All the "metallic" fabric I have ever seen is printed on. There are not metallic threads, it is one of the inks used to print the design. It is very common in Asian themed fabrics and I have used it in quilts extensively. On some of the inks used to print the design the metallic shimmery look can eventually wash out leaving a gold colored design behind without the sparkle. I have not had that happen to me but most of the quilts I have made I have given away. It seems to be holding up quite well in this one:
Scrappy log cabin clam shell setting
I would not hesitate to use fabric with metallic inks in the print in any quilt.