Academic literature on the topic 'Structural Queensland Mount Isa Inlier'

An unknown sedimentary sequence was first recorded during a Geoscience Australia/ Geological Survey of Queensland/ pmd*CRC deep seismic reflection survey in the Mount Isa Inlier and adjacent undercover terrains, during 2006/07. The sequence occurs unconformably underneath the Carpentaria Basin succession in the Julia Creek area, east of Cloncurry in north Queensland, and is named the Millungera Basin. A section through the basin is recorded along seismic line 07GA–IG1, recorded between north of Cloncurry to east of Croydon. In this section three internal sequences are noted—with two strongly reflective units separated by a poorly reflective unit. As well as deep crustal seismic reflection profiles, magnetotelluric profiles were collected along the same traverse. These data show a moderately conductive Millungera Basin underlying the strongly conductive Carpentaria Basin. Zones of limited reflectors beneath the basin in the seismic sections have been interpreted as granites, raising the possibility of raised geothermal gradients. The Millungera Basin may comprise a potential geothermal target. The Millungera Basin sequence is interpreted to overlie granites. Adjacent Proterozoic granites of the Williams Batholith are known to be high heat producing granites, containing high levels of potassium thorium and uranium. The hydrocarbon potential of the basin is similarly uncertain. Strong reflectors in the seismic sections may be coal beds. Although the depth of the basin in the seismic section is insufficient to have reached the oil window, interpretation of gravity profiles by Geoscience Australia suggest the basin deepens to the south, possibly reaching 4,000 m. If fertile beds have reached the oil window, the structurally more complex eastern side of the basin may contain petroleum traps. The age of the rocks in the Millungera Basin is not known. Constraints from the seismic suggest between the early Mesoproterozoic and the Middle Jurassic. Investigations into the nature of the basin are continuing. A more detailed magnetotellurc survey is being undertaken to better define the shape of the basin. In order to reliably describe the basins components, a deep drilling program is required.

AbstractThe earliest of four distinct phases of deformation recognized in the central part of the Proterozoic Mount Isa inlier involved brittle extensional faulting at shallow crustal levels. Extensional faulting produced stacks of imbricate fault slices, listric normal faults and characteristic tourmalinerich breccias. Structures belonging to this phase occur over a large part of the inlier and indicate an important phase of basin-forming crustal or lithospheric extension at 1750–1730 Ma. Late intense ductile deformation and tight folding of the imbricate systems destroyed part of these older structures, and obscures their existence in many parts of the inlier.

The Mount Isa Basin is a new concept to describe the area of Palaeo- to Mesoproterozoic rocks south of the Murphy Inlier (not the Murphy Tectonic Ridge) and inappropriately described as the Mount Isa Inlier. The new basin concept presented in this paper allows the characterisation of basin-wide structural deformation and the recognition of areas with petroleum exploration potential.The northern depositional margin of the Mount Isa Basin is the metamorphic, intrusive and volcanic complex referred to as the Murphy Inlier. The eastern, southern and western boundaries of the basin are obscured by younger basins (Carpentaria, Eromanga and Georgina Basins). The Murphy Inlier rocks comprise the seismic basement to the Mount Isa Basin sequence. Evidence for the continuity of the Mount Isa Basin with the McArthur Basin to the northwest and the Willyama Block (Basin) at Broken Hill to the south is presented. These areas combined with several other areas of similar age are believed to have comprised the Carpentarian Superbasin.The application of seismic exploration within Authority to Prospect (ATP) 423P at the northern margin of the basin was critical to the recognition and definition of the Mount Isa Basin. The northern Mount Isa Basin is structurally analogous to the Palaeozoic Arkoma Basin of Oklahoma and Arkansas in the southern USA but as with all basins it contains unique characteristics, a function of its individual development history. The northern Mount Isa Basin is defined as the basin area northwest of the Mount Gordon Fault.

