Shows and Symposia: Pacific Northwest Chapter: Friends of,Mineralogy Mineral Symposium Tacoma,Washington

Fossil forgery, an old paleontological pastime, results in contrived specimens and/or their matrixes. It takes an educated and wary buyer to differentiate between the authentic and the fraudulent.     

The Challenges of Dewatering at the Victor Diamond Mine in Northern Ontario, Canada

The costs and efficiency of dewatering are particularly important at De Beers Canada’s Victor diamond mine in northern Ontario, where the bottom of the water-bearing carbonate country rocks is near the bottom of the planned pit, which limits the available drawdown in the perimeter wells. Most of the inflow to the wells comes from a limited number of discrete zones in the carbonate rocks, resulting in low hydraulic efficiencies. The variable hydrogeologic conditions require efficient pumping over a wide range of yields and lifts, and there are logistical issues associated with the isolated setting and the extreme cold winter temperatures. The hydrogeology of the Victor mine area was characterised over three winter field seasons using packer tests, pumping tests, step-drawdown tests, and downhole logging to define the lateral and vertical variation in the hydraulic conductivity of the carbonate aquifer. Based on these data, wells were designed and submersible pumps with variable frequency drives were installed. Two 3-D numerical groundwater flow models were constructed, one a ‘sub-regional’ model to provide input to the mine feasibility study and permitting process and the other a near-pit ‘window’ model to simulate groundwater conditions in the immediate vicinity of the mine. These models are used in tandem to direct design of the dewatering system, evaluate its effectiveness, and to predict long-term environmental effects.     

Composite paste barricade performance at Goldcorp Inc. Red Lake Mine,Ontario, Canada

Appropriate strength barricades and fill fences are a necessary component of underhand cut and fill mining operations and stoping operations in general. These important structures are subject to a number of stresses and strains as a result of the deposition and curing of the backfill material. Parametric monitoring of fill fences gives the engineer the required data to predict not only the behaviour of the paste backfill as it is being deposited, but also the ability to predict the deformation and eventual failure of the barricade. A study was undertaken to determine the performance of the paste barricades at Goldcorp Inc.'s Red Lake Mine using real time instrumentation to monitor the stresses, strains and deformation of paste and paste barricades during placement. The barricades at the mine are a standardised barricade comprised of 10 cm of shotcrete applied to a rebar skeleton spaced nominally 60 cm apart. In total, eight fill barricades were instrumented to determine the behaviour of the paste during the loading. Complementing the eight barricade tests, an instrumented destructive test was carried out to determine the ultimate capacity of the composite barricade. It was determined that the paste backfill behaves as a Rankine-like soil in the initial stages of placement with an average coefficient of lateral earth pressure, K _a, of 0.56. The destructive test determined that the yielding stress of a paste barricade is approximately 100 kPa. The results of the investigation have resulted in operational changes in the placement of paste at the mine.     

Assessment of Metal Attenuation in a Natural Wetland System Impacted by Alkaline Mine Tailings,Cobalt, Ontario,Canada

A natural wetland in the Farr Creek drainage basin near Cobalt, Ontario was studied because its floor is covered with alkaline mine tailings that contain elevated levels of metals, including As, Co, Cu, and Zn, due to mining that occurred intermittently from 1904 to the 1980s. Our objectives were to characterize the biogeochemical interactions occurring throughout the wetland and to assess its ability to effectively attenuate the metal contamination. We were not able to conclusively determine if this wetland is a net source or net sink for As, Co, Cu, and Zn; it is not clear whether this wetland has reached its capacity for attenuating these trace elements. Both oxidizing and reducing bacteria were quantified and found to be prevalent throughout the wetland, with similar population densities. It is likely that the presence of localized oxic zones in the root zones of Typha latifolia supported the oxidizing bacteria populations observed. The results indicate the importance of understanding the conditions in systems being used to treat mine drainage, as well as the importance of having a detailed understanding of the metals of concern in the mine waste.