Magnetic responses from an iron-rich gossan in a volcanic terrain and a limestone-hosted strata-bound manganese deposit, Central Province, Papua New Guinea

Abstract

Author: Mosusu, N1*., Saroa, D1., Abiari, I1., Verave, R1., Irarue, P1., and Kolotein, P2. To interpret magnetic responses ('magnetic signature') of different mineral settings in Papua New Guinea (PNG), field campaigns were conducted by the Geological Survey Division in mineral fields in the Rigo District, Central Province of Papua New Guinea. Geological mapping accompanied by a ground magnetic survey was conducted over iron-rich gossans within a volcanic sequence at Kore. A similar program was undertaken in a sedimentary-hosted manganese field near Kemaea village. The gossans are within the Middle Miocene Kore Volcanics which are bounded to the south by the Middle Miocene Gidobada Limestone. In contrast, the manganese nodules at Kemaea, are within the Late-Middle Eocene Port Moresby beds and are bounded to the north-east by the Early Eocene-Middle Oligocene Sadowa Gabro. The results of the magnetic survey show significantly different responses that are apparently related to the style of mineralisation. The total magnetic response of a gossan within the volcanic rock unit is characterised by high frequency signals that require extensive filtering to outline the trend of distinct magnetic source. In contrast, the limestone-hosted strata-bound manganese deposit has a well-defined north-westerly structural trend that is easily distinguished within the response of the total magnetic field. Applying a reduced to magnetic equator algorithm and generating an upward continuation of the magnetic field enhances these structural trends. The analytical signal of the magnetic field also enhances the interpretation of the signal from the two different sources. The results of the survey demonstrate that background knowledge of mineral systems, including major mineral composition and style of deposit is essential to interpret imagery from ground magnetic surveys of mineral deposits and that different styles of mineralisation generate unique magnetic responses.