The present work aims at identifying Nb-Ta-, Zr-Hf-, REE-, Th-U-bearing two-mica granite from geological, geophysical cross-sections and mineral chemistry studies from three boreholes at G. El Sela shear zone. Microscopically, the three boreholes are composed mainly of two-mica granite. They are composed of K-feldspar, plagioclase, quartz, biotite and muscovite. Accessories are pyrite, zircon, fluorite, rutile, monazite with Th-U-mineralization identified by scanning electron microscope (SEM) and electron probe-microanalyses (EPMA). Chlorite, muscovite, sericite, kaolinite are secondary minerals. Geochemically, two-mica granite boreholes are A-type granites and peraluminous characteristics. They are enriched in large ion lithophile elements (LILE; Ba, Rb and Sr), high field strength elements (Y, Zr and Nb), and LREE but depleted in HREE with negative Eu anomaly. U-enrichment associated with chloritization, muscovitization, albitization, sericitization, kaolinization and argillization results from convective hydrothermal circulation of fluids through brittle structures along the ENE-WSW main shear zone. The ratios Nb/Ta (7.7 - 17.7) and Zr/Hf (16.9 - 26.4) are relatively enriched in the lighter isovalents Ta and Hf. The accessory minerals observed in the two-mica granites are represented by metallic sulfides (pyrite, arsenopyrite, chalcopyrite, galena and sphalerite), Nb-rutile, Hf-zircon, fluorite, monazite, columbite, betafite, thorite, phosphothorite, uranothorite, brannerite, uraninite, coffinite and pitchblende at G. El Sela shear zone. Uraninite with a low Th content indicates a hydrothermal origin of U-mineralization, Thorite, uranothorite, monazite and zircon is the main uranium bearing minerals of magmatic origin within the enclosing granite. The primary U-mineralization has been observed in two boreholes. In order to illustrate the geophysical signature of El Sela U-mineralization, the radiometric, magnetic, and VLF-EM data as well as radon concentration are included. The magnetic, electrical conductivity and radiometric profiles were produced from detailed ground surveys. The shear zone is characterized by relatively weak levels for both K and eTh, but very high eU anomalies (<3500 ppm), Therefore, the Sela shear zone acts as a good trap for U-mineralization. The Sela Shear zone coincides with positive conductivity anomalies, which are the most prominent features on the respective profiles. The magnetic field over the Sela shear zone is also conspicuous by the sharp contrast which makes with the strong negative signatures of the altered microgranite. The radon distribution map showed the presence of seven high anomalies that are mostly controlled by the structures due to the easy movement of radon through them.
Uranium ore is the indispensable raw material for nuclear fuel preparation and is currently heavily prospected. Unlike the majority of metals, the metallogeny of uranium is specifically characterized by an extreme diversity of deposits that are directly related to the various conditions under which U deposits formed in geological environments [
Generally, granitic rocks are one of the most favourable host rocks for U-mineralization in many parts of the world. Genetically, the economic uranium deposits associated with granites are mostly located in analectic melts or in strongly peraluminous two-mica granites [
Most Egyptian uranium occurrences in granite rocks of G. Um Ara [
El Sela two-mica uraniferous peraluminous granite [
El Sela granitic pluton is composed of two-mica (muscovite-biotite) granite intrusions trending ENE-WSW (
A microgranite dike hosts the most radioactive anomalies in the study area. It is injected into the two-mica granite along an ENE-WSW shear zone with dip of about 75 to south. It is whitish pink, pale pink, reddish pink to pale grey colors and is 3 to 20 m thick.
It is also essentially composed of quartz, K-feldspar, plagioclase, biotite and muscovite. It is enriched with mineralized with uranophane and pyrite cubes. Ferrugination, silicification, albitization, episyenitization, fluoritization and illitization are different alterations mainly occurring with the ENE-WSW shear zone. Some of these alterations are possibly related to U remobilization, but probably not all. To be discussed in detail later.
Dolerite dikes are greyish green to dark grey colors, fine- to medium-grained and range in thickness from 0.5 to 6 m . They are injected into the two-mica granite along ENE-WSW, NNW-SSE and N-S directions with dip of about 75 to south. They are mainly composed of plagioclase, olivine and pyroxene. Accessories are apatite and opaque minerals while chlorite, sericite and calcite are alteration minerals. The dolerites have higher U-contens which may reach up to 3500 ppm eU and 75 ppm eTh. They are highly altered to clay minerals and cavities are filled with pyrite cubes and/or secondary uranium minerals (uranophane and autunite). Many open cuts have been made to recognize the importance of the U mineralization within the microgranite and dolerite dikes. Many semi-industrial technological procedures for the leaching and recovery of the U incorporated within these mineralized dikes have been performed.
Along the main ENE-WSW shear zone three generations of quartz veins with different colors have been identified. The milky quartz vein occurs at the shear margins, is the oldest one, highly brecciated, barren, and range in thickness from 1 to 4 m . The milky quartz vein is crosscut by two younger generations of quartz with obvious displacement. Red and grey to black jasper veins are commonly parallel to the shear zone and the older milky quartz vein and are mineralized. They are strongly jointed, fragmented, brecciated and are 0.5 to 1 m thick, containmacroscopically visible pyrite and uranophane. Within the ENE-WSW shear zone, the quartz veins brecciate the microgranite and dolerite dikes. Some other quartz veins are trending NNW-SSE and N-S. Bostonite dikes invade two-mica granite along N-S and NNE-SSW structures. They are usually fine-grained, pale brown to deep red colors, fractured, jointed, sheeted, and range in thickness from 0.5 to 2 m . They are essentially composed of K-feldspar, plagioclase, little quartz and iron oxides set in a finely crystalline groundmass of K-feldspar microlites. They have U-contents from 4.1 to 25.4 ppm eU.
The Sela shear zone is clearly evidenced from its rugged topography by a sharp increase in the eU values as well as from a marked decrease of the K and eTh values. These characteristics result from multiple magmatic, tectonic and hydrothermal activities, confined to a wide elongated domain of average 20 m in width and 1.5 km [
Solid state nuclear track detectors (SSNTDs) have been recognized by IAEA as a standard method for estimation of radon, thoron and their daughter products in the environment. The detectors that are commonly used in environmental monitoring are generally made from cellulose nitrate (LR-115) and polycarbonates (CR-39). These Track Etch cups are placed in shallow holes (30 - 50 cm) and left undisturbed for one month to accumulate the tracks produced by the radon soil emanations. Track Etch detectors are responsive to the alpha radiation from radon (Rn-222) which originates from radium (Ra-226) in the uranium (U-238) decay chain as well as to thoron (Rn-220) which originates from radium (Ra-224) in the thorium (Th-232) decay chain. The track density is converted to radon concentration in the environment. The radon concentration was calculated through the following equation [
Track Etch detectors are responsive to the alpha radiation from radon (Rn-222) which originates from radium (Ra-226) in the uranium (U-238) decay chain as well as to Thoron (Rn-220) which originates from radium (Ra-224) in the thorium (Th-232) decay chain. Thus, if significant amounts of thorium are present in the area that is being explored, it can produce an unwanted thorium related signal when looking for uranium. In the present work the cups which have been used have been produced by ALGADE. They use a solid-state nuclear track detector type Kodak LR115R films. They have a water tight polyethylene membrane to avoid water entrances and which is used also as a thoron filter. This membrane decrease de rate of passage of throne into the cup (because of its short half-life) bu allows radon to pass into the cup. The radon concentration in the cup is not reduced significantly by this kind of filter.
