b'Geophysics in the surveysNewsMineral Resources Tasmania: New 3D modelling seriesMineral Resources Tasmania is starting a new series of 3D geological and geophysical models. The intention for the new series is that it operate in near-conjunction with MRTs ongoing programme of regional geological mapping, which proceeds on the basis of 20 x 10 km 1:25 000 scale map sheets. These are grouped in pairs thus comprising a 20 x 20 km square for 3D modelling purposes, in part so that the maximum potential wavelengths that can be represented in the model are the same in north-south as well as east-west directions. The 3D models are envisaged to become a standard adjunct to the more traditional map publication output of the State geological survey.The inaugural model is based on the Lily and Lagoon sheets in northwestern Tasmania (Figure 1). In outcrop this area mainly consists of Rocky Cape Group Mesoproterozoic siliciclastics thatFigure 1.Cross-sections originally drawn by MRT field mapping geologists John Everard and Grace have been deformed and faulted andCumming, used to guide implicit geometric construction of Rocky Cape Group and granite units, indicated then intruded in the Devonian by theat lower left. Interpolated fault network shown semi-transparent. The model extends to 5 km below sea Interview Granite, which is exposed inlevel. Red and green numbers are respectively eastings and northings of the Map Grid of Australia Zone 55.the southwestern corner of the area. No drilling has been recorded anywhere in the model volume.The models are initially produced in close cooperation with the geologists undertaking the regional mapping, hence the new understanding and ideas that they have generated can be readily incorporated and tested with minimal diversion from their project workload. The main vehicle for this is the serial cross sections shown in Figure 1. These are used to guide lithostratigraphic unit geometry extrapolation from the primary geological contact and structural data observed at the topographic surface (not shown here), via the GeoModeller implicit engine.Following assignment of physical properties estimated from MRTs database, the initial model has been modified first by constrained inversion of gravity, serving mainly to determine a revised granite intrusion surface (Figure2 and 3). As implemented in GeoModeller, voxets attributed with propertiesFigure 2.The pink shell is the most probable Devonian granite surface indicated by gravity inversion. indicating uncertainty in location ofSpheres depict occurrences of commodities as shown in the legend at lower right. Entropy values indicate the granite surface are generated andthe level of spatial uncertainty associated with this and other model unit contacts in the inversion process. incorporated in the model product suite.Apparent susceptibility values from 0.05 to 0.03 SI define the anomalous magnetic volume shown.Subsequent magnetic inversion has defined anomalous magnetic volumesto the granite intrusion, suggesting athis magnetic material. However, the within the Rocky Cape Group units.genetic link. Known mineralisation ismagnetic volume extends significantly These appear to exist largely as a haloalso associated to some extent withfurther from the mineral occurrences in 27 PREVIEW APRIL 2023'