This report provides an initial summary of the hydrogeochemistry of the McBride Basalt Province (MBP) and Nulla Basalt Province (NBP) of the Upper Burdekin Region of North Queensland, completed as part of Exploring for the Future (EFTF)—an eight year, $225 million Australian Government funded geoscience data and information acquisition program focused on better understanding the potential mineral, energy and groundwater resources across Australia. Groundwater hydrogeochemistry studies can improve system understanding by reflecting host formation compositions and groundwater processes. These studies also provide regional baseline groundwater datasets that can inform environmental monitoring, resource use and decision making. During 2017 and 2018 Geoscience Australia collected 38 groundwater samples and 80 surface water samples (including quality control samples) to evaluate groundwater system processes including potential flow paths, recharge and groundwater-surface water-interactions. These surveys were conducted across three months of fieldwork, sampling water for a comprehensive suite of hydrogeochemical parameters. The present report includes surface water and groundwater data and information on: 1) sampling sites; 2) field physicochemical parameters (EC, pH, Eh, DO and T); 3) field measurements of total alkalinity (HCO3-); 4) laboratory results of major anion and cation results; 5) laboratory results for isotopes of water (δ18O and δD), DIC (δ13C), and dissolved strontium (87Sr/86Sr); and 6) hydrogeochemical maps representing the spatial distribution of these parameters. Pending analyses include: CFCs, SF6 and radiogenic isotopes δ14C and δ36Cl. Analysis that were largely below detection limit include: trace element concentrations, dissolved sulfide (S2-), ferrous iron (Fe2+), and dissolved sulfate (affecting sampling of δ34S and δ18O). This study demonstrates that hydrogeochemistry surveys, with full suites of chemical parameters including isotopes, can reveal fundamental groundwater system processes such as groundwater flow paths, groundwater recharge and groundwater-surface water interactions. The chemical ‘fingerprints’ identified here indicate groundwater flow paths are largely restricted to within the MBP and NBP aquifers, which have little interaction with adjacent and underlying non-basaltic rocks. The results also indicate groundwater is largely recharged from rainfall in higher elevations of the basalt provinces, with variable rainfall inputs to groundwater from lower elevation and rivers along flow paths. Groundwater-surface water interactions show several chemical signatures linking groundwater to springs, tributary rivers and the Burdekin River. Results from the Upper Burdekin Hydrogeochemistry Survey for the MBP and NBP have been plotted and mapped with initial interpretations presented below. Further detailed interpretation of this hydrogeochemistry data will be the focus of future publications. This data release is part in a series of staged outputs from the EFTF program. Relevant data, information and images are available through the Geoscience Australia website.

The Upper Burdekin Chloride Mass Balance Recharge web service depicts the recharge rates have been estimated at borehole locations in the Nulla and McBride basalt provinces. Using rainfall rates, rainfall chemistry and groundwater chemistry, the recharge rates have been estimated through the Chloride Mass Balance approach.

This grid dataset is an estimation of the relative surface potential for recharge within the Nulla Basalt Province. This process combined numerous factors together as to highlight the areas likely to have higher potential for recharge to occur. Soil permeability and surface geology are the primary inputs. Vegetation and slope were excluded from consideration, as these were considered to add too much complexity. Furthermore, this model does not include rainfall intensity – although this is known to vary spatially through average rainfall grids, this model is a depiction of the ground ability for recharge to occur should a significant rainfall event occur in each location. The relative surface potential recharge presented is estimated through a combination of soil and geological factors, weighting regions that are considered likely to have greater potential for recharge (e.g. younger basalts, vent-proximal facies, and highly permeable soils). Near-surface permeability of soil layers has been considered as a quantified input to the ability for water to infiltrate soil strata. It was hypothesised that locations proximal to volcanic vents would be preferential recharge sites, due to deeply penetrative columnar jointing. This suggestion is based on observations in South Iceland, where fully-penetrating columnar joint sets are more prevalent in proximal facies compared to distal facies in South Iceland (Bergh & Sigvaldson 1991). To incorporate this concept, preferential recharge sites are assumed to be within the polygons of vent-proximal facies as derived from detailed geological mapping datasets. Remaining geology has been categorised to provide higher potential recharge through younger lava flows. As such, a ranking between geological units has been used to provide the variation in potential recharge estimates. <b>Reference</b> Bergh, S. G., & Sigvaldason, G. E. (1991). Pleistocene mass-flow deposits of basaltic hyaloclastite on a shallow submarine shelf, South Iceland. Bulletin of Volcanology, 53(8), 597-611. doi:10.1007/bf00493688

<p>Summary <p>Spring point locations compiled for the Nulla Basalt Province <p>A compilation of spring locations as identified through various methods, including existing Queensland Springs Database, topographic mapping, fieldwork visits, landholder citizen scientist mapping, and inspection for neighbouring similar features in Google Earth. This compilation has had locations adjusted through inspecting visible imagery and elevation data to identify the likely positions of springs at higher resolution.

