Mexico-focused gold producer Gold Resource Corporation (NYSE MKT: GORO) says it has reached a settlement in a dispute with its concentrate buyer.

The company, with operations in the southern state of Oaxaca, Mexico, has returned more than $63 million to shareholders in monthly dividends since declaring commercial production at its El Aguila mine in July 2010. It is also the first company, it noted, to offer shareholders the option to convert their cash dividends into physical gold or silver.

In October, the company said that a dispute arose during the third quarter with the buyer of its metal concentrates, regarding the resulting assays the buyer obtained from samples of concentrates.

The buyer was claiming net reductions to the company’s provisional invoices of around 2,300 gold equivalent ounces, which was not reflected in Gold Resource’s third quarter preliminary mill production of 22,300 ounces, it said.

The settlement reached late Thursday requires the buyer to accept the company’s provisional assays taken prior to shipment of its metal concentrates for April, May and June for final invoice and payment, but not the provisional assays relating to February and March, for which gold equivalent ounces of around 1,800 will not be paid.

As a result, Gold Resource Corp said it will restate its first and second quarter 2012 financial statements to reflect a net reduction to revenues of around $3.7 million for the six months ended June 30, of which $3.0 million represents the cash settlement with the buyer, and $0.7 million represents a non-cash derivative adjustment.

Due to the work involved on the restatement, the company anticipates it will file a request for an extension of time to file its third quarter report on Form 10-Q, it said.

Typical invoicing of concentrates between the company and its buyer begins with a provisional invoice using Gold Resource Corp’s sampling and assaying results to calculate a provisional invoice and payment of 90% of that invoice, with the balance due upon agreement of final invoice.

Once arrived at the buyer’s facilities, another concentrate sample is taken and distributed for assays to determine the final sales price of the shipment.

The company said its management first became aware of a problem concerning significant variances between its internal laboratory results and the external assay results used to determine final invoice and payment in the third quarter.

To mitigate any potential future issues concerning the sampling and assaying process of its shipments, Gold Resource Corp said it has instituted additional security, including using its own representatives to accompany and remain with all shipments until samples of the concentrates have been obtained at the buyer’s concentrate yard to ensure chain of custody and proper sampling.

Since implementing this additional security, there has been no material variance between its preliminary assays and the buyer’s final assays.

“In addition, the concentrate buyer has assured the company that it has improved its controls concerning security, handling and sampling of the company’s concentrates,” it said in a statement.

Gold Resource also said it will make a decision in the near future whether to retain a new concentrate buyer. The gold producer has a 2012 production outlook of a range of 85,000 to 100,000 gold equivalent ounces.