An airborne survey was undertaken on the Mount Isa inlier in 1990–1992. During this survey, both airborne magnetic and gamma‐ray spectrometric data were recorded over 639 170 line-km. Because of perceived value of the radiometric data, stringent calibration procedures, including the creation of a test range, were adopted. In addition to the data from the newly‐flown areas, 76 760 line‐km of existing data were acquired from other companies, and were reprocessed and merged with the Mount Isa survey. The total area covered by the Mount Isa airborne survey was 151 300 km2. Over the last five years, several studies have been undertaken that seek to exploit the Mount Isa region gamma‐ray database and maximise the use of radiometrics for mineral exploration. This paper highlights the results of these studies by focussing on radiometric signatures of major mines in the Mount Isa Inlier, radioelement contour maps, geomagnetic/radiometric interpretation maps, lithological mapping, regolith mapping, geochemical sampling, and spatial modeling using geographical information systems (GIS). Due to the recent introduction of GIS technology and better techniques for handling high quality digital data, there has been a revived interest in making more use of image data sets. The integration of raster and vector data sets for both spectral and spatial modeling has maximized the potential of this approach.

Thesis (B.Sc.(Hons.))--University of Adelaide, Dept. of Geology and Geophysics, 1999.
National grid reference Quamby (6957) 1:100 000 sheet. One col. folded map in pocket pasted onto back cover. Includes bibliographical references (4 leaves).

Thesis (B. Sc.(Hons.))--University of Adelaide, Dept. of Geology and Geophysics, 1997?
National Grid reference SF53-14 (Alice Springs), SF54-1 (Mount Isa) (1:250 000). Includes bibliographical references (leaves [32-36]).

This item is only available electronically.
The Ernest Henry Iron-oxide Copper Gold (IOCG) deposit is by far the largest in the Eastern Succession of the Mount Isa Inlier. In the current genetic model, the release of CO2 from fluids sourced from enriched mantle was critical to brecciation and mineralisation. However, a weakly mineralised and brecciated shear zone within the orebody named the ‘Inter-lens’ separates the orebody into two distinct lenses. The Inter-lens was not well reported early in the life of the mine and has not been taken into account in the current ore deposit models. Establishing the relative timing of the Inter-lens structure provides strong geological constraints for the formation of the orebody. In this study, optical petrographic investigations, Scanning Electron Microscopy (SEM) and Mineral Liberation Analysis (MLA) were used to investigate the protolith. Key mineral relationships and textures were assessed to reveal the paragenesis of the Inter-lens. Structural observations in oriented drill core complemented underground mapping of exposures of the Inter-lens to reveal the deformational history of the Inter-lens with respect to the Ernest Henry orebody. The protolith was revealed to be Mount Fort Constantine Metavolcanics that have undergone intense deformation with a metasomatic evolution broadly consistent with the main orebody. Mineralisation stages overprinted tectonic fabrics via veining, replacement and infill, providing direct evidence that the Inter-lens is a pre-mineralisation structure. Preservation of the Inter-lens during brecciation and mineralisation of the Ernest Henry deposit requires that the currently accepted ‘explosive’ breccia model must be revised.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2016

