There is nothing wrong with lending the gold as long as it is paid back with the same weight. The Prophet (peace be upon him) said:
Gold is to be paid for by gold with equal weight, like for like.
Moreover, there is no harm if it is paid with excess provided that it is offered without a stipulation. The Prophet (peace be upon him) said:
The best of people are those who are best in paying off the debt.
It is noteworthy that its value should be paid according to the current rate hand to hand, for
Ibn `Umar (may Allah be pleased with them both) reported:
We said: O Messenger of Allah! We sell for dirhams and take dinars and we sell for dinars and take dirhams. The Prophet (peace be upon him) said: There is no harm in taking them at the current rate so long as you do not separate leaving something to be settled.
May Allah grant us success. May peace and blessings of Allah be upon our Prophet Muhammad, his family and Companions!