Sulfur Isotope Constraints on the Conditions of Pyrite Formation in the Paleoproterozoic Urquhart Shale Formation and George Fisher Zn-Pb-Ag Deposit, Northern Australia

2020 ◽  
Vol 115 (5) ◽  
pp. 1003-1020
Author(s):  
Philip Rieger ◽  
Joseph M. Magnall ◽  
Sarah A. Gleeson ◽  
Richard Lilly ◽  
Alexander Rocholl ◽  
...  
Keyword(s):  
Sulfate Reduction ◽  
Sulfur Isotope ◽  
Coarse Grained ◽  
Drill Core ◽  
Northern Australia ◽  
Fine Grained ◽  
Mount Isa ◽  
History Of ◽  
Shale Formation ◽  
Stage 1

Abstract The Carpentaria province (McArthur basin and Mount Isa inlier) in northern Australia is one of the most important districts for clastic-dominated (CD-type) massive sulfide deposits. The George Fisher Zn-Pb-Ag deposit, located in this province, is hosted by the carbonaceous Urquhart Shale Formation (ca. 1654 Ma) in a region that has an active history of metamorphism and tectonism. In this study, paragenetically constrained pyrite in samples from the George Fisher deposit and unmineralized Urquhart Shale have been analyzed in situ using secondary ion mass spectrometry (SIMS) of sulfur isotopes (δ34S values). Samples were taken from four drill cores through the main orebodies at George Fisher and one drill core through correlative, unmineralized Urquhart Shale (Shovel Flats area). Five generations of pyrite were identified at George Fisher and record a protracted history of sulfate reduction under diagenetic and subsequent hydrothermal conditions: (1) fine-grained, subhedral-spheroidal pyrite (Py-0), (2) coarse-grained, anhedral pyrite (Py-1) associated with ore-stage 1 sphalerite and galena, (3) coarse-grained, euhedral pyrite (Py-2) associated with ore-stage 2 sphalerite, galena, and pyrrhotite, (4) massive subhedral to euhedral pyrite (Py-3) associated with ore-stage 3 chalcopyrite, pyrrhotite, galena, and sphalerite, and (5) coarse-grained euhedral pyrite (Py-euh), which occurs only in unmineralized rocks. In the unmineralized Shovel Flats drill core, only Py-0 and Py-euh are present. Whereas pre-ore pyrite (Py-0) preserves negative δ34S values (–8.1 to 11.8‰), the ore-stage pyrites (Py-1, Py-2, and Py-3) have higher δ34S values (7.8–33.3, 1.9–12.7, and 23.4–28.2‰, respectively). The highest δ34S values (7.2–33.9‰) are preserved in Py-euh. In combination with petrographic observations, the δ34S values of pyrite provide evidence of three different processes responsible for the reduction of sulfate at George Fisher. Reduced sulfur in fine-grained pyrite (Py-0) formed via microbial sulfate reduction (MSR) under open-system conditions prior to the first generation of hydrothermal pyrite (Py-1) in ore-stage 1, which most likely formed via thermochemical sulfate reduction (TSR). During deformation, previously formed sulfide phases were then recycled and replaced during a second hydrothermal event (ore-stage 2), resulting in intermediate sulfur isotope values. Another syndeformational hydrothermal Cu event, involving a sulfate-bearing fluid, formed ore-stage 3 via TSR. This study demonstrates that the fine-grained pyrite formed pre-ore under conditions open to sulfate and outlines the role of multiple stages of sulfide formation in producing high-grade Zn-Pb-Ag orebodies in the Mount Isa inlier.

Crystallisation of fine- and coarse-grained A-type granite sheets of the Southern Oklahoma Aulacogen, U.S.A.