This item is only available electronically.
The Mount Cuthbert mine is situated ~100km NE of Mt Isa near the eastern edge of the Kalkadoon Leichhardt Belt (KLB); a Proterozioc block of the Mt Isa Inlier that divides the world class mineral regions of the IOCG-style Eastern Fold Belt (EFB) and the Mount Isa style copper deposits of the Western Fold Belt (WFB). KLB hosted deposits display characteristics related to both the EFB and WFB style of mineralisation; however mineralisation at Mount Cuthbert is indicative of a genesis for KLB hosted deposits related to metasomatic and tectonic events responsible for mineralisation in the EFB. The Mount Cuthbert mine is a low tonnage-high grade, shear controlled, retrograde chalcopyrite-pyrite-pyrrhotite deposit hosted within silica-dolomite and biotite-chlorite altered schists and felsic volcanic units of the Leichhardt Volcanics. The paragenetic alteration sequence is composed of 5 alteration stages: Stage 1) sodic alteration (albite + quartz); Stage 2) K-Fe-Ca alteration (siderite + calcite + dolomite+ quartz + biotite ± magnetite ± ilmenite ± apatite ± pyrite); Stage 3) mineralisation (chalcopyrite + quartz ± pyrite ± pyrrhotite ± calcite ± chlorite); Stage 4) major chloritisation; Stage 5) oxidation and localised enrichment to chalcocite. The alteration halo within the deposit is characterised by a proximal alteration envelope (<50m) consisting of chalcopyrite, pyrite, quartz, dolomite and chlorite, an intermediate alteration envelope (50-500m) described by quartz-carbonate veining with minor chalcopyrite, pyrite and pyrrhotite, in addition to extensive biotite and chlorite alteration and minor magnetite alteration. A distal alteration envelope (>500m) is identified tentatively as albite dominant. The trace geochemistry of the main chalcopyrite ± pyrite ore phase reveals elevated Ni, Zn, Cd and Hg in pyrite and elevated Sn, Pb, Se, V, Cr, Te, Ga, As, Cd, Mo, Ga, Bi and Sb in chalcopyrite. Differing elemental trends within the ore minerals supports paragenetic evidence suggesting several phases of sulphide growth. The characteristics and features of the Mount Cuthbert deposit outlined in this study show the greatest number of similarities to other low tonnage-high grade, shear hosted deposits present in the KLB (i.e. Mighty Atom, Orphan). This suggests that despite having a genesis related to that of the EFB, KLB deposits are uniquely their own style of mineralisation. This supports a shear-zone associated exploration model that is specific to the KLB.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2015

Numerous studies on the Mount Isa copper orebodies have assumed the role of the Paroo Fault, which has juxtaposed the Mount Isa Group against the Eastern Creek Volcanics, and forms a footwall to the copper and lead-zinc-silver orebodies. The copper orebodies have largely been considered to have formed during east northeast-west southwest shortening, late during the 1590-1500 Ma Isan Orogeny. This thesis examines the Paroo Fault from the km-scales to the sub mm-scales in order to understand its development and role in the mineralisation of the copper orebodies. Recent techniques such as Gaussian Curvature analysis, fold profile analysis, dilation and slip tendency analysis, spanned length analysis as well as established techniques such as thickness analysis and geological mapping have been used to examine the km-scales geometry of the Paroo Fault. This has lead to a new proposed timing for initial reactivation of the Paroo Fault during the final stages of deposition of the Mount Isa group, followed by folding during east-west shortening and refolding during east northeast-west southwest shortening. Detailed geological mapping of the Paroo Fault Zone at 10s of m-scales supports the conclusions drawn from the macro-scale observations and suggests a new interpretation of the timing for the formation of the copper orebodies, before or early in the east-west shortening event, at Mount Isa. Re-examination of the mapping database collected by mine geologists (MIM and Xstrata Copper) has demonstrated that at the hunreds of metres scale, folds formed during the east northeast-west southwest shortening bend around the copper orebodies, indicating that the copper orebodies formed earlier than this event, consistent with conclusions drawn from the mapping of the Paroo Fault at the tens of m scale. Previously unrecognised east-west orientated folds which have no relationship to the copper orebodies and appear to predate them have also been recognised, indicating a phase of north-south shortening prior to ore genesis and prior to the east-west shortening. Halogen systematics on fluid inclusions from the copper orebodies, Paroo Fault Zone filling, silica-dolomite halo and basement rocks demonstrate that the ore system penetrated into the footwall, thus predating the sealing of the Paroo Fault Zones quartz-rich infill. The copper orebodies have a bittern brine source for halogens, which in the previous model for late metamorphic ore genesis, posed some problems because of the high Br/Cr ratios requiring an exotic (unknown) basin to have been placed above the Mount Isa Group during ore genesis. In the revised model here, such basinal brines are inferred to be residual evolved diagenetic brines within the Mount Isa Group or broader sedimentary package, which mixed with metamorphic fluids (with lower Br/Cl) during ore genesis, early in the inversion and shortening history.

Pieter Creus undertook a detailed 3D structural geological study of the Dugald River Zn-Pb-Ag deposit. In the study he found that the deposit formed during two successive mineralisation events. The mineralisation model is a new style of shear-zone hosted Zinc mineralisation in the region.

