Zinc prices surged to their highest level in more than four years on Tuesday, extending a months-long rally driven by mounting signs of supply tightness, with the metal used for galvanizing steel jumping as much as 2.5% on the London Metal Exchange (LME) to $3,980.50 per metric ton before paring some gains.

A confluence of factors has propelled prices higher in recent weeks, ranging from the Middle East conflict disrupting Iranian ore supplies to production outages at mines across multiple regions including China. "Supply-side disruptions have been frequent," wrote analysts at Chaos Ternary Futures Co. in a note, adding that market expectations are building for China to export more zinc metal to alleviate tightness in the global market.

August marked the fifth consecutive monthly gain for the metal, with LME zinc futures climbing 27% so far this year—outperforming copper and aluminum, both of which have also faced significant supply-side shocks. While zinc inventories in LME warehouses have ticked up slightly recently, they remain below 100,000 tons, still relatively low by historical standards.

The tightness is starkly reflected in benchmark treatment charges (TC), which plunged further last month, sinking to a negative $117.50 per ton by end of August. Lower TCs signal that ore shortages are forcing smelters to accept tougher terms from mining companies, although smelters can often offset the gap through sales of by-products.

In related metals trading, copper extended its gains on Tuesday, with LME copper rising 0.6% to $14,382 per ton at last check. The red metal has continued its upward trajectory after hundreds of thousands of tons were shipped to the United States, squeezing global supply. The LME was closed on Monday for a UK bank holiday.