What is the significance of Silas' mistaking the yellow curls for his gold in Silas Marner?
The significance is that it denotes the insane obsession that Silas Marner had over the gold that he had lost, and it is also significant because what would happen now is that Silas will start believing that, by giving the child a home and by caring for it, maybe his gold will be returned to him. It was sort of a protoidea of Karma: If God was so good to send this child with locks of "gold", maybe then there is a possibility that by him caring for this thing sent by God, he would "earn brownie points" so to speak, and God will be kind enough to produce a miracle and return the gold.
We know that he eventually receives his gold, but the real miracle was that the child's main influence was not helping Silas return his gold, but helping Silas care for someone for the first time in his life. That was the true miracle of the child in Silas's life.