2000 ◽  
Vol 91 (1-2) ◽  
pp. 139-150 ◽  
Author(s):  
John P. Hogan ◽  
M. Charles Gilbert ◽  
Jon D. Price
Keyword(s):  
Solidus Temperature ◽  
Direct Consequence ◽  
Progressive Increase ◽  
Coarse Grained ◽  
Fine Grained ◽  
Mafic Complex ◽  
Southern Oklahoma ◽  
History Of ◽  
Volcanic Pile ◽  
Crustal Magma

A-type felsic magmatism associated with the Cambrian Southern Oklahoma Aulacogen began with eruption of voluminous rhyolite to form a thick volcanic carapace on top of an eroded layered mafic complex. This angular unconformity became a crustal magma trap and was the locus for emplacement of later subvolcanic plutons. Rising felsic magma batches ponding along this crustal magma trap crystallised first as fine-grained granite sheets and then subsequently as coarser-grained granite sheets. Aplite dykes, pegmatite dykes and porphyries are common within the younger coarser-grained granite sheets but rare to absent within the older fine-grained granite sheets. The older fine-grained granite sheets typically contain abundant granophyre.The differences between fine-grained and coarse-grained granite sheets can largely be attributed to a progressive increase in the depth of the crustal magma trap as the aulacogen evolved. At low pressures (<200MPa) a small increase in the depth of emplacement results in a dramatic increase in the solubility of H2O in felsic magmas. This is a direct consequence of the shape of the H2O-saturated granite solidus. The effect of this slight increase in total pressure on the crystallisation of felsic magmas is to delay vapour saturation, increase the H2O content of the residual melt fractions and further depress the solidus temperature. Higher melt H2O contents, and an extended temperature range over which crystallisation can proceed, both favour crystallisation of coarser-grained granites. In addition, the potential for the development of late, H2O-rich, melt fractions is significantly enhanced. Upon reaching vapour saturation, these late melt fractions are likely to form porphyries, aplite dykes and pegmatite dykes.For the Southern Oklahoma Aulacogen, the progressive increase in the depth of the crustal magma trap at the base of the volcanic pile appears to reflect thickening of the volcanic pile during rifting, but may also reflect emplacement of earlier granite sheets. Thus, the change in textural characteristics of granite sheets of the Wichita Granite Group may hold considerable promise as an avenue for further investigation in interpreting the history of this rifting event.

Characteristics and origins of ridges and troughs on the top of the Middle Miocene strata in the Beijiao sag of the Qiongdongnan basin, northern South China Sea

2020 ◽  
pp. 1-57
Author(s):  
Yufeng Li ◽  
Renhai Pu ◽  
Gongcheng Zhang ◽  
Hongjun Qu
Keyword(s):  
High Resolution ◽  
Seismic Data ◽  
Middle Miocene ◽  
Northern South China Sea ◽  
Qiongdongnan Basin ◽  
Coarse Grained ◽  
Bottom Currents ◽  
Fine Grained ◽  
Sediment Waves ◽  
History Of

Sedimentary structures generated by bottom currents are poorly understood worldwide. Ridges and troughs are imaged for the first time by 3D high-resolution seismic data and drilled by a well, YL19-1-1, in the Beijiao sag of Qiongdongnan basin (QDNB). Combined with 2D high resolution seismic data, they are analyzed in detail. The results show that ridges and troughs occur on the top of the Middle Miocene, dominantly present a wave-shaped structure. Their magnitudes are larger on the middle (regional) slope than on the upper and lower slope. They extend for tens of kilometers, dominantly parallel to one another, evenly spaced and nearly E-W directed distribution, some of which locally merge and bifurcate. They are aligned oblique to the regional slope. Both internal mounded reflections and parallel underlying-strata reflections, occur within ridges. The presence of polygonal faults and weak-to-moderate amplitudes within the ridges and troughs, suggests that they consist of fine-grained mudstones, as confirmed by well YL19-1-1. High amplitudes filled within troughs are probably composed of coarse-grained turbidite sandstones where polygonal faults are inhibited. Truncated reflections and onlaps occur along the thalweg of a trough, and are also clearly observed on the sides of ridges and troughs. We conclude the troughs are a product of erosion of bottom currents, and ridges are remnant underlying (sediment waves) strata as a result of this erosion. Besides, troughs are filled by turbidite sandstones with high amplitudes in the southwestern part of the study area, where ridges and troughs a combined result of early erosion by bottom currents and later reworking by turbidity flows. Conceptual schematic models are proposed to show the evolutionary history of ridges and troughs. This study provides new insights into further understanding of erosion and deposition of bottom currents.

scholarly journals EFEITO DO TAMANHO DOS SEDIMENTOS SOBRE A ÁREA ATINGIDA POR FLUXOS DE DETRITOS: ESTUDO DE CASO DA BACIA DO ARROIO BÖNI, SERRA GAÚCHA.