The ground geophysical studies get information about the subsurface configuration of the shear structures controlling uranium mineralized zones. In studied area, Track Etch survey (60 cups) for radon gas were placed in shallow bore holes (30 - 65 cm deep) and undisturbed left for 1 - 1.5 month to accumulate the reading produced by the varying radon soil activities.
The ground gamma-ray spectrometric measurements were conducted using a Geophysica Brno GS-256 spectrometer having a 0.35 L sodium iodide (NaI) thallium activated detector. All the ground magnetic and VLF measurements were collected using the Scintrex proton magnetometer and ENVI-VLF. The data were generally recorded of 20 m spacing interval along each of the two studied profiles.
Twenty samples were selected from the host rocks two-mica granite of three drill cores from the El Sela shear zone. Minerals were investigated in thin polished and thick double-polished sections using optical microscope and scanning electron microscope (Hitachi S-4800, SCMEM, Henri Poincaré University, France). Minerals were analysed by electron microprobe (CAMECA SX 100, SCMEM, Henri Poincaré University, France) at 10 nA and at 20 kV, counting time 10 s for peak and 5 s for background. Natural albite, orthoclase, wollastonite, hematite, olivine and monazite were used as standards for Al (Kα), Si (Kα), Ca (Kα), Fe (Kα), Mg (Kα) and Yb (Lα), respectively; synthetic V, ZrO2, PbCrO4, UO2, MnTiO3, ThO2, MnTiO3, YPO4, CePO4, NdPO4, SmPO4, DyRu2Ge2, EuRu2Ge2, GdTiGe and ErNi2Si2 were used as standards for V (Kα), Zr (Lα), Pb (Mα), U (Mβ), Ti (Kα), Th (Mα), Mn (Kα), Y (Lα), Ce (Lα), Nd (Lα), Sm (Lα), Dy (Lα), Eu (Lα), Gd (Lα), Er (Lα), respectively. After agate mortar crushing, the rocks were analysed by ICP-AES and ICP-MS (SARM, CRPG, Nancy, France) for 11 major and 44 trace elements.
The three boreholes are composed mainly of two-mica granite. It is whitish to pale pink, buff, reddish brown, medium- to coarse-grained, highly fractured and jointed. Microscopically, it is composed essentially of K-feld- spar, quartz, plagioclase, biotite and muscovite. Monazite, pyrite, Zircon, galena, sphlerite, Nb-rutile, columbite, titanite, apatite, fluorite and uraninite are accessories, while sericite, chlorite, muscovite, epidote and kaolinite are alteration minerals.
K-feldspar is represented by orthoclase microperthite. It occurs as subhedral to anhedral prismatic crystals showing simple twinning and compressed patchy, string and flame perthitic intergrowths (
crystals poikilitically occur in perthite, plagioclase and biotite. Plagioclase of albite and oligoclase composition (An9-15) occurs as subhedral to euhedral tabular crystals. Biotite occurs as subhedral flakes, which are commonly altered to ferrichlorite (pennite) and/or muscovite along the crystal margins and cleavage planes (
Zircons occur as metamict, zoned, mostly euhedral crystals with prismatic a shape and bipyramidal terminations, associated with quartz, perthite, plagioclase and opaques (
gates or scattered grains as well as tiny inclusions in biotite and quartz. Uraninite filled micro-fractures in kaolintized and sericitized feldspars and generally surrounded by pyrite cubes (
The geochemical data have been used to determine the characteristics of granites enclosing the Sela shear zone and their uranium fertility. The uranium fertility of the granites depends essentially on the level of their U background concentration and the leache ability of the uranium bearing accessory minerals. Peraluminous, high-K and low Na and Ca contents and presence of two-mica are also good indicators of the U-fertility of granite rocks. Under certain conditions of alteration, the high-calc-alkaline (HKCA) granite can form uranium ore but generally with lesser tonnage than the peraluminous leucogranites [
El Sela two-mica granites have high SiO2, Al2O3, Na2O and K2O contents with the following average contents 76.5 wt.%, 12.95 wt.%, 3.9 wt.% and 4.3 wt.%, respectively. They are also poor in Fe2O3, CaO, MnO and MgO with average concentrations of 0.73 wt.%, 0.53 wt.%, 0.04 wt.% and 0.17 wt.%, respectively
S. No. | W1-1 | W1-2 | W1-3 | W1-4 | W1-5 | W1-6 | W1-7 | W1-8 | W2-1 | W2-2 | W2-3 | W2-4 | W2-5 | W2-6 | W2-7 | W2-8 | W2-9 | W3-1 | W3-2 | W3-3 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
