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美国衣阿华州诺克斯维尔以东8.5英里的达勒姆矿是由Kaser公司在1972年开始开发的。1974年春开始开采石膏,1975年底开始开采石灰石。现在单班产量可达4万吨/月。石膏在200英尺水平,矿脉12英尺(3.66米)厚。石灰石矿脉在400英尺水平,19英尺(5.79)厚。到目前为止,已采完石膏面积近10英亩(约4万多平方米),石灰石为18英亩(约7.28万平方米)。开采方法为无支护房柱法。有两台华格纳铲斗拖车,分别为ST-11型和ST-8
The Durham mine, 8.5 miles east of Knoxville, Iowa, was developed by Kaser in 1972. Mining began in the spring of 1974, and limestone mining began in late 1975. Now the single shift production can reach 40,000 tons/month. The gypsum is at 200 feet and the vein is 12 feet (3.66 meters) thick. The limestone vein is at 400 feet and 19 feet (5.79) thick. So far, nearly 10 acres (about 40,000 square meters) of plaster have been collected, and 18 acres (about 72,800 square meters) of limestone. The mining method is the unsupported house column method. There are two Wagner bucket trailers, ST-11 and ST-8 respectively