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Organic maturity is a key property for assessment of hydrocarbon potential and generation of black shales. Early Paleozoic strata are usually void of terrestrial organic matter such as vitrinite, thus evading conventional, reflectance based maturity analysis. To overcome this, graptolites in samples from the basal hot shales of the Silurian Qusaiba Formation, with known, reflectance based vitrinite equivalent maturities from 0.54 to 1.76 VRE%, were analyzed with Raman spectroscopy to establish a spectroscopic maturity scale. All samples provided spectra showing the D isorder (D) peak and the G raphite (G) peak typical for organic carbons. Systematic variation of these peaks with sample maturity is used to quantify the relationship of reflectance with the graptolites molecular condition. Several spectral properties were tested for use as maturity indicators. The most reliable maturity tracers are the variation of position of the G peak between 1570 and 1610 cm − 1 and the widening band distance (Δ (G-D) ) between the G peak and D peak position at 1320 to 1370 cm − 1 . Comparison of the mean and modal maxima of peak positions showed that the mean of G peak position and Δ (G-D) provide the best fit of Raman and optical reflectance determinations with R 2 of 0.884 and 0.935, respectively. Algorithms for the calculation of vitrinite equivalent reflectance from the Raman spectral properties were developed based on best fit exponential regressions, with a linear cross correlation of the measured and calculated values at R 2 = 0.9178 for the mean of Δ (G-D) . Raman based maturity measurements on graptolites provide a welcome alternative method for on particles as small as 3 μm diameter.

The Lower Silurian Qusaiba Hot Shales (QHS) are proven source rocks for oil within the Paleozoic, and possibly some of the Mesozoic, reservoirs in Saudi Arabia. Moreover, these shales have oil shale potential where they are immature and shallow enough for mining, as well as unconventional shale oil and shale gas potential, in areas where they are within oil-maturity and gas-maturity levels, respectively. The QHS were deposited in relatively shallow marine environments under anoxic water conditions, resulting in accumulation of amorphous kerogen, organic-walled graptolites and acritarchs. Across the Arabian Basin, organic matter quality does not show much variation for the QHS, but the maturity varies greatly as a result of varying burial history. Thermal maturity assessment of shale source rocks that lack vitrinite, such as the Qusaiba Hot shales, continues to be challenging, especially where conflicting measurements are obtained from different sources. This paper presents an integrated assessment of QHS thermal maturity parameters, based on cores from 13 carefully selected boreholes that – based on regional basin models – are believed to cover a wide maturity range (ca. 0.5 to 2.0% Ro). We conducted some analyses on kerogen (maceral petrography, graptolite reflectance, UV-fluorescence, whole rock pyrolysis, Raman spectroscopy of graptolite) and other analyses on bitumen extracts (GC and GC–MS of saturate and aromatic fractions, and FTIR spectroscopy of the asphaltene fraction). We show that using many thermal maturity parameters reduces uncertainty significantly, and we therefore recommend that graptolite reflectance analyses should be conducted in support of other maturity indicators. Proper reflectivity measurements of the graptolites set the reference for comparison of other maturity parameters obtained from petrographic, geochemical, and spectroscopic techniques. Our work provides a template by which Qusaiba thermal maturity can be more accurately estimated when only a limited set of maturity parameters is available.

