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.lm 0 .rm 73 .pl 300 THE GEOLOGY OF GENTRY'S RADIOHALOS SAYS NO TO FAIT CREATION J. Richard Wakefield 385 Main Street Beaverton, Ontario, Canada L0K 1A0 [AUTHOR'S NOTE: This is an abridged version of a paper which was submitted, and accepted by the JOURNAL OF GEOLOGICAL EDUCATION. Publication date, Summer '88. A less techincal version also appeared in CREATION/EVOLUTION journal. I have decided to give this file to CREVO.BBS because I respect the people of SOR. I do not feel people on the two sides who are honestly looking for THE TRUTH should be at odds, but should work together for a better understanding. Unfortunately, some "facts" supporting young-earth creationism leave much to be desired. This comes in three files (RADHALO1, RADHALO2, and RADHALO3 {references}). Unfortunately this does not have the photos, or maps --so get a copy of my paper!! This is presented to you for your information, some will be reading-and-weaping, others will enjoy it --I hope you are the latter. Please repect the normal copyright, thank you. JRW March 27, 1988] Gentry's Basic Premise Gentry has described his work and interpretation in a series of papers and a recent book titled Creation's Tiny Mystery. How these halos form is not difficult to understand. They are formed by alpha particles released during the decay of radioactive nuclides. As an alpha particle nears the end of its path and slows it causes disruption of the crystal structure and leaves a small damage track. Over time, repeated decays from the parent nuclide will leave a spherical halo of discolouration. The distance that an alpha particle travels depends on the energy of the decay and that, in turn, is a function of the particluar nuclide that decays. Theoretically, then, the radii of a series of halos that surround a radioactive inclusion permit identification of the specific decaying nuclides. Gentry has claimed that certain of these halos indicate that the "basement rocks" of the Earth are "the primordial Genesis rocks" and were created instantaineously about 6,000 years ago. Essentially, Gentry has found that in certain samples of Precambrian biotite (a mica) the inner halos for uranium and other nuclides in the decay chain which should be producing Po210, Po214, and Po218 are missing; only the polonium rings for these three isotopes are present. In addition Gentry observed little or no uranium in the radioactive inclusion. His conclusion is that the polonium must have been primordial and because of the short halflives of the Po isotopes (138.4 days, .000164 sec., and 3.04 min. respectively) the granite, therefore, must have been created in the solid state in "...only a brief period between 'nucleosythesis' and crystallization of the host rock" (Gentry, 1975, p.270). In his scientific literature, Gentry has avoided making direct creationist statements, but from the above and other statements one gets the distinct impression that Gentry is trying to link the rocks of the Precambrian to the rocks that existed right after Earth's formation --or creation. For example: "It is also apparent that Po halos do pose contradictions to currently held views of Earth history. (Gentry, 1974, p.63)", "The Question is, can they be explained by presently accepted cosmological and geological concepts to the origin and development of Earth? (1974, p. 66)", and "Do Po halos imply unknown processes were operative during the formative periods of the Earth? (Gentry et al, 1974, p.564)" His book, however, is far more bold and less cryptic than his refereed papers. Comments like "Were tiny polonium halos God's fingerprint in Earth's primordial rocks? Could it be that the Precambrian granites were the Genesis rocks of our planet?" (Gentry, 1986, p.32) and "... polonium halos in Precambrian granites identify these rocks as some of the Genesis rocks of our planet --created in such a way that they cannot be duplucated without intervention of the Creator" (p.133) are common. In the young-earth creationist perspective, this puts Gentry in agreement with John Whitcomb and Henry Morris (Whitcomb and Morris, 1961, p.228) in claiming that the Precambrian is the created rock and of granitic composition. This is an overly simplified view of the complex Precambrian terrains of the world and it is simply not true that Precambrian rocks are those left from the Earth's formation --far from it!! They are rocks formed by the same or similar process that formed the post-Precambrian rocks. The only significant