Waste Rock
Waste rock is typically sampled for similar reasons as tailings.
Waste rock is the overburden material that is excavated and disposed
of in order to access valuable ore bodies. This material is composed
of various rock types which vary in size. Ideally, sampling should
take place before the rock is excavated. If this is not feasible
for one reason or another, sampling can also take place after the
initiation of mining activities and after mining activities have
ceased. The advantage of sampling before the rock is blasted/excavated
is that it is much easier to define the geological units, and to
ensure that each unit is adequately characterized by the sampling.
Preferably, sampling will occur before, during, and after decommissioning
of the mined area for the same reasons that tailings are sampled.
See the tailings section for more information.
After waste rock has been excavated from its original location,
it is more difficult to characterize the geological units. Mixing
and segregation of rock types occurs and depending on the waste
rock excavation sequence and the type of dump composition, it can
be difficult to obtain samples of all the rock types present. Also,
there are difficulties sampling any part of the dump but near the
surface. Samples may be taken of the waste rock itself as well as
of the pore water and gas in the pore spaces. Methods of sampling
waste rock are conducted similarly to tailings with the use of drilling
methods. For more information on the different drilling methods,
see the tailings section (link to the tailings section). Pore water
samples may be taken from installed monitoring wells or lysimeters.
Gas samples are taken for identification of volatile compounds in
soil and water. Various instruments are used for this purpose including:
photoionization detectors (i.e. gas chromatography) and flame ionization
detectors. For more information on photoionization detection, click
here.
The determination of what constitutes a "representative sample"
of a waste rock pile is a challenging task. A record of the placement
of waste rock in the pile is useful for determining how to sample
the pile. For abandoned mines, records are often not available making
sampling plans more difficult to design. Both horizontal and vertical
characterizations are required, however drilling into the pile may
be difficult because the rock fragments are large and unconsolidated
and therefore, the sample results may not be representative of the
entire rock pile. It must be decided which statistical parameters
(i.e. mean, variance) will be used to assess "representativeness",
which strategies should be used to determine how many samples are
required, and at which locations these samples should be taken (MEND,
2001). For more information on developing an efficient, representative
sampling plan, see the data quality
section.
Problem | Compliance
| Health & Safety | Sampling
| Analytical | Data
Quality
Site Assessment | Prediction
| Construction | GIS
| Monitoring & Assessment
|
