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The Southwest McQuesten-northern Carmacks area is primarily underlain by rocks of the Yukon-Tanana terrane which is divided into two distinct belts separated by the Willow Creek fault: 1) a central belt of polydeformed, upper greenschist-amphibolite facies metasedimentary and metaplutonic rocks of Permian and older ages; and 2) a northeastern belt of generally undeformed and unmetamorphosed volcano-plutonic rocks of the Early Mississippian Reid Lakes complex. The southern part of the area is underlain mainly by rocks of Quesnellia and Stikinia, including: 1) Paleozoic retrogressed metamorphic rocks of the Boswell assemblage; 2) Upper Triassic augite-phyric volcanic rocks; and 3) Early Jurassic granitoids of the Aishihik plutonic suite. These rocks are dissected by a series of dextral strike-slip faults, probably related to the Teslin fault system. Post-accretion rocks include: 1) mid-Cretaceous biotite monzogranite plutons; 2) dacite and minor basalt of the Upper Cretaceous Carmacks Group; and 3) Quaternary basalt of the Selkirk volcanics. The southwest McQuesten-northern Carmacks area is under-explored, but shares many geological attributes with nearby, highly prospective districts such as the Dawson Range mineral belt, the recently discovered White Gold area and the producing Minto Mine.

The MacMillan Pass district (map sheet 105O) located in east Yukon contains several sedimenthosted Ba ± Zn ± Pb deposits including the Tom and Jason deposits, as well as a multitude of 'barren' sediment-hosted barite occurrences. A classic sedimentary-exhalative (SEDEX) model has been postulated for these occurrences in which the barite horizons represent distal expressions of a hydrothermal vent system. Fieldwork was completed at the Walt and Tyrala barite occurrences that occur within the MacMillan Pass district in order to examine the deposit-scale geology and to sample undeformed barite horizons for subsequent geochemical analysis. Samples were also collected from drill core from the Hess barite occurrence. Barium mineralization occurs in both the Devonian Portrait Lake Formation (Lower Earn Group) and in underlying Ordovician-Silurian limestone of the Road River Group. A variety of textures were encountered that were indicative of both synsedimentary deposition of barite, as well as diagenetic to epigenetic barite mineralization. Base metal sulphides that are interpreted to post-date the barite mineralization were encountered at depth in drill core and are primarily hosted by Road River Group carbonates.

The Macmillan Pass area, in east-central Yukon Territory, contains what promises to be some of the most valuable mineral deposits yet discovered in the Territory. In addition to the TOM and JASON stratiform lead-zinc-silver-barite deposits, the area contains one of North America's largest tungsten deposits (Mactung deposit) as well as a relatively large tonnage stratiform barite deposit (TEA deposit) presently being exploited for use as oil well drilling mud. This report specifically deals with the TOM and JASON deposits, based on field investigations carried out by the writer during July and August. This report is accompanied by a 1:111 111-scale bedrock geology map of the TOM and JASON claims, Macmillan Pass area, east-central Yukon Territory (NTS 105 O/1 east half).

The Dromedary property consists of 344 claims on Dromedary Mountain, Kalzas Mountain, and the intervening Macmillan River valley, all immediately northeast of Tintina Trench and 240 km northeast of Whitehorse. The property lies within Selwyn Basin geological terrane, and the following rock units are present: Proterozoic-Cambrian Hyland Group, Kechika phyllite and limestone, minor Road River shale and siltstone, Earn Group conglomerate, limestone, black silty shale and baritic chert, and overlying Permian shelf sediments. South Fork subvolcanic intrusions and Cretaceous granitic plugs have induced local biotite and calc-silicate hornfels and skarn. The area was staked by Anaconda in 1980 and four areas of interest identified: Dromedary Creek, Dromedary Mountain, François and Kal-Cave. Blackstone Resources Inc. optioned the property in 1996 and has drilled the Dromedary Creek and François areas, encountering massive sulphide mineralization in all five holes. Economic grade Pb-Zn and massive pyrrhotite with significant gold occur on the François grid. In 1997 the magnetic signature of the pyrrhotite on the François grid was traced 5 km, and soil anomalies were detected further to the west. In the Kal-Cave area a 7.5 km long lead-zinc soil anomaly was refined and numerous new occurrences of iron-sulphide mineralization, carbonate porphyroblasts, manganese and iron oxide were detected. Best samples from this area contain 5.53% Pb and 5.83% Zn.

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.

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Mainly schitose clastic strata of the northern Selwyn basin underlie Lansing map area. These strata form rounded mountains, although jagged ridgelines occur in the thermal metamorphic aureoles surrounding six Cretaceous granitic plutons. Major faults occupy some broad northwest-trending valleys: two of these extend eastward as the Hess and Macmillan faults (Abbott and Turner, 1990) in the Macmillan Pass area; another appears to contine westward as the Robert Service Thrust Fault. Argentiferous galena veins were intermittently mined from the east edge of the map area from 1976 to 1985; whereas the stratiform base metal and disseminated gold potential of these rocks have been investigated during the 1990s.