To start, I would like to share some photos taken across the Amazon Basin, primarily within the Guiana Shield. Artisanal miners exploit alluvial gold shedding off of gold-rich regions (likely eroded orogenic gold deposits) of the amazon and in some cases mine in-situ gold deposits in chemically weathered environments. Their methods are simple yet effective. Often pumping a few days worth of slurry over a sluice box, panning the trapped concentrate and repeating until the area is depleted of accessible gold.
Fine gold in a pan concentrate. Additional work is required to separate the gold from iron-rich minerals or "black sands".
Hard work and skill can pay off big. These workers are part of a modern day gold rush, prospecting in remote areas, pushing the boundaries of known gold occurrences.
An artisanal miner shows off his spoils. He explains, four miners working a single stream for a month produced the amount shown. Others are not as fortunate, junior explorers included.
Quicksilver. Despite the health hazard, mercury is still used in the recovery of fine gold. Here excess mercury in a pan is poured into a submerged cup for later use.
The current dependence on mercury to recover gold has caused environmental concerns. If used irresponsibly mercury can contaminate soil and drainages with devastating long-term effects. Development and promotion of efficient gravity recovery methods, such as centrifugal concentrators, are important to help eliminate the risks of mercury contamination.
A gold amalgam is produced by mixing a gold-rich concentrate with mercury. The mercury is later removed by heating in a retort.
Governments are pushing for the replacement of mercury recovery techniques with the use of gravity recovery methods. I plan to expand on these methods in future posts.
For more information on mercury and its effects check out the Mineralogical Association of Canada Short course series Volume 34, Mercury: Sources, Measurements, Cycles and Effects.
Brodie