Figure 6e. Norseman geology and EagleEye magnetics correlation.
The left map is the geology of Norseman (Norseman Gold Mines report) showing the main mines and the NNW faults that control the NS lode system.The outcrop of the main lode system stops to the east of the OK mine (OK) and to the West of the North Royal Mine (NR).
However, in the EagleEye image the NS, main line of lode of Norseman can be seen to continue nearly unbroken right through to the north under Lake Cowen. It also continues for 30 km south of the OK mine as a NNW, NNE fault system.
The other more exciting point is the nature of the broad, brittle geology from just south of Norseman OK mine (OK) to north of the North Royal mine (NR). The EagleEye plan shows this area to be part of a large dextral twist in the brittle structures. This is because of the interaction of the strong NNE and NNW structures seen in the EagleEye plan. The central zone of this complicated structural geology is the Main Line of lode from the OK mine in the south to the North Royal mine in the north.
The central zone of this complicated structural geology is the Main Line of lode from the OK mine (OK) in the south to the North Royal mine (NR) in the north. The area looks like chess board squares that have been attenuated in a NS line by shuffling the brittle areas to the NE and NW depicted by the N and S yellow arrows. this area has the appearance of a narrowing between the broader areas of less complicated NNE trending brittle geology to the north and south. This ‘shuffled/stretched’ structural geology may be a new exploration targeting tool for Norseman, I have not seen it applied there – or elsewhere??
The NNE trending felsic porphyry intrusions are from the 1904 J.D. Campbell plan on the top left. The main lode system at Norseman formed shortly after the felsic intrusives thus the lodes formed during this final, brittle stage at the end of tectonism. The opening of the structures the porphyries follow suggest dextral extensional movement in the main line of lode at the time of ore formation (see Riedel diagram right side of figure).
The left image is of a local magnetic survey, enhanced by EagleEye to highlight structure and the difference between the granite and greenstone.
The right image is The EagleEye enhancement of the Australia-wide survey from which it has been enlarged about 200 times. There is good detail of the stratigraphy and brittle structures. The overall pattern is similar but there is a lot of difference in the detail. The boundaries are more structural rather than lithologically defined as in the Local survey. For example the Local survey of the granite east of Norseman shows the granite outline but does not show the different structural domains seen within the granite in the right side EagleEye image. This increased structural definition is good for structural analysis and exploration targeting.
Another example is that the NS, main line of lode of Norseman can be seen to continue nearly unbroken right through to the north under Lake Cowen. This is definitely not obvious on the local magnetics or any other Norseman plan that I’m aware of and we would have made good use of it for exploration when I worked at Norseman.
The EagleEye image gives a less cluttered, clearer definition of through-going lode structures than the local magnetics and is thus better for exploration targeting??
Next we will look more closely at the south end of the Norseman field (MainField) to see if, as we did at Kalgoorlie, that the structural geology controlling the mines can be observed in a different way that is useful for exploration targeting.
Cheers
Bob