Potash–rich Magmatism and Associated Gold-Copper Mineralization in the Yishu Deep Fault Zone and Its Vicinity, Eastern China     

Jiansheng QIU  Ching–Hua LO  Brent I. A. MCINNES  Jincheng ZHOU 《Resource Geology》2000,50(4):269-280

Abstract: The Mesozoic potash‐rich volcanic rocks which hosted several gold or gold (copper) deposits are widely distributed around the Yishu deep fault zone, eastern China. Lithologically, these rocks include basaltic trachyandesite, trachyandesite, latite and trachyte, of which the trachyandesite and latite are the predominant rock types. Whole‐rock Rb‐Sr isochron ages and ⁴⁰Ar‐³⁹Ar plateau dates of them are 108.2 ? 119.6 Ma and 114.7 ? 124.3 Ma, respectively. Chemically, they are characterized by high and variable Al₂O₃ contents, high K₂O+Na₂O values, and high K₂O/Na₂O and Fe₂O₃/FeO ratios. The rocks also have enriched LILE and LREE concentrations, low HFSE abundance, and display extraordinary Sr‐Nd isotope signatures (I_Sr = 0.7084 ? 0.7125, ε_Nd(t) = ‐9.43 ? ?18.07). Integrated geological and geochemical data suggest that they were formed in a continental‐arc setting and most likely originated from the partial melting of enriched mantle which was induced by source contamination of subducted continental crustal materials. Gold (copper) deposits in this district are closely related to Mesozoic volcanic‐subvolcanic magmatism. They are frequently located either at the margin or adjacent to the volcanic basins. Most of them are spatially associated with maar‐diatreme systems and/or flow‐dome complexes. The formations of two gold (copper) deposits, the Qibaoshan breccia pipe‐porphyry type Au‐Cu deposit and the Guilaizhuang tellurium‐gold type epithermal Au deposit, have been proved to be in close relation with potash‐rich magmatism. The genetic relations between potash‐rich magmatism and Cu‐Au mineralization is still quite unclear. Detailed review of the previous works demonstrates that the high contents of volatiles (such as H₂O, CO₂, S, F and Cl, especially F and Cl) and the high oxidation state of the potash‐rich magmas may be the main favorable factors for the formation of the Cu‐Au deposits.  相似文献   

Distal Magmatic-Hydrothermal Origin for the Camaquã Cu (Au-Ag) and Santa Maria Pb, Zn (Cu-Ag) Deposits, Southern Brazil     

M.V.D. Remus  L.A. Hartmann  N.J. McNaughton  D.I. Groves  J.L. Reischl 《Gondwana Research》2000,3(2):155

The Camaquã Cu (Au, Ag) and Santa Maria Pb-Zn (Cu, Ag) deposits are the largest base-metal deposits discovered so far in the sedimentary clastic sequences of the Neoproterozoic-age Camaquã Basin. The origin of the Camaquã-Santa Maria deposits has been the centre of dispute, with three alternative genetic hypotheses proposed: a syngenetic model, a diagenetic model, and a magmatic hydrothermal model. In detail, this mineralization has been suggested to be related to sedimentary clastic-diagenetic processes, volcanic-related processes, or deep granitic magmatism.Reevaluation of previous data and new studies in the area yield the following conclusions: (1) mineralization is fracture-controlled and magmatic-hydrothermal in origin rather than stratiform syngenetic or diagenetic; (2) the temperature of deposition of the main ore minerals was 210 to 300°C; (3) the ∂³⁴S of sulphides of around 0% indicates an external magmatic-hydrothermal source of sulphur; (4) Pb isotope ratios of sulphides indicate that metals were derived at the end of the Brasiliano Cycle from a large crustal source with very primitive Pb and that (5) the age of mineralization is 594 Ma, as constrained by U/Pb SHRIMP (Sensitive High Resolution Ion Microprobe) determinations on zircons of the Lavras Granite.Thus, the Camaquã and Santa Maria deposits are interpreted to be of magmatic-hydrothermal origin, with the metals derived from an old crustal-basement source during the end of Dom Feliciano Collisional Orogeny, at 594 Ma, late in the Brasiliano Cycle.The interpretation above is critical for base-metal exploration in the Sul Riograndense Shield. Previous exploration methodologies mainly followed models based on a sedimentary hypothesis for the origin of the deposits. However, the occurrence of mineralization along fractures within specific wall-rocks requires consideration of alternative exploration parameters. These include: (1) ancient EW- and NW-trending regional fractures and their intersections, which are potential structural sites for base-metal mineralization, and (2) preferential wall-rock sites, either rocks with high initial porosity or secondary fracture-induced porosity or soluble rocks which are susceptible to replacement processes. Post-collisional plutonism of the Dom Feliciano Orogeny was the most likely heat source, and also the source of sulphur and base metals. Gravity surveys and alteration studies would be useful to determine the presence of intrusive bodies at depth which may have the potential to host porphyry-style Cu-Au deposits.  相似文献   

