scholarly journals Constraints of S–Pb–Sr Isotope Compositions and Rb–Sr Isotopic Age on the Origin of the Laoyingqing Noncarbonate-Hosted Pb–Zn Deposit in the Kunyang Group, SW China

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-21
Author(s):  
Hongsheng Gong ◽  
Runsheng Han ◽  
Peng Wu ◽  
Gang Chen ◽  
Lingjie Li
Keyword(s):  
Isotopic Composition ◽  
Linear Trend ◽  
Age Dating ◽  
Composition Analysis ◽  
Isotopic Ratios ◽  
Mississippi Valley ◽  
Basement Rocks ◽  
New Ideas ◽  
Peripheral Areas ◽  
Upper Sinian

The Laoyingqing Pb–Zn deposit is located on the southwestern margin of the Yangtze block and on the east side of the Xiaojiang deep fault in the Sichuan–Yunnan–Guizhou Pb–Zn metallogenic triangle area (SYGT). This deposit was first discovered in the silty and carbonaceous slate of the Middle Proterozoic Kunyang Group that is structurally controlled by thrust faults and anticlines. This study is aimed at investigating whether the Laoyingqing deposit has the same ore-forming age and type as other Pb–Zn deposits related to the Pb–Zn metallogenic system and prospecting prediction of the deep and peripheral areas of the deposits in the SYGT. Based on the sphalerite Rb–Sr age dating and S–Sr–Pb isotopic composition analysis of the Laoyingqing Pb–Zn deposit, the following results were obtained. First, the Rb–Sr isochron age of sphalerite is 209.8 ± 5.2 million years (Ma), consistent with the ages of most Pb–Zn deposits in the SYGT (approximately 200Ma), thereby potentially indicating that these Pb–Zn deposits may have been formed synchronously during the late Indosinian orogeny. Second, the Pb isotopic compositions of sulfides show a linear trend on the average crustal Pb evolution curve in 207Pb/204Pb vs. 206Pb/204Pb plot. In addition, Pb isotopic ratios were consistent with the age-corrected Pb isotopic ratios of basement rocks, consequently suggesting that the source of mixed crustal Pb is mainly derived from basement rocks. Combined with the initial 87Sr/86Sr ratios of sphalerite between the (87Sr/86Sr)200Ma value of the basement rocks and that of the Upper Sinian–Permian carbonates, it can be concluded that the ore-forming metals were mainly derived from basement rocks. Third, sulfur isotopic composition of sphalerite from the Laoyingqing deposits shows δ34SCDT values that range mainly from -2.62‰ to 1.42‰, which is evidently lower than the δ34SCDT values of sulfides (8–20‰) from other Pb–Zn deposits in the SYGT. This can be interpreted as a result of mixing with reduced S that was mainly derived from the thermochemically reduced S in the overlying strata and a small amount of reduced S produced by the pyrolysis of S-containing organic matter. We conclude that the Laoyingqing deposit and most of the Pb–Zn deposits in the SYGT are Mississippi Valley-type deposits, thereby providing new ideas for investigating the deep and peripheral areas of Pb–Zn deposits.

Isotopic composition of lead from a paleo-island arc: Shasta, California

1983 ◽  
Vol 20 (10) ◽  
pp. 1521-1527
Author(s):  
W. F. Slawson
Keyword(s):  
Isotopic Composition ◽  
Lead Isotope ◽  
Linear Array ◽  
Linear Trend ◽  
Lead Isotopes ◽  
Isotopic Ratios ◽  
The West ◽  
Geochemical Tracers ◽  
Good Linear ◽  
Isotope Analyses

Twelve new lead isotope analyses of samples from the West and East Shasta districts, California are presented. The measured isotopic ratios 206Pb/204Pb versus 207Pb/204Pb exhibit a good linear trend with a slope of 0.1794 ± 0.0066. Arguments are presented that the two-stage ages calculated from this slope are not real events. It is suggested the linear array is due to fortuitous addition of contaminants to the volcanogenic mineralizations. Thus common lead isotopes are possibly better geochemical tracers than they are geochronometers. This may be particularly true in cases where the total lead content is low.

