Ideally, nongovernmental organizations (NGOs) should not have to play any sort of a role in reducing these impacts. Ideally, the governments of the various countries in which gold is mined would take care of this themselves. In the real world, NGOs should take the lead in the reducing these impacts. The only reason that they should not take sole responsibility is because they should allow people in the affected communities to participate as much as possible.
The best solution would be for international NGOs to help local organizations. They would help to build up these organizations to the point where they could be politically strong enough to be a force. If the international NGOs can help build more local NGOs and interest groups, the locals could pressure their governments to take more of an interest in making sure that the gold mines did not harm the environment.