* Abu Dhabi index suffers biggest drop since June
* Saudi's Ma'aden bucks weak blue chip trend
* Nama Chemicals surges on shareholder demand, then retreats
* Qatar National Bank retreats sharply
* Dubai's Arabtec gains after unit wins contract
By Abinaya Vijayaraghavan and shakeel ahmad
Nov 20 (Reuters) - All major Gulf stock markets fell on Tuesday with Abu Dhabi suffering its biggest one-day drop since June as bank shares weighed on the index.
Oil prices fell on Tuesday and were set to snap a four-day winning streak because of concern about rising global supplies. Meanwhile, world stock markets declined on a tech sell-off.
"Weak sentiment is clear across the region. It's accompanied by geopolitical issues, the recent developments in Saudi (with the killing of journalist Jamal Khashoggi) and the possible outcome from that incident," said Tariq Qaqish, managing director for asset management at Menacorp Financial Services in Dubai.
In the United Arab Emirates, third-quarter corporate earnings were not impressive despite a strong performance from the banking sector. All other sectors are slowing down, Qaqish added.
The Abu Dhabi index fell 1.8 percent, its biggest drop since June, with First Abu Dhabi Bank dropping 2.2 percent and Commercial Bank International tumbling 8.6 percent in light trade.
Dana Gas dropped 3.6 percent to trade at a two-month low of 1.06 dirhams.
Saudi Arabia's main index slid 0.7 percent, weighed down by petrochemical stocks. Saudi Basic Industries lost 2.0 percent and National Commercial Bank decreased 1.3 percent.
Saudi Arabian Mining (Ma'aden) added 1.3 percent after energy minister Khalid al-Falih said King Salman would inaugurate on Thursday the Waad Al-Shamaal project, a 440-square-km city for mining industries in the country's north.
Nama Chemicals jumped as much as 7.2 percent after shareholders owning more than 5 percent of the firm requested a meeting to consider the dissolution of the current board and the election of a new one. But the stock ultimately closed 0.9 percent lower.
The Qatar index was also hurt by bank shares, losing 1.3 percent after three straight sessions of gains in its biggest fall since August. The Middle East's largest lender, Qatar National Bank. lost 3.4 percent.
In Dubai, the index dropped 1.2 percent with property firms sliding. DAMAC Properties fell 2.8 percent and Emaar Development was down 2.6 percent. The emirate's largest lender, Emirates NBD, lost 2.1 percent.
But Arabtec rose 1.4 percent after its unit Target Engineering secured a 521 million dirham ($142 million) contract for construction work on a project for Abu Dhabi's state oil firm.
Markets in Egypt, Oman and Bahrain were closed for religious holidays. SAUDI ARABIA * The index fell 0.7 percent to 7,505 points. DUBAI * The index shed 1.2 percent to 2,750 points QATAR * The index lost 1.3 percent at 10,268 points. ABU DHABI * The index fell 1.8 percent at 4,991 points KUWAIT * The index lost 0.3 percent at 5,271 points. (Editing by Andrew Torchia/Mark Heinrich)