ERC calculator mining – Module 10 transcript

Watch the video Mining ERC calculator training – Module 10 – Pits and underground mines to see examples of the user input sheets for pits and underground mines.

Welcome back to the training for the 2022 edition of the estimated rehabilitation cost calculator for mining.

This is Module 10. In this module we'll work through examples in the user input sheets for pits and underground mines.

The pits sheet comprises of five treatments including safety bunding and fencing, blasting of benches and highwall, reshaping and making safe low walls, backfilling open pits, and backfilling/rehabilitating open pit ramps. The sheet works a little differently to others in that pit inputs such as backfill volume entered to the top table, flow down into the appropriate treatment tables. The calculated cost flows back up from the treatment tables to the basic pit information to give a total cost for each pit and the overall total cost for the pit domain. As in other sheets, the total cost for this input sheet is shown at the very top of the sheet as well as the overall total estimated rehabilitation cost.

The treatment tables can be accessed by hyperlinks in the top ribbon of the sheet. We will enter inputs and then use the hyperlinks to go down to each treatment table. As in all the sheets the user enters the map ID and then the name of the element, the pit in this case. The open pit void surface area is the first input in the basic information section and this is used in the backfill open pit table and as a general reference in other tables.

The next input is the safety bund or highwall length, and this is used in the safety bund and fencing table that we will go to now via the hyperlink at the top ribbon. You can see the map ID, the name of the pit, the open pit void surface area, and the safety bund length automatically populate in the safety bund and fencing table from the basic pit information. For bund construction, there are defaults as shown, but the user can enter their own bund height, bund base width, and bund top, and the bund specific volume in cubic meters per meter of bund length is calculated from these inputs multiplied by a swell allowance as shown. If the user enters these values the calculation uses those entries, otherwise the defaults are used. The next column calculates the volume of material in the bund. The bund surface preparation column calculates the cost to prepare the surface using the footprint calculated from the safety bund length and the bund base width. The safety bund construction method column allows the user to select whether the bund will be constructed by hauling material and placing it, or whether a local excavation will be undertaken to construct the bund.

If excavate and place is selected, the next column excavate and place calculates the cost to undertake this activity, multiplying the bund length by the default unit rate or the alternate rate if the user enters one. As in other sheets, if the user enters an alternate rate, they must provide justification in the column to the far right. For the hall in place option, the user can either select the distance from which they will source the material or accept the default of four kilometres. The user selects no from the drop-down menu in the user input haulage distance column if they wish to accept the default. If the user selects yes in the user input haulage distance column, they then must select the distance from which material will be sourced and the appropriate fleet size. The selections determine the load and haul rate in dollars per cubic meter, and this is multiplied by the total volume of the bund to get the total cost to load and haul the material to the construction site. The total cost for safety bund construction is then shown in the next column.

The next part of the table is for fencing and signage, and the default length for fencing is 1.2 times the length of the bund input by the user, to account for the offset distance of the fence from the bund. The user can change this length and is encouraged to provide information to the department if they do so. The next input is for highwall security fencing. These inputs are multiplied by the default rates for fencing and signage, or highwall security, or alternate rates if the user enters these. The last column, the blue one shows the total for this treatment and the individual total cost is populated back to the basic pit information table at the top of the sheet.

The next treatment is benches, highwall, drill, and blast which includes dozing to reshape and make the area safe. As in the previous table, the map ID and name of the pit are automatically populated from the basic pit information table. As is the high wall bench area and volume requiring blasting, and highwall bench volume requiring bulk push. The drill and blast costs are calculated using the default rate or alternate rate if the user enters one, multiplied by inputs populated from the basic pit information table. For the dozer shape, high wall to make safe section, the user must select a slope, angle, length of dozer, push and dozer size. The length of dozer push and dozer size determines the dozer push rate and this is multiplied by the high wall bench volume to get the cost for that activity. The slope angle and dozer size determine the reprofile unit rate and this is multiplied by the area to be reshaped to get the cost for that activity. As for all slope angles for dozer push, the higher the number, the steeper the slope and consequently the less effort the dozer has to exert and the lower the unit rate cost. Further, unit rates for dozers are typically lower for larger machines because the productivity increase typically outweigh the increase in hourly cost.

The next section of this table is for growth media, soil amendments and vegetation, and these work similarly to the tables described previously for the waste structures. As a recap, an automatic calculation of growth media volume is made by multiplying the default thickness by the footprint, and the user can change the volume by entering the growth media volume directly or entering a growth media thickness. The growth media load and haul rate is determined by the load and haul distance and the fleet size, and this gets multiplied by the volume of growth media to get the total cost for that activity. The amendment section works the same as for all other sheets. There are three soil amendment applications available and several material types that can be added, including gypsum and lime. The user enters the area over which each amendment will be applied and this gets multiplied by the default rate or the alternative rate if entered to gain the total cost for each amendment. The three amendments are added together to get the total cost for soil amendment. If no amendments are to be added, the user either leaves the area entirely blank, or selects no amendment in the dropdown selection for each.

The seeding part of the table works the same as for all other sheets, in that the user either accepts the area or enters the area to be seeded, then enters the proportion of land that is pasture or native, or makes both those 0's if the land is desert. If the total land area exceeds 100%, an alert is raised and the user must adjust the proportions. At the end of the table, the totals for each activity are added and those totals populated into the basic pit information for each pit.

