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.

On-going compositional studies of gold from placer and lode deposits and occurrences in western Yukon provide new insights into their nature and origin. Two main compositional populations are present in placer and lode deposits in the Klondike District. The dominant population has high fineness and low mercury content, and appears to be mainly derived from lode sources in the Lone Star, King Solomon Dome and lower Gold Run Creek areas. A second population of low fineness, high-mercury-content gold is derived from lode sources on the left limit of Eldorado Creek and in the headwaters of Bear and Last Chance creeks. Placer gold in the Sixtymile District was not derived from epithermal vein occurrences like those in the Sixtymile River valley but rather has compositions more similar to Klondike-type metamorphogenic veins. Placer gold in Scroggie Creek in southern Stewart River map area appears to be derived from intrusion-related vein occurrences.

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.

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.

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

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.

Placer gold mining in Clear Creek extends back to 1900, when the discovery claim was staked. Approximately 129,000 crude ounces (4012 kg) of gold have been reported since 1941 which includes 49,637 crude ounces (1544 kg) obtained by dredging operations (1941 to 1955, and 1981 to 1987). Placer gold morphology ranges from crystalline gold in quartz to rounded nuggets to flattened gold. The largest nugget, recovered from the headwaters of Left Clear Creek, weighed 7 ounces (218 g). Clear Creek valley was filled by ice during the pre-Reid glaciation (early Pleistocene). Pre-Reid glacial drift is preserved as till, resedimented till, and glaciofluvial sediments on the lower slopes along main Clear Creek and parts of Left Clear Creek. Alpine glaciers formed at the headwaters of Left Clear Creek, however most of the moraine deposits have been eroded. During the subsequent Reid and McConnell glacial periods local alpine glaciers formed in the headwaters of Josephine and Big creeks. Alpine glaciers, the pre-Reid ice sheet and their melt waters redistributed the gold in the Clear Creek drainage. The distribution of heavy minerals in Clear Creek drainage is varied. Over the years dredging operations intersected pockets of gravel containing cassiterite, scheelite and galena, but their precise locations were not documented. Contemporary placer mining and our heavy mineral studies have located concentrations of pyrite, arsenopyrite, scheelite and galena, in addition to gold. Exploration for the source of placer gold has resulted in the discovery of numerous gold veins in the surrounding area.

Description and analysis of the geology of quartz veins containing gold ores in the Yukon Territory.

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