The San Jorge porphyry copper deposit, Mendoza, Argentina: a combination of orthomagmatic and hydrothermal mineralization |
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| Authors: | W C Williams E Meissl J Madrid B C de Machuca |
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| Abstract: | The San Jorge porphyry copper deposit (SJPCD) is hosted by Carboniferous clastic sedimentary rocks and Permian intrusions located within the Permo-Triassic belt of Chile and Argentina. Its hypogene mineralization and alteration are products of superposed orthomagmatic and hydrothermal events that were strongly fault controlled. Copper related to orthomagmatic processes includes disseminated chalcopyrite in the matrix of porphyritic granodiorite and andesite, and chalcopyrite with tourmaline and quartz in breccias, both of which have accompanying potassic alteration. Soon thereafter, disseminated chalcopyrite is associated with a structurally controlled silicification of the sedimentary sequence. Finally, multiple episodes of hydrofracturing, probably driven by a deep-seated intrusion, deposited sulfide minerals in veinlets throughout the sedimentary sequence; the centers of these systems are characterized by potassic alteration. Total sulfides, which include chalcopyrite, pyrite, arsenopyrite, and pyrrhotite, and pyrite:chalcopyrite form a linear NNE trend, parallel to the main faults. Quartz–sericite is the dominant alteration and is ubiquitous. Zones of potassic alteration can be delineated even though phyllic alteration can be superposed. Much of the system evolved under reducing conditions. Despite uplift along a reverse fault during the Tertiary, and subsequent erosion, the system is preserved at high levels. Supergene processes redistributed copper in secondary oxides and sulfides. These processes were more effective where the deposit is covered by unconsolidated alluvial sediments. The unique history of the San Jorge deposit renders it an important variation of porphyry copper-style mineralization. |
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| Keywords: | San Jorge porphyry copper deposit orthomagmatic Permo-Triassic belt |
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