The DMLZ ore body lies below the DOZ underground mine at the 2,590-meter elevation and represents the downward continuation of mineralization in the Ertsberg East Skarn system and neighboring Ertsberg porphyry.

The DMLZ mine fleet consists of over 230 pieces of mobile equipment, which includes 27 LHD units and 15 haul trucks used in production and development activities.

Targeted production rates once the DMLZ underground mine reaches full capacity are expected to approximate 80,000 metric tons of ore per day in 2021.

The mill produces copper and gold concentrate from mined ore through a process to separate valuable minerals from the impurities covering them. The main steps in the process are crushing, grinding, flotation, and dewatering. Crushing and grinding transform ore size into fine sand in order to release particles containing copper and gold.

Flotation is a separation process to produce copper-gold concentrate. Concentrate slurry consisting of finely ground ore and water mixed with reagents is introduced into a series of mixing tanks called flotation cells, where air is pumped into the slurry.

The reagents used are lime, frothers and collectors. Frothers form stable bubbles that float to the surface of the flotation cell as froth. Collectors react with valuable metal sulfide mineral particle surfaces. rendering these surfaces hydrophobic. The hydrophobic sulfide mineral particles adhere to the air bubbles rising from the slurry zone into the froth floating on the surface of the cell. The froth containing valuable minerals, resembling metallic detergent froth spills over the top of the flotation machine into launders where valuable minerals collect. The valuable minerals collected in the launders are called concentrate. Concentrate (in the form of slurry containing 65% solids by weight) is pumped to Portsite through four 115 km-long slurry pipelines. Upon reaching Portsite, the concentrate is dewatered until only 9% moisture content remains, and is then shipped for sale.

Crude and free gold particles do not react well in the flotation process. The Knelson concentrator, a gravity recovery system uses centrifugal force to separate and recover the crude and free gold. Gold recovery from ore is thus enhanced overall.

Ore milled from the DMLZ underground mine averaged 3,200 metric tons of ore per day in 2017, 4,400 metric tons per day in 2016, and 2,900 metric tons per day in 2015.