ARLINGTON — Pawn store operator First Cash Financial Services cut its earnings guidance for the year on Tuesday because of falling gold prices and volatility in the Mexican peso. Its stock fell 10 percent in extended trading.The company also said it is buying 19 large pawn shops in Texas for $70 million. First Cash said it now expects to earn $2.75 to $2.90 per share for the year, down from $3.10 to $3.24 per share. Analysts surveyed by FactSet had been expecting a profit of $3.12 per share. First Cash predicted a second-quarter profit of 56 to 59 cents per share, not counting 4 cents per share in expenses from the latest deal to buy pawn stores. Analysts had been expecting 60 cents a share. That pawn-shop deal includes stores mostly under the Valu + Pawn brand in the Houston, Dallas and Fort Worth areas. The all-cash deal closed on Tuesday. The new stores give the company 866 locations. It operates in 12 states in the U.S. and in 24 Mexican states. The company said it would pay for the stores out of a revolving line of credit. First Cash’s stock slipped $5.49 to $49.71 in after-hours trading following the announcement.