“Transmute!!” Immediately, the huge dart flew out like a bullet at Stiyl’s eye with a golden chain attached at the end. Stiyl bent his body downwards and the snake-like golden dart flew overhead. A second golden chain flew out of Aureolus’ sleeve, ripped through the air and grazed Stiyl’s face.
[...]
With the sound of a fruit being sliced open, the tip of the dart stabbed into the back of a fallen student.
[...]
BAM! As if piercing a balloon, the student’s body burst into bits and fluids. It was as if someone had used a powerful acid to dissolve the body but… something was strange. It was not an ordinary liquid but a shiny gold… It was pure gold that melted from the intense heat. With a swish, the chain curled and the dart was back into Aureolus’ sleeve.
[...]
“Anyone who’s touched by my Instant Alchemy Limen Magna, will be forcefully transmuted into pure gold. It can’t be defended from nor avoided."
[...]
The golden dart was merely a materialized tool. Limen Magna’s actual identity was the entire fortress called Misawa Cram School.

Even if the tool’s mana supply were cut off, as long as the main body was supplied with mana and the shape was recreated, it was reusable.

Toaru Majutsu no Index vol.2 ch.2 pt.6,8