We are looking into it, although it's relatively difficult / expensive to source quality operational data for these types of companies. This has been discussed in the Forums and the general view seems to be that it would not be that useful because of the subjectivity of reserves information. We are still considering it though, so any feedback is welcome.
We're also not aware of much research indicating that a quantitative approach to screening for these types of companies is effective. This isn't to say that resource companies can't make great investments, but just that the (rare) successes tend not to be predictable based on historical or even forecast financial performance.