Weeds And Mining

According to Wikipedia, a 'weed is a plant considered undesirable in a particular situation, "a plant in the wrong place"'. They range in scope from pesky little intruders that mar the smooth perfection of your bowling green lawn right through to marauding invaders that take over entire tracts of land. Either way, they're a nuisance and potentially a competitive threat to native species. They can cause significant environmental impact and modification of ecosystems including changing soil nutrient profiles, altering hydrological and geomorphological cycles by clogging water ways and altering their flow or contributing to erosion, impacting fire regimes though build up of additional fuel loads, and preventing regeneration of indigenous species which may also impact on native fauna that relies on that vegetation for survival. In some cases, if the weed is genetically similar to local species, it may also result in cross-pollination and subsequent genetic changes.

Some weeds have been intentionally introduced into a local environment. Australian Eucalypts for example have been used for landscaping in places like California where their extreme flammability and fuel load has subsequently played a significant role in the spread of major bushfires. Echium plantagineum, more commonly known as Patterson's Curse, is a native species in western and southern Europe, southwest Asia, and northern Africa. It was introduced into other countries as a flowering garden plant but is now considered an invasive weed in those countries where it chokes out native grasses and other species. Lupinus angustifolius or blue lupin likewise was introduced into countries outside its native northern Africa and Eurasia as a 'green mulch' crop due to its nitrogen fixing properties. It's now a pest weed in many agricultural areas. Similarly, Rumex hypogaeus (double gee or southern threecornerjack) is native to South Africa but has been introduced into other countries as a herb and is now classed as an invasive weed because it's a major agricultural threat when it gets into grain and fodder crops.

Countries like Australia have several weed classifications that dictate the requirements needed to control them. Declared weeds must be controlled by landowners when present because they have the potential to cause significant economic threat. Environmental weeds are weeds that modify natural ecosystems, usually detrimentally, if they are allowed to establish themselves. Weeds of significance are weeds that are considered invasive with the potential to spread and cause environmental and socio-economic issues.

Weed Control In Mining 

Whilst weed control is an accepted part of a gardener's life and most of us are familiar with council spraying programs, many people outside mining may not be aware that the mining industry in many countries is also heavily regulated with respect to weed control. This is because mining activities such as clearing of native vegetation, disturbance of soil, construction and commissioning of mining infrastructure, movement of vehicles, and rehabilitation projects all have the potential to spread weeds and promote their growth.

Many weeds for instance thrive on 'cultivation' and when soil is disturbed during the construction of a new mine site and related facilities they're usually the first type of vegetation to pop their heads back above ground. In the absence of competition from other vegetation, they flourish. Movement of machinery, vehicles, and personnel around mine and accommodation sites helps spread seeds, and rehabilitation projects can introduce new species of weeds into an area previously clear of them. For these reasons governments generally require mining companies to have documented weed control policies in place as part of the approval process.

For example, mining companies typically have to ensure their weed control measures will control the growth and spread of weeds during all phases of an operation – construction, operation, and rehabilitation. They are also required to ensure that stock piles do not become weed infested, particularly if it has to be moved off site or is going to be re-used during the rehabilitation phase. Therefore, in order to prevent the spread of weeds and their seeds mining operations typically must have, develop, put in place, or carry out:
  • Detailed weed surveys prior to commencing operations and generate maps that delineate the species, location, and density of weeds in the area to be disturbed
  • Include relevant weed data in mine management planning decisions
  • Have measures in place to control weeds prior to an operation commencing
  • Inspect and clean all machinery and equipment to be used on the site prior to commencing operations
  • Inspect and clean all vehicles, plant, and equipment being moved between sites prior to movement
  • Establish and maintain a flat, easily accessed 'clean down' area and ensure all water used in this process is contained and filtered clean prior to release and does not drain into any waterways. Likewise, dust and dirt removed from vehicles must be disposed of in a way that ensures seeds won't be spread and subsequently germinate.
  • Ensure the clean down area is regularly inspected, particularly after rain, and any emerging weeds destroyed
  • Inspect and treat stockpiles, access roads and tracks, and haul roads on a regular basis
  • Ensure on site staff can identify weeds appropriately
  • Follow weed management plans
  • Eradicate certain types of weeds considered particularly detrimental to the local ecosystem
  • If disturbing seeding weeds ensure they and the topsoil they're growing in are stockpiled in an adequate bund to prevent their spread, and then dealt with appropriately
  • Plan and take steps to minimise disturbance to native vegetation and soil
  • When drawing up rehabilitation plans, ensure they include measures to minimise the growth of weeds during the closure or when reducing an exploration permit area
  • Not use, import, or export raw materials ie rock, gravel, sand or fill that is contaminated with weeds or weed seeds
  • Not use contaminated soils or other materials for rehabilitation

If all this sounds like a whole heap of work, you're right! Some mining companies deal with it by having an entire department devoted to environmental issues like weed control. Other companies employ the services of specialists in environmental weed control from mapping right through to eradication and maintenance, whilst others have partnered with companies and start-ups like Astron and eMapper™. These companies, and others like them, are developing programs ie Astron's Rehabilitation Performance Metrics (RPM) that can map and measure vegetation populations, including weeds, during rehabilitation.  It's innovative solutions like these that make managing compliance a lot simpler and far more accurate!

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Wednesday, 25 November 2020
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