In the last five years, eroding gold prices, increasing production costs and the depletion of reserves have resulted in a dramatic increase in the use of drilling to evaluate placer deposits. Accurate sampling and deposit evaluation would enable planning for cost-effective mining and reclamation. However, sampling placer gravel accurately is an extremely difficult task due to the nugget effect (inclusion or loss of a single particle of gold) and any errors are compounded by the small size of the drill samples. Additional sampling errors result from contamination, splitting and fire assaying. More placer mine failures can be attributed directly to improper sampling and sample processing practices during property evaluation than to any other cause. There is very little impartial, accurate information available to guide the selection of modern drills. Drillers and their equipment are often selected for their penetration rate or cost-per-foot rather than for sampling accuracy or gold recovery. A brief description of several types of drills including churn, auger, rotary tricone, reverse circulation, Becker hammer, down-the-hole hammer and Sonic drills is summarized in Section 6 from references. Three solid auger drills and two types of reverse circulation (R/C) drills were evaluated under typical Yukon field conditions using radioactive placer gold as tracers (radiotracers). A frozen cylindrical core of compacted gravel containing four sizes (-10+14, -20+28, -35+48 and -65+100 mesh) of radiotracers was placed in 35 drill holes and the holes were redrilled. Hand-held scintillometers were used to track gold losses during drilling, sample recovery and sample processing. Radiotracers lost due to spillage and blow-by around the collar (top) of the hole, and those trapped in drilling equipment (carry-over) were easily located. The results of these tests are summarized Table 1. There was no significant difference between the recovery of the four sizes of gold particles with any of the reverse circulation or auger drills tested. Observations and down-hole scintillometer records indicate that the radiotracers did not follow the bit down the hole and were either carried out of the hole or forced onto the sides of the hole at or above the depth at which the radiotracer core was positioned.

In the last five years, eroding gold prices, increasing production costs and the depletion of reserves have resulted in a dramatic increase in the use of drilling to evaluate placer deposits. Accurate sampling and deposit evaluation would enable planning for cost-effective mining and reclamation. However, sampling placer gravel accurately is an extremely difficult task due to the nugget effect (inclusion or loss of a single particle of gold) and any errors are compounded by the small size of the drill samples. Additional sampling errors result from contamination, splitting and fire assaying. More placer mine failures can be attributed directly to improper sampling and sample processing practices during property evaluation than to any other cause. There is very little impartial, accurate information available to guide the selection of modern drills. Drillers and their equipment are often selected for their penetration rate or cost-per-foot rather than for sampling accuracy or gold recovery. A brief description of several types of drills including churn, auger, rotary tricone, reverse circulation, Becker hammer, down-the-hole hammer and Sonic drills is summarized in Section 6 from references. Three solid auger drills, two types of fully cased normal circulation (N/C) drills and two types of reverse circulation (R/C) drills were evaluated under typical Yukon field conditions using radioactive placer gold as tracers (radiotracers). A frozen cylindrical core of compacted gravel containing four sizes (1.2-1.7, 0.60-0.84, 0.3-0.42 and 0.15-0.21 mm) (-10+14, -20+28, -35+48 and -65+100 mesh) of radiotracers was placed in 44 drill holes and the holes were redrilled. Hand-held scintillometres were used to track gold losses during drilling, sample recovery and sample processing. Radiotracers lost due to spillage and blow-by around the collar (top) of the hole, and those trapped in drilling equipment (carry-over) were easily located. The results of these tests are summarized Table 1. There was no significant difference between the recovery of the four sizes of gold particles with any of the fully cased nomal circulation, reverse circulation or auger drills tested. Observations and down-hole scintillometre records indicate that the radiotracers did not follow the bit down the hole and were either carried out of the hole or forced onto to the sides of the hole at or above the depth at which the radiotracer core was positioned.

In theory, very fine sediment sampling (<53 microns) has the potential to improve the usefulness of stream sediment data for gold. The key theoretical advantages over traditional techniques are less local sample site variation, improved reproducibility, and the potential to preferentially define anomalies associated with significant bedrock mineralization. An orientation survey is required to test the actual effectiveness of these techniques and to establish practical sampling and processing procedures.

