The Mani-Kanchan Sanyog (union of gold and emerald) is a significant event in the history of Neo- Vaishnavism in Assam. It marks the meeting of the two prominent saints, Mahapurush Damodardev and Mahapurush Madhavdev, where Madhavdev accepted Damodardev as his Guru after a spiritual debate. The question incorrectly states Sankardev met Madhavdev at Dhuwaha for this event; it was Damodardev who met Madhavdev. However, among the given options, Dhuwaha is associated with this significant spiritual encounter. If the question implies the meeting of Sankardev and Madhavdev, it's crucial to note that Madhavdev was a principal disciple of Sankardev, and their association was foundational. The term "Mani-Kanchan Sanyog" is most famously associated with the meeting of Sankardev and Madhavdev, though the location mentioned here points to a specific narrative. Historical accounts generally place the significant meeting and acceptance of Guru by Madhavdev at Dhuwaha with Sankardev.