depth m. | 20 | 24 | 35 | 53 | 55 | 59 | 62 | 63 | 1 | 4 | 10 | 17 | 26 | 35 | 37 | 42 | 44 | 12 | 30 | 43 |
Major oxides (wt.%) | ||||||||||||||||||||
SiO2 | 76.2 | 76.3 | 77.7 | 74.6 | 76.9 | 76.2 | 76.9 | 76 | 77.4 | 76.8 | 76.7 | 76.8 | 78 | 77.5 | 76.8 | 74.8 | 76.8 | 75.5 | 77 | 74.7 |
TiO2 | 0.13 | 0.13 | 0.13 | 0.10 | 0.12 | 0.10 | 0.09 | 0.13 | 0.10 | 0.10 | 0.10 | 0.14 | 0.10 | 0.14 | 0.12 | 0.16 | 0.14 | 0.13 | 0.13 | 0.09 |
Al2O3 | 13.3 | 13.3 | 12.5 | 12.6 | 12.8 | 13.7 | 12.7 | 13 | 12.9 | 13.3 | 13.2 | 13 | 12.6 | 12.3 | 13.1 | 13.1 | 12.8 | 12.7 | 12.5 | 13.7 |
Fe2O3 | 0.7 | 0.9 | 0.9 | 1.2 | 0.5 | 0.6 | 0.9 | 0.9 | 0.6 | 0.5 | 0.6 | 0.9 | 0.7 | 0.8 | 0.7 | 0.6 | 0.6 | 0.8 | 0.7 | 0.5 |
MnO | 0.05 | 0.06 | 0.04 | 0.10 | 0.02 | 0.03 | 0.08 | 0.06 | 0.01 | 0.01 | 0.01 | 0.01 | 0.01 | 0.01 | 0.03 | 0.02 | 0.03 | 0.09 | 0.08 | 0.06 |
MgO | 0.12 | 0.22 | 0.15 | 0.12 | 0.07 | 0.11 | 0.12 | 0.16 | 0.10 | 0.09 | 0.10 | 0.19 | 0.23 | 0.25 | 0.17 | 0.35 | 0.38 | 0.20 | 0.16 | 0.12 |
CaO | 0.5 | 0.3 | 0.2 | 0.9 | 0.2 | 0.4 | 0.7 | 0.8 | 0.4 | 0.4 | 0.4 | 0.5 | 0.3 | 0.3 | 0.4 | 1 | 0.4 | 1.1 | 0.7 | 0.7 |
Na2O | 4.4 | 3.8 | 4 | 4.1 | 4.1 | 4.5 | 4.2 | 4.3 | 4 | 4.4 | 4.1 | 4 | 3.2 | 3 | 4.1 | 2.8 | 2.6 | 4.1 | 4.3 | 4.3 |
K2O | 4.1 | 4.2 | 3.7 | 4.2 | 4.2 | 4.5 | 4.3 | 4.3 | 4.6 | 4.5 | 4.8 | 4.3 | 4 | 4.2 | 4.4 | 4.2 | 4.4 | 4 | 3.8 | 5 |
P2O5 | 0.1 | 0.1 | 0.1 | 0 | 0 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.2 | 0.1 | 0.1 | 0.1 | 0.2 | 0.2 | 0.1 | 0.1 | 0.1 |
IL | 0.8 | 1.5 | 0.9 | 1.6 | 1 | 1 | 1.1 | 1.1 | 0.7 | 0.7 | 0.7 | 1 | 1.9 | 2 | 1.1 | 3.1 | 2.8 | 1.4 | 1.2 | 0.9 |
Total | 100 | 101 | 100 | 100 | 100 | 101 | 101 | 101 | 101 | 101 | 101 | 101 | 101 | 101 | 101 | 100 | 101 | 100 | 101 | 100 |
Trace elements (ppm) | ||||||||||||||||||||
Be | 5.4 | 4.4 | 4.9 | 8.4 | 3.2 | 5.4 | 7.4 | 7.6 | 3.1 | 3.5 | 2.8 | 4.2 | 2.9 | 4.1 | 5.2 | 3.4 | 3.5 | 7.8 | 8.5 | 8.7 |
Sc | 4.9 | 5.1 | 5.2 | 6.8 | 3.9 | 5.1 | 6.7 | 7.7 | 3.4 | 2.6 | 2.6 | 4.1 | 2.3 | 3.8 | 4.1 | 3.8 | 3.6 | 8.4 | 7.7 | 6.2 |
Ti | 1.6 | 1.6 | 1.6 | 1.2 | 1.5 | 1.3 | 1.2 | 1.6 | 1.3 | 1.2 | 1.3 | 1.8 | 1.2 | 1.7 | 1.5 | 2 | 1.7 | 1.6 | 1.6 | 1.2 |
V | 9.7 | 8.7 | 9.1 | 5.8 | 6.3 | 5.6 | 4.4 | 5.8 | 5.2 | 5.1 | 3.5 | 8.2 | 3.6 | 7.9 | 6.6 | 8.2 | 6.8 | 8.2 | 6.7 | 5.5 |
Cr | 62.2 | 132 | 95 | 100 | 62.7 | 89 | 70.3 | 78.9 | 80.2 | 50.3 | 62.7 | 93 | 93 | 88 | 92 | 78.2 | 83 | 77.8 | 95 | 69 |
Mn | 0.8 | 0.8 | 0.6 | 1.4 | 0.2 | 0.4 | 1.1 | 0.9 | 0.1 | 0.1 | 0.1 | 0.2 | 0.2 | 0.1 | 0.4 | 0.3 | 0.4 | 1.3 | 1.1 | 0.8 |
Co | 0.8 | 1.5 | 1.4 | 1.8 | 0.7 | 0.9 | 1.1 | 1.1 | 0.6 | 0.8 | 0.7 | 1.1 | 0.9 | 0.8 | 1 | 0.9 | 0.9 | 1 | 0.9 | 0.7 |
Zn | 35.2 | 39.5 | 30 | 57.9 | 24.7 | 33.9 | 45.9 | 78 | 39.7 | 33 | 29.4 | 59 | 38.9 | 27.3 | 48.8 | 62.1 | 36.7 | 51.2 | 57.3 | 43.2 |
Ga | 24 | 24 | 23 | 26 | 21 | 25 | 25 | 27 | 21 | 21 | 22 | 23 | 20 | 21 | 25 | 23 | 23 | 25 | 26 | 30 |
Ge | 1.5 | 1.4 | 1.7 | 2.2 | 1.3 | 1.8 | 2.2 | 2.2 | 1.3 | 1.4 | 1.4 | 1.5 | 1.3 | 1.5 | 1.9 | 1.4 | 1.3 | 2 | 2.2 | 3 |
Rb | 248.8 | 275.5 | 244.6 | 427 | 211 | 280 | 412 | 394 | 195 | 184 | 206 | 188 | 174 | 204 | 267 | 196 | 198 | 364 | 357 | 464 |
Sr | 151 | 121 | 107 | 79 | 101 | 72 | 72 | 100 | 55 | 103 | 47 | 99 | 62 | 110 | 89 | 116 | 96 | 91 | 110 | 87 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Y | 7.2 | 6.7 | 6.9 | 4.8 | 5.1 | 4.3 | 4.9 | 5.3 | 11.3 | 4.2 | 3 | 6.4 | 3.4 | 5.9 | 5.8 | 19.9 | 5.4 | 5.4 | 7.2 | 5.7 |
Zr | 90.4 | 88.2 | 85.6 | 66.9 | 80.9 | 69.5 | 66.2 | 92.5 | 62.8 | 62.2 | 53.7 | 79.3 | 68.4 | 82 | 73 | 89 | 80 | 88 | 97 | 61 |
Nb | 13.7 | 13.3 | 14.8 | 16.4 | 9.5 | 13.2 | 16 | 22.9 | 7.2 | 5.7 | 5.3 | 6.9 | 5.3 | 8.9 | 14.5 | 9.3 | 7.1 | 22.3 | 21.1 | 31.4 |
Mo | 0.8 | 2.7 | 1.3 | 2.6 | 0.9 | 2 | 2.9 | 3.4 | 1.2 | 0.8 | 1 | 1.6 | 1.3 | 1.2 | 1.3 | 1.1 | 1.1 | 3.7 | 5.3 | 1.3 |
Sn | 2.1 | 2.6 | 2.2 | 5.8 | 1.5 | 1.6 | 2.3 | 2.5 | 1.1 | 0.9 | 1.1 | 1.5 | 0.7 | 1.4 | 1.5 | 1.7 | 1.7 | 2.8 | 2.7 | 2.1 |
Cs | 5.9 | 6.3 | 4.6 | 11.5 | 4 | 6.9 | 10.2 | 10.9 | 4.5 | 5.2 | 4.4 | 7.5 | 2.9 | 3.8 | 6.6 | 4.8 | 5 | 10.2 | 10.1 | 11.7 |
Ba | 351 | 296 | 222 | 137 | 263 | 155 | 132 | 173 | 147 | 261 | 83 | 198 | 94 | 179 | 167 | 204 | 213 | 154 | 168 | 167 |
Hf | 4.2 | 3.9 | 4.4 | 3.5 | 3.3 | 3.3 | 3.6 | 4.7 | 2.7 | 2.8 | 2.2 | 3 | 2.8 | 3.5 | 3.3 | 3.5 | 3.4 | 4.4 | 4.7 | 3.6 |
