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.

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.

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.

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.

not_specified

not_specified

Most of the historic placer gold recovered from the Indian River has been from the modern river gravel; however, a significant amount of placer gold has been mined from older deposits, including low-level, intermediate-level and high-level gravel terraces. Significant placer gold reserves exist in Indian River drainage in various forms. Prospective targets include 1) modern (Holocene) alluvial channels, alluvial fans and tributary gulches; 2) modern (Holocene) low-level buried and/or abandoned alluvial terraces; 3) early to late Pleistocene intermediate-level buried abandoned terraces and alluvial fans; 4) early Pleistocene (pre-Reid) glaciofluvial gravel sequences; 5) Pliocene high-level alluvial terraces (White Channel gravel); and 6) technogenic (tailings) deposits. Fine-grained placer gold existing in size ranges not recovered efficiently by conventional sluicing operations has been found in alluvial and glaciofluvial gravel and tailings deposits. These deposits may represent an important resource and any future mining operations must address the metallurgical implications to maximize recovery.

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.

We have determined the major and trace element composition of approximately 2700 gold particles from 21 gold-bearing mesothermal quartz veins and 35 placer gold samples from the Klondike District in western Yukon Territory. Measured Au, Ag, Cu, and Hg contents were used to define a characteristic geochemical signature for each of the vein samples. These signatures were then compared with the various compositional populations that we have distinguished within each of the placer samples. Preliminary conclusions derived from the study include: 1) placer gold in both recent stream deposits and in the Plio-Pleistocene White Channel Gravels is detrital in origin; 2) the placer gold is mainly, if not entirely, derived from mesothermal quartz veins; 3) all lode sources for the placer gold have not yet been located; and 4) composition data can be used to link placer gold to its specific lode source.