210 research outputs found

    Source Constraints of Ore Metals in Mississippi Valley-type Deposits in Central and Eastern Tennessee using Pb Isotopes

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    The Mississippi Valley-Type (MVT) Central and East Tennessee (TN) Districts contain economically significant lead-zinc deposits that occur in the Early Ordovician carbonates of the Knox Group. Although both districts share similar host rock, have similar temperatures of formation, and typically fill open spaces of collapse breccias or replace their host carbonates, previous studies may suggest that these ores did not form from the same mineralizing fluids and may have different Pb sources. Nu Plasma MC-ICP-MS Pb isotopic analyses on sulfides from Central and East TN were conducted and the metal sources evaluated. Results were plotted on covariation diagrams with respect to the average crustal growth curve from Stacy and Kramers (1975) and the orogene curve from Zartman and Doe (1981). Lead isotope data from both Central and East TN plot beyond the present day age (0 m.y. ago) indicative of a crustal source of Pb-Zn. Central TN 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios range from 19.334 - 20.128, 15.548 - 16.034, and 38.837 - 40.034 respectively. Eastern TN 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios range from 19.341 - 19.455, 15.638 - 15.789, and 39.045 - 39.591 respectively. Pb isotope ratios from the Young Mine in the East TN District plot within ranges defined by other East TN District samples from previous studies. Three Pb isotope ratios from the Elmwood Mine in the Central TN District plot near these East TN samples, while the remaining Elmwood samples remain suspect to analytical error as they plot away from any other recorded Central TN deposits. It appears that the thick, black, metal-rich shales of the Appalachian Basin have been the source of the Pb-Zn and ore fluids of MVT deposits that formed the East TN deposits. When East TN Pb data from this study are compared to Central TN Pb data from previous studies, Central TN Pb is commonly more radiogenic, suggestive of a mineralizing fluid with different compositions. Further analysis of Central TN Pb deposits is needed to further constrain this source

    Geochemical Analysis of Basement Rock as a Potential Metal Source in Mississippi Valley-Type Ores, Southern Midcontinent U.S.A.

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    Mississippi Valley-Type (MVT) ores are epigenetic, sedimentary hydrothermal base metal deposits that exist worldwide with type localities in the midcontinent United States. These Permian-aged sulfide ores represent an extraordinary concentration of economic metals, Pb and Zn. Ore deposits occur in vast districts that have a rich mining history. The Pb and Zn from these deposits account for 24% of worldwide reserves. The geologic processes responsible for MVT ore genesis are not fully understood, especially the sourcing of ore constituents. In the midcontinent, the Ouachita Orogeny expelled saline hydrothermal brines in response to high rates of subsidence. These fluids migrated through Arkoma Basin carrier beds and faults to deposit MVT ores up-dip within basin flank carbonate hosts. Base metals were leached into solution from surrounding wall rock, and metals traveled within the fluid to the ore deposition site. Which lithologies had a greater metal contribution is unconstrained. Lead (Pb) isotopes can be used to investigate potential relationships between geologic features. Southern midcontinent ores show highly radiogenic Pb signatures, so a lithologic metal source must have a similar isotopic nature. Precambrian basement rock has been a long-hypothesized metal source due to generally higher concentrations of radiogenic Th and U, evidence of hydrothermal alteration, and ore Pb source model ages yielding a 1.01 and 1.05 Ga Pb source. Fifty-three basement samples from the Central Plains Orogen (1.65-1.8 Ga) and Southern Granite Rhyolite Province (1.3-1.4 Ga) were collected from cores and cuttings retrieved during drilling operations. The full suite was analyzed for trace element concentrations, and thirty-nine samples were analyzed for radiogenic isotopes Pb, Sr, and Nd. Present-day Pb isotope ratios of basement rocks create linear trends similar to MVT ore trends and three samples are enriched in radiogenic Pb. Age-corrected Pb isotope ratios reflect the sample Pb signatures at the time of MVT ore deposition, and these ratios plot less similarly to ore Pb signatures. Age-corrected Pb isotope ratios alone suggest the basement rocks and the MVT ores are not genetically related. Present-day ratios are only slightly promising. The three highly radiogenic samples are unique from the rest not only because of their Pb signature but also their enrichment in 87Sr/86Sr and unique enrichment in heavy rare earth elements (HREEs). These data suggest that the basement as a whole did not supply metals to midcontinent MVT ores, but perhaps localized features within the basement such as younger intrusions or igneous dikes supplied the highly radiogenic Pb. The three anomalously enriched samples may represent one of these more local features. This would be consistent with the 1.01 and 1.05 Ga model Pb source ages because the expected age of midcontinent basement is 1.3-1.8 Ga. These new data provide valuable geochemical results to the limited database of southern midcontinent basement, and they have implications for understanding the formation of economic MVT deposits of the southern midcontinent

