Hi David, I have designed the Gecko underground mine optimally from a block model (Gecko Mine N.T. 80 stopes). It is easier than pit optimisation because you do not have to consider waste removal in the manner as an open pit. I will outline the process here assumming you have one metal and you are using a cutoff grade. If you have two metals and a sale to a concentrator you use a dollar value cutoff and a Net Smelter Return for revenue, i.e. you must set the dollar values in the block model. If you want details of this please contact me.
1. The first step is to calculate cutoff grade. This is based on operating costs. e.g. gold mine with cip plant. cutoff = (drill&blast $/t + haulage $/t + admin $/t + cip $/t) / (gold price $/g * cip recovery%) Note that development costs are not included in this calculation, development costs are capital and will be considered later. The cutoff is the grade of material which will make profit once it has been accessed by development. The next step is to identify your ore zones(those above cutoff) and draw in your decline and development. 2. Once drawing in your development you outline the ore zones based on your cutoff grade. Say you have identified a region to design a stope and you have two ore zones marked based on the cutoff grade. 3. You must then design your stope around these two ore zones. You have three options for your stope. You can mine ore zone 1, ore zone 2 or both ore zones. To decide which option you choose for your stope you must select the option which returns the maximum profit. So you must design each of the three stopes and evaluate each profit individually. 4. The profit figure is simply Profit = Revenue - Operating cost. = Stope tonnes*stope grade*metal price*recovery - Stope tonnes*(drill&blast $/t + haulage $/t + admin $/t + cip $/t). So the option of the three which returns the maximum profit figure is selected. Note that it can be easier to calculate the profit figure if you place the profit figure into each block of your block model, then depending on what software you are using you just total the profit figure for the blocks within each stope. Now your stope is designed and you have a profit figure calculated. 5. You must now compare the profit of your stope against your development costs. This must be done in a number of stages e.g. firstly if the stope will pay for the level development access and secondly if all stopes will pay for the decline access. So say you have a decline with one access drive to your stope. The profit figure for your stope must be greater than the cost of the access drive. If the profit figure for the stope is less than the cost of development of the access drive then the stope is not economic. 6. Repeat this process for all stopes and then develop a cashflow based on the economic stopes to determine if the mine is economic. Stopes are generally designed using wireframes and evaluating each wireframe against a block model. Software is available which will crudely perform this automatically only creating stopes which are RECTANGULAR in shape so may have little or no use to your situation. Genrally for a final mine design you should be creating the wireframes. The other thing to consider is Net Present Value this may be ignored or you may wish to raise cutoff grades in early years to increase early year cashflow, however this is entirely dependent on each case and different for each mine. Also relevant is the decision of which blocks you are going to design against e.g. normally you would design against blocks which are classified as Measured and Indicated, to produce a Proven and Probable reserve. If you design against blocks which are inferred these will be in the Possible category of your reserve and would not usually be considered in your financial evaluation of the project. Regards Digby Millikan Geolite Mining Systems [EMAIL PROTECTED] http://www.users.on.net/digbym >Hello >Does anyone know of an undeground alternative to >open pit optimisation? How would you derive underground >reserves from a 3-dimensional resource block model? >Thanks >David Boakye >Ashanti Goldfields Company Ltd >[EMAIL PROTECTED] -- * To post a message to the list, send it to [EMAIL PROTECTED] * As a general service to the users, please remember to post a summary of any useful responses to your questions. * To unsubscribe, send an email to [EMAIL PROTECTED] with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list * Support to the list is provided at http://www.ai-geostats.org