BlackRock World Mining Trust's net asset value (NAV) fell 6% last month on fears over sovereign debt and demand from China, but the recent dip in equity markets has made valuations more attractive, it thinks.On a capital only basis the net asset value dropped to 668.59p a share, leaving the shares at a 12.9% discount to NAV compared with a discount of 14.4% in April. The trust, which had total assets of £1.23bn at 31 May, pointed to a 19% decline in nickel prices and 16% slip in zinc prices over the month. More than 18% of its portfolio is exposed to companies involved in base metals.Gold improved though, rising to an all time closing high of $1,238 an ounce as investors fled to 'safe haven assets'."We believe that while short term volatility in the sector is likely, stock selection and commodity selection will be key in order to take advantage of opportunities in these markets," said lead manager Evy Hambro. "The recent pull back has provided potential opportunities as valuations are now looking more attractive."He believes the medium to long term outlook for the mining sector appears "robust" due to strong growth in emerging markets and supply constraints in some commodities. "Whilst some investors may be fearful of monetary policy change in China, we view this as a long term positive as it is indicative of a strong economy and a government that is looking to manage that growth."