Ta | 1.7 | 1.6 | 1.8 | 1.8 | 1.1 | 1.5 | 1.8 | 2.2 | 0.8 | 0.5 | 0.5 | 0.9 | 0.3 | 0.9 | 1.7 | 1 | 0.7 | 2.1 | 2.2 | 3.9 |
W | 3.7 | 12.9 | 10.6 | 6.4 | 4.3 | 5.7 | 4.5 | 5.1 | 5.5 | 3.3 | 4.6 | 6.8 | 6.2 | 6.2 | 6 | 5.9 | 5.7 | 5.4 | 6.8 | 4.5 |
Pb | 27.4 | 23.9 | 30.1 | 36.3 | 18.3 | 21.8 | 43 | 32.4 | 17.9 | 16.6 | 14.9 | 19 | 20.5 | 13.8 | 25.7 | 22 | 21.8 | 34.8 | 67 | 50 |
Th | 18.3 | 18.1 | 16.3 | 22.5 | 17.3 | 19.9 | 23.2 | 29 | 21 | 13 | 23 | 17 | 24 | 18 | 18 | 20 | 16 | 28 | 29 | 19.6 |
U | 6 | 7.8 | 8.1 | 15 | 4.1 | 9.5 | 18 | 33 | 5.8 | 3.2 | 3.4 | 4.7 | 3.9 | 4.4 | 9.1 | 7.5 | 3.9 | 15 | 23 | 25 |
REE (ppm) | ||||||||||||||||||||
La | 14.7 | 15.1 | 12.9 | 13 | 12.5 | 13.4 | 14.8 | 21 | 17 | 13.4 | 17.4 | 16.3 | 12.4 | 19.8 | 15.7 | 22.9 | 17.8 | 18.5 | 20.1 | 14 |
Ce | 29.2 | 29.3 | 27.8 | 18.6 | 20.9 | 18.3 | 22 | 29.5 | 27.7 | 21.8 | 25.2 | 25.5 | 20.3 | 26.6 | 25.1 | 39.5 | 30.4 | 26.6 | 27.9 | 20 |
Pr | 2.9 | 2.8 | 2.4 | 1.5 | 2.1 | 2 | 1.8 | 2.2 | 3 | 2.2 | 2.3 | 2.5 | 1.9 | 3.2 | 2.4 | 3.8 | 2.9 | 2.1 | 2.1 | 1.6 |
Nd | 10.6 | 9.5 | 8.1 | 4.6 | 7.4 | 6.5 | 5.8 | 6.7 | 10.4 | 7.8 | 7.5 | 8.8 | 6.3 | 11.5 | 8.5 | 13.2 | 10.2 | 6.5 | 6.5 | 4.9 |
Sm | 1.7 | 1.5 | 1.3 | 0.7 | 1.2 | 0.9 | 0.9 | 1 | 1.7 | 1.3 | 0.9 | 1.4 | 0.9 | 1.8 | 1.4 | 2.5 | 1.7 | 0.9 | 1 | 0.8 |
Eu | 0.3 | 0.2 | 0.2 | 0.1 | 0.2 | 0.2 | 0.1 | 0.2 | 0.3 | 0.2 | 0.2 | 0.3 | 0.2 | 0.3 | 0.2 | 0.3 | 0.3 | 0.2 | 0.2 | 0.2 |
Gd | 1.3 | 1.1 | 1 | 0.6 | 0.9 | 0.6 | 0.7 | 0.7 | 1.2 | 0.9 | 0.7 | 1 | 0.7 | 1.2 | 1.1 | 2 | 1.2 | 0.7 | 0.8 | 0.6 |
Tb | 0.2 | 0.2 | 0.2 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.2 | 0.1 | 0.1 | 0.2 | 0.1 | 0.2 | 0.2 | 0.4 | 0.2 | 0.1 | 0.1 | 0.1 |
Dy | 0.9 | 0.9 | 0.9 | 0.5 | 0.7 | 0.6 | 0.5 | 0.6 | 1.8 | 0.6 | 0.5 | 1 | 0.5 | 0.9 | 0.8 | 3.2 | 0.9 | 0.6 | 0.9 | 0.7 |
Ho | 0.2 | 0.2 | 0.2 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.4 | 0.1 | 0.1 | 0.2 | 0.1 | 0.2 | 0.2 | 0.7 | 0.2 | 0.1 | 0.2 | 0.2 |
Er | 0.6 | 0.6 | 0.6 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 | 1.6 | 0.4 | 0.3 | 0.7 | 0.3 | 0.5 | 0.6 | 2.9 | 0.5 | 0.4 | 0.7 | 0.6 |
Tm | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.3 | 0.1 | 0.1 | 0.2 | 0.1 | 0.1 | 0.1 | 0.6 | 0.1 | 0.1 | 0.2 | 0.1 |
Yb | 0.9 | 0.8 | 0.9 | 0.7 | 0.6 | 0.7 | 0.6 | 0.8 | 2.7 | 0.5 | 0.4 | 1.2 | 0.5 | 0.7 | 0.9 | 5 | 0.6 | 0.8 | 1.3 | 1.3 |
Lu | 0.1 | 0.1 | 0.2 | 0.2 | 0.1 | 0.1 | 0.1 | 0.2 | 0.4 | 0.1 | 0.1 | 0.2 | 0.1 | 0.1 | 0.2 | 0.8 | 0.1 | 0.2 | 0.2 | 0.3 |
Parameters and ratios | ||||||||||||||||||||
P | −64 | −39 | −54 | −59 | −46 | −57 | −56 | −62 | −38 | −53 | −37 | −46 | −23 | −13 | −46 | −19 | 3 | −67 | −70 | −45 |
Q | 188 | 208 | 222 | 182 | 203 | 178 | 192 | 182 | 198 | 184 | 187 | 200 | 241 | 241 | 196 | 224 | 244 | 189 | 200 | 162 |
B | 9.0 | 12.8 | 11.0 | 11.8 | 6.4 | 7.8 | 9.8 | 11.3 | 7.5 | 6.6 | 7.5 | 12.1 | 11.4 | 13.0 | 10.1 | 14.5 | 15.0 | 11.6 | 10.0 | 7.3 |
A | 13.8 | 38.1 | 30.2 | −6.7 | 22.2 | 13.4 | −3.0 | −3.9 | 11.8 | 8.8 | 10.2 | 16.5 | 48.0 | 44.3 | 16.7 | 41.5 | 59.2 | −7.6 | 0.5 | −1.5 |
Th/U | 3.1 | 2.3 | 2.0 | 1.5 | 4.2 | 2.1 | 1.3 | 0.9 | 3.6 | 4.1 | 6.8 | 3.6 | 6.2 | 4.1 | 2.0 | 2.7 | 4.1 | 1.9 | 1.3 | 0.8 |
Rb/Sr | 1.6 | 2.3 | 2.3 | 5.4 | 2.1 | 3.9 | 5.7 | 3.9 | 3.5 | 1.8 | 4.4 | 1.9 | 2.8 | 1.9 | 3.0 | 1.7 | 2.1 | 4.0 | 3.2 | 5.3 |
Nb/Ta | 8.1 | 8.3 | 8.2 | 9.1 | 8.6 | 8.8 | 8.9 | 10.4 | 9 | 11.4 | 10.6 | 7.7 | 17.7 | 9.9 | 8.5 | 9.3 | 10.1 | 10.6 | 9.6 | 8.1 |
Zr/Hf | 21.5 | 22.6 | 19.5 | 19.1 | 24.5 | 21.1 | 18.4 | 19.7 | 23.3 | 22.2 | 24.4 | 26.4 | 24.4 | 23.4 | 22.1 | 25.4 | 23.5 | 20.0 | 20.6 | 16.9 |
The peraluminosity is calculated as the difference between the total amount of Al present in the rock and the amount of Al bound to the feldspars: A = Al – (Na + K + 2Ca), calculated in cations. This index indicates the excess or the deficiency of Al with respect to the quantity needed to make the feldspars. The granites have compositions varying from slightly metaluminous (A = −7) toperaluminous (A = 62). The peraluminous composi- tions correspond mineralogically to the presence of Al-rich biotite and small amounts of muscovite. The four most peraluminous samples (W2-5, 6, 8 and 9) present the lowest Na contents (3.2 to 2.6 wt% Na2O, instead of more than 4 wt% for the other samples) and the highest ignition losses (1.9 to 3.1 wt% instead of about 1 wt% for the other samples).
