To: Richard Mazzarella who wrote (6066 ) 10/13/1998 10:31:00 PM From: Tim Hall Read Replies (3) | Respond to of 11603
Richard, <<Alan, I just got off the phone with Maxam's office. You called it, the ore is screened to 20 mesh. That ore is then milled to 150 mesh for recovery testing. Something we fail to appreciate here is that the screening operation is of such low cost, that we could almost triple results as a pseudo head ore >> I find this information very interesting for several reasons. I doubt that screening of desert dirt to 20 mesh will be low cost. You can't just throw desert dirt on a 20 mesh screen. It will have to be done in stages. They will probably have to start with a grizzly with 6" to 12" openings. This will remove the large boulders etc. They will then have to use a series of screens starting with two to three inch working down to about 1/2". Then the ore will have to be dried. (Even pure perlite which doesn't contain any clay and only has 4% moisture has to be dried before it can be screened below 3/8".) After drying, The ore will have to pass through another series of screens ranging from 8, 12, 16 to finally get down to 20 mesh. The 20 mesh can then be fed into the vibra mills for reduction to 150 mesh. This will have to be closed loop with rescreening to keep the mesh below 150. ( The ore doesn't have to be dried if wet screening is used from the 3" down but wet screens are much more expensive to operate and maintain. Wet screening will also result in possible waste water problems.) As Maxam has pointed out, these deposits are not homogeneous. Therefore I would suspect the material size ranges will very greatly from one location to another with changes happening within a few feet. This would indicate that the screening plant will have to be overdesigned for those times when the material is on the large size, ie. not to much fines in the feed. This is typical for desert alluvial deposits. It is also possible to now speculate the pm's are contained in the material that is minus 20 mesh but can't be efficiently recovered until this material is ground to minus 150 mesh. If Maxam has narrowed this down, they should be able to report on the minerals that contain the precious metals. I present this not as criticism of Maxam but just some practical food for thought. Tim