FACTBOX-Three major iron ore indices

June 4 (Reuters) - BHP Billiton (BHP.AX) has been approaching Chinese steel mills with an offer of iron ore supplies based on index-linked prices rather than the traditional benchmark, sources said on Thursday. [ID:nSP356938]

Following are details of three iron ore indices gaining momentum in the burgeoning financial and physical iron ore market. ---------------------------------------------------------------- -- The Steel Index * Location: delivered CFR to Tianjin port in China.

* Frequency: Daily excluding UK bank holiday.

* Quality: Publishes two iron ore reference prices -- one for 62 percent Fe content fines and one for 58 percent Fe content fines.

* Data collection: Price data based on actual transactions which are fed to its online systems, collected from more than 375 companies.

* Data calculation: It normalises data submitted to the reference product specifications and excludes outliers before calculating the average reference prices from the remaining normalised data.

* Lot size: Minimum 20,000 metric tonnes.

* Delivery period: Loading within 4 weeks of transaction.

* Unit: US$ per dry metric tonne. --------------------------------------------------------------- --- The Metal Bulletin * Location: Delivered CFR to China. Base Qingdao-Rizhao-Lianyungang, normalised for any Chinese mainland sea port.

* Frequency: Every Friday at 08:00 London time. Plans to issue daily data soon.

* Quality: Base 62 pct Fe content, range 58 pct to 66 pct

* Data collection: Actual transactions, which are reported to Metal Bulletin by any market participant conducting trades on a CFR China spot basis. Data collected between Monday 8:00 Singapore time and Thursday 17:00 London time.

* Data calculation: Separates data into three sub-indices, based on a tonnage weighted average of the trade information. The final index is the non-weighted average of the three sub-indices and only the final index is published. It seeks to utilise at least 12 trades, or four for each sub-index, as a minimum to calculate the index.

Relevance: Used as a reference price of the world's first cleared over-the-counter iron ore swaps contract launched Singapore Exchange (SGXL.SI) in April. Also used to settle OTC swaps that Credit Suisse and Deutsche Bank launche in May 2008.

* Lot size: Minimum 30,000 tonnes, maximum 350,000 tonnes.

* Delivery period: Within 8 weeks.