    Geochemical Analysis of Basement Rock as a Potential Metal Source in Mississippi Valley-Type Ores, Southern Midcontinent U.S.A.

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    Mississippi Valley-Type (MVT) ores are epigenetic, sedimentary hydrothermal base metal deposits that exist worldwide with type localities in the midcontinent United States. These Permian-aged sulfide ores represent an extraordinary concentration of economic metals, Pb and Zn. Ore deposits occur in vast districts that have a rich mining history. The Pb and Zn from these deposits account for 24% of worldwide reserves. The geologic processes responsible for MVT ore genesis are not fully understood, especially the sourcing of ore constituents. In the midcontinent, the Ouachita Orogeny expelled saline hydrothermal brines in response to high rates of subsidence. These fluids migrated through Arkoma Basin carrier beds and faults to deposit MVT ores up-dip within basin flank carbonate hosts. Base metals were leached into solution from surrounding wall rock, and metals traveled within the fluid to the ore deposition site. Which lithologies had a greater metal contribution is unconstrained. Lead (Pb) isotopes can be used to investigate potential relationships between geologic features. Southern midcontinent ores show highly radiogenic Pb signatures, so a lithologic metal source must have a similar isotopic nature. Precambrian basement rock has been a long-hypothesized metal source due to generally higher concentrations of radiogenic Th and U, evidence of hydrothermal alteration, and ore Pb source model ages yielding a 1.01 and 1.05 Ga Pb source. Fifty-three basement samples from the Central Plains Orogen (1.65-1.8 Ga) and Southern Granite Rhyolite Province (1.3-1.4 Ga) were collected from cores and cuttings retrieved during drilling operations. The full suite was analyzed for trace element concentrations, and thirty-nine samples were analyzed for radiogenic isotopes Pb, Sr, and Nd. Present-day Pb isotope ratios of basement rocks create linear trends similar to MVT ore trends and three samples are enriched in radiogenic Pb. Age-corrected Pb isotope ratios reflect the sample Pb signatures at the time of MVT ore deposition, and these ratios plot less similarly to ore Pb signatures. Age-corrected Pb isotope ratios alone suggest the basement rocks and the MVT ores are not genetically related. Present-day ratios are only slightly promising. The three highly radiogenic samples are unique from the rest not only because of their Pb signature but also their enrichment in 87Sr/86Sr and unique enrichment in heavy rare earth elements (HREEs). These data suggest that the basement as a whole did not supply metals to midcontinent MVT ores, but perhaps localized features within the basement such as younger intrusions or igneous dikes supplied the highly radiogenic Pb. The three anomalously enriched samples may represent one of these more local features. This would be consistent with the 1.01 and 1.05 Ga model Pb source ages because the expected age of midcontinent basement is 1.3-1.8 Ga. These new data provide valuable geochemical results to the limited database of southern midcontinent basement, and they have implications for understanding the formation of economic MVT deposits of the southern midcontinent

    Effects of Landscape Disturbances on Autotrophic Processes Within Arkansas Ozark Streams

