Mining 100 years ago or even 60 years ago was very different from mining today. Mining historically has been known to cause serious damage to the environment. The modern mining companies try very hard to avoid this. (Additionally, greater recycling reduces the need to mine in the first place.)
The most obvious environmental damage from classical mining is removal of rock and soil. Mining makes a hole in the ground. Open pit mining makes a very large hole in the ground. Additionally, the overburden that is removed must be dumped somewhere. Both of these disturbances are visible scars (right).
Less visible effects of digging result from exposing new rock. This new rock will have new, different chemistry when it oxidizes in air or dissolves into runoff water. Sulfide rocks can have the biggest environmental effect, and sulfides are common metal ores. The sulfide radical creates acidic water that can threaten plants and wildlife downstream from the mine.
Mining takes a lot of water. That hasn't changed; if anything, it has increased. Water keeps down dust and lubricates the cutting blades. Ore processing uses more water. Additionally, water seepage into the mine must be pumped out and disposed of. In the past, contaminated water would be discharged into the nearest stream or lake.
Historically, some processing of ores to isolate the metals has required toxic or dangerous chemicals. Gold cyanide leaching may be the most notorious example. Any processing of cinnabar (mercury ore) involves mercury, which is itself toxic. Sulfuric and nitric acid are commonly used. Such toxic or caustic chemicals are still used, though alternative methods are substituted when possible.
Smelting of ore is a common process that involves heating the ore with coke (carbon) to remove oxygen. A smelter therefore generates carbon dioxide, carbon monoxide, and possibly sulfur dioxide and other airborne pollutants. Other ore processing plants that don't include smelting will still need a source of power. That source itself may be a coal power plant or other source of air pollution.
In the past, the lowest priority of mining companies has often been restoration. The mining company might very well replace overburden, but that could be the end of the effort. Failed mining companies could not even do that much. Abandoned mine shafts dot the western United States.
To summarize, then, traditional mining on the American frontier and elsewhere on the edges of civilization was characterized by casual disregard of the environment, including air, water, and ground pollution.
In the United States, regulation of mining falls mainly to the states. This includes general business and labor laws, but the states' greatest concern is restoration. States do regulate the manner and amount of mining, but more importantly they require a plan and performance bond against restoration. If the company fails, money is still available for cleanup.
Federal regulation of mining includes the 1872 Mining Law that allows mining claims on a considerable amount of federal land in the American West, consistent with local laws. More important, though, is the role of the Environmental Protection Agency. The EPA regulates discharges into the air and into the "navigable waters" of the United States.
Modern mining methods are not very similar to the older approach described above. Mining companies make an effort to treat the environment responsibly, both for good public relations and because prevention is cheaper than cleanup.
Every mining project starts with a plan, and the plan includes environmental protection. Each mining site is unique as to geology, geography, and environmental risks. Each plan submitted for approval is therefore unique. In addition to state approval, many plans for good or bad must be defended in lawsuits by environmental groups.
A typical mining plan provides for handling the soil and overburden that will be removed. Commonly, it will be stored and put back in place at the end of operations, then seeded for regrowth (right, same mine as pictured above).
A mining plan will take care to contain various possible sources of spillage and runoff. Ore dumps and tailings might be placed on rubber mats and surrounded by ditches. Water is recirculated, as supplying enough water is always a challenge. Any water pumped out of the mine will be stored for treatment. (It is a curiosity of environmental law that water pumped out of the mine can't simply be put back in at the end of operations.)
Smaller mining operations have adopted a method of moving and filling. A small mining company will work perhaps 5 acres of its claim at a time, then shift locations. The vacated location will be filled and reclaimed immediately. Companies do this in order to reduce the bond they must post with the state, because it is based on the amount of land yet to be cleaned up. The result, for whatever reason, is that environmental damage is minimized.
Historical mining operations were somewhat wasteful by modern standards. An ore dump is lower-grade ore that was removed from a mine in its historical period to permit access to higher-grade deposits. Up to 40% of the material removed might have been consigned to a dump. The famous King Solomon Mine in California, for example, left 50,000 tons of gold-bearing ore unprocessed, representing 40,000 ounces of gold.
A more modern ore dump may result from a company mining and then seeing prices drop or going out of business. The performance bond will take care of this latter case (see above). In any case, a later entrepreneur might purchase and process the ore when technology and markets improve. An ore dump requires no drilling or chipping, merely scooping and processing the available material.
A tailing dump is similar to an ore dump, but represents processed material. Tailings may contain gold that was unrecoverable by older methods but might be accessible now. Tailings, like discarded ores, may also contain metals that were previously unwanted, such as molybdenum. The advantages of purchasing tailings are similar to the advantages of an ore dump, but with a smaller payoff.
Why does tailings waste exist? Some historical miners were notoriously impatient, many were inexperienced, and all had only the science and technology of the time. For an early example, recall the Spanish gold miners of Central America who discarded unwanted platinum before shipping their gold back to the Old World.
Additionally, a tailing dump might be an environmental problem, and a government body might require someone to process and dispose of it. One notorious and recurring example of this is gold cyanide leaching (see above). Another process used mercury. These tailings may contain trace amounts of mercury that would have to be isolated and disposed of. This is not particularly hazardous, but it must be planned and executed with care. Other components of the tailings would depend upon the specifics of the prior mining procedures.