Marathon Digital, the world's leading Bitcoin miner by market capitalization, experienced a significant 18% surge in its shares following confirmation of its addition to the S&P SmallCap 600 index fund.

The announcement by S&P Dow Jones Indices on May 3 stated that Marathon would be replacing Aaon, a heating and ventilation manufacturing firm, in the index, effective May 8.

The S&P SmallCap 600 index tracks 600 U.S. companies with market capitalizations ranging from $1 billion to $6.7 billion, demonstrating profitability in both the most recent quarter and the last four quarters.

Marathon Digital's (MARA) shares rallied to $20.67 on Monday, May 6, marking an impressive 18% increase, according to Google Finance. The surge comes despite challenges faced by the cryptocurrency mining industry, including the Bitcoin halving on April 20, which reduced miner block rewards from 6.25 BTC to 3.125 BTC.

Although MARA shares are down 9.86% year-to-date, they reached a peak of $31.03 on Feb. 28. With a market capitalization of $5.6 million, Marathon is expected to hold significant weight in the S&P SmallCap 600 index, particularly considering the index's float-adjusted market capitalization weighting method.

The timing of Marathon's inclusion in the index coincides with its upcoming first-quarter earnings report on May 9. Investment research firm Zacks anticipates a remarkable 280% year-on-year increase in revenue to $193.9 million and a 166.7% year-on-year surge in earnings per share to $0.02.

The positive performance of Marathon Digital shares also resonated with its competitors in the Bitcoin mining sector. CleanSpark (CLSK) and TeraWulf (WULF) observed respective jumps of nearly 8% and 10.7% on May 6.

These upward movements in Bitcoin mining stocks occur amidst a backdrop of declining miner revenue following the halving. While transaction fees initially offset the reduced block subsidy post-halving, they have since tapered off, underscoring ongoing dynamics within the cryptocurrency mining ecosystem.