Tin, tantalum, tungsten and gold, known as the 3TG, are commonly used in electronics, andother high tech and manufactured products. Their extraction in the Democratic Republic of theCongo, where human rights and civil war are prevalent, means that many 3TG from the regionhave been categorised as ;;conflict minerals.” The Conflict-Free Sourcing Initiative (CFSI, nowknown as the Responsible Minerals Initiative), founded in 2008, now has over 350 originalequipment manufacturer (OEM) member companies. The industry group addresses conflictminerals and other risk issues in their supply chains. The CFSI runs the Conflict-Free SmelterProgram (CFSP, now known as the Responsible Minerals Assurance Process), which definesstandards and validates smelters and refiners as conflict free through third-party audits. Asubgroup of the CFSI includes approximately fifty OEM members, constituting the SmelterEngagement Team (SET). The SET targets smelters and refineries deep upstream in theelectronics supply chain. This sustainable supply chain management is characterized by both itsbusiness collaboration, as well as its focus deep into manufacturing supply chains.The research investigated mechanisms and effectiveness of deep supply-chain engagement of theSET and its member firms to connect with 3TG smelters and refiners. Specifically, the researchaddressed methods and frequency of engagement, barriers encountered (e.g. geographical andcultural), resources utilized, and allocation of responsibilities associated with efforts toencourage conflict-free compliance from smelters and refiners. This study employed a parallelconvergent mixed methods approach to identify the external forces and internal tactics that allowcorporations to engage deeply in their supply chains, beyond the visible horizon, to connect withupstream 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 timelinesdescribing forces and events from 2010 to 2017 regarding the participation of 3TG suppliercompanies in the CFSP. Second, six individuals from the SET were interviewed, and withreference to the timelines, were questioned regarding supplier engagement. An establishedframework (mostly recently revised by Sauer and Seuring, 2017) on sustainable supply chainmanagement of minerals was used to frame the study and to structure coding and analysis of theinterviews.Contributions of this research to scholarship include testing of the sustainable supply chainmanagement framework, with suggested modifications to categories: Contextual dimensions(Liability of foreignness and Unique industry considerations), Supply-chain visibility andSustainable pro-activity. The understanding of mechanisms of deep supply-chain engagementcontributes to industry practice by, identifying successful supplier engagement practices andencouraging firms with similar motivations of sustainable supply chain management to considerresponsible sourcing of minerals. Numerous tactics for deep supply-chain engagement wereidentified, including Targeted Outreach, Regionally Specific Engagement, Incentives, and MassOutreach.Although the research was limited in the number of interviews, and limited in scope to conflictminerals used in the electronics industries, the generalizability of results to other industries isdiscussed.