HELEN REID PRICES for aluminium ore bauxite from Guinea hit their highest in almost 18 months in top metals consumer China on Monday as buyers fretted about supply after a coup in the West African country, though no mines reported any disruption. Guinea is the world's second-biggest producer of the raw material that is refined into alumina, a substance used to make aluminium metal, and is the top supplier to China. Guinean bauxite for delivery to China was last assessed by Asian MetaL at $50.50 a tonne, up 1% from Friday and the highest since March 16 last year. Prices…