Ferromanganese metasediments in the immediate vicinity of the Mid-Proterozoic Broken Hill Pb-Zn-Ag lodes, have undergone high grade (upper amphibolite facies) metamorphism,to form Mn-pyroxenoid (rhodonite,pyroxmangite) and garnet- rich lithologies. Such lithologies bear compositional (bulk rock,rare earth element)and morphological similarities to recent and ancient ferromanganese hydrothermal sediments of the Pacific._x000D_
The non-metasomatic,stratiform garnetites are predominantly composed of magnesia-rich, calcium-poor almandine spessartine and quartz, which possess a bulk chemistry comparable to alumina-rich ferrommanganese oxide deposits of the Pacific. Such sediments are attributed to a mixed protolith comprised of clay and ferro- manganese oxides (mainly amorphous goethite with lesser todorockite-birnessite). Manganiferous pyroxenoid rocks are probably derived from alumina- poor ferromanganese cherts,similar to Japanese tetsusekiei._x000D_
Rare earth element compositions of Broken Hill garnetites are very similar to those of recent ferromanganese seafloor accumulations, suggestive of some genetic link.