oa Potential field modelling of the Tingha Monzogranite and tin mineralised Gilgai Granite, Inverell NSW

The Gilgai Granite and the Tingha Monzogranite are located south of Inverell in northeastern NSW (see Figure 1). Potential field data has been modelled to determine the morphological relationship of these two granites. Total Magnetic Intensity (TMI) data, acquired by the NSW government Discovery 2000 program, was used to generate a 2.5D model. Presented within this paper are the results of modelling the southwestern corner of the Gilgai Granite, which accounts for approximately one third of the Gilgai Granite that is visible in TMI imagery.

The Gilgai Granite is highly mineralised with disseminated and vein-type cassiterite and polymetallic sulfide occurrences. Tin has been historically mined, mainly from shallow workings. Better understanding the mineralisation and formation controls may increase exploration in this area.

Eleven TMI cross-sections were modelled. The results indicate that the Gilgai Granite is steeply dipping and tapers with increasing depth. It has a vertical extent of approximately 1000–1400 m and intruded around and over the Tingha Monzogranite, but not beneath the Tingha Monzogranite. The Gilgai Granite has sill-like bodies, isolated masses and/or roof pendants that intrude the Tingha Monzogranite. The source rock has magnetic zonation, with modelled magnetic susceptibilities ranging from 4.8–14.0×10^-3 SI with a mode of 5.5×10^-3 SI.