Search

Several gentle hills close to the crest of the East Pacific Rise are covered with extensive Fe-Mn-rich deposists. The setting of the sediments precludes the possibility that turbidite flows, slumping or downhill winnowing of material can have been responsible for the accumulation of these sediments, as is also indicated by the lack of reworked faunas or crushed shells. Palaeontological dating and the magnetic anomalies of the crustal substratum show that the sediments must be very young, that is, the sedimentation rates are very high; thus, 8–10-m-thick sediments were formed in 600,000 yeas. The accumulation rates on these hills for several elements, such as Fe, Mn, Cu and Ba, are much higher than in ordinary pelagic regions. The element deposition is best described as an exhalative-sedimentary process. The areal extent of these sediments is considerably larger than that of any other currently forming analogous deposits. The results have far-reaching implications for the discussion of how sedimen...

Unaltered hausmannite ores from Langban, Sweden, contain two rhombohedral carbonate phases, namely calcite and a carbonate with a disordered calcite structure; the latter with the approximate composition Ca0.4Ba0.4(Pb, Mg)0.2CO3 and cell dimensions (hexagonal setting) a = 5.12 and c = 18.12A. The carbonate phases were emplaced together with the ore minerals before the metamorphic events, which in their turn preceded the late vein and vug forming period in Langban. It appears likely that such carbonates are much more common than was previously realized, and that they were the source of most of the Pb, Ba and Ca present in the native lead-pyrochroite veins.