upto 1945, Australian silver coins were 92.5%, or "sterling".
1946+ were 50% silver.
These were withdrawn from circulation from 1966, when we "decimalized", and adopted dollars & cents, instead of pounds, shillings, & pence (pennies).
The mintmark S means SanFrancisco; D is Denver.
The shilling was worth 12 pence; and the florin was worth two shillings.