The Hillside Cu-(Au) deposit, Yorke Peninsula, South Australia, is a recently-discovered ore system within the 1.6. Ga World-class Olympic iron oxide-copper-gold (IOCG) Province. The deposit is characterized by a skarn-style alteration zone. Analyses of feldspar, calcite, skarn minerals (garnet, pyroxene, clinozoisite and actinolite) and accessories (titanite, apatite and allanite), and grain-scale element mapping by laser-ablation inductively-coupled plasma mass spectrometry are used to assess the distributions of rare earth element (REE), incompatible and ore-forming elements in host rocks, prograde and retrograde skarn.Garnet is a major repository of HREE, especially in prograde skarn, whereas LREE-enriched clinozoisite is the principal REE-host in retrograde skarn. REE distribution patterns define a pronounced partitioning of elements among the dominant coexisting minerals. Compositional variation between assemblages, and also within individual grains, defines an evolution from early feldspar-pyroxene skarn through main-stage calcic skarn to the ore-stage. A switch from a prograde, HREE-dominant signature to a LREE-enriched signature is observed in both retrograde and distal skarn. Zr-in-titanite geothermometry supports transition from magmatic to hydrothermal, skarn-forming processes at temperatures of ~. 660. °C; the initiation of ore-stage is about 100. °C lower.Understanding REE distributions in all minerals within a complex, multistage ore system assists the development of vectoring tools that use trace element chemistry in exploration for similar IOCG deposits beneath regolith cover across the Olympic Province. Titanite and apatite show particular promise because of their characteristically distinct REE patterns in magmatic and hydrothermal stages, trace element responses to redox changes, and their widespread abundance throughout different lithologies in the area. Refereed/Peer-reviewed

Fe-oxide micro-concretions are examined as a possible sampling medium in geochemical exploration for base metal mineralisation. Samples were extracted from loose, partly transported regolith overlying the Hillside Fe-oxide-Cu-Au deposit (Rex Minerals Ltd., South Australia) along two traverses across the deposit, using a rare earth magnet. Fe-oxide minerals in the magnetic separates are maghemite (25–35 Wt.%) and hematite (15-40Wt%). Results of the chemical analysis are compared to the bulk regolith composition. Combined content of Cu + Pb + Zn + Ni of the magnetic mineral separates of up to 1300 ppm compare to 150 ppm in the bulk sample. Electron Microprobe analysis of the Fe-oxide phase in the petrographically complex Fe-oxide rich micro-concretions revealed base metal contents of > 3000 ppm Ni + Cu + Zn (average 490 ppm) indicating the selective accumulation of base metals in this phase. A Manhattan distance cluster analysis was performed on the bulk regolith and magnetic separate samples to determine geochemical affinities of elements within the sample types. Based on this a base metal index (Cu + Pb + Zn + Ni) was generated and used to identify positions of base metal anomalies. The results clearly reproduce the established anomaly and demonstrate the viability of using magnetically separated mineral fractions of regolith as a geochemical sampling medium.

Calcrete (pedogenic Ca carbonate) is an important sampling medium for geochemical gold (Au) exploration in semi-arid and arid regions of Australia, because it is widespread, easy to sample and calcium (Ca) shows a strong positive correlation with Au, but not with base metals, in calcrete overlying buried Au mineralization. In this study we show that the formation of Au-anomalous calcrete can be biomediated through the activity of resident microorganisms, and may not simply be the result of passive nucleation on inactive cells or evapotransporative processes. Calcified microfossils are highly abundant in calcrete from the Barns Au-prospect in South Australia. These microfossils are morphological analogues of calcified cells and biofilms formed in laboratory experiments conducted with active bacterial cultures enriched from Au-anomalous calcareous sand from the Barns prospect. Calcium carbonates precipitated by these cultures consisted mostly of calcite, which is the main carbonate mineral in calcrete. Synchrotron micro-X-ray fluorescence (S-μXRF) mapping was used to assess the distribution of Au, Zn, Ca and other metals in Ca carbonates precipitated by active bacterial cultures. On a μm-scale the distribution of Au was heterogeneous in these Ca carbonates and differed from base metal distribution, thus mimicking the spatial separation of these metals observed in calcrete. The speciation of Au in Ca carbonates precipitated by active bacteria was measured using micro-X-ray absorption near edge structure spectroscopy (μ-XANES) and resembled that observed in Au-anomalous calcrete closely. While metallic Au was observed in Au ‘hotpots’, ionic Au was detected in the halo surrounding the ‘hotspot’. In contrast, the precipitates produced in the presence of dead bacterial cells or by raising solution pH or pCO 2 , i.e., hydroxylapatite, portlandite and vaterite, respectively, did not reflect the mineralogy of calcrete. Gold distribution and speciation in vaterite, formed by raising pCO 2 , were homogenous and did not reproduce the variation observed in calcrete and Ca carbonates precipitated by active cells. Increasing the supersaturation with respect to Ca in solution by incremental drying of the medium produced only X-ray amorphous precipitates, or hydroxylapatite in the presence heat-killed cells. In conclusion, this study shows that active microbial processes that combine biogenic Ca carbonatogenesis with Au precipitation are likely to drive the formation of Au-anomalous calcrete.

