Volcanic Exhalations and Metal Enrichments at Matupi Harbor, New Britain, T.P.N.G

Abstract

Geochemical investigations have been carried out in the volcano-exhalative-sedimentary environment at Matupi Harbor, New Britain, T.P.N.G., in an attempt to elucidate the potential of such environments for stratiform ore formation.Matupi Harbor is a sheltered basin with hot, acid springs entering at its eastern and northern shores. These springs carry up to about 100 ppm iron, 100 ppm manganese, 2.5 ppm zinc, and slightly less than 0.1 ppm copper and lead. In comparison with the hot brines under the Red Sea, the Matupi springs have similar iron, manganese and zinc contents, and roughly one tenth the copper and lead contents.These springs are causing significant enrichments in the iron, manganese and zinc contents of the harbor sediments. The most enriched sediments are reddish-brown silts, which are abundant in the vicinities of the major thermal springs.In contrast to other volcano-exhalative-sedimentary areas, there is very little iron sulfide forming in the Matupi area. Laboratory studies indicate that sulfate-reducing bacteria are not noticeably active in the Matupi Harbor sediments unless organic matter is added. The apparent rarity of organic matter on the floor of the harbor was unexpected.It is concluded that stratiform iron-manganese deposits could form in volcano-exhalative-sedimentary environments if the rate of influx of detrital materials was much lower than at Matupi. For the formation of economic deposits of other metals, the conditions before, during or after precipitation, would have to be suitable for separating these metals from the predominant iron and manganese.