The Challenge of Finding New Mineral Resources<subtitle>Global Metallogeny, Innovative Exploration, and New Discoveries</subtitle>, 2010
ABSTRACT The late Paleoproterozoic upper McArthur Group (River Supersequence) is a dominantly sha... more ABSTRACT The late Paleoproterozoic upper McArthur Group (River Supersequence) is a dominantly shallow marine carbonate platform sequence. Deeper water shaley rocks of the Barney Creek Formation of this Superse- quence host the supergiant HYC Zn-Pb-Ag deposit. Three higher order sequences, the Emmerugga Deposi- tional Sequence, the Barney Creek Depositional Sequence, and the Lynott Depositional Sequence, make up the River Supersequence in the southern McArthur basin. Within the Barney Creek Depositional Sequence, there are 26 lithofacies that can be grouped into seven facies associations, each representing specific and coeval sedimentary environments. This complex facies mosaic formed in response to a sinistral transpression event during regional north-south extension. Basin architecture was controlled by major meridional strike-slip structures, such as the Emu, Tawallah, and Hot-Springs faults. Although these structures have a later, postsedimentation history, they also controlled the distribution of the different facies of the Barney Creek Depositional Sequence. North- to north- west-trending segments of these structures were transtensional, whereas structures oriented east of north were transpressional. Transtension resulted in the development of significant local accommodation and sub-basin development and allowed substantial thicknesses of deeper water, fine-grained sediments, which are potential hosts to Zn-Pb-Ag SEDEX deposits, to accumulate. Locally, in platform and slope facies of the Barney Creek Depositional Sequence, the orientation and vergence of kinematic indicators, such as neptunian dikes and intrafolial folds, may indicate the direction to deeper shaley facies.
ABSTRACT A new locality near the Permo-Triassic boundary in Tasmania, Australia, has yielded a nu... more ABSTRACT A new locality near the Permo-Triassic boundary in Tasmania, Australia, has yielded a number of specimens of the brachyopid stereospondyl, Bothriceps australis, whose provenance was unknown previously. An articulated diplospondylous vertebral ...
Abstract The Zambian Copperbelt accounts for approximately 46 percent of the production and reser... more Abstract The Zambian Copperbelt accounts for approximately 46 percent of the production and reserves of the Central African Copperbelt, the largest and highest grade sediment-hosted stratiform copper province known on Earth. Deposits in the Zambian Copperbelt ...
Redox-sensitive trace elements and sulfur isotope compositions obtained via in situ analyses of s... more Redox-sensitive trace elements and sulfur isotope compositions obtained via in situ analyses of sedimentary pyrites from marine black shales are used to track atmosphere-ocean redox conditions between ∼1730 and ∼1360 Ma in the McArthur Basin, northern Australia. Three black shale formations within the basin (Wollogorang Formation 1730 ± 3 Ma, Barney Creek Formation 1640 ± 3 Ma, and Upper Velkerri Formation 1361 ± 21 Ma) display systematic stratigraphic variations in pyrite trace-element compositions obtained using LA-ICP-MS. The concentrations of several trace elements and their ratios, such as Se, Zn, Se/Co, Ni/Co, Zn/Co, Mo/Co, Se/Bi, Zn/Bi, Ni/Bi, increase from the stratigraphically lower Wollogorang Formation to the Upper Velkerri Formation. Cobalt, Bi, Mo, Cu, and Tl show a consistent decrease in abundance while Ni, As, and Pb show no obvious trends. We interpret these trace element trends as a response to the gradual increase of oxygen in the atmosphere-ocean system from ∼1730...
