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Juramento

Salta, Argentina

Main commodities: Cu Ag
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The Juramento stratabound, sediment hosted copper-silver deposit is located in Salta province, northwest Argentina, approximately 1250 km NW of Buenos Aires and 55 km SE of the capital Salta.

The deposit is hosted by the Cretaceous to Early Tertiary Salta rift basin, part of an extensive system that extends into Chile, Bolivia, Peru and Paraguay. The deposit is on the south-eastern margin of the Salta-Jujuy basment high that is surrounded by rift sediments.

The deposit comprises fine-grained disseminated base-metal sulphides within marine to lacustrine greybeds of the basal whitish Late Cretaceous Lecho Sandstone and shallow-water carbonates of the overlying Maastrichtian Yacoraite Formation, which in turn overlie the thick syn-rift red bed sequence of the Pirgua Subgroup.

The Pirgua Subgroup commences with a thick sequence of high energy alluvial sediments overlain by fluvial, aeolian and distal playa sediments. Flood basalts are intercalated with the red beds in various levels. Subsequent, post-rift sediments comprise shallow-water sediments that transgressed from red-beds to light-grey basal shore sands of the Lecho Formation, to an overlying limestone-calcareous oolitic stromatolitic dolomitic siltstone unit, the Yacoraite Formation. The Yacoraite Formation contain minor evaporites in the form of gypsum/anhydrite and pseudomorphs. These are overlain by a number of hangingwall fluvial-lacustrine silts and claystones.

The host reduced greybeds are the basal sandstone and overlying oolitic and stromatolitic units of the Yacoraite Formation. These beds are carbonaceous and originally contained very fine-grained, disseminated, syn-diagenetic pyrite. They are interpretted to have been sufficiently porous and permeable in early diagenetic time to allow infiltration of metalliferous fluids from the underlying redbeds, resulting in the observed progressive replacement of in situ pyrite by base-metals to produce new sulphides, specifically sphalerite, galena, argentiferous tetrahedrite, and copper-rich sulphides. The Cu sulphides commenced with chalcopyrite, followed by bornite, and finally chalcocite as more Cu was progressively added.

Sulphur isotope studies indicate that a portion of the sulphur of ore-stage sulphides is isotopically heavier than that of pyrite, possibly contributed by associated gypsum.

There is a zonation within the peneconformable mineralised body, both vertically and laterally, of the ore-stage sulphides through the mineralised zones, from cupriferous sulphides at lower stratigraphic levels to Pb- and Zn-rich mineralisation at higher levels, with unreplaced pyrite remaining within upper Yacoraite units.

The influx of ore-stage metals terminated with a silicification event that effectively sealed the host carbonates.

The total drill-indicated inferred resource in 1998 was quoted as 44.7 Mt at 0.8% Cu and 21.8 g/t Ag (Alexander Mining plc, 2005) and a reserve of 11 Mt @ 0.83% Cu, 19 g/t Au (Durieux and Brown, 2007).

The most recent source geological information used to prepare this summary was dated: 2007.    
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:
Durieux C G and Brown A C,  2007 - Geological context, mineralization, and timing of the Juramento sediment-hosted stratiform copper–silver deposit, Salta district, northwestern Argentina : in    Mineralium Deposita   v42 pp 879-899


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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