Papers by Andreas Schmidt Mumm
ABSTRACT Hematite, the most abundant mineral in Iron Oxide Copper Gold (IOCG) deposits in the Gaw... more ABSTRACT Hematite, the most abundant mineral in Iron Oxide Copper Gold (IOCG) deposits in the Gawler Craton of South Australia, may incorporate significant amounts of U, W, Mo and radiogenic Pb. These elements are concentrated in hematite grains which display either oscillatory and/or sectorial compositional zoning, or are porous. The presence of U and Pb raises the potential for novel geochronology applications aimed at constraining the timing of mineralization. Meaningful preliminary age data were obtained for U-bearing hematite by LA-ICP-MS techniques on zoned grains. In the absence of suitable, matrix-matched standards, GJ-1 zircon was used as the primary standard. 207 Pb/ 206 Pb ages obtained on the zoned hematite (1590±7, 1583±3 Ma; Fig. 1) are statistically indistinguishable from ages for emplacement of the Gawler Range Volcanics and associated Hiltaba Intrusive Suite, and consistent with a major ore-forming event in the region at ~1.59 Ga. Fig. 1 U/Pb Concordia plots for dated U-hematite. All lower intercepts are at zero. BSE image shows typical zoning in dated grains. Provided that matrix-associated mass fractionation can be constrained, and suitable standards are fabricated, the ability to date an abundant refractory mineral like hematite could represent a valuable tool for dating IOCG deposits and, potentially, other iron-bearing ores. The subseafloor microbiota is diverse and complex, hosting metabolically active communities down to depths of more than 1000 meters below the seafloor (mbsf), as revealed by molecular and metagenomic studies. It harbors representatives from the three domains of life, i.e., numerous endemic and/or as yet uncultured Archaea and Bacteria, in addition to bacterial endospores, protists and fungi belonging to Eukarya. Although background molecular data on bacterial and archaeal lineages inhabiting subsurface sediment above 1000 mbsf exists, most deep-subsurface microorganisms detected so far were refractory to cultivation. Deeply buried microorganisms form an almost untapped diversity, as sub-sea-floor prokaryotic culturability in most studies is less than 0.1% of all microscopically detected cells. So far, active prokaryotes have been discovered down to 1626 mbsf, and microeukaryotes down to 113 mbsf, but the lower limit of the deep subsurface biosphere remains elusive. Here we report on the microbial prokaryotic and eukaryotic communities of a core of nearly 2 km collected in the Canterbury basin during IODP Expedition 317. A very stringent high-throughput 454-pyrosequencing approach targeting the 16S/18S rRNA genes for Bacteria, Archaea and Eukarya, along with real-time PCR analysis (genetic markers and functional genes), cell counts and cultures, were performed to assess microbial abundance, diversity and activity at different depths. Our results suggest that a diversity of microorganisms exists down to 1922 mbsf in the seafloor of the Canterbury basin and that this diversity is to a certain extent alive.
GSA Annual Meeting in Indianapolis, Indiana, USA - 2018, 2018
International Journal of Coal Geology, May 1, 2016
Organic maturity is a key property for assessment of hydrocarbon potential and generation of blac... more 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 1.98 VRE%, were analyzed with Raman spectroscopy to establish a spectroscopic maturity scale. All samples provided spectra showing the Disorder (D) peak and the Graphite (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 1610cm-1 and the widening band distance ( (G-D)) between the G peak and D peak position at 1320 to 1370cm-1. Comparison of the mean and modal maxima of peak positions showed that the mean of G peak position and (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 (G-D). Raman based maturity measurements on graptolites provide a welcome alternative method for on particles as small as 3m diameter.
Gold mineralisation constitutes an important economic factor in the Palaeoproterozoic terrane of ... more Gold mineralisation constitutes an important economic factor in the Palaeoproterozoic terrane of West Africa. The largest and most prominent mines, with a cumulative past production in excess of 1500 t of gold, are located in Ghana, more specifically in the Ashanti belt (Fig. 1). Geologists of the German Federal Institute for Geosciences and Natural Resources (BGR) and the Ghanaian Geological Survey Department have mapped and explored large parts of Ghana in the course of a number of projects of bilateral technical cooperation in recent years. Lately, work concentrated on gold mineralisation in the Ashanti belt of Ghana as part of the project “Metallogenesis of Gold in Africa”. This paper reviews and summarises the results of continuous geological work (Leube and Hirdes, 1986; Eisenlohr, 1989, 1992; Hirdes and Leube, 1989; Leube et al., 1990; Eisenlohr and Hirdes, 1992; Hirdes et al., 1992; Taylor et al., 1992: Blenkinsop et al., 1994; Davis et al., 1994; Hirdes and Nunoo, 1994; Hoh...
