projects > cueva del chacho uranium
The Cueva del Chacho property of is a tenement running 9,250 m N-S by 3,243 m E-W located approximately 70 km south-southwest of the provincial capital city of La Rioja adjacent to a major paved road. The 3,000 hectare (11.5 sq mi) claim is immediately adjacent to a major highway in low-lying desert terrain accessible year round. The property lies on-trend, 8 kms north of the Los Colorados Mine, on a regional sedimentary reduction-oxidation boundary where approximately 55,000 kg of uranium concentrates were produced from classic sedimentary roll-fronts between 1992 and 1996 by a local Argentine company under contract to the Argentine National Atomic Energy Commission (CNEA).
In February 2010, Pacific Bay reported soil and rock samples strongly anomalous in Rare Earth Elements, with values up to 832 ppm Cerium and 338 ppm Lanthanum. The strongly anomalous samples were taken in 2006 over zones of elevated radioactivity in an area of poor outcrop exposure during a uranium exploration reconnaissance program. Most of the radioactivity was determined to be caused by Thorium, but the two REE results included in the multi-element analysis package, Lanthanum and Cerium, were not reviewed at the time.
A follow-up reconnaissance program carried out in April 2010 by Dr. Richard Culbert, Ph.D., P.Eng. yielded encouraging results. Dr. Culbert stated:
"Initial collection of 39 samples over an area of roughly 6 square kilometers on the Cueva del Chacho Property has returned strong Rare Earth Element values in both coarse sediments and in leucocratic granites, with total REE values of up to a quarter of a percent . This summation does not include Yttrium, whose values ranged to over 700 ppm. The hosts and controls of this mineralization are now better understood as a model for future exploration, and the property has been expanded accordingly.
Unlike many REE concentrations, the heavier rare earths have not been depleted, with the exception of Europium. Ratios of heavier to lighter elements, have maintained values similar to those reported for crustal averages. The heavy rare earths comprise an average of 29% of the total rare earths, ranging up to 71% if Yttrium is included, and an average of 14% with a high of 44% if it is not. The sampling also returned uranium values as high as 551 ppm in carbonaceous phyllites and those of zirconium to 3710 ppm, with samples over a quarter of a percent Zr in grits, phyllites and intrusives."
Download Dr. Culbert's detailed geological report related to his findings.
Based on geological field work done in the 1970's by the CNEA, the Los Colorados uranium mine and the surface radiometric anomalies on the Cueva del Chacho claim are hosted in a series of gently dipping continental sediments of the Carboniferous age Saladillo Fm. which, together with redbeds of the Permian Patquía Fm., overlie Paleozoic granite that is the likely source of the uranium. The Saladillo Fm. outcrops consist of a succession of mostly siltstones and arkosic sandstones with lesser carbonaceous shales and thin conglomerates. These Saladillo Fm. sediments host radiometric anomalies in multiple stratigraphic horizons throughout the approximately 420 m of section exposed on the Cueva del Chacho property and can be seen in purplish-gray colors on the Landsat photo. The overlying redbeds of the Permian age Patquía Fm. are thoroughly oxidized and show up as a striking orange color on the photo. To the north and east of the Cueva del Chacho property the underlying, strongly fractured Paleozoic age granites of the Paimán Fm. can be seen forming the extreme southern tip of the prominent Sierra de Velazco Massif.
The regional oxidation- reduction front within the Carboniferous age clastic sediments of the Saladillo Fm. which was responsible for ore deposition at the Los Colorados Mine very clearly extends to the north into the Cueva del Chacho property. PacBay geologists believe that the discovery potential for additional roll front uranium deposits similar to the roll front exploited in the 1980' and 1990's at the Los Colorados Mine is potentially much greater on the Cueva del Chacho property due to the greater thickness of exposed favorable stratigraphy hosting reported radiometric anomalies and uranium minerals at multiple stratigraphic horizons at Cueva del Chacho.