CHAPTER 8 MIGRATORY BIRD KILLS AT GOLD MINING OPERATIONS
| Jurisdiction | United States |
(May 1990)
MIGRATORY BIRD KILLS AT GOLD MINING OPERATIONS
Reno, Nevada
INTRODUCTION
The high priced gold in the 1980's has created a modern day gold rush in the west. Nevada, Arizona and California have been among the most active new gold mining states. A Bureau of Land Management analysis reported 748 mining operations completely or partially on public lands in fiscal year 1988, with 471 of those operations mining precious metals. Over 150 of those mines used cyanide as a basic chemical for recovering gold.
RECOVERY METHODS
There are basically two types of recovery methods used in gold mining which employs cyanide to recover gold from ore. Those two methods are heap leaching and milling techniques.
In the heap leaching process relatively low grade ores are crushed and piled on a leach pad. The leach pad is usually constructed with a plastic material to prevent any cyanide solution from entering the ground water. Cyanide solution is distributed across the surface of the ore and as it percolates through the ore heaps, it collects the gold in the solution. The gold bearing solution is then collected in a pregnant solution pond below the leaching area. The pregnant solution is then processed to recover the gold and the solution is once again used in the leach process after adding additional cyanide to replace what has been lost through the gold recovery process.
There are several variations of the heap leach process used in various mining operations.
MILLING OPERATIONS
When relatively high ore grades are available, it is common for gold mines to utilize milling techniques. This entails crushing and grinding the ore to a very fine consistency and then adding cyanide solution to recover the gold. The waste product is then discharged into a tailings pond. Depending on the size of the mining and milling operation, a tailings pond may cover from 20 acres to over 100 acres of surface area. This tailings pond is typically, relatively high in cyanide content.
[Page 8-2]
WILDLIFE DEATHS
Sodium cyanide is a deadly poison. In fact, the State of Nevada was the first to use cyanide to carry out the death penalty. Cyanide is relatively safe as long as the solution in which it is kept is maintained at a Ph level which is alkaline rather than acidic. Unfortunately, when any type of wildlife consumes water containing cyanide, the acid in the digestive system of the wildlife will cause cyanide gas to be released which is fatal if the cyanide is in a high enough concentration and the amount of solution consumed is large enough.
Most of the gold mines located in the western United States are often in arid desert areas. Because of the relative lack of water, the ponds containing cyanide are very strong attractors to any type of wildlife or livestock looking for a drink. Livestock can be easily protected by fencing the toxic impoundments. Wildlife are not so easily kept from the toxic impoundments and large kills involving a wide variety of species have occurred.
Various sources put the migratory bird deaths in the neighborhood of 2,500 to 3,000 birds each year. Because of the proliferation of gold mining activity and increase in ponds containing cyanide the impact of the gold mining operations on migratory birds has become substantial.
TOXIC CONCENTRATIONS
A frequently claimed "safe concentration" of cyanide is believed to be below 50 parts per million. The United States Fish and Wildlife Service has no data upon which to define a universal toxic threshold for cyanide solutions and it appears that certain species may be more susceptible to cyanide poisoning than others. Further, birds which are under stress because of lack of water, food or exhaustion may be more susceptible than others. It is believed that raptors (birds of prey) are more susceptible.
METHODS USED TO AVOID MIGRATORY BIRD DEATHS
Hazing Techniques:
Numerous types of hazing techniques have been employed by various mining operations. Some of the hazing techniques used by mines include scarecrows, propane canons, guns with exploding projectiles, motor
[Page 8-3]
boats, miniature motor boats, water dyes, flagging of ponds, owl decoys and even loud rock music. It is fairly universally accepted among mine operators that hazing techniques are not effective for more than a short period of time and therefore a wasted effort. Once the birds became accustomed to the hazing techniques, they are no longer deterred from landing on the toxic ponds.
Netting...
To continue reading
Request your trial