Neues Jahrbuch für Geologie und Palaontologie - Abhandlungen, Sep 26, 2001
Ore Geology Reviews, 2004
Sulphide mineralisation associated with rocks from the Palaeoproterozoic Olary Domain (OD) and ov... more Sulphide mineralisation associated with rocks from the Palaeoproterozoic Olary Domain (OD) and overlying Neoproterozoic Adelaidean sequences has undergone a complex history of metamorphism and remobilisation. In this study, new trace element and sulphur isotopic analyses of pyrites from a large number of deposits and paragenetic generations are combined with an existing data set to build up a sequence of mineralising events linked to the tectonometamorphic evolution of the region. The typically high Co/Ni ratios (>10) indicate that early strata-bound pyrite precipitated from a volcanic-related fluid, which had fluctuating activities of the two metals during the early stages of the evolution of the Willyama basin. This period of mineralisation was followed by a diagenetic concentration of sulphide mineralisation at the horizon known as the Bimba Formation, which occurred as a result of the differing redox conditions between the upper and lower sequences in the Willyama Supergroup. During the Mesoproterozoic (f1600 to 1500 Ma) Olarian Orogeny, metamorphic remobilisation of strata-bound pyrite resulted in an epigenetic signature; the trace element concentrations of this generation were controlled primarily by the proximity of mineralisation to the mafic intrusive bodies found throughout the terrane. Further reworking of existing sulphides during the Delamerian Orogeny and associated granitoid-intrusive rocks led to the formation of a new generation of epigenetic pyrite that occurs in quartz veins in the Adelaidean sequences and veins that crosscut Olarian fabrics in the Olary Domain. y 34 S results range from 16x to 11x, but most data fall between 2x and 4x. This association is suggestive of an initial uniform deep-seated crustal reservoir of sulphur, which has been repeatedly tapped throughout the metallogenic history of the region. The isotopic outliers can be explained by the input of biogenic sulphur or sulphur derived from oxidised, possibly evaporitic, sediments, respectively. Previous workers have invoked the Kupferschiefer and the Zambian Copperbelt as analogues to mineralisation processes in the Olary Domain. This study shows that y 34 S and trace element data are suggestive of some affinities with the aforementioned analogues, but a more likely link can be made between epigenetic remobilisation in the Olary region and the iron oxide copper gold (IOCG) style of mineralisation found at the nearby Olympic Dam deposit.
Mineralium Deposita, 1997
Fluid inclusions were studied in samples from the Ashanti, Konongo-Southern Cross, Prestea, Aboss... more Fluid inclusions were studied in samples from the Ashanti, Konongo-Southern Cross, Prestea, Abosso/ Damang and Ayanfuri gold deposits in the Ashanti Belt, Ghana. Primary fluid inclusions in quartz from mineralised veins of the Ashanti, Prestea, Konongo-Southern Cross, and Abosso/Damang deposits contain almost exclusively volatile species. The primary setting of the gaseous (i.e. the fluid components CO 2 , CH 4 and N 2) fluid inclusions in clusters and intragranular trails suggests that they represent the mineralising fluids. Microthermometric and Raman spectroscopic analyses of the inclusions revealed a CO 2 dominated fluid with variable contents of N 2 and traces of CH 4. Water content of most inclusions is below the detection limits of the respective methods used. Aqueous inclusions are rare in all samples with the exception of those from the granite-hosted Ayanfuri mineralisation. Here inclusions associated with the gold mineralisation contain a low salinity (<6 eq.wt.% NaCl) aqueous solution with variable quantities of CO 2. Microthermometric investigations revealed densities of the gaseous inclusions of 0.65 to 1.06 g/cm 3 at Ashanti, 0.85 to 0.98 g/cm 3 at Prestea, up to 1.02 g/cm 3 at Konongo-Southern Cross, and 0.8 to 1.0 g/cm 3 at Abosso/Damang. The fluid inclusion data are used to outline the PT ranges of gold mineralisation of the respective gold deposits. The high density gaseous inclusions found in the auriferous quartz at Ashanti and Prestea imply rather high pressure trapping conditions of up to 5.4 kbar. In contrast, mineralisation at Ayanfuri and Abosso/Damang is inferred to have occurred at lower pressures of only up to 2.2 kbar. Mesothermal gold mineralisation is generally regarded to have formed from fluids characterized by H 2 O > CO 2 and low salinity (± 6 eq.wt.%NaCl). However, fluid inclusions in quartz from the gold mineralisations in the Ashanti belt point to distinctly different fluid compositions. Specifically, the predominance of CO 2 and CO 2 >> H 2 O have to be emphasized. Fluid systems with this unique bulk composition were apparently active over more than 200 km along strike of the Ashanti belt. Fluids rich in CO 2 may present a hitherto unrecognised new category of ore-forming fluids.