Changes of Ionic and Oxygen Isotopic Composition of the Snowpack at the Glacier Austre Okstindbreen, Norway, 1995

1998 ◽  
Vol 29 (1) ◽  
pp. 1-20 ◽  
Author(s):  
Peter Raben ◽  
Wilfred H. Theakstone
Keyword(s):  
Isotopic Composition ◽  
Sea Level ◽  
Oxygen Isotopes ◽  
Oxygen Isotopic Composition ◽  
Isotopic Ratios ◽  
Vertical Variations ◽  
Oxygen Isotopic ◽  
The Difference ◽  
Liquid Precipitation ◽  
Different Altitudes

Marked vertical variations of ions and oxygen isotopes were present in the snowpack at the glacier Austre Okstindbreen during the pre-melting phase in 1995 at sites between 825 m and 1,470 m above sea level. As the first meltwater percolated from the top of the pack, ions were moved to a greater depth, but the isotopic composition remained relatively unchanged. Ions continued to move downwards through the pack during the melting phase, even when there was little surface melting and no addition of liquid precipitation. The at-a-depth correlation between ionic concentrations and isotopic ratios, strong in the pre-melting phase, weakened during melting. In August, concentrations of Na+ and Mg2+ ions in the residual pack were low and vertical variations were slight; 18O enrichment had occurred. The difference of the time at which melting of the snowpack starts at different altitudes influences the input of ions and isotopes to the underlying glacier.

scholarly journals Radiogenic Pb Enrichment of Mississippi Valley-Type Metallic Ore Deposits, Southern Ozarks: Constraints Based on Geochemical Studies of Source Rocks and Their Diagenetic History

Geosciences ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 172
Author(s):  
Jonathan Chick ◽  
Sydney E. McKim ◽  
Adriana Potra ◽  
Walter L. Manger ◽  
John R. Samuelsen
Keyword(s):  
Linear Trend ◽  
Ore Deposits ◽  
Source Rocks ◽  
Mississippi Valley ◽  
Isotopic Signatures ◽  
Boone Formation ◽  
Tripolitic Chert ◽  
Geochemical Studies ◽  
Mississippi Valley Type ◽  
Valley Type

Southern Ozark Mississippi Valley-type ores are enriched in radiogenic Pb, with isotopic signatures suggesting that metals were supplied by two end-member components. While the less radiogenic component appears to be derived from various shale and sandstone units, the source of the more radiogenic component has not yet been identified. Analyses of cherts from the Early Ordovician Cotter Dolomite and tripolitic chert from the Early Mississippian Boone Formation contain highly radiogenic Pb, with isotopic ratios comparable to those of ores. However, most samples have lower 208Pb/204Pb and 207Pb/204Pb for a given 206Pb/204Pb compared to ores. These relationships demonstrate that the enriched Pb isotopic values of the ore array cannot be related to the host and regional lithologies sampled, suggesting that the source of high ratios may lay further afield. The slope of the linear trend defined by the Pb isotope ratios of ores corresponds to an age of about 1.19 Ga. Therefore, an alternative for the linear array is the involvement of Precambrian basement in supplying ore Pb. Rare earth element patterns show that diagenetic processes involving the action of groundwater and hydrothermal fluids affected the sampled lithologies to various degrees, with Cotter Dolomite having experienced the highest degree of alteration.

Isotopic composition analysis of dissolved mercury in seawater with purge and trap preconcentration and a modified Hg introduction device for MC-ICP-MS

2015 ◽  
Vol 30 (2) ◽  
pp. 353-359 ◽  
Author(s):  
Haiying Lin ◽  
Dongxing Yuan ◽  
Bingyan Lu ◽  
Shuyuan Huang ◽  
Lumin Sun ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Isotopic Analysis ◽  
Composition Analysis ◽  
Analysis Method ◽  
Purge And Trap ◽  
Icp Ms ◽  
Dissolved Mercury ◽  
Preconcentration Method

A modified introduction device and a preconcentration method were developed to enhance the sensitivity of the Hg isotopic analysis method.

