Śrī brahma-saṁhitā 5.18
tasya padmaṁ viniryayau
brahmaṇo lokam adbhutam
When Viṣṇu lying in the ocean of milk wills to create this universe, a golden lotus springs from His navel-pit. The golden lotus with its stem is the abode of Brahmā representing Brahmaloka or Satyaloka.
"Gold" here means the dim reflection of pure cognition.