The Mt. Mulga barite Cu–Au deposit in the central part of the Olary Domain is hosted by the Palaeoproterozoic Willyama Supergroup of the Curnamona Craton. The lenticular, stratiform ore bodies are hosted by the Ethiudna Subgroup at and near the contact to the underlying Wiperaminga Subgroup. The ore bodies consist of massive, coarse crystalline barite up to 6 m thick interspersed with granular ( A pronounced positive Eu-anomaly of the mineralisation hosting unit indicates a reducing character of the mineralising fluids and is characteristic for exhalative sediments. 87 Sr/ 86 Sr-isotope ratios of barite fall into a narrow range of 0.708 to 0.713 suggesting an origin of the mineralising fluids from the underlying Lower Willyama sequence. The δ 34 S values of barite from the main ore body range from + 13 and + 16‰, while the barites of the other ore bodies range from + 6 and + 11‰. Chalcopyrite revealed δ 34 S values of − 1.3 to + 4.5‰. Barite is suggested to be formed by mixing of a hydrothermal, reduced, hydrothermal Ba-rich fluid with oxidised, sulphate-rich water of a non-marine basin. Although an epigenetic formation of the Cu–Au mineralisation during the Olarian Orogeny is possible, we suggest a cogenetic formation with the barite–iron-oxide mineralisation.

The research of fluids in the earth's crust is greatly benefiting from methodological (analytical) and experimental advances and the rapid development of increasingly powerful numerical modelling systems. New experimental data continuously refine the accuracy of numerical models aiming to quantitatively reconstruct geological processes. Geological modelling programs have moved on from linear or 2-dimensional approaches to integrating 3 or 4D geology with geothermal aspects, fluids flow and reactive transport processes into complex, quantitative scenarios. These combinations of refinement of the data base and advances in computational capacities are the stepping stones for the development of the predictive quality of mineralising models and hydrocarbon migration and accumulation, access to geothermal energy and the sequestration of CO 2 . This special issue presents a selection of contributions on “Fluids in Geological Processes” following the VIth GEOFLUIDS meeting in Adelaide in 2009, emphasizing on recent developments in the different research trends in this field.

The formation of pedogenic carbonate (calcrete) in terrestrial environments is commonly mediated by microorganisms. In Australia, Au-anomalous calcrete is an important sampling medium for geochemical exploration, but current models describing its formation do not include a confirmed microbial component. This study demonstrates that bacterial communities in calcareous sands from dunes overlying the Barns Gold Deposit in semi-arid South Australia, are capable of mediating the biomineralisation of Au-anomalous carbonates. Bacterial enrichment cultures obtained from calcareous sands at three depths (0.1, 0.64 and 2.1 m, plus abiotic control) were incubated in urea and Ca 2+ -containing growth media (pH 8), unamended and amended with Au (100 parts-per-billion, ppb) as Au–aspartic-acid complex. During the incubation of the enrichment cultures urea was turned over to NH 4 + within 96 h to 220 h. The solution pH increased concurrently by approximately 1.2 units, and Au-anomalous Ca-carbonate crystallites were precipitated on cells, which functioned as nucleation sites; no carbonate precipitation was observed in abiotic controls. Compared to the medium, Au was strongly enriched in these carbonates and appeared to be uniformly dispersed in the individual crystallites, as shown using LA-ICP-MS; a similar distribution is present in naturally occurring Au-anomalous calcrete. Phylogenetic 16S rRNA PCR DGGE analyses, shotgun cloning and functional microbial analyses (BioLog, ureC quantitative PCR) demonstrated that naturally occurring and culture-enriched bacterial communities were dominated by alkaliphylic, halotolerant Bacillus spp. The indigenous bacterial communities were capable of utilising amino acids (including l -aspartic acid) and urea, which appears to lead to the destabilisation of the Au–amino acid complexes and concomitant co-precipitation of Au in the Ca-carbonates. In conclusion, a model combining geomicrobial– with evapotranspiration– and plant-based components is likely to best describe the formation of (Au-anomalous) calcrete in semi-arid and arid zones.

