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Compositional studies have been undertaken on gold particles recovered from hypogene ore, eluvial material and placer samples in and around the Klaza property. These data have been correlated with previous descriptions of in situ mineralization to elucidate placer-lode relationships and systematic change in gold compositions between porphyry and epithermal environments. Gold alloy from the porphyry environment is Ag-poor with respect to Au formed in later stage veins. Silver, and to a lesser extent Cu, have been the main discriminants for inferring the source of Au within the placers, and in general, vein mineralization is a more important source-type than porphyry mineralization. The signature of Pb-Bi-Te previously identified in the inclusion suites of Au grains from Nucleus/Revenue, Casino and Sonora Gulch has also been identified at Klaza, demonstrating that generic compositional signatures can underpin a robust exploration methodology. The relative sizes of porphyry and epithermal footprints of detrital Au together with their respective compositions are important considerations when targeting Cu-Au systems.

Placer gold is a notable resource in the western Yukon; however, identification of the lode sources feeding these placer deposits has been difficult. Previous studies have used electron microprobe (EMP) and manual morphological analyses of gold grains with some success to define source-mineralization-style areas, but have not been able to accurately predict lode locations. This study utilizes EMP in conjunction with a new method for morphological analysis based on semiautomated digital image analysis to re-examine this problem. Examination of a sample suite collected over the entire Klondike goldfields area demonstrates that there is significant complexity in Yukon placer gold deposits that has not previously been recognized. Confronting this complexity using a statistical approach based on this new shape analysis method, EMP and a planned future laser ablation mass spectroscopy study will hopefully produce a method for locating lode gold sources.

The link between organic matter and gold in sediment-hosted Carlin-type deposits is controversial. This study aims to tackle this potential link by documenting the occurrence of organic matter in a single borehole from a Carlin-type gold deposit in Yukon and byconsidering, in a preliminary way, the spatial and/or temporal relationship between organic matter and gold mineralization. The sedimentary succession hosting the Conrad deposit was relatively rich in organic matter, possibly related to Archea. Despite the high maturation of samples, the totalorganic carbon (TOC) content of the limestone unit averages 1.31 wt. % (maximum = 3.18 wt. %). Petrographic observations indicate that pore and fracture filling pyrobitumen is the dominant organic matter maceral in the studied samples. This type of pyrobitumen was matured after its emplacement,indicating that hydrocarbon fluids cannot have served as an agent for gold transport. Pyrobitumen disseminated in the rock or associated with stylolites are also documented. The correlation between TOC and Tl (the best proxy for Au) for selected samples and the high As content of pyrobitumen fillingpores may suggest a link between organic matter content and gold deposition, but this was not demonstrated by LA-ICP-MS micro-scale mapping. This study also highlights the challenges of establishing a direct spatial relationship between 'invisible' gold and very small (< 10 µm) pyrobitumenparticles.

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New mapping and drilling associated with gold exploration has elucidated the structural and lithological controls on hydrothermal gold systems in the White River area. The Paleozoic basement consists of a sequence of amphibolite facies clastic metasedimentary and meta-igneous rocks that host lower grade ultramafic rocks, some magmatically and some tectonically emplaced during the Late Triassic – Early Jurassic. Mapped ultramafic bodies show close congruence with published airborne magnetic anomalies. All of these rocks are cut by brittle normal faults and fractures, and dykes correlated with middle Cretaceous to early Tertiary extension-related intrusive rocks. Gold mineralization associated with these fractures is strongly controlled by host rock types. Two main rock types, felsic gneiss and quartzite, are preferentially fractured and hydrothermally altered. Other rock types are only weakly fractured and locally altered. In particular, ultramafic bodies and micaceous lithologies locally impeded fluid flow.

Quantitative mineralogy, U-Pb geochronology of zircon and monazite, 40Ar/39Ar geochronology of muscovite and sericite, and Pb isotopes from galena in veins and feldspar in plutons provide insight into the age of metamorphism, mineralization, intrusion emplacement and the sources of metals at the Plateau South (MINFILE 105N 034, 035, 036) occurrences in central Yukon. Orogenic mineralization and metamorphism is ca. 110 Ma to 100 Ma, and possibly as old as ca. 130 Ma. Following deformation and regional metamorphism, two biotite-muscovite plutons, the Russell stock and Armstrong pluton, were emplaced at 95.39 ± 0.03 Ma and 95.51 ± 0.03 Ma, respectively. These plutons are here reassigned to the Tungsten suite based on mineralogy, chemistry and age. Coeval with these plutons are contact metamorphism and possibly intrusion-related mineralization. Lead isotopic data from galena cluster into two groups: Group 1 is enriched in thorogenic Pb with 206Pb/204Pb values between 18.31 and 18.14, 207Pb/204Pb between 15.62 and 15.55 and 208Pb/204Pb between 38.77 and 38.30. Group 2 is isotopically evolved with 206Pb/204Pb values between 19.13 nd 18.91, 207Pb/204Pb between 15.78 and 15.63 and 208Pb/204Pb between 39.24 and 39.07. We suggest that late Early Cretaceous mineralization is related to large-scale orogenic fluids that tapped primitive (deep?) metal sources and early Late Cretaceous mineralization, coeval with local intrusions, sourced isotopically distinct metals from the intrusions. Alternatively, all mineralization could relate to Early Cretaceous orogenic fluids but with heterogeneous, locally derived metal sources and thermal resetting of Ar ages near the intrusions.

The Conrad zone, east-central Yukon is a newly discovered gold prospect. It is strongly analogous to Carlin-type mineralization, and represents the first Carlin-type gold deposit discovered in Yukon. The regional geological framework and style of mineralization bear similarities to the Carlin trend in Nevada. Structurally, the Conrad area is bounded to the south by the regional-scale Dawson thrust and the Kathleen Lakes fault to the north. This structural setting lies at the interface between the dominantly clastic Neoproterozoic to Paleozoic rocks of Selwyn basin and coeval carbonate rocks of Mackenzie platform. The principal host rock to mineralization is a variably decarbonatized silty limestone, although where permeability has been enhanced by shearing, siliciclastic rocks may also contain significant amounts of gold. Alteration and associated processes related to mineralization include decarbonatization of host limestone with subsequent silicification and brecciation. Gold is hosted within arsenic-rich pyrite growth rims around pre-existing pyrite. Significant post-mineralization realgar, orpiment, calcite, and trace stibnite are found locally as open-space minerals.

Placer gold is widely distributed throughout the western Yukon; however, lode sources for most of these deposits remain unknown. Previous studies of gold compositions in this region using scanning electron microscope (SEM) and electron microprobe (EMP) methods showed 1) that there are consistent differences in average composition (although with considerable overlap) between gold from different styles of lode gold mineralization; and 2) the composition(s) of placer gold can be matched with specific lode sources, or the most likely style of lode source can be identified. In the current study we employ SEM and EMP methods together with laser ablation ICP-MS trace element analysis and study of the micro-inclusion suite(s) to more completely characterize the major, minor and trace element composition of the gold as well as the mineralogy of the lode sources themselves. We also report new data for placer and lode gold, mainly from the Klondike District.