Ann: Report on drilling for tin and tungsten at Aberfoyle Tas, page-7

To mine Tin underground the average grades would need to be a lot higher than the grades/widths given.

Heres a comparison:

RENISON TIN MINE • Sn Reserves 5.7Mt @ 1.28% Sn (72Kt) ~ 8 yrs. • Resources 11.5Mt @ 1.44% Sn (165Kt) ~16yrs

Note the average grades. Look up the ITRI information on the sort of grades that can be mined economically underground and above ground. And always look at the average grades and width and depth of the higher grade intervals.