differences are: 1) Fossils are rarer in Precambrian rocks, and 2) Many Precambrian rocks have had more complex histories because they are much older. I do not intend to discuss the physics of halos in this paper. What I will describe here is the specific geology of three of the locations where some of Gentry's biotite samples came from --the Fission Mine, the Silver Crater Mine and the Faraday Mine all near Bancroft in southern Ontario (see Figure 1). I will, however, present a case solving the origin of the polonium from the geological desriptions of the area which seems to indicate that the uranium, and hence the polonium, were deposited by precipitation from circulating fluids. Geology of the Canadian Sites It was quite a suprise to me to find out that the above last two Canadian sites mentioned in Gentry's papers (Gentry, 1971 and 1974) are only a two-hour drive from my home. They are located in the late Proterozoic Grenville Supergroup of the Precambrian Canadian Shield. The Precambrian is divided into two main eras, the Archean, from 4,500 million years ago (Ma) to 2,500 Ma, and the Proterozoic from 2,500 Ma to 700 Ma. Each of these eras is subdivided into observable events such as large scale metamorphic activity or sedimentary and volcanic deposition. The location of the first site above, the Fission Mine, I found by asking the staff of one of the museums who had sent Gentry biotite samples (sample no. 30996, National Museum of Canada, L. Moyd, National Museum, Ottawa, Personal communications, Apr. & Aug. 1987). Nowhere does Gentry describe this site, but it is also within rocks of the Grenville Supergroup. In his book Gentry mentions only the one site, the Silver Crater Mine. He does mention other places, like Norway, New Hampshire, and Madagascar but only in a general way. This is very unsatisfactory. He should have given more exact locations and formation names for each sample --but he did not. This is rather strange in a book whose avowed intent is to explain and justify his claim. Why were specific sites, save this one, omitted? Before knowing his specific sites I suspected that Gentry had used samples from the Superior Province of Archean age in northern Ontario because this Province contains some of the oldest rocks in North America. Thus, I was suprised to find that his sites were in the much younger Grenville Province. It is a major blunder on Gentry's part. Louis Moyd made this very point to Gentry in person, when he visited to get samples (Moyd, Personal communication, Feb. 1987). It is apparent that Gentry knows next to nothing about Precambrian geology because he lumps all of the Precambrian rocks into one unit --the created one. The Grenville Supergroup is a very complex succession of metasediments, metavolcanics, alkalic intrusive rocks, mafic intrusive rocks and granitic intrusive rocks. It is located in a region of low- to very high-grade metamorphism that has altered many of the igneous, sedimentary and volcanic rocks into recrystallized rock called gneisses. However, many original igneous, sedimentary and volcanic features are preserved. Hydrothermally altered rocks are also common as well as metasomatic rocks (wall-rocks that have been included within and altered by intrusive melts). The metavolcanics (the lowermost rock units in the Supergroup) consist of pillow lavas (indicative of underwater extrusion), breccias (fragmented lavas), tuffs and pyroclastics (similar to what came out of Mt. St. Helens) altered to varying degrees by metamorphism. The intrusive rocks consist of varying types like gabbros (a dense rock high in the mafic minerals which contain iron and magnesium), granites (light-coloured rocks low in mafic minerals but high in potassium and sodium silicates like feldspar and quartz), diorites (intermediate in composition between the former two), syenites (poor in quartz), nepheline syenite (like syenite but higher in alkali metals and lower in silica), and pegmatites (any of the above in small dikes with large to very-large crystals) (see Table one). Many, but not all, of these intrusive rocks have been altered by low-grade metamorphism. The minerals in which Gentry found Po halos are biotite and fluorite. Biotite is a hydrous-potassium-mafic-aluminum-silicate and a common rock-forming mineral. Fluorite, calcium fluoride, is a common accessory mineral found deposited in veins, vugs and sometimes in metamorphic rocks like carbonates. Let us look at the specific geology of the three sites. The Fission Mine The Fission (also known