Academic literature on the topic 'Western Australia Basaltic Rocks'

ABSTRACTLate Archaean granitic rocks from the southern Yilgarn Craton of Western Australia have a close temporal relationship to the basaltic and komatiitic volcanism which occurs within spatially associated greenstone belts. Greenstone volcanism apparently began ∼2715 Ma ago, whereas voluminous felsic magmatism (both extrusive and intrusive) began about 2690 Ma ago. A brief but voluminous episode of crust-derived magmatism ∼2690-2685 Ma ago resulted in the emplacement of a diverse assemblage of plutons having granodioritic, monzogranitic and tonalitic compositions. This early felsic episode was followed immediately by the emplacement of mafic sills, and, after a further time delay, by a second episode of voluminous crust-derived magmatism dominated by monzogranite but containing plutons covering a wide compositional range, including diorite, granodiorite and tonalite. The products of this 2665–2660 Ma magmatic episode now form a significant fraction of the exposed southern Yilgarn Craton. Later magmatism, which continued to at least 2600 Ma ago, appears largely restricted to rocks having unusually fractionated compositions.The magmatic sequence basalt-voluminous crust-derived magmatism-later diverse magmatism, is interpreted in terms of a dynamically-based model for the ascent of the head of a new mantle plume. In this model basalts and komatiites are derived by decompression melting of rising plume material, and the crust-derived magmas result after conductive transport of heat from the top of the plume head into overlying continental crust. This type of magmatic evolution, the fundamentally bimodal nature of the magmatism, the presence of high-Mg volcanics (komatiites), and the areal extent of the late Archaean magmatic event, are all suggested to be characteristic of crustal reworking above mantle plumes rather than resulting from other processes, such as those related to subduction.

With new advances in rapid-acquisition geochemical and hyperspectral techniques, exploration companies are now able to detect subtle halos surrounding orebodies at minimal expense. The Nimbus Ag-Zn-(Au) deposit is unique in the Archean Yilgarn Craton of Western Australia. Due to its mineralogy, alteration assemblages, geochemical affinity, and tectonic setting, it is interpreted to represent a shallow water (~650 mbsl) and low-temperature (<250 °C) volcanogenic massive sulfide (VMS) deposit with epithermal characteristics (i.e., a hybrid bimodal felsic deposit). We present a detailed paragenetic account of the Nimbus deposit, and establish lithogeochemical and hyperspectral halos to mineralization to aid exploration. Mineralization at Nimbus is characterized by early units of barren massive pyrite that replace glassy dacitic lavas, and underlying zones of polymetallic sulfides that replace autoclastic monomict dacite breccias. The latter are dominated by pyrite-sphalerite-galena, a diverse suite of Ag-Sb ± Pb ± As ± (Cu)-bearing sulfosalts, minor pyrrhotite, arsenopyrite, and rare chalcopyrite. The main sulfosalt suite is characterized by pyrargyrite, and Ag-rich varieties of boulangerite, tetrahedrite, and bournonite. Zones of sulfide mineralization in quartz-sericite(±carbonate)-altered dacite are marked by significant mass gains in Fe, S, Zn, Pb, Sb, Ag, As, Cd, Ni, Cu, Ba, Co, Cr, Tl, Bi, and Au. Basaltic rocks show reduced mass gains in most elements, with zones of intense quartz-chlorite-carbonate±fuchsite alteration restricted to thick sequences of hyaloclastite, and near contacts with dacitic rocks. Broad zones of intense silica-sericite alteration surround mineralization in dacite, and are marked by high Alteration Index and Chlorite-Carbonate-Pyrite Index (CCPI) values, strong Na-Ca depletion, and an absence of feldspar (albite) in thermal infrared (TIR) data. White mica compositions are predominantly muscovitic in weakly altered sections of the dacitic footwall sequence. More paragonitic compositions are associated with zones of increased sericitization and high-grade polymetallic sulfide mineralization. Chlorite in dacitic rocks often occurs adjacent to zones of sulfide mineralization and is restricted to narrow intervals. Carbonate abundance is sporadic in dacite, but is most abundant outside the main zones of Na-Ca depletion. Basaltic rocks are characterized by strongly paragonitic white mica compositions, and abundant chlorite and carbonate. Shifts from Ca carbonates and Fe-rich chlorites to more Mg-rich compositions of both minerals occur in more intensely hydrothermally altered basaltic hyaloclastite, and near contacts with dacitic rocks. Hanging-wall polymict conglomerates are characterized by minor amounts of muscovitic to phengitic white mica (2205–2220 nm), and an absence of chlorite and carbonate alteration.

High temperatures in the interior of the young Earth led to the initiation of melting at great depths in the mantle (> 150 km) and the production of large volumes of magma that erupted to form a >40 km thick basaltic crust. The ubiquitous presence of this crust dominated Archaean tectonics. Granitoid rocks, the source for >4 Ga Western Australian zircons, formed by partial melting at the base of the crust during the first 600 Ma of Earth history, but were always subordinate to basalt. The lunar record provides evidence that both the Moon and Earth experienced major impacting during this period. The impacts mixed granitoid with mantle-derived basalt to produce a composite granitoid-basalt layer with isotopic composi­tions close to bulk-Earth values. No record of its existence was retained in the oldest extant continents which formed - 3.9 Ga ago, after major impacting had ceased.

