Metallurgy

The Howard's Pass deposits contain large tonnages of moderate and high grade zinc-lead mineralization. This mineralization consists of high grade bands of zinc and lead minerals separated by barren or weakly mineralized bands of mudstone. Selwyn undertook preliminary heavy media separation (HMS) testwork during fall of 2004 to confirm preliminary testwork completed by US Steel Corporation in 1970's. The test work found that HMS (utilizing heavy liquids to make the gravity separation) was quite effective in separating the less dense waste mustone material from more dense mineralized material and indicates that gravity techniques may provide an effective means of pre-concentration of run-of-mine open pit mineralization.

Additional testwork was conducted in the fall of 2005 on drill core from several of the zones and on a bulk sample of dump materials from the previous test mining. This more detailed test work has confirmed the previous favourable results indicating that HMS may be an effective pre-concentration step in the processing of ores.

New Dense Media Separation (DMS) technology utilizes gravity to separate materials of different density in a cyclone. DMS cyclone technology is used extensively in the coal industry to clean coal; in this case it removes the heavier shale beds from the less dense coal. DMS technology could be very effective in upgrading ores at Howard's Pass and improving project economics. The goal is to obtain an approximate 150% up grade of ores with moderately high recovery.

Effective pre-concentration of the ores requires fine crushing of the ore and processing through a dense media separation plant prior to sending the sink material (dense ore) to the mill for fine grinding and flotation recovery of separate zinc and lead concentrates. The heavy media separation concentration step would result in rejection of approximately half of the feed material and result in a much smaller mill processing at a higher grade of feed. The capital saving would be very significant and could have a very favourable impact on project economics.

Placer and Cygnus undertook extensive metallurgical testwork including metal leaching studies in the 1970's and concluded that with fine grinding they could achieve acceptable recoveries of zinc and lead in the low to mid 80 percent range. Selwyn has undertaken additional flotation testwork and is forecasting 83% zinc and 75% lead for the preliminary economic evaluation. Testwork is continuing to determine optimum grind size and the application of pre-float of carbon before undertaking differential flotation to recover separate zinc and lead concentrates. Typically SEDEX deposits achieve average recoveries of about 85% for zinc and 75% for lead. Concentrate quality has generally been good with zinc grade of 52.5% for the zinc concentrate and 60% for the lead concentrate. The concentrates are low in iron and have very low levels of deleterious materials and should be attractive feed for most zinc smelters. Silver grades in the concentrates are low and not likely to be at levels for which payment will be received.

The lack of pyrite in the ores results in better recoveries than what might be otherwise expected given the grain size of the average run-of-mine materials; higher grade ores tend to be coarser grained and may provide generally higher recoveries. Testwork is continuing towards increasing recoveries and evaluating ore variability effects.