GREEN GOLD–DIRTY GOLD, TADO, DEPT. CHOCO, COLOMBIA

In place of mercury, small-scale alluvial gold miners in Tadó, Dept. Chocó, Colombia produce green gold (oro verde) using locally available plant extracts. The leaves of balso (Ochroma pyramidale) or malva (Hibiscus furcellatus) are crushed by hand and mixed with water to make a foamy liquid that is added to the gold pan (batea) instead of mercury. After the plant extract is added, the gold and magnetite sink and the lighter minerals are floated out of the gold pan. For final clean-up, a combination of other methods may be used: 1) a hand magnet to remove the magnetite (jagua) from the dried gold concentrate; 2) the aventadero method in which the dried concentrate is tossed into the air allowing lighter minerals to be removed by the wind; and 3) because green gold is typically in flat nuggets, the concentrate may be placed on an inclined pan that is gently tapped and the sub-rounded, waste minerals tumble away leaving the gold. Regionally, plant extracts from cedro playero and yarumo (Colombia) and cuiguyum and murmuncho (Perú) are also used.

However, ICP (Inductively Coupled Plasma) analyses indicate that even green gold may contain 200-4500 ppm Hg–this mercury may have been released from dragas or other small-scale gold mining operations that use mercury; native mercury released from cinnabar outcrops; coal burning; or volcanism. ICP also indicated 300-106000 ppm Ag and 450-585 ppm Pt.