Partitioning Tracer Tests for Evaluating Remediation Performance   总被引：1，自引：0，他引：1  

R. Brent Cain  Gwynn R. Johnson  John E. McCray    William J. Blanford  Mark L. Brusseau 《Ground water》2000,38(5):752-761

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Temporal and spatial changes in grain size on a macro-tidal channel-flat complex: results from Kingsport,Nova Scotia,Bay of Fundy     

Law  Brent A.  Hill  Paul S.  Milligan  Timmothy G.  Zions  Vanessa 《Ocean Dynamics》2019,69(2):239-252

Ocean Dynamics - Understanding the processes that lead to seasonal changes in grain size on muddy macro-tidal flat and channel complexes will assist efforts to predict future changes caused by...  相似文献   

Quantitative Evaluation of Wastewater Feed Quality for Struvite Crystallization     

Bing Li  Irina Boiarkina  Wei Yu  Brent Young 《洁净——土壤、空气、水》2019,47(8)

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Dissolved inorganic carbon sourcing using δ13CDIC from a karst influenced river system          下载免费PDF全文

Kegan McClanahan  Jason Polk  Chris Groves  Laura Osterhoudt  Scott Grubbs 《地球表面变化过程与地形》2016,41(3):392-405

Rivers, representing the primary conduits of dissolved inorganic carbon (DIC) from the continents to the oceans, are important components to the global carbon cycle. To better understand the complex carbon cycling dynamics within two nested, mixed lithology watersheds, two sites were studied along the karst influenced upper Green River in south‐central Kentucky, USA. Weekly samples were collected from June 2013 through May 2014 and analyzed for δ¹³C_DIC. The mixing model IsoSource was employed to better understand source partitioning differences over seasonal time spans and across the two nested basins. In both the lithologically mixed upstream basin (53% carbonate rocks, 47% siliciclastic) and carbonate rock dominated downstream basin (96% carbonate rocks in the drainage area between Greensburg and Munfordville, 78% in the total area upstream from Munfordville), DIC was primarily derived from soil respiration. The proportion of DIC from dissolved carbonate minerals derived from the downstream carbonate rock dominated basin was similar to the upstream basin, due to carbonate mineral dissolution having such a consistent effect on the overall DIC content of the river. Seasonally, soil respiration provided the most DIC from fall to winter. Early spring precipitation, combined with limited seasonal photosynthesis, shifted groundwater to be the primary source of DIC, bringing in a flush of carbonate mineral‐rich water during higher flows. This study provides insight into carbon dynamics across multiple lithologies and the important influence of seasonality using carbon isotope sourcing to determine carbonate mineral dissolution variability and aid in understanding its contribution to global carbon flux quantification. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

A simplified approach to analysing historical and recent tritium data in surface waters          下载免费PDF全文

Robert L. Michel  Pradeep Aggarwal  Luis Araguas‐Araguas  Brent D. Newman  Tomas Vitvar 《水文研究》2015,29(4):572-578

Tritium concentrations in river and stream waters from different locations can be compared by normalizing them using the ratio of tritium concentrations in precipitation and surface water (C_p/C_s) in the study area. This study uses these ratios in a hydrological residence time context to make regional‐ and global‐scale comparisons about river basin dynamics. Prior to the advent of nuclear weapons testing, the C_p/C_s ratio was greater than or equal to 1 everywhere because of the decay of tritium in the watershed after it was deposited by precipitation. After an initial increase in the ratios during the bomb peak, the ratio dropped to less than 1 for most surface waters in the following years. This post‐bomb change in the ratio is due to the retention of the bomb‐pulse water in watersheds on timescales that are long relative to the residence time of tritium in the atmosphere. Ratios were calculated for over 6500 measurements of tritium in river and stream waters compiled by the International Atomic Energy Agency. These measurements span the post‐nuclear era (1940s to present) and include many long‐term datasets, which make it possible to examine residence times of waters in watersheds on a global basis. Plotting C_p/C_s versus time shows that ratios tended to reach a minimum in approximately one to two decades after the bomb peak for most locations. This result suggests that changes affecting quantity and quality of river flows need to be assessed on a multi‐decadal timescale. These long lag times have significant implications for assessing climate or land‐use change impacts on a large number of river systems around the world. The continuing value of tritium in studying surface water systems for both the Southern and Northern Hemisphere is also demonstrated. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

