March was a tough month for the S&P/ASX 200 Index (ASX: XJO). A broad market selloff led to the benchmark index recording a monthly decline of 7.8%.
While that was bad, some ASX 200 shares posted even greater declines. Here's why these were the worst-performers on the index last month:
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Iperionx Ltd (ASX: IPX)
The IperionX share price was the worst performer on the ASX 200 with a decline of 48.7% in March. Last month, the advanced materials company released its half-year report for the six months to 31 December 2025. IperionX revealed that it recorded a net loss of US$34.8 million for the period. This was much larger than the US$16.2 million loss reported in the prior corresponding period. Despite this heavy decline, IperionX's shares remain up 30% on a 12-month basis.
Northern Star Resources Ltd (ASX: NST)
The Northern Star share price was out of form and sank 35.8% last month. The main catalyst for this was the gold miner downgrading its production guidance for FY 2026 a second time. Northern Star revealed weaker-than-planned milling performance at the KCGM operation and reduced mining productivity across several operating areas. As a result, it now expects FY 2026 production to come in ~1.5 million ounces. This compares to its most recent guidance of 1.6 million to 1.7 million ounces, which was downgraded from 1.7 million to 1.85 million ounces.
Deep Yellow Ltd (ASX: DYL)
The Deep Yellow share price wasn't far behind with a decline of 33.7%. As well as broad weakness in the uranium industry, this may have been triggered by speculation that the company could soon launch a capital raising. However, Deep Yellow denied this will be the case. It stated: "Deep Yellow Limited notes the media speculation on 4 March 2026 regarding a potential capital raising. In response to the report, Deep Yellow confirms the Company is not undertaking a capital raising at this time."
Regis Resources Ltd (ASX: RRL)
The Regis Resources share price was a poor performer and tumbled 31.9% in March. This was driven by significant weakness in the gold price during the month. The precious metal came under pressure after surging oil prices sparked fears of rising inflation and higher interest rates. The latter are bad for the gold price as they boost Treasury yields, which reduces the appeal of gold as a safe haven asset.
