It's not that a drop in one directly implies a drop in the...

It's not that a drop in one directly implies a drop in the other, however a drop in one is usually reflective of a broader economic trend that also affects the other. Namely that both energy consumption and steelmaking output depend heavily on the global economic situation.

I was actually going to say the same thing in my last post about the de-coupling of the two due to the US shale gas revolution, but so far that doesn't seem to have happened - HCC prices have crashed as hard as thermal, maybe worse. And it has flucutated a bit over time, but I remember for most of the 2000s HCC was roughly double the thermal coal price - from $50/100 in the early 2000s to $150/300 in the peak boom just before the GFC. Coking coal prices seem to be significantly less than double the price of NEWC now. If shale gas was having a big effect it should widen the gap, not narrow it.

But it doesn't really matter - it's still true to say that a drop in thermal coal prices is likely to be indicative of a drop of metallurgical coal prices.

Another reasonable proxy for the met coal price is, obviously, the price of iron ore.