TORONTO (miningweekly.com) – Rising grades and an improving performance at base metals producer Capstone Mining’s Pinto Valley, in Arizona, and strong results from Minto, in Canada’s Yukon Territory,  offset the second-quarter production shortfall at Cozamin, in Zacatecas state, Mexico.

TSX-listed Capstone on Monday announced operating results for the three and six months ending June 30, reporting consolidated output of 21 100 t of copper for the quarter and 44 800 t of red metal during the first six months of 2015, with added by-products of zinc, molybdenum, lead, silver and gold.

"We are pleased to report good results from our operational improvements at Pinto Valley with respect to mill reliability and we approached our targeted run rate by the end of the second quarter. In total, second-quarter production met our expectations, which called for lower grade at Pinto Valley,” Capstone president and CEO Darren Pylot said in a statement.

At Pinto Valley, mill throughput improved 7% over the first quarter with successive month-over-month improvement throughout the second quarter, averaging over 50 000 t/d so far in July. The asset improvement plan was on track, with the various tasks ranging from 65% to 85% complete and operational reliability was improving, the company said.

Throughput for June exceeded 52 000 t/d for one-third of the month and was over 50 000 t/d for half of the month, with the mill posting an all-time daily high of more than 58 000 t/d. Production remained on plan with better-than-predicted block grades continuing in the second quarter. The 2015 mine plan called for the second and third quarters to be the lowest-grade quarters of the year.

At Cozamin, grade, throughput and recoveries were all lower than planned for the quarter. While progress was made on improving development performance and increasing long-hole inventory, the mine continued to work through changes made to mining procedures and the need to adapt practices to increase ore output from the footwall zone. Despite practices currently being refined, most particularly related to grade control, Capstone did not expect Cozamin to reach its production guidance for 2015.

At Minto, output continued above plan in the second quarter and as a result, Minto was expected to exceed its full-year production guidance. Ore from underground Area 118 continued to run significantly above model grades and enhanced mining practices resulted in lower dilution than budgeted.

Further, unplanned ore output came from the Area 2 Stage 2 pit above the water storage level. The Yukon Water Board issued a draft water use licence on May 29 and was now in the process of issuing the final licence.

Capstone continued to process underground and stockpiled ore, while the company awaited receipt of the final licence.

Capstone's 2015 production guidance of 90 000 t of copper remained unchanged; however, the distribution by mine was expected to be different than originally guided, with outperformance at Minto expected to make up most of the anticipated shortfall at Cozamin for the year.