Prepare Value Block Model

This command makes a block model that represents the profit of each block. . There are two options, to just Enter the Economic Parameters or to Read Grid Parameters File. A 3-D fixed block model is used for computerized optimization techniques. Carlson defines a block model with a block file (*.blk) and top elevation grid file, bottom elevation grid file and grid files with grade parameters for each layer. The block dimensions are dependent on the physical characteristics of the mine, such as pit slopes, dip of deposit and grade variability as well as the equipment used.  The center of each block is assigned, based on drill hole data and a numerical technique, a grade representation of the whole block. Carlson uses inverse distance method, 3D Kriging, and discrete method to estimate grades for each block. A block model can be created using the “Make Block Model” (Command: blkmodel) or the Input-Edit Block Model commands from “Ore” menu.

A value block model consists blocks with profit ($/block) values associated with them. These profit values are calculated based on the grade values of the blocks. The command to make value block model starts with a dialog to choose Carlson block model to process. The first dialog is for selecting the Method for Preparing the Value Block Model. The first option, to Enter the Economic Parameters brings up the following window where the final Ore or Metal Price is set in $/lb for all the key ore.

  The second option, to Read Grid Parameters File, brings up the following window where price for each grade ($/lb) appears just as it is entered in the Grade Parameters file GPF.

Each of the input parameters are described below:

Using the above input values, first the Net value/lb for ore is calculated as follows:

n= Netvalue/lb = (Metal Price – Treatment cost) * recovery/100$/lb

c = ore mining cost + ore processing cost + waste mining cost

Then calculate the Cutoff grade: x %

 (x/100) * lb/ton * n = c

And Mill cutoff grade: y%
 (y/100) * lb/ton * n = (c – Ore processing cost)

Now we already know the block size (height, width and length) so we can calculate its volume V = h*w*l ft3. And with tonnage factor we can calculate tons/block = Tb = V/tonnage factor. Then Profit associated with each block is calculated based on its Grade value that is read from GPF file:

For any block
(a)    if Grade is less than (<) y
(b)    if Grade is greater than ‘y’ but less than ‘x’
(c)    if Grade is greater than “x”

The blocks with positive Profit are treated as profitable block and the profit value associated with each block is saved in new BLK and GRD files. Then the Lerchs Grossmann Algorithm is used on this Economic Value Block Model to calculate the optimum pit. If the grade block model has more than one attribute (grades) then economic parameters are read from gpf file, otherwise economic and physical parameters are entered directly to create the new value block model. A surface grid file is read to create the surface of the new block model. All the blocks that lie between surface grid and top elevation of the grade block model are treated as waste blocks i.e. grade is assigned to zero for those blocks. The number of blocks and size of blocks in the new block model are  calculated based on the physical parameters, pit layback slope angle and number of vertical divisions. The block values (grade) for the new block model are estimated using the original block model. Profit (dollars/block) associated with each block is calculated based on its physical and economical parameters. The blocks with positive profit are treated as ore block. The Value Block Model is saved as a new Carlson block model file (*.blk).  There are file selection windows to first select the existing block model (BLK file), the surface Topo grid file and the new Value Block Model to write. The final step is to write out the Value Block Model that may be used in other routines, such as Optimized Pit Design. Keyboard Command: mkvalblkm

Pull-down Menu Location: Block Model

Prerequisite: Need a BLK model file, a topo grid file and optionally a GPF grade parameter file.