of uncertain age, comprises granodioritic to granitic gneiss and contains abundant xenoliths of country rock. Younger (Jurassic?), post-kinematic quartz monzonite (in the north) to quartz-diorite (in the south) plutons also intrude the area. The youngest intrusive rocks are small plugs of Tertiary quartz-feldspar porphyry. A pervasive transposition foliation and mineral lineation are developed throughout the area, except in local low-strain domains where primary textures are preserved. The transposition foliation is axial-planar to tight south southwest-vergent folds whose axial surfaces become progressively upright to south southwest-dipping toward the northeast. These structures are deformed by younger crenulation cleavages and associated open folds.

Geological mapping in Wolverine Lake area has outlined new Yukon-Tanana Terrane stratigraphy, constrained the stratigraphic position of the Wolverine Lake volcanogenic massive sulphide (VMS) deposit, and clarified the relationship of Yukon-Tanana Terrane to the Campbell Range belt. Yukon-Tanana Terrane comprises two stratigraphic successions separated by an angular unconformity. Beneath the unconformity are polydeformed felsic and mafic meta-volcanic rocks, carbonaceous meta-clastic rocks, marble and granitic orthogneiss. The Kudz Ze Kayah VMS deposit occurs in felsic meta-volcanic rocks of this sequence. Yukon-Tanana Terrane rocks above the unconformity are deformed by only one phase of deformation and consist primarily of carbonaceous meta-clastic rocks and quartz- and feldspar-phyric felsic meta-volcanic rocks. The Wolverine VMS deposit occurs in this succession, associated with siliceous exhalite and baritic magnetite iron formation. Meta-basalt of the Campbell Range belt, included previously in Slide Mountain Terrane, overlies the upper succession of Yukon-Tanana Terrane with sharp contact. This contact has been observed at several localities and it appears depositional. There is no evidence that it is a terrane boundary fault.

The Livingstone Creek area is underlain by metasedimentary and metaigneous rocks of Yukon-Tanana Terrane. It is intruded by at least five distinct suites of intrusive rocks of probable Mississippian to Late Cretaceous ages, at least three of which provide timing constraints on the development of tectonic foliations. Two phases of isoclinal folding, the development of a transposition foliation and late, northeast-vergent open folds characterize the ductile deformation in the area. Brittle-ductile dextral strike-slip deformation is localized along the north-trendingd Abbadie fault zone in the eastern part of the area. Bedrock in the area has potential for lode gold, copper-gold massive sulphide and nickel (platinum-group element?) mineralization along d'Abbadie Fault.

Recent discoveries of at least two types of volcanogenic massive sulphide (VMS) deposits hosted in varying terranes have greatly expanded the mineral potential of the Yukon Territory. Kuroko style deposits at Kudz Ze Kayah and Wolverine are hosted by an Early Mississippian felsic metavolcanic and carbonaceous sedimentary package within the Yukon-Tanana Terrane in the Finlayson Lake area. The massive sulphide lenses at Wolverine have spectacular grades and constitute a geological resources, as of November 1996, of 5,311,000 tonnes with 1.81 g/t Au, 359.1 g/t Ag, 1.41% Cu, 1.53% Pb and 12.96% Zn. New discoveries at the Fyre Lake and Ice properties continue to expand the volcanic hosted massive sulphide potential of the Finlayson Lake area. Fyre Lake is a copper-cobalt-gold Besshi-type deposit hosted by chlorite schist. Towards the end of the season DDH 65 at Fyre Lake intersected 31.3 m of 2.29% Cu, 0.53 gpt Au and 0.07% Co. The enigmatic, ""Cyprus-type"", Ice occurrence has copper-cobalt mineralization in mafic volcanic rocks that are interpreted to belong to the Slide Mountain Terrane. The last hole of the season, DDH IC96-34 intersected 20.56 m of massive pyrite, chalcopyrite and bornite with grades of 5.2% Cu, 0.6 gpt Au, 25 gpt Ag and 0.6% Co. Prior to discovery of Ice, volcanic hosted massive sulphide mineralization was unknown in the Slide Mountain Terrane in the Yukon. The Yukon-Tanana and Slide Mountain Terranes are not restricted to the Finlayson Lake area but cover a considerable portion of the Yukon Territory. West of Dawson the Yukon-Tanana Terrane contains several exhalite occurrences in the Devono-Missisippian Nasina Assemblage and the Permian Klondike Schist. Devono-Mississippian strata in the Yukon-Tanana Terrane may correlate with similar aged units in the Pelly-Cassiar Platform and Selwyn Basin where there are several massive sulphide occurrences. The Marg Deposit occurs at the northern edge of the Selwyn Basin; the MM, Bnob and Chzerpnough properties are hosted by extension related, pyritic, brecciated, felsic metavolcanic rocks within the Pelly-Cassiar Platform. The Yukon-Tanana Terrane extends westward into the Delta District of Alaska where there are at least 26 stratiform and replacement massive sulphide deposits and occurrences. Strata potentially correlative with the Yukon-Tanana Terrane hosts several volcanogenic massive sulphide deposits and occurrences in northern British Columbia.

Paleozoic platformal and basinal strata of Cassiar Terrane are separated from rocks of Yukon-Tanana Terrane to the west by an unexposed fault in southeast Glenlyon map area. Quartzite, marble, phyllite, and amphibolite are grouped in Cassiar Terrane, and no rocks of Slide Mountain Terrane are recognized. The mid-Cretaceous Glenlyon batholith contains pendants of Cassiar Terrane and is intruded by at least five andesite dykes. West of the fault, the Yukon-Tanana Terrane includes: (1) mafic volcaniclastic rocks with preserved primary textures; (2) coarse-grained quartz-feldspar grit; and (3) metasiltstone and semi-pelitic schist. The grit is intruded by foliated hornblende granodiorite, likely of early Mississippian age. Small outcrops of tectonized serpentinite were tectonically emplaced into Yukon-Tanana Terrane, and a positive magnetic anomaly parallel to the fault suggests an unexposed extension to the southwest. Two mylonite localities and evidence of brittle cataclasis up to 1 km on either side of the presumed buried fault suggest a complex structural history along this terrane boundary.