The Wallal Rift System (new name) extends north-northwest for more than 300 km along the southwestern margin of the Canning Basin. The rift contains the Wallal and the Waukarlycarly embayments and the Samphire Graben. The rift segments vary in depth to 4.5 km and are all under-explored. Seismic coverage is better in the north than in the south. Six shallow wildcat and stratigraphic wells in the north provide some control on the age of the pre-Permian section. Another well on the northeastern flank of the Samphire Graben terminated in Neoproterozoic granitic rocks beneath the Lower Ordovician Nambeet Formation. The well is tied to a seismic line that indicates a synrift Ordovician section in the graben. An equivalent section is inferred in the Wallal and the Waukarlycarly embayments, and Permian syn-rift sediments are recognised in all rifts. Transtension along a regional geosuture—the Camel-Tabletop Fault Zone—may have caused initial rifting during the waning of the Paterson Orogeny (c. 550 Ma), co-incident with extrusion in the Kalkarindji Large Igneous Province. Thus, Cambrian volcano-clastics deposits may be present at the base of the (2–3 km thick) pre-Permian section, which is considered to be primarily Early Paleozoic sediments and expected to contain potential source rocks. A relatively hot Proterozoic crust and eruption of continental flood basalts during the Cambrian may have facilitated source rock maturation. Reservoirs may be more common along rift-margins and intra-rift ridges, where fault-controlled traps are also present.

Dissolution of dry-milled basalt, dolerite, gneiss, and K-feldspar added to 23 soils has been related to milling time and soil properties. The rocks milled for 10, 60, and 120 min were mixed with 23 type of soils from south-western Australia at a rock/soil ratio of 1/100 (≈10 t/ha), wetted to 110% field capacity, then incubated at 20°C for 2 and 10 months. Measurements of cations extractable by 1 M CH3COONH4 at pH 7 indicate that substantial dissolution occurred in the soil and that milling increased dissolution. After 10 months of incubation, about 18% of Ca and Mg had dissolved from basalt and dolerite milled for 120 min and 40% of Na and K from gneiss and K-feldspar milled for 120 min. Some dissolution occurred with 1 h extraction of non-incubated rock–soil mixtures and these released elements are considered to be readily available plant nutrients. The silicate rocks had minor effects on soil pH and EC of soil-rock mixtures (i.e. increased pH by ≤0.5 unit and EC by ≤127 μS/cm in 1 : 5 water extracts). The large increases in silicate rock dissolution in soils due to milling indicate that milled basalt and dolerite may be used as Ca and Mg fertilisers, and K-feldspar as a K fertiliser. Further research is needed to identify soils and plants for which the application of the silicate rock fertilisers will be most beneficial.

Between October 2008 and January 2009, Geoscience Australia conducted a marine mapping survey to document the seabed environments and subsurface geology of the Zeewyck, Houtman, Exmouth sub-basins and the deep-water Wallaby (Cuvier) Plateau, Western Australia. The seabed mapping survey, the second and largest mapping survey of the Federal Government’s Offshore Energy Security Program, documented seabed environments and biota from multibeam sonar and sub-bottom profiler data, towed video footage and physical samples. Preliminary analysis of the data indicates that for all of the sub-basins the seabed is comprised of carbonate mud that supports relatively sparse infaunal populations. Rocky substrates, principally in the numerous submarine canyons, supported sparse communities of sessile organisms. Interestingly, some of these hard-grounds were associated with volcanic (basaltic) peaks on the upper slope that attain 200 metres above the surrounding seabed. Data collected from the survey are being analysed in conjunction with existing environmental data to establish a series of environmental summaries that describe the key seabed habitats and biota for the offshore basins. The environmental summaries are being made available to support future acreage release in the sub-basins. The marine mapping survey was run in combination with a regional 2D seismic survey of the same offshore basins, also completed as part of the Offshore Energy Security Program.

Minor intrusions in the Menzies – Kambalda greenstone belt of the Archean Eastern Goldfields Province, Western Australia, range from quartz–feldspar porphyry to plagioclase–hornblende porphyry. The porphyries display enrichment of mobile and incompatible elements (K to Zr) and depletion of relatively compatible elements, with negative Nb, P, and Ti anomalies, on mid-ocean-ridge basalt-normalized spidergrams. The composition and timing of emplacement of the porphyries are consistent with a genetic relationship with spatially related granitoids. Porphyries occur in 30% of gold mines in the Menzies–Kambalda belt. The association appears to be largely structural, since both the intrusions and the mineralizing fluids exploit zones of weaknesses, such as lithological contacts and shear zones. Porphyries have been modified to varying degrees by hydrothermal alteration, especially pervasive albitization. Textural evidence indicates that secondary albite and associated sodic amphibole formed late in the deformation history of the greenstones and were broadly contemporaneous with secondary phyllosilicate, carbonate and sulphide minerals related to gold mineralization. Recent studies in the Alleghany district of California suggest the initial rock composition may critically influence the nature of alteration associated with gold mineralization. Therefore, albitization of porphyries may be caused by the same hydrothermal fluids that deposit gold and produce potassic alteration in mafic rocks.

