Make no mistake, I think they use adrenochrome as well.

But the gold is the end-game target.

Since antiquity gold has had a significant impact on human cultures. Often it is associated with life and death.

Take a look at the Mayans, Incas, and Aztecs. What were they known for?

Gold, Chocolate, and Human Sacrifice.

Chocolate is saturated with heavy metals like copper, silver, and gold.

The Gulf of Mexico was the impact of a large asteroid (possibly the moon) which provided the region with tons of gold deposits. One other such impact site leading to a civilization of gold is Lake Victoria (source of the Nile) where the Egyptians got all their gold from.

Native Central Americans ate vegetation heavy in gold, realized you can get gold from people's organs and blood, and went on mass-murder sprees including child sacrifice to get the gold and adrenochrome serum.

Why was El Dorado never found? Probably because it wasn't a city of gold, but a people of gold. Kill them all, burn the corpses, smelt the gold, make bank, blame it on "Eastern Diseases". https://www.funeralwise.com/plan/cremation/cremation-process/ https://www.cremationsolutions.com/information/scattering-ashes/all-about-cremation-ashes

There is a reason all the gold the Conquistador's brought back was in the form of copper-gold alloys. It is because they didn't bother to separate the copper and gold harvested from the natives. https://en.wikipedia.org/wiki/Tumbaga

On the vampire angle, why did they sleep in coffins? Maybe they were copper-lined faraday cages to keep out the magnetic waves? Why did they avoid sunlight? Maybe because gold deposits turned blue in the skin when exposed to UV light? Why did aristocrats wear makeup out of mercury to white-wash their faces? Maybe because they were trying to hide/extract the gold deposits in their skin with mercury's ability to bind to gold in an amalgam? https://www.youtube.com/watch?v=yAGYGGmUmUw&t=1s

The well I've tapped goes deep.