Underground Limestone Mining at the Portal-Access Okolona Quarry

In past years, the usual justification for underground mining of limestone has been the depth of the overburden, perhaps 100 feet thick or more. At our Okolona Quarry in suburban Louisville, Kentucky, the overburden is usually shallow -- it averages 8 to 10 feet in thickness. However, in July 1980, we began development of an underground limestone mine on that property which also includes surface mining operations.