The companies' top brass only spoke last Friday, when BHP shot across its non-binding and indicative bid to OZ's Adelaide offices, and asked for six-weeks' due diligence and a friendly board recommended deal.

Instead of being flattered by the attention, OZ Minerals' board is playing it cool and defensive.

OZ Minerals' board, advised by Macquarie Capital and Greenhill, is understood to be staunchly against giving BHP a look at its books at a $25 a share offer, reckoning it's both invasive and disruptive to the business. It has said as much to investors in recent days.

Analysts who have spent the past few days canvassing the OZ Minerals register said the shareholders were on the same page as the board.

But at what price OZ would be willing to grant BHP due diligence, is pretty much anyone's guess at this point. Citi and Barrenjoey are in BHP's corner.

What's OZ Minerals worth

The approach and the retreat were so swift that investors haven't had time to think what the company's worth to a bidder.

But they are taking heart from three things: that OZ smacked the $25 a share bid really hard (so BHP must be way off mark) and that the two had been talking about offtakes (so BHP's interest isn't just tyrekicking).

Investors reckon they still need a week or so to come up with a number they reckon would be fair, and OZ's half-year results are due about the same time. But early talk is any suitor wanting to unlock OZ's data room would have to present it with a low-thirties bid.

The offtake revelations have also revived investors' early read of the approach: that BHP's after better performance for Olympic Dam and its copper operations, but is also thinking strategically about securing nickel concentrate for its WA smelters.

Eoin Treacy's view

Building new mines is expensive and time consuming. Those challenges are becoming more burdensome as regulations tighten. OZ Minerals has the benefit of producing resources in a politically stable area, in relatively close proximity to existing mines so additional infrastructure requirements are minimal. That should command a premium and if BHP can get away with paying less than peak values it’s a good buy.

The challenge in the short term is no one knows for sure how China’s demand is going to evolve. Since China accounts for more than half the market and a good part of demand growth too, the outlook for liquidity and infrastructure growth matter.

Copper continues to unwind the short-term oversold condition as the needs of the green movement vie with China’s demand growth slowdown . 
BHP is firming from the region of the 200-day MA and the upper side of the underlying trading range.