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

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.

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.

Placer gold has been reported in small amounts throughout the South Nahanni river drainage; however, the original source of the gold is uncertain. This study focuses on two types of placer gold in the area: (1) locally abundant grains derived from near Selena Creek, and (2) scattered grains recovered from streams throughout the South Nahanni drainage area. A shape analysis of all gold grains was completed and representative grains from each sample population were selected for imaging on the scanning electron microscope, along with analysis for Au-Ag-Cu-Hg values on the electron microprobe. The gold grains are typically >700 fineness and mercury is below detection levels (<0.20%). Approximately half the grains analysed from the Selena Creek area registered near to, or slightly greater than, detection levels of copper (<0.04%), whereas the majority of grains from the isolated showings had copper contents below detection levels. The results are compared with published morphological and compositional data for placer and lode gold in other regions.

The Livingstone Creek area is located 100 km northeast of Whitehorse, Yukon Territory, Canada. Hydrothermal gold-sulphide mineralization (MINFILE 105E 001) occurs in quartz-carbonate veins and veinlets which cut Paleozoic metamorphic rocks of the Teslin Suture Zone. The metamorphic rocks are also cut by Cretaceous(?) feldspar-porphyry dykes with an average thickness of 2 m. The mineralization appears to be structurally controlled by NNE-striking faults and a set of NNW-trending joints. The vein minerals consist of gold, pyrite, chalcopyrite, galena, hessite/stuetzite, tetradymite, Au-Ag tellurides, tennantite, hematite, pyrrhotite, quartz, and carbonate. Gold occurs as: 1) "free gold" in cracks and interstices of quartz gangue, 2) inclusions in galena, usually rimmed by hessite, 3) minute grains associated with chalcopyrite and galena in aggregates of coarse-grained pyrite and 4) individual grains or fracture fillings in iron hydroxides. The coarse-grained gold in Livingstone Creek appears to be derived from gold-quartz veins in the metamorphic bedrock. This is indicated by: 1) similar silver and mercury contents in primary and placer gold 2) identical trace element composition of galena from gold-quartz veins and galena inclusions in placer gold, 3) similar telluride mineral assemblages in both gold-quartz veins and placer gold grains and 4) similar homogenization temperatures and salinities in fluid inclusions from both gold-quartz veins and placer nuggets. A limited amount of gold appears to have formed by supergene leaching and precipitation. This kind of gold occurs as irregular-shapd grains in the stream placers and in iron hydroxide along fractures in quartz veins. Relative to the pirmary gold it is enriched in silver and mercury.

A reconnaissance study of the composition of gold from several placer streams in the Stewart River map area was carried out to characterize the likely style(s) of lode mineralization from which the placer gold in each stream was derived. Results of the study indicate that placer gold from Eureka and Black Hills creeks, as well as gold grains from colluvium in exploration pits at the head of Eureka Creek, have relatively low fineness, low copper contents and high mercury contents. These compositions are consistent with both the gold in colluvium and most of the placer gold having been derived from epithermal sources in the Eureka Dome or Henderson Dome area. Gold in placers in the Moosehorn Range is likely derived from intrusion-related, gold-bearing quartz veins exposed in the headwaters of the placer creeks, and is characterized by relatively high fineness, high copper contents and low mercury contents. Placer gold in Thistle, Kirkman and Blueberry creeks is very similar to that from streams in the Moosehorn Range, suggesting that an undiscovered intrusion-related gold deposit is present within the Thistle/Kirkman drainage basin.

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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.

Conglomerates belonging to the Indian River formation (IRF), south of the Klondike goldfield, have recently become the focus of exploration activity owing to their potential as hosts for paleoplacer gold derived from the Klondike. However, textures within the conglomerate have been interpreted as indicative of hydrothermal activity, and the possibility exists of in situ epithermal gold. Paleocurrents in conglomerates indicate dominant transport from the southeast, incompatible with gold transport from the Klondike. Gold grains from unconsolidated conglomerate at Montana Creek reveal an epithermal signature (20-50% Ag, 0.3 to 3% Hg and opaque inclusion suite containing complex polymetallic sulphotellurides and sulphosalts), distinct from the signature of placer and lode sources in the central and southern Klondike (12-20% Ag, Hg absent and opaque inclusion suite of simple base metal sulphides). Gold grain morphology and alteration textures within unconsolidated conglomerates suggests that Montana Creek gold is derived from in situ epithermal mineralization related to that previously reported at Eureka Dome.