The Mesoproterozoic Prominent Hill iron-oxide copper–gold deposit lies on the fault-bound souther... more The Mesoproterozoic Prominent Hill iron-oxide copper–gold deposit lies on the fault-bound southern edge of the Mt Woods Domain, Gawler Craton, South Australia. Chalcocite–bornite–chalcopyrite ores occur in a hematitic breccia complex that has similarities to the Olympic Dam deposit, but were emplaced in a shallow water clastic–carbonate package overlying a thick andesite–dacite pile. The sequence has been overturned against the major, steep, east–west, Hangingwall Fault, beyond which lies the clastic to potentially evaporitic Blue Duck Metasediments. Immediately north of the deposit, these metasediments have been intruded by dacite porphyry and granitoid and metasomatised to form magnetite–calc–silicate skarn ± pyrite–chalcopyrite. The hematitic breccia complex is strongly sericitised and silicified, has a large sericite ± chlorite halo, and was intruded by dykes during and after sericitisation. This paper evaluates the age of sericite formation in the mineralised breccias and provides constraints on the timing of granitoid intrusion and skarn formation in the terrain adjoining the mineralisation. The breccia complex contains fragments of granitoid and porphyry that are found here to be part of the Gawler Range Volcanics/Hiltaba Suite magmatic event at 1600–1570 Ma. This indicates that some breccia formation post-dated granitoid intrusion. Monazite and apatite in Fe-P-REE-albite metasomatised granitoid, paragenetically linked with magnetite skarn formation north of the Hangingwall Fault, grew soon after granitoid intrusion, although the apatite experienced U–Pb–LREE loss during later fluid–mineral interaction; this accounts for its calculated age of 1544 ± 39 Ma. To the south of the fault, within the breccia, 40Ar–39Ar ages yield a minimum age of sericitisation (+Cu+Fe+REE) of dykes and volcanics of ∼1575 Ma, firmly placing Prominent Hill ore formation as part of the Gawler Range Volcanics/Hiltaba Suite magmatic event within the Olympic Cu–Au province of the Gawler Craton.
Introduction Recently it has been proposed by Large et al. that diagenetic pyrite may be the sour... more Introduction Recently it has been proposed by Large et al. that diagenetic pyrite may be the source of gold and arsenic in shale hosted orogenic gold deposits in areas such as Sukhoi Log, Russia (Large et al., 2007) and Bendigo, Australia (Large et al., 2009). The research presented in this poster has been conducted to determine whether diagenetic pyrites or organic matter from modern ocean sediments are enriched in gold and trace metals. This is done by conducting laser ablation inductively coupled plasma mass spectrometer (LA-ICPMS) analysis on different pyritic, carbonaceous modern sediments from around the world. Model for Mineralization at Bendigo and Sukoi Log A summary for the model for gold deposition at Sukhoi Log and Bendigo based on work by Large et al. (2009) is as follows. Sedimentation in an anoxic/euxinic ocean basin leads to deposition of large amounts of organic sediments. This is because the anoxic conditions limit biological breakdown of the organic matter. These ...
ABSTRACT The Randalls district comprises three individual gold deposits–Cock-Eyed Bob, Maxwells, ... more ABSTRACT The Randalls district comprises three individual gold deposits–Cock-Eyed Bob, Maxwells, and Santa-Craze–hosted in the same unit of banded iron-formation (BIF) in the southern Eastern Goldfields Superterrane, Yilgarn Craton, Western Australia. The iron formation is a silicate/oxide-facies unit with overprinting sulfides, and has undergone metamorphism (upper-greenschist facies) and deformation (two generations of folds). The gold deposits are hosted in two structural locations: hinge zones of anticlinal folds (e.g., Santa-Craze and Maxwells) and overturned, steeply-dipping limbs of anticlinal folds (e.g., Cock-Eyed Bob). Gold dominantly occurs as inclusions of native gold and/or electrum within or around pyrrhotite, magnetite, and arsenopyrite. The earliest mineral assemblage preserved in the banded iron formation at Randalls is banded magnetite-quartz. Magnetite in all forms has elevated Mg, Al, Ti, V, Mn, Cr, Zn, and W, but very low Ni compared to other BIFs globally. Pyrrhotite, the most abundant sulfide, is restricted to ore zones and occurs as laminae, “blebs”, and veinlets, all of which have replaced magnetite. Some pyrrhotite in the hydrothermally altered BIFs (especially in near-surface samples) has been re-sulfidized to pyrite. Trace elements associated with pyrrhotite include Co, Ni, Ag, Sb, and Pb. Large, coarse-grained arsenopyrite overgrows the pyrrhotite-defined foliation; it is enriched in Co, Ni, Sb, and Te, but contains very