Includes copies of articles co-authored by author during the preparation of this thesis in back pocket.
Includes bibliographical references (leaves 113-124).
viii, 172 leaves : ill. (some col.), maps ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Focuses on the impact of change in the distribution of heat producing elements on lithospheric thermal regimes and on temperature dependent processes such as metamorphism, magmatism and deformation, with application to Proteozoic Australia (Mount Isa and Mount Painter inliers).
Thesis (Ph.D.)--Adelaide University, Dept. of Geology and Geophysics, 2001

Includes copies of articles co-authored by author during the preparation of this thesis in back pocket.
Includes bibliographical references (leaves 113-124).
viii, 172 leaves : ill. (some col.), maps ; 30 cm.
Focuses on the impact of change in the distribution of heat producing elements on lithospheric thermal regimes and on temperature dependent processes such as metamorphism, magmatism and deformation, with application to Proteozoic Australia (Mount Isa and Mount Painter inliers).
Thesis (Ph.D.)--Adelaide University, Dept. of Geology and Geophysics, 2001

[Part A] The Mount Isa Zn-Pb-Cu-Ag deposit contained almost 30 million tonnes of base metals, prior to mining, in spatially separate copper and Zn-Pb-Ag orebodies. The origin of the Zn-Pb- Ag ores is debated due to apparently conflicting features at intermediate to microscales. Ambiguity is associated with small scale features, which can be interpreted either in terms of syndeformation mineralisation or in terms of remobilisation of a predeformation orebody when considered in isolation of larger scale characteristics of the orebody. Understanding the relationship between metal distribution and the structural framework at the mine-scale helps to determine whether the orebody is deformed and leads to a better understanding of its formation. The deposit contains ten stratabound Zn-Pb-Ag lenses in an en echelon array. The extremities of the orebodies correlate with F4 folds, and high grade shoots are centred on F4 hinges and short limbs that contain older F2 folds. Contours of Pb/Zn ratios throughout the lenses are parallel to F4 hinges and silica-dolomite alteration fronts. Restoring the large scale effects of folding by rotating bedding and the lenses to horizontal indicates that a sedimentary exhalative style of mineralisation cannot account for the present geometries of the Zn-Pb-Ag lenses. This reconstruction places the depositional basin in a compressional setting, or places the ores on topographic highs. These scenarios are considered to be incompatible with synsedimentary processes. There are a number of important similarities between the geometries of the Zn-Pb-Ag lenses and the copper orebodies, which are interpreted to have a syntectonic origin. The Zn-Pb- Ag lenses display the same structural controls as the syntectonic copper ores and appear to have been emplaced at the same time in D4. Older F2 folds are preserved on the hinges and short limb areas of F4 folds and are interpreted to have behaved as structural heterogeneities during D4, which caused the dilation that led to metal deposition. F4 folds closest to the copper orebodies contain the highest grade Zn-Pb-Ag ore shoots, possibly indicating decreasing metal deposition away from the copper ores as fluids became progressively depleted in metals and/or concentration of fluid flow near the copper orebodies. In some areas, Zn-Pb-Ag ores wrap around silica-dolomite alteration associated with syntectonic copper mineralisation, suggesting a similarly late timing. The continuity of metal grades and Pb/Zn ratios throughout the Zn-Pb- Ag lenses indicates that the ores are not the result of local remobilisation. Instead, large-scale processes whereby the metals were introduced from an external source in D4 must have been involved in the formation of the Zn-Pb-Ag orebody. [Part B] Asymmetric folds that are intimately associated with the development of the Zn-Pb-Ag and copper orebodies in the Mount Isa Lead Mine were examined and found to have formed over several deformations (D3 and D4). The mechanism of folding provides insights into dilation mechanisms that led to orebody formation. Folds with vertical NNW-SSE-striking axial planes were initiated from zones affected by localised horizontal shearing during an earlier deformation event. These initially horizontal folds were tightened significantly during D4 by opposite shear senses operating on either limb along the actively developing axial planar foliation, S4. Shearing along S4 in the long limb domains reflects the bulk shear sense for this deformation. The shear sense operating along S4 on the minor limbs of asymmetric folds was caused by the presence of a D3 high strain zone. Reactivation of the D3 high strain zone and bedding surrounding it in D4, prior to establishment of the axial plane cleavage in the short limb