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.

The early Mesoproterozoic Olympic Cu-Au province extends over 500 km along the eastern margin of the Gawler Craton. Although the boundaries are not yet well defined, and much of the province is concealed beneath Neoproterozic to Cainozoic cover, the metallogenic belt is inferred to transgress several tectonic domains of mainly Palaeoproterozoic meta-sedimentary and meta-igneous basement. Iron oxide - rich hydrothermal systems of the Peake and Denison Inlier, Mabel Creek Ridge, and south-central Gawler Craton may prove to be extensions of the Cu-Au province. We have identified three major regions of early Mesoproterozoic hydrothermal and magmatic activity: in the Mount Woods Inlier in the north, in basement to the Stuart Shelf (which hosts the Olympic Dam Cu-U-Au deposit), and in the Moonta-Wallaroo-Roopena region in the south of the metallogenic province. Each of the regions contains high- to low-temperature Fe-oxide bearing alteration, Cu-Au±U mineralisation, and felsic to mafic magmatism of the ~1590 Ma Hiltaba Suite intrusions, with or without Gawler Range Volcanics. The three regions are inferred to represent the imprint of separate crustal-scale thermal anomalies. Re-logging of drill core, and petrological studies reveal important similarities and systematic variations in hydrothermal mineral assemblages along the length of the metallogenic belt. The key assemblages are: a. calcsilicate - alkali feldspar ± magnetite ± pyrite ± pyrrhotite ± chalcopyrite (CAM); b. magnetite - biotite ± pyrite ± chalcopyrite (MB), and c. hematite - sericite - chlorite - carbonate ± pyrite ± Cu-Fe sulfides ± U, REE minerals (HSCC) Higher grade and more extensive Cu-Au±U mineralisation is generally associated with the relatively oxidised and lower temperature HSCC assemblage (250-300°C, or less, based on fluid inclusion data). In most cases, this assemblage overprints the CAM and MB assemblages, which represent the products of high- to moderate-temperature (~500° - 350°C) hydrothermal fluids of intermediate, or in places, reduced oxidation state (i.e. magnetite-pyrite or magnetite-pyrrhotite stability). Based on drill holes examined to date, albite and biotite are the dominant alkali alteration products in the Moonta-Wallaroo district, whereas K-feldspar or sericite are the main alkali silicates in basement to the Stuart Shelf. All three assemblages (CAM, MB and HSCC) including albite and K-feldspar are well represented in the Mount Woods Inlier (e.g., CAM & MB at the Manxman and Joes Dam prospects; HSCC at the Prominent Hill prospect). Sodium- and chlorine-bearing varieties of scapolite, or pseudomorphs of scapolite, have been identified in all three regions of hydrothermal activity. The sources of halides and metals in the hydrothermal fluids are currently under investigation using fluid inclusion microanalytical techniques. The crustal levels of the hydrothermal systems as they are currently exposed at the base of cover rocks are inferred to vary dramatically, even within the three regions of hydrothermal activity. Brittle-ductile shear-hosted CAM and MB assemblages, such as those in the Moonta-Wallaroo district, developed at deeper crustal levels than breccia-hosted HSCC assemblages (e.g., Olympic Dam). We suggest that uplift or unroofing of some of the hydrothermal systems occurred during and/or after their development, resulting in ‘telescoping’ of deeper and shallower alteration patterns. CAM, MB, HSCC alteration and associated Cu-Au±U mineralisation represent a possible spectrum of settings from deeper, higher-temperature environments to near-surface, low-temperature settings where there was greater involvement of surficial fluids in the hydrothermal systems.