as the Richardson) Mine is located 2 km east of Wilberforce on lot 4, concession XXI, Cardiff Township (Lat. 45o3'15"N; Long. 78o11'40"W) and consists of a single abandoned adit driven into a hill. The following geological description of this site is from the International Geological Congress Guidebook Field Excursion A47 - C47. "The country-rocks are variably syenitized biotite-gneisses and amphibolites, underlane by a thick series of partly silicated marbles. The altered gneisses are of many types,... The main deposit consists of a series of closely spaced vein-dikes... Most of the vein-dikes are more or less conformable with the structures of the enclosing gneisses, but some transect these structures. The bodies are extremely irregular in shape, thickness, and extent. Some of the individual vein-dikes exceed 300 feet in length, with maximum thickness of more than 10 feet. Last in this sequence [of rock units] are the vein-dikes, in which the core zone constitutes a substantial proportion of the whole mass. The bodies are generally more or less tabular, with crystals projecting inward from the walls. Some of the crystals are partly cavernous and enclose semi-isolated masses of the core-materials. Others may be more nearly euhedral, but contain completely isolated, rounded pellets of core-minerals... --calcite, fluorite, or mixtures of both. The composition and structure of these vein-dikes indicate origin by hydrothermal "fluxing" and recrystallization of wall rocks along bedding planes, joins and other fractures. The abrupt termination of the vein-dikes,..., strongly favours such an origin --the hanging-wall [top of dike] curving around to become the foot-wall [floor of dike]. Uraninite occurs as cubic crystals and also as irregular masses. It is very erratic in distribution and can be found in various associations... Most fluorite is the deep purple variety, antozonite. ...smells of fluorine and ozone when crushed or abraded, all of which reflect radiation damage. The depth of colour of the fluorite is an indicator of the proximity of uraninite (Hogarth, D.D., Moyd, L., Rose, E.R., and Steacy, H.R., 1972)" From this description it is clear that this is a small calcite vein-dike (a rock containing mostly large crystals of calcium carbonate and other minerals like mica) body. Gentry's sample came from the vein lining. The biotite grew outward, replacing the calcite, from the syentized wall-rock (see Figure 12) as a result of reactions between the wall-rock, calcite core and volatile fluids (Moyd, Personal Communication, Aug. 1987). The vein-dike is small in length and width, it cuts metasedimentary rocks which still retain bedding planes, and radioactive minerals abound. In another mineral collecting guidebook it was noted that at this site "Uraninite was found in cavities in pegmatites with magnetite, mica or calcite-fluorite intergrowths." (Sabina, 1986, p.79). Clearly radioactive minerals abound in this locality. Purcolating water from the hill the deposit occupies is strongly radioactive and was sold in the 1920's for therapeutic purposes. Hornblende crystals 2 meters long, biotite 30 centimeters across, apatite 30 cm long, feldspars 1 meter long, and zircons 5 cm long have been seen in this deposit. Also mentioned are pegmatites completely surrounded by metasediments and derived from partial melting of those metasediments during metamorphism. The Silver Crater Mine The Silver Crater Mine is located 12 km west of Bancroft on lot 31, concession XV, Faraday Township (Lat. 45o01'50"N; Long. 78o00'30"W). This abandoned mine consists of an adit with some drifting and a raise. The calcite vein-dike body here was mined for its biotite content. This is the locality of the mica, like the one that contains his 'spectacle' halo which "...exibits true radiohalo characteristics". This site is similar to the Fission site and the calcite vein-dike is part of the same group of calcite vein-dikes dotting the country side near Bancroft. Here are some quotes from the Ontario Dept. of Mines (now the Ontario Geological Survey) report for 1957, written by D.F. Hewitt, on the geology of the site: "The [calcite vein-dike] body occurs in a small band of amphibolite lying in syenitic and nepheline syenite gneiss in the trough of a V-shaped south-pitching syncline between the Cardiff plutonic complex on the west and the Faraday granite sheet on the east. The [calcite vein-dike] body consists of a coarse-grained calcite (1-5 inches in size), containing accessory black mica (lepidomelane [high mafic biotite]) in books up to 2 feet in diameter. Contacts of the [calcite vein-dike] body with the enclosing biotite amphibolite gneiss are irregular, and long inclusions of gneiss extend into the [calcite vein-dike]. Tongues of the wall-rock gneiss finger out into interfingering tongues of carbonate. This deposit has some features characteristic of the metasomatic replacement deposits in marble, of the hydrothermal calcite-apatite-fluorite vein deposits, and of intrusive carbonate deposits. Its mode of origin is in dispute. The coarse pegmatite crystallization of the calcite, black mica, hornblende, and albite suggest crystallization from a fluid medium, rich in volatiles. ... The wall-rock alteration, involving addition of fluorine, carbon dioxide, and soda into the surrounding wall-rock, favours crystallization of the [calcite vein-dike] body from a fluid state, such as a carbonate intrusive or hydrothermal solution. The orientation of the apatite and biotite suggest flowage after crystallization. The irregular replacement of the wall-rock gneiss and the long relic bands of biotite amphibolite in the [calcite vein-dike] indicate metasomatic replacement of the wall-rock gneiss by [calcite vein-dike]. The author believes that the [calcite vein-dike] has originally been largely derived from marble but that it has been assimilated or desolved and recrystallized from hot solutions rich in fluorine and soda. This would account for the extensive wall-rock alteration and the metasomatic type of replacement of wall-rock gneiss, without disturbance of relic mafic gneiss bands. Such relict bands are incompatible with an origin of the [calcite vein-dike] body involving tectonic movement of a marble bed in a plastic state. The author feels that the deposit is therefore best classed as a special variety of the hydrothermal deposit in which the solutions have carried out extensive metasomatic replacement of the wall-rocks (Hewitt, 1957, pp.77-78)" Let me make one thing clear at this point. The Silver Crater and the Fission Mines are not in granites at all. The composition and mode of origin is totally wrong for a granite and Gentry has made a major error in identifying them as granites for the source rocks for his biotite. In his book he erroneously criticizes Dalrymple for making a comparison between the textures of basaltic lava and granite (Gentry, 1986, p.130), yet he can't tell the difference between granite and calcite vein-dike! There is a consensus from more recent research about the origin of the calcite vein-dike material, the biotite and other large minerals in the dikes. Because of the presence of rounded calcite in the minerals themselves it is thought that the biotite grew as a replacement within the solid calcite vein-dike matrix. This process occurs when the solid calcite vein-dike, which was hydrothermally deposited, or injected as a molten liquid, is reheated enough to cause the evenly distributed minerals of biotite, hornblende, betafite, apatite, etc. in the wall-rock and calcite vein-dike to start to migrate and form larger crystals in the calcite vein-dike. Gentry made the claim that "Halos occur in many mica samples which have not undergone metamorphism of any kind (1986, p.299)." However, these micas were indeed formed during metamorphism at moderate-depth (10-15km) and the overburden has since been erroded off. Let me state it another way --the biotite was metamorphically derived! The Faraday Mine The Faraday Mine is located 5 km west of Bancroft on Highway #28 on the north-east end of Bow Lake (Lat. 77o55'30"N; Long. 45o00'15"W). The mine workings consisted of several adits, drifting and several levels. The mine was opened for the uranium in a granite pegmatite, which cuts a gabbro/metagabbro intrusive body, which itself cuts metasedimentary rocks, including marble. In the early 1950's Jack Satterly mapped the Bancroft area specifically for radiactive minerals. Here are some quotes from the Ontario Department of Mines report for 1956 on the geological setting of the Faraday Mine. "The radioactive minerals occur in bodies of leucogranite, leucogranite pegmatite, and pyroxene granite (or syenite) pegmatite, cutting metagabbro and gabbroic amphibolite. The metagabbro and amphibolite form the western part of the Faraday metagabbro, a metamorphosed basic intrusive body about 6 miles in length and up to 3/4 mile wide, which cuts the Grenville metasediments, chiefly marble, amphibolite, and paragneiss in this area. Inclusions and relict bands of marble