b'ASEG newsCommitteesclassifications show good correlationmagnetite to hematite with decrease inand monzogranite gneiss (Figure 1(c)). and the four broad lithologies aremagnetic susceptibility. The syenograniteThe importance of field geological recognised: a monzogranite migmatiteshows a wide range in MS, which can beevidence to ground truth a geophysical gneiss (I-type and magnetite-series)explained by the presence of unevenlyinterpretation was demonstrated with characterised by high MS, a syenogranitedistributed coarse grains of magnetitethree major changes proposed to the (I-type and magnetite-series) with high(possibly secondary).published regional bedrock geology MS, a monzogranite (S-type and ilmeniteThe aeromagnetic data was processedmap of the area: (1)Change of a series) with low MS and a porphyriticto create a series of products: reducedmetamorphosed siliciclastic sedimentary monzogranite with two subgroups: onetopole (RTP) total magnetic intensityunit to an ilmenite series reduced with high MS (I-type and magnetite(TMI), upward continuation (UC) andmonzogranite, (2) Change of a tonalite-series) and the other with bimodal MSresidual of UC and RTP at a seriestrondhjemite-granodiorite unit to a (boundary of I-type and S-type andof depths, the 1st and 2nd verticalsyenogranite and (3) Extension of the magnetite-series). derivativesand the tilt derivative. Themafic gneiss along structures into the MS data demonstrates a high amountinterpretation of the magnetic datawest of the area. All the regions of low of variation within rock types at theinvolved combining the TMI productsmagnetic intensity had previously been outcrop scale necessitating a substantialwith satellite imagery, regional geologyclassified as a metasedimentary unit, number of measurements (sometimesmaps and all the data from the fieldwork.which through ground-truthing has been up to a 100) per outcrop for reliableThe orientation and geometries ofdisproved in this study. The low magnetic MS averages. In the monzograniteseveral NE-SW trending faults, a N-Ssignature of these regions is due to an gneiss, MS is observed to increase inregional shear, E-W and NE-SW maficilmenite series granite, as supported the mafic mineral rich melanosomedikes and lithological contacts have beenby the MS data (Figure 1(a), Site 3), layers when compared to the quartz- delineated using the derivative productsabsence of magnetite in thin sections feldspathic leucosome, even though no(Figure 1 (b-c)). Magnetic intensityand a presence of biotites characterised significant difference in the distributionand texture of anomalies in the RTPby high FeO, Al 2 O 3and low MgO of magnetite was observed. In someand residual of UC and RTP were usedcomposition. The magnetic responses in regions the porphyritic monzograniteto map the four outcropping granitoidthis area have been identified to primarily shows bimodality in MS, while in otherlithologies and an inferred mafic gneissbe controlled by different oxygen regions it shows strongly ferromagneticunit associated with intense magneticfugacity conditions giving rise to the two character, with thin sections showinghighs predominantly present along majortypes of granites along with some local an increased degree of martitisation ofstructures within the monzograniteeffects of weathering and alteration. Figure 1. (a) Magnetic susceptibility frequency histograms, (b) grey scale image of the 1st vertical derivative of the RTP-TMI and (c) the interpreted bedrock geology of the area. FEBRUARY 2024PREVIEW 15'