It was an open pit operation until 1974 when the newly discovered underground deposit was brought to production.
Chemical analysis of rocks and plants may indicate the presence of an underground deposit.
Upon their departure, they left behind underground deposits of the black oil virus, in preparation for their return.
These underground deposits were built with limestone walls and floor slabs.
Natural gas is taken from underground deposits where it has been trapped for centuries.
The oceans that once covered the earth left a generous supply of salt beds and underground deposits.
The Frasch process is a method to extract sulfur from underground deposits.
The mine was depleted by 1991 and after a failed expansion to more underground deposits it was closed in early 1992.
Like seeking out underground deposits of various minerals, for instance.
The surveyors found evidence of underground deposits of oil and gas.