Research subject. Zircons from the Saf’yanovskoe Cu-Zn deposit rhyolite (Middle Urals). For the first time, zircon U-Pb dating for the rhyolite of the ore-bearing volcanic-sedimentary rocks of the Saf’yanovskoe deposit was performed. The volcanites are characterized by an andesite-rhyodacite composition and are localized at the southern edge of the Rezhevskaya structural-formation zone (SFZ) of the Eastern Ural megazone. A number of publications assign these rocks either to the basalt-rhyolite formation of the Middle Devonian, or to the basalt-andesite-dacite-rhyolite formation of the Lower-Middle Devonian.Aim. To estimate the age of the ore-bearing volcanic rocks under study using the U-Pb SHRIMP-II isotop ic system of zircon from the rhyolite of the eastern side of the Saf’yanovskoe deposit. By its chemical composition, the rhyolite belongs to the silicic varieties of subvolcanic rocks. Methods and results. The U-Pb isotopic system of zircon was studied by 5-collector mass-spectrometer of high precision and emission of the secondary ions SHRIMP-II (ASI, Australia) in the VSЕGEI Institute. U-Pb relations were investigated by a procedure developed by I.S. Williams. The U-Pb data obtained based on 13 zircon grains showed the age of 422.8 ± 3.7 Ma. Conclusions. The U-Pb dating of zircon obtained previously from the lens-shaped andesite bodies of the western side of the Safyanovskoe deposit gave the age of 422.8 Ma, which corresponds to the Przydoli series epoch of the Upper Silurian. We established that, among the volcanic rocks of the Saf’yanovskoe deposit, the effusive formations of the Upper Silurian are present.