Anomalously high Au concentrations (2.5 to 50 ppb) in regolith carbonate accumulations, such as calcrete and calcareous sands in aeolian sand dunes overlying Au mineralisation of the Gawler Craton, South Australia, show a marked covariance of Au with K, Mg and most notably Ca. This relationship appears to be linked to the authigenic formation of smectites and carbonates within the aeolian dunes in the region. However, little is known about the processes involved in the formation of carbonates under semi-arid and arid conditions. In this study the geochemical properties of aeolian dunes along several depth profiles of 2 to 4 m are investigated in order to assess the relationship between Au mobility and calcrete formation. In the profiles a strongly systematic relationship between Au and the increasing Ca–Mg contents at depth highlights the close association between the enrichment of Au in the calcrete and the underlying hydrothermal mineralisation. Intense calcrete formation and concurrent Au enrichment also occurs in the vicinity of roots penetrating the dune. Thin section petrography and cathodoluminescence show that most of the calcrete in the regolith profiles is micritic; some sparic crystallites have also been identified. To demonstrate the presence of microbial processes that may mediate the formation of calcrete, samples from a depth profile in the dune were taken under sterile conditions. After amendment with urea and incubation of up to 24 h, up to 18 mg/l of NH 4 + were detected in near surface samples. At depth of 2.3 m 1 mg/l NH 4 + were detected compared to a control that contained below 0.05 mg/l NH 4 + . These results suggest that the genesis of calcrete and pedogenic carbonate in the area may be partly biologically mediated via processes such as the metabolic breakdown of urea by resident microbiota which generates a pH and pCO 2 environment conducive to the precipitation of carbonate. In the process of urea breakdown organic Au complexes such as Au-amino acid complexes may become destabilised in solution and Au may be co-precipitated, resulting in the fine, non-particulate distribution of Au throughout the micritic calcrete carbonate. In conclusion, this study suggests a coupled mechanism of biologically mediated and inorganic mechanisms that lead to the formation of Au-in-calcrete anomalies.

Conditions during the formation of breccias in the Curnamona Province (eastern South Australia) have been investigated through a detailed fractal, microstructural, structural and fluid inclusion study of the breccias, syn-tectonic quartz veins and surrounding rocks. Fractal analysis of clast shapes and clast size distributions were able to distinguish two styles of breccia and indicate that fluid pressure fluctuations played a significant role, though to differing degrees, in the initiation of the brecciation process. Approximate palaeostress orientations prevalent during brecciation and their relationship to the deformational history of the terrane have been reconstructed by combining the orientations of microfractures (sealed microfractures and fluid inclusion planes) with structural field data. Fluid pressure fluctuations of ∼80 MPa during the brecciation process have been quantified by structurally constrained microthermometric analysis of syn-tectonic fluid inclusions coupled with an analysis of the metamorphic history of the area. Results from this study allow brecciation within the Curnamona Province to be placed within a structural framework and relate the process of brecciation to the interaction between regional hydrothermal alteration/fluid flow systems, shear zone formation and lithological contrasts within the upper crust during the Palaeoproterozoic Olarian Orogeny. These methods and findings provide a template for the study of brecciation processes in other terranes where fluid-induced brittle deformation is a controlling factor in the localisation of major ore deposits.

