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Resolution |
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Arizona, USA |
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Cu Mo
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Super Porphyry Cu and Au
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The Resolution project deposit in the Superior (Pioneer) district is located in east-central Arizona, USA. It lies within a prominent ENE trending belt of porphyry copper deposits, mantos and copper-bearing veins that extends over a distance of 50 km from the Old Dominion mine to the north-east, to the Magma mine in the south-west (Ballantyne, et al., 2002).
The deposit is some 3.5 km SW of the Superior East deposit and immediately southwest of the east-west trending zone of vein and manto deposits that were exploited by the Magma Mine at Superior. It is the deep porphyry that underlies the Superior/Magma vein and manto system.
Geology
The regional geology and stratigraphy in the district and as encountered on the project area is described in the Globe/Miami District record in this database.
This succession within the project area includes the Mesoproterozoic Dripping Spring Quartzite, Mescal Limestone, Apache Basalt and the Troy Quartzite. These rocks are intruded by a series of multiple dolerite (diabase) sills up to 400 m thick. This dolerite is typically strongly magnetic, dark grey to black, and comprises medium grained, sub-ophitic intergrowths of plagioclase and pyroxene with lesser amphibole, biotite and Fe-Ti oxides and ranges in texture from aphanitic to pegmatitic to amygdaloidal. It is a good host to copper mineralisation, containing 40% of the >1% Cu resource (Ballantyne, et al., 2002).
The Proterozoic sequence is unconformably overlain by Palaeozoic rocks, particularly the carbonates of the upper Carboniferous (Pennsylvanian) Naco Formation Limestone.
A concealed depression within these older rocks, below young post mineral cover rocks, contains a local faulted inlier of up to 1300 m of probable Cretaceous volcaniclastics comprising tuffs, volcanic sediments, conglomerates and sandstones, including crystal and lithic tuffs and host 9% of the >1% Cu resource (Ballantyne, et al., 2002).
Felsic intrusives include the Quartz-eye Porphyry, Feldspar Porphyry and Quartz Monzonite Porphyry of Laramide age, while matrix poor heterolithic breccias occur as irregular bodies that cross-cut the Proterozoic sequence near the centre of the deposit. This breccia which occurs near the centre of the deposit and is mainly developed within the dolerites, has angular to rounded clasts which include the Proterozoic sediments, Cretaceous (?) volcaniclastics, the Laramide felsic intrusives and strained quartz set in a hydrothermal biotite matrix (Ballantyne, et al., 2002).
The mineralised Mesozoic, Palaeozoic and Mesoproterozoic host rocks are masked by 600 to 1200 m of unmineralized overburden composed of Oligocene-Miocene Whitetail Conglomerate and Miocene (18.6 Ma) Apache Leap dacite tuff (Manske and Paul, 2002).
Alteration
Strong pervasive alteration is evident within the deposit. The core of strongest copper mineralisation is associated with either 1). strong secondary biotite development within the volcaniclastic hosts, siltstones, breccia and dolerite, -or- 2). garnet-diopside (with minor garnet-magnetite) skarn which has been variable subjected to retrograde alteration to produce clays, chlorite, epidote and actinolite within calcareous protoliths.
The lateral boundaries to the >1% Cu zones grade outwards from biotite alteration with accompanying chalcopyrite-pyrite mineralisation through a zone of biotite veining with increasing propylitic alteration to chlorite-epidote with predominantly pyrite. In this transition the chlorite has been destabilised to smectite clays and carbonate to produce an 'intermediate argillic' interval.
A thick zone of intense, pervasive quartz-muscovite-illite (phyllic alteration) overlies the central part of the high grade copper zone, persisting upwards to the erosional surface (at the base of the Tertiary Whitetail Conglomerate) 400 m above the 'ore zone'.
Parts of the biotite core and the entire phyllic zone are commonly overprinted by structurally and bedding controlled argillic kaolinite, dickite and zunyite with associated bornite-chalcocite mineralisation (Ballantyne, et al., 2002).
Mineralisation
The higher grade copper mineralisation occupies a dome shaped zone of >1 km in diameter in which Cu grades exceed 1% in the most receptive lithologies. This is underlain by a gentler dome shaped lower-grade core which lies 750 m below sea level (Ballantyne, et al., 2002). Early drilling indicated a zone that was at least 750 m long, 250 m wide and 300 m high carrying between 1 and 2% Cu (Manske & Paul, 2002).
Copper grade exhibits a strong lithological control, with dolerite (diabase) and limestone locally carrying >2% Cu, while immediately adjacent Quartz-eye Porphyry dykes and quartzite locally carry <0.5% Cu. An unusually intense pyrite halo overlies and flanks the >1% Cu shell, ranging up to 10% pyrite for 100 to 200 m above the rich Cu zone. Laterally the pyrite fringe decreases into the propylitic zone (Ballantyne, et al., 2002).
Molybdenite occurs in early copper poor quartz-molybdenite veins, with subordinate 'Moly paint' on slickenside surfaces. In general the distribution of copper and molybdenite are coincident.
The early chalcopyrite-pyrite phase is overprinted by late chalcocite-bornite which is controlled by permeability and is more pervasive, replacing both chalcopyrite and pyrite in veinlets and selvedges, and is found mainly in the upper chalcopyrite interval and the lower part of the overlying pyrite shell. High grade bornite-chalcopyrite veins cutting Mesozoic volcaniclastics, similar to those found at Superior, are best developed from 250 m above to 250 m below sea level. They die out upwards and downwards and pass into massive pyrite veins.
Thin sphalerite-galena ± chalcopyrite veins are found in the peripheral propylitically altered rocks (Ballantyne, et al., 2002).
Mineral Resources
Published Mineral Resources are as follows at December 31, 2017 (Rio Tinto 2017 Annual Report):
Indicated Resource - 132 Mt @ 2.63% Cu, 0.042% Mo;
Inferred Resource - 1655 Mt @ 1.45% Cu, 0.034% Mo;
TOTAL Resource - 1.787 Gt @ 1.54% Cu, 0.035% Mo.
The most recent source geological information used to prepare this decription was dated: 2003.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Cooke, D.R., Wilkinson, J.J., Baker, M., Agnew, P., Phillips, J., Chang, Z., Chen, H., Wilkinson, C.C., Inglis, S., Hollings, P., Zhang, L., Gemmell, J.B., White, N.C., Danyushevsky, L. and Martin, H., 2020 - Using Mineral Chemistry to Aid Exploration: A Case Study from the Resolution Porphyry Cu-Mo Deposit, Arizona: in Econ. Geol. v.115, pp. 813-840.
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Favorito, D.A. and Seedorff, E., 2020 - Laramide Uplift near the Ray and Resolution Porphyry Copper Deposits, Southeastern Arizona: Insights into Regional Shortening Style, Magnitude of Uplift, and Implications for Exploration: in Econ. Geol. v.115, pp. 153-175.
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Hehnke, C., Ballantyne, G., Martin, H., Hart, W., Schwarz, A. and Stein, H., 2012 - Geology and Exploration Progress at the Resolution Porphyry Cu-Mo Deposit, Arizona: in Hedenquist, J.W., Harris, M. and Camus, F. (Eds.), 2012 Geology and Genesis of Major Copper Deposits and Districts of the World: A Tribute to Richard H. Sillitoe, Society of Economic Geologists, Denver, Special Publication 16, Ch. 7, pp. 279-299.
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Manske S L, Paul A H 2002 - Geology of a major new porphyry Copper center in the Superior (Pioneer) district, Arizona: in Econ. Geol. v97 pp 197-220
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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