First program of aircore drilling, Sussex area

The first program was completed in March 2001 over 17 days. 138 holes totalling 2583m were drilled along the roadside of the Booroomugga, Coolabah and Elmore roads. The road traverses covered approximately 140km at an average spacing of 1km. 1724 aircore samples were analysed for 22 elements. Rock fragments or 'sticks' of core allowed 138 thin sections to be made. Investigations indicate that possibly 20-50% of the rocks covered by the drilling are of Siluro-Devonian age. They appear to lie within a complex of imbricated rock packages in northerly-trending thrust belts or zones. All the rocks in this zone were previously assumed to be Ordovician.

The 676 page report on the drilling, GS2001/200 includes a complete record of assay data and drill logs, chip tray images, thin section images and descriptions, core stick photos and interpretive maps.

A Siluro-Devonian Crinoid Fossil was found in a sandstone host rock in an area mapped as Ordovician. It was located on Boorooma Station at AMG 444323mE 6541875mN.

Second program of aircore drilling, Hermidale area

Between October 24th and November 4th, 2001, 49 aircore holes were completed totalling 2275m. Most holes were from 30 - 80m depth, with cover depth usually either very thin or 10 to 40m+. About 640 samples were collected for geochemical analysis. A complete set of aircore sub-samples were collected by a PhD student for specialised geochemical studies related to the regolith. Petrological samples are currently being processed. The results of the drilling are compiled in our March 2002 Interim Report, GS2002/018.

A third program of aircore drilling was completed over 12 days from May 27th 2003, during which time 59 holes were drilled for a total of 2713.1 metres with an average depth of 50 metres. During this drilling program 1000 samples were collected for geochemical analysis and 120 "core sticks" were collected for petrology. Results of this work were published in December 2003 in the Interim Report GS2003/048. Holes were drilled along roadside verges both east and west of the village of Byrock. Data gathered during this drilling will be used to update our preliminary "Basement Interpretation Map".

A number of aircore drilling intersections gave anomalous geochemical results. CBAC238 intersected a mineralised shear system with sericite-chlorite-magnetite alteration and anomalous Au values (up to 0.149ppm Au) over 42 metres. CBAC217 intersected a weakly mineralised Au-Cu (Pb-Zn) extension south of Mt Dijou/Bald Hills.

Latest work

To date some 248 holes have been completed throughout the Girilambone belt for a total of 7571.1 metres. 3364 samples have been collected and analysed for a variety of elements providing a good understanding of background geochemistry throughout the project area. A number of holes have returned elevated results for Pb, Zn and Au and we have been able to discern "geochemical associations" which may act as pathfinders to mineralisation in the district. Detailed petrographic descriptions of 323 "core stick" samples collected during the drilling, together with field investigations throughout the project area have led to the realisation that up to 30% of the study area is composed of younger sediments, possibly Siluro-Devonian in age. This differs from previous maps, which suggest the belt is entirely composed of Ordovician sediments.

A basement interpretation map has been compiled by NSWDMR. It utilises high resolution gravity data and new overburden filtered airborne magnetic data. Version 2 of the basement interpretation map is currently in preparation. All of our available GIS and field data (outcrop, petrology, drilling, geochemistry) will be incorporated into the updated interpretation. The preliminary basement interpretation has highlighted a number of previously unidentified prospective units worthy of further investigation.

Interim Report GS2003/065 (available now) includes details of our drilling plans and recent data collected from the Glenariff granite and a magnetic anomaly south of Hermidale ("Hermitage Plains Igneous Complex"). Preliminary Byrock 1:100 000 regolith mapping results and basement interpretation data will also be included in the report.

CRC-LEME has compiled a detailed report on the regolith geology and geochemistry in the Hermidale area (GS2003/131). Regolith maps for the Hermidale, Sussex and Coolabah 1:100 000 map sheets are obtainable from CRC-LEME.

Girilambone Project Geochemical Data Set to Download

Future plans

• Basement interpretation map compilation - Version 2
• Compilation of all drilling and field data into a GIS and into MapInfo DISCOVER formats
• Further analysis of geochemical and petrological data

For further information, please contact geoscience.products@dpi.nsw.gov.au