I would suggest 95-97 % are junk using classical cut off...

I would suggest 95-97 % are junk using classical cut off parameters.

For gold the resources should be 2 g/t Au open cut, plus 5 g/t underground.

For copper 1 per cent open cut plus 10 mt oxide. Greater than 2% underground at better than 10mt.

Zinc, forget oxide, underground better than 7% underground thanks to dilution/recovery grade/smelter charges.

Credits ignored as the smelter keeps most of these.

Using these guidelines you will not loose too much money. The trick is to ignore one hole wonders, e.g. KGL.
Look at consistency in the orebody.

Cheers Tas