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Updates on the Rio Grande Project
For the latest updates on the Rio Grande project, please visit our Press Releases page.
(last updated on 29/04/2008)
 The Rio Grande Cu-Au-(Ag) porphyry project is located in the high Puna of NW Argentina, 450km west of the city of Salta. The project was discovered by Mansfield Minerals during regional prospecting in late 1999. The Rio Grande project is very favourably located along the prominent NW-trending Archibarca Lineament which also controls the location of the world-class Escondida porphyry Cu deposit (BHP-Billiton), a short 150 km to the west-northwest in Chile. The Rio Grande project shares many geologic similarities with the large Bajo de Alumbrera porphyry Cu-Au deposit (Xstrata Copper) which is located approximately 300km to the south, along a similar west-northwest trending regional structural lineament. The Rio Grande project is a 50/50 joint venture between Mansfield Minerals Inc. (TSX V.MDR) and Antares Minerals Inc. (TSX V.ANM) with Antares as the operator.
Cu-Au-(Ag) mineralization at Rio Grande occurs within a distinct 2-km diameter ring-shaped fracture zone defined by IP chargeability, as well as Cu- and Au-soil geochemical anomalies. Systematic surface trenching shows the majority of the ring structure is mineralized in several zones/targets; moving clockwise from the north these zones are (a) North, (b) Sofia, (c) Discovery, (d) Southwest, and (e) #7. The majority of the past and current exploration has focussed on the better exposed Discovery and Sofia zones, however recent drilling on the North and #7 zones has intersected significant mineralization thereby increasing the area of known mineralization by more than 50%. A total of 29,606 m of drilling have been completed at the Rio Grande project as of year-end 2007.
Mineralization consists of partially oxidized chalcopyrite-magnetite hosted in fractures and breccia-infillings associated with variable degrees of K-feldspar, calc-silicate (diopside, actinolite), and secondary biotite alteration. Better mineralized intervals are typically associated with crackle breccia zones which locally grade into heterolithic milled-matrix breccias. Some of the better mineralized intercepts encountered to-date are:
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RGA-07-34 (Sofia Zone): 189m @ 0.70% Cu, 0.67g/t Au, 11.1 g/t Ag
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RGA-06-26 (Sofia Zone): 158m @ 0.46% Cu, 0.51g/t Au, 4.2 g/t Ag
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RGA-06-24 (Sofia Zone): 128m @ 0.47% Cu, 0.71g/t Au, 4.4 g/t Ag
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RGA-07-40 (Discovery Zone): 103m @ 0.58% Cu, 0.75g/t Au, 13.1 g/t Ag
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RGA-07-56 (#7 Zone): 135m @ 0.53 Cu, 0.65g/t Au, 8.9 g/t Ag
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RGA-07-43 (North Zone): 151m @ 0.40% Cu, 0.46g/t Au, 12.4 g/t Ag
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RGA-07-48 (North Zone): 152m @ 0.44% Cu, 0.41g/t Au, 5.32 g/t Ag
The joint venture partners are currently in the midst of the 2008 drilling campaign on this, potentially the next world-class porphyry Cu-Au-(Ag) discovery.
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