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    Land-use change is one of the most widespread human impacts and can influence abiotic and biotic processes within surrounding streams. For example, streams in agricultural and urban watersheds receive greater light and nutrient inputs that can promote increased algal growth and primary production. Natural gas (NG) infrastructure development, a recent land use change in many regions, may also stimulate forested stream primary production, by reducing forest cover and increasing sediments and nutrient transport. I sampled streams across a NG activity gradient for algal biomass and gross primary production (GPP) to assess potential effects of this emerging land-use type. Algal biomass and GPP were positively associated with NG activity during winter, suggesting algal stimulation by nutrient enrichment of streams impacted by NG activity. To examine the nutrient limitation status of my study streams, I experimentally manipulated nitrogen (N) and phosphorus (P) in diffusing substrata and found that while P was not limiting, N-limitation was negatively related to NG activity (R2= 0.57; p= 0.03). Best management practices (BMPs) have been implemented to help reduce sediment inputs, associated with NG activity on streams, though little has been done to assess their effectiveness. I used a before-after control-impact design to test the effectiveness of implemented BMPs at reducing impacts to autotrophic processes in headwater streams and the South Fork Little Red River. There were no differences between reference and impacted sites before and after the disturbance occurred for the autotrophic processes measured. These results suggest that BMPs were effective at mitigating effects of low levels of NG activity. However, NG activity in the study watersheds was less than in surrounding areas, potentially contributing to the absence of change. In my final study, I examined how human land-use affects recovery of algal communities and metabolic processes to flood disturbances. Biomass and metabolism recovered more rapidly in urban and agricultural streams than forested streams likely due to increased nutrient availability. These findings highlight the defining role of increased nutrient availability as one main driver of effects of human land-use change on autotrophic processes in stream ecosystems

    Carbonate-Hosted Base Metal Deposits

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    Geochemical Analysis and Numerical Modeling of Central and East Tennessee Mississippi Valley-Type Ore Districts: Constraints on Ore Genesis

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    A simple two-way stochastic mixing model is presented for analysis of the lead (Pb) isotope compositions of the North American Mississippi Valley-Type (MVT) districts of East Tennessee, Central Tennessee, and Central Kentucky. Four distinct mixing scenarios were run to critically evaluate the stochastic model and examine different hypotheses regarding the genesis of Central Tennessee and Central Kentucky MVT deposits. Additionally, Pb isotope analysis was conducted on sphalerite samples from the Central and East Tennessee MVT districts. Model and sampling results suggest that Central Tennessee and Central Kentucky ores likely formed by mixing of three fluids. In contrast to conclusions from previous workers, our results suggests that Central Tennessee and Central Kentucky deposits may have formed via mixing between Appalachian Basin brines and a unique source that is distinct from the Upper Mississippi Valley and Illinois-Kentucky trend. The possible third source has a composition lying along the Ozark Pb isotope trend and may have also contributed metals to the Central Tennessee ores. Alternatively, Pb isotope observations can be explained if Upper Mississippi Valley ore metals were derived from a single fluid which evolved over time. Although it is still unclear whether these model results can be relied on for analysis of MVT ore compositions, the methods employed here present a promising means for Pb isotope analysis of sulfide ores. Stochastic generation of hypothetical ore deposits as the result of mixing between different sources of Pb has the potential to allow researchers to test their hypotheses regarding the nature of the mineralizing fluids in a more rigorous and semiquantitative manner. Nonetheless, further sampling is required before confidence regarding the origin of Central Tennessee and Central Kentucky ores is warranted

    Geochemical Analysis and Numerical Modeling of Central and East Tennessee Mississippi Valley-Type Ore Districts: Constraints on Ore Genesis

