Browsing by Subject "Mineralogy"
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Item Chemical and mineralogical analyses of contaminated soils at the Anaconda Smelter Site, Montana(2011-08) Zhou, Jian; Ridley, Moira K.; Hetherington, Callum J.; Barnes, Melanie A. W.The Anaconda Copper Smelter site in Montana, USA was deemed a superfund site by the U.S. Environment Protect Agency (USEPA) in 1983. Disposal of large quantities of tailing material caused toxic heavy metal contamination of the surrounding environments. Toxic metals included As, Cd, Cu, Pb, and Zn. In this study, samples from a tailing impoundment, "opportunity pond", and surrounding physically undisturbed soils were analyzed. Geochemical analysis following the Tessier Sequential extraction procedure (Tessier et al., 1979) and EPA digestion method 3050B (USEPA, 1996) were performed. Select samples were examined further by optical microscope and scanning electron microscopy. Results indicate that sampled weathered tailing material contain lower concentration of metals than the surrounding contaminated soils. Results also show that metal content in the samples varied as function of depth. For contaminated soils, the maximum metal concentrations occur in samples from 15 – 30 cm depth. Results from optical and electron microscope observation indicate that there is a positive correlation between metal content and the presence of opaque mineral phases. Most opaque mineral phases are secondary phases. The secondary mineral phases were predominantly iron oxides (goethite and hematite) and copper oxides. Geochemical process controls the formation of secondary minerals, and the migration of toxic heavy metals. Hydrological processes such as infiltration and evaporation of surface precipitation facilitates the migration of metals.Item Epithermal gold mineralization in the Velvet District, Pershing County, Nevada(1981-12) Masterson, Wilmer Dallam; Kyle, J. RichardGold mineralization in the Velvet District occurs in an eastward dipping sequence of Miocene tuffs, flows, and tuffaceous sediments on the west flank of the Trinity Range in Pershing County, Nevada. Numerous north-northeast trending normal faults extend through the district. These faults served as conduits for ascending hydrothermal fluids which deposited gold and silver along poorly defined zones of brecciation, argillic alteration, and quartz veining. Concentration of gold does not exceed a few parts per million and is highest in zones of intersecting fractures. The hydrothermal solutions which deposited the gold were the near-surface expression of a larger geothermal system. Meteoric water leached gold, silver, arsenic, antimony, and other metals from the surrounding rock as it percolated downward towards a deep heat source. The hot fluids escaped upward along fracture zones and precipitated precious metals in veins near the surface. Fluid inclusion studies indicate that the quartz veins were deposited in the temperature range 218-264°C from fluids which had salinities equivalent to 0.2-0.8 weight percent NaCl. δ¹⁸0 of quartz veins varies from -2.5 to +6.7 %, and the low values appear to define a zone of concentrated fluid flow and potential subsurface mineralization in the southeast part of the district. The lowest value, -2.5 %, indicates that the ore fluid must have been Tertiary meteoric water with δ¹⁸0 equal to -13 %. Reaction of hydrothermal fluids with wall rock produced an alteration assemblage of illite-kaolinite-quartz which underlies most of the shafts, adits, and prospect pits in the district. The illite-kaolinite-quartz assemblage is laterally gradational into a kaolinite (or dickite)-smectite-alunite-quartz assemblage which is indicative of lower temperatures. Pyrite and other sulfides are rare, but limonite and jarosite are widespread in surface outcrops. Alteration of tuffs released abundant silica which precipitated as quartz veins and discharged in hot springs at the bottom of lakes, where thick deposits of diatomaceous earth accumulated.Item Epithermal vein and carbonate replacement mineralization related to caldera development, Cunningham Gulch, Silverton, Colorado(1984-05) Hardwick, James Fredrick, 1955-; Kyle, J. RichardEpithermal vein and carbonate replacement deposits in Cunningham Gulch are located within the western San Juan Tertiary volcanic field in southwestern Colorado. The Pride of the West epithermal vein system is hosted within the intracaldera facies of the Sapinero Mesa Tuff, a voluminous ash-flow tuff that erupted from and resulted in the formation of the San Juan Caldera at 28 mybp. The Pride of the West vein system is developed along a radial fracture formed during resurgence of the San Juan Caldera prior to eruption of the Crystal Lake Tuff (27.5 mybp). This eruption led to the concomitant collapse of the Silverton Caldera, nested within the larger San Juan Caldera. The Pride of the West, Osceola, and Little Fanny mines are positioned near the intersection of the Pride radial fracture system and the buried structural margin of the San Juan Caldera, suggesting that ore concentration was controlled by this structural setting. Large limestone blocks of the Mississippian Leadville Formation are incorporated into