Early-phase Strategically-targeted Mining-scale Resource Evaluation

摘要

In 2014, Toro Energy geologists and SRK consultants successfully tested an alternative method to extensive 'Measured' drilling grids for obtaining mining scale confidence in the resources of the Wiluna Uranium Project. In 2011, some 25 per cent of Toro Energy's Centipede Deposit, part of the Wiluna Uranium Project, was drilled so that the drill hole spacing (35-50 m) was half that of previous (80-100 m) exploration campaigns. The corresponding updated Resources were deemed 'Measured' according to the competent person and JORC Code, a change from the previous 'Indicated' status. However, observations of the nature of mineralisation in individual drill holes led Toro geologists and consulting engineers to conclude that 'Measured' status didn't provide the required confidence in mineability; short-scale risk remained. Such short-scale variability in grade is highly important to a project as it determines such things as mining technique proposed, mining equipment to be used, mining factors in the economic model, such as dilution, and the ability to maintain predicted ore feed grades to the mill. To test this, Toro developed and implemented a plan to drill 100 x 100 m target zones on a tightly spaced 5 x 5 m drilling pattern in each of the four main deposits to be mined. The selected resource evaluation areas specifically targeted different geologies and average grades from the existing block model. Resource estimation and block modelling was then conducted and assessed at a 'true' mining block scale, as was geology. The short-scale variability revealed was then compared to the original 'Indicated' resource drill spacing assessment on geology and resources. The test was a success for the project, but more importantly, it is argued that this method allowed geologists, resource estimators and mining engineers to gain a level of confidence about mineability and resource viability that would not have been gained by 'infilling' the deposit with drill holes to a 'Measured' status. Just as important for small to mid-cap companies, such a technique of resource evaluation is potentially far more cost effective than 'drilling out' an orebody, particularly for spatially extensive deposits, such as the calcrete associated uranium cieposits of the Wiluna Uranium Project.