Product no longer exists, please refer to GeoCat #30413 for the data

Product no longer exists, please refer to GeoCat #30413 for the data

Geology of the B Lode, A Lode and 1 Lens on CML7, Broken Hill, N.S.W. - Richard Tully BSc (Hons) thesis, La Trobe University

This work presents a "snapshot" of research into the crustal architecture around the Olympic Dam Iron Oxide Cu-Au deposit, and makes some preliminary inferences on the fault architecture and alteration systems on the basis of filtering, interpretation, modelling ad inversion of public domain potential field datasets. At the time of presentation (Dec 2002), this work was still ongoing. The main results from this work are that the Neoarchean-Mesoproterozoic basement geology in the region around Olympic Dam has a history consistent with areas exposed on Eyre Peninsula to the south and west; that the system was actively deforming at the time of alteration and mineralisation which occurred at ca. 1590 Ma; that faults show geophysically detectable alteration patterns which suggest they transported and buffered at least two generations of fluids related to ore deposition; and that the regional wall rocks are reasonable sources for metals that were concentrated in the Olympic Dam deposit. However some of the other initial inferences (e.g. for an overall regional extensional tectonic environment during ore deposition) were not borne out by further testing and modelling.

The Harris Greenstone Belt in the central Gawler Craton of South Australia has potential for Archaean Ni-Cu-PGE sulphide and Archaean-Proterozoic lode-Au mineralising systems. This map is a preliminary interpretation of the Precambrian basement geology based on aeromagnetics, gravity, and diamond drilling. It highlights the extensive distribution of poorly exposed Archaean komatiites and associated rocks (green) that have a strike extent of at least 300 km. The regional pattern of linear komatiitic sequences associated with ovoid granitic plutons and province-wide shear systems, is very similar to the economically important Eastern Goldfields Province in the Yilgarn Craton, Western Australia. The ca. 2520 Ga Lake Harris Komatiite in the central Gawler Craton of South Australia is the first documented komatiite outside the West Australian Craton and the easternmost occurrence of such primitive ultramafic rocks in Australia. The steeply dipping ultramafic sequence consists of komatiite cumulates, high- to low-Mg komatiite, komatiitic and tholeiitic basalt, and pyroxenite cumulates. The komatiitic rocks display a range of quenched and cumulus textures defined by the different habits of olivine and its alteration products. Trace sulphides form very small (0.01-0.2 mm) single-phase disseminated grains and coarser disaggregated grains. Thick ponded lava lake and distal composite sheet flow facies have been identified in the magmatic environment. Systematic whole rock and mineral chemical trends indicate that despite the effects of recrystallisation and re-equilibration during amphibolite-facies metamorphism, the original magmatic geochemical profiles are largely preserved. The whole-rock data for the Lake Harris Komatiite does not show any obvious Ni depletion during fractionation but indicate a strong olivine control in dominantly S-undersaturated environments. The Lake Harris Komatiite has chemical and initial Nd isotope characteristics similar to typical Al-depleted Archean komatiites.

We report new and reinterpreted geological and geophysical results for the basement to the Stuart Shelf, in the north-eastern Gawler Craton. Regridding of gravity and magnetic datasets at optimal cell sizes allows resolution of basement structures with subtle geophysical expression. New processing techniques applied to these data, such as multi-scale edge detection (worming), and reassessment of available drill cores permit a reinterpretation of the stratigraphy and structure of units underlying the Pandurra Formation and Neoproterozoic cover sequences. In particular, we describe a three-fold Palaeoproterozoic basement sequence, analogous to that exposed in the southern Gawler Craton on the Eyre and Yorke Peninsulas. From west to east, we identify deformed BIF, schists, and gneisses equivalent to the Hutchison Group; orthogneisses equivalent to the Donington Granitoid Suite; and deformed and preserved metasedimentary rock equivalent to the Wallaroo Group. Intruded into the basement are structurally-controlled, high-level plutons of the ~1590 Ma Hiltaba Suite. These magmas fed extensive, flat-lying felsic sheets of the Gawler Range Volcanics (GRV), as well as more localised mafic centres equivalent to the Roopena Volcanics. Forward modelling of potential-field data and worming reveal that basement appears to have formed in a thick-skinned, transpressive regime. Structures suggestive of duplexes, megaboudinage, positive flower structures, and thrust stacks with non-ramp, flat geometry are consistent with modelled solutions. A similar structure to (or extension of) the Kalinjala Shear Zone is inferred to lie beneath the Stuart Shelf and GRV. In contrast, the ~1590 Ma volcanic-plutonic province appears to have formed in an overall extensional regime, with plutons elongated NE/SW in inferred dilational jogs within a conjugate dextral transtensional fault system. Thicker depocentres of GRV also appear to have formed in graben and half-graben nested above reactivated basement faults. To the south-west, four major sheets of GRV are inferred to rest on a basement of Archaean paragneisses. There is no geophysical requirement for a massive, sub-horizontal, mafic underplate. All geophysical anomalies can be explained with reference to realistic petrophysical properties of basement rocks found elsewhere in the Gawler Craton. Mass-balance calculations for a deposit such as Olympic Dam show that the source-rock volume for Cu is in the order of 102-103 km3. Under the hypothesis that the mineral system is controlled by faulting related to ~1590 Ma extension, faults of about 50-100 km by 10 km are required to create a large enough strain-envelope to ensure that fluids have access to the required volume of source-rock; and that those fluids may be mobilised and transported (Cox et al., 2001). Further, faults of this size are capable of tapping fluids from a variety of rock-types. Assuming that the regional NNW-to NW-trending transtensional structures penetrate to 10 km, their interpreted lengths are sufficient for them to have imposed a first-order control on the mineral system. The loci of mineralisation may be controlled by the second-order, NE- to ENE-trending, normal faults that connect the first-order regional structures and define the margins of the dilational jogs. The limiting factor to the size and spacing of deposits may be the quantity of metal available to the system, particularly Cu.

Product no longer exists, please refer to GeoCat #30413 for the data

F1 poster

F1 presentation

This map is part of the series that covers the whole of Australia at a scale of 1:250 000 (1cm on a map represents 2.5 km on the ground) and comprises 513 maps. This is the largest scale at which published topographic maps cover the entire continent. Each standard map covers an area of 1.5 degrees longitude by 1 degree latitude or about 150 kilometres from east to west and 110 kilometres from north to south. There are about 50 special maps in the series and these maps cover a non-standard area. Typically, where a map produced on standard sheet lines is largely ocean it is combined with its landward neighbour. These maps contain natural and constructed features including road and rail infrastructure, vegetation, hydrography, contours (interval 50m), localities and some administrative boundaries. The topographic map and data index shows coverage of the sheets. Product Specifications Coverage: The series covers the whole of Australia with 513 maps. Currency: Ranges from 1995 to 2009. 95% of maps have a reliability date of 1994 or later. Coordinates: Geographical and either AMG or MGA (post-1993) Datum: AGD66, GDA94, AHD. Projection: Universal Traverse Mercator (UTM) Medium: Paper, flat and folded copies.