Metals of antiquity Metals of antiquity The metals of antiquity are the seven metals which humans had identified and found use for in prehistoric times: gold, silver, copper, tin, lead, iron, and mercury. These seven are the metals from which the modern world was forged; until the discovery of arsenic in the 13th century, these were the only known elemental metals, compared to the 86 known today. The metals of antiquity generally have low melting points, with iron being the exception. While all the metals of antiquity but tin and lead occur natively, only gold and silver are commonly found as the native
Regolith-hosted rare earth element deposits Regolith-hosted rare earth element deposits Regolith-hosted rare earth element deposits (also known as ion-adsoprtion deposits) are rare-earth element (REE) ores in decomposed rocks that are formed by intense weathering of REE-rich parental rocks (e.g. granite, tuff etc.) in subtropical areas. In these areas, rocks are intensely broken and decomposed. Then, REEs infiltrate downward with rain water and they are concentrated along a deeper weathered layer beneath the ground surface. Extraction technology of the deposits has been evolving over the last 50 years. In the past, REEs were primarily extracted in small amount as by-products in mines of other metals or