Abstract Introduction and geodynamic setting. – Syn-rift exhumation of mantle rocks in a continental breakup zone was highlighted along the present-day west Iberian passive margin [e.g. Boillot et al., 1988, 1995; Whitmarsh et al., 1995, 2001; Beslier et al., 1996; Brun and Beslier, 1996; Boillot and Coulon, 1998; Krawczyk et al., 1996; Girardeau et al., 1998] and along the fossil Tethyan margins [e.g. Froitzheim and Manatschal, 1996; Manatschal and Bernoulli, 1996; Marroni et al., 1998; Müntener et al., 2000; Desmurs et al., 2001]. Along the west Iberian margin, serpentinized peridotite and scarce gabbro and basalt lay directly under the sediments, over a 30 to 130 km-wide transition between the thinned continental crust and the first oceanic crust [Girardeau et al., 1988, 1998; Kornprobst and Tabit, 1988; Boillot et al., 1989; Beslier et al., 1990, 1996; Cornen et al., 1999]. The formation of a wide ocean-continent transition (OCT), mostly controlled by tectonics and associated with an exhumation of deep lithospheric levels, would be an essential stage of continental breakup and a characteristic of magma-poor passive margins. The southwest Australian margin provides an opportunity to test and to generalize the models proposed for the west Iberian margin, as both margins present many analogies. The south Australian margin formed during the Gondwana breakup in the Mesozoic, along a NW-SE oblique extension direction [Willcox and Stagg, 1990]. From north to south, the continental slope is bounded by (1) a magnetic quiet zone (MQZ) where the nature of the basement is ambiguous [Talwani et al., 1979; Tikku and Cande, 1999; Sayers et al., 2001], (2) a zone where the basement shows a rough topography associated with poorly expressed magnetic anomalies [Cande and Mutter, 1982; Veevers et al., 1990; Tikku and Cande, 1999; Sayers et al., 2001], and which is the eastward prolongation of the Diamantina Zone, and (3) an Eocene oceanic domain. The continental breakup zone is believed to be located near or at the southern edge of the MQZ [Cande and Mutter, 1982; Veevers et al., 1990; Sayers et al., 2001]. Breakup is dated at 125 Ma [Stagg and Willcox, 1992], 95 ± 5 Ma [Veevers, 1986] or at 83 Ma [Sayers et al., 2001], and followed by ultra-slow seafloor spreading until the Eocene (43 Ma), and fast spreading afterwards [Weissel and Hayes, 1972; Cande and Mutter, 1982; Veevers et al., 1990; Tikku and Cande, 1999]. The western end of the margin (fig. 1) is starved and bounded in the OCT by basement ridges where peridotite, gabbro and basalt were previously dredged [Nicholls et al., 1981]. Altimetry data [Sandwell and Smith, 1997] show that some of these ridges are continuous over 1500 km along the OCT of the south Australian margin and of the conjugate Antarctic margin. The objectives of the MARGAU/MD110 cruise (May-June 1998; [Royer et al., 1998]; fig. 2) were to define the morpho-structure and the nature and evolution of the basement in the SW Australian OCT. An area of 180 000 km2 was explored with swath bathymetry. Gravimetric data (11382 km) were simultaneously recorded whereas few single channel seismic (1353 km) and magnetic (5387 km) data were obtained due to technical difficulties. Crystalline basement rocks, made of varied and locally well-preserved lithologies, were dredged at 11 sites located on structural highs. Main results. – The bathymetric map unveils three E-W domains (fig. 2). From north to south, they are the continental slope of Australia, prolonged westward by that of the Naturaliste Plateau, a 160 km-wide intermediate flat sedimented area corresponding to the MQZ, and a 100 km-wide zone of rough E-W oriented topography which continues the Diamantina Zone (fig. 3). The first two domains are cut through in three segments by two major fracture zones (FZ), the Leeuwin FZ along the eastern side of the Naturaliste Plateau, and the Naturaliste FZ along its western flank. These NW-SE trending FZ terminate north of the E-W trending fabric of the Diamantina Zone. Accordingly, extension occurred along the NW-SE direction during the formation of the slope and of the MQZ, and then turned to N-S during the formation of the Diamantina Zone. In the Diamantina Zone, the mantle rocks dredged at Site MG-DR02 are mainly lherzolites, rich in pyroxenitic micro-layers, and pyroxenites. They contain spinel rimmed by plagioclase and locally coronas of olivine + plagioclase between opx and spinel, which suggest that they underwent some subsolidus reequilibration in the plagioclase field (fig. 4C). Westward (Site DR09), the mantle rocks are harzburgitic, with lesser pyroxenitic bandings and no plagioclase. The rocks have coarse-grained porphyroclastic textures that are locally overprinted by narrow mylonitic shear bands, and then by a cataclastic deformation, which indicate decreasing temperatures and increasing stresses during their evolution. Basalts were sampled at Sites MG-DR01, −04, −05, and together with gabbros at Sites MG-DR02, -03, -09. They have a transitional composition as shown by their REE patterns, except one sample from site MG-DR-05 which is an alkaline basalt (fig. 5). The gabbros are clearly intrusive in the peridotite at Sites DR02 and -09. They contain olivine and clinopyroxene (cpx) at Site DR02, cpx, plagioclase and hornblende at Site DR03, and cpx and amphibole or orthopyroxene or olivine at Site DR09 (fig. 4D). At that site, a tonalite containing K-feldspar and biotite and alkaline in composition (fig. 5), has also been sampled. All these plutonic rocks display either their primary magmatic textures or secondary porphyroclastic ones that are locally overprinted by mylonitic shear zones (fig. 4E). Retrograde minerals of amphibolite to greenschist facies developed during the deformation. The basalts are clearly intrusive in the gabbros at Site DR03. They are altered and exhibit porphyric textures with abundant plagioclase and plagioclase + olivine phenocrysts at Sites DR03, -04, -08, -10, and have a transitional composition (fig. 5). The nature and evolution of the peridotites and associated gabbros are compatible with an exhumation under a rift zone, on both sides of the Leeuwin FZ. It includes a mylonitic deformation which attests that these rocks underwent a shearing deformation under lithospheric conditions, in probable relation with their exhumation during the early stages of the oceanic opening. The crustal rocks are represented only by intrusive gabbros and by transitional basalts. In the MQZ, the peridotites recovered at Site MG-DR06 are mainly spinel and plagioclase lherzolites (fig. 4B) and a few pyroxenites (fig. 4A) with high temperature porphyroclastic textures. Their discovery indicates that the basement in the MQZ is not exclusively formed of thinned continental crust. Lavas sampled westward of the Leeuwin FZ at Site DR10 have also transitional compositions (fig. 5). On the Australian slope, samples dredged at Site MG-DR07 are continental quartz-bearing rocks (mostly gneisses and rare granites), some showing a high grade paragenesis (upper amphibolite to granulite facies) marked by the presence of K-feldspar, biotite, sillimanite and/or kyanite and garnet, and without primary muscovite (fig. 4G). Some of these rocks underwent an intense mylonitic shear deformation followed by post-tectonic recrystallisation or migmatization. Depending on the age of the high grade evolution (metamorphism and shearing), these rocks document either the syn-rift exhumation of lower continental crust, or the formation of the older Australian craton. On the slope of the Naturaliste Plateau, at Site DR11, rocks of oceanic origin (gabbro-diorites/dolerite/basalt; fig. 4F) were dredged together with acid rocks (gneiss and granites) of probable continental origin, some having a quartz, K-feldspar, biotite and garnet metamorphic paragenesis (fig. 4H). At that site, the transitional basalts intrude the gabbros and associated dolerites. The presence of metamorphic acid rocks indicate that the Naturaliste Plateau is likely a continental fragment that was later intruded by mafic rocks, whose origin and ages of intrusion have to be determined. Discussion and conclusions. – The retrograde tectono-metamorphic evolution of the peridotites recovered in the MQZ, which includes a reequilibration in the plagioclase field (marked by the development of olivine and plagioclase after spinel and pyroxene), is compatible with an exhumation under a rift zone [Girardeau et al., 1988; Kornprobst and Tabit, 1988; Cornen et al., 1999]. By analogy with the Iberia Abyssal Plain, the MQZ could represent a wide OCT where the mantle was exhumed and stretched mostly by amagmatic extension before the initiation of oceanic accretion [Beslier et al., 1996; Boillot and Coulon, 1998] (fig. 6). This hypothesis is supported by the tectonic structures (horsts and grabens) imaged in the seismic data over the MQZ [Boeuf and Doust, 1975]. Accordingly, the limit of the continental crust would be located at the foot of the slope, i.e. 160 km (or 250 km in the NW-SE extension direction) northward of the assumed location of the OCT at the southern edge of the MQZ. The age of the Australia-Antarctic breakup would thus be (1) older than that inferred from the magnetic anomalies (circa 95 Ma [Cande and Mutter, 1982; Veevers, 1986]), which would rather date the onset of oceanic accretion, and (2) older than the age of the breakup unconformity estimated as Santonian (83 Ma), further east, in the Great Australian Bight [Sayers et al., 2001]. The origin of the Naturaliste Plateau, continental or oceanic, is still disputed. The discovery of metamorphic rocks of probable continental origin on the southern flank of the Plateau (Site DR11) shows that it consists at least partially of rocks of the Gondwana continent. All the samples from the Diamantina Zone confirm that its basement is made of a peridotite-gabbro-basalt assemblage. The nature and age of the peridotites and of the associated magmas will help understanding the origin of this domain, which can result either from Neocomian seafloor spreading with further remobilization during the Australia-Antarctic separation, or from post-Neocomian ultra-slow seafloor spreading. Because of the omnipresence of extensive tectonic structures (fig. 3) and of the relatively small proportion of crustal rocks relative to the mantle rocks, we argue that the formation of the Diamantina Zone was mainly controlled by tectonics rather than by magmatic processes. In conclusion, the data collected along the southwest Australian margin during the MARGAU/MD110 survey evidence two major tectonic phases with formation of a wide OCT where abundant mantle rocks, in association with few mafic rocks, outcrop or lay directly beneath the sediments. The evolution of the crystalline rocks is compatible with an exhumation under a rift zone during a phase of magma-poor extension primarily controlled by tectonic processes. The domains where basement highs were sampled seem to be continuous over more than 1500 km eastward along the south Australian margin. Additional evidence on such large-scale structural continuity and on the nature of the associated basement highs may help generalizing the models for continental breakup and formation of non-volcanic passive margins, where oceanic accretion does not immediately follow continental breakup.

