A dollar weak index and lower US treasury yield are also making the yellow metal attractive for investors.

The writer is referring to the ‘dollar index’. The U.S. Dollar Index is an index (or measure) of the value of the United States dollar relative to a basket of foreign currencies. According to the given sentence, the dollar index has become weak. Therefore, a ‘weak dollar index’ should be used here instead of ‘dollar weak index’ so as to make the sentence correct.