The ongoing global transition to low- and zero-CO2 energy generation and transport will require more raw materials and metals than ever produced before in human history to develop the necessary infrastructure for solar and wind power generation, electric power grid distribution, and electric vehicle componentry, including batteries. In addition to numerous critical elements, this transition will also require increased production of a range of other metals. This includes copper, with increased production of this metal providing the minerals industry with enhanced opportunities to secure the additional supply of associated or potential by-product elements. These include tellurium, selenium, bismuth, and antimony (among others), some of which are already predominantly produced as by-products from copper anode slimes. This study examines the geologic origins of over 240 active copper mines and over 200 electrolytic and electrowinning copper refineries worldwide. Although porphyry copper deposits dominate the copper supply trend, significant amounts of copper are supplied from the mining of sediment-hosted, massive sulfide, volcanogenic massive sulfide (VMS), and iron oxide-copper-gold (IOCG) mineral deposits. We integrate sources of copper concentrate with publicly available operational data for 32 copper electrorefineries to evaluate the geologic controls on the by-product supply potential of tellurium, selenium, bismuth, and antimony from copper anode slimes. These data represent some 32% of worldwide copper refineries and indicate that electrolytic refining of copper has the potential to supply ~777 t/yr tellurium, ~4,180 t/yr selenium, ~1,497 t/yr antimony, and 1,632 t/yr bismuth if 100% recovery of the by-product critical element proxies outlined in this study could be achieved. This is compared to current global production of ~490, ~2,900, ~153,000, and ~17,000 t/yr from all sources (rather than just copper by-products), respectively. Our analysis shows that there is no correlation between by-product potential and the amount of refined copper cathode production per year, but instead, the geologic origin of the copper concentrates is the key control on refinery by-product potential. This is exemplified by the fact that copper anode slimes derived from concentrates sourced from magmatic sulfide and VMS orebodies have an order of magnitude higher tellurium concentrations than those derived from porphyry deposits, reflecting the different abundances of tellurium within these mineral systems. These results are not surprising but demonstrate the possibilities for the development of robust proxies for by-product critical element supply potential using downstream data from copper (and potentially other base and precious metal) refineries. Equally significant, this study demonstrates the importance of downstream-up assessments of critical element potential as a complement to the more typical upstream-down deportment analyses undertaken to date. Finally, this type of approach allows the more accurate targeting of key parts of the metal supply chain with the capacity to increase by-product critical element production, rather than diluted or scattered approaches that assume that by-product metals are derived from one or two mineral deposit types (e.g., porphyry systems for the copper sector).