With regard to understanding the approx 57% FE content discount...

With regard to understanding the approx 57% FE content discount to 62% content FE benchmark - below is a site which provides a daily price index for 58%/62%/65%

Currently 58% is trading at a discount of 16.5% to 62% benchmark

http://www.custeel.com/en/csi.jsp

Your 20% therefore appears within ball park.

Here is a copy of an old post I made on the matter:

From the BFS inputs the total discount to the benchmark 62% fe US$90.35 used in the study can be approx calculated - assume that the total discount includes not only content grade but also Prospertity's margin,cost recovery etc under the offtake and any price adjustments for low impurities.

Inputs:
62% Fe price US $90.35/.68 = $A 132.86
Sales Volume 1.6mt
Net sales $172.82m
A$ to US$ .68

Discount = 172.82m / 1.6m = $A108 per tonne net sale
Gross sale price per tonne $A 132.86
Total Discount 18.71%

https://hotcopper.com.au/threads/vms-game-changer-events.5708544/page-176?post_id=49412584

cheers