domain, imposes a clockwise sense of rotation (looking north), which is opposite to that along the actively forming foliation in the long limb areas. The continuity of folds is related to the scale of competency domains controlling localisation of the fold initiating shear band in D3. A general model for folding is presented in which alternate limbs of folds form in different deformations. Fold limbs should be viewed as shear domains with fold hinges forming from strain gradients near the margins of domains belonging to separate deformations with one determining the location of the fold. [Part C] New mechanisms for the formation of asymmetric boudins and flanking structures are linked to the deformation history by examining these structures from exposure to microscopicscales. It was found that these structures formed by overprinting deformations, so they can only be used as kinematic indicators when their precise relationship to the deformation history is known. The processes of determining this relationship reveals much information about the deformation of the volume in which the structures are situated. The development of asymmetric boudins commenced with D2 segmentation of competent layers interbedded with weaker rock types. Disjunctive cleavages in massive siltstones and mudstones formed interboudin planes at the same time as distributed crenulation cleavage was produced in adjacent shale beds. Rotation and separation of boudins occurred to some degree in all subsequent deformations, but the bulk of these effects are attributed to D4. The formation of the interboudin planes during cleavage formation demonstrates that the maximum principal stress was perpendicular to them and at a low angle to bedding. Flanking structures at Mount Isa formed by dilation of S2 shear bands in D4 followed by rotation of the external host element by shearing along S4. Dilation of the shear band occurred to accommodate D4 deformation in the surrounding rocks. Relative rotation between the external and internal host element domains is caused by more intense deformation in the former, as shown by the density of S4 seams. In this process the internal host element remains more or less stationary, which is substantially different from present models. Flanking structures and asymmetric boudins preserve details of deformation that may have been destroyed or largely masked by ongoing deformation in the rocks around them and as such can be useful in understanding the deformation history. These structures should therefore be given significant attention when attempting to determine the deformation history of an area, especially in high strain areas where few other heterogeneities are preserved. [Part D] The Mount Isa Zn-Pb-Ag orebody consists of conformable sulphide bands and breccias whose enveloping surfaces are parallel to layering at hand specimen and exposure-scales. The range of textural variation in the bands and breccias and their distribution has been determined by logging drill core throughout the orebody. The deposit is zoned with respect to ore textures and it contains a core of breccias surrounded by sulphide band textural styles. All ore textural styles have NNW-SSE-striking trends, which is the same orientation as fold-hosted mine-scale high-grade shoots. All sulphide band and breccia textural variants exhibit a similar paragenetic sequence indicating that they formed at similar times. There are no overprinting relationships indicating remobilisation occurred within the deposit. Microstructural examination of each band and breccia style using oriented samples shows that all sulphide deposition was structurally controlled and the kinematics of processes involved in orebody development. Localisation of shearing strain throughout the deformation history played an important role in the formation of the host structures to the sulphides. It produced heterogeneities at a range of scales that were vital for dilation during mineralisation. Dilation occurred to accommodate differential progressive deformation between adjacent volumes. Localisation between competency domains defined by rock type led to mineralisation being limited to some specific beds or zones and ultimately producing stratiform style ores. Higher strains occurred in shaly rock types compared to siltstones and mudstones and produced the bedding parallel sulphide textures that are commonly misinterpreted to represent predeformation mineralisation. The difference in scale of deformation partitioning between the copper and Zn-Pb-Ag orebodies could explain the separation of metals between the two orebodies. Such a difference in the scale of structures hosting ore minerals would produce a sharp contrast in the fluid/rock ratio between the ore bodies, which would ultimately influencing the chemical environment. Consequently, copper was deposited within the silica-dolomite bodies but lead and zinc were permitted to pass beyond it before being deposited.