Prepare Value Block Model
Function
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:
- Metal Price ($/lb): The price obtained for a lb of final
product
- Ore Mining Cost ($/ton): Cost associated with mining a ton of ore
- Ore Processing Cost ($/ton): Cost associated with processing a ton of
ore
- Waste Mining Cost ($/ton): Cost associated with mining a ton of waste
- Metal Treatment Cost ($/lb): Cost associated with treatment of a lb of
ore
- % Recovery: The fraction of contained product
recovered during processing
- lbs/ton (Default=2204.6): Factor used to convert tons into lbs,
2204.6 for long ton and 2000 for short ton
- Ore Tonnage Factor or Sp. Gravity
(cubic ft/ton): Density of the ore
- Waste Tonnage Factor (cubic ft/ton): Density of the waste
- Pit Layback Slope (degree): Overall slope of the pit highwalls
- Vertical divisions (# of
Benches):This is the number of benches allowed for the surface
pit
Using the above input values, first the Net value/lb for ore is calculated
as follows:
n= Netvalue/lb = (Metal Price – Treatment cost) *
recovery/100$/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
- Revenue = 0
- Cost = Tb * Waste Mining Cost
- Profit = Revenue – Cost
(b) if Grade is greater than ‘y’ but less than ‘x’
- Revenue = Tb * (ore grade of the block/100) * (Metal Price *
lb/ton)
- Cost = Tb * (Ore Mining Cost + Ore Processing Cost + Ore
Treatment Cost)
- Profit = Revenue – Cost
(c) if Grade is greater than “x”
- Revenue = Tb * (ore grade of the block/100) * (Metal Price *
lb/ton)
- Cost = Tb * (Ore Mining Cost + Ore Processing Cost + Ore
Treatment Cost)
- Profit = Revenue – Cost
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 modelare 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.