The Cloncurry Lineament: a long-lived deep crustal structure that acted as a metasomatic pathway during ca 1530-1500 Cu-Au mineralisation, Mount Isa Inlier, Australia

Austin, James R. (2007) The Cloncurry Lineament: a long-lived deep crustal structure that acted as a metasomatic pathway during ca 1530-1500 Cu-Au mineralisation, Mount Isa Inlier, Australia. PhD thesis, James Cook University.

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Abstract

Major geophysical lineaments are commonly associated with active to ancient faults at a variety of scales. They may correlate with the edges of rifts, depositional basins, orogenic belts or plate boundaries, and they commonly represent corridors along which deformation, mineralisation, magmatism and intra-crustal heat flow is concentrated. In many instances, they encompass a number of these features.

The Cloncurry Lineament, a major feature in wavelet processed magnetic and gravity potential field (worm) data over the Mount Isa Inlier Eastern Succession, displays several such characteristics. It is over 200 km long and inferred to extend to at least 30 km depth. It delineates a contact between two major Paleoproterozoic sedimentary sequences, implying that it originated as a normal fault during rifting and basin formation. Magnetic forward modelling results suggest it corresponds to the eastern margin of a 5-10 km wide deformation zone within the calc-silicate Doherty Formation; the Cloncurry Fault Zone.

The Cloncurry Fault Zone encompasses a continuum of deformation from ~1.6 to1.5 Ga. While D₁-D₂ deformation is regionally dominant, D₃ is more significant in the fault zone itself as evidenced by much lower temperatures during mylonitisation (500- 350°C) and the superimposition of mylonitic fabrics on Maramungee aged (~1550 Ma) granites. Mapping and structural fabric analysis of the Cloncurry Fault Zone show that D₃ involved WSW shortening, sub-perpendicular to a pre-existing basin-bounding fault. D₃ created an anastomosing shear zone system displaying variable slip vectors with synchronous variably NNW or SSE plunging folds. Penetrative fabrics are attributed to strain partitioning in the D₃ event, rather than a more complex history of overprinting. During D₄-D₅ a sinistral Riedel strike-slip fault system formed, coincident with massive Na-Ca brecciation. Intrusive magmatism and IOCG, Cu, and Au mineralisation also occurred during the D₃-D₅ history of the Cloncurry Fault Zone, highlighting its importance as a magmatic and hydrothermal pathway.

Sodic-calcic (Na-Ca) metasomatism, associated with Cu-Au mineralisation in the Mount Isa Eastern Succession, is widely recognised but heterogeneously distributed, and difficult to map regionally. Hence, a method to map Na-Ca alteration remotely was developed. ASTER Band ratios were ineffective for mapping amphiboles and carbonates as a proxy for sodic-calcic alteration due to numerous mineral species having similar absorption features in ASTER band 8. Therefore, the low Kradiometric and highly magnetic properties of Na-Ca alteration were integrated with ASTER band 8 to form a Sodic-Calcic Alteration Index. The Index highlights albiteactinolite- magnetite assemblages that are coincident copper with Cu-Au mineralisation in the Eastern Succession, and the Index is useful for regional exploration in the Mount Isa Inlier.

Weights-of-evidence analysis identifies the Cloncurry Lineament as an important crustal-scale control on Au, Au-Cu, Cu-Au, and Cu mineralisation, and autocorrelation is used to identify local structural controls within the broad regional control. This integrated approach, using worms and weights-of-evidence and autocorrelation, may prove a useful exploration tool for mineralised terrains under Phanerozoic cover.

Mineralisation along the Cloncurry Lineament appears to be facilitated by two main factors. Firstly, it is associated with long, deep-crustal structure lying above dynamic lower crust/mantle, which has concentrated magmatism and metasomatism. Secondly, the associated structures have been repeatedly reactivated; increasing the chances that dilation may coincide in space and time with upflow of mineralising fluids to form a mineral deposit. These two factors appear to be consistent in several of the world's major mineralised lineaments.

Item ID: 18948
Item Type: Thesis (PhD)
Keywords: Cloncurry Lineament; Mount Isa Inlier Eastern Succession; fault; crust; mineralisation; mineralization; magmatism; metasomatism; magnetic worm
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Appendix 5 (data) is not available through this repository.

Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 1: Austin, J. R., and Blenkinsop, T. G. (2008) The Cloncurry Lineament: geophysical and geological evidence for a deep crustal structure in the Eastern Succession of the Mount Isa Inlier. Precambrian Research, 163 (1-2). pp. 50-68.

Chapter 2: Austin, J.R., and Blenkinsop, T.G. (2010) Cloncurry Fault Zone: strain partitioning and reactivation in a crustal-scale deformation zone, Mt Isa Inlier. Australian Journal of Earth Sciences, 57 (1). pp. 1-21.

Chapter 4: Austin, J.R., and Blenkinsop, T.G. (2009) Local to regional scale structural controls on mineralisation and the importance of a major lineament in the eastern Mount Isa Inlier, Australia: review and analysis with autocorrelation and weights of evidence. Ore Geology Reviews, 35 (3-4). pp. 298-316.

Date Deposited: 29 May 2014 04:15
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040306 Mineralogy and Crystallography @ 50%
04 EARTH SCIENCES > 0403 Geology > 040312 Structural Geology @ 50%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840102 Copper Ore Exploration @ 100%
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