Radiometric Dating of Ochoan (Permian) Evaporites, Wipp Site, Delaware Basin, New Mexico, Usa

1986 ◽  
Vol 84 ◽  
Author(s):  
Douglas G. Brookins ◽  
Steven J. Lambert
Keyword(s):  
New Mexico ◽  
Clay Minerals ◽  
Early Stage ◽  
Local Area ◽  
Radiometric Dating ◽  
Delaware Basin ◽  
Geochemical Study ◽  
Sulfate Salts ◽  
The Stability ◽  
Evaporite Minerals

AbstractWe have attempted radiometric dating of halide-sulfate salts and clay minerals from the Delaware Basin, New Mexico, USA, as part of geochemical study of the stability of the evaporite sequence at the WIPP (Waste Isolation Pilot Plant--a US DOE facility) site. We undertook this dating to determine: (1) primary age of evaporite genesis or time(s) of recrystallization, (2) if previously undated evaporite minerals (leonite, polyhalite, kieserite) give useful data, and (3) if the detrital clay minerals have been radiometrically reset at any time following their incorporation into the evaporite medium. We have shown earlier that polyhalites can indeed be successfully dated by the K-Ar method, and once corrections are applied for admixed halide minerals, dates of 210-230 Ma for the Delaware Basin are obtained. Rb-Sr isochrons from early stage sylvites-polyhalites- anhydrites yield 220 ± 10 Ma, even when some sylvites yield lower K-Ar dates due to l1s of 40Ar*. K-Ar dates on leonites and kieserites are also low due to 40Ar* loss, but their Rb-Sr dates are higher. Detrital clay minerals from the Delaware Basin collectively yield a highly scattered isochron (390 ± 77 Ma), but samples from a local area, such as the WIPP Site, give a much better age of 428 ± 7 Ma. These dates show that the interaction between the clay minerals and the evaporitic brines was insufficient to reset the clay minerals Rb-Sr systematics. In a related study, we note that a dike emplaced into the evaporite at 34 Ma had only very limited effect on the intruded rocks; contact phenomena were all within 2 m of the dike. All of our geochemical (radio-metric and trace element) studies of the WIPP site argue for preservation of the isotopic and chemical integrity of the major minerals for the past 200 Ma.

Authigenic Clay Minerals in the Rustler Formation, WIPP Site Area, New Mexico

1989 ◽  
Vol 176 ◽  
Author(s):  
D. G. Brookins ◽  
S. J. Lambert ◽  
D. B. Ward
Keyword(s):  
New Mexico ◽  
Clay Minerals ◽  
Isotopic Exchange ◽  
Late Permian ◽  
Delaware Basin ◽  
Data Yield ◽  
Chemical Integrity ◽  
Transuranic Waste

ABSTRACTTransuranic waste is planned for disposal in the Late Permian evaporites of the Delaware Basin, southeastern New Mexico, at the WIPP Site. The disposal horizon is located in the bedded halite of the Salado Formation, which is overlain by the impure halite-anhydrite (gypsum)-siltstone-mudstone of the Rustler Formation. The Rustler Formation also contains two dolomite members, the Magenta and Culebra, which transmit water. The Culebra Member is suspected to have actively interacted with waters at time(s) from the Late Permian to the present, and it is important to assess the reactivity of these waters in conjunction with WIPP stability.We have investigated the Rb-Sr systematics of clay minerals from the Culebra Member and elsewhere in the Rustler Formation. By separating the less than 0.125 μm size material we are able to deal with presumed true authigenic clay minerals. The authigenic fraction is especially sensitive to chemical and isotopic exchange with waters, and an episodic exposure to a large amount of water will re-set the clay minerals to such a time. Our data yield 259 ± 22 Ma Rb-Sr isochron, which is consistent with the Late Permian age of the Rustler Formation. This age demonstrates that age-determining cations in these clay minerals have preserved their isotopic and chemical integrity since the Late Permian.

