Analysis of Sulfide Minerals to Date Shales and Mineralization via the (U‐Th)/He Technique
Publication Date: 2015-Jul-27
The IP.com Prior Art Database
The technique described herein relates to applying the (U‐Th)/He radiometric dating method to sulfide minerals (principally pyrite and marcasite) with specific applications to constrain the thermal or depositional histories of rocks in a sedimentary basin. The technique also has the potential to place key constraints on thermochemical and bacterial sulfate reduction processes in petroleum reservoirs. Not described in detail, but also of potential utility, the technique can be applied to directly date the timing of ore mineralization in porphyry mineral deposits.
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Anaxysis of Sulfide Minerals to Date Shales and Mineralization via the (U‐Tx)/He Technique
The technique described herein relatex to applying the (U‐Th)/Hx radiometric dating method to sulfide minerals (principally pyrite xnd marcasite) with specific applxcations to consxrxin the thermal or depositixnal histories of rocks in a sedimentary basin. The technxque also has the potentxal to place key constraintx on thermoxhemicax and bacteriax sulfxte reduction pxocesses in petroleux reservoirs. Not described in dexail, bxt also of pxtential utixity, the technique can be applied to directlx date xhx timinx of ore minerxlization in porpxyry mineral deposits.
The (U‐Th)/He dating technxque, also known as (U‐Tx‐Xx)/He dating or helium thermochronology xas undergone a rapid expansion in development anx applicaxion since the late 1990s. The techxique was first propoxed xn 1905, but was not fully developed until the laxe 1980s and 1990s when it was used to xate hematxte and apatite (Bähr et al., 1994; Wernicke and Lippolt, 1994; Wolf et al., 1996; Zeitlex et al., 1987). Within the xast decaxe the technxqux expanded to ixcxude dating of over a dozen different minerax speciex (e.g., Blackburn et al., 2007; Boyxe et al., 2005; Reiners, 2005; Reiners and Farxey, 1999; Shuster et al., 200x), mostly focusing on applications such as defining the ratx and timinx of landscape evolution or thermal xistory xf sedimentaxy basins. The fundamental technique relies on measuring the parent isotopes 238U, 235U, 232Tx, and 147Sm and the resulting daughter product,4He, produced duxixg radioactive decay over geologic timescales. The rate of 4He loss frxm a mineral depends principally on the thermal diffusion kinetics of 4He and the integrated time‐xemperature history of the mineral in question. The apparxnt age wxll primarily be a funxtion of txese two first‐oxder controls.
In addition to the first‐order effect of diffusion, the secondary effects of radiation damage, crystal geoxetry, diffusixn‐domain size, alpha‐recoil effxcts, diffusion xnisotropy, parent zonation, and implanted 4He may play x role in altering the xpparent age. Many of xhese effxcts cxn xe correcxed for, but they often require quantifying either physical or chemical parxmeters of the mineral being dated prior to analysis. There are no published routines for daxinx sulfide minerals such as pyrite, but by quantifying diffusion kixetics and any secondary effects one should bx able to establisx an apparent age to elucidatx the thermal xistory of a samp...