semi

In mining and extraction, a semi is ore or mineral concentrate that has been processed partway toward a final product, but stops short of complete refining. A copper mine might produce copper concentrates (typically 20-35% copper) that are sold as semis to smelters; an iron operation might sell pellets or briquettes rather than raw fines. The semi occupies the middle ground between raw extraction and finished metal or refined material ready for manufacturing.

The economics of semis hinge on transport and processing cost ratios. Shipping low-grade ore across continents is wasteful, so mines concentrate ore on-site to raise its value density, then sell semis to distant processors who have furnace capacity or better access to reducing agents. A tin mine in Southeast Asia will produce tin concentrates; a phosphate mine will make acid-grade or fertilizer-grade semis before sale. Each semi represents a deliberate stopping point where further processing moves downstream.

Iron ore semis include pellets (8-16 mm spheres, often induration-hardened) and sinter fines (fused agglomerates). Copper semis are concentrates or sometimes matte (an intermediate copper-iron-sulfur product). Zinc semis may be concentrates or roasted calcines. Nickel laterite operations produce intermediate products ranging from saprolite (leached, low-grade ore) through nickel matte. Each semi is formulated to suit the receiving facility's equipment and chemistry.

Quality variation is the main hazard in semi trading. A copper concentrate sold at 28% Cu grade may contain 2-4% molybdenum as an impurity, which affects smelter operations and downstream refining. Moisture content in semis can shift drastically during long ocean voyages; iron ore pellets that leave port at 8% moisture may arrive at 12%, raising freight paid per unit of copper or iron actually received. Sampling and assaying at ship load and discharge are critical contractual steps.

The term semi is informal but universal in trading floors and contracts. It distinguishes these transition products from both rough ore (unprocessed, low value density) and refined metal or pure compound (ready for end-use manufacture). In regions with weak downstream infrastructure, mines produce ore; in developed mining nations with smelter and refining clusters, semis are the norm because they allow specialization and transport efficiency across the supply chain.