The Officer Basin described in this paper includes four Proterozoic to Lower Palaeozoic sub-basins (Gibson, Yowalga, Lennis, Waigen) which extend in a northwest to southeast belt across 200 000 sq. km of central Western Australia. These sub-basins are bounded by Archaean to Proterozoic basement blocks and are almost entirely concealed by a veneer of Permian and Cretaceous sediments. Depth to magnetic basement locally exceeds eight kilometres.Until recently, information on the sub-surface geology was limited to shallow levels, based on the results of a petroleum exploration campaign in the 1960s and the work of State and Federal Geological Surveys. In 1980, the Shell Company of Australia was awarded three permits (46 200 sq. km) covering the Yowalga and Lennis Sub-basins. The results of 4700 km of seismic data and three deep wildcat wells, combined with gravity, aeromagnetic, Landsat, outcrop and corehole information, has led to a better understanding of the regional subsurface geology.The Lennis Sub-basin appears to contain Lower to Middle Proterozoic sediments, whereas the Yowalga Sub- basin is primarily an Upper Proterozoic to Lower Cambrian sequence which comprises a basal clastic section, a middle carbonate and evaporite sequence and an upper clastic section. Widespread Middle Cambrian basalts cap the Upper Proterozoic to Lower Cambrian prospective sequence. Late Proterozoic uplift resulted in salt- assisted gravity tectonics leading to complex structural styles, especially in the basin axis.Despite oil shows, organic matter in the oil and gas generation windows and reservoir-quality sandstones with interbedded shales, no convincing source rocks or hydrocarbon accumulations have yet been located. The area remains, however, one of the least explored basins in Australia.

