短语词组短語gold placer -mining 採金場placer gold mining 砂金鑛開採placer r mining 砂鑛淘採beach placer mining industry 海濱砂鑛開採業beach placer mining 海濱砂鑛開採method of littoral placer mining 濱海砂鑛開採法hydraulic mining of placer 砂鑛露天水力開採 返回 placer mining