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Part 1 — Dynamic counterparty weighting
1.1 What exactly is changing?
From 8 January 2027, the weighting between the implied smelters purchase and implied traders purchase components in the final calculation of the combined index changes from a fixed 50:50 split to a dynamic weighting based on reported transaction volumes.
The affected price series are:
- MB-CU-0287 Copper concentrates TC index, cif Asia Pacific, $/tonne
- MB-CU-0288 Copper concentrates RC index, cif Asia Pacific, US cents/lb
1.2 Are there other indices affected by the change to a volume-weighted average?
The implied smelters purchase and implied traders purchase indices themselves are unaffected:
- MB-CU-0508 Copper concentrates TC implied smelters purchase
- MB-CU-0509 Copper concentrates TC implied traders purchase
- MB-CU-0510 Copper concentrates RC implied smelters purchase
- MB-CU-0511 Copper concentrates RC implied traders purchase
The pricing of these four series, the data that feeds them, the normalization applied to that data, and the specifications they are assessed against are all unchanged. Only the way the two are combined into MB-CU-0287 and MB-CU-0288 changes.
Participants who wish to continue referencing a simple midpoint between smelter and trader purchase levels can continue to calculate one from MB-CU-0508 and MB-CU-0509, which remain published.
1.3 How is the weighting calculated?
The weighting is derived from reported transaction volumes over a rolling six-month period and will be reviewed and updated weekly.
If, for example, over the rolling six-month window, smelter purchases account for 65% of qualifying reported transaction volume and trader purchases 35%, the combined index is calculated using a 65:35 weighting rather than the previously used 50:50.
Given the six-month rolling observation window, updated on a weekly basis, the weighting mechanism is designed to reflect sustained market participation and therefore is not materially influenced by an individual pricing session that does not reflect typical trading activity.
1.4 Which data types feed the weighting calculation?
The weighting is calculated from transaction-type data only: confirmed transactions and reported transactions (“deals heard”).
Bids, offers, indications and estimates do not feed the weighting calculation. These data types continue to feed calculation of the index itself, at the minimum volume weighting.
1.5 Why was the change made?
The methodology change is a response to market developments. These are the three main findings from the public market consultation and from Fastmarkets’ own data:
- The spread between the trader purchase and smelter purchase TCs has widened substantially. It was historically around $5-10 per tonne. It has recently been of the order of $60-70 per tonne.
- Trader buying within the 13-week spot window has declined, with trader purchasing activity extending into delivery periods well beyond that window — in some cases into 2027, 2028 and 2029.
- Spot trade activity is not distributed equally between the two counterparty types, and a fixed 50:50 weighting therefore gives equal influence to two sides of the market transacting materially different volumes within the assessment window.
A weighting aligned to reported spot volumes tracks what is actually being traded in the window the index assesses.
1.6 What was the consultation process?
3 February 2026 — open consultation on counterparty weighting and byproduct credits.
8 April 2026 — formal proposal published, with a proposed implementation date of 3 July 2026.
27 May 2026 — feedback period extended to 31 July; implementation date revised to 4 September 2026.
24 June 2026 — further detail published on potential pricing impact, including modeled price history.
10 August 2026 — decision published. Implementation date moved to 8 January 2027 following market feedback requesting more time to manage existing contracts.
Feedback was received from more than 30 companies across the supply chain.
1.7 What would the price impact have been?
Fastmarkets modeled the index against what it would have been under the dynamic weighting between 1 January and 2 October 2026 if the change had already been in place. Over that period the TC index would have averaged $16.25 per tonne higher — that is, less negative — than the published index.
That figure is specific to that period. The size of the difference depends on the prevailing weighting, which moves with reported volumes.
1.8 Is there a minimum number of transactions required to publish?
No. Fastmarkets does not set a minimum data threshold for publication, because liquidity varies considerably across the copper concentrates spot market.
Where a dataset in a given session is not considered suitably robust, a defined sequence of fall-back procedures applies, set out in the published methodology.
Part 2 — Gold and silver normalization (under consultation, open until 30 October 2026)
2.1 What is proposed?
Where gold or silver content in a parcel sits below the payable threshold, the reported TC/RC may reflect a credit or deduction relative to base-specification material. The proposal is to normalize for this, so that parcels with and without precious metal credits can be compared on a like-for-like basis.
The proposed base specifications of gold and silver are below, and the consultation is open till 30 October 2026:
- Gold (Au): from 1.1 g/dmt to 1.0 g/dmt
- Silver (Ag): from 75 g/dmt to 30 g/dmt
Maximum specifications are unchanged at 30 g/dmt for gold and 350 g/dmt for silver.
