Its not really that strange. The Sister Sam open pit has 70k oz...

Its not really that strange.

The Sister Sam open pit has 70k oz in it. If there were 95% recovery of that estimate, and gold remains around A$3,700/oz then the gold in the Sister Sam pit is $246m of gold. If you go a gold extraction first, you basically lower the ground surface so that in some places it is the final pit wall for the subsequent lithium operation. In many locations its close to the lithium pegmatite. At current prices of gold you might even be making some useful dollars.

After taking out the gold from Sister Sam, most of the waste rock needed to access the Sister Sam lithium pegmatite is also removed. Most of the mining cost is not in removing the lithium ore, its in removing the waste rock to enable access to the lithium ore. If the DFS for lithium is written at this point what was previously a high strip ratio with large gold byproduct credits is now a low strip ratio with no Sister Sam byproduct.

GL1's scoping study for Manna is below. The cost of mining the lithium ore is probably <$10m/yr but there's >$117m of waste rock removal costs each year. Delta doing Sister Sam gold first is basically akin to taking the cost structure below, striking out the $127m/yr mining figure and replacing it with some new, much lower figure (at least for the Sister Sam element of the project). The DFS for lithium then becomes a low cost ore in the startup years.