What are the black spots on the lid of my expensive oil bottle?
Notice that this is in a silvery patch that differs in color from the rest of the cap, and that there are similar small silver spots on the interior ridges of the cap screw closure (visible in your first picture). To me it looks like the cap was inexpertly coated with some kind of gold-colored treatment, probably to prevent corrosion, but part of the treatment was missed or rubbed away. The black spots are most likely corrosion of the underlying, exposed metal, possibly caused by contact with tiny amounts of moisture on the spout of the bottle at some point when it was sealed. It doesn't appear to show up anywhere on the gold-colored treatment, and the spots appear to be quite small.

If there is no evidence of mold within the oil (such as clouding of the oil or exposed glass, other black spots on the lip of the oil container, etc.) then most likely this is metal corrosion that is unlikely to cause a problem unless you're planning to store this oil for months or years. I probably wouldn't reuse this cap if you're recycling the oil container for another purpose - it looks to be cheaply made, and already showing it.