Carbon geo sequestration (CGS) is considered one of the promising approaches to reducing anthropogenic greenhouse gas emissions into the environment. Furthermore, Underground Hydrogen Storage (UHS) has been also identified as a viable solution to effectively stored hydrogen in geological formations. The underground storage of hydrogen (UHS) project has the potential to overcome the supply and demand imbalance by a subsequent withdrawal during periods of renewable energy shortage. Depleted petroleum reservoirs and deep saline aquifers are considered favorable candidates for long-term H2 and CO2 storage. H2 and CO2 become trapped in the reservoir by various physical and chemical mechanisms, and these mechanisms mainly include residual trapping and structural trapping, dissolution, and mineralization trapping. The wettability of rock minerals for storage gas in the presence of brine is a significant physicochemical factor that largely affects the trapping mechanism. The reservoir formations naturally contain small concentrations of water-soluble organic components in particular humic acid (HA). These organic components in formations also assist the growth of various natural organotrophic microorganisms. While the earlier investigations suggest the impact of organic matter and microorganisms on wetting behaviour for enhanced oil recovery applications, we here argue that these organic matter and microorganisms have a significant effect on the CO2 and H2 wettability of the subsurface formations as well. Therefore, we prepared organic acid and bacteria-treated surfaces, and the effects of these treated surfaces on the H2 and CO2 wettability of subsurface reservoirs were evaluated via advancing and receding contact angle measurements, streaming zeta potential, and NMR techniques, at various organic acid concentrations, high pressures (up to 25 MPa), elevated temperatures (up to 333 K) and brine salinity (up to 0.3 M NaCl), that simulate the subsurface reservoir conditions. The surface characterizations were examined by high-resolution scanning electron microscopy (SEM) and atomic force (AFM) microscopy imaging while other characterization tools (e.g. TOC, EDX, and FTIR) were also implemented to gain a broader insight into the observed wetting behaviour. Our results demonstrate that water-soluble organic acid concentration significantly changes rock wettability from water-wet (0-50o) towards CO2-wet (90-110o). Furthermore, a strong correlation exists between surface adsorption of organic acid and streaming potential coefficient, where the amount of residual water saturation decreases in organic acid aged cores – suggesting the presence of organic acid changes wettability towards CO2 wet in pores. The low organic content WA basalt was initially water-wet but with increasing pressure, it was also converted into a completely CO2-wet at pressures exceeding 15 MPa and 323 K. The results of bacteria-treated quartz surfaces suggest that (1) bacterial growth is prominent on the quartz surfaces with organic matter and, (2) the originally hydrophilic surfaces tend to become less hydrophilic while the hydrophobic surfaces turn less hydrophobic in the presence of microorganisms. The results of this investigation provide a fundamental understanding of H2 and CO2 wettability alteration in the subsurface microbial environment along with organic acid, thus, having implications for de-risk the large-scale carbon geo-sequestration (CGS) and underground hydrogen storage (UHS) projects.

[Truncated abstract] The Neoarchean (2800 to 2600 Ma) Eastern Goldfields Superterrane (EGST) comprises elongated belts of deformed and metamorphosed volcanic and sedimentary rocks intruded by granitoids. The Superterrane is made up of five distinct tectonostratigraphic terranes. From west to east these are the Kalgoorlie, Gindalbie, Kurnalpi, Laverton and Duketon Terranes. The Kalgoorlie Terrane is characterised by 2720 to 2680 Ma marine mafic-ultramafic volcanic successions interlayered with, and overlain by, 2710 to 2660 Ma dominantly trondhjemite-tonalite-dacite (TTD) dacititic volcaniclastic rocks (Black Flag Group). The adjacent Gindalbie and Kurnalpi terranes are characterised by 2720 to 2680 Ma calc-alkaline volcanic successions representing oceanic island arcs. To the west of the EGST, the Youanmi Terrane is characterised by older, dominantly 3000 to 2900 Ma greenstone rocks and complex granitoid batholiths derived from older crustal sources. The southern Kalgoorlie Terrane comprises five elongate NNW-trending tectono-stratigraphic domains. Three principal marine komatiitic to basaltic suites, collectively referred to as the Kambalda Sequence, are present, including the wellpreserved massive to pillowed Lower and Upper Basalt Sequences, separated by the Komatiite Unit, as well as numerous dyke suites. The Lower Basalt Sequence comprises the Woolyeenyer Formation, Lunnon, Wongi, Scotia, Missouri Basalts and Burbanks and Penneshaw Formations, whereas the Upper Basalt Sequence contains the Paringa, Coolgardie, Big Dick, Devon Consols, Bent Tree, and Victorious basalts. ... Instead, the data suggest that discrete PGE-bearing phase (s) fractionated from the basaltic magmas. Such phases could be platinum group minerals (PGM; e.g. laurite) and/or alloys, or discrete PGE-rich nuggets. In summary, data on the three magmatic sequences record decompression melting of three distinct mantle sources: (1) long-term depleted asthenosphere for prevalent depleted tholeiitic and komatiitic basalts, and komatiites; (2) long-term enriched asthenosphere for Paringa Basalts and similarly enriched rocks; and (3) shortterm enriched continental lithospheric mantle (CLM) for HREE and Al-depleted dykes. Some of these rocks were contaminated by TTD-type melts. Taken with the existing geophysical and xenocrystic zircon data, the most straightforward interpretation is eruption of a zoned mantle plume at the margin of rifted continental lithosphere. The Kalgoorlie Terrane extensional basin was subsequently tectonically juxtaposed with the adjacent arc-like Gindalbie and Kurnalpi Terranes at approximately 2660 Ma at the start of orogeny in a Cordilleran-style orogen to form the EGST. Collectively, uncontaminated basalts have Nb/Th of 8-16, compared to 8-12 reported for the Lunnon basalts in a previous study. To a first approximation these asthenosphere melts are complementary to average Archean upper continental crust with Nb/Th =2, consistent with early growth of large volumes of continental crust rather than models of steady progressive growth.