Mineral exploration in areas of little bedrock exposure must increasingly rely on the predictive quality of geological, geochemical and geophysical data. In this contribution analysis of fluid inclusions is used to characterize fluid systems associated with alteration and mineralization in two locations in South Australia. In the Curnamona Province, fluids related to albitization and calc-silicate alteration with associated brecciation evolve from a saline sodic composition to a metalliferous, saline fluid also found associated with sulphide mineralization. The microthermometric distinction of inclusion types is evidence for pressure fluctuation as a cause for breccia formation. In the Central Gawler Craton gold province fluid inclusion studies have characterized the compositional and constrained the physical conditions of mineralizing fluids. Regionally identified low salinity CO2-bearing fluids at temperatures < 350 °C and pressures < 1.5 kbar indicate a shallow-level orogenic [Groves, D.I., Goldfarb, R.J., Gebre-Mariam, M., Hagemann, S.G., Robert, F., 1998. Orogenic gold Deposits: A proposed classification in the context of their crustal distribution and relationship to other gold deposit types. Ore Geology Reviews, 13, 7–27.] or intrusion-related [Lang, J.R., Baker, T., 2001. Intrusion related gold systems: the present level of understanding. Mineralium Deposita, 36, 477–489.] setting for the mineralization.

Two distinct generations of fluid flow associated with shear zone activity have been identified in Willyama Supergroup rocks of the southern Curnamona Province in northeastern South Australia. Fluids in the first event are inferred to have been sourced from the devolatilisation of Willyama Supergroup metasedimentary rocks during prograde metamorphism associated with the (1.61–1.58 Ga) Mesoproterozoic Olarian Orogeny. The second episode of fluid flow occurred during the (c. 500 Ma) Cambrian Delamerian Orogeny and resulted in localised rehydration of the Willyama Supergroup. Fluids were isotopically light and most likely sourced from prograde Delamerian metamorphism and dehydration of fault rocks and entrained meteoric waters that originally were involved in (c. 700 Ma) Neoproterozoic Adelaidean rifting. A key outcome of this study is the identification of this previously unrecognised fluid flow system that was active during the Delamerian Orogeny.

The thermal regime and the distribution of heat flow at the base of sedimentary basins is fundamental to the understanding of the process of basin evolution and the associated mobilization and migration of hydrocarbon and other fluids. For the Northeastern-German sedimentary basin, available information on structure, temperature, and thermal properties along a seismic DEKORP reflection profile allow high resolution 2-D forward and inverse simulations. This approach is attractive in situations where much information is available, if only with considerable uncertainty. In particular, this allows to introduce “soft” information into the analysis. In our case, forward simulations yield initial a priori estimates of the parameters while inversion calculations yield a posteriori estimates of the parameters and their uncertainty. The a priori parameters as well as their assumed uncertainty are input for a Bayesian parameter estimation scheme. In respect to the Northeastern-German sedimentary basin, the inverse analysis postulates a significant and characteristic a posteriori variation of thermal conductivity of the Zechstein unit along the entire profile as well as a generally large a posteriori thermal conductivity of the (pre-Permian) basement in the northern part of the basin. For inverse calculations, we used two alternative scenarios: One assumes the thermal conductivity of the Zechstein unit to be homogeneous along the profile while the other allows a lateral variation. A posteriori heat flow across the base of the model varies from 40 to 60 and 50 to 65 mW m−2 for models in which values for thermal conductivity and radiogenic heat generation rate were either based on literature values or direct measurements, respectively.

Samples of diagenetic and hydrothermal minerals from drillcores along the DEKORP 9601 seismic traverse in the North German Basin were investigated for their fluid inclusion and sulphur isotope composition to reconstruct the thermal and chemical evolution of fluid systems during basin evolution. The stages of basin subsidence and subsequent inversion are marked by fluid systems of distinct composition. The basinwide Zechstein evaporite units formed an aquiclude, disconnecting convecting fluids in the underlying Rotliegend volcanics from the overlying units. δ 34 S ratios of sulphides suggest a sedimentary sulphur source. δ 34 S ratios of diagenetic and hydrothermal sulphates indicate that sulphur was derived partly from Rotliegend volcanic units and partly from the evaporitic Zechstein.

