A new porphyry-type mineralization in Cañada Honda district, San Luis, Argentina

MARTÍN ARCE; NILDA URBINA; PATRICIA SRUOGA

Potsdam, Alemania

Congreso; 19th Colloquium on Latin American Geosciences (LAK); 2005

A porphyry copper deposit has been recognized at Mario in the southwestern Cañada Honda district within the Tertiary metallogenic belt of the Sierras Pampeanas of San Luis, central west Argentina. The copper deposit is part of the NW-SE-trending volcanic belt constructed during the late Miocene to late Pliocene period. Tertiary volcanism took place immediately prior to, and during the final stages of slab flattening between 27º and 33º S. Elsewhere in the belt andesitic and trachytic magmas belonging to normal to high-K calc-alkaline and shoshonitic series are emplaced as domes, lava flows, dykes, and volcaniclastic rocks hosted by the Precambrian to Paleozoic igneous-metamorphic basement. At the Cañada Honda district the volcanic rocks cropping out in the surrounding area of Mario deposit comprise hornblende-bearing andesites, autoclastic breccias, ignimbritic and base surge pyroclastic deposits, sanidine-bearing trachytic lavas, domes and the latest emplacement of a dyke. The outcrop of Mario is restricted to a bulldozer trench 180 m long, with most of the inferred extent of the deposit concealed beneath the present surface. The mineralization hosted by hornblende-bearing andesitic rock occurs as a multidirectional stockwork and disseminations. Chalcopyrite with traces of bornite are coincident with the stockwork of quartz veinlets. Abundant pyrite is present in dominantly disseminated form. Hematite and magnetite occur abundantly disseminated in altered rock, and in veinlets alone or with quartz. Much of the hematite is developed by hypogene martitization of hydrothermal and accessory magmatic magnetite, although minor specular hematite is also present. The associated hydrothermal alteration is intense over an area of  approximately 300 m wide and 400 m long and comprises K silicate alteration (biotite accompanied by K feldspar) and peripheral propylitic (chlorite, calcite, epidote) assemblages. Intermediate argillic (sericite, chlorite, calcite, smectite) and sericitic (sericite, quartz, pyrite) alterations are believed to have overprinted and partially destroyed earlier K silicate alteration. Much of the hydrothermal quartz is present as stockwork veinlets which were formed along with biotite-rich K silicate alteration. Chalcopyrite + pyrite ± magnetite are also thought to have been introduced with early K silicate alteration. The isolated remnants of K silicate alteration and the strongly intermediate argillic/sericitic overprinted alteration at Mario suggest that the present level of erosion is showing the shallow parts of a porphyry copper deposit and can be taken as evidence to expect a well-developed K silicate alteration at deeper levels. Supergenic products are present as iron oxides (goethite and hematite) and copper carbonates (malachite and azurite), in the form of coatings and as complete replacements of sulfides from quartz-veinlets stockwork in the upper part of Mario.Finally, Mario deposit is located 1200 m east from Diente Verde gold-rich porphyry copper deposit and was emplaced approximately at the same topographic level. The relation between both deposits is not yet well defined, but mineralogical affinities, and spatial and temporal linkages suggest that Mario may be genetically associated with the main magmatic event at Diente Verde. Therefore, the recently discovered Mario porphyry copper deposit may be considered to enhance the exploration potential of Cañada Honda district. A porphyry copper deposit has been recognized at Mario in the southwestern Cañada Honda district within the Tertiary metallogenic belt of the Sierras Pampeanas of San Luis, central west Argentina. The copper deposit is part of the NW-SE-trending volcanic belt constructed during the late Miocene to late Pliocene period. Tertiary volcanism took place immediately prior to, and during the final stages of slab flattening between 27º and 33º S. Elsewhere in the belt andesitic and trachytic magmas belonging to normal to high-K calc-alkaline and shoshonitic series are emplaced as domes, lava flows, dykes, and volcaniclastic rocks hosted by the Precambrian to Paleozoic igneous-metamorphic basement. At the Cañada Honda district the volcanic rocks cropping out in the surrounding area of Mario deposit comprise hornblende-bearing andesites, autoclastic breccias, ignimbritic and base surge pyroclastic deposits, sanidine-bearing trachytic lavas, domes and the latest emplacement of a dyke. The outcrop of Mario is restricted to a bulldozer trench 180 m long, with most of the inferred extent of the deposit concealed beneath the present surface. The mineralization hosted by hornblende-bearing andesitic rock occurs as a multidirectional stockwork and disseminations. Chalcopyrite with traces of bornite are coincident with the stockwork of quartz veinlets. Abundant pyrite is present in dominantly disseminated form. Hematite and magnetite occur abundantly disseminated in altered rock, and in veinlets alone or with quartz. Much of the hematite is developed by hypogene martitization of hydrothermal and accessory magmatic