POSSIBILITY OF RARE-EARTH MINERAL FORMATION DURING HYDROTHERMAL-SEDIMENTARY MASSIVE SULFIDE DEPOSITION

Abstract

Recent reports of relatively high concentrations of rare-earth elements in hot springs on the East Pacific Rise and their accumulation in metalliferous sediments are stimulating investigations of rare-earth mineralization in old volcanogenic ore deposits of different types, including massive sulfide. The finding of rare-earth mineralization in a deposit where its relationship to syngenetic sulfide mineralization, the low level of regional metamorphism and the absence of any sign of late intrusive igneous activity make it very unlikely that it is young and superposed is theoretically very interesting and indicates the possible hydrothermal-sedimentary mode of rare-earth accumulation, particularly during the formation of massive sulfide ore. In an isolated case, rare-earth minerals like monazite, the fluocarbonate and, most probably, bastnasite are associated with a veinlet of more complex composition, containing calcite, quartz, albite, potassic feldspar, hyalophane, sphalerite, chalcopyrite, fahlore and cubanite. Such veinlets probably were formed at higher temperatures, when primary syngenetic mineralization was redeposited upon reacting with later hydrothermal solutions.