Revenue decreased at Lucapa Diamond Company in the fourth quarter as demand for its rough slowed and prices dropped. Sales from the company’s mines slipped 1% year on year to $40.8 million for the period, it reported last week. The average selling price slid 9% to $2,458 per carat, outweighing a 9% rise in volume to 16,600 carats. At the company’s Lulo mine in Angola, revenue fell 4% to $34.9 million, with sales volume plunging