magnetite, although minor specular hematite is also present. The associated hydrothermal alteration is intense over an area of  approximately 300 m wide and 400 m long and comprises K silicate alteration (biotite accompanied by K feldspar) and peripheral propylitic (chlorite, calcite, epidote) assemblages. Intermediate argillic (sericite, chlorite, calcite, smectite) and sericitic (sericite, quartz, pyrite) alterations are believed to have overprinted and partially destroyed earlier K silicate alteration. Much of the hydrothermal quartz is present as stockwork veinlets which were formed along with biotite-rich K silicate alteration. Chalcopyrite + pyrite ± magnetite are also thought to have been introduced with early K silicate alteration. The isolated remnants of K silicate alteration and the strongly intermediate argillic/sericitic overprinted alteration at Mario suggest that the present level of erosion is showing the shallow parts of a porphyry copper deposit and can be taken as evidence to expect a well-developed K silicate alteration at deeper levels. Supergenic products are present as iron oxides (goethite and hematite) and copper carbonates (malachite and azurite), in the form of coatings and as complete replacements of sulfides from quartz-veinlets stockwork in the upper part of Mario.Finally, Mario deposit is located 1200 m east from Diente Verde gold-rich porphyry copper deposit and was emplaced approximately at the same topographic level. The relation between both deposits is not yet well defined, but mineralogical affinities, and spatial and temporal linkages suggest that Mario may be genetically associated with the main magmatic event at Diente Verde. Therefore, the recently discovered Mario porphyry copper deposit may be considered to enhance the exploration potential of Cañada Honda district. A porphyry copper deposit has been recognized at Mario in the southwestern Cañada Honda district within the Tertiary metallogenic belt of the Sierras Pampeanas of San Luis, central west Argentina. The copper deposit is part of the NW-SE-trending volcanic belt constructed during the late Miocene to late Pliocene period. Tertiary volcanism took place immediately prior to, and during the final stages of slab flattening between 27º and 33º S. Elsewhere in the belt andesitic and trachytic magmas belonging to normal to high-K calc-alkaline and shoshonitic series are emplaced as domes, lava flows, dykes, and volcaniclastic rocks hosted by the Precambrian to Paleozoic igneous-metamorphic basement. At the Cañada Honda district the volcanic rocks cropping out in the surrounding area of Mario deposit comprise hornblende-bearing andesites, autoclastic breccias, ignimbritic and base surge pyroclastic deposits, sanidine-bearing trachytic lavas, domes and the latest emplacement of a dyke. The outcrop of Mario is restricted to a bulldozer trench 180 m long, with most of the inferred extent of the deposit concealed beneath the present surface. The mineralization hosted by hornblende-bearing andesitic rock occurs as a multidirectional stockwork and disseminations. Chalcopyrite with traces of bornite are coincident with the stockwork of quartz veinlets. Abundant pyrite is present in dominantly disseminated form. Hematite and magnetite occur abundantly disseminated in altered rock, and in veinlets alone or with quartz. Much of the hematite is developed by hypogene martitization of hydrothermal and accessory magmatic magnetite, although minor specular hematite is also present. The associated hydrothermal alteration is intense over an area of  approximately 300 m wide and 400 m long and comprises K silicate alteration (biotite accompanied by K feldspar) and peripheral propylitic (chlorite, calcite, epidote) assemblages. Intermediate argillic (sericite, chlorite, calcite, smectite) and sericitic (sericite, quartz, pyrite) alterations are believed to have overprinted and partially destroyed earlier K silicate alteration. Much of the hydrothermal quartz is present as stockwork veinlets which were formed along with biotite-rich K silicate alteration. Chalcopyrite + pyrite ± magnetite are also thought to have been introduced with early K silicate alteration. The isolated remnants of K silicate alteration and the strongly intermediate argillic/sericitic overprinted alteration at Mario suggest that the present level of erosion is showing the shallow parts of a porphyry copper deposit and can be taken as evidence to expect a well-developed K silicate alteration at deeper levels. Supergenic products are present as iron oxides (goethite and hematite) and copper carbonates (malachite and azurite), in the form of coatings and as complete replacements of sulfides from quartz-veinlets stockwork in the upper part of Mario.Finally, Mario deposit is located 1200 m east from Diente Verde gold-rich porphyry copper deposit and was emplaced approximately at the same topographic level. The relation between both deposits is not yet well defined, but mineralogical affinities, and spatial and temporal linkages suggest that Mario may be genetically associated with the main magmatic event at Diente Verde. Therefore, the recently discovered Mario porphyry copper deposit may be considered to enhance the exploration potential of Cañada Honda district.