San Juan, Argentina

Main commodities: Au Ag
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The Veladero orebody is located in San Juan Province, Argentina, around 220 km north-west of the city of San Juan, approximately 150 km east of La Serena on the Pacific coast of Chile, and is immediately to the south of the Pascua-Lama deposit (see the El Indio District and Pascua record for regional geology and setting).

It is largely hosted by late Oligocene and middle Miocene volcanic and volcaniclastic rocks, particularly the poorly bedded subaerial heterolithic breccias, volcaniclastic rocks and subordinate air-fall tuffs of the middle Miocene Cerro de las Tórtolas Formation, dacitic flows, tuff and sandstone of the Oligocene Tilito Formation, and to a lesser degree the rhyolitic tuffs of the Permian Guanaco Sonso Formation, but also to a lesser degree by the underlying Permian rhyolitic pyroclastic rocks. The Miocene host rocks unconformably overlie the deformed and structurally interleaved late Oligocene and late Palaeozoic rocks which form a steeply dipping fold and thrust belt that was cut and eroded by the regional Miocene Frontera-Deidad paleogeomorphic surface.

At Veladero, the Cerro de las Tórtolas Formation, which was deposited across the Frontera-Deidad surface, is an approximately 16 Ma vent complex characterised by domes and the coeval sub-volcanic Infiernillo intrusive unit which include a massive, brecciated core of heterolithic vent facies tuffisite. These are surrounded across a contact zone by coarse, poorly sorted volcaniclastic breccia that grade eastward onto a volcaniclastic apron of bedded and reworked detritus with interbedded air-fall tuff and local lacustrine tuffaceous sandstone and siltstone. Large parts of the deposit are covered by up to 150 m of colluvium.

The mineralised system occurs as silicified volcanic breccias at the core of a 9 sq. km high sulphidation alteration zone controlled by both stratigraphy and structural trends. The deposit takes the form of a broad, disseminated, 3 km long blanket following a structural trend of 345° which also controls the orientation of the sub-volcanic complex and parallels steeply dipping faults in rocks beneath the Cerro de las Tórtolas Formation.

This NNW elongated silicified horizon cuts the host stratigraphy and has a subhorizontal top ranging between 4200 and 4400 m asl and is at the approximate elevation or slightly below the 14.5 to 12 Ma Azufreras-Torta surface, that controlled formation of the El Indio, Tambo and Pascua-Lama high-sulphidation deposits also within the El Indio belt. This upper limit is inferred to represent the paleowater table at the time of ore formation.

At Veladero, fine-grained disseminated, oxidised gold mineralisation associated with hematite, goethite and jarosite, occurs within the silicified horizon as two ore zones, Filo Federico to the north and Amable to the south.

The intense silicification with minor hypogene alunite is flanked outward by argillic and propylitic mineral assemblages typical of high-sulphidation epithermal deposits. Above the silicified horizon, the rocks are commonly leached, porous, and contain native sulphur in voids, representing a steam-heated altered zone above the water table.

Late Miocene 40Ar/39Ar ages between 11 and 10 Ma on alunite from the Filo Federico zone and from uneconomic prospects nearby suggest that advanced argillic alteration and possibly the gold deposition is 5 m.y. younger than the ~16 Ma host rocks.

At the end of 2004 proven mineral resources were of 397 t (12.9 Moz) of contained gold comprising 405 Mt @ 0.98 g/t Au. The probable mineral resource comprised 22 Mt @ 0.64 g/t Au, accounting for another 14 t (0.45 Moz) Au.

The most recent source geological information used to prepare this summary was dated: 2005.    
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.


  References & Additional Information
   Selected References:
Charchaflie D, Tosdal R M and Mortensen J K,  2007 - Geologic Framework of the Veladero High-Sulfidation Epithermal Deposit Area, Cordillera Frontal, Argentina : in    Econ. Geol.   v102 pp 171-192
Holley, E.A., Bissig, T. and Monecke, T.,  2016 - The Veladero High-Sulfidation Epithermal Gold Deposit, El Indio-Pascua Belt, Argentina: Geochronology of Alunite and Jarosite : in    Econ. Geol.   v.111 pp. 311-330
Holley, E.A., Monecke, T., Bissig, T. and Reynolds, T.J.,  2017 - Evolution of High-Level Magmatic-Hydrothermal Systems: New Insights from Ore Paragenesis of the Veladero High-Sulfidation Epithermal Au-Ag Deposit, El Indio-Pascua Belt, Argentina: in    Econ. Geol.   v.112, pp. 1747-1771.

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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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