The close association of basalts, bedded ferromanganese ore and red cherts is observable at the Kawame Quarry in the Hayachine Belt. Major, trace and rare earth element contents and chemical compositions of constituent minerals were determined for these three types of rocks. The basalts are composed of chlorite, albite, epidote, quartz, calcite, sphene, pumpellyite and actinolite, and locally preserve primary clinopyroxene relicts. The chemical compositions of these clinopyroxene relicts are generally similar to those of modern mid-ocean ridge basalt (MORB). In addition, bulk-rock chemical compositions of the basalts show that there is a general similarity between the Kawame basalts and modern MORB. The chondrite-normalized rare earth element (REE) patterns of the basalts are subtly light REE-enriched, suggesting the basalts appear to have an affinity for enriched MORB.
The ferromanganese ores are dominated by hematite with minor amounts of quartz. They exhibit significant enrichment of Fe, Mn, P, V, Y and REE except for Ce. There is a gross positive correlation between Fe+Mn and these enriched elements. The average pattern of these elements/Fe ratios of the ferromanganese ores is similar to that of modem hydrothermal metalliferous (ferromanganese) sediments near MOR. The Post-Archean Average Australian Shale-normalized REE patterns of the ferromanganese ores are characterized by negative Cc anomalies. Their geochemical features mentioned above demonstrate consistently that the Kawame ferromanganese ores are ancient counterparts of modem MOR hydrothermal sediments. Red cherts comprise of quartz and hematite with trace calcite, rhodonite, stilpnomelane, apatite, actinolite and andradite. They are simple mixtures of ferromanganese ores and pelagic cherts in varying proportions. In conclusion, the Kawame basalts associated with ferromanganese ores and red cherts are most likely remnants of late Devonian oceanic crust.
