Construction on the New Mine in Cerro Rico was begun by House Vetrini approximately fifty years ago. As the Old Mines began to be played out, the Vetrini began a highly ambitious project to fully exploit the mountain.
An expansive new drift (called The Main Drift) was tunneled starting at the very base of the mountain. In addition to being wide enough for a full wagon or two rails of mine carts, the Vetrini artificers put much thought and effort into building a backbone for an advanced ventilation and water pumping backbone that made deep mining practical for the first time.
Tens of thousands of workers, many no better than slaves labored for the next fifty years expanding the New Mine and expecting vast quantities of silver and mithril from the mountain. Despite the work put into ventilation and pumping efforts the conditions were extremely harsh, most of the workers had relatively short lifespans.
The New Mine was a success, but more at extracting silver than mithril. While several mithril veins were discovered they were relatively puny compared to the larger veins near the mountain peak. Silver they found in abundance however.
Ten years ago, a Vetrini artificer developed a theory on the formation and distribution of mithril veins which convinced him that a vast mithril deposit could be found deeper down to the north, under the roots of the mountain. At great expense the Deep Drift was built, at the very bottom of the New Mine, It extended over two miles, angling downward, deeper under the earth where a great mithril deposit was indeed found. A new mine, the Deep Workings was built there.