A drill program has boosted the estimated resource of the Piedras Verdes project in northwestern Mexico. The figure now stands at almost 1.3 billion lb. of contained copper.
Based on a 0.2% copper cutoff, owner Azco Mining (TSE) estimates the resource at 154 million tons grading 0.41% copper (equivalent to almost 1.3 billion lb. of contained copper). This represents an increase of more than 50% over the previous estimate, calculated in July, 1993. Using a cutoff of 0.3% copper, the resource drops to about 100 million tons grading 0.5% copper. Preliminary estimates put the stripping ratio at 1.3-to-1. The mineral inventory is based on 88,500 ft. of reverse-circulation drilling in 242 holes spaced 330 ft. apart on lines 200 ft. apart.
The deposit, situated in Sonora state, remains open to the east and along several segments of the perimeter.
Azco is working to develop a heap-leach, solvent extraction-electrowinning (SX-EW) operation, and the resource estimate is based only on the oxide (not the primary sulphide) mineralization.
Column leach tests indicate copper recoveries, for a minus-1-inch crush size, at about 85% in 120 days of leaching. Using a minus-2-inch size, the testing returned recoveries of more than 80% in 240 days of leaching. Based on initial projections, the company anticipates annual production of 100 million lb. for more than 10 years at a cash cost of less than US50 cents per lb. A feasibility study is expected within the next 12 months. Meanwhile, at Azco’s Sanchez project in southeastern Arizona, all environmental permits are in place and construction is set to begin. Plans call for annual production of 12 million tons by means of leaching and SX-EW. The capital cost is estimated at US$79 million (or US$100 million including working capital).
To date, Azco has lined up US$51 million in financing, including a US$15-million lease on mining equipment, plus loan commitments of US$36 million. The balance of the funding was to be raised through an equity issue, but poor market conditions forced the company to consider alternative approaches, including recruiting a partner.
The minable reserve at Sanchez is estimated at 229 million tons grading 0.29% copper at a stripping ratio of 0.81-to-1. Construction is expected to last 15 months, and will commence upon completion of financing.
Sanchez’s annual output, at full production, is projected at 56 million lb. for 20 years at an average cash cost of US52 cents per lb.
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