эфель or эфеля is rock of a small and light fraction containing gold, is obtained as a result of washing placer gold or processing ore gold; the fine-grained part of beneficiation tailings. Gold prospectors often call the fine-grained sand found in placers "эфель or эфеля." I don't know an exact translation--perhaps "fine-grained tailings dump."

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Note added at 56 mins (2007-07-20 18:49:50 GMT)
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Эфель (эфеля), мелкозернистый материал (обычно мельче 12—16 мм), отделяемый промывкой и классификацией на грохотах песков россыпных месторождений золота, платины, алмазов, олова, вольфрама, титана и др. Э. обычно имеют повышенное содержание ценных компонентов и обогащаются гравитационными методами — на шлюзах, концентрационных столах, в отсадочных машинах, тяжелых средах, на винтовых сепараторах и др.; для золотосодержащих Э. применяют также цианирование и амальгамацию.

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Note added at 1 hr (2007-07-20 19:03:37 GMT)
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Added to O.M.'s response in the event a dredge is involved.

Dredge Tailings

Dredge tailings can be found along waterways and washes anywhere there was enough natural flowing water or wherever the miners could dam a stream or wash to gain an ample water supply. It is truly amazing some of the places that huge dredges are found with no visible water supply anywhere to run it.

These operations left long lines of tailing piles along the water course the dredge was working as the material was processed. Again material is classified down to a given size before being fed into the separators where the gold is removed. The material that is discarded ends up in these tailing piles and again nuggets, some of incredible size are also discarded unknowingly. Often a man was hired to watch the conveyer to make sure no big ones got away, but they still did being covered with dirt or a dozen other reasons.

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Note added at 1 hr (2007-07-20 19:23:38 GMT)
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After seeing/reading your other questions which involve dredging, I'm inclined to agree with O.M.