Chris Lau, Kapitall: Alcoa shares rallied after reporting weak earnings. Does this signal it's time to look closely at mining stocks? The sharp rebound in shares of Alcoa (AA) seems confusing: after reporting weak fourth quarter earnings on January 10, the stock closed at close to a 52-week high. Trading volume was above average, too. With such bullish convictions, should investors believe the worst is over for mining stocks? Weak quarter for Alcoa To assess the health of the sector, investors could look first at Alcoa. The company earned 5% less than last year's Q4, and lost $2.34 billion. Revenue declined 5.3% to $5.59 billion, thanks to a drop in aluminum shipments. [Read more from Kapitall: Does the Net Neutrality Debate Present Investing Opportunities?] Despite the poor results, Alcoa expects global demand for aluminum to improve this year. But investors should still be cautious. Stronger demand from the aerospace and automotive sectors, along with higher home and office building needs, will likely be necessary to support the aluminum market. Comparable investments Right now Alcoa trades at a premium. Its forward P/E is 31, similar to some other large cap metal companies. Nucor (NUE) stands at 35.7, compared to 12 for Freeport-McMoRan (FCX) – although part of Freeport's valuation is probably due in part to the extremely low prices for gold. Freeport also has a much larger market cap. Click on the interactive charts below to view data over time.Costs a worry? Investors in this sector should also be mindful of electricity costs. This is the most expensive cost factor in the production of aluminum. If firms were to lower their costs using more natural gas, which is cheaper, big companies like Alcoa could stand to benefit.