Toro Energy Limited (ASX:TOE) is pleased to announce positive disequilibrium results following detailed studies of drill sample data from the Theseus Uranium Project in WA.
The key conclusions of the disequilibrium study are:
- consistently positive disequilibrium ratio of 1.34 (all samples) and 1.54 (for samples reporting above 300ppm uranium);
- a disequilibrium factor of 1.34 can therefore be applied to all gamma-radiation data taken from Theseus.
If this disequilibrium factor is applied to all gamma-radiation data, the size and grade of the Exploration Target Range will increase. The Exploration Target Range presently stands at:
20Mt to 40Mt @ approx 400 to 500parts per million (ppm) U3O8, for10,000t to 20,000t U3O8 or 22Mlb to 44Mlb U3O8#
# CAUTIONARY STATEMENT: The Exploration Target Range is conceptual in nature and there has been insufficient exploration completed to define this material as a Mineral Resource. There is no certainty that the further work referred to herein will result in the determination of a Mineral Resource
Disequilibrium analysis indicates a consistently positive disequilibrium ratio of 1.34 (all samples) and 1.54 (for samples reporting above 300 ppm uranium) for 47 representative and widely-spaced pulp samples distributed across the deposit (see Figure 1). These results confirm that gamma-radiation data previously reported for the Theseus Project have significantly underestimated the grade for the majority of the drillholes probed in 2011.
Additional Prompt Fission Neutron ("PFN") data obtained from the current drilling program is adding to Toro's confidence in applying a "correction factor" of approximately 1.34 (34%) to existing gamma-radiation data.
Toro is currently working with external consultants to determine if a maiden Inferred Resource can now be defined in accordance with the JORC Code at Theseus.
Toro Managing Director, Mr Greg Hall said:
"This study potentially provides significant upside to the magnitude of the Theseus uranium discovery. Toro will continue to work hard to provide independent validation of this ratio so we can utilise it for on-going drill reporting and resource modelling. It is hoped that Theseus will develop into a large economically robust ISR uranium deposit and one of the more significant new uranium discoveries in Australia in recent times."
Technical Discussion
Analysis is herein reported for 47 representative and widely-spaced pulp samples collected at Theseus during the 2011 drilling program (Figure 1; Appendix 1). Analytical work was carried out by Radiation Detection Systems in Adelaide to determine the degree of disequilibrium between uranium and it's shorter-half-life radioactive daughter products. It is critical to understand this phenomenon in "young" sediment-hosted deposits, because ambient groundwater movement can often lead to fractionation of these elements and therefore affect the application of gamma-radiation logging to establishing uranium grade and cut-off thickness in drill holes.
Disequilibrium is represented as a ratio of the radiation predicted from the known uranium content of a given sample (via chemical assay), versus the actual radiation emanating from the sample (via precision "lead canister" radiometric analysis). Generally speaking, a positive disequilibrium ratio (>1) is where uranium is present in concentrations greater than it's daughter products and is therefore underestimated by radiation measuring methodologies such as gamma-radiation logging. Conversely, a negative disequilibrium ratio (<1) is where daughter products are present in the sample in excess of the parent uranium. Early establishment of the disequilibrium characteristics of deposit types that are largely assessed by gamma-radiation logging can have a marked impact on the estimated grades, resources and ultimately economics.
At Theseus, a plot of data shown on Figure 2, depicts a significant and consistent degree of positive disequilibrium in most samples, with a "best fit" ratio in the order of 1.34. Importantly, Figure 2 indicates that positive disequilibrium is the norm for samples above 300 ppm, and the arithmetic average of the ratio is 1.54. This ratio might be more statistically valid for assessing data above an economic cut-off. Below 300 ppm, both positive and negative disequilibrium ratios are evident in Figure 3, at least partly due to precision and accuracy limitations at low radiation levels. The overall quantum of this positive ratio is also born out in a preliminary comparison of gamma and PFN data collected so far this year, the latter measuring in-situ uranium, not a proxy like gamma.
The veracity of the data is also supported by the project-scale spatial consistency of the disequilibrium ratio at Theseus shown on Figure 1 and by the consistency of the disequilibrium ratio in adjacent samples and duplicates within individual drillholes. The exceptionally high ratios in the west around LM0027 (highlighted in yellow on Figure 1) imply that groundwater flow and parent-daughter fractionation is greatest in this area. Nearer the edges of the palaeochannel mapped from drilling in 2011, the ratio is closer to equilibrium or is negative, as expected. Local variations such as between LP0187 and LM0015 also fit a model of small-scale redox contrasts associated with an individual roll-front.
This data is consistent with the currently held "roll front" model for Theseus, whereby uranium and its' daughter products are currently mobile in the saline groundwater regime and have been systematically separated throughout the known spatial extent of the mineralising system. It is not known if the daughter products have moved out of the deposit (as it is currently defined) into local low-permeability zones that are below the cut-off, or regionally down the large-scale palaeochannel trend. Most importantly, the consistency of the data above 300 ppm U3O8 allows the global application of the disequilibrium ratio to Toro's existing gamma-radiation database, thereby substantially increasing the grades and broadening mineralised intervals at any given cut-off level.
