Radiogenic daughter products! Back to the Future lead lead age dates. There is way way too much radiogenic lead in Upper Mississippi Valley deposits of NW Illinois. Reports suggest the percentage of radiogenic lead is on the order of 50% at least locally!
Radon gas is heavy and short lived and should not go far from its source and should leave a "trackway". I enclose an article describing the unusual and erratic ratio of radiogenic daughter products and a graph.
The other expected daughter products in the decay chain are not present or at least not reported.
So....where did all the radon come from...some kind of S type granite?
I am dubious of it's being leached off a granite. In Colorado the Silverplume Granite is relatively "hot". It is easy to peg a scintillometer here and there...likely from "shrockingerite" or some relatively mobile uraniferous constituent. Furthermore, in Colorado there are obvious signs of the radioactive daughter products between the rimming granite outcrops and a mined uranium roll front deposit at Tallahassee Creek at the edge of South Park. I know it because I drilled some radon springs in South Park long ago. But...there seem to be no such radiogenic trails between granites in the Wisconsin/Ashton Arch, see below, and the abundant J type lead of the historic Galena mining district of NW Illinois.
The paragenetic studies are predicated on a hydrothermal process for galena deposition. I think there is more to the story.
See below.
I show a recent find of galena megacrystals from a discovery site in pockets located at the top of the Ordovician Galena Group and the base of the Ordovician Maquoketa bounding the Ordovician at the proverbial GICE interval See stratigraphic diagram.
There may have been a strong Radon event of some kind that caused the J-type lead but how does that fit into the conventional depositional model described below dated 1986.
Maybe it's from the deeper "k-bentonites" at the base of the Galena near the top of the Decorah. I attach an article from 1996 from GSA for your convenience. The multiple K-bentonites are at or near the base of the Galena Group. That's pretty far but it's not unreasonable to postulate fracture flow of some kind...at the proposed date of zinc mineralization...roughly 250my ago.
Has anyone else considered the problem of anomalous radiogenic lead in UMV deposits. If the source is merely K-bentonite...it should be widespread. But..I understand J-type lead is relatively localized...(getting its name from Joplin Missouri and presenting itself most abundantly in Jo Daviess Co. Illinois).
I suspect the geological provenance of radiogenic lead is confounded by the mobility of radon.
The attached study seems to ignore the migration of radiogenic radon as a gas that might fractionate the isotopic ratios enough to complicate sampling if not large area interpretation. The movement of radon seems significant.
Geosciences | Free Full-Text | Radiogenic Pb Enrichment of Mississippi Valley-Type Metallic Ore Deposits, Southern Ozarks: Constraints Based on Geochemical Studies of Source Rocks and Their Diagenetic History (mdpi.com)
Any radiogenic lead deposited as a decay product of gaseous radon should behave just like regular natural lead. The result might well be isotopic "stripes" of some kind as a result of normal "hydrothermal" processes.
The chalky "cerrusite like" partly coated galena crystal masses in images below are from recent finds found within the visible chalky pockets exposed during excavated. They were removed by hand from large "openings" exposed on and visible below, a phosphate nodule bearing "corrosion surface" present likely bounding Upper middle Ordovician Galena Group and the overlying GOBE related Maquoketa formation of Elizabeth Illinois. See below for reference. The specimens are in the Elizabeth Museum...see map. (stalagtites in the bucket in DSC01128 are not related to this find but are attributed to historic observations during historic mining activities).
These are what the "openings" look like. They are pockets on the corrosion surface. No veins or fractures visible. However, images below show mining generally followed folds and fractures. Image "guttenberg brown liberty" shows oil bearing units that are generally encountered at or below the zone of pb/zn mineralization. I can believe the Zinc followed oil and oil field brines and that lead may have been liberated from calcium carbonate minerals during dolomitizaton...but did the carbonates "scavange" uraniferous ionic species prior to dolomitization. If so...what was the source of the radioactive material....penecontemporaneous S type granite outcrops? Did the radiogenic lead actually move with normal lead and zinc as a dissolved constituent?
I enclose a recent document uploaded by the author who sampled several districts and ran isotopic ratios to determine the source of the radioactive material. I believe the radioactive radon is sourced from radium which would move with the calcium...but...the half life of radon is so short it would not have travelled miles and miles and seems unlikely to have followed the stable methane gas. There should be "breadcrumbs"...i.e. signs of other daughter products that point to a significant source...even if it is merely a basement type S granite such as what would be expected to be associated with the basement rhyolite granite precambrian terrane.