2017 ◽  
Vol 39 (2) ◽  
pp. 299
Author(s):  
Maurício Andrades Paixão ◽  
Masato Kobiyama
Keyword(s):  
Debris Flow ◽  
Natural Disasters ◽  
Coarse Grained ◽  
Fine Grained ◽  
Sediment Size ◽  
History Of

The present paper aimed to evaluate the size sediment effects on runout area damaged by debris flow by using Kanako-2D in Böni Watershed, Serra Gaucha. This watershed presents a vast history of natural disasters, highlighting the events occurred in 1982 and 2000. The sediment sizes considered in the simulations and evaluated in terms of erosion, deposition and reached area were 0.15, 0.30, 0.50, 1.0, 1.3, 2.0 and 3.0 m. The sediment size strongly influenced on the erosion, deposition and total area reached by debris flow. Fine-grained sediments presented higher mobility, traveling greater distances and reaching larger areas than coarse-grained sediments. The obtained results confirm that Kanako-2D can be an important tool to predict susceptible areas to debris flow.

The Northwest Atlantic Mid-Ocean Channel of the Labrador Sea. V. Sedimentology of a giant deep-sea channel

1987 ◽  
Vol 24 (8) ◽  
pp. 1595-1624 ◽  
Author(s):  
Reinhard Hesse ◽  
Sung Kwun Chough ◽  
Allan Rakofsky
Keyword(s):  
Deep Sea ◽  
Coarse Grained ◽  
Labrador Sea ◽  
Turbidity Currents ◽  
Layer By Layer ◽  
Seismic Profiles ◽  
Northwest Atlantic ◽  
Fine Grained ◽  
Meandering Channel ◽  
History Of

The Northwest Atlantic Mid-Ocean Channel (NAMOC) is one of the largest deep-sea channels of the world's oceans. During the late Cenozoic glacial period, the channel played a major role in the depositional history of the Labrador Sea and northwest Atlantic in controlling sedimentation of a broad (approx. 500 m thick and 200 km wide) lens of turbidites. This sediment sequence interfingers laterally with the acoustically transparent pelagic and contourite facies found in the Labrador Basin. The meandering channel is a depositional–erosional feature formed by submarine mass flows, predominantly turbidity currents.The channel contains a meandering talweg that appears to be associated with a sequence of submarine point bars containing thick-bedded, coarse-grained turbidites and gravel layers (channel-fill facies). Old channel positions on seismic profiles indicate that the channel has migrated laterally up to 30 km both to the west and to the east.Natural levees flank the channel for its entire length, extending laterally into turbidite plains 60–100 km wide. The spill-over facies comprises thin-bedded, fine-grained turbidites dominated by thinly laminated muds. Individual units of parallel-laminated mud, which result from single turbidity currents overtopping the channel banks, average 3 cm in thickness. A layer by layer correlation of a sequence of spill-over turbidites is possible between two adjacent cores 70 km apart. Coarse-grained off-channel sediments recently discovered on both levees at distances up to 55 km from the NAMOC occur in tributary channels.Turbidity current activity in the channel probably started with the onset of glaciation at about mid-Pliocene time and ceased at about 7000 years BP, when deglaciation proceeded rapidly. The sedimentation rate for the last episode of overbank deposition on the levees, which probably occurred between 11 000 and 7000 years BP, is 13 cm/1000 years. Towards the end of glacial episodes the northwestern Labrador Sea was probably covered with sea ice.

Sedimentologic, petrographic, and sulfur isotope constraints on fine-grained pyrite formation at Mount Isa Mine and environs, Northwest Queensland, Australia

1999 ◽  
Vol 94 (6) ◽  
pp. 883-912 ◽  
Author(s):  
Matthew G. M. Painter ◽  
Suzanne D. Golding ◽  
Keith W. Hannan ◽  
Martin K. Neudert
Keyword(s):  
Sulfur Isotope ◽  
Fine Grained ◽  
Mount Isa ◽  
Pyrite Formation

scholarly journals Early Holocene aeolian sediments in southwestern Crete−preliminary results