2.2 Why is this being proposed now?
Because side terms for gold and silver have moved to the point where reported TC/RCs for previously comparable parcels are no longer like-for-like.
Until recently, gold below around 1 g/dmt and silver below around 30 g/dmt were generally not paid for, and their presence had little bearing on the TC/RC agreed between the parties. The rise in precious metals prices has changed that. Fastmarkets is now seeing contracts in which buyers pay for content that was previously unpaid, typically after applying a deduction, and the terms on which they do so vary between counterparties and transactions.
Where a buyer pays for that content through the TC/RC rather than separately, the reported number carries the value of the precious metals inside it. At current prices that is material, where two parcels of clean concentrate, both well within the index specification, can therefore be reported at quite different TC/RCs for reasons that have little to do with the copper.
The index exists to compare like with like. Normalizing this content is how reported data is brought to a common basis, so that the published TC/RC reflects the treatment and refining of copper rather than the value of the byproducts that happen to accompany it.
2.3 Which series would be affected?
MB-CU-0287 Copper concentrates TC index, cif Asia Pacific, $/tonne
MB-CU-0288 Copper concentrates RC index, cif Asia Pacific, US cents/lb
MB-CU-0508 Copper concentrates TC implied smelters purchase, cif Asia Pacific, $/tonne
MB-CU-0509 Copper concentrates TC implied traders purchase, cif Asia Pacific, $/tonne
MB-CU-0510 Copper concentrates RC implied smelters purchase, cif Asia Pacific, cents/lb
MB-CU-0511 Copper concentrates RC implied traders purchase, cif Asia Pacific, cents/lb
2.4 How would the normalization be calculated?
Using the reported gold or silver content, the applicable deduction or payable threshold, the payable percentage, the relevant precious metal price, and standard market unit conversions — including the troy ounce to gram conversion and the ~1.5 concentrate conversion factor.
As published on 10 August, the proposal uses a base quotational period of M+1 for valuing gold and silver content, with transactions priced on other quotational periods normalized to that basis using the futures forward curve. This is separate from the index base quotational period for the TC/RC itself, which is M+3 and is unchanged.
Feedback during the consultation has indicated that there is no single market standard for gold and silver quotational periods, with month of shipment, M+1 and optionality all reported. Fastmarkets is considering that feedback as part of the open consultation, and welcomes further views on how the precious metals leg should be valued. Comments are open until 30 October.
2.5 What happens where the contract does not contain enough detail?
Where the precious metal impact on the reported TC/RC cannot be established, the transaction cannot fairly be compared with base-specification material and would not be included in the index on an adjusted basis. It may still be retained as market information.
Under the proposal, Fastmarkets reserves the right to exclude data reported without sufficient detail on gold and silver credits to allow normalization.
2.6 What happens to parcels where gold or silver is separately payable below the base specification, or already paid?
Where content is below the base specification, Fastmarkets will normalize to base specifications per specific trading terms, and for those where credits have already been fully reflected and priced separately, the headline TC/RC is used.
2.7 Would transactions with different gold contents be averaged?
No. Any adjustment is made at transaction level. Each lot is reviewed individually, including its stated content, deduction and payable percentage. Fastmarkets would not infer a credit that the contract does not evidence.
2.8 Does the base specification determine where payment for gold and silver begins?
No. The base specification is the reference point against which reported data is normalized, so that parcels of differing quality can be compared. Payability is set between the parties. What the proposed normalization uses is the deduction and payable percentage agreed in each transaction, which is what captures the variation in practice below the base.
This is why the proposed changes to the two base specifications differ in size. The proposed gold base moves from 1.1 to 1.0 g/dmt, and the silver base from 75 to 30 g/dmt, in each case to sit closer to observed market practice.
2.9 Do the published specifications change now?
No. The current published specifications — gold base 1.1 g/dmt, silver base 75 g/dmt — remain in force. They would only change if the proposal is adopted, and any adoption would be announced by pricing notice with an effective date.
Part 3 — What is not changing
3.1 How are different copper grades handled?
The base copper content is 26%. Grades away from that base are normalized using the copper value-in-use (VIU) coefficient, which measures the value in $/tonne of one additional percentage point of copper. The coefficient is published as MB-CU-0423 and updated fortnightly.
3.2 How are different brands handled?
Material is normalized first by copper content and second by brand or mine. Brand normalization captures factors affecting price that cannot be separately observed — chemistries, company reliability, relationships, and similar. Brand coefficients are derived from historic market data for that brand against traded clean, standard-grade concentrate, and are updated fortnightly.
