Geology topics

John S. Stuckless

Publications and source records attributed to John S. Stuckless.

21 records · Page 2Linked to original sources

USGS1977

Geochemical and petrological studies of a uraniferous granite from the Granite Mountains, Wyoming

Granite rocks from the Granite Mountains, Wyo. have been proposed as the source of uranium deposits in the Crooks Gap, Gas Hills and Shirley Basin uranium districts, Wyoming. We have divided these granitic rocks into four units: (1) a biotitic phase which forms the dominant unit at the western end of the Granite Mountains, (2) a leucocratic phase which was found from 215 to 405 metres in drill hole GM-1, (3) silicified zones which crosscut the granitic rocks and form topographic highs, and (4) fractured zones, in drill hole GM-1, which seem to have been hydrothermally altered. The biotitic phase is hypidiomorphic-granular to xenomorphic-granular alkali granite with anomalously high contents of U (10 parts per million), Th (50 ppm), and Pb (50 ppm). Fission-track studies show that uranium is located in zircon, sphene, apatite, monzite, xenotime, biotite, chlorite, epidote, and magnetite; no intergranular uranium was found. The leucocratic phase is mineralogically similar to the biotitic phase, but contains less than half as much iron. It is xenomorphic granular and commonly contains rounded and retrograded garnets, which suggests that this phase is either metamorphic or contaminated with metamorphic materials. The leucocratic phase has anomalously high contents of U (8 ppm) and Pb (55 ppm), but has a low Th content (10 ppm). The silicified phase and fracture zones exhibit cataclastic and crystalloblastic textures and are highly variable in mineralogy. Potassium-bearing minerals are generally absent. Microcline is replaced by albite and (or) quartz, and biotite is replaced by clinozoisite. Uranium values may be anomalously high in the fracture zones. One sample contains 1100 ppm radium-equivalent uranium. In this and other uranium-rich samples from the fracture zones, the uranium is associated with iron oxides which commonly fill microfractures. According to our model and currently available data, an alkali granite is the best crystalline source rock for uranium, especially if it is unmetamorphosed and rapidly exposed to near-surface conditions for the first time when a favorable basin existed nearby.

Wyoming↗

USGS1977

A comparison of some analytical techniques for determining uranium, thorium, and potassium in granitic rocks

Geochemical exploration for uranium requires accurate and precise determinations of low-level concentrations. We have used seven different techniques and four different treatments of the fluorometric method to analyze for uranium in granitic rocks. In addition we have used four analytical techniques for thorium and three analytical techniques for potassium, two elements that are commonly present in anomalous amounts within uranium provinces. Our results show that commonly used techniques for thorium and potassium determinations are both adequately precise and accurate, but that many techniques used for uranium determinations lack the necessary precision or accuracy for complete geochemical prospecting. We suggest that a combination of delayed-neutron determinations for uranium and γ -ray spectrometric analyses for radium equivalent uranium, thorium, and potassium provides the best data base for geochemical exploration for uranium. If more detailed interpretations are desired, the combination of γ -ray spectrometry and α -spectrometry may be best. Carefully done fluorometric analyses should be adequate for water, ore, mineralized rock, and other applications where high precision and accuracy are not required.

Journal of Research of the U.S. Geological Survey↗

USGS1973

Petrogenesis of the Superstition-Superior volcanic area as inferred from strontium- and oxygen-isotope studies

Apparent initial Sr 87 /Sr 86 ratios of five ash-flow tuffs (0.7063 to 0.7139) and several mafic to silicic lavas (0.7055 to 0.7131) indicate that the magmas were derived below the base of the Precambrian granitic crust (0.7231 to 1.0906). Liquidus compositions in the system Q-Or-Ab-H 2 O and oxygen-isotope geother-mometry suggest that the silicic magmas started to crystallize quartz, magnetite, and two feldspars in a water-undersaturated environment of high pressure (∼10 kb) and moderate temperature of at least 830°C. During or after ascent into the crust, the magmas underwent varying degrees of crystal-melt re-equilibration. Measured plagioclase-biotite O 18 fractionations (0.5 to 0.7) imply a temperature that is too high for the observed mineral assemblage, and the inference is that the two minerals did not crystallize in equilibrium. Prior to eruption, the upper part of the magma column assimilated crustal Sr such that the base of each ash flow is now enriched in Sr 87 . In some cases, this assimilation was too rapid to allow crystal-melt equilibration of Sr isotopes. δO 18 values for the magmas are within the range typical of similar magma types, indicating that no significant interaction took place between the melts and meteoric water; however, some rocks have exchanged oxygen isotopes with meteoric water at low temperatures after eruption. Some of the magma appears to have had a long residence in the crust at lower pressure (1 kb) and temperature (750°C), because two of the ash-flow tuffs and one lava are greatly enriched in Sr 87 and have largely re-equilibrated under the P-T conditions of a shallow magma chamber. Even these, however, have retained evidence for a multistage genesis.

Geological Society of America Bulletin↗