The Ashanti belt of Ghana is the key district of gold mineralization in the Paleoproterozoic terrane of West Africa. The area considered in southwest Ghana is covered by lithologies of the volcanic-sedimentary Birimian Supergroup and the overlying elastic sedimentary Tarkwaian Group which were jointly folded and metamor- phosed under greenschist facies conditions during the Eburnean teetonothermal event at about 9..1 Ga. Regional fotiation md subparallel shear zones hosting mesothermal gold mineralization developed during deformation coeval with metamorphism. Four major tsoes of primary gold mineralization are present in the Ashanti belt: (1) mesothermal, generally steeply dipping quartz veins in shear zones mainly in Birimian sedimentary rocks, (9,) sulfide ores with auriferous arsenopyrite and pyrite, spatialty dosely associated with the quartz veins, (3) sulfide disseminations and stockworks in granitoids, and (4) paleoplaeers of the Tarkwaian Group. This study concentrates on types (1) and (9,) of the hydrotherlnal gold mineralization. Stable isotope analyses of host-rock and ore components were performed with the ailn of obtaining parameters relevant to the origin and evolution of the fluids that produced gold mineralization. Carbonaeeous matter in the Birimian metasediments displays 93C values ranging from -11.4 to -9,8.3 per mil relative to PDB, indicating an organogenie origin. Carbonates display a unimodal distribution of 9aC values ranging from -9.9 to -17.0 per rail relative to PDB. COz extracted from fluid inclusions in the auriferous quartz veins has 93C values ranging from -9.5 to -15.7 per mil relative to PDB. It is proposed that these carbon isotope compositions of carbonates and COz reflect extensive interaction of the CO,2-rieh hydrothermal fluids with reduced carbon in Birimian sediments in the deeper parts of the hydrothermal systems. Carbonates and auriferous vein quartz have 6So values ranging from 19,.9 to 9,9,.9, and 19,.8 to 15.6 per mil relative to SMOW, respectively. Carbonates and quartz were deposited in near isotopic equilibrium with respect to 6So, indicating fluid-dominated conditions during ore formation, from fluids of metamorphic or magmatie origin. Such an origin is corroborated bySD values of water extracted from fluid inclusions in vein quartz (-37 to -53% relative to SMOXV). Pyrite of synsedimentary-diagenetie origin in Birimian schists displays sulfur isotope compositions ranging from +7.3 to -9,0.9 per rail (median ca. -10% relative to CDT). Similar compositions and wide ranges are usually attributed to sulfide generation by bacterial sulfate reduction from seawater. Arsenopyrite and eogenetie pyrite from the sulfide ores generally have 534S values in the range -5.3 to -10.9, per rail relative to CDT. The tight unimodal distribution of 534S values indicates a large, homogeneous fluid reservoir. The low (534S values are interpreted as source-inherited, not related to unusual pH, Eh, temperature, or depositional conditions. Sulfides in Birimian sediments represent the most likely sulfur reservoir tapped by the fluid systems. The C, O, H, and S isotope compositions of ore-related hydrothermal minerals and fluid inclusion compo- nents indicate that the mineralizing fluids interacted extensively with the Paleoproterozoie rocks, especially Birimian sediments, at deeper crustal levels and at high temperatures. The isotopic compositions are most compatible with the formation of fluids from devolatilization reactions invoMng Birimian strata during pro- grade metamorphism at depth (metamorphic fluids).

