Production looks like increasing at Northern Vertex Mining’s recently started up Moss gold-silver mine, in Arizona, USA, as recent modifications to the Merrill Crowe facility and additional output from the heap leach kick in.
The company produced 7,482 oz of gold and 45,876 oz of silver during the three months to the end of June, compared with 6,057 oz of gold and 25,558 oz of silver, marking the company’s strongest quarter to date. In June, alone, Northern Vertex saw 2,580 oz of gold and 18,051 oz of silver come out of the operation.
The Moss open pit and heap leach gold and silver mine hit its commercial straps in September 2018, at which point the company said expected fiscal 2019 production guidance was 36,000-40,000 oz of gold equivalent production.
Northern Vertex said this week that its operations team has made progress in correcting issues that have hampered the process plant since started up, with modifications to the filter press piping, clarifiers and vacuum pump system nearing completion.
“We have observed a large decrease in reagent consumption and an immediate improvement in recoveries of gold and silver from the pregnant solutions,” the company said.
Such improvements to the Merrill Crowe facility recently resulted in the company’s single largest gold shipment to date – of $1.2 million representing nine days of production.
The Moss team initiated a recovery study of the heap leach pad in May 2019, with the purpose to confirm consistent moisture percolation throughout the pad; measure solution volume and solution grade retained in various areas (panels) of the pad, in order to determine the gold and silver inventory remaining on the pad; obtain samples for further bottle roll testing, in order to estimate the amount of gold inventory that can be recovered by re-leach; and design and implement a leach solution application plan to recover additional gold from the leach pad inventory.
Results from the first panel (known as the ‘Central Panel’), which contains approximately 235,000 t of ore have been received, the company said. “Results show remarkable consistency in the percolation of solution, both laterally and vertically. Furthermore, the study confirms there are no dry areas, channelling is not occurring, the pad is retaining its moisture as expected and that the recoverable gold and silver in inventory will meet or exceed feasibility predicted recoveries.”
While the full study, which will include an additional five panels is ongoing, Jim Gubler, Process Manager at Northern Vertex, said the results from the Central Panel indicated there are around 5,000 oz of recoverable gold contained in this area, of which an “estimated 3,000 oz have already been dissolved in the water held in the heap and need only to be flushed and collected”.
He added: “With the leach solution application plan that we have designed, we are projecting that a significant portion of this gold will be recovered over the next several months, which should add to our normal monthly production.”
The ongoing column test program (using crushed ore samples) is predicting ultimate recoveries of approximately 80% for gold and 60% for silver from the heap leach. The column test work on the crusher samples and the heap leach pad recovery study described above will also be used to optimise and shorten the recovery curves going forward, using live ore panels for testing rather than bulk samples that were used in the feasibility, Northern Vertex said.
“Every current test being run indicates that we should be able to outperform the feasibility recovery curves,” the company concluded.