Shares of Northern Star Resources Ltd (NST.AU) plummeted 5% in Monday's trading session following the release of the company's operational update and future guidance. The gold miner's stock faced significant selling pressure as investors digested the implications of its fiscal year 2026 (FY26) outlook.

Northern Star reported that its total gold sold for the June quarter was 444,000 ounces, which was within expectations. However, the company's forward-looking statements seemed to have spooked investors. For FY26, Northern Star forecasts gold sales of 1,700,000 to 1,850,000 ounces, but with a notably higher all-in sustaining cost (AISC) guidance range of A$2,300-2,700 per ounce. This represents a significant increase from the FY25 revised cost guidance range of A$2,100-2,200 per ounce, potentially signaling margin pressure in the future.

Adding to investor concerns, the company announced that exploration expenditure in FY26 is forecast to be approximately A$225 million. While this investment in future resources is necessary for long-term growth, it may impact near-term profitability. The market's negative reaction suggests that investors are wary of the rising costs and their potential impact on the company's financial performance, despite the projected increase in gold production.