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New Dart Mining data shows Rushworth structure akin to Fosterville

Updated: Mar 21

Cross-section of LiDAR data point cloud across surface workings at Dart Mining’s Rushworth tenement. Credit: File

Dart Mining has used Airborne Light Detection and Ranging (LiDAR) data to identify several historic surface gold workings and says it confirms the structural model at its wholly-owned Rushworth Goldfield tenements in Victoria.

The data was collected from a 72-square-kilometre area across the entire goldfield and has generated a substantial number of gold targets for follow-up geological investigation. The company says more than 4600 reef workings and extensive alluvial gold workings are concentrated along the 6.5km strike length of Rushworth, which has seen very little modern exploration.

Dart says the only exploration since 1996 concentrated on the Phoenix Hill prospect, covering less than 1km of the strike length on the goldfield’s north side.

The recently completed LiDAR survey over the historic Rushworth Gold Field is very encouraging for us, not only because it conforms to our structural modelling, but also because of the sheer scale of the historic workings that have been identified. We’ve known for some time that it has been underexplored, and this new data provides very compelling evidence of the regions excellent prospectivity. Dart Mining chairman James Chirnside

The company applied LiDAR technology to Rushworth after its successful application to its north-eastern Victoria tenements. The technology used to interpret LiDAR data for the goldfield included semi-automated machine learning and artificial intelligence algorithms.

Management says its discoveries represent a significant advancement in knowledge of the historic development of the site. Structural trends interpreted from the reprocessed LiDAR data support Dart’s model for hard-rock gold mineralisation at Rushworth.

The goldfield is unusual in Victoria in that it has east-west-trending folded strata, where almost all of that State’s other goldfields generally have north-south-trending rocks. In other aspects, Rushworth is similar to the Central Victorian Goldfields, which has about 80 million ounces of historic production, rich shallow alluvial gold with many nuggets and quartz vein-hosted gold mineralisation that continues at depth. Gold mineralisation is interpreted to be of an orogenic, epizonal style similar to that forming high-grade gold shoots at the nearby Fosterville mine.

Rushworth is 140km north of Melbourne and 65km east of Bendigo and has rock strata well exposed at surface. Rock strata is tightly folded into east-west upright folds, with two primary lines of gold-quartz veining extending for a cumulative strike length of about 14km. The Rushworth township sits in a small east-west valley between the two lines of gold-quartz-mineralised low hills.

The site’s gold-mineralised quartz veining has been intersected at depths below 400m in some historical mines and to 200m in drilling. Most workings on the goldfield are less than 100m in depth and rarely go below the water table, leaving most veins untouched at depth.

The stunning recent success at Fosterville, which for a few years has been the most profitable gold mine in the world, has heightened interest in the Victorian goldfields. In 2020, Fosterville produced 640,647 ounces of gold at a grade of 33.9 grams per tonne with 98.9 per cent gold recovery.

Production the following year was 509,601 ounces of gold with total cash production costs of US$282 (AU$426) per ounce of gold.

Dart says competition for tenure in central Victoria is fierce. Its 254 sq km landholding in the region spans the entire Rushworth Goldfield and is bordered by Chalice Mining’s operations to the north-west and Nagambie Resources to the south and east.

The company’s structural model for Rushworth shares several common elements with the classic central Victorian structural style of orogenic gold mineralisation at the Fosterville, Bendigo, and Ballarat systems. High-grade, often nuggety gold mineralisation is hosted by quartz-filled limb-thrust faults that run parallel to sub-parallel to bedding trends in anticline limbs, before breaking through the arch or nose of the folded structure.

Anticline folds can be considered as upside-down U-shapes in the rock strata, with the limbs being either side of the apex, or at the top of the inverted U. Shallow-dipping saddle reefs near the apex of the anticlines, similar to those at Bendigo, also occur at Rushworth.

Dart says the stacked nature of the structural targets represents a significant exploration possibility. It believes the extent of alluvial workings provides a solid indication of the prospective gold endowment of the catchment area.

LiDAR has identified multiple limb-thrust faults hosting gold workings in an east-west direction parallel to the rock units and north-south cross-cutting faults. The data has resolved the geological structures beyond the historic reef gold workings, providing the new gold targets.

Dart now believes the historic gold workings are present in a much bigger area than initially anticipated and ground-based exploration, including mapping, will follow up interpreted trends … and its prize may just prove to be substantial.

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