Quantitative model of the growth of floodplains by vertical accretion     

John A. Moody  Brent M. Troutman 《地球表面变化过程与地形》2000,25(2):115-133

A simple one‐dimensional model is developed to quantitatively predict the change in elevation, over a period of decades, for vertically accreting floodplains. This unsteady model approximates the monotonic growth of a floodplain as an incremental but constant increase of net sediment deposition per flood for those floods of a partial duration series that exceed a threshold discharge corresponding to the elevation of the floodplain. Sediment deposition from each flood increases the elevation of the floodplain and consequently the magnitude of the threshold discharge resulting in a decrease in the number of floods and growth rate of the floodplain. Floodplain growth curves predicted by this model are compared to empirical growth curves based on dendrochronology and to direct field measurements at five floodplain sites. The model was used to predict the value of net sediment deposition per flood which best fits (in a least squares sense) the empirical and field measurements; these values fall within the range of independent estimates of the net sediment deposition per flood based on empirical equations. These empirical equations permit the application of the model to estimate of floodplain growth for other floodplains throughout the world which do not have detailed data of sediment deposition during individual floods. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Sedimentary evidence of prehistoric distant-source tsunamis in the Hawaiian Islands     

Seanpaul La Selle  Bruce M. Richmond  Bruce E. Jaffe  Alan R. Nelson  Frances R. Griswold  Maria E. M. Arcos  Catherine Chagué  James M. Bishop  Piero Bellanova  Haunani H. Kane  Brent D. Lunghino  Guy Gelfenbaum 《Sedimentology》2020,67(3):1249-1273

Over the past 200 years of written records, the Hawaiian Islands have experienced tens of tsunamis generated by earthquakes in the subduction zones of the Pacific ‘Ring of Fire’ (for example, Alaska–Aleutian, Kuril–Kamchatka, Chile and Japan). Mapping and dating anomalous beds of sand and silt deposited by tsunamis in low-lying areas along Pacific coasts, even those distant from subduction zones, is critical for assessing tsunami hazard throughout the Pacific basin. This study searched for evidence of tsunami inundation using stratigraphic and sedimentological analyses of potential tsunami deposits beneath present and former Hawaiian wetlands, coastal lagoons, and river floodplains. Coastal wetland sites on the islands of Hawai΄i, Maui, O΄ahu and Kaua΄i were selected based on historical tsunami runup, numerical inundation modelling, proximity to sandy source sediments, degree of historical wetland disturbance, and breadth of prior geological and archaeological investigations. Sand beds containing marine calcareous sediment within peaty and/or muddy wetland deposits on the north and north-eastern shores of Kaua΄i, O΄ahu and Hawai΄i were interpreted as tsunami deposits. At some sites, deposits of the 1946 and 1957 Aleutian tsunamis are analogues for deeper, older probable tsunami deposits. Radiocarbon-based age models date sand beds from three sites to ca 700 to 500 cal yr bp , which overlaps ages for tsunami deposits in the eastern Aleutian Islands that record a local subduction zone earthquake. The overlapping modelled ages for tsunami deposits at the study sites support a plausible correlation with an eastern Aleutian earthquake source for a large prehistoric tsunami in the Hawaiian Islands.  相似文献   

Are seagrass beds indicators of anthropogenic nutrient stress in the rocky intertidal?     

Susanna E. Honig  Brenna Mahoney  Jess S. Glanz  Brent B. Hughes 《Marine pollution bulletin》2017,114(1):539-546

It is well established that anthropogenic nutrient inputs harm estuarine seagrasses, but the influence of nutrients in rocky intertidal ecosystems is less clear. In this study, we investigated the effect of anthropogenic nutrient loading on Phyllospadix spp., a rocky intertidal seagrass, at local and regional scales. At sites along California, Washington, and Oregon, we demonstrated a significant, negative correlation of urban development and Phyllospadix bed thickness. These results were echoed locally along an urban gradient on the central California coast, where Phyllospadix shoot δ¹⁵N was negatively associated with Phyllospadix bed thickness, and experimentally, where nutrient additions in mesocosms reduced Phyllospadix shoot formation and increased epiphytic cover on Phyllospadix shoots. These findings provide evidence that coastal development can threaten rocky intertidal seagrasses through increased epiphytism. Considering that seagrasses provide vital ecosystem services, mitigating eutrophication and other factors associated with development in the rocky intertidal coastal zone should be a management priority.  相似文献