little ‘invisible’ gold (&lt;0.01 ppm Au), unlike arsenopyrite in many orogenic Au systems globally (commonly ≥ 0.1 ppm Au). Petrographic studies of several mineralized BIFs from Randalls reveal that pyrrhotite and arsenopyrite are associated with Fe(-Ca) amphibole, which grew during contact metamorphism caused by granite plutons. This spatial sulfide-amphibole relationship indicates that gold mineralization likely occurred during granite intrusion, consistent with prior studies on Randalls. The trace element characteristics of the sulfides show that they were not inherited from replaced magnetite. Further, these characteristics suggest that the fluid from which sulfides crystallized was not indigenous to the BIFs, and that this S-rich fluid either contained S in abundance originally, or interacted with a lithology/lithologies that were rich in S before reaching the BIFs. Black shale containing diagenetic nodular pyrite occurs in the upper Black Flag Group, which unconformably underlies the Belches Supersequence at depth (∼3 km). The trace element composition of nodular pyrite from this unit fits well with the trace element characteristics of the BIF pyrrhotite and arsenopyrite, and the nodular pyrite contains an average of 0.5 ppm Au. However, the nodular pyrites have an average δ34S value of 5.6 ‰ (n = 13), which contrasts markedly with the δ34S average of pyrrhotite, pyrite and arsenopyrite in mineralized BIFs (0.8 ‰, n = 17). Thus, a definitive source of gold, arsenic, silver, and tellurium in the Randalls system remains elusive, although we would contend that the upper Black Flag Group should be considered as a possible metal and S source in areas of the Yilgarn where it forms a thick substrate to ore camps.
The Paleoproterozoic Aravalli basin of Rajasthan, India hosts a number of PbZn sulphide deposits... more The Paleoproterozoic Aravalli basin of Rajasthan, India hosts a number of PbZn sulphide deposits. Various ore genetic models for these deposits are available in the literature, but none of them are backed by comprehensive basin models reconstructed on the basis of ...
Dicynodonts are herbivorous synapsids found in Permian and Triassic deposits in all of the Pangea... more Dicynodonts are herbivorous synapsids found in Permian and Triassic deposits in all of the Pangean continents. The fossil evidence of this group from Australia is limited to a quadrate, part of a tusk (Thulborn, 1983a 38. Thulborn, RA 1983a. A mammal-like reptile from ...
The Challenge of Finding New Mineral Resources<subtitle>Global Metallogeny, Innovative Exploration, and New Discoveries</subtitle>, 2010
ABSTRACT The late Paleoproterozoic upper McArthur Group (River Supersequence) is a dominantly sha... more ABSTRACT The late Paleoproterozoic upper McArthur Group (River Supersequence) is a dominantly shallow marine carbonate platform sequence. Deeper water shaley rocks of the Barney Creek Formation of this Superse- quence host the supergiant HYC Zn-Pb-Ag deposit. Three higher order sequences, the Emmerugga Deposi- tional Sequence, the Barney Creek Depositional Sequence, and the Lynott Depositional Sequence, make up the River Supersequence in the southern McArthur basin. Within the Barney Creek Depositional Sequence, there are 26 lithofacies that can be grouped into seven facies associations, each representing specific and coeval sedimentary environments. This complex facies mosaic formed in response to a sinistral transpression event during regional north-south extension. Basin architecture was controlled by major meridional strike-slip structures, such as the Emu, Tawallah, and Hot-Springs faults. Although these structures have a later, postsedimentation history, they also controlled the distribution of the different facies of the Barney Creek Depositional Sequence. North- to north- west-trending segments of these structures were transtensional, whereas structures oriented east of north were transpressional. Transtension resulted in the development of significant local accommodation and sub-basin development and allowed substantial thicknesses of deeper water, fine-grained sediments, which are potential hosts to Zn-Pb-Ag SEDEX deposits, to accumulate. Locally, in platform and slope facies of the Barney Creek Depositional Sequence, the orientation and vergence of kinematic indicators, such as neptunian dikes and intrafolial folds, may indicate the direction to deeper shaley facies.
ABSTRACT A new locality near the Permo-Triassic boundary in Tasmania, Australia, has yielded a nu... more ABSTRACT A new locality near the Permo-Triassic boundary in Tasmania, Australia, has yielded a number of specimens of the brachyopid stereospondyl, Bothriceps australis, whose provenance was unknown previously. An articulated diplospondylous vertebral ...