Marine and Petroleum Geology, 2002
Samples of diagenetic and hydrothermal minerals from drillcores along the DEKORP 9601 seismic tra... more Samples of diagenetic and hydrothermal minerals from drillcores along the DEKORP 9601 seismic traverse in the North German Basin were investigated for their¯uid inclusion and sulphur isotope composition to reconstruct the thermal and chemical evolution of¯uid systems during basin evolution. The stages of basin subsidence and subsequent inversion are marked by¯uid systems of distinct composition. The basinwide Zechstein evaporite units formed an aquiclude, disconnecting convecting¯uids in the underlying Rotliegend volcanics from the overlying units. d 34 S ratios of sulphides suggest a sedimentary sulphur source. d 34 S ratios of diagenetic and hydrothermal sulphates indicate that sulphur was derived partly from Rotliegend volcanic units and partly from the evaporitic Zechstein.
Journal of Metamorphic Geology, 2005
The development of shear zones at mid-crustal levels in the Proterozoic Willyama Supergroup was s... more The development of shear zones at mid-crustal levels in the Proterozoic Willyama Supergroup was synchronous with widespread fluid flow resulting in albitization and calcsilicate alteration. Monazite dating of shear zone fabrics reveal that they formed at 1582 ± 22 Ma, at the end of the Olarian D3 deformational event and immediately prior to the emplacement of regional S-type granites. Two stages of fluid flow are identified in the area: first an albitizing event which involved the addition of Na and loss of Si, K and Fe; and a second phase of calcsilicate alteration with additions of Ca, Fe, Mg and Si and removal of Na. Fluid fluxes calculated for albitization and calcsilicate alteration were 5.56 • 10 9 to 1.02 • 10 10 mol m)2 and 2.57 • 10 8-5.20 • 10 9 mol m)2 respectively. These fluxes are consistent with estimates for fluid flow through mid-crustal shear zones in other terranes. The fluids associated with shearing and alteration are calculated to have d 18 O and dD values ranging between +8 and +11&, and)33 and)42&, respectively, and eNd values between)2.24 and)8.11. Our results indicate that fluids were derived from metamorphic dehydration of the Willyama Supergroup metasediments. Fluid generation occurred during prograde metamorphism of deeper crustal rocks at or near peak pressure conditions. Shear zones acted as conduits for major crustal fluid flow to shallow levels where peak metamorphic conditions had been attained earlier leading to the apparent ÔretrogradeÕ fluid-flow event. Thus, the peak metamorphism conditions at upper and lower crustal levels were achieved at differing times, prior to regional granite formation, during the same orogenic cycle leading to the formation of retrograde mineral assemblages during shearing.
Journal of Geochemical Exploration, 2009
Journal of Geochemical Exploration, 2007
Anomalously high Au concentrations (2.5 to 50 ppb) in regolith carbonate accumulations, such as c... more 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.
Journal of Geochemical Exploration, 2006
Two distinct generations of fluid flow associated with shear zone activity have been identified i... more 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.
Journal of Geochemical Exploration, 2006
Mineral exploration in areas of little bedrock exposure must increasingly rely on the predictive ... more 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 CO 2-bearing fluids at temperatures b 350°C and pressures b 1.5kbar indicate a shallow-level orogenic [
Journal of Geochemical Exploration, 2010
The Mt. Mulga barite Cu-Au deposit in the central part of the Olary Domain is hosted by the Palae... more 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 (b 2 cm) magnetite and quartz. In the southern section the massive barite contains Cu-Au mineralisation consisting of chalcopyrite, bornite and native gold. Along strike the mineralised unit grades into a stratiform quartzmagnetite layer which can be traced for several kms. Several smaller (b 1 m thickness) barite lenses occur about 1.5 km north of main barite body in the upper parts of the Ethiudna Subgroup close to the contact to the Saltbush Subgroup. 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 bariteiron-oxide mineralisation.
Journal of Geochemical Exploration, 2000
... IV) quartzcalcite. Rotliegend volcanics (dacites, rhyolites, basalts) Primary parageneses ar... more ... IV) quartzcalcite. Rotliegend volcanics (dacites, rhyolites, basalts) Primary parageneses are quartz, chalcedony, calcite and albite at variable quantities with amounts of pyrite, hematite, chlorite and illite. Late diagenetic assemblages ...
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Papers by Andreas Schmidt Mumm