The Neoproterozoic (815.4 ± 4.3 Ma) Aries kimberlite intrudes the King Leopold Sandstone and the Carson Volcanics in the central Kimberley Basin, northern Western Australia. Aries is comprised of a N-NNE-trending series of three diatremes and associated hypabyssal kimberlite dykes and plugs. The diatremes are volumetrically dominated by massive, clast-supported, accidental lithic-rich kimberlite breccias that were intruded by hypabyssal macrocrystic phlogopite kimberlite dykes and plugs with variably uniform- to globular segregationary-textured groundmasses. Lower diatremefacies, accidental lithic-rich breccias probably formed through fall-back of debris into the vent with a major contribution from the collapse of the vent walls. These massive breccias are overlain by a sequence of bedded volcaniclastic breccias in the upper part of the north lobe diatreme. Abundant, poorly-vesicular to nonvesicular, juvenile kimberlite ash and lapilli, with morphologies that are indicative of phreatomagmatic fragmentation processes, occur in a reversely-graded volcaniclastic kimberlite breccia unit at the base of this sequence. This unit and overlying bedded accidental lithic-rich breccias are interpreted to be sediment gravity-flow deposits (including possible debris flows) derived from the collapse of the crater walls and/or tephra ring deposits that surrounded the crater. ... This Fe-enrichment may have resulted from Fe-Mg exchange with olivine during slow cooling of the peridotite host rocks. Textures reflecting the cooling history of some mantle xenoliths are preserved in the form of fine exsolution rods of aluminous spinel in diopside and zircon in rutile grains in aluminous spinel- and rutile-bearing serpentinised ultramafic xenoliths, respectively. These textures suggest nearly isobaric cooling of host rocks in the lithospheric mantle, and indicate that at least some aluminous spinel in spinel-facies peridotites formed through exsolution from chromian 4 diopside. Episodes of Fe-Ti-rich metasomatism in the spinel-facies Kimberley mantle are the likely source of high-Ti phlogopite-biotite + rutile and Ti, V, Zn, Ni-enriched aluminous spinel ± ilmenite associations in several ultramafic xenoliths. U-Pb SHRIMP 207Pb/206Pb zircon ages for one granite (1851 ± 10 Ma) and two serpentinised ultramafic xenoliths (1845 ± 30 Ma; 1861 ± 31 Ma) indicate that the granitic basement and lower crust beneath the central Kimberley Basin are at least Palaeoproterozoic in age. However, Hf-isotope analyses of the zircons in the ultramafic xenoliths suggest that the underlying lithospheric mantle is at least late Archaean in age.

Humanity's relationship with rocks is a long-standing one. Belk (1995, p.2) describes archaeological evidence of early assemblages of rocks found in Cro-Magnon caves that would not be out of place in contemporary rock-collections. Historically, apart from being used as material for tools and buildings. rocks were also used for magical, pharmaceutical and decorative purposes. During the Renaissance and Enlightenment, the practice of collecting rocks became associated with the sense of discovery and the colonial expansion of western European civilization across world, and with advances in mining, science and industry. It is a practice that continues through to the present day. This thesis is an ethnography that asks contemporary rock collectors: why do they collect rocks? How do they collect rocks? And, how do they talk about them? Adapting Foucault's theoretical framework on discourse (1970) and utilising positions on collecting put forward by Baudrillard ( 1994), Belk ( 1995), Benjamin (1999), and others, the thesis analyses interviews and images of rock-collectors and their collections and puts forward a snapshot of the discourse of rocks and rock-collecting as currently practiced. The thesis's theoretical framework is first tested on texts of popular culture on rocks and rock-collecting to locate and identify the statements and discursive formations that make up the discourse, and then it is applied to the interviews of contemporary collectors talking about their collections. While some rock collectors practice alone and their approaches may appear idiosyncratic, others, sharing knowledge and experience, practice in a club environment. The collectors' approaches to rock collecting range from the taxonomic and scientific to the aesthetic and utilitarian, personal and historical, and, for some, to the metaphysical. In Australia some aspects of rock-collecting are allied to prospecting and mining. For some collectors the rocks are souvenirs, and are connected to travel. For other collectors rock-collecting is associated with understandings of nature, time and space. The interviews reveal that in a consumer society rocks are also commodities, with many of the collectors not only acquiring their rocks in the field, but also buying what they cannot find, or trade, for their collection. The analysis of the collectors' interviews demonstrates that the discourse does not stand as an isolated figure, but shares statements and configurations of statements with many other discourses in the field of knowledge, including science, history, archaeology and metaphysics. The interviews also illustrate how discourse and their associated practices are subject to external and internal rules and regulations, imposed by the State, and by institutions of academia and cultural and scientific practices, such as museums and universities. Some collectors aspire to emulate museums, and wish to share with others knowledge about to their collection through exhibition. The variety of themes and practices found in the interviews reinforce Foucault's proposition that within a discourse statements and configurations of statements may arise that are incompatible and form diffractions in the discourse. While apparently incompatible themes, variations and differences exist within the discourse, the analysis of the interviews and the conclusion of the thesis underscore the underlying unities of the discourse of rocks and rock-collecting.

Thesis (Ph. D.)--Dept. of Geology and Geophysics, University of Adelaide, 1992.
Typescript (Photocopy). Includes copies of 4 papers by the author as appendix 4 (v. 1). Errata slip inserted. Includes bibliographical references (leaves 170-192 (v. 1)).

Thesis (Ph. D.)--University of Adelaide, Dept. of Geology and Geophysics, 1987.
Typescript. Maps in back pocket of v. 1. Microfiches in back pocket of v. 2. Microfiches contain petrographic descriptions, total rock XRF analyses and microprobe analyses. Includes bibliographical references (leaves 160-183 (v. 2)).