Abstract The Zambian Copperbelt accounts for approximately 46 percent of the production and reser... more Abstract The Zambian Copperbelt accounts for approximately 46 percent of the production and reserves of the Central African Copperbelt, the largest and highest grade sediment-hosted stratiform copper province known on Earth. Deposits in the Zambian Copperbelt ...
Redox-sensitive trace elements and sulfur isotope compositions obtained via in situ analyses of s... more Redox-sensitive trace elements and sulfur isotope compositions obtained via in situ analyses of sedimentary pyrites from marine black shales are used to track atmosphere-ocean redox conditions between ∼1730 and ∼1360 Ma in the McArthur Basin, northern Australia. Three black shale formations within the basin (Wollogorang Formation 1730 ± 3 Ma, Barney Creek Formation 1640 ± 3 Ma, and Upper Velkerri Formation 1361 ± 21 Ma) display systematic stratigraphic variations in pyrite trace-element compositions obtained using LA-ICP-MS. The concentrations of several trace elements and their ratios, such as Se, Zn, Se/Co, Ni/Co, Zn/Co, Mo/Co, Se/Bi, Zn/Bi, Ni/Bi, increase from the stratigraphically lower Wollogorang Formation to the Upper Velkerri Formation. Cobalt, Bi, Mo, Cu, and Tl show a consistent decrease in abundance while Ni, As, and Pb show no obvious trends. We interpret these trace element trends as a response to the gradual increase of oxygen in the atmosphere-ocean system from ∼1730...
The Mesoproterozoic Prominent Hill iron-oxide copper–gold deposit lies on the fault-bound souther... more The Mesoproterozoic Prominent Hill iron-oxide copper–gold deposit lies on the fault-bound southern edge of the Mt Woods Domain, Gawler Craton, South Australia. Chalcocite–bornite–chalcopyrite ores occur in a hematitic breccia complex that has similarities to the Olympic Dam deposit, but were emplaced in a shallow water clastic–carbonate package overlying a thick andesite–dacite pile. The sequence has been overturned against the major, steep, east–west, Hangingwall Fault, beyond which lies the clastic to potentially evaporitic Blue Duck Metasediments. Immediately north of the deposit, these metasediments have been intruded by dacite porphyry and granitoid and metasomatised to form magnetite–calc–silicate skarn ± pyrite–chalcopyrite. The hematitic breccia complex is strongly sericitised and silicified, has a large sericite ± chlorite halo, and was intruded by dykes during and after sericitisation. This paper evaluates the age of sericite formation in the mineralised breccias and provides constraints on the timing of granitoid intrusion and skarn formation in the terrain adjoining the mineralisation. The breccia complex contains fragments of granitoid and porphyry that are found here to be part of the Gawler Range Volcanics/Hiltaba Suite magmatic event at 1600–1570 Ma. This indicates that some breccia formation post-dated granitoid intrusion. Monazite and apatite in Fe-P-REE-albite metasomatised granitoid, paragenetically linked with magnetite skarn formation north of the Hangingwall Fault, grew soon after granitoid intrusion, although the apatite experienced U–Pb–LREE loss during later fluid–mineral interaction; this accounts for its calculated age of 1544 ± 39 Ma. To the south of the fault, within the breccia, 40Ar–39Ar ages yield a minimum age of sericitisation (+Cu+Fe+REE) of dykes and volcanics of ∼1575 Ma, firmly placing Prominent Hill ore formation as part of the Gawler Range Volcanics/Hiltaba Suite magmatic event within the Olympic Cu–Au province of the Gawler Craton.
Introduction Recently it has been proposed by Large et al. that diagenetic pyrite may be the sour... more Introduction Recently it has been proposed by Large et al. that diagenetic pyrite may be the source of gold and arsenic in shale hosted orogenic gold deposits in areas such as Sukhoi Log, Russia (Large et al., 2007) and Bendigo, Australia (Large et al., 2009). The research presented in this poster has been conducted to determine whether diagenetic pyrites or organic matter from modern ocean sediments are enriched in gold and trace metals. This is done by conducting laser ablation inductively coupled plasma mass spectrometer (LA-ICPMS) analysis on different pyritic, carbonaceous modern sediments from around the world. Model for Mineralization at Bendigo and Sukoi Log A summary for the model for gold deposition at Sukhoi Log and Bendigo based on work by Large et al. (2009) is as follows. Sedimentation in an anoxic/euxinic ocean basin leads to deposition of large amounts of organic sediments. This is because the anoxic conditions limit biological breakdown of the organic matter. These ...
