The S&P/ASX 200 Index (ASX: XJO) is having a good start to the week. In afternoon trade, the benchmark index is up 0.65% to 7,839.8 points.

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

Navigator Global Investments Ltd (ASX: NGI)

The Navigator Global share price is up 2% to $1.80. This morning, this investment company revealed that it has entered into an agreement to acquire a strategic minority stake in 1315 Capital and its affiliates. The release notes that 1315 Capital is a private equity firm with over US$1 billion assets under management that provides growth equity and growth buyout capital to commercial-stage medtech and pharma outsourcing, healthcare services, medical technology, and health and wellness companies. They target markets where high-quality management teams can rapidly scale platform companies into large and important businesses that positively impact patients, physicians, and the broader healthcare system.

Pilbara Minerals Ltd (ASX: PLS)

The Pilbara Minerals share price is up almost 8% to $1.96. This is despite there being no news out of the lithium miner. However, a number of lithium miners are pushing higher today as investor sentiment improves. They may believe that this side of the market has been oversold in recent time and created a buying opportunity.

Smartpay Holdings Ltd (ASX: SMP)

The Smartpay share price is up 48% to 78.5 cents. Investors have been scrambling to buy the payments company's shares after it received a takeover approach from both Tyro Payments Ltd (ASX: TYR) and another third party. Tyro Payments' indicative proposal is to acquire 100% of the issued ordinary shares of Smartpay by way of scheme of arrangement for a price of NZ$1.00 (approximately A$0.90) per share. This comprises a majority of Tyro shares as well as cash consideration.

Spartan Resources Ltd (ASX: SPR)

The Spartan Resources share price is up 9% to $1.75. This follows news that the gold miner has agreed to merge with Ramelius Resources Ltd (ASX: RMS). It has accepted a deal that will see Ramelius acquire all outstanding Spartan shares for $0.25 in cash and 0.6957 new Ramelius shares per share. This valued the company at $1.78 per share, which represented a relatively modest 11.3% premium to its last close price but a 27.5% premium to its 30-day average price. Ramelius' managing director, Mark Zeptner, said: "With the Spartan Effect, Ramelius has a vision for the Combined Group to be a +500koz/pa producer in FY30."