* Official's comment first sign of challenge to Lopez's order

* Dismissed Lopez also ordered mine closures, suspensions

* Philippines is world's top nickel ore supplier (Adds quotes, background)

By Enrico Dela Cruz

MANILA, June 29 (Reuters) - A ban on open-pit mining in the Philippines enforced by former environment minister Regina Lopez has "no legal basis" and is under review, a senior government official said, the first sign that drastic measures she had ordered could be challenged.

"In the Philippines ... surface mining or 'open-pit' is technically and financially feasible," Larry Heradez, head of the Mines and Geosciences Bureau's legal division, told reporters on Thursday.

It was the first time a government official has countered a policy previously issued by Lopez, who was dismissed last month.

A staunch environmentalist, Lopez led a 10-month mining crackdown, ordering the closure or suspension of 26 mines in the world's top nickel ore supplier and imposing a ban on open-pit mining, which she said "kills the economic potential of the place."

Heradez is part of a team that is reviewing Lopez's policy orders, including the cancellation of 75 contracts for undeveloped mines to protect watersheds.

Some of the 75 contracts may still be cancelled, he said, "not because the projects are within watersheds but because of possible violations like non-payment of taxes and non-implementation of work programme."

Once the team has completed its review of all previous policy orders and made recommendations, they will be submitted to Lopez's replacement, Environment Secretary Roy Cimatu, who then "can revise or amend or supersede" them.

Cimatu, who took over on May 8, has been taking a slow approach towards mining. He said on Tuesday he may decide in July what to do about the mining operations and contracts that Lopez ordered closed, suspended or cancelled.

The former military chief told Reuters in May it was possible to strike a balance between mining and natural resources, signalling his intent to settle a dispute that has been one of the biggest economic conundrums of President Rodrigo Duterte's presidency.

(Reporting by Enrico dela Cruz; Writing by Manolo Serapio Jr.; Editing by Tom Hogue)