Ann: Plomosas operations update, page-7

Just checked their figures:

"3,958 tonnes of ore in May, for 719 tonnes of zinc concentrates and 184 tonnes of lead concentrates."

If the Zinc concentrate has a typical grade of 51% Zn metal and Lead concentrate has a typical grade of 60% Lead metal then CZL numbers are:

719 tonnes of Zinc concentrate = 367 tonnes Zinc metal
184 tonnes of Lead concentrate = 94 tonnes of Lead metal

then back calculate from 3958 tonnes of ore put through the mill in May:

So the May ore grade would be somewhere around 9.2% Zn and 2.3% Pb (assuming 100% recovery of ore to concentrate which never happens).

So they must be either losing Zinc metal in the plant, or out to the tailings dam, or they have a significan reconciliation/dilution problem in the ore because everything I have seen in the mining metrics seem to indicate better ore grades than that? Isn't this supposed to be the highest Zn grade mine in the world?