The next treatment is for low wall shaping and the map ID, the name of the pit, the area of low wall to make safe, and the volume that will require pushing are automatically populated from the basic pit information table. This activity comprises primarily reshaping and pushing and the calculations work the same as for others previously described. The user selects the reprofile slope angle, which is downslope, the length of dozer push, and the dozer size and these select the appropriate unit rate which are multiplied by the volume and area to get the cost for those activities. The growth media and soil amendment section work exactly the same as previously described. The total for low wall shaping for each pit is summed in the right-hand column, and this is populated into the basic pit information table for each pit.

The next treatment is backfill open pit with waste rock or other material, and this includes some additional items not yet spoken about. As in the other tables, the map ID, name of the pit, and the key input quantities like open pit void area and open pit backfill volume in this case are automatically populated from the basic pit information table. The first bit of this table is associated with pumping and treatment of water from the pit and various water treatment options are available.

The first column is pumping water from the pit and the user enters the total volume to be pumped, which is multiplied by the unit rate or alternate rate if one is entered. The next two columns are adjusting acidic water to neutral, and again the user enters the volume to be adjusted and these are multiplied by the default or alternate rate. The next column is for removal of salt, which assumes the application of reverse osmosis, and if this section is used, entries must be made to the mobilization of reverse osmosis column and the mass of salt which will be required to be managed from the operation of reverse osmosis. Organics removal is for constituents like petroleum hydrocarbons and work similarly with the user entering the volume which is multiplied by the default or alternate rate. The next two columns are per dam with the first being the cost associated with monitoring natural evaporation from a pond. The user enters the number of dams from which monitoring will be applied to evaluate ongoing natural evaporation of water. The next column assumes the addition of an atomiser or other enhancement of evaporation and the entry is similarly number of dams. With these kinds of item entries, the calculator restricts the entry to whole numbers, and if this is the case, it is indicated by a whole number in this row. The last water management entry is establishment and engineering of the water treatment system and is entered by the volume of water anticipated to be managed. Each pit could have several water treatment options applied, and these are all added up to get the total water management cost for that pit.

The next part of the table is associated with sourcing and hauling the rock material to backfill the pit and work similarly to the other tables in other sheets. The rate for load and haul of locally sourced rock or other material is determined by the one-way distance for backfill rock and fleet size. If the source of rock is selected as long haul, this rate is set to 0 and the calculator looks at the distance one-way for rock if not local column to determine the cost for load and haul. The user selects the one-way distance and this is used to source from subrates table 9 the dollars per cubic meter per kilometre cost, which is then multiplied by the distance to the source of rock and the volume of rock to get the total cost for sourcing rock that is not local.

The next section of the table is backfill tip head and doze and this works similarly to the other dozer tables whereby the user selects the length of push and the dozer size, and this determines a rate that is multiplied by the volume to get the cost of that activity. The growth media, soil amendments and vegetation sections of the table work exactly the same as for those previously described. The total cost to backfill the open pit is summed and the number populated back into the basic pit information table against each specific pit.

The last table is for open pit ramp backfill or rehabilitate. The table allows two treatments. The first, backfill open pit ramp, and the second, removal of contaminated material. If the user enters the backfill volume in the basic pit information, the calculator uses this to determine the backfill requirements. Alternatively, the user can enter the average ramp depth, roadway width, ramp length, and number of ramps in the pit, in the open pit ramp backfill table and the calculator calculates the volume to be backfilled from these entries. The user can enter the contaminated material thickness which will override the default, or directly enter the volume of contaminated ramp material to remove. The rest of the remove and dispose ramp material table is the push of the material with the rate determined by the user selections of dozer push length, and fleet, and the haulage of the spoil to a distance and fleet size selected by the user. These selections and imports then determine the total cost to remove and dispose the roadway material. The remainder of the open pit ramp backfill rehabilitate table is calculating the cost of backfill and operates the same as for the open pit ramp backfill table. The total for each pit for open pit ramp backfill and rehabilitate activities is populated back to the basic pit information table. All the treatments applied to each pit are then summed to get a total cost for each pit, and these totals are summed to provide the total for the pit domain and are reported back to the summary sheet.

In the underground mines sheet, the user enters details in the first part of the table and the costs are calculated in the second part of the table. The sheet allows for termination of services, management of shafts, adits and declines, and rehabilitation of damaged land. The shaft options include backfill, plug, and cover and the user decides which options to use. These options are available for ventilation and hoisting shafts. If the backfill option is selected, the total depth for all the shafts in the row must be entered. The options for adits are cover and or seal, and the user again makes the decision as to which one is most appropriate. The user enters the number to be treated by each method. For declines and drifts, the number is entered and if these contain conveyors, the length is also required in the next column. For small historical shafts that would be closed, the user just enters the number of them.

The next section of the quantity part of the table is for rehabilitation of damaged land, including subsidence. The table of values description provides further information on which may be appropriate to use. As in other tables similar to this one, the quantities are multiplied by the default rates above the cost portion of the table and the user can enter an alternate rate which will override the default if they can justify its entry. The user can also enter an alternate rate for the whole row, which bypasses all of the default rates for the row and must provide justification. As with all the sheets, the total for that sheet or domain is reported to the summary sheet.

As always, for more information or specific instructions, please consult the user guide, which is also available on the Business Queensland website below the download for the calculator. See you in the next module.

Watch the video: Module 10 – Pits and underground mines.