The Rosemont deposit is a typical representative of the porphyry copper class of deposits. Similar to many other southwestern USA deposits in this class, Rosemont consists of broad-scale skarn mineralization developed in Paleozoic-aged carbonate sedimentary rocks adjacent to their contact with quartz-latite or quartz-monzonite porphyry intrusive rocks. The deposit has been extensively drilled using diamond core holes. Broadly disseminated sulfide mineralization occurs in the Paleozoic units. Near surface weathering has resulted in the oxidation of the sulfides in the overlying Mesozoic units.

The mineralization is primarily in garnet-diopside (with minor magnetite) skarn that formed in the Paleozoic rocks as a result the intrusion of quartz latite to quartz monzonite porphyry. Marble was developed in the more pure carbonate rocks, while the more siliceous, silty rocks were converted to hornfels. Bornitechalcopyrite-molybdenite mineralization occurs as veinlets and disseminations in the garnet-diopside skarn and associated marble and hornfels, accompanied by quartz, amphibole, serpentine and chlorite alteration. Quartz latite to quartz monzonite intrusive rocks host strong quartz-sericite-pyrite mineralization with minor chalcopyrite, molybdenite and bornite. Where the mineralized package of Paleozoic rocks and quartz-latite intrusives outcrops on the western side of the deposit, near surface weathering and oxidation has produced disseminated and fracture-controlled copper oxide minerals.

Silver occurs in minor, but economically significant quantities in the primary sulfide mineralization in the Paleozoic sequence. The silver is associated with the copper mineralization. The gold content of the deposit is generally very low, but contributes to a by-product credit.

The Rosemont deposit is a large tonnage, skarn-hosted, porphyryintruded, copper-molybdenum deposit located in close proximity to the surface and is amenable to open pit mining methods. The proposed pit operations will be conducted from 50-foot-high benches using largescale equipment, including: 12.25-inch-diameter rotary blasthole drills, 70-cu-yd electric mining shovels, 36-cu-yd front-end loaders, 320-ton off-highway haul trucks, 580- to 850-hp crawler dozers, 500-hp rubber-tired dozers, 270- to 500-hp motor graders and 30,000-gallon off-highway water trucks.

The Rosemont process plant includes the following unit processes and facilities:
- Primary crushing.
- Crushed ore stockpile and reclaim.
- Parallel SABC grinding lines with pebble crushing.
- Copper flotation comprising rougher flotation, concentrate regrind, and two stage cleaning.
- Cu-Mo concentrate thickening.
- Molybdenum flotation including roughing, concentrate regrind and five stages of cleaning.
- Molybdenum concentrate thickening, filtration and drying.
- Copper concentrate thickening and filtration.
- Copper concentrate load out and storage.
- Tailings thickening, filtration and dry stacking.
- Reagents storage and distribution (including lime slaking, flotation reagents, water treatment and flocculant).
- Grinding media storage and addition.
- Water services (including fresh water, fire water, gland water, cooling water and process water).
- Potable water treatment and distribution.
- Air services (including high pressure air and low pressure process air).
- Plant control rooms.

The flowsheet consists of primary crushing, followed by two parallel SAG, ball milling and pebble crushing (SABC) circuits, copper flotation with regrinding ahead of cleaning, a moly separation circuit, concentrate thickening and filtering and tailings thickening, filtering and dry stacking.

With minor modifications, the process plant is designed to treat on average 90,000 tons/d (or 32.8 million ton/y).