0416 GMT - Mining shares and mined commodities tend to outperform when the yield curve steepens, and underperform when it flattens, says Jefferies. "This holds true across physical copper, gold, silver, and platinum, as well as copper and gold equities," the bank says. By comparison, the S&P 500 tends to perform best when there is no clear trend, it says. Jefferies says this poses a risk for the mining sector ahead. "We seem to have exited the bull steepening of the past two years and may be heading for bear flattening, where yields rise and spreads compress," it says. "History suggests a headwind for mining, with copper faring best" and iron ore the worst, says Jefferies.