Reporting tailings and waste rock: examples of calculations

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These example calculations are provided as an additional resource to guide the National Pollutant Release Inventory (NPRI) reporting facilities that may be affected by the new requirements to report on tailings and waste rock as found in the Canada Gazette notices published December 5, 2009.

They are illustrative of possible reporting scenarios based on the characteristics of different mining operations. Please note that the examples below pertain only to the waste rock and tailings disposal component of NPRI reporting requirements. Facilities also need to consider releases (to air, water and land), disposals and transfers for recycling of NPRI listed substances from other facility sources. 

Example 1

A metal ore mine produces 21 million tonnes of waste rock per year and 24 million tonnes of tailings. The operating permits do not specifically deal with the classification of waste rock. However, the sulphur content of the waste rock is below 0.2% and the arsenic concentration is below 12 mg/kg.  As a result, reporting is not required for waste rock.

The tailings have been characterised for their metal content. The results are presented in Table 1. The table uses the chemical symbol for each metal. Those substances with a less than sign (<) are below detection limits (with the detection limits shown in the table).

The concentrations of each metal are multiplied by the total amount of tailings:

[24 000 000 tonnes x metal %] / 100 = tonnes of metal

Where the concentration is below the detection limit, half the detection limit is used. The results are listed for each metal in Table 1. There is no concentration threshold for NPRI substances in tailings. The mass reporting threshold for ‘core’ NPRI substances (Part 1A [Group 1 of Part 1]) is 10 tonnes. The mass threshold is 5 kg for mercury and cadmium, and 50 kg for lead and arsenic.

In this example no NPRI-listed substances are used to separate the metal ore from the rock, and as such there are no NPRI substances to be reported from process chemicals.

Table 1: Example calculation for metal ore mine (for 24 million tonnes of tailings)
Metals Ag As Cd Co Cr Cu Mn Ni Pb Se V
Concentration
(%)
0.00001 0.00057 <0.00001 0.00076 0.0051 0.0002 0.45 0.00025 0.00004 <0.00005 0.0009
Concentration
(mg/kg)
0.1 5.7 <0.1 7.6 51 2.0 4500 2.5 0.4 <0.5 9.0
Total Metals
in tailings
(tonnes)
2.4 136.8 1.2 182.4 1224 48 108000 60 9.6 6 216
Metals reportable
to the
NPRI
(tonnes)
-
136.8 1.2 182.4 1224 48 108000 60 9.6
-
216

Result: The 24 million tonnes of tailings contain a total of 109 889 tonnes of metals. Of these, silver and selenium are below the mass reporting threshold and do not need to be reported to the NPRI. Therefore, individual NPRI substances totalling 109 878 tonnes would be reported for disposal to the tailing management area (<1% of the total mass of the tailings).

Example 2

This is a second example of a metal ore mine. In this case, waste rock is also excluded because of the low sulphur content and concentration of arsenic below 12 mg/kg. This example is similar to the first except that the types of metals measured and their concentration are different. In this case, 20 million tonnes of tailings were produced. See Table 2.

Table 2: Example calculation for metal ore mine (for 20 million tonnes of tailings)
Metals As Cr Co Cu Hg Mn Ni
Concentration
(%)
0.00011 0.00035 0.00025 0.00027 0.0000039 0.0051 0.00033
Concentration
(mg/kg)
1.1 3.5 2.5 2.7 0.039 51 3.3
Metals in tailings
(tonnes)
22 70 50 54 0.78 1020 66
Metals reportable
to the NPRI
(tonnes)
22 70 50 54 0.78 1020 66

Result: The largest reported quantity is again for manganese, but in this example the weight is just over 1000 tonnes and accounts for 80% of the amount reported.The 20 million tonnes of tailings contain 1282.8 tonnes of NPRI-listed metals. Of these, all are above the mass reporting threshold. Therefore, individual NPRI substances totalling 1282.8 tonnes would be reported as disposals to the tailing management area (<0.01% of the total mass of the tailings).

Example 3

This is an example of a non-metal mine that produces 20 million tonnes of waste rock and 7 million tonnes of tailings per year.

For this mine:

  • The exclusion for unconsolidated overburden applies.
  • Waste rock is excluded because the sulphur content of the waste rock is below 0.2% and there is no arsenic present in the waste rock (i.e. < 12mg/kg). 
  • Unaltered constituents (e.g. sand) of the tailings are excluded.
  • The remaining tailings contain negligible amounts of NPRI listed substances that are below the NPRI mass reporting thresholds for these substances.   

 Result: No reporting for tailings and waste rock would be required for this facility. 

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