The meaning behind that simile is that ‘they’ are getting tons of gold like they were corn grains which if you’ve seen them, there’s a lot in just one corn. So basically those people were getting a lot of gold.
1) B. Sentinel is a soldier or guard whose job is to stand and keep watch
2)C I think
1. olivine and quartz
2. olivine and pyroxene
3. pyroxene and orthoclase
4. orthoclase and quartz