The ore body at El Porvenir 9 runs to the southern section of Atacocha, where further work will be done.

The ore bodies can be classified as replacenwnt bodies and veins. Both types are found at Machean and Atacocha, but replacen1ent has not been an important process at Milpo.

Bedding replacen1ents or ''mantos'' in Pucani linwstone are co1nmon at Machcan, where nearly half of the prospect pits and small adits explore manto-type deposits. The majority of the deposits are small, ranging from 50 centimeters to 1 meter in thickness and from 1 to 20 meters in lateral extent; only two ore bodies more than 50 meters long were observed. The bedding replacements are always assoeiated with veins and extend out from them. The veins probably served as feeders for the ore bodies. The walls of the mantos are often sharp and delineated by sinall bedding-plane faults.

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 :Nfitu and Pucara formations; and the series of northwesterly-striking faults.

It began operations in 1949, producing concentrates of zinc, lead and copper, with contents of gold and silver, through mineral flotation process in the concentrator plant, which has modern systems of hoisting, crushing and ore concentration, with an installed 5,600 tpd capacity.