These features indicate an argilic alteration of the plagioclase in these samples. The metaluminous samples tend to have the highest Ca contents (0.7 to 1.1 wt% CaO), without a corresponding increase of the ignition loss indicating the presence of Ca silicates and the absence of a significant carbonate contribution (
The granites of the three drill holes tend to define three distinct magmas batches in the A-B and Q-P diagrams (
The compositions and the global trends defined in the A-B and Q-P diagram (
pyroxenes), and possible assimilation of peraluminous crustal material during their ascent, and/or incipient alteration of the feldspars in K-micas or clay minerals.
The granitesfrom the El Sela shear zone areatend to been riched in most large ion lithophile elements (LILE; Ba, Rb, Sr) and high field strength elements (HFSE; Y, Zr and Nb)
In the Nb versus Sn diagram (
In the diagram Zr versus Hf two groups of granites (one for most samples from W2 and another with the samples from W1 and W3) are well defined with distinct Zr/Hf ratios (
Nb and Ta are very well correlated (
The concentrations of trace elements are normalized to the primitive mantle [
The El Sela granite has variable total REE contents: 44 to 98 ppm in samples W1-6 and W2-8 respectively (
strongly reverse HREE fractionation, indicating the abundance of a HREE-rich mineral, which may correspond to xenotime. The negative Eu suggests that plagioclase was an early fractionating phase.
Scanning electron microscope (SEM) and electron microprobe analyses (EMPA) were used to identify the nature of the sulfides and Nb-Ta-, Zr-Hf-, REE-, Th-, U-bearing minerals in the e the El Sela granite (
Pyrite, chalcopyrite, arsenopyrite, galena, and sphalerite, occur as disseminations and fracture-fillings in mineralized smoky and red jasperoid veins, dolerite and microgranite dikes, in the El Sela graniteas illustrated by Fig- ure 11(a). Magnetite, hematite, illmenite, rutile and apatite are also spatially associated with the sulfide minerals. Pyrite (FeS2) is the most common sulfide mineral which occurs as well developed octahedral crystals.
Pyrite is preserved in the samples from the drillings and seems to control the deposition of uraninite, branne-
S. No. | W3-3 -C3 | W3-2 -C2 | W1-7 C10-4 | W1-4 C1-2 | W2-5 -C3 | W2-9 -C2 | W1-4 C4-1 | W1-4 C4-2 | W1-7 C10-3 | W2-5 -C3 | W2-9 -C10 | W3-3 -C4 | W3-3 -C4 | W3-3 -C4 | W1-7 -C6-2 | W1-7 -C6-3 | W3-3 -C3 | ||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
depth m. | 43 | 30 | 62 | 53 | 26 | 44 | 53 | 53 | 62 | 26 | 44 | 43 | 43 | 43 | 62 | 62 | 43 | ||
oxides | Beta-fite | rutile | Zircon | REE-rich uranothorite | columbite | ||||||||||||||
SiO2 | 1.56 | 0 | 0.5 | 0.56 | 0.73 | 4.6 | 30.4 | 26.6 | 32.4 | 29.1 | 32.3 | 29.5 | 27.7 | 28.8 | 19.0 | 11.4 | 0.09 | ||
P2O5 | 0.05 | 0 | 0 | 0 | 0 | 0 | 0.43 | 0.85 | 0.42 | 0.56 | 0.45 | 0.3 | 0.71 | 0.44 | 1.04 | 1.1 | 0 | ||
SO2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0.01 | 0 | 0 | 0 | 0.16 | 0 | 0 | ||
CaO | 2 | 0.34 | 0.18 | 0.29 | 0.04 | 0.2 | 0.85 | 1.48 | 0.1 | 0.44 | 0.02 | 0.6 | 1.21 | 0.68 | 7.81 | 7.7 | 0.14 | ||
TiO2 | 46.3 | 85.8 | 64.1 | 90.1 | 92.7 | 82.3 | 0.1 | 0.1 | 0 | 0.13 | 0 | 0 | 0.08 | 0 | 0.15 | 0.02 | 11 | ||
MnO | 0.24 | 0.05 | 1.05 | 0.08 | 0.05 | 0.02 | 0.63 | 0.38 | 0.07 | 0.1 | 0 | 0.49 | 0.36 | 0.46 | 0.08 | 0.03 | 9.76 | ||
FeO | 8.48 | 4.4 | 21.6 | 1.47 | 0.39 | 5.78 | 1.2 | 0.87 | 0.22 | 2.5 | 0.03 | 1.41 | 1.26 | 1.53 | 1.89 | 0.13 | 7.6 | ||
Y2O3 | 0.1 | 0.04 | 0 | 0 | 0 | 0.03 | 0 | 0.89 | 0 | 0 | 0 | 0 | 0.44 | 0 | 1.11 | 1.58 | 0.84 | ||
ZrO2 | 0.64 | 0.04 | 0.07 | 0.15 | 0 | 0.03 | 59.9 | 54.6 | 63.9 | 59.9 | 66.0 | 59.5 | 49.3 | 60.4 | 2.84 | 0 | 0.55 | ||
Nb2O5 | 22.8 | 7.56 | 1.61 | 1.18 | 0.51 | 0.94 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0.28 | 0.04 | 62.3 | ||
SnO | 0.08 | 0.3 | 0 | 0 | 0 | 0 | 0 | 0.01 | 0 | 0 | 0.01 | 0 | 0 | 0 | 0 | 0 | 0.15 | ||
La2O3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0.02 | 0 | 0 | 0 | 0 | 0.02 | 4.51 | 4.02 | 0 | ||
Ce2O3 | 0.15 | 0.26 | 0.2 | 0.28 | 0.27 | 0.27 | 0 | 0.04 | 0 | 0 | 0.01 | 0 | 0 | 0.08 | 7.74 | 7.3 | 0 | ||
Nd2O3 | 0.08 | 0 | 0.03 | 0 | 0 | 0 | 0.01 | 0.13 | 0.02 | 0 | 0.12 | 0 | 0.15 | 0.07 | 2.24 | 2.16 | 0.03 | ||
Yb2O3 | 0.08 | 0 | 0 | 0 | 0 | 0.02 | 0 | 0.4 | 0.12 | 0.01 | 0 | 0.16 | 0.43 | 0 | 0.02 | 0 | 0.28 | ||
HfO2 | 0.55 | 1.22 | 0.9 | 1.23 | 1.33 | 1.27 | 2.24 | 3.09 | 1.68 | 1.49 | 1.26 | 2.2 | 10.9 | 1.7 | 0 | 0 | 0.1 | ||
Ta2O5 | 2.7 | 0.33 | 0.03 | 0.03 | 0 | 0.05 | 0.28 | 0.13 | 0.34 | 0.22 | 0.33 | 0.37 | 0.56 | 0.29 | 0 | 0 | 2.91 | ||
PbO | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0.11 | 0.02 | 0 | ||
ZnO | n.d | n.d | 0.02 | 0.06 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | n.d | n.d | n.d | 0 | 0 | n.d | ||
Al2O3 | n.d | n.d | 0.26 | 0.43 | 0.24 | 1.3 | 0.21 | 0.56 | 0.03 | 0.1 | 0 | n.d | n.d | n.d | 7.52 | 0.66 | n.d | ||
ThO2 | 5.8 | 0 | 0.06 | 0.03 | 0 | 0.04 | 0.04 | 0.54 | 0.03 | 0.6 | 0 | 0.27 | 0.68 | 1.22 | 25.9 | 42.2 | 0.2 | ||
UO2 | 1.57 | 0 | 0.27 | 1.21 | 0.01 | 0 | 1 | 1.57 | 0 | 0.79 | 0.17 | 1.33 | 2.24 | 1.61 | 1.3 | 1.19 | 0.75 | ||
Total | 93.** | 100.** | 91 | 97 | 96 | 97 | 97 | 92 | 99 | 96 | 101 | 96 | 96 | 97 | 84 | 80 | 97 | ||
rite, pitchblende and coffinite at the margin of the crystals. In the El Sela shear zonethe cavities left after pyrite dissolution are by uranophane and autunite because of the alteration of the pyrite and primaru U minerals by meteoric fluids [
Sulfides are more effective reductant because sulfur can act as reducing agent where one mole of pyrite can reduce six more uranium than Fe+2 [
Rutile, fluorite, zircon, monazite, LREE-carbonates, columbite and betafite have been also identified by SEM and EMPA analyses.