This study assessed the geochemical characteristics of lignite and other waste rock of the future South Jimblebar Iron Ore Mine in Western Australia. Results indicated that lignite of CzD 2 and black shale of MU stratigraphic units were potentially acid forming (PAF) materials and relatively enriched in certain elements of environmental significance. In contrast, non-carbonaceous mudstones were non-acid forming (NAF). These findings indicate potential for acid mine drainage generation that will requires specific waste rock management.

International reference materials were employed to investigate the efficacy of ICP-MS for determination of selenium in rocks. Results indicate that significant inaccuracies may occur in the reported Se content of rocks, particularly those containing high Fe and Al, using routine procedures employed by commercial laboratories in trace element analysis. Analysis of waste rocks from three Pilbara iron ore mines revealed significant potential sources of selenium contamination with lignite and carbonaceous shales particularly enriched in selenium.

Samples of every rock type present along a traverse through the Jack Hills belt were examined and processed for zircon, monazite and xenotime isotopic study. Zircon U-Pb ages range from 1618±22 Ma to 4381±5 Ma, confirming the presence of both Archean and Proterozoic successions. Lutetium-Hf data for Hadean zircons imply a primitive source that was reworked with little juvenile input from the mantle. Monazite data confirm that the Archean rocks were metamorphosed at 2.65 Ga.

Rocky, an ornate dragon, lives on granite rocks in the south-west of Australia. But further north, where it is getting hotter and wetter, his desert relatives are having trouble with their eggs. As the lizards trek through country in search of a new home, Rocky shares local Indigenous and Western understanding of these changing environments and the animals that live in them. Written by Felicity Bradshaw, a retired Research Officer at University of Western Australia, and illustrated by Norma MacDonald, an Aboriginal Yamatji artist, The Great Lizard Trek will delight, entertain and inform primary aged children.

Abstract Neoarchean greenstone-hosted gold deposits in the Eastern Goldfields Superterrane of the Yilgarn craton of Western Australia are diverse in style, timing with respect to magmatic activity, structural environment, host rocks, and geochemical character. Geologic constraints for the range of gold deposits indicate deposit formation synchronous with volcanism, synchronous with syn- and postvolcanic intrusion, synchronous with postvolcanic deformation in faults and shear zones, or some combination of superposed events over time. The gold deposits are distributed as clusters along linear belt-parallel fault zones internal to greenstone belts but show no association with major terrane boundary faults. World-class gold districts are associated with the thickest, internal parts of the greenstone belts identified by stratigraphic preservation and low metamorphic grades. Ore-proximal faults in those regions are more commonly associated with syn- and postvolcanic structures related to greenstone construction and deformation rather than major terrane amalgamation. Using the Kalgoorlie district as a template, the gold deposits show a predictable regional association with thicker greenstone rocks overlain unconformably by coarse clastic rock sequences in the uppermost units of the greenstone stratigraphy. At a camp scale, major gold deposits show a spatial association with unconformable epiclastic and volcaniclastic rocks located above an unconformity internal to the Black Flag Group. Distinct episodes of gold deposition in coincident locations suggest fundamental crustal structural controls provided by the fault architecture. Late penetrative deformation and metamorphism overprinted the greenstone rocks and the older components of many gold deposits and were accompanied by major gold deposition in late quartz-carbonate veins localized in crustal shear zones or their higher order fault splays.

The earth is divided into three layers: the crust, the mantle, and the core. There are two principle regions within the crust: continents and ocean basins. The rocks that make up these layers differ from one another in chemical composition and density. The mantle is composed of dense ultramafic rocks, rich in magnesium-iron silicate minerals such as olivine and pyroxene. Ultramafic rock is the main source of serpentine soil in the continental crust. Most of the lighter crustal rocks are made up of silicate minerals that are enriched in the lighter elements sodium, calcium, and potassium, which have large cations, rather than magnesium (also a light element) and iron, which have smaller cations (table 2-1, appendix A). Over geological time living organisms have evolved on continents or in oceans with elemental concentrations dependent more on the crust than on the mantle. In the oceanic realm, new oceanic crust forms at spreading centers between active plates where hot, decompressed mantle rock rising toward the surface partially melts to form basaltic magma. The spreading centers develop at mid-ocean ridges, behind volcanic arcs (back-arc basins), in front of volcanic arcs (forearc basins), or as continents rift apart, as with the Red Sea. Cracks formed between the spreading plates are intruded by basaltic magma that forms thin vertical sheets (sheeted dikes). New cracks and dikes are continually forming as the plates spread apart. Some of the magma rising into the cracks reaches the ocean floor and, as the hot lava is quenched by ocean water, it solidifies to form distinctive rounded, pillowlike structures. As magma above the partially melted mantle cools, some of the first crystals to form settle to the bottoms of liquid magma chambers, producing layered gabbros—a process called differentiation. The layered sequence of pillow lava, diabase dikes, and gabbro built upon the ultramafic mantle is typical of new ocean crust. New crust formed at spreading centers slowly migrates away from the spreading center and cools into a rigid oceanic crust that ranges in thickness from 6 to 12 km.