World emissions of mercury from artisanal and small scale
 gold mining and the knowledge gaps about them.

Kevin H. Telmer1 and Marcello M. Veiga2
1. School of Earth and Ocean Sciences, University of Victoria, Canada
2. Norman B. Keevil Institute of Mining Engineering, University of British Columbia, Canada
Download PDF Version

Abstract
 

We estimate mercury releases from artisanal and small scale gold mining (ASGM) based on available data about mercury and gold exports and imports by country and from field reports from the countries known to have active ASGM communities. The quality of the estimates ranges from reasonable to poor across the countries. One of the aims of this paper is to give a first order estimate of the amount and location of mercury being released into the environment globally by ASGM, another is to motivate stakeholders to improve the quality of these estimates, a third is to illustrate the linkages between global mercury trade and its use in ASGM, and the fourth objective is to provide a practical outline of the options available for reducing mercury use in ASGM.
 
We estimate that artisanal and small scale gold mining releases between 640 to 1350 tonnes of mercury per annum into the environment, averaging 1000 tonnes/a, from at least 70 countries. 350 tonnes/a of this are directly emitted to the atmosphere while the remainder (650 tonnes/a) are released into the hydrosphere (rivers, lakes, soils, tailings). However, a significant but unknown portion of the amount released into the hydrosphere is later emitted to the atmosphere when it volatilizes (latent emissions). The rate of latent emission is unknown but is particularly high where mercury is used in combination with cyanide processing – a growing trend. Considering that ASGM is growing, the use of cyanide in ASGM is growing, and the production of mercury contaminated waste from ASGM is growing (multi-year accumulation of tailings), latent emissions conservatively amount to at least 50 tonnes/a bringing the total emission of mercury to the atmosphere from ASGM to 400 tonnes/a.

This estimate of emission to the atmosphere differs from the previous one provided in the 2002 UNEP Global Mercury Assessment both in terms of its magnitude (400 tonnes/a, versus 300 tonnes/a) and in the way the estimate has been made. The current estimate is based on a more robust understanding of ASGM and on a more robust dataset that includes a wider variety of information sources, more field evidence, better extrapolation methods, and independent testing by analysis of official trade data.

The estimate is based on combining the following evidence:
  1. Relatively good estimates of gold production and mercury use from pilot studies in 2 countries, Brazil and Indonesia – multiple sites per country.
  2. Reasonable information from 7 more countries.
  3. Some but poor information (mostly anecdotal) from 14 more countries.
  4. Enough information to hazard a guess at a specific level of mercury consumption for 24 more countries.
  5. The identification of the presence of ASGM sites in a further 22 countries. These were assigned a fixed minimum amount of mercury consumption. This amount does not significantly alter the estimated total release, and has almost no effect on the estimated minimum of 640 tonnes/a, but seems reasonable in order to identify potential localities of release.
  6. Independent analysis of officially recorded trade in mercury and gold.