The artisanal and small-scale gold mining (ASGM) sector in Tanzania began with the exploitation of alluvial gold due to its ease of recovery and high quality. However, as alluvial deposits dwindled and extraction technology advanced, miners shifted to vein or lode deposits. Unlike alluvial gold, the gold in lode deposits is disseminated throughout the rock, requiring more complex extraction methods. In response, miners adopted the crushing and mercury amalgamation process, which proved more effective for extracting vein gold.
As production and profitability soared, this shift opened new opportunities for ASGM miners and external investors. Equipment manufacturers and mercury vendors also benefited from the increase in demand. Despite this, the mercury amalgamation process was highly inefficient, recovering only about 30% of the gold, leaving significant grades of gold in the tailings. This led to the introduction of improved extraction methods like VAT leaching and Carbon-in-Pulp (CIP) or Carbon-in-Leach (CIL) technologies, which offered higher recovery rates.
However, the use of mercury poses serious health and environmental risks, which prompted the establishment of the Minamata Convention on Mercury. This global agreement, to which Tanzania is a signatory, aims to regulate and reduce mercury use, encouraging safer alternatives like cyanidation and gravity concentration. These methods not only yield higher recovery rates but also produce purer gold.
Despite these advances, mercury continues to be used in many ASGM areas due to its ease of use, low capital investment, and its ability to quickly provide miners with funds to sustain operations. Nonetheless, from a technical standpoint, mercury is less effective compared to modern alternatives. It results in lower gold quality and substantial losses during smelting, contributing to its lower overall recovery rate.
