Why American Pacific Borates, NAB, Perenti, & Xero are tumbling lower

The S&P/ASX 200 Index (ASX: XJO) looks set to continue its poor run on Thursday. In afternoon trade, the benchmark index is down 0.6% to 7,000.8 points.

Four ASX shares that have fallen more than most today are listed below. Here's why they are tumbling lower:

American Pacific Borates Ltd (ASX: ABR)

The American Pacific Borates share price has sunk 15% to $1.45. This mineral exploration company's shares have come under significant pressure this week after announcing that it would defer its Phase 1A plans for the Fort Cady Borate Mine. Instead, the company intends to shift its focus to a larger borate operation and production of borate specialties combined with sales of boric acid.

National Australia Bank Ltd (ASX: NAB)

The NAB share price is down 2.5% to $25.90. Almost all of this decline is attributable to the banking giant's shares going ex-dividend this morning for its fully franked 60 cents per share interim dividend. This dividend will now be paid to eligible shareholders in just over seven weeks on 2 July.

Perenti Global Ltd (ASX: PRN)

The Perenti Global share price has crashed 28% lower to 70.5 cents. This follows the release of an operational update this morning by the mining services company. That update reveals that Perenti will no longer be delivering on its guidance for second half revenue and margins in line with what it reported in the first half. Instead, due to the combined impact of COVID-19, Australian labour market shortages, and the stronger Australian dollar, it is expecting softer earnings in the second half. It also expects these headwinds to continue for the next 12 to 18 months.

Xero Limited (ASX: XRO)

The Xero share price has sunk 12% to $118.87. Investors have been selling the cloud-based business and accounting platform provider's shares following the release of its full year results. Although Xero delivered strong growth on both the top and bottom lines, it was still short of the market's expectations. In addition to this, weakness in the tech sector is adding to the selling pressure.