thank you, page-8

Tibbs

Let me give some very clear understanding of an open cut mine in relation to the width and depth of an open cut, i have 15 years experience in open cut mining.

In your post you showed that a poster had posted that it would take a 300m depth of an open cut to have to top 900m removed from each side, a total of 1800m, let me tell you that this statement is abosulte BS.

It all depends on the type of material that is being removed, im not sure about Namibia but in Australia most open cuts start with either soft oxide material or a laterite type of material commonly known as cap rock, in western australia, goldfeilds in particular you will get anywhere between 20m and up to 100m of oxide material before blue rock is hit, now depending on the pit design, mining company's will make the wall's (Batter's) as steep as possible to remove as little overburden as possible.

Now lets get down to a 300m pit design which i have worked on a few of them, at the start in the oxide material, very often the walls will be cut at a 45 degree to 55 degree angel, with a 300 meter depth it will more likely be 45 degree's to avoid wall failure, if a wall failure occur's it has to be dug out to allow the pit design to continue, this isnt a big deal, a 45 degree angel is basically a 1 to 1 angel, every 1 meter down the wall goes out 1 meter, these walls are generally 15 meters in height followed by a 5 meter step out burm for structual support of the mine walls, over a 300 meter interval you will have 20 walls with about 20 burms, if the walls are at a 45 degree angel you have a total depth of 300m so the top of the wall on one side will be 300m away center of the pit plus 20 burms at 5m each which gives a total of 400m on one side of the pit at a worse case senario, the bottom of the pit can usually be touched from side to side with an excavator at this point and i will tell you that its not a pleasant place to work, if one of those walls fails and your at the bottom of the goodbye cut you will be burried alive.

Anyway that is a maximum distance of 400m on one side, now what needs to be taken into consideration the fact that when the pit material transitions from oxide material 45 degree cuts to a transition material, maybe the walls will go to 55 degree's because of the bony more rocky oxide material, then changing into solid blue rock which is then pre split by drill and blast at a 70 degree angle,

Now that you have entered the blue rrock zones and your walls have gone from 45 degree's to 70 degree's, they are almost vertical. So the original distance of 400 meters is greatly reduced in the pit design for one side.

So at the end of the day, even if Bannerman had a pit design with oxide material all the way to the bottom of the pit, the maximum width of the pit will be 400m + 400m + what ever distance that the company wants at the bottom to work comfortably, lets be generous and give 100 meters at the bottom which wont happen because of costs that wont produce, at the most extreme case of the width of the pit will be 900m wide, which is half of the 1,800 m that was posted, that number is absolute BS.

Again if bluerock/sulphide material is hit and the walls go to a 70 degree cut, also the company not leaving a pit 100 meters wide at the bottom for no reason at all, the 900m width could be greatly reduced.

I hope this helps clarrify the design of a pit.

Go BMN!!