Gold Mining the Moon. Quick read, #2

The year is 2055 and a successful gold mining operation has been set up on the Moon. Everything proceeded efficiently, while enhanced by the discovery of helium-3, until a nearly impenetrable metal plate, while buried three miles under the lunar surface, stops the profitable drilling. After several failed attempts to cut through the plate, a way around it is sought, which provokes a technologically advanced alien species to defend their thousands of years, old, operation..
A book from the quick read series.