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To: Amark$p who wrote (94412)	10/7/2007 2:15:51 PM
From: E. Charters	Read Replies (1) \| Respond to of 313046

Well if you believe Margaret Kent, yes you can do it as she documented in one NR that it was tried in Timmins over the winter. Others tell me that the reaction of gold to CN below 70 degrees F is so slow that it is not feasible. In the leach pile, the temp is higher than freezing because of the chemical reaction. Snow won't stay on a heap that is being leached. Outdoor leach pads were tried at Brewery Creek in the Yukon with limited success commercially. Leaching rates etc, and recoveries I am not familiar with in this op, but it was reported to be getting gold out at a cash cost of $184 an ounce. All up cost I do not know. The operation caved at low gold prices in the late nineties, but it may not have been because of leaching problems or refractory ore problems so much as a combination of economic factors. *********************************** MINE OPERATIONS The Brewery Creek mine achieved commercial production in May, 1997. During 1997, a total of 72,387 ounces were produced from the Kokanee and Golden zones, at a cash cost of US$184 per ounce. A total of 2.1 million tonnes of ore were mined and 2 million tonnes of ore with an average grade of 1.87 gpt gold were delivered to the leach pad. For the nine months ending September 30, 1998, a total of 52,638 ounces of gold were produced at a cash operating cost of US$197 per ounce. A total of 2.3 million tonnes of ore grading 1.46 gpt gold were mined and 2.2 million tonnes of ore grading 1.46 gpt gold were delivered to the leach pad. Ore was mined from the Kokanee and Golden pits. An intermediate leaching circuit was commissioned at the Brewery Creek mine which effectively doubles the amount of ore under leach. *************************** The Study: The study area is located at the Brewery Creek Mine, situated approximately 50 kilometres east of Dawson City, Yukon. The objectives of the study were to: determine whether micro-organisms capable of breaking down cyanide complexes were present in soils from the Yukon Territory, if present, to test if these organisms could be established on the processed ore heap, and demonstrate that the mico-organisms could bio degrade the cyanide substances from both solution and solids in the processed ore heap. Results: This study provides the first look at the possibility of using biological detoxification of cyanide at mines in Northern locations. Phase 1 of the study established that cyanide-degrading bacteria are naturally abundant and relatively widespread at the Brewery Creek mine site in Northern Canada. Phase 2 confirmed that these micro-organisms can be established on processed ore from the heap pile, and that they can bio-degrade cyanide associated with the ore, both in solution and in metal-cyanide complexes. Test results also showed that bio-degradation of cyanide was more efficient that the conventional use of hydrogen peroxide to break down cyanide in the processed ore piles. Further studies were recommended. emr.gov.yk.ca ******************************* Cyanide Leaching "Heap leaching with cyanide is a newer technology which is currently being utilized at Viceroy Minerals Corporation's Brewery Creek gold mining property near Dawson, and is proposed to be used at the Dublin Gulch property near Mayo." emr.gov.yk.ca

To: Amark$p who wrote (94412)	10/7/2007 2:40:31 PM
From: Nostradameus	Respond to of 313046

I don't know mining but never heard on leaching from EPM....

To: Amark$p who wrote (94412)	10/7/2007 3:34:19 PM
From: hank2010	Read Replies (1) \| Respond to of 313046

Pegasus/Degerstrom did not bust their gut trying to leach at -20 degrees. When freezing weather came they just shut down the pumps, drained all the lines and waited 5 months for it to warm up. In the spring, the first flush was the most rewarding as most of the dis-solution of the gold over the 5 months came out right away. Only cost for that 5 months of inactivity is the time value of money, and in a rising gold market who cares. High PH of a cyanide solution lowers the freezing point somewhat but that is not significant IMO. Don't fight it, Shut it down before damage is done to the lines etc.

To: Amark$p who wrote (94412)	10/7/2007 11:30:51 PM
From: Breccia	Read Replies (2) \| Respond to of 313046

Read all that interesting info EC posted. The metallurgist who managed the Brewery Ck is a friend and at that time he mentioned that there was quite a pile of SNOW on top of the leach pad and that may have been important for insulation. Note that no NEW rock was added to the pad in the winter. I do not know but assume the solution was sprayed underneath the snow cover. In any event it worked very well with surprisingly few problems. A pile without snow cover may have issues ?