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technical report on the nechalacho deposit, thor lake project ...

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The main mine dewatering pumps will be designed to operate <strong>on</strong> automatic c<strong>on</strong>trols. The low<br />

head pumps at <strong>the</strong> sump will operate <strong>on</strong> automatic c<strong>on</strong>trols such that high levels in <strong>the</strong> sump<br />

activate <strong>the</strong> operati<strong>on</strong> of <strong>the</strong> pumps.<br />

BACKFILL<br />

In order to maximize <strong>the</strong> extracti<strong>on</strong> of <strong>the</strong> higher grade resources in <strong>the</strong> basal unit <strong>the</strong> use of a<br />

fill based mining method is proposed. The selected fill should be competent to stand over a 20<br />

to 30 m vertical height while <strong>the</strong> sec<strong>on</strong>dary stope is being extracted. The key alternatives for<br />

back fill are:<br />

• Crushed cemented waste rock<br />

• Cemented hydraulic fill<br />

• Paste fill<br />

Scott Wils<strong>on</strong> RPA c<strong>on</strong>siders paste fill to be <strong>the</strong> best alternative as <strong>the</strong> material is readily<br />

available, it reduces <strong>the</strong> tailings impoundment needs, suitable strength can generally be<br />

attained and <strong>the</strong>re is no additi<strong>on</strong> of water to be handled by <strong>the</strong> mine dewatering system.<br />

Distributi<strong>on</strong> of <strong>the</strong> paste fill is proposed to be via pipeline installed in <strong>the</strong> main decline. This<br />

locati<strong>on</strong> while posing some clean up risk in <strong>the</strong> event of a broken line, has <strong>the</strong> advantage of<br />

being in a warmer envir<strong>on</strong>ment and is more readily available for servicing. The paste plant<br />

would be installed as part of <strong>the</strong> process plant to allow operati<strong>on</strong> as part of <strong>the</strong> mill operati<strong>on</strong>s.<br />

Satellite plant operati<strong>on</strong> would involve operati<strong>on</strong> of such a plant in a relatively hostile<br />

envir<strong>on</strong>ment.<br />

It may be practical to delay <strong>the</strong> c<strong>on</strong>structi<strong>on</strong> of <strong>the</strong> paste fill plant for <strong>on</strong>e to two years, however<br />

at that time <strong>the</strong> paste fill plant will be required to operate <strong>on</strong> a c<strong>on</strong>tinuous basis to fill <strong>the</strong> voids<br />

created by <strong>the</strong> primary stopes and allow mining of <strong>the</strong> sec<strong>on</strong>dary stopes to commence in a<br />

timely fashi<strong>on</strong>.<br />

Scott Wils<strong>on</strong> RPA recommends that paste fill design work be included in <strong>the</strong> current testing to<br />

determine <strong>the</strong> suitability of <strong>the</strong> tailings and to estimate <strong>the</strong> quantity of paste fill which can be<br />

generated from <strong>the</strong> tailings stream.<br />

In <strong>the</strong> shallow secti<strong>on</strong>s of <strong>the</strong> <strong>deposit</strong> <strong>the</strong> use of waste fill to provide a mucking floor may be<br />

practical. The mine plan does include a large amount of waste development for <strong>the</strong> generati<strong>on</strong><br />

of waste rock for backfill.<br />

Technical Report 43-101 – March 13, 2011 Page 18-27<br />

Prepared by Aval<strong>on</strong> Rare Metals Inc.

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