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Minerals
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
Molybdates, Arsenates, and Vanadates may also be considered with these classes. All generally occur in hydrothermal fluids that develop late in the crystallization of a granite magma and permeate the cooling igneous intrusion.
A mid-Permian mafic intrusion into wet marine sediments of the lower Shoalhaven Group and its significance in the volcanic history of the southern Sydney Basin
Published in Australian Journal of Earth Sciences, 2022
G. R. Bann, B. G. Jones, I. T. Graham
A micro-dolerite dyke/sill and intruded sediments are described from Kinghorn Point to the north of Jervis Bay, New South Wales.The dyke/sill intruded into, and possibly flowed onto, shallow marine, wet unconsolidated sediment penecontemporaneous with the deposition of the mid-Permian upper Wandrawandian Siltstone.The intrusion exhibits many classical fluidisation and flow structures characteristic of igneous intrusion into wet, unconsolidated sediments, including definitive peperite and sediment deformation.As it is geochemically different from the early latite extrusions of the Gerringong Volcanics, the intrusion may have been associated with an early (mid-Permian) non-shoshonitic eruptive phase of the Gerringong Volcanics or may represent a distinct magmatic event that occurred before or during the same period.Regular thin tuffaceous fine-grained sandstone horizons throughout the succession indicate that mafic island volcanoes were forming, erupting, and eroding to the south and/or southeast. These volcanoes may be the first eruptions of the Gerringong Volcanics, but further work is needed to clarify this.Regional mafic volcanism was active during the mid-Permian in the southern Sydney Basin.These intrusive rocks are very similar to other mid–late Permian igneous rocks from Karuah, and both are older than the presently known earliest flows of the Gerringong Volcanics. The association between this intrusion and the Gerringong Volcanics is therefore presently uncertain, with further work needed for clarification.