This report is a product of the continuation of a study begun in 2007/08. The 2007/08 report focused on selenium concentrations and pathways in the aquatic ecosystems of various tributaries of the Francis, Finlayson and Pelly rivers, which drain portions of the Yukon Tanana-Terrane and Cassiar Platform between Ross River and Watson Lake. In 2008/09 the sampling program was expanded to another area of the Yukon that is recognized as being highly mineralized: areas within the Selwyn Basin. The 2008/09 study area is located along the North Canol Road, northeast of Ross River.

Valley-filling basalts of the Selkirk Volcanics north and west of the Pelly River-Yukon River confluence, range in age from early Pleistocene to Holocene. Soils formed on the older surfaces have complex parent materials reflecting early Pleistocene glaciation and significant loess accumulation. A diamicton overlying the early Pleistocene basalt is covered by up to 1 m or more of calcareous loess, and shows no field evidence of weathering or soil formation. Middle Pleistocene basalt has a similar depth of loess cover and appears fresh and unweathered. Lava flows originating on the south side of the Volcano Mountain cinder cone display vegetation ranging from discontinuous lichen and moss cover to white spruce-aspen forest. Soil profile development varies correspondingly from almost nil to reddish-brown Brunisolic soils with ~30 cm of B horizon, depending on substrate age and/or the presence of lapilli deposits overlying the flows.

This study investigated background levels and uptake rates of organophilic metals, particularly selenium, in ten streams draining portions of the Yukon-Tanana Terrane and Cassiar Platform between Ross River and Watson Lake, Yukon. The study area is suspected to have elevated background metals concentrations and is of interest for mineral exploration and development due to high mineralization. Information on natural metals levels is lacking for this region and for the Yukon in general. Water, sediments, benthic invertebrates and fish (slimy sculpin; Cottus cognatus) were sampled and analyzed for metals concentrations. Benthic invertebrates were identified to genus and percent composition of each species in each stream was calculated. The lack of anthropogenic activity in the area indicates that selenium concentrations found in all sample media and natural, background concentrations. Of all the sample media, concentrations of selenium were highest in sediment; however, sediment selenium concentrations were found to be in a range similar to levels documented at the Kudz Ze Kayah and Viceroy Brewery Creek mines in other regions of the Yukon. Selenium concentrations in water generally exceeded CCME guidelines, but also fell within a range similar to the Kudz Ze Kayah and Viceroy Brewery Creek mines. These findings with respect to selenium levels in water and stream sediments highlight the importance of developing site-specific selenium guidelines for management of aquatic systems. The rate of uptake of selenium in benthic invertebrate and fish tissues was greater than that of the other organophilic metals investigated. Selenium concentrations were generally higher in benthic invertebrates than in fish, likely owing to the detritus-feeding and bottom-dwelling life history of these invertebrates. Weak positive trends were noted in the relationship between selenium concentrations in fish and benthic invertebrates, and between fish and the water column. A significant positive relationship was noted between selenium concentrations in fish and stream sediments. These findings are consistent with past studies documenting dietary sources as the most common uptake pathways for selenium, with water comprising a secondary source. Examination of benthic invertebrate community composition revealed commonly abundant species and species typical of fast-flowing streams with high water quality, which is characteristic of the streams in the study area. The findings of this study provide valuable baseline information on background concentrations of metals, particularly selenium, as well as documentation of benthic invertebrate community composition, in an aquatic system that may experience resource development in the future.

The following tables have been compiled from information derived from the Yukon MINFILE 2008 — An database of mineral occurrences (Deklerk, 2008), and from various technical reports and information that have been filed in the SEDAR system by, or on behalf of, public companies. Reserve and resource figures presented are not calculated by Yukon government personnel, but are quoted from referenced industry sources, publications, assessment and/or technical reports, etc. (see next page). The reader is encouraged to refer to the original data for detailed information.

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One third of the gold and gold-silver deposits in Yukon were examined and sampled in 1980 to establish a framework of geology and rock chemistry from which variations within and between deposits could be detected and evaluated. Lithologic units within the samples were analyzed for Au, Ag, B, Mn, Cu, Zn, As, Se, Tl, Pb, Bi, Sb, Te, W, Hg, Mo and Cd - elements commonly associated with precious metal deposits. A problem which prevented systematic sampling of many deposits is the lack of underground access and the locally intense oxidation of vein outcrops. Three aspects of the rock geochemistry are discussed:: 1) different levels of element concentration in the deposits and implications regarding pathfinder elements; 2) distribution of elements in deposit types; and 3) element distribution in specific deposits. The geology of the deposits is summarized from published works and interpreted in light of recent theories on gold deposits. This report emphasizes common features of the deposits and several genetic models.

The volcano-sedimentary rocks of the Semenof block of central Yukon have not been closely studied in the past. Recent bedrock mapping in the southern Semenof Hills highlights the presence of possibly two exceptionally well preserved, undeformed and unmetamorphosed volcanosedimentary sequences of Late Paleozoic age. The main sequence is composed, from bottom to top, of (1) 2- to 3-km-thick thinly bedded fragmental volcanic rocks interbedded with few limy intervals, (2) thick massive plagioclase- and clinopyroxene-phyric basaltic lava fl ows with clastic intervals, and (3) a 1- to 3-km-thick volcanic conglomerate. The other sequence, of lesser extent, consists of (1) a thin quartz-porphyritic felsic volcanic unit, less than 50 m thick, (2) 2- to 3-km of massive to pillowed fine-grained basaltic lavas, and (3) 100 m of fossiliferous Upper Carboniferous limestone. These two sequences sit in faulted contact on ~2 km of a deformed clastic sequence of unknown affinity.

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