Radon mitigation services are common in Dubuque and are attributed to the presence of ordinary carbonates/dolomites.
However, basement lithologies in Iowa and much of the Great Plaines are not granite/rhyolite, they are "oceanic" and should be much less radiogenic.
Is there such a broad brushed change in radioactive daughter products going from granite/rhyolites of Illinois east of the "mississippi" to oceanic litholigies of mavic/gabbrotic affinity west of the Mississippi depending on whether underlying material is "Yavapai" or "Mazatzal"?
I enclose a little snippet from a gravity map. Maybe the two terranes show up geophysically and on the basis of "tramp" radioactive emanations.
S type granites (continental) are commonly radioactive and I types (oceanic) are not....
Is there an unrecognized precambrian "diorite" line through the midcontinent like the one reported along the Wasatch Front of Utah?
Looks like the radon comes from oil field brines that are or have been present. It is a known thing....see attachment below dated 1953 from the USGS.
The oil field brines carry radium salts and the oil carries uranium salts...or so it seems. There should be radium salts present within the ordovician galena group. For some reason the underlying aquifers are distinctly fresh water systems in the area. So...my question is...what happened to the oil field, its saline components and how did the "formation water" in the underlying St. Peter sand for instance become fresh? It is very fresh...I drink it all the time as part of a municipal water supply system. So do lots of people.
Applied radon geochemistry in oil and gas exploration (Conference) | OSTI.GOV
TENORM: Oil and Gas Production Wastes | US EPA
So...my claim that Upper Mississippi Valley Lead Zinc deposits reflect the former existence of oil and gas deposits and represents the remnants of their soluble constituents is supported by the widely known problem of radon associated with oil and gas production. There is even a term for it...TENORM. Technically Enhanced Naturally Occurring Radioactive Material.
I suggest that the radon comes from clays. I enclose some images.
It is my opinion that there are lunreported sources of radium contaminated smectites, maybe even those that host zinc such as sauconite.
The article below describes radium selective clays. I enclose some images of material found locally that is likely some kind of hydrozincite/hemimorphite associated with speleogenetic processes in what was likely to have been a hypogene karst cave process that was rejuvenated.
The phyllosilicate enclosing Ordovician Galena Group dolomite units probably hosted oil/gas material which is now gone. The existing clays from previous regoliths and argyllaceous mudstone carbonates likely picked up zinc from the oil and radium from the salt water, both of which are gone leaving the host lithologies "yellowed"...possibly from zinc bearing clays. There are examples of books of phyllosilicates growing adjacent to small vugs. My guess is that is where the radium is and possibly the source of radon.
The natural lead...I can only make suppositions that it travelled with the zinc in oil from local carbon sources as would be expected in an active petroleum process within the oil generation window.
The natural isotopic lead and zinc mined extensively and was likely effectively removed from local ordovician limestone/dolomite during permian? mineralizaton and perhaps continued dolomitization but the timing of mineralizing events, metallization and recrystallization are confusing.
The oil that hosted the zinc, and presumably natural isotope lead.likely was derived from nearby Maquoketa...a source rock lithology that reportedly still hosts sufficient carbon to generate oil.
There are local reports of oilstone in Decorah/guttenburg units near the base of the middle ordovician galena group, see images above. Undoubtably there was remobilization and migration of the in situ units following each karst event...the first of which was Ordovician followed by permian? and ultimately by Pleistocene/holocene. The radium went with the oil field brines and was selectively captured by smectite. The clays then grew into "papyrus like" books of phyllosilicate material (see below) which outgassed radon as the radium decayed. Those clays likely expanded as smectites do and decomposed to release radon. Local construction workers remarked on the strange abundance of paper-rock. That material is likely the sink and source of considerable mineralization not the least of which would be radon and ultimately radiogenic lead.
Most likely the radon comes from radium enriched clays that have not been reported.
Superselective clay for radium uptake | Nature
See below:
The radon cannot have been stored in any kind of geologic "trap". It must be regenerated anew from its parental element, likely radium trapped in a selectively absorptive clay.
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