Assessment of the Jabiluka Project : report of the Supervising Scientist to the World Heritage Committee
Johnston, A.; Prendergast, J. B.; Bridgewater, Peter
E-Publications; E-Books; PublicationNT; Supervising Scientist Report; 138
Alligator Rivers Region
Main report--Appendix 2 of the Main Report. Submission to the Mission of the World Heritage Committee by some Australian Scientists ... --Attachment A. Johnston A. and Needham S. 1999. Protection of the environment near the Ranger uranium mine--Attachment B. Bureau of Meteorology 1999. Hydrometeorological analysis relevant to Jabiluka--Attachment C. Jones, R.N., Hennessy, K.J. and Abbs, D.J. 1999. Climate change analysis relevant to Jabiluka--Attachment D. Chiew, F and Wang, Q.J. 1999. Hydrological anaysis relevant to surface water storage at Jabiluka--Attachment E. Kalf, F. and Dudgeon, C. 1999. Analysis of long term groundwater dispersal of contaminants from proposed Jabiluka mine tailings repositories--Appendix 2 of Attachment E. Simulation of leaching on non-reactive and radionuclide contaminants from proposed Jabiluka silo banks.
Uranium mill tailings - Environmental aspects - Northern Territory - Alligator Rivers Region; Environmental impact analysis - Northern Territory - Jabiluka; Uranium mines and mining - Environmental aspects - Northern Territory - Jabiluka; Jabiluka - Environmental aspects
Supervising Scientist Report; 138
1 volume (various pagings) : illustrations, maps
https://hdl.handle.net/10070/462403; https://hdl.handle.net/10070/462400; https://hdl.handle.net/10070/462405; https://hdl.handle.net/10070/462406; https://hdl.handle.net/10070/462408; https://hdl.handle.net/10070/462409; https://hdl.handle.net/10070/462411
78 The Jabiluka orebody No 2 to be mined is contained within the Cahill Formation which is mostly schist although it includes some carbonate. To the west, the Cahill Formation underlies the Magela floodplain and forms the bedrock which dips east and south beneath the overlying Kombolgie sandstone (see fig 6.3.3). The Kombolgie Formation is comprised mainly of quartz sandstone with a little siltstone and forms the broad north-south topographic ridge across the site and terrain further east. Most of the sandstone is better described as quartzite because of the deposition of secondary silica, although some relatively friable layers do occur. The intergranular porosity is very low and the groundwater flow at the mine site is restricted mainly to the joint and fracture system. Inspection of the decline being constructed to gain access to the orebody showed appreciable groundwater inflow only at one fracture zone. Most of the other joints were dry. Along the Magela floodplain mainly grey and organic clays, silts and sandy alluvial sediments overlie the Cahill Formation. The bedrock in contact with the sediments is weathered. Immediately east and west of the topographic divide the weathered bedrock in the lower drainage valley slopes is overlain by sands and silts. Drilling has revealed that weathered bedrock can occur up to 50 m below ground surface. Strongly developed lineaments comprising joints/fracture systems in the sandstone are evident from aerial photographs of the Jabiluka outlier and the elevated sandstone outcrop north of orebody No 2. These structures strike at 60 to 80 degrees with another less dominant set at 350 degrees. The structural lineaments are less well defined in Mine Valley; however, it is possible that Mine Valley may have formed along zones of rock weakness created initially in the past by one or a number of these structures that have now been filled in with weathered material. Other structural features include the Hegge fault that dissects the orebody and a pegmatite dyke that crosses the western part of the ore-body (fig 6.3.2). The pegmatite dyke has not been assigned any special properties for the modelling work undertaken, which is a conservative assumption because there is some indication that it may retard flow. A hydrogeological section based on that given by Milnes et al (1998) is shown in figure 6.3.3. The orientation and extent of this section is shown in figure 6.3.1 as A-B-C. The section extends from the Magela floodplain in the west across the site through the orebody, the topographic ridge, Swift Creek, and then north until it reaches a branch of the Magela floodplain. Tailings derived contaminants were modelled by Kalf and Dudgeon (1999) along this section. There are four main sub-surface water-bearing zones with essentially different hydraulic characteristics within this section at Jabiluka. They include: A shallow sandy aquifer overlying weathered bedrock in Mine Valley and east of the topographic divide. A weathered bedrock aquifer. A deeper fractured rock aquifer. Floodplain non-indurated sediments.
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