Barbarian
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- Jun 5, 2003
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I meant "Gentry", not "Snelling."
The Silver Crater and Fission Mines are lithologically different, but they, too, contain abundant radioactive minerals—especially betafite, a radioactive variety of the mineral pyrochlore, which is a complex calcium-sodium-(uranium)-niobate-tantalate-hydroxide. It was noted by Satterly that "Betafite [at the Silver Crater]
is often found in close association with clusters of mica books and apatite crystals. Small crystals of betafite have been found within the books of mica" (p. 130; emphasis mine). In my phone conversation with Gentry in February, he admitted the betafite was with his samples. Why did he leave that observation out of his papers? Why is it, with so many radioactive minerals and so much groundwater at these sites, that there is very little uranium in the halo centers? Or is there? Did Gentry err? Clearly, there is something complicated going on here, considering the nature of the host intrusive rocks, the low-grade metamorphism that the intrusive rocks have undergone, the high-grade metamorphism of the surrounding wall rock, the hydrothermal activity and the metamorphic replacement by the biotite within the calcite vein dikes. Gentry noted that "the great majority of minerals containing polonium halos show no evidence of high temperature episodes" (1975, p. 270). Gentry also noted in that same paragraph that "halo coloration disappears within minutes in [the 300 degree Celsius] temperature range" for fluorite. He continued:
An equally strong objection to the uranium-daughter hypothesis in uranium poor (p.p.m. or less) minerals is that many Po halos (such as the `Spectacle' halo [from Silver Crater]) are located in the interior of large pegmatite crystals as well as in small granitic mica flakes where they are often more than 10 cm. and sometimes much less than 100 cm. away from a significant uranium source.
[1975, p. 270]
This is quite an extraordinary claim to make for four reasons: (1) it contradicts Satterly's observation of betafite within some of the biotite; (2) it shows that he knows it is a pegmatite body and therefore must be intrusive; (3) it admits that heat, such as that from a metamorphic event, erases halos; and (4) it acknowledges the proximity of radioactive minerals.
http://ncse.com/book/export/html/3436
The Silver Crater and Fission Mines are lithologically different, but they, too, contain abundant radioactive minerals—especially betafite, a radioactive variety of the mineral pyrochlore, which is a complex calcium-sodium-(uranium)-niobate-tantalate-hydroxide. It was noted by Satterly that "Betafite [at the Silver Crater]
is often found in close association with clusters of mica books and apatite crystals. Small crystals of betafite have been found within the books of mica" (p. 130; emphasis mine). In my phone conversation with Gentry in February, he admitted the betafite was with his samples. Why did he leave that observation out of his papers? Why is it, with so many radioactive minerals and so much groundwater at these sites, that there is very little uranium in the halo centers? Or is there? Did Gentry err? Clearly, there is something complicated going on here, considering the nature of the host intrusive rocks, the low-grade metamorphism that the intrusive rocks have undergone, the high-grade metamorphism of the surrounding wall rock, the hydrothermal activity and the metamorphic replacement by the biotite within the calcite vein dikes. Gentry noted that "the great majority of minerals containing polonium halos show no evidence of high temperature episodes" (1975, p. 270). Gentry also noted in that same paragraph that "halo coloration disappears within minutes in [the 300 degree Celsius] temperature range" for fluorite. He continued:
An equally strong objection to the uranium-daughter hypothesis in uranium poor (p.p.m. or less) minerals is that many Po halos (such as the `Spectacle' halo [from Silver Crater]) are located in the interior of large pegmatite crystals as well as in small granitic mica flakes where they are often more than 10 cm. and sometimes much less than 100 cm. away from a significant uranium source.
[1975, p. 270]
This is quite an extraordinary claim to make for four reasons: (1) it contradicts Satterly's observation of betafite within some of the biotite; (2) it shows that he knows it is a pegmatite body and therefore must be intrusive; (3) it admits that heat, such as that from a metamorphic event, erases halos; and (4) it acknowledges the proximity of radioactive minerals.
http://ncse.com/book/export/html/3436