Rutile is common mineral in most samples from the El Sela granite. It occurs as angular to subangular, elon-
S. No. | W2-9 -C10 | W1-7 -C10-2 | W2-5 -C3 | W2-5 -C3 | W2-5 -C3 | W2-9 -C10 | W2-9 -C10 | W1-7 -C6-1 | W1-7 -C10-1 | W3-3 -C4 | W3-2 -C1 | W3-2 -C1 | W3-2 -C2 | W3-2 -C3 | W3-2 -C3 | W3-2 -C3 | W3-2 -C3 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
depth m. | 44 | 62 | 26 | 26 | 26 | 44 | 44 | 62 | 62 | 43 | 30 | 30 | 30 | 30 | 30 | 30 | 30 |
oxides | thorite | phosphothorite | uranothorite | brannerite | |||||||||||||
SiO2 | 33.73 | 11.5 | 14.2 | 16.3 | 8.77 | 21.1 | 28.7 | 17.9 | 16.8 | 20.8 | 6.8 | 6.08 | 13.35 | 3.02 | 11.4 | 5.48 | 2.85 |
P2O5 | 1.48 | 1.51 | 15.11 | 4.84 | 10.28 | 8.68 | 10.61 | 0.47 | 0.28 | 1.85 | 0.14 | 0.03 | 0.29 | 0.18 | 0.61 | 0.22 | 0.07 |
SO2 | 0.07 | 0.08 | 0.34 | 0.05 | 0.21 | 0.34 | 0.08 | 0.07 | 0.08 | 0.05 | 7.76 | 0 | 0 | 0 | 0 | 0 | 0 |
CaO | 1.96 | 5.29 | 7.85 | 2.61 | 4.84 | 8.82 | 12.95 | 1.52 | 1.73 | 2.63 | 2.42 | 3 | 3.42 | 3.19 | 1.51 | 4.69 | 1.75 |
TiO2 | 0.04 | 0.1 | 0 | 0 | 0.01 | 0 | 0 | 0 | 0.04 | 0.26 | 22.9 | 31.3 | 17.2 | 31.4 | 41.6 | 22.7 | 62.8 |
MnO | 0.07 | 0.02 | 0 | 0.05 | 0.01 | 0.03 | 0.01 | 0.01 | 0 | 0.09 | 0.19 | 0.72 | 0.13 | 0.35 | 0.07 | 0.69 | 0.34 |
FeO | 3.12 | 0.67 | 0.57 | 0.59 | 0.6 | 0.55 | 0.49 | 0.11 | 0.06 | 1.18 | 7.25 | 2.07 | 0.78 | 2.48 | 2.17 | 0.9 | 0.99 |
Y2O3 | 0.2 | 1.22 | 0.88 | 1.97 | 3 | 1.53 | 1.24 | 0.77 | 0.06 | 2.23 | 0 | 1.23 | 1.56 | 0 | 1.44 | 0 | 0 |
ZrO2 | 0.6 | 1.45 | 0.07 | 0 | 0 | 1.69 | 2 | 0 | 0.26 | 11.6 | 2.72 | 1.37 | 9.32 | 1.63 | 3.96 | 1.66 | 0.64 |
Nb2O5 | 0.19 | 0.09 | 0 | 0.15 | 0 | 0.01 | 0 | 0.09 | 0 | 0.3 | 2.21 | 3.54 | 0.3 | 1.59 | 0.74 | 1.67 | 0.96 |
La2O3 | 0.01 | 0.28 | 0.28 | 0.04 | 0.06 | 0.01 | 0.03 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Ce2O3 | 0 | 0.56 | 0.03 | 0.22 | 0.28 | 0.09 | 0.11 | 0.11 | 0.04 | 0.15 | 0.17 | 0.53 | 0.21 | 0.14 | 0.23 | 0.15 | 0.25 |
Nd2O3 | 0.38 | 0.47 | 0.52 | 0.82 | 0.27 | 0.66 | 0.29 | 0.24 | 0.13 | 0.31 | 0.01 | 0.43 | 0.08 | 0.07 | 0.08 | 0 | 0.07 |
Yb2O3 | 0.03 | 0 | 0.23 | 0 | 0.09 | 0.19 | 0 | 0 | 0 | 0.36 | 0.09 | 0.37 | 0.21 | 0 | 0.21 | 0 | 0 |
HfO2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0.03 |
Ta2O5 | 0.06 | 0 | 0.03 | 0 | 0 | 0 | 0.07 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
PbO | 0.12 | 0.17 | 0.09 | 0.09 | 0.13 | 0.09 | 0 | 0.31 | 0.75 | 0.12 | 0 | 0 | 0 | 0.63 | 0 | 0 | 0 |
ZnO | 0 | 0 | 0 | 0 | 0 | 0 | 0.02 | 0 | 0.02 | n.d | n.d | n.d | n.d | 0 | 0 | 0 | 0 |
Al2O3 | 3.23 | 0.16 | 1.62 | 0.25 | 0.49 | 2.85 | 6.34 | 0.11 | 0.03 | n.d | n.d | n.d | n.d | n.d | 0.44 | 0.22 | 0.46 |
ThO2 | 48.1 | 63.5 | 54.4 | 62.7 | 61.9 | 45.1 | 27.5 | 52.0 | 53.5 | 33.0 | 1.4 | 2.19 | 1.28 | 0.66 | 0.57 | 0.59 | 0.18 |
UO2 | 0 | 0 | 0.22 | 0.84 | 2.1 | 0.19 | 0.45 | 18.4 | 14.5 | 11.4 | 36.4 | 39.0 | 39.8 | 36.8 | 26.3 | 49.1 | 15.7 |
Total | 93.4 | 87.1 | 96.4 | 91.5 | 93.0 | 91.9 | 90.9 | 92.1 | 88.4 | 86.5 | 90.5 | 91.9 | 88.5 | 82.1 | 91.4 | 88.1 | 87.1 |
S. No. | W3-2 -C10 | W3-2 -C10 | W1-7 -C8-3 | W1-4 -C1-3 | W3-2 -C5 | W3-2 -C5 | W3-3 -C2 | W3-3 -C2 | W1-4 -C2-1 | W1-4 -C2-4 | W3-3 -C4 | W3-3 -C4 | W3-3 -C6 | W3-3 -C6 | W3-3 -C6 | W3-3 -C6 | W3-3 -C6 |
depth m. | 30 | 30 | 62 | 53 | 30 | 30 | 53 | 53 | 53 | 53 | 43 | 43 | 43 | 43 | 43 | 43 | 43 |
oxides | brannerite | coffinite | uraninite | pitchblende | |||||||||||||
SiO2 | 6.86 | 5.23 | 1.8 | 25.1 | 18.6 | 12.0 | 16.0 | 22.2 | 6.89 | 3.06 | 9.45 | 13.55 | 4.08 | 4.69 | 3.56 | 4.31 | 1.05 |
P2O5 | 0.03 | 0.11 | 0.08 | 0.06 | 1.16 | 2.28 | 0.66 | 0.72 | 0.25 | 0.17 | 1.06 | 1.56 | 0.15 | 0.1 | 0.11 | 0.43 | 0.13 |
SO2 | 0 | 0 | 0 | 0 | 1.28 | 0.41 | 0.25 | 3.41 | 0.09 | 1.09 | 1.88 | 0.02 | 0 | 1.3 | 0.04 | 0.06 | 6.68 |
CaO | 1.96 | 2 | 2.14 | 2.17 | 2.15 | 1.84 | 7.66 | 2.63 | 3.95 | 7.56 | 6.59 | 3.78 | 4.44 | 4.18 | 5.28 | 3.36 | 3.36 |
TiO2 | 28.2 | 41.4 | 45.1 | 3 | 0.26 | 0.28 | 0.2 | 0.17 | 1.47 | 1.1 | 0.63 | 2.4 | 0 | 0 | 0 | 0 | 0 |
