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Santa Cruz |
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Arizona, USA |
| Main commodities:
Cu Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Santa Cruz porphyry copper resource is located up to 10 km to the southwest of the Sacaton deposit in southern Arizona where it forms a ridge of bedrock buried below 240 to 1100 m of un-indurated conglomerates.
Mineralisation and alteration associated with the deposit extends over an area that is more than 11 km in length by 1.5 km in width. Its present configuration and depth of burial are mainly the result of horst and graben faulting, tilting and low angle faulting associated with the Mid-Tertiary extension and subsequent 'basin and range' tectonics. Apart from a small outcrop near the Sacaton mine, the deposit is covered by up to 1100 m of post-mineralisation alluvium, conglomerate, sandstone and minor volcanic rocks (Kreis, 1995).
Host rocks in and around the deposit include the Mesoproterozoic Oracle Granite (82%), dykes of Laramide biotite-quartz-feldspar porphyry of quartz monzonite composition (15%), and dykes of Proterozoic diabase (dolerite) and other rock types. The Laramide porphyry dykes and mineralisation are of Late Cretaceous age. Hypogene sulphides include chalcopyrite, pyrite and local bornite. The primary mineralisation and alteration is zoned with an innermost core, surrounded by a chalcopyrite zone and a pyritic periphery. The core and inner chalcopyrite zones have been subjected to alteration that produced an assemblage of biotite-orthoclase-quartz, while the outer chalcopyrite and pyrite zones have undergone quartz-sericite alteration (Kreis, 1995).
A complete supergene profile comprising leached capping, oxide copper zone and sulphide enrichment blanket are preserved. Normal faults on either side of the deposit cut the supergene profile and locally juxtapose an allochthonous block of Mid-Tertiary volcanic and volcaniclastic rocks. These Mid-Tertiary rocks are not hydrothermally altered, but do host atacamite and chrysocolla mineralisation which extends down into the structurally underlying Laramide and pre-Laramide hosts. Copper is interpreted to have been transported into the allochthonous block by supergene solutions to form an 'exotic' deposit. No exotic mineralisation has however, been observed within the overlying alluvium and gravels. The main episode of enrichment is older than the faults which bound the allochthonous block of volcanic and volcaniclastic rocks, although the timing of the initial supergene activity with respect to Mid-Tertiary volcanism is uncertain. It is likely that supergene processes were active both before and after the Mid-Tertiary Orogeny, but had ceased before deposition of the alluvium and gravels.
The combined Santa Cruz and Sacaton deposits comprise a resource of 1450 Mt @ 0.59%Cu, 0.011 g/t Au.
The most recent source geological information used to prepare this decription was dated: 2004.
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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Vikre P G, Graybeal F T and Koutz F R, 2014 - Concealed Basalt-Matrix Diatremes with Cu-Au-Ag-(Mo)-Mineralized Xenoliths, Santa Cruz Porphyry Cu-(Mo) System, Pinal County, Arizona: in Econ. Geol. v.109 pp. 1271-1289
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| References in PGC Publishing Books: | |
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Cook S S and Porter T M, 2005 - The Geologic History of Oxidation and Supergene Enrichment in the Porphyry Copper Deposits of Southwestern North America, in Porter T M, (Ed), Super Porphyry Copper and Gold Deposits: A Global Perspective, v1 pp 207-242
 Abstract
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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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