EXPLORATION - NON-GOLD

LASCANO CU/AU PROJECT

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Overview:

Orosur Mining Inc is seeking a joint venture partner for this exciting opportunity. The Lascano Project is located 250km north-east of the capital city of Montevideo in the department of Rocha. Access to the project from Montevideo is by route 8 then 13 to the city of Lascano.

The Lascano conceptual exploration target is considered to have the potential to host significant alkaline intrusion related rare earth, niobium, thorium and zirconium plus copper and gold ores. Orosur holds exploration and prospecting permits over the geophysical anomaly totaling 353,000 hectares.

Historic work:

• 1970´s: Regional geophysic survey by the Uruguayan government, and detection of a positive magnetic and gravity anomaly coincident with the center of the Cretaceous Merín basin.
• May 2002: Orosur first diamond drillhole (LMD1) to test the anomaly
• December 2005 – February 2006: Air FTG and Air Magnetics by Bell Geospace. Four 20 to 30 km in diameter circular positive magnetic and gravity anomalies were identified composing the regional anomaly.
• December 2007 – November 2008: Nine diamond drill holes in two separate campaigns, over and around the principal circular feature, named Lascano-East. Identification of Cu and Au anomalies.
• January 2008 – February 2010: MS thesis at Oregon State University fully sponsored by Orosur Mining Inc. entitled “Geology of the Cretaceous Lascano-East intrusive complex: Magmatic evolution and mineralization potential of the Merín basin, Uruguay” by Federico Cernuschi, advised by Dr. John Dilles. This study has identified an alkaline province in the basin and the potential of the project to host niobium, zirconium, thorium and rare earths mineralization.

Drilling Programs:

To date drilling has been focused on the central circular geophysical anomaly named Lascano-East. 7321 meters in 10 holes were completed between 2007 – 2008 to investigate the geophysical features and associated structures and search for signs of mineralization. Widespread hydrothermal alteration was encountered in intrusive and volcanic rocks along with some local, anomalous copper-gold sulphide mineralization.

Main conclusions from the MS Study:

Geologic Setting and Geophysics:

A) Regional gravity from Uruguayan government, B) airborne reduced to pole magnetic and C) airborne gravity image from OMI survey, showing the location of inferred intrusive complexes and drillhole collars in the Merín basin (simplifed from Ellis and Turner, 2006; taken from Cernuschi, 2010a)

The Merín Basin is a Cretaceous aborted–rift in eastern Uruguay composed of sub-alkaline Parana basaltic flows, 1-2km thick, shallow mildly alkaline to alkaline intrusive complexes, minor sediments and later rhyolitic ignimbrites. Ar-Ar dates of the intrusive, flows and pyroclastic lithologies fall into a narrow band from 133-127 Ma.

The intrusive rocks occur as four sub-circular complexes each being 20-30 km in diameter based on gravity and concentric magnetic anomaly patterns. The four complexes, named Valle Chico, Lascano-West, Lascano-East and San Luis, are roughly aligned in a NE-SW trend paralleling the margins of the Merin Basin. At Valle Chico, highly magnetic, mildly alkaline syenites are widespread while Lascano East is characterized by mostly alkaline gabbros and trachytic dikes and lavas. The Lascano-West and San Luis complexes are concealed beneath recent shallow terrestrial sediments, and their gravity highs are inferred to be caused by mildly alkaline-alkaline dikes and sills.  Possibly large, deep seated mafic alkaline intrusives are responsible for the bulk of the gravity anomaly in each center. 

In all complexes a deep source (+1km) has been modeled for the gravity and a shallow source (-1km) for the magnetics (Reytmeyer 2001; Ellis and Turner 2007) with the latter reflecting the distribution of basalt piles as well as gabbroic and syenitic dykes and sills including ring dykes

Magmatism at Lascano is sourced on interplay of shallow mantle sources with abundant crustal contamination for the sub-alkaline rocks (almost identical to Paraná rocks), and a deeper, ocean island basalt-like sources for the mildly-alkaline and alkaline rocks. Magmatism could be linked to the Tristan da Cunha mantle plume and it is possible that a metasomatized mantle was the main source area.

At Lascano-East where all the Orosur drilling took place, the interlayered basalts and rhyolitic ignimbrites cut by alkaline gabbroic and trachytic dikes and sills display potassium and a younger over-imprinted intermediate argillic alteration. Quartz-pyrite veins and fluorite veins are found locally especially in altered rhyolitic ignimbrites containing disseminated pyrite and these rocks kick up slightly in gold (to 11 ppb compare to a background of up to 3 ppb in fresh rock), bismuth (8 ppm), thallium (7 ppm) and molybdenum (7ppm). Copper is mildly anomalous (up to 813 ppm) at some of the basalt-intrusive contacts located in narrow quartz-calcopyrite veins.

Conceptual model of Lascano-East, taken from Cernuschi (2010a)

The only known outcropping mineralization in the Merin basin are fluorite-quartz-manganite-epidote-barite veins that cuts Precambrian granite-gneisses near the southern faulted edge of the basin (reserves of ca. 4500 tonnes at 80% CaF2, Bosse et al. 1982). At least some of these veins are enriched in yttrium (ca. 0.5%, Rossini & Arana, 2002), tungsten (100 ppm) and barium (4434 ppm). Epithermal quartz veins with tabular calcite blades replaced by quartz were identified nearby.

Mineralization potential:

Orosur has barely scratched the surface of this large, and potentially economically interesting cluster of alkaline intrusive complexes located near sea level in an easily accessible part of eastern Uruguay, an economically advanced and stable country.

The Merín basin has potential of hosting concealed carbonatites and a mineralization potential including niobium, zirconium, phosphate, uranium, thorium and rare earths based on common ores of mineralized complexes from Brazil and Namibia. The Basin has overlapping ages, geochemical composition and was emplaced near the Damaraland and Luderitz alkaline provinces in Namibia and some complexes in southern brazil as Poço de Caldas, with known mineralized carbonatites and syenites, hosting niobium, zirconium, phosphate, uranium, thorium and rare earths.

In comparison with the Namibian complexes, which are mostly deeply eroded, the Merín basin complexes are well preserved, enlarging the possibilities of preservation of the mineralized intruded roof-wall rock. This difference in the erosion levels can be explained by the uplift of the African plate after the break up of Gondwana, due to changes in the pole of rotation in comparison with a mostly stable South American plate. However, variations in the level of exposure are recognized in the Merín basin and subsidence of the basin due to the emplacement of mafic intrusions may have played a role as well.

Fluorite deposits are also typical deposits associated with the Cretaceous alkaline Magmatism in Brazil and Namibia. Larger ores than the known one at present time, together with associated elements such as Y and W, are possibility at least in the basin faulted edge contact against the Precambrian wall-rock.

Gold and Copper mineralization are not typical in the known mineralized alkaline complexes from Brazil and Namibia. However there are a potential ore in Lascano-East based on results from drilling.

Paleogeographical reconstruction (Franke et al. 2007) of the breaking up of Gondwana at ca. 133 Ma and showing location of broadly coeval magmatism. Taken from Cernuschi (2010a)

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