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Hydrothermal alteration within the Coalstoun Porphyry Copper Prospect, Gayndah, Queensland

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posted on 2022-03-29, 01:56 authored by W. G. Billington
The Coalstoun porphyry copper prospect lies adjacent to the north-northwest trending Perry Fault system. The intrusives of the prospect comprise porphyritic biotite ± hornblende quartz diorite and tonalites, their porphyritic microcrystalline equivalents and associated dykes. The composite intrusion appears to have attained shallow crustal levels which has produced fracturing and brecciation of the overlying, and surrounding sediments. Pervasive hydrothermal alteration / sulphide mineralization accompanied the final states of crystallization and culminated in the formation of veins and fracture fillings. The zonal pattern of this alteration / mineralization resulted in a deep core low in both copper and total sulphides, a surrounding biotite zone within which all significant copper mineralization occurs, and a fringe of chloritized - pyritized intrusive and surrounding metasediments. These alterations are almost isochemical, with dominant variations in K, Ca, Rb, Sr and Cu. Petrographic observations and microprobe analyses of hydrothermal biotites showed that they are characteristically different in composition and form to those of primary magmatic biotites, including lower Ti, lower total Fe as FeO, lower Fe/ Mg and Si / A1 ratios, and possibly an increase in the Fe3+ / Fe2+ ratio. They are much finer grained and possess a greenish colour to their pleochroism. A model is suggested to explain the high level of the intrusion, its effects upon the surrounding sediments, the association of copper mineralization and biotitization, the characteristics of this biotite, the surrounding chlorite zone and the subsequent veining and later andesitic-dacitic dyke emplacement. The model shows similarities to those proposed by Guilbert and Lowell (1974), and Carson and Jambor (1974).


Table of Contents

1. Introduction -- 2. Regional geology and structural setting -- 3. Geology within the Coalstoun Prospect -- 4. Hydrothermal alteration and sulphide mineralization -- 5. Hydrothermal alteration: chemical aspects -- 6. Ferromagnesian mineral studies -- 7.Summary and interpretation -- 8. References -- Index.


Bibliography: pages 124-130 "7th November, 1975 Thesis is submitted in partial fulfillment of the requirements for the degree of Bachelor of Arts with Honours"

Awarding Institution

Macquarie University

Degree Type

Thesis bachelor honours


BA, Macquarie University, School of Earth Sciences

Department, Centre or School

School of Earth Sciences

Year of Award


Principal Supervisor

P.F. Howard


Copyright disclaimer: Copyright W.G. Billington 1975. This thesis was digitised for the purposes of Document Delivery. Macquarie University ResearchOnline attempted to locate the author but where this has not been possible; we are making available, open access, the thesis which may be used for the purposes of private research and study. If you have any enquiries or issues regarding this work being made available please contact Macquarie University ResearchOnline -






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Former Identifiers

mq:31297 2175118