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    A simple two-way stochastic mixing model is presented for analysis of the lead (Pb) isotope compositions of the North American Mississippi Valley-Type (MVT) districts of East Tennessee, Central Tennessee, and Central Kentucky. Four distinct mixing scenarios were run to critically evaluate the stochastic model and examine different hypotheses regarding the genesis of Central Tennessee and Central Kentucky MVT deposits. Additionally, Pb isotope analysis was conducted on sphalerite samples from the Central and East Tennessee MVT districts. Model and sampling results suggest that Central Tennessee and Central Kentucky ores likely formed by mixing of three fluids. In contrast to conclusions from previous workers, our results suggests that Central Tennessee and Central Kentucky deposits may have formed via mixing between Appalachian Basin brines and a unique source that is distinct from the Upper Mississippi Valley and Illinois-Kentucky trend. The possible third source has a composition lying along the Ozark Pb isotope trend and may have also contributed metals to the Central Tennessee ores. Alternatively, Pb isotope observations can be explained if Upper Mississippi Valley ore metals were derived from a single fluid which evolved over time. Although it is still unclear whether these model results can be relied on for analysis of MVT ore compositions, the methods employed here present a promising means for Pb isotope analysis of sulfide ores. Stochastic generation of hypothetical ore deposits as the result of mixing between different sources of Pb has the potential to allow researchers to test their hypotheses regarding the nature of the mineralizing fluids in a more rigorous and semiquantitative manner. Nonetheless, further sampling is required before confidence regarding the origin of Central Tennessee and Central Kentucky ores is warranted

    A geochemical investigation of regional sedimentary-hosted Pb-Zn mineralization in the Paleoproterozoic Karrat Group, West Greenland

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    Pb-Zn mineralization is hosted in two formations of the Karrat Group in arctic West Greenland: the Marmorilik Formation (carbonate-hosted, 12.3% Pb, 4.0% Zn, 29ppm Ag), home to the historical Black Angel Mine, and the recently defined Qaarsukassak Formation (shale-carbonate-hosted, ~20% Zn). These two sedimentary units were deposited directly on crystalline basement rocks and might have similar depositional timing, however, they are separated by a basement topographic high and are not observed in stratigraphic contact. The timing of their mineralization is also enigmatic. This study uses a combination of field and geochemical approaches to understand the origin of the Pb-Zn mineralization in both formations by using the following methods: field mapping, petrography, pyrite and ore sulfide sulfur isotope analysis, Pb isotopic analysis, and Re-Os analysis of pyrite grains associated with the mineralization. Marmorilik and Qaarsukassak mineralization textures suggest a late stage remobilization event after the emplacement of ore mineralization. Additionally, remobilized sulfides from both formations are linked to the regional D3 deformation, thus constraining the mineralization prior to D3 deformation. Sulfur isotope results from both traditional isotope-ratio mass spectrometry and secondary ion mass spectrometry show a range of 34S values between +0.2‰ and +7.2‰ on sulfide minerals, suggesting contributions from both bacterially reduced and thermochemically reduced seawater sulfate. Pb-Pb isotopic analysis of galena from the Marmorilik Formation shows a homogenous signature (206Pb/204Pb = 16.091-16.102 and 207Pb/204Pb = 15.378-15.385), with Pb isotopic compositions consistent with a crustal source for Pb, indicating local basement as a likely source for the metals. Results from Re-Os analysis of pyrite grains derive an indicated age of 1919 Ma +/- 44 Ma, providing a maximum age constraint for the mineralization. Combining structural, petrographic, and Re-Os isotopic data, a timeframe for the Pb-Zn mineralization of ca. > 1900 to < 1830 Ma is proposed. Sulfur isotope results suggest a SEDEX model for the mineralization, while petrographic, Pb-Pb, and Re-Os isotope results could indicate either a SEDEX or MVT type model

    The Paleozoic Sedimentary Rocks of the Ouachita Mountains and their Genetic Relationship to the Mississippi Valley-Type Mineralization in the Southern Ozark Region: Insights from Radiogenic Pb Isotopes and Trace Elements Studies