2021 ◽  
Author(s):  
Fabian Kirsten ◽  
Alexander Fülling ◽  
Susann Heinrich ◽  
Birgit Schneider ◽  
Jürgen Heinrich
Keyword(s):  
Source Area ◽  
Alluvial Fan ◽  
Early Holocene ◽  
Coarse Grained ◽  
Western Coast ◽  
Preliminary Results ◽  
Fine Grained ◽  
Time Period ◽  
History Of ◽  
Specific Source

AbstractThe soilscapes along the southern and western coast of Crete (Greece) are dominated by coarse-grained reddish-brown slope sediments whose natural (pre-anthropogenic) configuration and properties are difficult to reconstruct due to the long history of intense land use. As a consequence, datable terrestrial sediment archives of pre-anthropogenic genesis are scarce. We present preliminary results of a study performed on an accumulation within an alluvial fan south of Stomio Bay in southwestern Crete. The studied profile is located in a small depression and is composed of a sequence of sandy to silty yellowish-brown calcareous sediments overlying coarse-grained slope sediments, including a fossil topsoil horizon. Based on macroscopic, micromorphological, geochemical, geophysical and mineralogical analysis, we interpret the fine-grained sediments to have a local aeolian origin. OSL dating indicates a final deposition phase during the early Holocene. Considering the scarcity of early Holocene terrestrial archives in Crete, the analysed profile provides valuable data for the reconstruction of landscape dynamics and paleoecological conditions as well as soil-sediment configurations during this time period. Additional research is needed to address the specific source area(s) as well as the ages of the deposition of slope sediments and formation of the fossil topsoil.

scholarly journals Identification of Forearc Sediments in the Milin-Zedong Region and Their Constraints on Tectonomagmatic Evolution of the Gangdese Arc, Southern Tibet

Lithosphere ◽  
2020 ◽  
Vol 2020 (1) ◽  
pp. 1-20
Author(s):  
Shao-Hua Zhang ◽  
Wei-Qiang Ji ◽  
Hao Zhang ◽  
Guo-Hui Chen ◽  
Jian-Gang Wang ◽  
...  
Keyword(s):  
Early Cretaceous ◽  
Detrital Zircon ◽  
Age Distribution ◽  
Detrital Zircons ◽  
Coarse Grained ◽  
Southern Tibet ◽  
Fine Grained ◽  
Lhasa Terrane ◽  
Isotopic Analyses ◽  
History Of

Abstract The Xigaze forearc sediments revealed the part of the tectonomagmatic history of the Gangdese arc that the bedrocks did not record. However, the sediments’ development is restricted to the region around and west of Xigaze City. Whether the eastern segment of the arc had a corresponding forearc basin is yet to be resolved. In this study, a field-based stratigraphic study, detrital zircon U-Pb geochronology (15 samples), and Hf isotopic analyses (11 of the 15 samples) were carried out on four sections in the Milin-Zedong area, southeast Tibet. The analytical results revealed the existence of three distinct provenances. The lower sequence is characterized by fine-grained sandstone, interbedded mudstone, and some metamorphic rocks (e.g., gneiss and schist). The detrital zircon U-Pb age distribution of this sequence is analogous to those of the Carboniferous-Permian strata and metasediments of the Nyingtri group in the Lhasa terrane. The middle and upper sequences are predominantly composed of medium- to coarse-grained volcaniclastic/quartzose sandstones, which are generally interbedded with mudstone. The detrital zircon U-Pb ages and Hf isotope signatures indicate that the middle sequences are Jurassic to Early Cretaceous in age (~200–100 Ma) and show clear affinity with the Gangdese arc rocks, that is, positive εHft values. In contrast, the upper sequences are characterized by Mesozoic detrital zircons (150–100 Ma) and negative εHft values, indicative of derivation from the central Lhasa terrane. The overall compositions of the detrital zircon U-Pb ages and Hf isotopes of the middle to upper sequences resemble those of the Xigaze forearc sediments, implying that related forearc sediments may have been developed in the eastern part of the Gangdese arc. It is possible that the forearc equivalents were eroded or destroyed during the later orogenesis. Additionally, the detrital zircons from these forearc sediments indicate that this segment of the Gangdese arc experienced more active and continuous magmatism from the Early Jurassic to Early Cretaceous than its bedrock records indicate.