MnO | 0.09 | 0.19 | 0.49 | 0.36 | 0.01 | 0 | 1.62 | 0.14 | 0.81 | 0.69 | 0.44 | 0.44 | 0.12 | 0.04 | 0.17 | 0.08 | 0.13 |
FeO | 1.6 | 1.14 | 2.1 | 3.04 | 2.28 | 1.06 | 4.59 | 3.36 | 11.65 | 4.69 | 3.66 | 1.02 | 1.92 | 3.98 | 1.58 | 0.47 | 6.51 |
Y2O3 | 0.04 | 0 | 0 | 0 | 3.34 | 3.77 | 1.53 | 1.7 | 0 | 0 | 2.02 | 2.96 | 0.06 | 0.08 | 0.14 | 0.96 | 0.22 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
ZrO2 | 1.7 | 0.87 | 1.65 | 2.92 | 3 | 3.13 | 6.34 | 5.91 | 8.29 | 4.34 | 7.14 | 8.65 | 0.01 | 0 | 0.16 | 0.25 | 0.05 |
Nb2O5 | 3.99 | 4.41 | 1 | 0.83 | 0.13 | 0.1 | 1.82 | 1.51 | 1.99 | 2.08 | 2.29 | 2.12 | 0 | 0.03 | 0.34 | 0.48 | 0.08 |
SnO | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
La2O3 | 0 | 0 | 0 | 0 | 0.07 | 0.02 | 0.03 | 0 | 0 | 0.02 | 0.06 | 0 | 0.1 | 0.13 | 0.13 | 0.09 | 0.07 |
Ce2O3 | 0.3 | 0.28 | 0.45 | 0.13 | 0.28 | 0.26 | 0.17 | 0.09 | 0.29 | 0.21 | 0.3 | 0.26 | 0.5 | 0.5 | 0.45 | 0.54 | 0.52 |
Nd2O3 | 0.03 | 0.19 | 0.21 | 0 | 0.26 | 0.24 | 0.2 | 0 | 0.02 | 0 | 0.21 | 0.36 | 0.21 | 0.04 | 0.23 | 0.34 | 0.16 |
Yb2O3 | 0.01 | 0 | 0.1 | 0 | 0.62 | 0.47 | 0.44 | 0.36 | 0.03 | 0 | 0.27 | 0.44 | 0 | 0 | 0.07 | 0.24 | 0 |
HfO2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Ta2O5 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
PbO | 0 | 0 | 0 | 0.92 | 0 | 0 | 0.34 | 0.36 | 2.13 | 1.16 | 2.35 | 0 | 0.73 | 0.69 | 0.38 | 0.15 | 0.47 |
ZnO | 0.05 | 0 | 0 | 0 | 0 | 0 | n.d | n.d | 0 | 0 | n.d | n.d | n.d | n.d | n.d | n.d | n.d |
Al2O3 | 0.24 | 0.21 | 0.64 | 12.13 | 1.99 | 0.49 | n.d | n.d | 1.19 | 0.38 | n.d | n.d | n.d | n.d | n.d | n.d | n.d |
ThO2 | 1.9 | 2.17 | 0.2 | 1.1 | 1.31 | 2.33 | 1.29 | 0.71 | 2.97 | 1.65 | 1.1 | 2.37 | 0 | 0 | 0 | 0.03 | 0 |
UO2 | 43.7 | 33.4 | 36.7 | 34.1 | 56.8 | 61.7 | 32.6 | 27.8 | 47.2 | 63.0 | 51.2 | 49.2 | 76.8 | 77.8 | 82.2 | 78.8 | 80.4 |
Total | 90.7 | 91.7 | 92.6 | 85.8 | 93.5 | 90.4 | 75.8 | 71.1 | 89.2 | 91.2 | 90.5 | 89.1 | 89.2 | 93.6 | 94.8 | 90.7 | 99.9 |
Borehole No. | W1 | W2 | W3 |
---|---|---|---|
Rock types | · 0 - 12 m: wadi deposits. · 12 - 63 m: biotite ± muscovite granite. | · 0 - 44 m: biotite ± muscovite granite. | · 0 - 43 m: biotite ± muscovitegranite. |
Hydrothermal alteration | biotite highly altered into ferrichlorite pennite), muscovitization, albitization, sericitization, kaolinization and argillization. | ||
Sulfides | Pyrite, arsenopyrite, chalcopyrite, galena and sphalerite | ||
Nb-Ti-, Zr-Hf-, F-minerals | Columbite, betafite, rutile, zircon | Columbite, rutile, zircon | Columbite, betafite, rutile, zircon, fluorite |
REE-minerals | Allanite, LREE carbonate | Allanite | Allanite |
Th-minerals | Thorite | Thorite, phosphothorite with apatite | Thorite |
U-Th-minerals | uranothorite | ||
U-minerals | · Brannerite, coffinite, uraninite and pitchblende · W1-4 and W1-7 samples at depth 53 and 62 m , respectively. | · Brannerite, coffinite, uraninite and pitchblende · W3-2 and W3-3 samples at depth 30 and 43 m , respectively. |
gated, cylinder and -like grains of reddish brown to blackish brown colors associated with zircon, fluorite, monazite, uranothorite, and uraninite (Figures 11(b)-(d)). The EMPA analyses indicate that the rutile has 0.39 - 8.48 wt.% Fe2O3, 0.51 to 22.78 Nb2O3 and up to 2.7 wt.% Ta, 5.8 wt.% Th, and 1.57 wt.% U (
Zircon is generally included as idiomorphic crystals (
(1.26 < HfO2 < 10.87 wt.%), UO2 (up to 2.23 wt.%) and ThO2 up to (up to 1.22 wt.%). Similar Hf enrichment has been observed in Rare Metal Granites such as at Cinovec with 3 to 4 wt.% HfO2 [
Uranothorite crystals occur as brownish red and orange crystals, isotropic because of their metamictisation. SiO2 and ThO2 (25.93 - 42.2 wt.%) concentrations are quite variable and analytical total are low due to the strong metamictization of the crystals (
Columbite [(Fe, Mn)(Nb, Ta, Ti)O4] occurs as dark gray to black color, flattened, prismatic, massive subhedral to euhedral crystals (
Betafite (Ca, U)2(Ti, Nb, Ta)2O6(OH) is detected under the SEM-BSE image (
22.5, 26.95 and 31.9 wt.% with lower content in W3-3-C3 1.14 wt.%.
