Webinar- Unravelling the Grampians Geology has outstanding impact on Australian ore potential.
On the 28 august 2020, the GeoHUG regular geoscience webinar invited Ross Cayley of the Geological Survey of Victoria (Australia) to talk on “”Scissor detachments and oroclinal warps, Grampians / Gariwerd, western Victoria – a case study of semi-ductile cover sequence deformation driven by brittle trans-tensional bedrock deformation – the crucial key that unlocked the Stavely Arc puzzle”. About 45 people attended the webinar that was delivered in English with around 290 slides, including amazing cartoon animations of unwinding the geological history.
This is a fantastic presentation, and of huge significance for the understanding of Australian geology, plus eye-opening insights for ore mineral targeting. Ross intends to make several formal publications on this life’s work.
The talk was very technical, but easy to follow. Ross Cayley and Dave Taylor started out some 20 years ago mapping the Silurian- Devonian sediments that comprise the Grampian mountains in Western Victoria. This complex and perplexing fold and fault structure became alive when latter Australian government data on gravity and magnetics was released. Two regional seismic lines provided data to interpret the underlying sequence down to about 6km. Mapping of the poorly outcropping nearby Cambrian fault bound sequences became more interesting when a major copper deposit was discovered in this region. “Thursday’s Gossan” core drilling has returned assays of 32m at 5.88%Cu, 1.0g/t Au, 58g/t Ag from 62m depth, and includes some very high grades of such metals. The drive to understand the regional geology was motivated further, as investors were reluctant to explore an area that was not well understood. Ross used the Monash digital facilities to unwind their structural data, and linked this to identifying the nature of plate collision theory.
The implications are: -
· The geology of the Grampians, and underlying / adjoining rocks now have a geological story.
· The prospectivity for more world class copper deposits is greatly improved for exploration targeting.
· The implications for this north (Queensland) and south (Tasmania) extensions of this belt will change our understanding of Australian geology, and increase prospectivity for minerals over a 1,000 km or more.
Personal, post webinar considerations for Indonesia.
The Indonesian geological survey developed an Indonesian wide series of 1:250,000 scale geological maps that were published around 1990. These maps provided a fantastic incentive to exploration companies to invest in greenfield exploration. The Geological survey wished to proceed with developing a series of 1:50,000 scale maps, but this initiative was not well supported by the government. The mining law 4/2009 introduced the concept of research (geological mapping etc) to be undertaken to develop the data package for issuing of new exploration tenements. District mines departments sought government funds to undertake exploration, but all were rejected. The new mining law 3/2020 now provides the budget for the regional mine’s inspectors, but no mention of supporting district / provincial geological surveys.
The Geological Survey of Victoria, as also supported by federal geological survey grants (Geoscience Australian etc), have full-time long-life surveys to develop the geoscience data and understanding of the States geological setting. This effort is providing Victoria with unexpected findings, and great incentives for investment in exploration.
The Indonesian government is slow to develop its full potential, including unexpected mineral resources. The possible growth of nickel sulphides, tin, copper in Australia may soon put Indonesian mineral resource companies under greater global trading pressure.
Developing and supporting regional geological surveys may boost employment of graduating geologists and local support teams, and create a positive social image for mining throughout Indonesia.