ABSTRACT The Randalls district comprises three individual gold deposits–Cock-Eyed Bob, Maxwells, ... more ABSTRACT The Randalls district comprises three individual gold deposits–Cock-Eyed Bob, Maxwells, and Santa-Craze–hosted in the same unit of banded iron-formation (BIF) in the southern Eastern Goldfields Superterrane, Yilgarn Craton, Western Australia. The iron formation is a silicate/oxide-facies unit with overprinting sulfides, and has undergone metamorphism (upper-greenschist facies) and deformation (two generations of folds). The gold deposits are hosted in two structural locations: hinge zones of anticlinal folds (e.g., Santa-Craze and Maxwells) and overturned, steeply-dipping limbs of anticlinal folds (e.g., Cock-Eyed Bob). Gold dominantly occurs as inclusions of native gold and/or electrum within or around pyrrhotite, magnetite, and arsenopyrite. The earliest mineral assemblage preserved in the banded iron formation at Randalls is banded magnetite-quartz. Magnetite in all forms has elevated Mg, Al, Ti, V, Mn, Cr, Zn, and W, but very low Ni compared to other BIFs globally. Pyrrhotite, the most abundant sulfide, is restricted to ore zones and occurs as laminae, “blebs”, and veinlets, all of which have replaced magnetite. Some pyrrhotite in the hydrothermally altered BIFs (especially in near-surface samples) has been re-sulfidized to pyrite. Trace elements associated with pyrrhotite include Co, Ni, Ag, Sb, and Pb. Large, coarse-grained arsenopyrite overgrows the pyrrhotite-defined foliation; it is enriched in Co, Ni, Sb, and Te, but contains very little ‘invisible’ gold (&lt;0.01 ppm Au), unlike arsenopyrite in many orogenic Au systems globally (commonly ≥ 0.1 ppm Au). Petrographic studies of several mineralized BIFs from Randalls reveal that pyrrhotite and arsenopyrite are associated with Fe(-Ca) amphibole, which grew during contact metamorphism caused by granite plutons. This spatial sulfide-amphibole relationship indicates that gold mineralization likely occurred during granite intrusion, consistent with prior studies on Randalls. The trace element characteristics of the sulfides show that they were not inherited from replaced magnetite. Further, these characteristics suggest that the fluid from which sulfides crystallized was not indigenous to the BIFs, and that this S-rich fluid either contained S in abundance originally, or interacted with a lithology/lithologies that were rich in S before reaching the BIFs. Black shale containing diagenetic nodular pyrite occurs in the upper Black Flag Group, which unconformably underlies the Belches Supersequence at depth (∼3 km). The trace element composition of nodular pyrite from this unit fits well with the trace element characteristics of the BIF pyrrhotite and arsenopyrite, and the nodular pyrite contains an average of 0.5 ppm Au. However, the nodular pyrites have an average δ34S value of 5.6 ‰ (n = 13), which contrasts markedly with the δ34S average of pyrrhotite, pyrite and arsenopyrite in mineralized BIFs (0.8 ‰, n = 17). Thus, a definitive source of gold, arsenic, silver, and tellurium in the Randalls system remains elusive, although we would contend that the upper Black Flag Group should be considered as a possible metal and S source in areas of the Yilgarn where it forms a thick substrate to ore camps.
The Paleoproterozoic Aravalli basin of Rajasthan, India hosts a number of PbZn sulphide deposits... more The Paleoproterozoic Aravalli basin of Rajasthan, India hosts a number of PbZn sulphide deposits. Various ore genetic models for these deposits are available in the literature, but none of them are backed by comprehensive basin models reconstructed on the basis of ...
Dicynodonts are herbivorous synapsids found in Permian and Triassic deposits in all of the Pangea... more Dicynodonts are herbivorous synapsids found in Permian and Triassic deposits in all of the Pangean continents. The fossil evidence of this group from Australia is limited to a quadrate, part of a tusk (Thulborn, 1983a 38. Thulborn, RA 1983a. A mammal-like reptile from ...
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