Petrogenetic implications of mineral crystallization trends of Troodos cumulates, Cyprus

1987 ◽  
Vol 124 (1) ◽  
pp. 1-11 ◽  
Author(s):  
P. Thy
Keyword(s):  
Magma Chamber ◽  
High Water ◽  
Coarse Grained ◽  
High Water Content ◽  
Drill Core ◽  
Troodos Ophiolite ◽  
Fine Grained ◽  
Intermediate Group ◽  
Rock Types ◽  
Ultramafic Cumulates

AbstractHole number CY-4 of the Cyprus Crustal Study Project penetrated the lower sheeted dyke complex, gabbros and ultramafic cumulates of the Troodos ophiolite. The lower part of the drill core sampled a coarse-grained plutonic complex revealing phase and cryptic layering and one major magma chamber replenishment. This magma chamber intruded medium-grained gabbroic rocks showing intricate chemical evolution trends reflecting several magma replenishments. In the upper part of the core, the gabbroic cumulates are intruded by fine-grained dykes, which grade into the sheeted dyke complex and chemically can be correlated with the lavas of the lower pillow sequence. The upper pillow lavas are best correlated with the ultramafic cumulates. A study of coexisting plagioclase (An) and mafic mineral (opx Mg #) compositions in the drill core revealed three main rock types: (1) a primitive group (An95–98, Mg #75–85) represented by the lower, coarse-grained gabbroic and ultramafic cumulates. (2) an intermediate group (An86–95 and Mg #70–78) represented by the upper level gabbroic cumulates, and (3) the lower part of the sheeted dyke complex (An60–80 and Mg #60–70). The plagioclase of the gabbros and ultramafic cumulates have an unusually high An content. Numerical simulation of the expected anhydrous, one atmosphere, crystallization trends show that the Troodos trends cannot be reproduced from known spreading or subduction related glasses. Mineralogical evidence indicates that the extrusives and the cumulate sequences of the Troodos ophiolite are genetically related. Glasses from the extrusives, nevertheless, also fail to reproduce the mineral crystallization trends observed in the plutonics. Attempts to model high PH2O crystallization produced trends more consistent with those observed in the cumulates. The very sodium-poor nature of the plagioclase may therefore mainly reflect high PH2O crystallization. High water content is consistent with the inferred subduction zone basin origin for the Troodos ophiolite.

Correlation between dislocation, grain boundary and interface of duplex SS in stress corrosion cracking(SCC)

1990 ◽  
Vol 48 (4) ◽  
pp. 928-929
Author(s):  
Wang Zheng-fang ◽  
Z.F. Wang
Keyword(s):  
Stainless Steel ◽  
Thermal Cycle ◽  
Secondary Phase ◽  
Corrosion Cracking ◽  
Coarse Grained ◽  
Test Environment ◽  
Fine Grained ◽  
Evaluation Test ◽  
Welding Thermal Cycle ◽  
Micro Analysis

The main purpose of this study highlights on the evaluation of chloride SCC resistance of the material,duplex stainless steel,OOCr18Ni5Mo3Si2 (18-5Mo) and its welded coarse grained zone(CGZ).18-5Mo is a dual phases (A+F) stainless steel with yield strength:512N/mm2 .The proportion of secondary Phase(A phase) accounts for 30-35% of the total with fine grained and homogeneously distributed A and F phases(Fig.1).After being welded by a specific welding thermal cycle to the material,i.e. Tmax=1350°C and t8/5=20s,microstructure may change from fine grained morphology to coarse grained morphology and from homogeneously distributed of A phase to a concentration of A phase(Fig.2).Meanwhile,the proportion of A phase reduced from 35% to 5-10°o.For this reason it is known as welded coarse grained zone(CGZ).In association with difference of microstructure between base metal and welded CGZ,so chloride SCC resistance also differ from each other.Test procedures:Constant load tensile test(CLTT) were performed for recording Esce-t curve by which corrosion cracking growth can be described, tf,fractured time,can also be recorded by the test which is taken as a electrochemical behavior and mechanical property for SCC resistance evaluation. Test environment:143°C boiling 42%MgCl2 solution is used.Besides, micro analysis were conducted with light microscopy(LM),SEM,TEM,and Auger energy spectrum(AES) so as to reveal the correlation between the data generated by the CLTT results and micro analysis.

Sign in / Sign up

Export Citation Format

Share Document