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While record-low TC/RCs dominated headlines around the event, traders and miners in Santiago said the commercial focus of spot copper concentrates negotiations had shifted from the TC/RCs themselves to the side terms, payables and byproduct-linked structures that increasingly determined how value was distributed across the copper concentrate supply chain, Fastmarkets learned.
“[There are] less concentrates to go around but the value you get in each tonne of concentrate has drastically increased,” a North American mining source told Fastmarkets. “That’s why you have lower utilization rates yet steady to higher profits.”
The source described a structural shift in the composition of copper smelters’ revenues over the past 24 months, away from TC/RCs and toward free metal credits and sulfuric acid income. Miners were now moving to recapture part of that byproduct value through payables, side terms and tolling arrangements, they said.
The shift came amid copper smelters’ repeated concessions to key trading terms in an unprecedented competition in the copper concentrates market, which have pushed the market down to an-time low since Fastmarkets began tracking it in 2013.
Fastmarkets calculated the weekly copper concentrates TC index, cif Asia Pacific – the midpoint between smelter and trader buying levels – at $(105.10) per tonne on Friday April 17, down by $2.40 per tonne from $(102.70) per tonne a week prior.
On the same day, Fastmarkets’ copper concentrates TC implied smelters purchase, cif Asia Pacific, was calculated at $(80.98) per tonne on Friday, down by $2.93 per tonne from $(78.05) per tonne a week prior, marking it down below $80 per tonne for the first time on record.
The copper concentrates TC implied traders purchase, cif Asia Pacific, was calculated at $(129.22) per tonne on Friday, down by $1.87 per tonne from $(127.35) per tonne a week prior.
Fastmarkets covered the broader acid and TC/RC dynamics at CESCO Week in a separate April 17 snapshot.
Multiple mining sources said traders had begun offering more generous silver payable tiers as elevated gold and silver prices increased the values of the byproduct credits they were competing to capture.
“[Traders are] trying to find ways to say ‘you can’t mess with the TC/RCs, let’s play with the payables,’” a second mining source told Fastmarkets, describing offers of silver payables that had progressively lowered the grade threshold above which traders would pay 90% of contained silver – first from 90 grams per tonne to 50 grams, and most recently to 30 grams. For silver content above 50 grams per tonne, some offers had moved to 92% payable, the source said.
The shift meant miners of silver-bearing concentrates were capturing values on materials that had previously sat below the payable threshold at lower silver prices, when the byproduct credit had not justified the same level of smelter or trader payment.
A European trader said the broader payable structure had moved in similar directions across a range of elements. Copper payable rates, as well as antimony and bismuth payables, had all shifted higher, and “the gold structure [had] changed forever,” the source said.
Smelters were constrained on headline TC/RC terms but were making adjustments into the quotational period (QP) and other side terms, the mining source said, adding that smelters would be expected to push back on improved payables, but that resistance had so far been muted.
A second trader source said the absence of a standard for how gold content was priced into concentrate deals had led to materially different terms for parcels with similar gold grades. The source cited Highland Valley Copper concentrate – which contains 0.8 grams of gold and 110 grams of silver, nominal basis – as trading at $(170) per tonne while other concentrates of similar gold content continued to trade closer to $(140) per tonne.
A third, small, Peruvian polymetallic miner source said they were preparing a spot tender for copper concentrate in late May or early June, covering 10,000-15,000 wet metric tonnes for shipment in July-August. Even at negative headline TC/RCs, the payables on contained gold and silver were generating material revenue on the tender, the source said – a dynamic that had become a larger share of the economics than in previous years.
The material was graded at 22-25% copper with 3,500-6,000 grams per tonne of silver and 5-10 grams per tonne of gold, the miner source said.
Some participants also noted ‘slower’ progress in copper smelters’ willingness to accept higher payables of silver compared with gold, however, and meanwhile, repeated concessions by some smelters to agree harsh payment terms also drew strong criticism from industry peers.
“Suppliers are offering high payables of silver after the market surged, but I didn’t hear much progress in this due to its big price volatility and huge import arbitrage loss between domestic and overseas markets,” one Chinese smelter source said.
London silver prices closed at $78.39 per ounce on April 21, up by 7.2% from $71.63 per ounce on December 31 2025. The silver price surged above $100 per ounce in January.
The same smelter added, “I understand the market is tight, but we should hold firm on key trading terms. Unfortunately, we saw many make concessions on trading terms over the past one and two years, like QP and gold payables, which is fueling cutthroat market competition.”
Fastmarkets is currently consulting the market on proposed changes to the weighting of its Asia copper concentrates TC index, including a dynamic weighting process based on reported tonnage, and on the normalization of gold and silver byproduct credits. The feedback period closes on May 22.
Sulfuric acid prices recently surged amid sulfur supply disruptions owing to the closure of the Strait of Hormuz, and some market participants expect sulfur content contained in copper concentrates to become a new lever that significantly impacts copper concentrates trades and TC/RCs, Fastmarkets learned.
The first trader source floated the idea that sulfur content itself could move toward becoming a priced attribute in copper concentrate deals, although they acknowledged the concept was at an early stage and had not been formalized in commercial terms.
