Here is a simplified version of the summary and conclusions you posted. Hope it's helpful.
The text discusses several topics related to the geology of the Dido Batholith in North Queensland, Australia. The main topics covered include the description of different rock formations in the batholith, the origin and composition of the underground mafic to ultramafic bodies (UMB), the absence of valuable mineral deposits in the UMB, the isotopic makeup of the Dido MFM rock formation, and the similarities and differences between the rock formations in the batholith. The Phantom Diorite is a type of rock that forms a significant part of the Dido Suite, which is a large rock formation in the Dido Batholith. The Phantom Diorite formed 470 million years ago from magma that mixed with rock and magma from the Earth's crust.
9.5 Summary
The Phantom Diorite is a type of rock that formed 470 million years ago. It is made up of a mix of different types of diorites and some other rocks. It was formed when magma from deep within the Earth mixed with rock and magma from the Earth's crust. The Phantom Diorite was formed at a relatively shallow depth in the Earth's crust, around 10-20 kilometers deep. Some of the diorites may have formed from the same magma, while others may have come from different batches of magma.The Phantom Diorite has similar properties to another rock formation called the Dido Suite, which formed 430 million years ago. Both rocks likely formed from a process called fractionation, where magma from the Earth's mantle mixed with rock from the crust and then solidified at depth. These findings suggest that the composition of the Earth's mantle in the Greenvale Province (in North Queensland, Australia) did not change much between the Mid-Ordovician and Silurian periods.
10 Conclusions
(1)The Dido Batholith is a large rock formation made up of several types of rock. The most common rocks are hornblende-biotite tonalites and granodiorites. However, in the southeastern quarter of the formation, there is a different type of rock called hornblende-biotite diorites and bronorites. This area also contains several smaller mafic to ultramafic bodies. These rocks have been dated and the hornblende-biotite diorites and bronorites are around 470 million years old, while the tonalite-granodiorite rocks and associated mafic rocks are around 430 million years old. Because of this, the older rocks have been given a new name, the Phantom Diorite, while the newer rocks are still called the Dido Suite.
(2)This describes different types of underground rock formations called UMB, which were formed by magma injections from the Earth's mantle. The UMB are divided into two categories based on their composition, a low-Fe type and a high-Fe type. The low-Fe UMB contain different types of minerals including olivine, clinopyroxene, plagioclase, and Cr-spinel, while the high-Fe UMB lack Cr-spinel but contain early crystallising Fe-Ti oxides and hornblende, and less primitive olivines and pyroxenes. The UMB are interpreted as composite intrusions that formed from multiple injections of related magmas from a common mantle-derived parent.
(3)The UMB were formed from magma that came from the earth's mantle. The low-Fe UMB had less iron and more magnesium and water than the high-Fe UMB. The magma was contaminated by the earth's crust as it rose up to the surface, which changed the composition of the magma. The UMB were formed from a mixture of the magma and the contaminated crust. The high-Fe UMB had more crustal contaminants and experienced a different type of chemical change compared to the low-Fe UMB.
(4)No valuable mineral deposits, specifically Ni-Cu-PGE, were found associated with the investigated large UMB, and the geochemical analysis shows that the magmas that formed them lacked valuable minerals. However, it is possible that these UMBs could still be potential targets for mineral deposits since other large deposits of valuable minerals were formed from later injections of magma. While there is currently no evidence to suggest that the magmas that formed the km-scale UMB carried large amounts of PGE-rich sulphides, future exploration might reveal the presence of valuable minerals.
(5)The Dido MFM is a type of rock that is classified as a medium-K calc-alkaline intrusion. It is similar in its isotopic makeup to another type of rock called high-Fe UMB, which has a low 87Sr/86Sr(430) (0.706746) and negative εNd(430) (-4.8). The MFM has a TDM age of approximately 1390 million years and contains magmatic zircons with negative εHf(430) values (-0.9 to -5.9). It is believed that the Dido MFM originated from a partially melted rock from the mantle that also assimilated around 12% of 2000-2500 million-year-old protocrust as it rose towards the surface.
(6)It's hard to figure out how the different parts of the Dido Suite are related to each other. Most of the differences between them are thought to be caused by the physical conditions of how the magma evolved in the crust, rather than differences in the original magma types. Differences in isotopes between the UMB and MFM may be due to variations in the amount of crustal material mixed into a common, mantle-derived magma, and when this happened. The residual tholeiitic magma could become enriched in iron and water through fractionation of cumulates similar to those found in the low-Fe UMB. Later, crustal contamination and fractionation of cumulates rich in iron and titanium oxides could generate a calc-alkaline liquid line of descent, eventually producing magma with compositions similar to the high-Fe UMB and isotopic signatures similar to the MFM. These processes may have occurred at deeper levels of the Earth's crust, and the low-Fe and high-Fe UMB represent only a small part of the cumulates produced by the mafic magmas involved in forming the MFM.
(7)The Phantom Diorite is a type of rock that formed around 470 million years ago. It has similar characteristics to the high-Fe UMB rock found in the Dido Suite. Both rocks have low 87Sr/86Sr ratios, negative εNd values, fractionated rare earth element profiles, and magmatic zircons with negative εHf values. These similarities suggest that both rocks formed from a mix of similar materials from the Earth's mantle and crust. It also suggests that the composition of the Earth's lithosphere did not change much between 470 million years ago and 430 million years ago. Both rocks were probably influenced by similar levels of crustal contamination, estimated to be between 8% and 12%.
(8)The Phantom Diorite and Dido Suite formed from mantle-derived magmas that mixed with crustal components, but they are different from other granitoids in the Georgetown Region. Most of the other granites were created from the melting of older crust, without any mantle-derived magma. However, the Dido Suite and Phantom Diorite contain less than 12% of crustal components, similar to the other granites in the area.
(9)The 470 Ma Phantom Diorite and 430 Ma Dido Suite were likely formed in an arc-backarc setting, and their geochemistry and mineral compositions suggest that they ascended through the Georgetown Region Precambrian crust of the North Australian craton. This indicates their genesis in a continental arc setting, probably in an arc that was actively rifting, given the tholeiitic nature of the primary magmas. These findings support a tectonic model proposed by Henderson et al. (2011) for the Palaeozoic evolution of the Greenvale Province.
(10)The rocks in the eastern margin of the Georgetown Region were formed in an arc environment, which means they are unlikely to have deposits of valuable minerals like Ni, Cu, and PGE. However, there are rare examples of such deposits in subduction-related settings. This means that small mafic intrusions in convergent margins should not be overlooked in the search for new Ni-Cu sulphide deposits. The remaining unexplored Dido UMB, including the high-Fe varieties, and other contemporaneous mafic-ultramafic intrusions in the surrounding area should be evaluated on a case-by-case basis.
Expand
(20min delay)