The Moonta Domain forms the southern part of the Olympic Cu-Au province on the eastern margin of the Gawler Craton. Historical production comprises over 330,000 tonnes of Cu from vein and shear-hosted mineralisation in the Moonta-Wallaroo district. The domain basement comprises metasediments and metavolcanics of the Palaeoproterozoic Wallaroo Group (~1760-1740 Ma) which were deformed and metamorphosed to upper greenschist-amphibolite facies during the Kimban Orogeny (~1720 Ma). These rocks were further deformed and intruded by granitoids and minor mafic intrusions of the Hiltaba Suite between about 1600 Ma and 1575 Ma. There is a close spatial association of high temperature Fe-Na-Ca-K metasomatism of the Wallaroo Group and Hiltaba Suite intrusions. Conor (1995) termed the most strongly altered rocks the Oorlano Metasomatites, although metasomatic mineral assemblages within this rock association vary widely. Intense albite-actinolite-magnetite ± carbonate ± epidote ± pyrite alteration of metasediments is strongly associated with the contact zones of Hiltaba Suite granites, particularly the Tickera Granite. More distal albitisation of the Wallaroo Group is common but is not generally associated with significant sulphides. Biotite ± albite ± magnetite ± quartz ± apatite ± monazite ± tourmaline alteration is commonly associated with pyrite ± minor chalcopyrite, and is particularly widespread south of Moonta where numerous magnetic and non-magnetic Hiltaba Suite granitoids (previously grouped as Arthurton Granite) intrude the Wallaroo Group. Late chlorite and K-feldspar alteration is typically of restricted extent, but may also be associated with sulphides. Biotite-rich alteration typically forms irregular magnetic anomalies, including a major 5 x 15 km alteration zone near Weetulta, and possibly a large area (~30 km x 40 km) of strongly magnetic rock beneath Spencer Gulf. Fluid inclusion data indicate that highly saline, multi-cation fluids are associated with the alteration. Preliminary U-Pb SHRIMP dating of hydrothermal monazite from biotite-rich alteration in the Weetulta and Wallaroo areas yields ages of approximately 1585 Ma and 1620 Ma respectively. The Weetulta district data indicate a close temporal relationship of the biotite alteration and Hiltaba Suite magmatism. However, the older Wallaroo district age suggests hydrothermal activity may have commenced prior to intrusion of Hiltaba Suite granites. Regional metamorphic and alteration characteristics of the Moonta Domain are similar to those of the Fe-Cu-Au mineral province of the Mt Isa Inlier Eastern Succession, where there are strong links between magmatism, regional albitisation, and Fe-Cu-Au mineralisation (eg., Oliver et al., 2001). Biotite-magnetite metasomatism commonly occurs proximal to major Fe-Cu-Au ore deposits in the Mt Isa Eastern Succession. The shear-hosted Cu lodes and associated alteration at Wallaroo may be an analogue in the Moonta Domain. However, apart from some very minor drill intersections in prospects in the Weetulta district, no other significant Cu-Au mineralisation associated with biotite-magnetite alteration has yet been discovered in the Moonta Domain. Given that most of the Proterozoic basement of the Moonta Domain is concealed by up to 100 metres of Neoproterozoic to Cainozoic sediments and remains largely untested by drilling, the potential for discovery of Ernest Henry-style Fe-Cu-Au deposits in the Moonta Domain remains high.

- Although exploration is languishing at a 20 year low, the outlook is the best for five years. - Metal prices are forecast to improve over the next several years. - Australia remains highly prospective and discoveries continue to be made both in proven and greenfields provinces. - Exploration in the past 10 years has added significant resources - notably gold, nickel, mineral sands, tantalum - at low cost. - Major potential exists undercover. - As a result of Government programs over the past decade, a wealth of geoscience data is available either free or at very low cost. These are playing an important role in opening up the under explored frontier provinces to exploration.

More than 100 bushfires raged across NSW from 25 December 2001 - January 8 2002, requiring over 20,000 regular and volunteer fire fighters and 85 aircraft. Vast stretches of forests were destroyed, including more than 60% of the Royal National Park. More than 11,000 people were evacuated from their homes and 560,000 hectares were burnt out. The image below was acquired from the SPOT satellite on 27 December 2001 by ACRES, Geoscience Australia. It is produced here as a mosaic of 8 SPOT scenes covering about 120km wide and 240km long, stretching from Wyong in the north to Jervis Bay in the south. Healthy vegetation shows as bright red, forest as dark red, ocean and lakes as dark blue, burnt areas as black and smoke as blue/white.

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

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

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

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

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