ECU Silver Mining Inc. provides an update on recoveries attained on its mineral resource.
ECU Silver’s mineral resource is primarily contained in sulphide mineralization plus additional oxide mineralization. The Company has been testing various methods to improve metallurgical recoveries within both these environments and has attained excellent results.
Metallurgical recoveries are very important to the success of any mining operation and we have undertaken several months of extensive testing to attain the best method for optimal recoveries on a cost efficient basis. Several months of tests were done in the Company’s own laboratories in Mexico as well as in various laboratories in Canada, the USA and Australia. These tests were done on the various types of mineralized material at the Company’s mines using a range of methods, including traditional methods to others that are still at the experimental stage.
Given that the Company has access to large scale facilities including a sulphide mill, an oxide mill and a roaster, we are able to implement certain lab test procedures on a commercial scale. The results of these are described below:
The best results in the oxide material were obtained by direct cyanidation through the oxide mill in which we have reached recoveries levels up to 80% for gold grading 1.0 grams per tonne (g/t) or more and up to 75% for silver grading 150 g/t or more. However, recoveries can be increased by leaching the tailings with grades between 0.5 g/t and 1.0 g/t in-situ. This process involves leaching the in-situ gold over a long period of time, using only water to reactivate the cyanide contained in the tailings pond. Tests results showed that 50% of this slow dissolving gold, as well as the silver, could be recovered by sprinkling water over the tailings pond and recovering the solutions that percolated through the pile.
More recently, the Company started installing a leaching system on the sulphide tailings based on sprinkling water over the sulphide tailings. Although, complete metallurgical balances cannot be calculated yet as the system is still being installed, the grades of gold in solution has more than doubled from 0.11 g/t gold up to 0.28 g/t gold in the solution recovered. This demonstrates that the leaching system is working and additional gold not recovered by the oxide mill will be recovered through this new stage.
The mineral product from the sulphide resource is derived from three different concentrates. A portion of the gold and silver is recovered in two of these, the lead and zinc concentrates. However, most of the gold is recovered in a pyrite concentrate which requires further treatment to liberate the gold from the pyrite crystals. Up until now, the Company has been stockpiling this concentrate and today the pyrite concentrate inventory stands at 13,825 tonnes grading 20.6 g/t gold and 151 g/t silver. This equates to a total content of 9,150 ounces of gold and 67,000 ounces of silver. Laboratory tests showed that several methods could be used to recover the precious metals, most involving first oxidizing the material and then recovering the gold and silver by leaching. For industrial level testing, the Company is using roasting, described more fully below, as it is the most traditional and proven method.
Over the past several months a third party built a roaster to oxidize the pyrite/gold concentrate. The construction of the roaster is completed and testing of the pyrite/gold concentrate is being accomplished. To date, the roaster has reached an operational level where it can treat about 30 tonnes of concentrate per day to generate about 20 tonnes of roasted product. The roasted product will then be further treated in the oxide mill enhancing the recoveries and grades of the oxide material.
These new developments will mean a significant increase in the generation of precious metals for the Company in the short term.