The geology of the Neara volcanics, near Elgin Vale, Esk Trough, Southeast Queensland

Johansen, Stephen Henry. (1986). The geology of the Neara volcanics, near Elgin Vale, Esk Trough, Southeast Queensland Honours Thesis, School of Physical Sciences, The University of Queensland.

       
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Author Johansen, Stephen Henry.
Thesis Title The geology of the Neara volcanics, near Elgin Vale, Esk Trough, Southeast Queensland
School, Centre or Institute School of Physical Sciences
Institution The University of Queensland
Publication date 1986
Thesis type Honours Thesis
Supervisor Dr A. Ewart
Professor A.F. Wilson
Chris Stevens
Total pages 91
Language eng
Subjects 260100 Geology
Formatted abstract An orogenic assemblage composed of volcanic conglomerates and basalts of the (?)Lower to Middle Triassic Neara Volcanics, and a basic-intermediate pluton, outcrop within the thesis area, located 6 km southeast of Elgin Vale within the Esk Trough of South-eastern Queensland. The oldest unit within the area , conglomerate, is the most widespread lithology and is interpreted to be of debris flow origin. The conglomerates are typically massive, poorly sorted, clast-supported, non-imbricated, and polymictic. The clasts are predominantly porphyritic andesites (> 95 %) with minor sandstone and plutonic types. The andesitic source that initiated the debris flows was probably located several tens of kilometres from the thesis area and within a separate and distinct eruptive province from that which produced the coeval basalts of the thesis area. These basalts are high-K tholeiites. Minor basaltic andesites also occur within the area. The pluton within the thesis area is a composite body of three petrogenetically unrelated phases: microgabbro; microdiorite; and diorite. The microgabbro phase is minor and is hypersthene-richi The microdiorite is probably a uniform body, geochemically. It consists of andesine, augite, biotite, quartz, magnetite, and apatite, and is completely devoid of hornblende. The diorite phase of the pluton is a fractionated body ranging from true diorite (51 % SiOj) to tonalite (66 % Si02),with minor granitic veins. It contains mainly andesine, hornblende, biotite, quartz, magnetite, and minor relict augite. Metalliferous and barren veins of hydrothermal origin occur within the pluton, in the area where the microdiorite and diorite phases coexist. Their localization was structurally controlled. The main ore mineral within the veins is chalcopyrite. The veins carry microscopic gold. Regional propylitic alteration is widespread within the conglomerates and basalts of the area. An inner propylitic zone dominated by secondary actinolite grades outward from the main pluton into chlorite-calcite assemblages and further into chlorite-epidote assemblages. The strata within the area form an antiform, and faulting (probably normal) is widespread.
Keyword Geology -- Queensland -- Elgin Vale Region.
Igneous rocks -- Queensland -- Elgin Vale Region.
Additional Notes Other Title: Neara volcanics, Esk trough.

 
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