If I recall correctly, Mormons teach that American Indians are the 10 lost tribes of Israel. A different kind of replacement??
Not quite. You are thinking of the Book of Mormon, which describes how two small groups migrated from Judea to the Americas about the time of the Babylonian Captivity (ca 600 BC). These groups mixed with other people in the Americas; some of their descendants are among the American Indians today.
The Ten Tribes were carried away captive by the Assyrians earlier (722 BC). The present location of the Ten tribes is unknown to us; however, Mormonism teaches that God will restore them in time.