Are item made of Mithral and/or Adamantine met…

Are item made of Mithral and/or Adamantine metals enchantable?

@Wizards_DnD , @DnDBeyond , @SageAdviceDnD , @mikemearls , @JeremyECrawford Not RAW, Not RAI, but a Lore question: Are item made of Mithral and/or Adamantine metals enchantable or does their innate magical essence block/push out other magical attempting to infuse with the item?