The challenge of cyanide: Can backfilling with gold tailings be consistent with the requirements of the International Cyanide Management Code?

2007

Pressure exerted on gold producers by regulators, project financiers and civil society in the wake of the Baia Mare tailings spill in Romania during 2000 prompted most responsible gold companies to sign up to the International Cyanide Management Code (the Code). The Code stipulates a ‘cradle to grave’ approach more comprehensive than that applied to any other mining reagent and is particularly challenging for operators who use cyanide-bearing tailings for backfill. This paper will examine some of the challenges for Code compliance facing both surface and underground operations that employ backfill technology, most particularly the requirement to demonstrate that the potential migration of cyanide (and its degradation products) from emplaced backfill will not have an unacceptable impact on worker health and safety or the receiving environment, either during mine life or after closure. This requirement is particularly challenging for gold mines on the Far West Rand of South Africa’s Witwatersrand, where the gold bearing reefs are overlain by dolomite which constitutes the most significant groundwater resource in the country. The dolomite also provides baseflow to the Vaal-Orange River system, which supplies water to millions of downstream users. The Far West Rand gold mines require dewatering on a massive scale to maintain safe conditions in ultra deep workings, which substantially modifies pre-mining groundwater levels, flow directions and gradients. Some mines on the Far West Rand use a small percentage of their tailings as backfill for roof support. Those who are Code signatories will need to demonstrate that use of cyanide-containing tailings for backfill will not compromise the ecological function or the beneficial use of this highly significant groundwater resource during either the operational or closure phases. This paper will discuss some of the challenges confronting these operators in demonstrating that their potential impacts have been identified and are of an acceptable magnitude.

Mots Clés: Backfill, Far West Rand, Health & Safety, Gold, Environment, Dolomite, International Cyanide Management Code, Mining, Cyanide