3.3 How is the quotational period normalized?
The index base quotational period is M+3, where M is the month of shipment. M+3 is therefore the third month after the shipment month, not the third month from the date of the deal or the date of reporting.
A transaction priced on any other quotational period is normalized to the M+3 basis using London Metal Exchange copper closing prices and forward indications for the two relevant months.
Where a transaction carries optionality — for example M+1/4, where the buyer rather than the seller elects the QP — each end of the range is normalized to M+3 separately and the two results averaged.
3.4 Why does Fastmarkets normalize for quotational period (QP)?
The quotational period carries real value in spot TC/RC negotiations. A parcel priced against a later or earlier month is worth a different amount to the seller depending on the shape of the copper curve, and that difference is reflected in the agreed TC/RC. Two otherwise identical parcels priced on different QPs will therefore be reported at different numbers for reasons that have nothing to do with the treatment and refining of the copper.
Normalizing to a common QP removes that difference, so the published index reflects the TC/RC rather than the value of the pricing timing attached to it.
Fastmarkets records and reviews the quotational period for all submitted data on a session-by-session basis. The index base QP is M+3, counted from the month of shipment. Data points reported on any other QP are normalized to an M+3-equivalent basis using the relevant LME copper forward curve.
Fastmarkets may consider QP normalization by market participants, but reviews those submissions for consistency and reasonableness.
3.5 How is proximity to market, freight or financing accounted for?
Fastmarkets does not apply a separate standardized freight or financing coefficient. Shipping distance, financing cost and similar factors are ordinarily embedded in the TC/RC that buyer and seller negotiate.
Where a transaction is concluded on a basis other than cif Asia Pacific — for example ex-works or in-warehouse at origin, with a freight allowance attached — the reported figure is not directly comparable with the index basis. In those cases Fastmarkets will seek the full structure of the transaction from the reporting party or the counterparty, including the freight and financing assumptions used, in order to net the reported value to a cif Asia Pacific equivalent.
Where sufficient verified detail cannot be obtained, the transaction is not normalized and does not enter the index, though it may be retained as market information. Transactions that remain outliers after normalization are subject to the standard deviation filter.
3.6 Are premiums for high-sulfur material adjusted for?
No separate adjustment is currently applied. Sulfur content is part of the published specification, with a base of 32% and a range of 20% to 38%. Where sulfur content attracts a premium, that is reflected in the TC/RC negotiated between the parties and therefore in the reported figure.
3.7 How are index-linked deals treated?
Deals concluded at a differential to the index — “index minus $30”, for example — are not included in the index calculation. Including them would create a circular reference, with the index calculated in part from prices derived from itself.
Such deals are reported in the rationale published each pricing session, for transparency. The index is derived from standalone fixed-price transactions and indications.
3.8 If most smelter purchases are moving to index-linked terms, is there enough fixed-price activity left to sustain the smelter purchase index?
Fixed-price deals continue to be reported and are tracked in every pricing session, though the balance between fixed and index-linked activity fluctuates. Fastmarkets tracks index-linked deals separately and publishes them in the rationale.
Fastmarkets monitors the proportion of fixed-price activity as part of its periodic methodology review.
Part 4 — Data, governance and integrity
4.1 Where can I see what went into a given index calculation?
Every pricing session is accompanied by a published rationale on the Fastmarkets dashboard, setting out the data points taken into account.
Contact the index team at pricing@fastmarkets.com and basemetals@fastmarkets.com. If the response is not satisfactory, the issue can be escalated to Fastmarkets’ internal compliance department. Fastmarkets’ Complaint Handling Policy is available on its website.
Published indices are peer-reviewed and signed off by a senior member of the editorial or index teams before publication. Where an index is published incorrectly it is rectified and republished, and a correction notice is issued to subscribers. Retrospective changes are made only in cases of administrative or calculation error.
4.3 How often is the methodology reviewed?
Fastmarkets reviews the methodology and specifications for this index annually, in line with International Organization of Securities Commissions (IOSCO) principles, and will review them sooner where market conditions warrant it.
Any change follows a public consultation process, beginning with an advance pricing notice setting out the proposal and a period for feedback. Where a change is confirmed, a further pricing notice specifies the decision and the effective date.
Participants can raise methodology questions or concerns with Fastmarkets at any point, not only during an open consultation.
For more detail, see Fastmarkets’ Internal and External Review Process and Change to the Methodology Consultation Process documents.