* Polls close after peaceful election
* Calm vote seen key to mining, oil investment
* Johnson-Sirleaf faces challenge from Tubman-Weah ticket
By Richard Valdmanis and Alphonso Toweh
MONROVIA, Oct 11 (Reuters) - Liberians wrapped up a peaceful presidential election on Tuesday -- the West African state’s second since a civil war -- though worries remained that the results could spark street clashes.
The vote pitted newly named Nobel peace laureate President Ellen Johnson-Sirleaf against former U.N. diplomat Winston Tubman and 14 others, and came as investors planned to sink billions of dollars into the country’s mining and oil sectors.
“I vote today, I‘m happy, I‘m happy,” shouted Cecilia Weah, dancing outside a polling station in the capital Monrovia . “I want free movement. I want all that has ever been sweet Liberia!”
Voters queued calmly, at times under pouring rain, to cast their ballots, and international election observers said they had received no reports of problems at the nation’s polling stations.
Passions have run high in the contest that some forecast will go to a second-round run-off between Johnson-Sirleaf and Tubman. The results of the first-round vote are expected within 15 days according to Liberia’s electoral law.
Many voters recall how a dispute over the outcome of the 2005 election led to days of rioting in Monrovia.
“From what I see there is no worry,” said Speciosa Wandira Kazibwe, head of the African Union observer delegation. “If the leaders take the results there will be no chance for violence.”
Eight years into peace, Liberia has seen growing investment in its iron and gold mines and has convinced donors to waive most of its debt, though many residents complain of a lack of basic services, high food prices, rampant crime and corruption.
Unemployment remains high, war-wounded beg on the streets and average income stands at $300 a year -- below the $1-a-day benchmark for extreme poverty.
“Ellen done nothing, I seen nothing,” said Anthony, an 18-year-old resident of West Point, a Monrovia slum where raw sewage trickles between a crush of makeshift brick and tin dwellings, home to many of the civil war’s ex-child soldiers.
Others in West Point credited her with paving their main road and building a school and said they had voted for her.
Johnson-Sirleaf initially ruled out a second term, but has since said she needs one given the huge challenge. Her jocular campaign slogan -- “Monkey Still Working, Baboon Wait Small” -- urges Liberians to have a bit more patience.
“DIFFICULT TO GOVERN”
Campaigning for the election has been mostly calm, though scuffles erupted between rival supporters in Monrovia during final rallies at the weekend.
The election will be Liberia’s first locally organised presidential poll since the end of the 1989-2003 conflict that killed nearly a quarter of a million people. Johnson-Sirleaf became Africa’s first freely elected female head of state in the 2005 election that was organized by the United Nations.
Tubman, whose running mate is ex-soccer star George Weah, is expected to give Johnson-Sirleaf her toughest challenge.
Analysts say Johnson-Sirleaf’s Nobel Peace Prize, awarded jointly with Liberian activist Leymah Gbowee and Yemeni rights activist Tawakul Karman last week, could give her the edge by galvanizing the female vote in her favour.
A Harvard-educated former U.N. diplomat, Tubman told Reuters on Saturday he is certain he will win and issued a veiled warning that his supporters could make it “difficult to govern” for anyone else.
Casting his vote on Monday, he said: “I will tell them (my supporters) to accept it if the election is free and fair ... I expect it will be.”
Johnson-Sirleaf, voting in her hometown of Fee Fee about two hours drive from the capital said she was also confident. “I am optimistic, I think the Liberian people will do the right thing.”
The United Nations said the return of mercenaries from a four-month civil war in Ivory Coast this year could be a threat though there has been no evidence of plans to disrupt voting.
Citing violent crime, instability in Ivory Coast and trafficking of drugs and arms across the region, the U.N. Security Council extended the mandate of the 9,200-strong peacekeeping mission UNMIL last month.
“I hope everybody, as I have appealed and appealed, will proceed peacefully and accept the results according to the rules,” Special Representative to the U.N. Secretary General Ellen Margreth Loj told Reuters as she visited a peacekeeper headquarters in the center of Monrovia.
A peaceful, free and fair election could bolster growing investor confidence in the country, which is rich in iron ore deposits and has promising agriculture and energy sectors.
Miners ArcelorMittal and BHP Billiton and oil companies Anadarko , Tullow and Chevron are already active in the country.
The head of Liberia’s National Oil Company, Christopher Neyor, predicted an offshore oil find is likely “pretty soon” and said majors Exxon Mobil , France’s Total , and Brazil’s Petrobras had made inquiries about acreage.