We present a multifaceted hydrogeological investigation of the McBride and Nulla basalt provinces in the Upper Burdekin region, north Queensland. The project aims to better understand their key groundwater system processes to inform future development and water management decisions. This work, carried out as part of the Exploring for the Future Upper Burdekin Groundwater Project, has shown that basalt aquifers in each province are typically unconfined where monitored. Groundwater recharge is widespread but highly variable, largely occurring within the boundaries of the basalt provinces. Groundwater salinity based on electrical conductivity is <1000 μS/cm in the McBride Basalt Province (MBP) and up to 2000 μS/cm in the Nulla Basalt Province (NBP). Groundwater levels have been declining since 2011 (following major flooding in Queensland), showing that the study period covers a small fraction of a longer-functioning dynamic groundwater system. The basalt provinces contain distinct lava flows, and the degree of hydraulic connectivity between them is unclear. Despite similarities in their rock properties, the geometry of lava emplacement leads to different groundwater flow regimes within the two basalt provinces. Radial flow away from the central high elevations towards the edges is characteristic of the MBP, while regional flow from west to east dominates the NBP. Basalt aquifers in both provinces support a range of groundwater-dependent ecosystems, such as springs, some of which sustain flow in tributaries of the Burdekin River. Where streams intersect basalt aquifers, this also results in direct groundwater discharge. Springs and perennial tributaries, particularly emanating from the MBP, provide important inflows to the Burdekin River, especially in the dry season. This work has highlighted that management of MBP and NBP groundwater sources is crucial for maintaining a range of environmental assets in the region and for ensuring access for existing and future users. <b>Citation:</b> Ransley, T.R., Dixon-Jain, P., Cook, S.B., Lai, E.C.S., Kilgour, P., Wallace, L., Dunn, B., Hansen, J.W.L. and Herbert, G., 2020. Hydrogeology of the McBride and Nulla basalt provinces in the Upper Burdekin region, north Queensland. In: Czarnota, K., Roach, I., Abbott, S., Haynes, M., Kositcin, N., Ray, A. and Slatter, E. (eds.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, 1–4.

This web service provides access to groundwater raster products for the Upper Burdekin region, including: inferred relative groundwater recharge potential derived from weightings assigned to qualitative estimates of relative permeability based on mapped soil type and surface geology; Normalised Difference Vegetation Index (NDVI) used to map vegetation with potential access to groundwater in the basalt provinces, and; base surfaces of basalt inferred from sparse available data.

<p>This is a raster representing the base surface of the Nulla Basalt Province, inferred from sparse data available, dominated by private water bore records. This interpretation was conducted by a hydrogeologist from Geoscience Australia. <p>Caveats <p>• This is just one model, based on sparse data and considerable palaeotopographic interpretation <p>• This model relies on the input datasets being accurate. However it is noted that substantial uncertainty exists both in the location of private bores and the use of drillers’ logs for identifying stratigraphic contacts. <p>• The location of palaeothalwegs is imprecise, and often it is only indicative of the presence of a palaeovalley. <p>• The purpose of this model is for visualisation purposes, so should not be considered a definitive depth prediction dataset.

This web service provides access to groundwater raster products for the Upper Burdekin region, including: inferred relative groundwater recharge potential derived from weightings assigned to qualitative estimates of relative permeability based on mapped soil type and surface geology; Normalised Difference Vegetation Index (NDVI) used to map vegetation with potential access to groundwater in the basalt provinces, and; base surfaces of basalt inferred from sparse available data.

This web service provides access to groundwater raster products for the Upper Burdekin region, including: inferred relative groundwater recharge potential derived from weightings assigned to qualitative estimates of relative permeability based on mapped soil type and surface geology; Normalised Difference Vegetation Index (NDVI) used to map vegetation with potential access to groundwater in the basalt provinces, and; base surfaces of basalt inferred from sparse available data.

<p>The outcrop extent of the Nulla Basalt Province, selected from the Queensland Detailed Surface Geology vector polygon mapping, March 2017. <p>© State of Queensland (Department of Natural Resources and Mines) 2017 Creative Commons Attribution