Effects

In the heap leaching process, a form of in-situ mining, piles of gold ore are placed on impervious surfaces and then treated with cyanide solutions. Used cyanide solution then is stored in a solution-retention basins usually on site. While basins are also lined with impervious materials, toxins can be leached into the ecosystem via surface or ground water. Storm waters and failure of structures can occur. In 1990, a dam failure caused in a major cyanide spill in South Carolina, with fish kills reported for almost 50 miles downstream. Although cyanide exists naturally in the ecosystem, it is acutely toxic to wildlife and humans in higher concentrations. Fortunately, it does not persist in the environment or accumulate in animal tissue. Rather, cyanide degrades fairly quickly.

What is Cyanide?

Cyanide is a chemical unit containing carbon and nitrogen and other compounds that is not toxic in all forms or concentrations. It is produced naturally by a variety of algae, bacteria and fungi species as sugars and other materials. It is neither radioactive nor a carcinogen. It is often found bound with other chemicals such as iron or sodium which can affect the degree of toxicity. For example, hydrogen cyanide used in mining is highly toxic. The primary threat to the ecosystem is immediate exposure. Cyanide is especially toxic to fish and aquatic invertebrates even in low concentrations. However, algae and macrophytes have a greater tolerance.

Prevention/Solution

Working with the EPA, the Brownfields and Land Revitalization Technology Support Center (BTSC) coordinates clean-up efforts to reclaim abandoned mine sites. The BTSC operates with the philosophy that reclamation is possible. Scientists and ecologists must be able to adapt practices in the field based on real-time monitoring. No longer must abandoned mines be environmental time bombs; they can be restored wildlife habitats, recreation areas and parks. (http://www.ehow.com/about_5505300_environmental-effects-mining-gold.html)

COMPREHENSION CHECK

Exercise 4. Are the statements true or false? Correct the false statement using the facts from text1.

1. In-situ mining uses a solution to extract the gold from the surrounding hard rock material.

2. The environmental risks escalate with the decreased threat of leakage or spills.

3. Toxins can be leached into the ecosystem via surface or ground water.

4. Cyanide is radioactive.

VOCABULARY

clearing – очистка

in a predetermined order - в заранее заданном порядке

simplest (method) to employ - простейший из используемых

will result in - приведет к

unless otherwise specified - если нет других обозначений

sluicing – промывка наносов

sluice box – ловушка шлюза

drain – осушать, дренаж, канава

recovery – восстановление металла

rig up – оборудовать

trestle – мост на рамных опорах, подмостки, козлы

brace – платформа, скреплять

grade – уклон

flume – лоток (шлюзный), желоб

riffl – створка шлюзных ворот

fork – приямок для храпка насоса

discharge – разгружать; спуск, сток

settling – осаждение

carry over – переносить

tailings – отходы, хвосты

tailing discharge – выгрузка

crack – трещина

leak – утечка

grating – решетка, сетка, грохот

hold up – удерживать

scrub – чистить

wire brush – проволочная щетка

set up – установка, наладка, устройство

tailings launder – желоб, лотковый конвейер

fouling – загрязнение, засорение

prohibit – защищать

dam – плотина, запруживать

impound – пруд для хвостов

water-tight – непроницаемый (для воды)

Exercise 5. Find the meaning of the word combinations in the dictionary and try to remember them:

clearing; bush; timber; drain; drainage; gravel; avoid; sequence; thickness; width; rig up; by means of; timber sluice; cheap; right; angle; riffle; pebble; stone; purpose; grade; fine; gold; pan; obtain.

Exercise 6. Fill in the blanks with one suitable word:

1. Excavation … overburden and gravel and cleaning … … the bedrock are the second stage … alluvial mining.

2. Sluice boxes may be rigged … … the ground, … ditches, or elevated … trestles.

3. Water … washing is brought … the head of the sluice, … means … a leaf or flume.

4. The grade … a sluice box is usually expressed … inches … 12-foot box.

5. New sluice are usually rum lightly … a couple … days … a very small head of water.

READING

Exercise 7. Read the text below looking for the main ideas concerning sluicing.