In afternoon trade, the S&P/ASX 200 Index (ASX: XJO) is on course to record a decent gain. At the time of writing, the benchmark index is up 0.35% to 8,251.3 points.

Four ASX shares that are rising more than most today are listed below. Here's why they are climbing:

Firefly Metals Ltd (ASX: FFM)

The Firefly Metals share price is up 9% to $1.15. This morning, this copper explorer released an update on its Green Bay copper-gold project in Newfoundland, Canada. According to the release, recent exploration activities have led to a 42% increase in the mineral resource estimate at Green Bay. The total resource is now 59Mt at 2% copper-equivalent for 1.2Mt of contained metal. FireFly's managing director, Steve Parsons, said: "This outstanding result confirms Green Bay's status as one of the fastest-growing high-grade copper projects with genuine scale in the western world."

Premier Investments Limited (ASX: PMV)

The Premier Investments share price is up 11% to $34.19. Investors have been buying the company's shares today after it announced a merger agreement with Myer Holdings Ltd (ASX: MYR). The deal will see Myer acquire Premier's Apparel Brands business in Australia and New Zealand in exchange for the issue of 890.5 million new shares. The Apparel Brands business comprises Just Jeans, Jay Jays, Portmans, Dotti, and Jacqui E. Upon completion, it will have $4 billion revenue and $152 million EBIT on a pro forma FY 2024 basis. The shares being issued will be distributed to Premier Investments shareholders on a 7.2 for 1 ratio.

Serko Ltd (ASX: SKO)

The Serko share price is up 25% to $3.08. This follows the release of the travel technology company's half year results this morning. It reported an 18% increase in total income to NZ$42.7 million and a net loss of NZ$5.1 million. The latter is a NZ$2.1 million improvement year on year. In other news, Serko is expanding its existing business in North America, including through a long-term partnership with global travel software and technology provider Sabre Corporation (NASDAQ: SABR). It will also acquire Sabre's business travel management solution, GetThere. This will make it the number two online booking tool provider in North America.

Zip Co Ltd (ASX: ZIP)

The Zip share price is up 11% to $3.09. Investors have been fighting to get hold of the buy now pay later provider's shares following the release of its first quarter update. For the three months, Zip reported group cash EBTDA of $31.7 million. This represents an increase of 233.7% over the prior corresponding period. A key driver of this was its US business. Zip's CEO and managing director, Cynthia Scott, said: "Our US business continued to deliver outstanding growth, with TTV up 42.8% and revenue up 43.9%, versus 1Q24, driven by ongoing engagement in higher-margin channels such as the App."