Why price signals fail for by-products: an intrinsic inelasticity risk metric for companion metals
摘要
Critical metals underpin key technologies, yet many are produced primarily as by-products (or “companion”) of “host” metals. This paper highlights an intrinsic supply-risk effect – companionality-driven inelasticity – that is distinct from exogenous access risks such as country concentration, trade restrictions, or governance shocks. In such companion-metal markets, higher prices may not translate into higher output because production is constrained by the host-metal value chain. This paper proposes a practical metric to quantify the additional economic and financial risk induced by companionality. Starting from observed production shares and relative value contributions within host operations, we define a perceived supply elasticity of a companion metal with respect to its own price. The associated companionality risk index is the inverse of this perceived elasticity, enabling consistent cross-element screening. In theory, the perceived elasticities satisfy an eigenvector condition implied by the joint-production structure; in practice, real-world price and production data are imperfect and make this condition ill-posed. We therefore estimate elasticities using an