VIMP Report 86 - Bendigo 1:250 000 and part of Deniliquin 1:250 000 map areas: A geological interpretation of the geophysical data
 |
| |||||||||||||||
Product description:AbstractThis report describes the results of a reinterpretation of the geophysical data of the Bendigo 1:250 000 map sheet area and gives the first interpretation of data on the southern part of the Deniliquin 1:250 000 area. The oldest rocks exposed are the Cambrian basaltic and boninitic volcanic rocks of the Heathcote Volcanic Group. The Proterozoic to Cambrian Selwyn Block is probably present in the subsurface, but does not crop out. It nevertheless seems to control deformation and mineralisation styles of the pre-Carboniferous rocks. In the west, the Selwyn Block is thin or absent, and the sediments seem to have been deposited on oceanic crust. Here the Bendigo Zone has the Heathcote Volcanic Group overlain by a thin unit of volcaniclastic sediments (the Knowsley East Shale) which is in turn overlain by a deep marine chert (the Goldie Chert). This is overlain by metaturbidites of the Castlemaine Group, the dominant unit in the west. All were deformed in two episodes of the Benambran Orogeny, the older at about 445 ± 10 Ma, and the younger at about 415 ± 10 Ma. Both episodes were accompanied by extensive gold mineralisation, typically in quartz veins with only minor amounts of other minerals, including arsenopyrite, pyrite and stibnite and with fluid inclusions suggesting temperatures of deposition of from 300 to 350°C and pressures of about 0.15 to 0.2 Gpa. Unexposed granites on the western edge of the area may have been intruded from about 410 to 400 Ma. In the northeast, a thin unnamed unit of Cambrian mafic volcanic rocks is interpreted to underlie metaturbidites of the Adaminaby Group. These rocks are probably part of the Tabberabbera Zone and have been thrust southwards over the Melbourne Zone. The Melbourne Zone comprises a series of mappable clastic units that tend to become finer in the east. In the region interpreted, all are either Silurian or Early Devonian and are interpreted to overlie the Selwyn Block. All were deformed in the Middle Devonian Tabberabberan Orogeny. The mineralisation in the Melbourne Zone and slightly to the west, typically contains abundant stibnite and was deposited at cooler temperatures (150 to 250°C) and lower pressures (a maximum of 4 km). Most of the granitic intrusions in BENDIGO were emplaced a short time after, in the Late Devonian. Permian glacial sedimentary rocks unconformably overlie Bendigo Zone rocks in the south and fill the Numurkah Trough in the northeast. Seismic data suggest a maximum thickness of about 400 m. The extent of Permian is poorly constrained and other areas may be present in the north below the Murray Basin. The Murray Basin covers the northern half of BENDIGO. It is almost entirely of fluvial sediments, the only exception being the marginal marine Parilla Sand. In the north, the fluvial sediments exceed 200 m thickness and contain poor quality brown coal. Minor basalt is also present, ranging in age from 7.1 to 1.6 Ma. Some of these flows have been faulted, and tectonic activity continues to the present, with earthquakes recorded in the Pyramid Hill Granite and the Pericoota pluton and along the Governor Fault. Bibliographic reference Moore, D.H., 2006. Bendigo 1:250 000 and part of Deniliquin 1:250 000 map areas: a geological interpretation of the geophysical data. Victorian Initiative for Minerals and Petroleum Report 86. Department of Primary Industries. Download The downloadable version of this report is supplied in PDF format: 34463 VIMP86 Report (PDF 48.5MB) Please be patient when downloading large files as this might take some time depending on your internet connection. Related products:
| ||||||||||||||||