PERFORMANCE OF THE ANALYTICAL PLOTTER

1963 ◽  
Vol 17 (2) ◽  
pp. 205-211
Author(s):  
T. J. Blachut
Keyword(s):  
Early Stage ◽  
Statistical Treatment ◽  
Measuring System ◽  
Stage Of Development ◽  
Pointing Accuracy ◽  
Analytical Accuracy ◽  
The Stability ◽  
Extensive Experimental Data ◽  
Mean Square Errors ◽  
Very High

In spite of the lack of extensive experimental data at this, in a sense, early stage of development, some very interesting indications of the eventual performance of the Analytical Plotter can be seen. The accuracy of the measuring system is very high; monocular grid measurements gave mean square errors of 2.5 - 3.5 μ. The stability is even better, repetition of readings being constant within 2 to 3 μ, that is, within the pointing accuracy. The accuracy of the complete system may be improved by using experimental corrections and proper statistical treatment of redundant observations. Complete relative and absolute orientations can be carried out in 10 to 15 minutes or less with analytical accuracy. Further economical advantages result from the use of the inherent computer capabilities to solve auxiliary problems and to carry out pertinent “real time” operations, such as automatic control of the plotting table.

scholarly journals Geological and Chronological Constraints on the Long-Lived Eocene Yulong Porphyry Cu-Mo Deposit, Eastern Tibet: Implications for the Lifespan of Giant Porphyry Cu Deposits

2017 ◽  
Vol 112 (7) ◽  
pp. 1719-1746 ◽  
Author(s):  
Jia Chang ◽  
Jian-Wei Li ◽  
David Selby ◽  
Jia-Cheng Liu ◽  
Xiao-Dong Deng
Keyword(s):  
Early Stage ◽  
Porphyry Copper ◽  
Copper Deposit ◽  
Granite Porphyry ◽  
Radiometric Dating ◽  
Time Interval ◽  
Porphyry Cu ◽  
Economic Significance ◽  
Vein Formation ◽  
Porphyry Cu Deposit

Abstract The Yulong porphyry Cu-Mo deposit, the third largest porphyry Cu deposit in China, contains proven reserves of > 6.5 million metric tons (Mt) Cu and 0.4 Mt Mo. Previous radiometric dating studies have provided numerous ages for this deposit, but the timing and duration of the process governing the deposition of Cu and Mo remains not well constrained. In this paper, we first document multiple stages of mineralization and hydrothermal alteration associated with distinct magmatic pulses at Yulong by field and textural relationships, and then present high-precision molybdenite Re-Os ages of 14 quartz-molybdenite ± chalcopyrite veins representing these stages to precisely constrain the timing and duration of Cu-Mo mineralization. The ore-hosting Yulong composite stock consists of three successive porphyry intrusions: (1) monzonitic granite porphyry (MGP), (2) K-feldspar granite porphyry (KGP), and (3) quartz albite porphyry (QAP). The vein formation, Cu-Mo mineralization, and ore-related alteration are grouped into early, transitional, and late stages with respect to the intrusive history. The first two porphyry intrusions are followed by cyclical sequences of veining that are mainly associated with potassic alteration and have formed (1) ME vein/USTT, (2) EBE/T veins, (3) A1E/T veins, (4) A2E/BT veins, and (5) A3E/T veins. A2E/BT and A3E/T veins of the early and transitional stages are dominated by quartz and chalcopyrite ± pyrite, respectively, and represent the main Cu-Mo mineralization events. More than 80% of Cu and Mo at Yulong were deposited in the early stage with the remainder being formed in the transitional stage. The late-stage pyrite-quartz veins (DL), which are characterized by sericitic alteration halos, postdate the intrusion of QAP dikes and have no economic significance. Molybdenite Re-Os ages of A2E and BT veins indicate that sulfide deposition at Yulong was episodic over a prolonged history lasting over 5.13 ± 0.23 m.y. (1σ). However, the bulk Cu-Mo ores formed in a shorter time interval of 1.36 ± 0.24 m.y. (1σ) with most Cu precipitated in a more restricted timespan of 0.82 ± 0.24 m.y. (1σ) in the early stage. These results, combined with geochronologic data from porphyry copper deposits elsewhere, confirm that multiple magmatic-hydrothermal pulses with a lifespan of tens to hundreds of thousands of years are sufficient to form a giant porphyry copper deposit. Factors such as metal concentration, volume, and focusing efficiency of ore-forming fluids could have played important roles in producing a giant porphyry Cu deposit regardless of a short- or long-lived magmatic-hydrothermal system.

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