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    Cluster of Pb and/or Zn deposits of the well-known Tri-State and Northern Arkansas Mississippi Valley Type (MVT) districts located north of the Arkoma basin and the Ouachita fold-thrust belt in north America are genetically connected to the Pennsylvanian-Permian Ouachita orogeny which triggered a South-North topographic gradient flow of basinal brines, leaching metal rich sediments en route. The objective of the research is twofold. First, to ascertain whether the organic-rich shales and sandstones from the study area provided metals during the mineralization event, which was coeval with the Ouachita orogeny. Second, to assess the depositional environment of the potential source rocks, which will shed light on their ability to sequester metals. The Pb isotope compositions of the ores (sphalerite) have been compared to their associated sedimentary rocks (Collier, Mazarn, and Polk Creek, Womble, Fayetteville, Stanley and Chattanooga shales and Jackfork Sandstone) and metal sources have been evaluated. In addition, the role of depositional redox of sedimentary rocks to sequester adequate amounts of metals has been appraised using redox sensitive trace elements (U, V, Mo, Cr, etc.). The Pb isotope compositions of the ores (sphalerite) have been compared to those of the sedimentary rocks of the Ouachita Mountains (Cambrian Collier Shale, Early Ordovician Mazarn Shale, Middle Ordovician Womble Shale, Late Ordovician Polk Creek Shale, Mississippian Stanley Shale, and Pennsylvanian Jackfork Sandstone) and the Ozark Plateau (Devonian/Mississippian Chattanooga Shale and Mississippian Fayetteville Shale).Metal sources evaluation indicate a mixing model of fluids sourced from high and less radiogenic rocks shown by a broad and linear trend of Pb isotope composition, with the Chattanooga rock and the Jackfork sandstone samples being the most prominent source rocks. Paleoredox proxies indicate deposition under anoxic and Euxinic conditions, which are favorable for metal enrichment. How-ever, oxic-suboxic conditions are also indicated by other geochemical proxies, suggesting the possible first order control of primary production that has resulted in increased flux of organic matter. Additional factors such as the basin geometry, the rates of sediment accumulation, the post depositional alteration processes associated with diagenesis and low-grade metamorphism during the Ouachita orogeny might have overprinted the depositional signatures

    Genesis of Pb-Zn-Cu-Ag Deposits Within Permian Carboniferous-Carbonate Rocks in Madina Regency, North Sumatra

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    DOI:10.17014/ijog.2.3.167-184Strong mineralized carbonate rock-bearing Pb-Zn-Cu-Ag-(Au) ores are well exposed on the Latong River area, Madina Regency, North Sumatra Province. The ore deposit is hosted within the carbonate rocks of the Permian to Carboniferous Tapanuli Group. It is mainly accumulated in hollows replacing limestone in the forms of lensoidal, colloform, veins, veinlets, cavity filling, breccia, and dissemination. The ores dominantly consist of galena (126 000 ppm Pb) and sphalerite (2347 ppm Zn). The other minerals are silver, azurite, covellite, pyrite, marcasite, and chalcopyrite. This deposit was formed by at least three phases of mineralization, i.e. pyrite and then galena replaced pyrite, sphalerite replaced galena, and pyrite. The last phase is the deposition of chalcopyrite that replaced sphalerite. The Latong sulfide ore deposits posses Pb isotope ratio of 206Pb/204Pb = 19.16 - 20.72, 207Pb/204Pb = 16.16 - 17.29, and 208Pb/204Pb = 42.92 - 40.78. The characteristic feature of the deposit indicates that it is formed by a sedimentary process rather than an igneous activity in origin. This leads to an interpretation that the Latong deposit belongs to the Sedimentary Hosted Massive Sulfide (SHMS) of Mississippi Valley-Type (MVT). The presence of SHMS in the island arc such as Sumatra has become controversial. For a long time, ore deposits in the Indonesian Island Arc are always identical with the porphyry and hydrothermal processes related to arc magmatism. This paper is dealing with the geology of Latong and its base metal deposits. This work is also to interpret their genesis as well as general relationship to the regional geology and tectonic setting of Sumatra
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