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.

In order to facilitate exploration and mining of placer gold in historic placer regions increasingly innovative mining and exploration methods must be employed. Using a combination of historic and modern exploration tools, it is possible to delineate placer gold deposits in areas which were previously thought to be exhausted of reserves. These placer settings are sometimes referred to as ‘technogenic’, a term used to describe original gravel remnants and gold-bearing tailings which formed as a consequence of inefficient technology or poor mining techniques. These deposits may now be exploited using modern exploration and mining methods.

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.

This project compares fine sediment geochemistry (-53 microns) with traditional -180 microns (-80 mesh) sediment geochemistry. The goal of this project is to confirm or deny the key theoretical advantages of fine fraction sediment sampling as outlined in YGS Open File 1993-9 (G), and to develop practical and efficient techniques for collecting and processing the samples. Those key theoretical advantages are less local sample site variation, improved reproducibility, and the potential to preferentially define anomalies associated with significant bedrock mineralization. Five study areas were selected in Yukon. Four of these areas contain known gold mineralization that has been mined in the past or contain significant drill indicated reserves. The Mt. Skukum deposit is a low sulfide quartz carbonate vein system that was mined in the mid 1980s. Ketza River is a sulfide-rich manto-style deposit with significant oxide reserves that was mined in the late 1980s. Dublin Gulch is a gold-bearing stockwork hosted within intrusive, similar to the Fort Knox gold deposit at Fairbanks, Alaska. Brewery Creek is a disseminated gold deposit hosted primarily within structurally disrupted intrusives. Samples of -2000 micron sediment were collected from streams draining these areas of known mineralization, as well as from streams draining areas with no known significant mineralization but with erratic gold values from government sponsored regional geochemical surveys (RGS), and from streams that have only background gold values from RGS. Gold concentrations for each sample were determined by duplicate 30 g fire assay and one 10 g aqua-regia analysis. Values for 32 other elements were determined by ICP analysis. Evidence from this orientation survey demonstrates the potential to improve the success rate of reconnaissance exploration for gold by collecting fine fraction sediment samples as a first step in exploration. Increased project cost at this stage could be greatly offset by more efficient and successful follow-up programs.

not_specified

Many people who want to get started placer mining in the Yukon have questions about many things including cost, types of equipment, government regulations, and of course, "Where is the gold?". The capital cost of equipment may be the determining factor and will vary according to the size of the operation. Research and geology are important, and drill results can prove valuable. Access, whether via river, winter road, air or all-season road is an important consideration. It is also crucial to have the right equipment for the job of mining and washing the gravel. Finally, being able to meet the effluent standards for water use is a vital consideration for an ongoing, successful mining operation.

Increased interest in oil and gas exploration in the Yukon is leading to an increase in the use of seismic exploration as a tool for identifying potential drill sites. Although there are a number of techniques that have been developed over the years to minimize disturbances associated with seismic exploration, in some cases the information that needs to be gathered dictates that a less than environmentally optimal treatment be employed. Seismic line cuts can cause a number of outcomes from significant environmental degradation to lines that are barely a whisper on the landscape. Studies conducted in the Eagle Plains and Peel Plateau areas in 2006 and 2007 have provided significant information on the ecology of recovery of seismic lines in these areas. The results of these studies were presented at the 2007 Oil and Gas Best Management Practices Symposium in Inuvik in October, 2007. The South Eastern region is different ecologically from the Eagle Plains and Peel Plateau region. The lower elevation sites in the South Eastern region are vegetated by substantial forests of white spruce, poplars and birch while the Eagle Plains area is tundra at higher elevation and black spruce / Labrador tea scrub forests at lower elevations. The relation to recovery processes in the North Yukon bears consideration as the general processes of recovery illustrate elements that should be considered when seismic lines are cut. This study builds on the studies completed in 2006 and 2007 and provides information that illustrates the ecological characteristics of seismic line recovery as a tool for the continued development of best management practices and standard operating procedures for oil and gas exploration.