Indirects covers things like engineering, construction temporary...

Indirects covers things like engineering, construction temporary facilities, construction equipment, construction management, project management, owners costs (spares, first fills, owners project management, project insurances etc).

Contingency is to cover the inaccuracies of the estimate and engineering - if you like a capital buffer. At PFS should be at least 15% if directs and indirects added together.

Sustaining capital is capital to replace Items that reach the end of their useful life or other modifications to maintain production at the design rate. Deferred capital is capital spend put off to later. Generally you add opex to sustaining and deferred and get and all in sustaining cost (AISC) which is a measure of how much cash you need to spend to stay in business.