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 adsorbed (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.
