Srimad Bhagavatam Canto 05, Chapter 24, Text 17

SB 5.24.17

tato ’dhastad vitale haro bhagavan hatakesvarah sva-parsada-bhuta-ganavrtah prajapati-
sargopabrmhanaya bhavo bhavanya saha mithuni-bhuta aste yatah pravrtta sarit-pravara hataki nama
bhavayor viryena yatra citrabhanur matarisvana samidhyamana ojasa pibati tan nisthyutam hatakakhyam
suvarnam bhusanenasurendravarodhesu purusah saha purusibhir dharayanti.
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
The next planet below Atala is Vitala, wherein Lord Siva, who is known as the master of gold mines, lives with his personal associates, the ghosts and similar living entities. Lord Siva, as the progenitor, engages in sex with Bhavani, the progenitress, to produce living entities, and from the mixture of their vital fluid the river named Hataki is generated. When fire, being made to blaze by the wind, drinks of this river and then sizzles and spits it out, it produces gold called Hataka. The demons who live on that planet with their wives decorate themselves with various ornaments made from that gold, and thus they live there very happily.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
It appears that when Bhava and Bhavani, Lord Siva and his wife, unite sexually, the emulsification of their secretions creates a chemical which when heated by fire can produce gold. It is said that the alchemists of the medieval age tried to prepare gold from base metal, and Srila Sanatana Gosvami also states that when bell metal is treated with mercury, it can produce gold. Srila Sanatana Gosvami mentions this in regard to the initiation of low-class men to turn them into brahmanas. Sanatana Gosvami said:
yatha kañcanatam yati
 kamsyam rasa-vidhanatah
tatha diksa-vidhanena
 dvijatvam jayate nrnam
“As one can transform kamsa, or bell metal, into gold by treating it with mercury, one can also turn a lowborn man into a brahmana by initiating him properly into Vaisnava activities.” The International Society for Krishna Consciousness is trying to turn mlecchas and yavanas into real brahmanas by properly initiating them and stopping them from engaging in meat-eating, intoxication, illicit sex and gambling. One who stops these four principles of sinful activity and chants the Hare Krsna maha-mantra can certainly become a pure brahmana through the process of bona fide initiation, as suggested by Srila Sanatana Gosvami.
Apart from this, if one takes a hint from this verse and learns how to mix mercury with bell metal by properly heating and melting them, one can get gold very cheaply. The alchemists of the medieval age tried to manufacture gold, but they were unsuccessful, perhaps because they did not follow the right instructions.
Srimad Bhagavatam Canto 05, Chapter 24, Text 16
Srimad Bhagavatam Canto 05, Chapter 24, Text 18