“Concentrates with 35% sulfur today have more value than [concentrates with] 10% [sulfur],” the source said. “Sulfuric acid has [a] higher premium than your [copper] cathode.”
The trader said they intended to start reviewing copper concentrate specifications on sulfur content as a factor in future bidding, with a view to paying a premium above the TC/RC index for higher-sulfur material. The idea had not been tested against market counterparties, they said.
The first mining source said they were not aware of any current arrangement in which sulfur content was being paid for as a byproduct but said copper smelters would likely need to develop some mechanism if sulfuric acid revenues remained elevated.
China’s domestic sulfuric acid prices have been surging owing to blocked sulfur shipments from the Middle East and the high demand season in the fertilizer industry, significantly improving copper smelters’ economics. Copper smelters doubted the sustainability of elevated sulfuric acid prices after the end of the high demand season, China’s export ban on sulfuric acid from May onwards and a weakening of sulfur prices, however.
The first trader also said miners had begun approaching traders at CESCO Week asking whether sulfuric acid could be swapped back as a part of concentrates sale agreements – a framing that bridged into wider discussions on tolling.
The first mining source said tolling agreements were being considered on the sulfuric acid side of smelter operations, mirroring structures that had previously been used for copper cathode.
“Sell concentrates to a smelter and, as part of the deal, you get sulfuric acid back,” the source said. “[Obtain the] right to get sulfuric acid back and get the right to market it yourself or get a marketer [or] trader [to do so].”
The arrangement was most commercially logical in Chile and in parts of Africa such as Zambia, where miners running solvent extraction-electrowinning (SX-EW) operations were also dependent on sulfuric acid as a leaching input, the source said. A miner could sell concentrates to a local or regional smelter and take a proportion of the resulting acid back to feed its own leaching circuits, reducing reliance on increasingly tight third-party acid supply.
The second mining source said tolling arrangements more broadly had expanded beyond the copper cathode market, with miners using them to build their own trading books in byproducts, including acid. “Always finding ways to make things happen,” the source said.
The third mining source said they had heard that some producers were now eyeing sulfuric acid tolling after having previously used copper cathode tolling linked to the COMEX-LME arbitrage. One concentrate seller that had previously tolled concentrates into cathode to capture arbitrage value was now considering a similar structure using sulfuric acid as the return leg, the source said.
Fastmarkets reported separately on the CESCO Week sulfuric acid dynamics and the 2026 benchmark fragmentation in its April 17 wrap of ten themes in focus at the event.
The third mining source said high-gold pyrite material that had historically been a low-priority byproduct for producers – “not their main business,” as the source put it – was being actively marketed by traders to smelters in China and Japan, driven by elevated sulfuric acid, sulfur and gold prices.
“[Pyrites containing] 1-12 grams of gold, no copper – between the sulfur and the gold it has become a business,” the source said. “Before, it was something thrown aside. Now people are trying to get this material.”
The material was typically mixed with copper concentrate at the smelter, with the absence of copper making the pyrite effectively a combined sulfur-and-gold play that smelters could blend to optimize overall feed economics, the source said. Payable terms on pyrite were favorable to the seller given the lack of copper payable friction.
Traders were approaching some Chilean producers and small-scale miners in Peru to source pyrite material for shipment to China, the source said.
The second trader source noted a parallel dynamic at Ivanhoe Mines’ Kamoa-Kakula operation, where concentrates carrying unusually low sulfur content were producing less acid than typical copper concentrates.
Kamoa-Kakula material is generally being retained for Ivanhoe’s on-site smelter rather than sold into the custom market, but the low-sulfur profile underlined the extent to which sulfur content – and the acid it generates – had become a point of differentiation across concentrate types.
Ivanhoe Mines said it was now evaluating local third-party concentrate purchases to advance the smelter’s ramp-up due to a shortage of concentrate feeds from Kamoa-Kakula’s own concentrators, Fastmarkets reported.
Higher metal prices had also expanded the working capital requirement smelters carried against their copper concentrate and cathode inventories, according to public commentary by Alejandro Carlos Karacsonyi, a commodities finance executive.
The “free metal” component of a concentrate typically represents only a small percentage of the total metal input, Karacsonyi said, while financing costs apply to the full working capital tied up in the inventory. The interest burden therefore scales with the overall metal price level rather than the byproduct portion, creating an asymmetric effect in which part of the revenue gain from higher precious metal credits is offset by a higher financing cost base.
With the Secured Overnight Financing Rate (SOFR) below its 2023-2024 peaks but remaining elevated by historical standards, the net bottom-line effect of higher metal prices on smelter margins is more nuanced than the byproduct revenue picture alone implies, Karacsonyi said.
A European smelter source separately said current TC/RC levels were “not sustainable” and described the smelter position as less secure than the byproduct revenue narrative suggested.
The durability of the mechanisms described during CESCO Week remained an open question among participants. The first mining source said that while nobody would build a long-term commercial structure on sulfuric acid price assumptions alone, the payable structure was more likely to prove structurally sticky.
“A lot of smelters are unhappy because if your KPI is one TC/RC headline number, structurally these TC/RCs are going to be low and that’s changed – you’re sitting on a bunch of revenue on this [other side],” the source said.
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