Geothermal Energy Potential in Selected Areas of Western Australia ...

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basement contour maps presented by Iasky (1994) 6 . All available data suggest that
Palaeozoic basement reaches a maximum depth of >13 km in the Perth Basin.
3.2. Basement Lithology
The basement underlying the Perth Basin is comprised primarily of Proterozoic
granulites, gneisses, metasediments and granite intrusions of the Pinjarra Orogen.
Basement outcrops can be seen in fault bounded mid-basin ridges in the
Northampton Complex at the northern end of the Perth Basin, and in the Leeuwin
Complex on the western margin of the Bunbury Trough.
Basement lithologies were estimated for the Perth Basin based on the known
basement lithology of nearby wells, and the continuation of geophysical signatures
(gravity and magnetics) from areas of known basement compositions. For some
wells, especially those in areas of very deep sedimentary sections (>10 km), a
determination was not made due to the lack of information available to allow for a
reasonable level of certainty in determining the lithologies. For all other wells in this
study, however, basement lithology was estimated. Attachment C details individual
lithology estimates for the 170 wells not previously studied, and Attachment D for the
80 previously studied wells.
While HDRPL has drawn on all available information, the exact nature of the
basement of the Perth Basin remains poorly constrained. Gravity data are of limited
use for lithology determination in much of the Perth Basin owing to the great
thickness of the post-Permian succession. Lithology estimates for basement were
guided by basement lithologies intersected in wells, and the assumption that a similar
lithology may be expected within a 10 km radius—the approximate size of a small
pluton. Wells outside these areas are denoted as having an “unknown” basement
lithology, although it is probable that many of these “unknown” lithologies are pre-rift
metasediments.
6 Iasky R.P. 1994, Onshore northern Perth Basin gravity project. In Geological Survey of Western Australia,
1993-1994 Annual Review
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