Summary:
World Copper presently considers mineralization at Zonia to be the product of a porphyry copper system, which is the conceptual deposit model on which current plans for future exploration are based.
Mineralization and Alteration
Copper mineralization at Zonia is thought to result from the following sequence of events:
• Deposition of disseminated pyrite-chalcopyrite sulfides in a subvolcanic porphyry setting, slightly post-dating intrusion of unit Qmp, approximately 1.75 Ga,
• Regional-scale vertical deformation imposed by the voluminous intrusion of the granitic batholiths around the greenstone belts, with greenschist facies metamorphism related to the Yavapai Orogeny from 1.75 to 1.69 Ga, followed by exhumation,
• Oxidation, mobilization, and supergene enrichment of primary copper sulfides along foliation and fracture planes, followed by burial, and
• Second exhumation and oxidation of the supergene-enriched sulfides and remobilization of the copper oxide minerals into structural anomalies, resulting in in-situ and transported copper oxides throughout the various lithologic units within the Project area.
Copper mineralization occurs primarily within the foliated Qmpf, the protolith of which is presumed to be argillically altered Qmp, but mineralization is also concentrated along the contacts of various felsic units, as well as between mafic and felsic units. The latter occurrence is considered a late-stage effect of supergene, mobilized copper reacting with the more calcic mafic units.
As described by Schmidt (2021), the pit geology is dominated by a leached cap of pervasive supergene alteration and limonite that typically forms over primary pyrite-chalcopyrite mineralization. Sericite alteration is extensive and obscures original rock textures in places. Clays representative of argillic alteration is readily observed in the South pit. Hematite, jarosite and goethite occur as fracture coatings and boxwork veinlets ranging from 0.1- to 0.5-inches in width, and hematite veins up to 2 inches thick suggest that the chalcopyrite-quartz veins and secondary chalcocite favor the sericite schist.
Known mineralization extends approximately 8000 feet along strike parallel to the regional (northeast) trend of foliation, with a dip of 80 to 85 degrees to the northwest. Width of the mineralized zone is quite variable, ranging from 250 to about 1000 ft. Ore minerals primarily consist of chrysocolla, black copper oxides (tenorite, melaconite, pitch), cuprite, native copper, malachite and azurite, though occasional shipments of chalcocite were reportedly made from the underground Cuprite shaft and from the North pit.
Current interpretation proposes that regional deformation related to the Yavapai Orogeny sheared the originally disseminated and blebby pyrite-chalcopyrite mineralized horizons into folia-form mineralization, parallel to schistosity, and ranging from vertical to a dip of ~45°. Subsequent oxidation remobilization of the copper from chalcopyrite (~35% Cu) followed the foliation down-dip to the groundwater table, where copper then reprecipitated as enriched sulfide minerals, primarily secondary chalcocite (~78% Cu). This chalcocite blanket was then oxidized during a second lowering of the water table and copper further mobilized into reactive units below. The early underground mining at Zonia exploited the high-grade chalcocite horizons preserved at depth.
As described by Schmidt (2021) pit geology is dominated by a leached cap of pervasive supergene alteration and limonite that suggests a primary percent-volume pyrite=chalcopyrite mineralization preexisted oxidation and weathering. Sericitic alteration is extensive and obscures original rock textures. Clays representative of argillic alteration is readily observed in the South pit. Hematite, jarosite and goethite occur as fracture coatings and boxwork veinlets ranging from 0.1- to 0.5-inches in width, and hematite veins up to 2 inches thick suggest that the chalcopyrite-quartz veins and secondary chalcocite favor the sericite schist.