(IDEX Onlie) - Lucara says profits more than doubled for the last quarter, up from $6m to $12.5m as the strength of the market outweighed economic uncertainties.The Canada-based miner reported a 13 per cent increase in revenue for the three months ending 30 June, up from $46.3m to $52.3m (figures are US dollars).It said strong rough and polished diamond market fundamentals were continuing, despite growing global economic uncertaintiesIt also provided an update on its $534m underground expansion at the Karowe mine (pictured), in Botswana, which is forecast to contribute $4bn in extra revenue."Momentum on the underground expansion continues to ramp up as we began the transition towards the main shaft sinking phase," said president and CEO Eira Thomas.She said: "In Q2, Lucara celebrated 10 years of continuous operations at its 100% owned Karowe Diamond Mine and delivered production on plan in combination with healthy diamond sales, reflecting stable polished diamond demand and a continued positive outlook for diamond prices longer term."Revenue on its Clara digital sales platform was up 13 per cent to $9.4m during the quarter.