Two separate areas situated at a distance to the north-west and north-east of Mount Grainger have been explored for possible sediment-hosted gold, after the licensee used research conducted by CODES at the University of Tasmania (UTAS) to identify...
Two separate areas situated at a distance to the north-west and north-east of Mount Grainger have been explored for possible sediment-hosted gold, after the licensee used research conducted by CODES at the University of Tasmania (UTAS) to identify gold bearing target areas within the Adelaide Geosyncline which appear to have favourable structural settings. The CODES study had investigated elevated levels of gold formed within pyrite through geologic time, to estimate the ages of periods of peak gold emplacement and resultant erosion/weathering, and therefore to identify sedimentary basins which are likely to be sources of economic amounts of shed gold mineralisation. Their work done using samples from the Nackara Arc region identified strata of the Ulupa Siltstone (542–590 Ma depositional time range) as falling inside one of six time periods recognised as more prospective for the occurrence of this type of gold mineralisation. Taking evidence from world class sediment-hosted gold deposits already found around the globe, such as 962 Mt Sukhoi Log in Russia, large antiformal trap sites in this particular region were targeted because there the prospective host strata have been brought close to the surface. Recently, the licensee's parent company DGO Gold Limited had entered into an agreement with CODES and UTAS to fund a research project in order to access the research findings and supporting database. During the first licence year, Yandan Gold Mines (Yandan) compiled and reviewed past exploration reports and data, including remote sensing data, to inform planning of its work programme. The Upper Nackara area was found to have reported weak to moderately anomalous gold and base metal mineralisation revealed by historical drilling (1993 SAEI / MESA - run ORROROO [mapsheet area] bedrock drilling campaign), and it had previously been noted by SADME in 1987 that probable sediment-hosted gold mineralisation is present in a similar geological and structural setting at the nearby Mount Grainger Goldfield. Within the confines of the subject EL 5737, anomalous 4-11 ppb Au mineralisation had been detected in siltstones encountered by MESA drillholes ORR 21 and ORR 22. A number of antiformal fold structures exist within the Dawson Project ground, including on EL 5737, and the main antiformal structure has been disrupted by a large north-northeast trending fault which could have acted as a fluid conduit. The eastern sub-block of EL 5737 covers the axis and nose of a large syncline of Ulupa Siltstone running thorough its centre. The smaller, north-western sub-block of EL 5737 covers part of an anticlinal axis in the slightly older Saddleworth Formation. This latter unit also contains potentially prospective carbonaceous mudstones and siltstones. The majority of the folded bedrock lies under shallow surficial cover. No work was done during licence Year 2. During Licence Year 3, a structural interpretation of available open file magnetic and gravity data was conducted by Yandan’s consultants, Terra Resources Pty Ltd and Clare Geological Services Pty Ltd, and was applied to target selection. It was recognised that Yandan's Dawson Project tenements occupy a structural position in the Nackara Arc where the fold trend flexes from a N-S to a NE-SW alignment, reflecting disturbance of Delamerian fold axes. The axial plane flexure was interpreted to occur where the folds meet a pronounced NW trending magnetic lineament. In addition, features shown on magnetic images and borne out by sparse drilling records also pointed to the presence of potentially influential igneous intrusions within the project area (as magnetic lows) that could represent hydrothermal heat sources. Lastly, the Ulupa Siltstone within the Dawson Syncline displays higher than typical magnetic attenuation that it was though could possibly represent pervasive alteration. Four priority targets identified by the geophysical data interpretation were located in the vicinity of the subject EL 5737. During the last year of tenure, after further considering the above interpretation and doing more background reviews of past drilling results, Yandan concluded that the potential of the project area to have world-class size, i.e. >1 Moz recoverable gold mineralisation on the scale of the Sukhoi Log system had been downgraded, however, the new research had demonstrated that the elements necessary for the development of sediment-hosted gold deposits are present. Because of the changed outlook concerning the gold deposit size likely to be found in the Upper Nackara area, it was decided to fully surrender the licence.
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