Mary is the "Domus Aurea," the House of Gold
Mary is called golden; because her graces, her virtues, her innocence, her purity, are of that transcendent brilliancy and dazzling perfection, so costly, so exquisite, that the angels cannot, so to say, keep their eyes off her any more than we could help gazing upon any great work of gold.
But why called a house or palace? And whose palace? She is the house and the palace of the Great King, of God Himself. Our Lord, the Co-equal Son of God, once dwelt in her. He was her Guest; nay, more than a guest, for a guest comes into a house as well as leaves it. But our Lord was actually born in this holy house. He took His flesh and His blood from this house, from the flesh, from the veins of Mary. Rightly then was she made to be of pure gold, because she was to give of that gold to form the body of the Son of God. She was golden in her conception, golden in her birth. She went through the fire of her suffering like gold in the furnace, and when she ascended on high, she was, in the words of our hymn,
Above all the Angels in glory untold,
Standing next to the King in a vesture of gold.