Most of the time, Gems are surrounded by jungle, but that means grassland, which means great land long term with Gems to power the short term. So yes for Gems.
Most of the time, Gold is located in the desert areas of the map. That means that there are floodplains from the river generated to go through your capital/fat cross, which are very powerful tiles, especially compounded with Expansive. So yes for Gold.
Most of the time, Silver is located in the Tundra. That means that there is no food in the area, unless you're lucky. And Food is of utmost importance, and a lack of food kills. So no for Silver.