A good start but there has to be a mechanism for assigning extra...

A good start but there has to be a mechanism for assigning extra value for grade and jurisdiction. Whilst ADT would lose on jurisdiction (Bosnia) its grades at 400g/t cannot be sneezed at. Then there is the differentiation between inferred, indicated & measured resource and whether the operation is an open pit or underground operation. ADT & MMA is/will be u/g operations so mining costs will be higher but their grades are significantly higher than the rest.

Then there is the matter of the higher base metal resources (BML, MMA, ADT, SVL) where, as silver begins to outperform base metals in percentage terms, that these companies silver equivalent oz begin to drop. For example, the drop in silver equiv oz is 15% should silver trades at $33 and pb at $2600/t. Even worse if pb does not get to $2600/t.

The only fair valuation on an apples for apples basis is on the gold/silver resource multiplied by the grade. The base metals could then be assumed to cover production costs so the profit margin would be greater for lead/silver/zinc/copper resources. The companies with DFS already know the costs so it is just a matter of tweaking the companies with no scoping or DF studies.

Just as an example of what I am trying to say, I have recreated my spreadsheet and highlighted the changes in brown. The changes only reflect the PM resource in silver equivalent oz multiplied by the PM silver resource grade divided by 31.1 which is the grams per oz for PM's. This is an apples for apples comparison taking into consideration the PM silver equiv grades to be mined but disregards the base metals. You could go one step further and halve MMA and ADT resource in brown to reflect the added u/g mining costs compared to an open pit operation. What this shows is that USL, ARD, MMA & RDM and ABRA (TSX) are the most undervalued stock when using these metrics.

The below spreadsheet shows what PM grade does to the calculation and where grade is king. MMA has double the lead grades as its next closest rival BML. All of the rest of the companies listed with base metals have grades at 1% or less with the exception of ADT which has 2.5% lead and 3.9% zinc.

The prices and percentages in yellow no longer reflect the value of the entire resource but reflect the Gold/Silver multiplied by grade component only.

I must admit that USL surprised me. I spent ages going over formulas trying to find an error but could not.