the intracaldera fill volcanics in the mine area. These blocks appear to have been engulfed within mudflow breccias of the Tertiary San Juan Formation (32.1 mybp). They were then emplaced in their present structural position within a caldera-collapse breccia which caved from the oversteepened margin of the San Juan Caldera. Regional propylitic alteration of the hosting volcanics to a chlorite-calcite-pyrite assemblage preceded vein-associated alteration and mineralization. The veins are enveloped by a narrow phyllic alteration assemblage of quartz, sericite, illite, kaolinite, and pyrite. The veins are comprised of sphalerite, galena, chalcopyrite, pyrite, hematite, magnetite, quartz, pyroxmangite, calcite, and minor barite. Substantial bodies of replacement ore are present where the vein structures intersect the limestone blocks; the mineral assemblages of the replacement deposits are identical to those of the feeding vein structures. Commonly, replacement textures are spectacular concentrations, especially the "zebra ore" which primarily consists of regularly spaced, alternating bands of sulfides and quartz. These "zebra" laminations are stratigraphically controlled and appear to represent replacement of a depositional or diagenetic fabric. Main ore-stage mineralization began with widespread deposition of quartz with or without pyrite, followed by sphalerite, chalcopyrite, and galena. Post ore-stage brecciation and silicification events are evident and were followed by deposition of calcite and minor barite during the waning stages of the hydrothermal system. The distributions of Fe, Mn, Pb, and Ca suggest a lateral component of fluid flow from northwest the southeast, away from the structural margin of the Silverton Caldera. Fluid inclusion data from both vein and replacement-type sphalerite and quartz indicate that mineral deposition occurred over a range of 200 to 312°C (mean 243°C) from solutions containing 1 to 5% total salts. The high base metal to precious metal content of the ore, the phyllic alteration assemblage, and the temperature and composition of the ore-forming fluid indicate that the mine workings are within the lower portion of a fossil geothermal system.Item Mineralogy and geochemistry of the non-sulfide Zn deposits in the Sierra Mojada district, Coahuila, Mexico(2010-08) Ahn, Hye In; Kyle, J. Richard; Bennett, Philip C.; Gilg, H. AlbertThe Sierra Mojada district consists of multiple types of mineral concentrations ranging from polymetallic sulfide deposits, "non-sulfide Zn" (NSZ) deposits, and a Pb carbonate deposit hosted by Upper Jurassic to Lower Cretaceous carbonates. This study focuses on the two non-sulfide Zn deposits, the Smithsonite Manto and the Iron Oxide Manto, that occur south of the San Marcos fault. The Smithsonite Manto shows karst features, including internal sediments interbanded with smithsonite (ZnCO₃). The Iron Oxide Manto consists of strata-bound zones dominantly of hemimorphite (Zn₄Si₂O₇ (OH)₂·H₂O) that fills pores in Fe-oxides. The mineralogy of the NSZ mineralization consists of smithsonite, hemimorphite and Zn clays (sauconite) associated mainly with calcite and Mn-Fe-oxides. Zn clays are abundant in the Smithsonite Manto, but no Zn clays have been found in the Iron Oxide Manto. This project attempts to constrain the origin of the NSZ concentrations through petrographic and mineralogical study of major Zn-bearing minerals, and their carbon and oxygen stable isotopes and Pb isotope geochemistry. Smithsonite in the Smithsonite Manto occurs as botryoidal aggregates consisting of scalenohedral or rhombohedral microcrystals and banded colloform or massive smithsonite in open spaces, whereas smithsonite in the Iron Oxide Manto occurs as rhombic microcrystals grown in pore spaces or finely intergrown with Fe-oxides. Both Fe-poor and Fe-rich smithsonite are found in the Iron Oxide Manto. Under optical-CL, smithsonite displays complex growth zoning that can be related to variable trace element content. Trace elements semiquantitatively analyzed using LA-ICP-MS show that most blue luminescent smithsonite has lower Mn contents than pink to bright red luminescent zones in smithsonite. Preliminary fluid inclusion petrography in hemimorphite and calcite suggests that fluid composition can be related to precipitation of NSZ minerals from freshwater to slightly saline waters. Calculated salinities for two phase (liquid +vapor) and single phase (liquid) inclusions in hemimorphite range between 0.0 and 1.6 wt. % NaCl equivalent, and salinities of inclusions in calcite were between 0.0 and 1.1 wt. % NaCl equivalent. The oxygen isotope values for smithsonite are relatively constant (avg. [delta]¹⁸O[subscriptVSMOW] = 21.9 ± 0.5[per mille]), whereas [delta]¹³C[subscriptVPDB] values range from -8.4 to -1.1 [per mille]. The oxygen isotope values in late calcite are within the same range of smithsonite, whereas the average values of the carbon isotope are lower by 5 [per mille]. Formational temperature of smithsonite is calculated to be between 26 ~ 40 °C using the modern groundwater composition at Cuatro Ciénegas. Similar Pb isotopic compositions of smithsonite and cerussite to galena suggest the source of metals in the NSZ deposits