and metasedimentary amphibolite occur in the metagabbro. The Grenville metasediments and the Faraday metagabbro are intruded by nepheline syenite, syenite and granite. ...the metagabbro itself is strongly affected by dynamic metamorphism and shearing. Structurally, the granitic [pegmatite] bodies of the Faraday mine intrude the metagabbro, which lies in the mixed hybrid gneiss zone that forms the hanging wall of the Faraday granite sheet. These bodies may be related genetically to the latter intrusive (Satterly, 1956, p.110)." In other words, material was erroded from some preexisting rock, deposited as a sedimentary rock (probably a volcanic island setting (Easton, 1986b)), then deformed and recrystallized by high-grade metamorphism (referred to as the Grenville Orogeny (Lumbers, 1982)) which altered this rock to paragneisses. This in turn was intruded by the gabbro, which later underwent another metamorphic episode during the latter stages of the orogeny. Finally, these rocks were intruded by the granite pegmatite. Gentry's biotite came from this pegmatite. S.L. Masson and J.B. Gordon note of the pegmatites of the mine: "Pegmatites hosting uranium mineralization intrude the metasediments, metagabbro and pyroxinite. They generally conform to foliation but locally cross-cut it. Pegmatites masses are 91.5 to 915 m long, 3 to 46 m wide and some extend down dip more than 300 m. ... The pegmatite is composed of feldspar, hornblende-chlorite, quartz, calcite, magnetite and zircon. Main accessory minerals are [biotite] mica, titianite, apatite, allanite, tourmaline, uraninite, uranophane and uranothorite (Masson and Gordon, 1981, p.60)." A.R. Bullis writing on the geology of the pegmatites of the mine: "...in other places [the pegmatites] are discordant and show cross-cutting relationship to all of the wall-rocks. The contacts are sharp and clear cut and others are in the nature of irregular, gradational zones that show a change, or alteration, from paragneiss to granitic pegmatite over widths of up to 24 inches. It is obvious that both injection and metasomatic processes have taken place during the intrusion of the pegmatites. Chilled edges are rare or non-existent. Magmatic stoping, or the engulfing of the country rock has taken place on a large scale; there are many blocks of paragneiss and pyroxenite within the pegmatite. Most of the inclusions are fresh looking, but many are highly altered and ghost-like in appearence (Bullis, 1965, p.717)." The Faraday Mine pegmatites have been dated at between 992 Ma to 1088 Ma by several methods (Easton, 1986a,c). The Faraday Batholith, just to the north, was dated at 1190 Ma. Though no dating of the Faraday gabbro has been done, other gabbros in the area of similar composition, like the Tudor Gabbro just to the south, have been dated at 1240 Ma (Easton, 1986a). The Silver Crater deposit has been dated at 1000 Ma (R. Gait, Mineralogist, Royal Ontario Museum, Personal communication, Feb. 1987) and the Fission mine is closely related in age. The interesting thing about Gentry's work is his claim that there is no uranium or thorium in the nucleus at the centre of the halos or around the biotite itself saying: "Application of [special acid technique] to regions of mica near polonium halos showed only evidences of trace amounts of uranium (a few parts per million) that exist throughout all mica specimens --there was no concentration of uranium in or near the halo centers in the clear areas (1986, p.31)." This is surprising since the Faraday pegmatite was mined for uranium. The most common radioactive mineral is uranothorite, hence lots of uranium and thorium. These minerals are very small (less than .1 mm) and scattered throughout the pegmatite becoming ore grade in the quartz and magnetite regions of the pegmatite. 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.^^ (Satterly, 1956, p.130, emphasis mine)" In my phone conversation with Gentry in Febuary he admitted that his samples contained betafite. Why did he leave that observation out of his papers? Why is it, with so much radioactive minerals and ground-water at these sites, is there very little uranium in the halo centres? Or is there? Did Gentry err? Some researchers think so (Moazed et al, 1973). 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 (Gentry, 1975, p.270)" Gentry also noted that same paragraph that "halo coloration disappears within minutes in [the 300 degree celcius] temperature range." He went on to say:


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