Comstock Valley

The geological setting of the valley is analogous to that of the Linda Valley in that it is a syncline flanked by ridges of Owen Group conglomerates with the valley floor known to be in part of Gordon Limestone (from limited drilling) but largely masked by Pleistocene glacials. There is no evidence yet for the existence of a Chamonix Shale equivalent here but there is a possibility that it is present but has not been recognised in drilling. There is no evidence for the complexity of the syncline as indicated at Linda Valley. An ESE-WNW splay off the Great Lyell fault zone may extend down the valley.

Copper-zinc mineralisation hosted by Tyndall Group altered schists had been identified early at the Tasman Crown deposits within the CMT mining lease. Drilling to the east, on the Corona ground had intersected pyritic mineralisation in Gordon Group limestone with low zinc and copper results.

Trial geophysical surveys were conducted by the then operators of the Mt Lyell Mine on the Corona ground in the 1960’s, looking for extensions of the Tasman Crown mineralisation, and conductor trends were detected on the south side of the valley, extending over about 1km E-W. The drilling of 3 diamond drill holes failed to intersect significant base or precious metal values although pyrite enrichment and copper values to 0.27% were obtained in basal limestone.

BHP held the ground in the late 1989-90 and conducted further geophysical surveys which enhanced the earlier ones and they drilled a single hole down dip from a MLMR hole. This intersected stronger pyritic veining in an argillaceous horizon in the limestone with metal values to 0.26% Zn & 1.5g/t Ag.

In the mid-1990’s CMT held the ground and reviewed the data from the aspect of targeting stratabound zinc mineralisation such as they had discovered at the Chamonix prospect in the Linda Valley but deemed that past exploration had effectively lessened the prospectivity.

The recent Corona VTEM survey, however, has indicated a strong anomaly over an area of 600x300m offset just north of the previously indicated conductor trends. Modeling of this is still awaited and it is not certain if it is due to mineralisation in the same stratigraphic position as that earlier intersected or even in the Chamonix Shale position overlying the limestone. The survey also indicated lower order anomalism extending from this to the west and east along the valley center.