The Sanskrit scholar, Dr. Douglas Brooks speculates that Tantrism emerged from primitive Hindu alchemical traditions. I don't quite agree with Doug Brooks. I think alchemy emerged from Tantrism. Tantra really is the root of everything that is Indian, be this Aryan or Pre-Aryan. Sir John Woodroffe discovered this and was very much a champion of the idea.
Alchemy comes in part from the ancient smiths.
The ancient smiths were outcasts, beyond cast. Tantra, yantra worship and alchemy are really very similar on many levels - even almost the same thing. These practices lead to very similar if not identical experiences on many scores. One thing that is for sure is that body, speech and mind must all be engaged. The cathedrals grew like yantra seeds.