a wing and a prayer maybe, page-2

Hey Crusty,

Concentrate grade can be the same, but unlikely IMO. It all depends on the metallurgical recovery during flotation. They have published 91%. By my calcs this should be 4% up (from 87%) if it means same volume of concentrate at same grade.

6.337Mtpa/[email protected]%=92kt Zn @91% recy=84ktpa contained Zn.
Working backwards from 84ktpa of recovered Zn to estimate original recovery:
5.856Mtp/[email protected]%=96kt Zn
To maintain grade the original recy must have been 87% to get 84ktpa of contained Zn.

I'm not sure what the original published recy was, but I just found this (Gunslung Nov 2006):

Mine life 12 years
Ore Reserves 6.3Mt
Ore per Vertical Metre 10,000 t
Plant Throughput 525,000 tpa
Head Grade 14.5% Zn!!!!!!!!!
Concentrate Production 132,000 tpa
Concentrate Grade 53%
Zn Recovery 92%!!!!!!!!!!!!
Metal Production 70,000 tpa Zn

In November 2007 more slinging with a 12.5 years mine life.

Anyway - you might be right DC, if the recovery was always 92%, then the product grade should be up to 56.5% not 53.8%.

Can anyone confirm the last published recovery at less than 91%?

Oh well back to the day job........