Uranium-bearing hematite (containing up to several wt.% U), also containing Al, Mo, W and radiogenic Pb, is described from Olympic Dam, South Australia. These elements are present in grains that display both oscillatory zonation and porous structures. Laser-ablation inductively coupled mass spectrometry (LA-ICP-MS) element mapping confirms oscillatory and sectorial zoned domains in hematite grains are enriched in 238U- and 206Pb, and are distinct from those of W and Mo. The crystal structure and absence of inclusions within zoned hematite was assessed by transmission electron microscopy on foils obtained by in situ slicing across zonation patterns using the scanning electron microscope-focused ion beam technique. Satellite reflections on the electron diffraction patterns obtained from banded zones in hematite are attributable to long-range superstructure ordering, that is inferred to assist metal incorporation via the substitution 2Fe3+ ↔ Me6+ + vacancy, where Me = U, W, Mo. The suitability of U-bearing hematite for Pb–Pb geochronology as a first pass was tested on both zoned and porous hematite grains via LA-ICP-MS, using the GJ-1 zircon as the primary external standard. Only Pb–Pb ages were considered and resulted in 207Pb–206Pb ages of 1590 ± 8 Ma and 1577 ± 5 Ma for oscillatory and sector zoned hematite from two samples. Although reconnaissance in nature, these ages potentially support the supposition that mineralization is coeval with emplacement of the Gawler Range Volcanics and associated Hiltaba Intrusive Suite. The geochronological application utilizing an abundant refractory mineral represents a new tool for dating iron-bearing ores.

Erratum to “Hematite/maghemite trace element geochemistry in base metal exploration” [J. Geochem. Explor. 118 (2012) 1–13] Andreas Schmidt Mumm⁎, Robert C. Dart, Patrick Say a EXPEC ARC, Saudi ARAMCO, Dhahran 31311, Saudi Arabia b Centre for Tectonics, Resources and Exploration, Institute for Mineral and Energy Resources, School of Earth and Environmental Sciences, The University of Adelaide, Adelaide, South Australia 5005, Australia c Rex Minerals Ltd., PO Box 626W, Ballarat West, Victoria 3350, Australia

Acoustic emission (AE) from quartz during heating was measured with a high resolution decrepitometer on more than 350 samples from various conditions of formation and geological settings. The emitted acoustic signals can accumulate in very sharp peaks or extend over a wide temperature range. Different types and conditions of quartz formation can be distinguished from total counts and individual AE-patterns. Correlation of the determined AE peaks with microthermometric investigations, optical and scanning electron microscopical (SEM) studies of polished and etched thin sections showed that the sound, generated during heating, is caused by several distinguishable mechanisms. The main cause is the thermal expansion mismatch and thermal anisotropy of the quartz. In all cases the sound is emitted from opening and propagating microcracks. At temperatures below 380° C the main sources of AE are the rupture of grain boundaries, transgranular fracturing and decrepitation of large fluid inclusions. In the temperature range of 350–550° C, intragranular fracturing, sometimes enhanced by Brasil twinning, and reopening of healed fissures, often decorated with large numbers of small secondary fluid inclusions, cause distinct peaks of acoustic emission. At the α-β inversion temperature (≈ 573° C) massive emission of sound occurs if the quartz is twinned according to the Dauphine law. Measurement of AE can help to determine critical temperatures of material failure and reveal information on the residual strain in rocks. Different generations of quartz veins can be distinguished, even if covered by soil and the extent of alteration zones can be determined by the varying AE patterns.

Quartz, as the most ubiquitously occurring mineral, was chosen for investigations of the acoustic emission upon heating. Various samples from a wide range of conditions of formation were analyzed in the frequency range of 400–10 000 Hz with a high‐resolution decrepitometer. The acoustic emission patterns showed a variation of 5000–80 000 total signals over the entire temperature range of 90 °C‐610 °C (1‐cm3 sample, grainsize fraction 250–500 μm). Microthermometric investigations of the sound‐emitting processes and correlation with microcrack patterns determined by scanning electron microscopy (SEM) showed that various sources contribute to the sometimes vehement noise production. Stress built up because of thermal anisotropy causes the formation of microcracks along inter‐ and intragranular grain boundaries over most of the observed temperature range. Accumulation of signals from the decrepitation of fluid inclusions reveals information about the conditions of formation and subsequent alterations of the i...