Glencore saw its output in copper, zinc, lead and nickel dip this morning as it struggled with a downturn in production but said it expects to exceed its long-term annual guidance – with trading profits reaching as high $4B (£3.1bn). The commodity giant said the half-year results were in line with expectations, with its full year production guidance remaining unchanged. It expects earnings before interest and tax (EBIT) to hit the top end of its guidance, between $3.5-4.0 billion (£3.1bn). Chief Executive Officer Gary Nagle,…