The sudoite occurs with illite, kaolinite and hematite, which together comprise the classic alteration suite seen in the Athabasca Basin. The Athabasca Basin is host to approximately one third of the world’s uranium resources.
“U3O8 Corp. has identified alteration zoning in the Roraima Basin that is characteristic of unconformitystyle uranium deposits in the Athabasca Basin,” said Richard Spencer, U3O8’s president and chief executive officer. “This is the first time that these key alteration minerals have been detected in the Roraima and underscore the potential of the basin for unconformity-related uranium. These alteration results augment a diverse data set that we are using to rank our targets so that the most compelling areas can be drilltested when financial markets improve.”
The archived core in which the alteration has been found was drilled by a company exploring for gold in the Roraima Basin in the mid-1990’s, and provides a cost-effective means of defining the most prospective parts of U3O8’s wider target areas. U3O8 was granted access to over 10,000
metres of this core from 41 bore holes that were archived by the Guyana Geology and Mines Commission. U3O8 geologists re-logged the core and identified the characteristic alteration with a TerraSpec Infrared Spectrometer. An independent alteration mineralogy expert verified the identification of these key minerals.
Exploration Approach
By analogy with unconformity-related uranium deposits in the Athabasca, U3O8 has defined targets that lie near the floor of the Roraima Basin where regional faults cut potentially graphite-bearing rocks in the underlying basement. Eight targets were initially identified, some of which are supported by radiometric anomalies from U3O8’s 2007 heliborne radiometric survey. Additional targets were identified and covered by an airborne geophysics survey contracted by U3O8 in late 2008.
Some targets lie within a few kilometres of prior drilling from which archived core is available for study. Alteration zoning identified in this core is being used to evaluate these targets. Targets that are not in close proximity to prior drilling are being assessed with field-based ground radiometric surveys and rockchip sampling to detect alteration and zoning in chemical pathfinder elements.
To date, five targets have been evaluated and field work is ongoing on a sixth. Results of this preliminary evaluation are discussed below. As the evaluation of each area is completed, it will be prioritized in terms of its potential to host unconformity-related uranium mineralization. Drilling of the targets with the most potential is expected to commence in due course as financial markets stabilize.
Overview of Target Results To Date
“Target 21” was defined on the basis of intense clay alteration (sudoite grading into illite) identified in archived core from a bore hole that was drilled approximately two kilometres south of a regional fault that is evident in magnetic data from the 2008 geophysics survey. The core also contains hematite that occurs above and below a central zone of iron sulphate.
The extensive sudoite and illite alteration could constitute the outer part of an alteration system that is related to the regional fault, analogous to the alteration systems at the McArthur River and the Key Lake deposits in the Athabasca. Hematite is an important pathfinder alteration mineral in the Athabasca, while the significance of iron sulphate in the archived core is not clear at this stage. Target 21 lies at a depth of about 200 metres below surface. U3O8’s interpretation of Target 21 is conceptual in nature, and aims to provide context to the observed clay alteration and iron minerals.
“Target 22” is associated with a cluster of radiometric anomalies that lie adjacent to a regional fault, which can be traced beneath the Roraima Basin in magnetic data. Archived core from a bore hole drilled two kilometres east of the radiometric anomalies contains sudoite, kaolinite and highaluminum muscovite clay alteration. Hematite occurs with the sudoite, and the core shows extensive silicification. The sudoite-kaolinite zone in the archived core is located some 400 metres vertically above the unconformity, and is reminiscent of alteration zoning that encloses the Athabasca’s McArthur River deposit where chlorite overlies kaolinite about 300 metres above the deposit.
U3O8 current interpretation is that the archived core from the bore hole near Target 22 was drilled in the outer parts of an alteration system that is most likely centred on the regional fault. The radiometric anomalies may be due to radioactive leakage along the fault zone from buried mineralization located where the fault intersects the unconformity. The principal target lies at approximately 400 metres depth below surface. U3O8 interpretation of Target 22 is conceptual in nature, and aims to provide context to the observed alteration.
“Target 11” is a linear radiometric anomaly identified in the 2007 geophysics survey, which straddles a fault zone that cuts potentially graphitic basement rocks that lie beneath the Roraima Basin. Field radiometric surveys validated the radiometric anomaly, and alteration studies of outcrop confirmed the presence of alteration minerals, illite, kaolinite and chlorite. Rock-chip sampling further identified slightly elevated levels of several pathfinder elements that, like alteration minerals, are commonly associated with uranium mineralization in the Athabasca Basin.
Field-based follow-up of two targets from the 2007 survey showed that the radiometric anomalies in these specific areas were due to edge effects from the escarpment of the Roraima Basin itself, and did not derive from mineralization. This finding provided a better understanding of the means by which other radiometric anomalies identified in the 2007 survey may be more efficiently screened and evaluated.
