The S&P/ASX 200 Index (ASX: XJO) is having a tough time on Thursday. In afternoon trade, the benchmark index is down 1.4% to 8,664.1 points.
Four ASX shares that are falling more than most today are listed below. Here's why they are tumbling:

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IperionX Ltd (ASX: IPX)
The IperionX share price is down 4% to $5.69. This morning, this titanium alloys producer released the results of the definitive feasibility study (DFS) for its 100%-owned Titan Critical Minerals Project in the United States. The DFS shows that the project is expected to deliver a "US$813 million after-tax NPV8, 39% IRR and US$1.9 billion after-tax free cash flow from an initial 14-year mine plan producing heavy rare earth concentrate, titanium minerals and zircon." It seems the market was expecting even stronger results.
Northern Star Resources Ltd (ASX: NST)
The Northern Star share price is down 5% to $20.62. Investors have been selling gold miners after the price of the precious metal fell overnight. The catalyst was a rise in oil prices on Wednesday after tensions between the US and Iran escalated. This has sparked fears that inflation may spike and require interest rate hikes to get it under control. The S&P/ASX All Ordinaries Gold index is down around 3% at the time of writing.
Opthea Ltd (ASX: OPT)
The Opthea share price is down a further 19% to 1.3 cents. This biotechnology company's shares have lost around 98% of their value over the past two sessions after returning from a suspension that lasted over a year. After a failed clinical trial, Opthea is ending its focus on retinal diseases and relaunching with a new strategy focused on OPT-302 as a potential treatment for lymphangioleiomyomatosis (LAM). It is a rare, chronic lung disease that primarily affects women. The company believes OPT-302 could have a role because the disease is associated with elevated VEGF-C and VEGF-D signalling, which OPT-302 is designed to inhibit. Opthea's executive chair, Dr Jeremy Levin, said: "Opthea is relaunching with a focused strategy centered on OPT-302 and a clear objective: to evaluate a differentiated, mechanism-driven therapeutic opportunity in LAM while leveraging the Company's substantial existing development, manufacturing and clinical infrastructure."
Superloop Ltd (ASX: SLC)
The Superloop share price is down 5% to $3.41. This may have been driven by the release of a broker note out of Macquarie this morning. According to the note, the broker has downgraded the telco's shares to a neutral rating (from outperform) but with a slightly improved price target of $3.70. Macquarie made the move on valuation grounds following a strong gain since the start of the year.