The Macmillan Pass area is underlain by Hadrynian to Middle Devonian fine grained sedimentary strata and volcanic rocks of Selwyn Basin. Widespread occurrences of Upper Devonian debris flows and turbidites record uplift and erosion of older rocks to the west or northwest. Deposition of overlying, locally derived coarse clastic assemblages are related to subsequent formation of a graben-like, fault-bounded trough in the study area. Stratiform barite-lead-zinc mineralization on the Tom claims is contained in two tabular zones separated by a fault. Both zones occur at the transition between Upper Devonian locally derived coarse clastic rocks and overlying basinal shales. Ore textures vary from massive quantities of poorly bedded galena, sphalerite and pyrite to finely laminated barite and cherty argil lite with disseminated sulphide minerals. A mineralized and altered breccia body underlies the stratiform massive sulphide mineralization. A copy of this thesis is available at the EMR library – QE195 C38. This thesis is available online at http://hdl.handle.net/2429/21561.

The Macmillan Pass area has been of economic interest since the discovery of significant barite-lead-zinc-silver mineralization by Hudson Bay Exploration and Development prospectors in 1951. In addition to barite-hosted mineralization of the MacMillan Pass area, the Upper Devonian to Lower Mississippian "Black Clastic" Unit and its correlative rocks in southeast Yukon and northeast British Columbia contain perhaps the world's largest known accumulations of sedimentary barite. TOM West Zone, TOM East Zone and JASON mineral deposits are syngenetic, stratiform accumulations principally composed of finely interlaminated barite, black siliceous argillite, sphalerite, galena and pyrite. The three deposits occur at approximately the same stratigraphic interval, marking the sedimentary transition between locally derived slump and slide debris deposits of Unit 3a with finer grained black shales and minor conglomerates of Unit 3b. This Open File includes:: Regional Geology-Selwyn Mountains (1::263 157-scale bedrock map) and Geology of MacMillan Pass area, Yukon Territory (1::111 111-scale bedrock map with cross-section).

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Mineralized zones on the Jason property are stratifrom, sediment hosed Pb-Zn-barite deposits that occur in a Late Devonian age marine carbonaceous shale and turbidite sequence. The Jason Property is located 400 km northeast of Whitehorse near Macmillan Pass on the Canol Road. Since the discovery of mineralization in 1975, eighty-nine diamond drill holes have delineated three mineral deposits. In order of their discovery, they are known as the Main, South and End zones. Geological reserves indicated and inferred for the three zones total 14.1 million tonnes averaging 7.1% Pb, 6.6% Zn and 79.9 g/t Ag. The following questions are the focus of the study:: 1) What is the stratigraphic position and setting of the South zone? 2) What is the geological relationship of the South zone to the Main zone? 3) What is the geometry of the South zone? 4) How can the mineralization in the South zone be described in terms of mineralogical and textural facies? 5) What constraints on the processes of ore formation can be demonstrated by utilizing the above studies?

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.

This report includes a summary of the mineral exploration history of Yukon, an overview of major discoveries and a survey of exploration trends in the territory.

Detailed exploration conducted during 2006 in the western part of the Skukum Creek deposit has revealed new structural, mineralogical and geochemical features. The deposit incorporates a number of (at least six or seven) sub- parallel narrow mineralized zones, coincident with andesite-dacite-rhyolite dyke swarms extending for at least 1 km along strike and for hundreds of metres down-dip. Various mineralized zones differ in size, structural setting, intensity and composition of mineralization, and, in total, form a large mineralized package more than 200 m wide, corresponding to a property- to district-scale fault zone extending for over 10 km and traced by a dyke belt. Significant potential exists for the exploration of these structures along strike and down-dip. The diamond drilling intersected numerous high-grade intercepts of gold and silver mineralization corresponding to the low-sulphidation sub-type of epithermal gold-silver deposits. However, strong enrichment in base metals (up to 25% of combined Zn+Pb+Cu) and arsenic suggests essential differences from typical epithermal mineralized systems.

A sequence of Permo-Triassic rocks within a 260 square kilometre part of the Kluane Ranges, southwestern Yukon, consists of Lower Permian volcaniclastic and sedimentary rocks, disconformably overlain by upper Triassic amygdaloidal volcanic rocks. Mafic to ultramafic rocks occur within the upper part of the Permian section and in the Triassic flows. Folding and faulting of this sequence is intense. The ultramafic rocks are peridotite-dunite complexes in the form of sills. Some gabbroic bodies have intruded along sill boundaries, but most are separate sills or dykes. Nowhere have they been found cutting rocks younger than the upper Triassic volcanics. Ni-Cu mineralization is spatially associated with the gabbros and peridotites. Dunite portions of ultramafic complexes are barren. Sulphide minerals include pyrrhotite, pentlandite and chalcopyrite, locally with pyrite, sphalerite and galena. Occurrences are classified as follows:: 1. Massive to stringer within country rock adjacent to gabbro intruding peridotite. 2. Massive to heavily disseminated at the country rock contact of gabbro intruding peridotite. 3. A) Heavily disseminated to nearly massive within gabbro intruding peridotite. B) Disseminated within separate gabbroic bodies. 4. Very weakly disseminated within peridotite. The mineralized gabbro-ultramafic intrusions are spatially related to the Triassic volcanic flows. The mafic and ultramafic rocks, their Ni-Cu deposits, and volcanic flows are believed to be related genetically. This report is accompanied by five geological maps as follows:: 1) Arch Creek (1::4760 scale; NTS 115 G/5 northeast); 2) Wellgreen area (1::4800 scale; NTS 115 G/5 northeast); 3) Linda Creek (1::2380 scale; NTS 115 G/6 northwest); 4) White River (1::4760 scale; NTS 115 F/15 northeast); and 5) Quill Creek (1::80 000; 115 G/5,6 north and 115 G/11,12 south).