Woodcutters 55 Years Later: A New Look at an Old Discovery

SEG Discovery ◽  
2020 ◽  
pp. 15-21
Author(s):  
Dave Shatwell
Keyword(s):  
Chloride Content ◽  
Mississippi Valley ◽  
Deep Basin ◽  
Widespread Occurrence ◽  
Great Oxidation Event ◽  
Basement Rocks ◽  
Reducing Conditions ◽  
Volcaniclastic Rocks ◽  
Pine Creek ◽  
Shallow Marine Sediments

Abstract The Woodcutters Zn-Pb-Ag deposit in the Rum Jungle district of the Pine Creek orogen in northern Australia was discovered in 1964 and produced 4.6 Mt of ore grading 12.3% Zn, 5.6% Pb, and 83 g/t Ag between 1985 and 1999. Woodcutters, together with several other polymetallic, uranium, and phosphate deposits, is within a Paleoproterozoic sequence of fluviatile and shallow marine sediments deposited in a deepening basin between ~2100 and 2025 Ma around the margins of an Archean granitic and gneissic dome. These sediments were overlain by turbidites and volcaniclastic rocks until the basin was inverted and the sediments and mineral deposits were deformed and metamorphosed at 1860 Ma. Whereas the polymetallic and uranium bodies at Rum Jungle are considered to be syngenetic or syndiagenetic, sulfides in the Woodcutters orebody replace dolomitic horizons in an otherwise carbonaceous unit. This suggests that Woodcutters is similar to Mississippi Valley-type mineralization and rules out affinities with younger sedimentary exhalative-style deposits elsewhere in the Pine Creek orogen. A model is proposed whereby metals were eroded from Archean basement rocks into Paleoproterozoic sandstone aquifers following the Great Oxidation Event, which also liberated sulfur by oxidation of pyrite. Evaporative conditions, as suggested by the widespread occurrence of dolomite and magnesite, may have increased the chloride content of seawater and enhanced its capacity to transport metals. Subsequently, deeply circulating seawater leached metals from the aquifers and ascended up a deep, basin-penetrating fault until it intersected carbonaceous sediments. In this environment, Zn and Pb sulfides were deposited under reducing conditions, while sulfur may have been provided by H2S from organic material. The Woodcutters and other deposits at Rum Jungle show how metals formerly locked up in Archean cratons were delivered by erosion under an oxygenated atmosphere to Paleoproterozoic shorelines, where they were further mobilized and concentrated by a variety of processes.

Isotopic Measurements of Inorganic Material by Time-Of-Flight SIMS

1998 ◽  
Vol 4 (S2) ◽  
pp. 412-413
Author(s):  
A. J. Fahey
Keyword(s):  
Isotopic Composition ◽  
Inorganic Material ◽  
Secondary Ion Mass Spectrometry ◽  
Time Of Flight ◽  
Isotopic Ratios ◽  
Tof Sims ◽  
Low Duty Cycle ◽  
Solar Material ◽  
Secondary Ion ◽  
Isotopic Measurements

Isotopic measurements via Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) have generally not been considered as practical because of the low duty cycle at which ToF-SIMS instruments operate and the corresponding low data rate. The recent discovery of pre-solar material in meteorites has shown that large variations in isotopic ratios (several orders of magnitude for some elements) exist in small (∼1 μm), refractory meteoritic grains. These grains are ideal candidates for ToF-SIMS, which consumes little sample material, compared to dynamic, magneticsector SIMS. ToF-SIMS also allows for parallel detection of all species present in the sample; thus, multiple isotopic systems can be studied in one measurement. As a prerequisite to studying the isotopic composition of meteoritic materials, preliminary determinations of ratios for a number of elements have been made on materials of known isotopic composition. This allows us to investigate problems that may be unique to ToF-SIMS for the measurement of isotopic ratios.

Mississippi Valley-type lead–zinc deposits through geological time: implications from recent age-dating research

2001 ◽  
Vol 36 (8) ◽  
pp. 711-740 ◽  
Author(s):  
David L. Leach ◽  
Dwight Bradley ◽  
Michael T. Lewchuk ◽  
David T. Symons ◽  
Ghislain de Marsily ◽  
...  
Keyword(s):  
Age Dating ◽  
Mississippi Valley ◽  
Geological Time ◽  
Lead Zinc ◽  
Mississippi Valley Type ◽  
Valley Type ◽  
Zinc Deposits
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