This map accompanies paper: Johnston, S.T. and Shives, R.B.K., 1995. Interpretation of an airborne multiparameter geophysical survey of the northern Dawson Range, central Yukon: A progress report. In: Yukon Exploration and Geology, 1994. Exploration and Geological Services Division, Yukon, Indian and Northern Affairs Canada, p. 105-111.

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

A quantitative gamma-ray spectrometric and aeromagnetic helicopter-borne geophysical survey was completed by Fugro Airborne Surveys. The survey was flown from September 10 to October 14, 2008. The nominal traverse and control line spacings were 400m and 2400m respectively, and the aircraft flew at a nominal terrain clearance of 125m. Traverse lines were oriented at 0 degrees with orthogonal control lines.

Regional till geochemistry surveys were conducted in the Finlayson Lake, Glenlyon and eastern Carmacks map areas. Detailed till sampling was completed at the Kudz Ze Kayah and Clear Lake massive sulphide deposits to evaluate glacial dispersal near mineralized rock in a mountainous region and a plateau, respectively. A comparative evaluation of the silt-and-clay-sized fraction versus the clay-sized fraction geochemistry indicates that the clay-sized fraction presents higher metal concentrations than the silt and clay, but both size fractions generally delineate the same base metal exploration targets. The correlation between the high gold concentrations in both size fractions is not as good as for base metals because gold occurrences are only refl ected in the silt- or clay-sized particles of till. The beryllium content of till might provide an indication of the occurrence of beryl in bedrock but the low analytical precision of beryllium analyses limits this approach.

Regional bedrock mapping has revised structural and stratigraphic relationships in the northeastern corner of the Glenlyon map area (NTS 105L). Three structural panels, separated by south and southwest dipping thrust faults, subdivide the area. Cambrian (?) to Ordovician metasedimentary and volcanic rocks underlie the southwestern panel and include all exposures southwest of the Duo fault. Ordovician to Silurian (?) siliciclastic and carbonate strata and phyllite units that are intruded by Late Devonian porphyritic rocks underlie the central panel. Silurian (?) to Triassic siliciclastic and carbonate strata in the northern panel occur to the north, and in the footwall of, the Twopete fault. Mid-Cretaceous granitic rocks that crop out near Kalzas Mountain and occur below the surface near Dromedary Mountain intrude the central and northern panels. Northeast-verging folds and thrust faults deform layered rocks in the northeastern Glenlyon area and are offset by north-south oriented, steeply dipping structures with both normal and strike-slip motion. Upper Devonian Earn Group strata host layered sulphide bodies and polymetallic veins that contain lead, zinc and silver. This mineralization occurs in the footwall of the Twopete fault, a regional structure that originally developed as a Late Devonian synsedimentary fault. Ordovician and Silurian (?) quartz-rich clastic rocks are unlike coeval basinal facies rocks mapped elsewhere within the Selwyn basin in Yukon. These rocks represent slope facies deposits that mark a transition from basin to platform that is the northern extension of the McEvoy platform–Selwyn basin boundary.

The Finlayson Lake fault zone forms the boundary between autochthonous North American rocks and rocks of the innermost accreted Slide Mountain and Yukon-Tanana terranes in southeastern Yukon. Geological mapping at 1::50 000 scale in a well exposed area of the Campbell Range, southeastern Yukon, was undertaken to examine the kinematics of the Finlayson Lake fault zone and rock types of the Slide Mountain terrane. Five units were identified: (1) chloritic schist and phyllite, (2) laminated metachert and carbonaceous black slate, (3) tan weathering metachert and maroon siliceous and argillaceous metasiltstone, (4) greenstone and associated breccia, gabbro, metagreywacke, metachert and maroon metasiltstone and (5) serpentinite. Unit 2 is structurally interleaved with submap-scale bodies or layers of serpentinite, hornblende-plagioclase porphyry, plagioclase-potassium fledspar porphyry, quartz-eye muscovite-chlorite phyllite or schist, chloritic schist and minor grey, calcareous metacarbonate. Serpentinite is also exposed in unit 4 and as small slivers along the thrust contact between units 3 and 4. Lithologically, units 4 and 5 are similar to the upper division of the Slide Mountain terrane in east-central and north-central British Columbia. Unit 2 has similarities with the lowest division of the Sylvester allochthon and is tentatively correlated with the Slide Mountain terrane. Maroon metasiltstone in unit 3 is indistinguishable lithologically from metasiltstone in the overlying greenstone unit suggesting that the eastern thrust fault juxxtaposes parts of the same depositional sequence, ie. The Slide Mountain terrane. Regional correlation of unit 1 is unclear. Unit 2 is inferred to be bounded to the east and west by northwest-striking faults and to the south, by an east-striking, steeply dipping, normal (north-side down) fault. The northern boundary of unit 2 is unconstrained. Greenstone (unit 4) is thrust towards the southwest over unit 1 in the western part of the map area along a northwest-striking, gently northeast-dipping thrust fault. In the eastern part of the map area, greenstone is thrust towards the northeast over unit 3 along a northwest-striking, moderately southwest-dipping thrust fault. Outcrop data and topographic patterns suggest that the eastern thrust fault is truncated by a northwest-striking, steeply dipping fault and that the normal fault truncates the westernmost northwest-striking fault. The northwest-striking faults are poorly exposed and their kinematics have yet to be determined. However, if they are steep faults, they are likely dextral strike-slip faults. Field data indicate that the Finlayson Lake fault zone consists of diverging thrust faults and subparallel strike-slip(?) faults. These structures are consistent with the interpretation of the Finlayson Lake fault zone as a transpressive fault zone. More constraints on the relative timing of faulting and the kinematics of the steep faults are required to test this hypothesis,

Quantitative gamma-ray spectrometric and aeromagnetic helicopter-borne geophysical survey was completed by Fugro Airborne Surveys. The survey was flown from September 10 to October 14, 2008. The nominal traverse and control line spacings were 400 m and 2400 m respectively, and the aircraft flew at a nominal terrain clearance of 125 m. Traverse lines were oriented at 0 degrees with orthogonal control lines.

Quantitative gamma-ray spectrometric and aeromagnetic helicopter-borne geophysical survey was completed by Fugro Airborne Surveys. The survey was flown from September 10 to October 14, 2008. The nominal traverse and control line spacings were 400 m and 2400 m respectively, and the aircraft flew at a nominal terrain clearance of 125 m. Traverse lines were oriented at 0 degrees with orthogonal control lines.

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).