Summary:
Deposit Type
The Project deposits consist of copper-molybdenum-silver-gold mineralization hosted in quartz monzonite porphyries, and in skarn. The skarn formed in the Paleozoic rocks from fluids associated with quartz latite to quartz monzonite porphyry intrusions. Genetically, skarns form part of the suite of deposit styles associated with porphyry copper centers. The skarns were formed as the result of thermal and metasomatic alteration of Paleozoic carbonate and, to a lesser extent, Mesozoic clastic rocks. Near-surface weathering has resulted in the oxidation of the sulfides in the overlying Mesozoic units at the East deposit, and in the near-surface Paleozoic units of the Copper World deposits.
Mineralization occurs mostly in the form of primary (hypogene) copper-, molybdenum-, and silverbearing sulfides, found in stockwork veinlets and disseminated in the altered host rock at depth. Near surface, along structural zones, and in quartzite units, oxidized copper mineralization is present. The oxidized mineralization occurs as mixed copper oxide and copper carbonate minerals. Locally, enrichment of supergene chalcocite and associated secondary mineralization are found in and beneath the oxidized mineralization.
Mineralization
Mineralization occurs as both copper -oxides and -sulfides in skarns and intrusive porphyry rock. A 3D model of five mineralization domains was completed based on analytical data, including the hole acid soluble data, and Quemscan analysis collected by Hudbay from the East, Bolsa, Broadtop Butte, West and Peach-Elgin deposits.
East Deposit
The East deposit ranges between 3,400 to 5,600 feet (1,000 to 1,700 m) in diameter and extends to a depth of approximately 2,600 feet (790 m) below the surface. The main fault systems partially delimit copper mineralization, dividing the deposit into major structural blocks with contrasting intensities, and types of mineralization (Figure 7-7). The north-trending, steeply dipping Backbone Fault juxtaposes marginally mineralized Precambrian granodiorite and Lower Paleozoic quartzite and variably mineralized limestone to the west (Backbone Footwall Block), against a block of younger, wellmineralized, Paleozoic limestone units to the east (Lower Plate). The Graben Fault on the southeast side of the East Deposit truncates significant mineralization.
Oxidized copper mineralization is present in the upper portion of the deposit. The oxidized mineralization is primarily hosted in Mesozoic rocks but is also found in Paleozoic rocks on the west side of the deposit, and deeper along some faults. The oxidized mineralization occurs as mixed copper oxide and copper-carbonate minerals. Locally, enrichment of supergene chalcocite and associated secondary mineralization are found in and beneath the oxidized mineralization. Oxide copper in the northwest of the East deposit extends considerably at depth on fractures within the Backbone Footwall.
Primary (hypogene) mineralization occurs mostly in the form of copper-, molybdenum-, and silverbearing sulfides, found in stockwork veinlets and disseminated in the altered host rock. Pyrite and chalcopyrite comprise approximately 25% and 35% of the total sulfides content, respectively; along with bornite (20%) and chalcocite (12%). The ratio of these main sulfide minerals is variable through the stratigraphy of the deposit owing to competing, over-printing pulses of mineralization and possible supergene effects. Molybdenite is a minor phase but appears to be distributed throughout the skarn and in peripheral portions of the deposit. Gold and silver are present in small amounts across the deposit and are thought to be contained in the primary sulfide minerals.
Bolsa Deposit
Drilling in 2022 has confirmed the mineralization of the Bolsa deposit is continuous with the Backbone Footwall mineralization of the East Deposit. Mineralization is hosted almost exclusively in the lower Paleozoic Bolsa quartzite, and the Abrigo, and Martin Limestone Formations within the Backbone Fault Domain. Stronger mineralization is truncated to the west at the disconformity, with generally unmineralized to weakly mineralized granitic rocks; although weaker, secondary copper oxide mineralization does occasionally occur on fractures a couple of hundred feet into the granitic rock. The eastern boundary is less distinctly defined by structure or stratigraphy. Near surface mineralization generally declines eastward towards, but not necessarily at, the fault contact with the Upper Plate lithologies. At depth, however, and especially in the southern half of the Bolsa Deposit, mineralization continues into both the Upper and Lower Plate Rocks. Mineralization in the Bolsa Formation Quartzite and in granitic rock, when present, is nearly entirely of non-carbonate copper oxide and copper silicate. In the altered skarn of the Abrigo and Martin Formations it is composed of a mix of copper oxides and sulfides.
Broadtop Butte Deposit
Mineralization is predominantly hosted by quartz monzonite porphyry, including an east-northeast striking brecciated zone. Skarns hosted in the Arkose Group and Glance group to the south of the quartz monzonite, and in the Glance Group, Scherrer Formation and Epitaph Formation to the north, east and below the quartz monzonite also host mineralization. Mineralization appears to be truncated on the east at Gunsight Pass by the Backbone Fault, although mineralization in the Bolsa Deposit is juxtaposed almost directly west of Broadtop Butte at Gunsight Pass. The extent of mineralization in all other directions does not appear to have strict stratigraphic or structural boundaries but seems to be related to the distance from the quartz monzonite porphyry and its associated skarn alteration halo. Mineralization in the unbrecciated quartz monzonite porphyry is dominated by sulfide mineralization, however, oxide copper mineralization is dominant in the breccia pipe portion of the quartz monzonite porphyry. Skarns at depth to the north and northeast of the quartz monzonite porphyry are relatively narrow, but with higher-grade sulfides.
West Deposit
Mineralization is hosted by Paleozoic quartzites, and skarn altered carbonate units on both the footwall and hanging wall of the Backbone Fault domain. In the northern half of the deposit, mineralization is also hosted in fractured coarse granitic rocks in the Backbone Fault domain footwall. The strongest mineralization is within the Backbone Fault structural zone and is dominated by sulfide mineralization. The Hanging Wall of the main Backbone structure has lower grades and is oxide dominated. The major host stratigraphies at the West deposit are the Precambrian coarse granitic rocks within the Backbone Fault Zone, and Paleozoic formations from Bolsa to Epitaph (footwall and lower plate units at the West Deposit). Mineralization nearly reaches the surface on the west slope of the low mountain that hosts most of the West deposit. Eastward no distinct structural or stratigraphic features limit mineralization. Drilling has defined the southern extent of mineralization, although the extent of mineralization to the north has not been completely defined.
Peach-Elgin Deposit
The Peach-Elgin mineralization is hosted in the hangingwall of the low-angle Helvetia Thrust Fault (Helvetia Klippe) which hosts several historically mined deposits including the Peach, Elgin, Mohawk, Old dick, and Heavy Weight mines. Drill holes, both historical and recent, have connected much of the Helvetia Thrust hanging wall mineralization.
Peach is entirely hosted in variably skarn-altered sedimentary rocks and is cut by moderately shallow, east dipping faults, producing gaps in the stratigraphic sequence. Host stratigraphies include Bolsa, Abrigo, Martin, Escabrosa, Horquilla, and Epitaph. The Peach mineralization hosts an irregularly intertwined mix of copper oxide and copper sulfide dominated units.