The ore bodies can be classified as replacement bodies and veins. Both types are found at Machcan and Atacocha, but replacement has not been an important process at Milpo.

Large irregular replacement bodies in Pucara limestone have provided most of the ore at the Atacocha mine. The ore bodies were formed by incomplete replacement of limestone by sulfides and clay minerals.

Veins at Atacocha are found in all rock types but those in limestone and quartz sandstone are most important; only one vein in porphyry is being mined. Most veins strike from N. 50° W. to west and dip steeply. Veins in limestone are concentrated near the axis of a small cross fold near the Atacocha fault and have been found only in the upper mine workings. They may have filled tension fractures opened during the formation of the cross fold. Veins in quartz sandstone and chert breccia are found on all levels and are the principal source of ore in the deeper workings. Vein width is usually less than 1 meter but occasionally it increases to 3 or 4 meters The most persistent vein has been mined for a strike length of 150 meters and over a vertical extent of 300 meters.

The geologic features on a district-wide scale that may have been important in the localization of the Atacocha ore deposits are: the porphyry intrusives; the Atacocha fault; the contact of the Mitu and Pucara formations; and the series of northwesterly-striking faults.

The Atacocha Mining Unit is a polymetallic underground mine. It produces zinc, lead and copper concentrates, with contents of gold and silver, through a mineral flotation process in the concentrator plant, which has an installed capacity of 4,400 tpd.