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

To interpret magnetic responses of different mineral settings in Papua New Guinea, field campaigns were conducted by the Geological Survey Division in two mineral fields in the Rigo District, Central Province.

In December 2011, geological mapping accompanied by a ground magnetic survey was conducted over iron-rich gossan within a volcanic sequence at Kore. In March 2012, an analogous program was undertaken in a sedimentary-hosted manganese field near Kemaea village.

Ground magnetic surveys in both areas comprised a series of north-south magnetic profiles, up to 1 km in length separated by 100 m.

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 a 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 by the response in 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 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.