Tin, tantalum, tungsten and gold, known as the 3TG, are commonly used in electronics, and other high tech and manufactured products. Their extraction in the Democratic Republic of the Congo, where human rights and civil war are prevalent, means that many 3TG from the region have been categorised as “conflict minerals.” The Conflict-Free Sourcing Initiative (CFSI, now known as the Responsible Minerals Initiative), founded in 2008, now has over 350 original equipment manufacturer (OEM) member companies. The industry group addresses conflict minerals and other risk issues in their supply chains. The CFSI runs the Conflict-Free Smelter Program (CFSP, now known as the Responsible Minerals Assurance Process), which defines standards and validates smelters and refiners as conflict free through third-party audits. A subgroup of the CFSI includes approximately fifty OEM members, constituting the Smelter Engagement Team (SET). The SET targets smelters and refineries deep upstream in the electronics supply chain. This sustainable supply chain management is characterized by both its business collaboration, as well as its focus deep into manufacturing supply chains. The research investigated mechanisms and effectiveness of deep supply-chain engagement of the SET and its member firms to connect with 3TG smelters and refiners. Specifically, the research addressed methods and frequency of engagement, barriers encountered (e.g. geographical and cultural), resources utilized, and allocation of responsibilities associated with efforts to encourage conflict-free compliance from smelters and refiners. This study employed a parallel convergent mixed methods approach to identify the external forces and internal tactics that allow corporations to engage deeply in their supply chains, beyond the visible horizon, to connect with upstream producers, and the practices through which OEMs work together to engage suppliers. First, data from the CFSI on 323 smelters and refiners were analysed to produce timelines describing forces and events from 2010 to 2017 regarding the participation of 3TG supplier companies in the CFSP. Second, six individuals from the SET were interviewed, and with reference to the timelines, were questioned regarding supplier engagement. An established framework (mostly recently revised by Sauer and Seuring, 2017) on sustainable supply chain management of minerals was used to frame the study and to structure coding and analysis of the interviews. Contributions of this research to scholarship include testing of the sustainable supply chain management framework, with suggested modifications to categories: Contextual dimensions (Liability of foreignness and Unique industry considerations), Supply-chain visibility and Sustainable pro-activity. The understanding of mechanisms of deep supply-chain engagement contributes to industry practice by, identifying successful supplier engagement practices and encouraging firms with similar motivations of sustainable supply chain management to consider responsible sourcing of minerals. Numerous tactics for deep supply-chain engagement were identified, including Targeted Outreach, Regionally Specific Engagement, Incentives, and Mass Outreach. Although the research was limited in the number of interviews, and limited in scope to conflict minerals used in the electronics industries, the generalizability of results to other industries is discussed.