Geochemical Analysis of Cored Rock Samples Along the Proposed Milton Ulladulla Bypass

The NSW Government is currently planning the development of a major road corridor in the Milton and Ulladulla region of southern NSW (“the Milton Ulladulla bypass”). There is a need for more information on the geology beneath the proposed road corridor, as this area has seen relatively limited geological studies conducted in the past. The work presented here aims to provide new geological data through the analysis of borehole samples collected along the proposed extent of the Milton- Ulladulla bypass. A total of 45 samples were examined. These were taken from 23 boreholes. Each core sample was cut vertically, with one side crushed and prepared for geochemical analysis through XRF, with the remaining half used as an archive copy and kept for visual analysis. XRF compositions were analysed and placed on differing plots for comparison along with maps made using ArcGIS Pro to investigate spatial trends. The results show that there is an area that has extensive alteration and is located in one zone near the boundary of the Milton Monzonite and Wandrawandian Formation. Remaining samples that demonstrate changes in structure and colour follow a pattern of being brown and crumbly which can be considered to be weathered samples that exist throughout the area. The alteration is visible within hand samples, which show degradation and loss of structure and texture. These altered samples also record geochemical data where elements with outliers are almost exclusively found within altered material. The project results have been summarised in several maps which show refined estimates of the boundaries of the geological units in the region, the ’depth to altered material’ to aid future drilling and foundation plans and regions of high sulphur (which potentially identify areas that are at higher risk of acid sulphate soils, which may impact foundation planning). Future work could build upon the results found within this study by further sampling to identify the true extent of the alteration zone and presence of acid sulphate soils.