Terminating the contract was done without penalty and by mutual consent with the mill-owner.
Processing began at the Juan Reyes mill in February this year after Arian halted processing at its previous mill in July last year after a dispute.
The firm is now focused on sealing a financing package so it can buy its own second-hand custom mill and to fund mine development to increase capacity up to 1,500 tonnes per day.
Jim Williams, Arian's chief executive, said: "In the context of current metal prices, we are preserving value by halting milling operations and, with the knowledge obtained from the toll milling operations, positioning the company to resume production with its own mill at a significantly reduced cost base."
He added: "The second-hand custom mill is expected to deliver cost savings of some 75% compared to previous toll milling operations, which, alongside the additional revenue from lead and zinc credits, would produce considerable profits even at today's silver price."
Shares in London dropped around 12% to 4.25p.
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