This chart illustrates the general steps in open-pit gold mining. The specifics of the process vary from mine to mine.
Geologists use the latest technology such as satellite surveys and geochemistry to locate an ore deposit.
Computers are used to design the mine which requires precise and accurate measurement of the ore deposit. Construction begins following the lengthy process of receiving permits.
As
holes are drilled for blasting, samples of ore are examined
to determine grade and metallurgical characteristics.
The broken rock is marked by type for efficient processing.
Based
on its metallurgical makeup, a dispatcher directs truck
operators to deliver the ore to the correct processing
location.
Low
Grade Ore is roughly broken into small chunks
and placed on carefully lined pads where a dilute
cyanide solution is distributed over the surface of
the heap. The solution percolates through the heap
and the cyanide dissolves the gold. This solution
containing dissolved gold is then collected.
High
Grade Ore is delivered to a grinding mill where
the ore is pulverized to a powder. Depending on its
metallurgical characteristics the ore may be treated
in one of three recovery circuits.
Refractory
ore containing carbon is roasted to over 1,000
degrees Fahrenheit, burning off the sulfide and
carbon. The product of this process is an oxide
ore, which is routed to the leaching circuit.
Oxide
ore is sent directly to the leaching circuit where
cyanide dissolves the gold.
Sulfide
refractory ore without carbon is oxidized in an
autoclave to liberate the gold from sulfide minerals,
then it is sent to the leaching circuit.
Treated,
high-grade ore is leached with cyanide.
The
gold is absorbed (collected) out of solution onto activated
carbon. The remaining cyanide solution is recycled.
The
gold loaded carbon is moved into a vessel where the
gold is chemically stripped from the carbon which is
then recycled.
Gold
is precipitated from the solution electrolytically or
by chemical substitution.
The
pure gold is then melted into dore' bars containing
up to 90 percent gold. Dore' bars are then sent to an
external refinery to be refined to bars of 999.9 parts
per thousand pure gold.
Reclamation is a long-term investment made by
every gold mining company, and can cost anywhere from
$2,000 to $10,000 per acre. It is the cornerstone of
every mine plan and is considered the first and last
step of the mining process. (For more information on reclamation, see the Reclamation section.)
* For information on how gold is used in electronics, telecommunications and medicine, see the gold uses page.