Thorite, phosphothorite, uranothorite, brannerite, coffinite, uraninite and pitchblende have been identified by SEM and EPMA analyses (
Uranothorite (U, Th)SiO4 is interstitially associated with iron oxides and/or found as numerous subhedral to anhedral inclusions in zircon. The EPMA analyses indicate that UO2 contents may reach 18.4 wt% and Y2O3 2.23 wt% composition of zircon up to 11.6 wt.%
Ti-U oxides are the most U minerals in the El Sela granites (
Uranium oxides occur in granites samples (W3-1, -2, -3 and W1-4) as minute crystals filling micro-fractures and/or associated with pyrite, rutile and fluorite or with other U-minerals such as brannerite (
EMPA analyses show the major elements are SiO2 vary from (11.98 to 25.13 wt.%) and UO2 vary from (27.48 to 61.73 wt.%) correspond to the composition of coffinite
EPMA analyses show a wide variation of the pitchblende composition which exhibit very weak zoning and occurs as botryoidally form or vein surrounded metallic sulfides especially pyrite (
The granite from the El Sela shear zone area are enriched in the lighter isovalents Nb and Zr relatively to the heavier isovalents Ta, Hf elements. The lower Zr/Hf ratio is in accordance with the presence of Hf-rich zircons (3 to 4 wt.% HfO2) (
Uranium exploration has been aided by the identification of radon anomalies near the surface [
daughter products or with normal surface geochemical techniques, which analyze uranium or radium. Radon, a relatively mobile gas, can originate from deeply buried deposits and gaseous or aqueous movement to the surface can transport it where it can be readily detected [
Shear zones, faults and joints are the main conducts for radon emanations to the surface especially for structure controlled deposits. Radon anomalies can be detected over deeply buried uranium mineralization. At the present time it is known that ore bodies at depths of 100 m to 200 m can generally be detected and that depth of up to 300 meters are possible in very favorable circumstances [
Obviously, the cluster distribution map of radon shows that the radon activity varies along shear zone over a wide range that lies between 960 Bq/m3 to 300,300 Bq/m3 (
The western part of the study area is occupied with an anomaly covering an area of medium intensity between the two previous two anomalies but the radon activity is up to half their values which is approximately 150,000 Bq/m3. In the middle of the study area there is a small radon anomaly reaches about 200,000 Bq/m3.
The variations of K, eU and eTh concentrations and their ratios, beside the VLF-EM and magnetic data are illustrated along two cross sections nearly perpendicular to the Sela shear zone as shown in
The VLF-EM profiles (
magnetic anomaly for the first profile passing through the W1 and W3 drill holes, probably caused by the lamprophyre which may have high magnetite content. Immediately to the East of the magnetic high, there is a sharp magnetite low which may correspond to a strongly oxidized zone at the southern margin of the Sela Shear Zone.
In the second profile passing through the drill hole W2, above the Sela shear zone, the conductivity high correspond to the opposite of the preceding profile to a low in the total magnetic field, narrower than the conductivity high. Such a low magnetic field should correspond to a zone were the Fe-Ti bearing minerals have been oxidized or pyritized. A similar total magnetic field low is observed to the south of the Sela shear zone covered by sand, but is not associated with a conductivity high this indicate the causative body is located at depth more than 30m where the sense detection of VLF technique. The magnetic field over the granitic rocks and the wadi sediments is characterized by low magnetic signatures.
The El Sela granite complex is composed of biotite and biotite ± muscovite granites. The three samples of drill holes have only intersected the biotite ± muscovite granites. Geochemically, the El Sela granites are very leucocratic, meta- to slightly per-aluminous and enriched in large ion lithophile elements (LILE: Ba, Rb and Sr), high field strength elements (HFSE: Y, Zr and Nb), light rare earth elements (LREE) mostly hosted in allanite, Th mostly hosted in uranothorite and allanite and uranium partly hosted in magmatic Th-bearing uraninite, but relatively poor in Ta, Sn, Be and heavy rare earth elements (HREE). Most of them have a negative Eu anomaly. Their characteristics correspond to those of A2-type granites (high-K cac-alkaline granites).
During most geological processes the chondritic ratios of the isovalent elements Nb/Ta (34.2 ± 0.3) and Zr/Hf (17.6 ± 1) are constant [
The Th/U ratios of the El Sela granites vary from about 6, indicating uranium leaching, to 0.8 indicating late magmatic and/or hydrothermal enrichment. 6 samples have Th/U ratios below 2 indicating that magmatic or hydrothermal U-oxides may be present as the main U-bearing minerals. Th-bearing uraninite has been identified in two samples (W1-53 with 15 ppm U and 23 ppm Th and W3-43 with 25 ppm U and 20 ppm). Uraninite may have been present in other shallower samples but may have been leached by hydrothermal and/or meteoric fluids. The presence of uraninite in the El Sela granite indicates that it can represent a good uranium source, even if uranothorite was not sufficiently metamict to liberate uranium at the time of the circulation of the hydrothermal fluids.
Two sets of structures are observed in the El Sela granite: a major E-W to ENE-WSW shear zone and N-S to NNE-SSW set of fault associated with different types of contemporaneous magmatic injections. These structures are reactivated several times in association with succession fluid circulations leading to the deposition of a series of quartz generations and U mineralization.
The main shear zone at G. El Sela is trending ENE-WSW and steeply dipping from 70˚ to 85˚ to the south. This trend has been reactivated many times by NNW-SSE extensional stress field, however to know that a detailed structural study would be necessary. The stress field may be transtensional with opening of tension gashes filled by the microgranite in the eastern part of the shear zone and filled by microgranite and dolerite dikes with white quartz and reddish to black jasperoid veins.
The main shear zone is affected by hydrothermal alteration as ferrugination, silicification, albitiation, epsyenitization, illitization and fluoritization with U-mineralization as hexavalent U minerals visible at the surface. The N-S strike slip sinistral fault cross-cut the ENE-WSW shear zone main trend. The width of the mineralized part of the shear zone varies from 3 to 40 m and is developed over a length of 1.5 km but reached 6 km in the east of G. El Sela area.
One of the aims of the present study is to detect U-mineralization in the drilled core samples and also to identify the depth of the reduced zone where the primary hydrothermal U-mineralization may be present.
The continuation of the uranium mineralization at depth is evidenced by the Track Etch Survey along the El Sela main shear zone with radon emission from 960 to 300,300 Bq/m3.
The γ-ray spectrometric profiles across the Sela shear zone indicate the strong increase of eU and, eU/eTh and eU/K ratios and a decrease of eTh and eK anomaly in relation with the enrichment of the shear zone in quartz. The strong direct increase of eU/eTh ratio is typical of hydrothermal uranium enrichment with no mobility of Th.
The VLF-EM profiles show marked high positive conductivity correlated with the shear zone within the granitic body, indicating higher fracturation and clay mineral content of the shear zone. The magnetic profile passing through W1 and W3 shows clearly an increase of total magnetic field above the El Sela shear zone associated with a magnetic low at its southern margin. To the opposite the magnetic profile passing through W2 showed only a strong magnetic low above the El Sela shear zone. Therefore, the association of spectrometric, radon, magnetic and electrical conductivity anomalies for the Sela shear zone clearly identifies the uraniumanomalous zones which can be selected for more drilling.
The occurrence of U-oxides along the margin of the pyrite crystals may indicate that they have played a role on the reduction of U6+ from the uranyl ion (
The occurrence of brannerite indicates a first phase of U remobilization at relatively high temperature, brannerite being stable above 250˚C - 300˚C. The U-oxides are also locally altered to coffinite [