presumably originate from the sulfide deposits.Item Numerical simulation and interpretation of neutron-induced gamma-ray spectroscopy measurements(2015-12) Ajayi, Oyinkansola Modupe; Torres-Verdín, Carlos; Peters, Ekwere J; Preeg, William E; Schneider, Erich A; Sepehrnoori, KamyNeutron-induced spectroscopy measurements are commonly used to quantify in-situ elemental and mineral compositions of rocks from the processing of measured gamma-ray energy spectra. However, geometrical effects on measured spectroscopy logs, such as thin beds, dipping beds, and deviated well trajectories, can cause shoulder-bed averaging that compromises the assessment of true layer elemental and mineral compositions. Traditional methods of interpreting neutron-induced gamma-ray spectroscopy measurements typically neglect such shoulder-bed averaging effects in the estimation of elemental and mineral compositions. Monte Carlo methods accurately reproduce borehole and formation geometrical effects on spectroscopy measurements but are extremely time consuming and impractical for use in routine interpretation. Reliable measurement interpretation must therefore begin with the development of a fast and accurate forward simulation method that explicitly incorporates measurement physics, borehole, tool, and formation geometry. This dissertation introduces a new algorithm to rapidly simulate elemental and mineral compositions from neutron induced spectroscopy measurements. The algorithm utilizes neutron-gamma ray spatial sensitivity functions to account for environmental and three-dimensional (3D) effects of formation porosity, fluids, dipping beds, thin beds, and arbitrary well trajectories. Simulations assume a logging-while-drilling (LWD) spectroscopy tool furbished with a 14-MeV pulsed-neutron source in the interpretation of gamma ray spectra obtained from high energy inelastic neutron scattering and thermal neutron capture. Results obtained with the rapid simulation method are benchmarked against rigorous Monte Carlo spectroscopy calculations for synthetic conventional and unconventional thinly-bedded reservoirs penetrated by vertical and high angle/horizontal (HA/HZ) wells. The fast simulation method yields calculations in approximately 1e6 the time required by Monte Carlo simulations, with an average difference below 5% between Monte Carlo and fast simulated logs. An inversion-based interpretation method is next introduced to accurately evaluate mineral concentrations from measured spectroscopy elemental logs based on the analytical relationship between elements and minerals through their chemical formulas. In the presence of geometrical effects, spectroscopy elemental and mineral logs are corrected for shoulder-bed averaging by the inclusion of spatial sensitivity maps, which account for such geometrical effects, in the inversion-based interpretation. Calculations are performed with both inelastic and capture gamma-ray spectroscopy measurements which arise from high-energy inelastic neutron scattering and low-energy thermal neutron capture, respectively. This strategy provides two sets of data that can ascertain chemical elements or minerals detectable in only one measurement mode and also independently validates estimated elemental and mineral compositions. In laminated formations, where layer thicknesses are below the vertical resolution of the tool, it is impossible to quantify layer properties with inversion methods. An additional interpretation method based on a new spectroscopy mixing law is therefore developed to estimate elemental and mineral compositions within individual laminae. The new inversion-based interpretation methods are successfully implemented in diverse synthetic and field cases with varying lithology types and well trajectories including vertical and HA/HZ wells. Results show that the developed methods reduce shoulder-bed averaging effects on measured spectroscopy logs by as much as 0.4 yield fraction, 0.17 weight fraction, and 0.34 mineral volume fraction. Finally, a new spectroscopy-based petrophysical interpretation method is introduced that utilizes estimated mineralogy to overcome the common assumption of homogeneous lithology in measured porosity logs, thereby improving the estimation of porosity and water saturation. Inclusion of shoulder-bed averaging effects on spectroscopy mineral logs also increases the accuracy of spectroscopy-based petrophysical interpretation.Item Quantitative analysis of minerals by x-ray powder diffraction(Texas Tech University, 1980-05) Yeko, John DGrain size, instrumental variations and preferred orientation are the three primary sources of experimental error for quantitative X-ray diffraction analysis and must therefore be controlled before any attempt can be made to quantify sample mineralogy. Previous equations have neglected the surface layer effect yet, this effect may account for as much as 50% of the observed intensity. In samples which contain absorbers, the effect is even more pronounced. Computer solutions of intensity equations have verified the surface effect relationship and allow for determination of weight percentage compositions for multi-component mineral systems with an accuracy of 3.5%. Standard curves are not needed.